Mining Engineer F. N. Shakhov

Materials on the Geology of the Tanalyk—Baimak Copper-Ore District in the Southern Urals

(Work of 1926).

Tomsk
1928

Mining Engineer F. N. Shakhov.

Materials on the Geology of the Tanalyk—Baimak Copper-Ore District in the Southern Urals.

(Work of 1926.)

PREFACE.

In the summer of 1926, at the invitation of the Bashkir Mining Trust, I carried out field work to elucidate the geology and ore-bearing character of the Tanalyk-Baimak copper-ore district of the Southern Urals. The work of that year covered, by geological survey, the areas adjoining from the west and north the main district of the Trust’s ore deposits. The area investigated represents a belt elongated meridionally along the Sakmara River and bounded by the latitudes of its right tributaries: the Agach-Kurgon River in the south and the Talashty River in the north. In the northern part of the district it proved possible to include in the investigations a broader area than in the south, extending eastward to the Irendyk Range, and to collect a small amount of material on the eastern slope of this range and in the steppe adjoining it from the east. The surveyed area occupies approximately about 2,000 sq. kilometers.

In the history of geological investigations of the Urals, its southern part is the most neglected. Since the investigations of the military geologists Meglitsky and Antipov (46), i.e., since the 1850s, Russian geological literature up to the present time has contained no summary works on the Southern Urals. In the second half of the last century the Southern Urals were investigated by a large number of persons, of whom the most important works were carried out by geologists of the Committee—Karpinsky, Krasnopolsky, Mushketov, Chernyshev, and Stuckenberg (28, 29, 80, 83, and 84). Unfortunately, far from all the materials from these investigations have been published. Geological investigations of recent decades have concerned chiefly the districts most important from the industrial point of view,¹ among which Tanalyk-Baimak was not included, and it has not to this day received proper geological treatment.

Only approximately from 1902 onward do the reports of the Geological Committee (58—69) begin to contain the first brief preliminary reports on investigations of recent years in the Southern Urals. In 1922—24 A. N. Zavaritsky published a monograph on the district of Mount Magnitnaya (21) and gave a scheme for the development of the volcanic cycle in the Urals, touching in this latter work also upon the Southern Urals (22). Finally, the recent works of D. V. Nalivkin (52 and 69), L. S. Librovich (44 and 69), and E. Ya. Perna (63, 34—33; 64, 48—51; 74) shed the first rays of light on the complex stratigraphy of the Paleozoic of the western and eastern slopes of the Southern Urals.

Despite the industrial importance of the Tanalyk-Baimak district proper, official geological literature contains extremely scant information about it. If one excludes the brief reports of Tikhonovich (58, 69—75) and A. N. Churakov (66, 35), whose investigations covered parts

¹ See the works of P. P. Gudkov (9) and A. N. Zavaritsky (21 and 26).

adjacent to our district, there is only one work by A. N. Zavaritsky (20), devoted chiefly to the description of certain ore deposits.¹

Naturally, the geological investigation of a district isolated from the more fully elucidated parts of the Southern Urals is, in terms of literary identification, extremely difficult. It is therefore not surprising that many questions set forth in the text of the present report will perhaps be insufficiently fully illuminated, or even left open, and for their resolution will require additional material, which, we may hope, will appear in the course of further research work.

The investigations of this summer had a sufficient number of factors that adversely affected the execution of the work. Route surveying in the area of the Sakmara River was carried out with a copy, not sufficiently satisfactory, of the hachured map at the one-verst scale, prepared by the Military-Topographic Department as early as the 1830s of the last century. In the most responsible places it was necessary to carry out reconnaissance surveying, which considerably slowed the progress of the work. As for the area of the Irendyk Range and its eastern slope, the topographic map pertaining to it² was so unsatisfactory that the material obtained could be used only in part and, of course, requires additional investigation. The topographic basis for the appended map was the two-verst-scale hachured map of the Military-Topographic Department. Despite the age of the survey (30–40 years of the last century), it was compiled comparatively satisfactorily. In any case, the reconnaissance surveys carried out by me in the course of the work for the most part coincided with the data of this map when superposed. Only in one case—namely, when the routes in the area of the villages of Iskakovo, Seitbatalovo, and Itkulovo were superposed—was the discrepancy so great that, in processing, it was necessary provisionally to plot the route data according to the reconnaissance survey. Corrections were entered in the direction of the Savalayr River and its tributaries, since the reconnaissance-survey data agree very closely with the two-verst-scale map available in the trust, whereas the material of the hachured map is plainly at variance with reality.

The following persons took part in the work: 1) V. A. Nuder, student of the Siberian Technological Institute; 2) G. S. Levchenko, student of the Ural Polytechnic Institute; and 3) D. D. Ponomarev, student of the same Institute. In certain cases the persons named were entrusted with independent routes. In the course of the winter processing the author repeatedly turned for advice and guidance to Prof. M. A. Usov, to whom he takes this opportunity to express his deep gratitude.

OROGRAPHIC OUTLINE

“The chief physical feature represented by the Southern Urals consists in the fact that, in direct contrast to the Northern Urals, which have only a single dominant ridge, it consists of several belts”… Thus writes Murchison on the Southern Urals (51, 174). Meglitsky and Antipov (46, 7) already distinguish in the Southern Urals “three watersheds of the first order: 1) the granite axis between the Urals and the Tobol; 2) the Kyrkty Mountains and the Irendyk; and 3) the belt of crystalline schists, whose axis is formed by the rocks of the Guberlinsky Mountains.” Between these principal ridges there are small elevations of the second order (46, 7).

¹ During the printing of the present work, A. N. Zavaritsky published “Geological Sketch of the Deposits of Copper Ores in the Urals,” which also included deposits of the Baimak district (Tr. G. K., new series, issue 173).

² I had at my disposal a two-verst-scale summary map of unknown origin, supposedly compiled by the Forestry Department.

The area studied, in its western part, includes the eastern slope of the Ural-Tau Range, corresponding to the third watershed of M e g l i t s k i i. At the foot of this meridionally extending range, along a serpentine belt, flows the Sakmara River, cutting into the mass of crystalline schists near the southern boundary of the surveyed area. Farther east, separated from the serpentines by narrow ridges of jasper hills, there extends as far as Irendyk a gently undulating steppe, composed of a sandy-clayey graywacke sequence of the Upper Devonian. The Irendyk Range is covered by the survey only in the northeastern part of the district. In this area the steppe is separated from the steeply rising western slope of Irendyk by narrow, meridionally elongated chains of jasper hills. In the deep, marshy valley between Irendyk and the jaspers rises the Tanalyk River, which flows through Lake Tolkach, situated a few kilometers south of the Tubinsk mine. East of the Irendyk Range, as far as the Kizyl River, we again have an almost level, gently undulating steppe, here and there crossed by small, meridionally elongated low hills.

Thus, the surveyed area presents a regular alternation of narrow, meridionally elongated ranges and level steppe spaces, the character of which, as was pointed out in their time by K a r p i n s k i i and C h e r n y s h e v (29, 13), is determined by the constituent rocks and by the conditions of their occurrence. The orography of Ural-Tau, Irendyk, and the steppe spaces adjoining these ranges has been described in such detail and with such great mastery by these geologists (29, 10—54) that it remains for the author only to note the local deviations from the general characteristic features of the orography of the Southern Urals.

Ural-Tau, within the limits of the studied district, is not distinguished by great height. According to the data of barometric leveling carried out by M e g l i t s k i i (46), the height of Ural-Tau at the latitude of the Kano-Nikol’skii works ranges from 1,500 to 2,200 feet above sea level (from 450 to 670 meters). Toward the south it lowers, is overgrown with dense forest, and is characterized by rare outcrops, which occur only along the larger right tributaries of the Sakmara River. Especially even, gentle low hills, overgrown with dense forest, are produced by the mica schists, evidently much more readily subject to destruction than the green schists, especially their massive varieties. The eastern slope of the range is very gentle¹) and imperceptibly passes into a sea of small hills composed of serpentines and peridotites of the Sakmara River.

The serpentines in our district do not form significant massifs, as is characteristic of other districts of the Urals. For the most part the surface composed of these rocks has a strangely tangled relief, the elements of which are small hills, usually devoid of vegetation and covered with fragments of serpentine of greenish-blue tones. The most resistant are the amphibolites, associated with quartz albitophyres that cut through the serpentinite masses. Usually they form meridionally elongated narrow crests of hills, standing out in height from the small serpentine knolls. In the vicinity of the Sharmaevo magnesite deposit, such amphibolite hills extend along the left bank of the Sakmara River as far as the village of Yaratova, where the river, skirting these rocks, turns sharply eastward.

East of Ural-Tau, as far as the Irendyk Range, there stretches a flat, broad plain composed of the graywacke sequence of the Upper Devonian. The same gently undulating steppe, approaching a peneplain, also extends east of Irendyk. This latter steppe area is hypsometrically situated lower above sea level than the plain adjoining Irendyk from the west. According to data

¹) K a r p i n s k i i notes a steep eastern slope at Ural-Tau and connects this phenomenon with the westward dip of the schists (29, 12). In our case the dip of the schists is easterly, and evidently this circumstance also accounts for the gentleness of the eastern slope.

According to Meglitsky, for these areas we have the following elevations: 1) the village of Tablykaeva, left bank of the Sakmara River—1366 feet; 2) the valley of the Tanalyk River, at the same latitude—1360 feet; 3) the Kizilskaya stanitsa—809 feet, and 4) Lake Koltuban—1007 feet. Amid the steppe expanses there are sometimes sharply distinguished ridges of jasper, usually elongated meridionally, occurring especially often in the area of the principal ore deposits of Baymak, between Ural-tau and Irendyk. The height of the jasper ridges reaches (46) 2000 feet above sea level. Erosion has worked considerably upon these steppe areas, and the character of their orography is apparently entirely analogous to the region of Mount Magnitnaya, where the forms of relief, in the opinion of A. N. Zavaritsky (21, 20), are determined by “the position of the region in the area of residual, disappearing mountains.”

The Irendyk Range represents in our district the highest mountainous area, reaching 10 kilometers in width. Being composed of greenstone-altered pyroxene porphyries, their tuffs, and jaspers—rocks sufficiently resistant to weathering processes—the range abounds in outcrops and steep cliffs, and reaches an elevation of 2240 feet above sea level. In the area studied, the dip of the rocks is everywhere eastward; evidently connected with this circumstance is the existence (29, 37) of a steep western slope and a gentle eastern slope, gradually passing into a broad, level steppe.

The area studied is watered chiefly by the Sakmara River. On the western slope of the Irendyk Range, in the northeastern corner of the area, the Tanalyk River rises in a broad, marshy valley; finally, from the eastern slope of Irendyk flows the Sultanka River, which passes through Lake Sultanskoye and empties into the Kizil River.

The general direction of the Sakmara River’s course is meridional. In most cases its valley is confined to the contact of serpentinites and crystalline schists, and only in some places does the river make bends, cutting through jasper hills into the Devonian graywacke sequence, as occurs near the village of Yaratova. Having emerged onto a flat plain, the river flows in a broad valley abounding in small marshes and lakes, until it again enters the serpentinite belt, making use of a narrow passage between high jasper hills, at the place where these rocks have the least thickness and are readily subject to erosion. Along almost the entire length of the investigated sector the Sakmara has a broad, sufficiently developed valley. The valley narrows sharply and its banks become steep and picturesque only where the river cuts into the sequence of crystalline schists. This is especially well seen near the village of Kuvatskaya, in the southern part of the investigated area.

The character of the valleys of the lateral tributaries of the Sakmara River is sharply dissimilar. The right tributaries, flowing within the sequence of crystalline schists, are often typical mountain streams with a steep gradient, narrow valleys, and sometimes steep and rocky slopes. Steep slopes are especially characteristic of the streams of those parts of Ural-tau where, within the sequence of crystalline schists, green schists, serpentinites, chlorite-garnet, or glaucophane rocks begin to predominate. In mica schists the river valleys are somewhat wider and have gentler slopes. The direction of flow is more often meridional and changes to latitudinal only in the lower reaches, near the mouth. The left tributaries of the Sakmara River usually have broad, developed valleys and are winding, with a predominantly latitudinal course. Usually these are slowly flowing streams, sometimes even possessing pond-like reaches and swampy sections. All of them flow within the limits of a weakly undulating steppe composed of sandy-clayey deposits of the Upper Devonian. Thus, we have two categories of small streams: mountain and steppe. Such a sharp distinction in the character of the river valleys of the right and left tributaries of the Sakmara River may be caused not only by the different rocks over which these rivers flow—

They indicate, however, that this may also be due to the circumstance that Mt. Ural-tau rose quite recently along a tectonic fissure separating it from the porphyrites and serpentinites of the Sakmara River (Sheets 17 and 18).

Large, broad peat bogs extend along the western slope of the Irendyk, in a deep valley bounded on the west by a narrow jasper ridge. They are fed by numerous small streams flowing mainly from the western slope of the Irendyk. The boggy valley has a slight fall to the south, and somewhat south of the Tubinsky mine lies Lake Tolkach, from which the Tanalyk River begins,^1 flowing in its upper reaches through a broad, very swampy valley.

Lake Tolkach is a typical example of the Ural mountain lakes (29, 53). Deep, elongated meridionally (parallel to the strike of the rocks of the Irendyk), with fresh water and slightly swampy, winding shores, it has a rocky island in its southern part. The Sultan Lake, situated in the steppe adjoining the Irendyk from the east, is the direct opposite of this lake. Its almost circular, saucer-like outline, comparatively small depth, and heavy swampiness bring it very close to the group of steppe drainless lakes; but, unlike them, it has the Sultanak River flowing through it and, according to Karpinsky, belongs to the category of lakes of an intermediate type, characteristic of peneplained ancient sedimentary strata (29, 54).

Geological-Petrographic Sketch

In terms of the composition of the formations that make it up, the area studied is very variegated and complex. Within the limits of the area studied, on the basis of the material collected this year, it appears possible to distinguish the following formations: 1) a series of metamorphic rocks composing the eastern slope of the Ural-tau; 2) porphyrites and their tuffs, closely associated with the jaspers of the Middle Devonian; 3) siliceous shales and tuffaceous sandstones of the upper horizons of the Middle Devonian (according to Librovich (44)—the “Lower Green Suite”); 4) a sandy-clayey graywacke series, apparently close in age to the Upper Devonian; 5) a complex assemblage of intrusive rocks of different ages, of which the oldest are the peridotites and serpentinites of the Sakmara belt, and the youngest are augite diorites and the quartz or quartz-free felsitic albitophyres evidently associated with them; and 6) Tertiary deposits.

1. Metamorphic Series

Crystalline schists occupy a broad belt of meridional extent, the western boundary of which extends far beyond the limits of the area studied. In the south this belt is cut by the route along the Agach-Kurgon River, a right tributary of the Sakmara River, and in the north it is crossed by the route along the Talashta River, which flows into the Sakmara on the right near the village of Temyasovo. The southern and northern boundaries of the crystalline schists lie far beyond the limits of the Tanalyk-Baimak district. The only boundary of this formation accessible for study is the eastern one, where the crystalline schists are in direct contact with diabase porphyrites and serpentinites of the Sakmara River; in this case both rocks are strongly fractured and schistose along steeply dipping planes of meridional strike. At the latitude of the Yuluk mines the crystalline schists form a beautifully expressed

^1 The bogs proper north of Lake Tolkach have a small stream draining them, with a flow of variable velocity; it is also called the Tanalyk.

an anticlinal fold, the axis of which plunges to the north. In the areas north of the village of Yumashevsky the survey takes in only the eastern limb of this anticline, complicated by small folds of the second order.

In composition, the metamorphic sequence represents a very variegated complex of rocks, which are sharply divided into two large groups: 1) a mica-schist sequence, in which the chief role belongs to rocks rich in quartz, and 2) green schists, whose characteristic feature is the almost complete absence of quartz and the usual presence of albite, epidote, actinolite, and other minerals characteristic of metamorphic rocks whose basis is a more or less basic igneous material. Marbles, serpentine lenses, and the accompanying chlorite-garnet, glaucophane, and talc rocks are usually associated with the green schists. Rocks of the first and second groups are often interbedded and linked with one another by transitional intermediate formations. For this reason it was sometimes not possible on the map to delineate accurately the belts of green schists. Moreover, the area of the metamorphic sequence is distinguished by a strong development of alluvial-eluvial formations, which greatly hamper accurate mapping, and therefore it is very probable that in reality the green schists have a greater distribution and a more complex pattern of outlines than is shown on the map. In composition, the mica-schist sequence may be divided into three quantitatively unequally represented groups: 1) quartzites, 2) mica, graphite, amphibole, and other schists, and 3) phyllites.

Quartzites. The rocks of this group are often distinguished from the metamorphic sequence of the Urals. P. Krotov (37, 307) and Krasnopolsky (33, 340) assign them to the most ancient horizon of the metamorphic sequence of the western slope of the northern Urals. V. Nikitin (53, 31), for the area of the Verkh-Isetsky and Revdinsky dachas, distinguishes quartzites as derivatives of a sedimentary sequence rich in quartz material and suggests (53, 34) that they may stratigraphically overlie the rest of the sequence. Vysotsky (3, 67—68), combining quartzites and mica schists into one group, assigns them tentatively to the Silurian, while considering the overlying phyllitic sequence to be unconformable upon the quartzites and, by age, to belong to the Lower Devonian. In the Southern Urals quartzites are likewise usually distinguished. Vysotsky’s studies (63, 31 and 64, 40—42) in the region of the Krykty Range indicate that quartzites make up the watershed ridges and lie west of the rest of the crystalline-schist sequence, i.e., have some claim to stratigraphic separation. Tikhonovich (66, 42) assigns the metamorphic sequence of the Guberlinsky Mountains to the Silurian, and considers the siliceous schists lying below the crystalline schists to be tentatively of Lower Silurian age. In his latest summary work Nalivkin (52, 73) regards the quartzites as formations of Silurian age, and assigns all the rest of the metamorphic sequence to the Precambrian.

The rocks described by us are not sharply differentiated stratigraphically from the rest of the metamorphic sequence and were encountered by me only at two points: 1) the Shakarady River, one kilometer east of its confluence with the Zilair River, and 2) the headwaters of the Belekai River west of the village of Verkhne-Bairamgulovo, situated on the Sakmara River. In both cases these rocks are massive, light-colored formations consisting of quartz, to which garnet, mica (muscovite), albite, and a little magnetite are admixed. Pure quartzites under the microscope show a distinct relict psammitic structure, thereby indicating their sedimentary origin. The appearance of albite, mica, and garnet is connected with the presence in the rock of very fine platy parting—schistosity—and a granoblastic structure approaching panallotriomorphic (quartzites of the Belekai River). Of interest in this respect is the observation of A. N. Zavaritsky (68, 176) in the crystalline schists of the Zlatoust ...

of the Mining District, where a fine injection of granite into quartzites is present, “and in places this injection passes into a kind of impregnation of the quartzite by individual crystals of feldspar.” Since our quartzites are connected by gradual transitions with the mica schists of the rest of the metamorphic sequence, sharply injected by quartz material, the presence of albite is most naturally connected with phenomena of injection metamorphism.

The quartzites of the Belebey River are connected with the other rocks of the mica-schist sequence by gradual transitions. Rocks similar to them are also observed in the crystalline schists near the village of Temyasovo. The quartzites on the Shakarady River appear more sharply and distinctly, where they are confined to the westernmost part of the strip studied, i.e., situated closer to the watershed ridge, and may perhaps have a right to be distinguished. Unfortunately, however, the material at our disposal does not yet permit us to separate the quartzites into an independent stratigraphic horizon; therefore, in further descriptions of the metamorphic sequence, when clarifying stratigraphic relationships, we shall combine these formations with the rocks of the second group of crystalline schists.

The rocks of the second group, rich in quartz, are the most widespread formations. In terms of the amount of quartz, they are connected on the one hand with the quartzites described above, and on the other, as it decreases, they approach in mineralogical composition the green schists, with which they are closely interbedded (especially in the southern part of the district). The main feature of the rocks of this group is the form in which the quartz occurs: most often it is separated into individual bands and lenses, varying in thickness from one millimeter to several tens of centimeters; in the latter case we are clearly dealing with injected quartz veinlets. In some cases such veinlets—lenses—reach considerable dimensions and contain miarolitic-like cavities, in which magnificently bounded crystals of short-prismatic quartz crystallize out.¹ Thus, since in the quartzites we are dealing with primary quartz, in the quartz-mica schists the quartz is mainly due in origin to processes of injection.

Most often, and in substantial quantity, the rocks of this group include, in addition to quartz, light mica, graphite, albite, garnet, and amphibole, depending on which we have mica, graphitic, amphibole, and other schists. In some cases these components begin to predominate so strongly in the rock that transitional varieties to green schists appear.

Mica schists in pure form are encountered very rarely; in their composition, besides quartz and mica, there is always some quantity of garnet, amphibole, albite, epidote, and sphene (?).² Tourmaline and apatite occur more rarely, and, as a product of alteration of the mica, chlorite often develops. Usually these rocks are perfectly schistose green-colored³ formations, consisting of thinly alternating bands of quartz and mica. An increase in the thickness of bands and lenses of quartz is connected with the development in the rock of strong platy or log-like jointing. Such jointing is especially well manifested in areas subjected, after metamorphism, to tectonic influences, expressed in the formation of small folds of the second order (such schists were observed, for example, in the middle course of the B. Yuluk River).

Quartz is sometimes present in such large quantity that in this case the rock should be called a quartzite of injection, in contrast to the quartzites described above, whose quartz material is of sedimentary origin.

The structure of the quartz is granoblastic. The grain size varies from 0.05 mm to 0.5 mm in diameter. It is of interest to note that in quartz bands of greater thickness a larger grain size also develops.

Light mica usually appears in long threadlike aggregates; it is also admixed with the quartz of the light bands, but chiefly forms green interlayers, with which all the other minerals are associated. The structure is nematoblastic. It passes into chlorite. The usual width of a thread is about 0.008 mm. Biotite is encountered very rarely.

Albite usually forms poikiloblasts with a large number of inclusions of amphibole needles, garnet, quartz, and sphene. Twins are usually simple according to the Carlsbad law; \(2V = +80^\circ\), \(BNg = 71^\circ\), \(BNm = 19.5^\circ\), \(BNp = 84^\circ\). No. 6 along [001].

Garnet occurs in small grains not exceeding 0.06 mm in diameter. It is transparent, almost colorless, often bounded in a splendid manner, sometimes anomalously biaxial. It approaches almandine. It is not present in all rocks of this type.

Sphene and epidote occur more frequently than garnet and are usually associated with mica. Sometimes zoisite accompanies them.

Graphitic schists are, in composition, entirely identical with the micaceous ones and differ from them by a large amount of graphite, which gives these rocks a black color. Among them one may also distinguish graphitic quartzites of injection, graphitic-micaceous schists, garnet-bearing and albitic varieties. Like the micaceous schists, they may be ideally schistose or banded and possess platy parting. Frequently, while retaining their black color, they yield transitional formations to green schists.

Amphibole schists are encountered very rarely. Usually they represent formations transitional to green schists. They are comparatively poor in quartz and rich in interlayers consisting of albite and actinolite. The latter plays the role of muscovite in the micaceous schists. Graphitic varieties occur. Of interest is a micaceous glaucophane schist, taken at the head of the Salalair River, where it is associated with quartz-free garnet-glaucophane rocks which, in composition, stand closer to green schists. This massive rock, with a parallel-crystalline structure, has a light, somewhat variegated coloration, emphasized by fine porphyroblasts of glaucophane. It consists, in decreasing order of abundance, of the following minerals: quartz, mica (muscovite), glaucophane, albite, garnet, epidote, and sphene. Noteworthy is the association of albite with glaucophane. Glaucophane usually develops in albite in the form of needles occupying the central part of the crystal (Fig. 1). Sometimes the glaucophane crystal increases so much in size that the albite remains only in the form of a small zonal rim. A phenomenon of the same character was described by Angel for the albite-bearing, green, gneiss-like schists of Steiermark (87, 176–177). Angel notes that the appearance of albite in these rocks is usually combined with the development in it of blue amphibole needles, and considers the cause of this phenomenon unknown. It may be thought that the source for the formation of albite and glaucophane was sodium migrating from the injected material, which, in combination with the primary and partly introduced material of the country rock, gave rise to mineral formations rich in them.

The rocks described often interlace closely with one another, rapidly pass one into another and even into green schists. For illustration I shall permit myself to present a section of crystalline schists, magnificently exposed on the left bank of the M. Yuluk River, at a distance of 300 m from its mouth. The strike of the schists here is NW 335°, with a dip to the east of 25°. The total thickness of the rocks described does not exceed 120 m. The description proceeds from the upper horizons to the lower ones (Nos. 67a–k).

Thinly schistose, green-colored mica schist. It consists of quartz and mica, partly altered into chlorite. A little epidote, zoisite, and leucoxene. The thickness is not more than 2 meters. Through a series of gradual transitions, consisting in an increase in the quartz interbeds, the rock passes into a chloritized albite-garnet mica schist, strongly platy, with a well-expressed foliated parting. Quartz veinlets are more than a centimeter thick. In the micaceous interbeds a nodular texture appears, caused by the development of albite poikiloblasts. Epidote, garnet, and tourmaline appear.

After 15 meters the number of quartz veinlets decreases; the rock consists, as it were, only of material of albite-chlorite nodular structure. Amphibole takes the place of mica, finely penetrating the albite poikiloblasts. Garnet disappears. There is much epidote, and calcite is mixed with the quartz veins. In this case we have a rock approaching the green schists in composition. Rocks of this type occupy a thickness of about 20 meters, after which they are succeeded by a thin interbed of chloritized mica-garnet schist, 2–3 meters thick, passing in turn into massive two-mica schists with a gneiss-like texture. Albite is not observed; there is very much garnet; biotite is strongly chloritized. The thickness of the rock is about 23 meters. The rock has a rod-like texture, but no sharp veinlets of injection quartz are noticeable in it. Evidently its quartz material is, to a greater degree, of primary character.

The rocks occurring over the next 60 meters differ from those described by their dark coloration, caused by the presence of graphite. In composition they exactly repeat the same variations. In abundant injection quartz formations, mica and albite develop more strongly. Varieties rich in micaceous interbeds, when the mica is altered into chlorite, acquire a sharply emphasized nodular texture. In this latter case calcite often appears together with quartz. Rocks transitional to green schists are distinguished by an extraordinary development of chlorite and amphibole. It is very possible that sometimes the appearance of chlorite in large quantity is connected with the primary composition of the metamorphic rock, but the association of this mineral with calcite and amphibole, and the transition of mica and amphibole into chlorite, indicate that in the vast majority of cases we are dealing with a process of subsequent alteration of the rocks. In any case, the development of mica and albite preceded the formation of chlorite, calcite, and perhaps amphibole. How separated in time these processes are is difficult to say, but it is highly probable that they are connected with phases of metamorphism differing in character and time. Proceeding from these considerations, I have not distinguished chlorite schists, since in the majority of cases they should be regarded as chloritized varieties of the rocks described.

Phyllites. Thinly schistose rocks, usually colored in green tones, with a silky luster of mica on the planes of schistosity. Normally the rock consists essentially of quartz, sericite (muscovite), epidote, zoisite, and chlorite. Radiating amphibole, calcite, garnet, and graphite very often appear. In the case of a large admixture of graphite the rock assumes a black coloration. In some cases formations of the same character contain a very large amount of quartz, become more massive, and vividly recall the carbonaceous sericite-quartz schists described by Vysotsky (3, 75) and characteristic of the phyllite series of the western slope of the northern Urals.

With the rocks of this series are associated anthophyllite schists and hornfels. In composition these are rocks very close to phyllites. They differ only in the sharp development of stellate aggregates—most often colored in brown tones—of pleochroic anthophyllite amphibole. Among them there are thinly schistose and massive varieties, poor in quartz or rich in it, light- or dark-colored. It is interesting to note that the appearance in the rocks of the phyllite series

anthophyllite associates with the contacts of quartz veins¹. The massive, dark-colored rocks of hornfels-like appearance consist almost entirely of quartz. The dark coloration is often connected with a fine impregnation of the rock by iron oxides; in other cases the pigment is dirty-brown flakes of a strongly polarizing material resembling titanomorphite. Sometimes these rocks pass into limestones, i.e. they are their silicified varieties. In the area of the village of Yumashevo, upstream along the Kuvashla River, approximately 500 meters from the mouth, a small lens of somewhat limestone was observed, passing into siliceous rocks of the type described.

The rocks of this complex are weakly developed in the area studied. Their thickness is so small and at times so indefinite that it does not seem possible to distinguish them on the map. The occurrences of the phyllites are situated along one straight line of meridional strike and are confined to the eastern contact of the metamorphic sequence with the porphyrites and serpentinites of the Sakmara River. The specimens in the collection were taken at the following localities: the village of Yumashevo, the village of Yaratovo, the left bank of the Sakmara River opposite the village of Sharmaevo, the environs of the village of Chingiz, the right bank of the Sakmara River opposite the village of Tavlyukaevo, the environs of the village of N. Itkul (on the Savalaïr River), and the right bank of the Sakmara River near the village of Temyasovo. All the localities enumerated lie precisely near the tectonic boundary of the metamorphic sequence and the porphyrites; thus, the phyllites compose the uppermost horizons of the eastern limb of the anticline of crystalline schists, which closely agrees with Vysotsky’s scheme (3, 68), assigning the phyllites of the northern Urals to the lower parts of the Lower Devonian ($D'_1 c$).

Green schists play an essential role in the composition of the metamorphic sequence. Alternating in places very closely with quartz rocks, these formations sometimes so predominate that it becomes possible to distinguish on the map areas where only green schists and the rocks accompanying them occur. Among the companions of the green schists, the most noteworthy are serpentinites, talc rocks, mica-glaucophane rocks rich in chlorite, garnet rocks, and marbles. Colored in various shades of green, the rocks described possess either a finely schistose or a massive structure. The massive varieties are predominantly associated with serpentinites.

The normal mineralogical composition of the green schists consists of quantitatively varying combinations of albite, epidote, acicular or uralitic amphibole, zoisite, leucoxene, and serpentine. Chromite occurs here and there. Pyroxene is a relict mineral, occurring in varieties that preserve a diabase appearance. Minerals not constantly present, but at times playing a significant role in the composition of the rock, are: graphite, chlorite, talc, calcite, anthophyllite, and sericite.

Albite always plays a very significant role in the composition of the green schists. The isometric, sieve-like poikiloblasts of albite, penetrated by actinolite and epidote, rarely possess polysynthetic twins, but usually show simple twins according to the Carlsbad law. $2V$ is from $+76^\circ$ to $+82^\circ$. Sometimes actinolite penetrates the albite crystals so densely that, because of the dense felt of actinolite needles, the mineral being replaced can only with difficulty be discerned.

Epidote, leucoxene, serpentine, and uralite usually associate with one another and are often encountered with fragments of primary pyroxene. This association is especially characteristic of the last three minerals. Epidote, apparently, appears together with albite as a product of alteration of the primary plagioclase. Graphite also appears, as in the graphitic quartz schists.

Chlorite sometimes plays a very substantial role in the green schists. Nodular albite schists usually consist of albite and chlorite. They are always accompanied by

epidote, sphene, quartz, talc, calcite, and occasionally chrome spinel are added in insignificant quantities. Of great interest is the form in which quartz occurs in such rocks. It is found as small lenses, veinlets, or separate grains (Fig. 2), situated along the margins of albite crystals or cutting across them. Often the quartz aggregates are accompanied by accumulations of limonite, possibly formed in place of primary sulfides. In such cases the quartz is typically metasomatic, and the formation of chlorite is probably also connected with its penetration into the rock. This position is partly confirmed by the strong development of chlorite in all rocks of the metamorphic sequence in the area of the Yuluk mines.

Calcite, which usually replaces albite, plays approximately the same role as quartz in the green schists. Sometimes the replacement proceeds so far that we have massive calcitic green rocks. Such formations were encountered by me in the area of the asbestos vein, near the northern Yuluk mine.

Anthophyllite, sericite, and talc, as a rule, develop in our rocks as a result of later metamorphic processes and are usually characteristic of rocks near ore districts or of thick quartz veins that cut the metamorphic sequence in large numbers. Sericite and talc often develop in nodular albite-chlorite schists penetrated by quartz. Talc forms at the expense of serpentine, and sericite at the expense of albite.

Thus, in the green schists, just as in the mica-quartzite sequence, we are dealing with complexly metamorphosed rocks. Moreover, both in the one case and in the other, the later process of alteration of the rocks is accompanied by approximately the same mineral complex and, in its character, approaches the phenomena accompanying processes of ore metasomatism.

Serpentinites are an invariable member of the most significant sequences of green schists. Black or yellowish-green, dense, with a polyhedral characteristic jointing, these rocks usually consist essentially of serpentine of antigorite structure. Almost always fragments of bastite can be observed. Chromite, chrome spinel, leucoxene, and pyrites occur as accessory minerals. The latter are clearly secondary. Leucoxene develops as a result of the decomposition of pyroxene. Its accumulations surrounded by chromite are of interest (Fig. 3). Apparently, chromite too is a secondary formation. In rare cases undecomposed rhombic pyroxene is encountered.

Most serpentinite bodies surrounded by green schists do not contain portions of primary igneous rocks. Only in one case, in the area of the village of Chingiz, along the Yarma-elga River, were we encountered olivine-poor werlitic rocks. Since investigations did not reveal a mesh structure of serpentine in the serpentinites of the metamorphic sequence, it must therefore be assumed that all the remaining serpentinite lenses also originated at the expense of olivine-poor pyroxenitic rocks.

Serpentinites are, so to speak, the first stage in the alteration of igneous rocks. The process of metamorphism does not stop with the transformation of pyroxenes and olivine into serpentine and bastite. Numerous talc, chlorite, and chlorite-garnet rocks, spatially closely associated with serpentinites, are undoubtedly the final products of transformation of pyroxenitic rocks (98). The transformation of serpentinites into formations of this kind is not rare for the Urals. V. V. Nikitin (53, 124) notes the development of talc in serpentinites and of chlorite in pyroxenites. The observations of B. Krotov (36, 175–187) in the Miass dacha on chlorite-garnet rocks indicate the undoubted connection of these formations with gabbro-pyroxenite rocks. Finally, E. A. Kuznetsov (39, 7), analyzing the processes of silicification of serpentinites in connection with the injection of quartz veins and pegmatites, notes the formation of leuchtenbergite and talc in serpentinites.

Talc rocks are rarely of massive structure. Usually they are finely schistose and colored in light-green tones. Of interest is an outcrop of massive talc rock along the Mayakan River, near the road from the village of Yuluk to the village of Niyazgulovo, approximately 1.5 kilometers from Yuluk. The rock is massive, light-colored, with fine needles of radiating amphibole, sometimes replaced by limonite and therefore brown in color. The formation of talc is closely connected with a quartz vein. Unusually distinct transitions are traced from talc to silicified serpentinite and quartz of milky-white color. Talc predominates in the composition of the rock, but serpentine and chlorite are always admixed with it in small quantities.

Talc rocks of the same character, only of schistose structure, were taken in a prospect pit (apparently for asbestos) on the left bank of the B. Yuluk River, near a mill, on the southern outskirts of the village of Yulukskoye. In this case we have talc schists of ordinary composition, in some varieties of which, together with injected quartz, radiating amphibole develops sharply. Thus, along with the formation of talc, amphibole also appears.^1) It is very probable that a certain quantity of amphibole schists owes its origin to later processes of metamorphism, having nothing in common with the broad process of formation of metamorphic schists.

Chlorites and chlorite schists are usually associated with serpentinite lenses. They are remarkably well represented in the broad serpentinite lens exposed along the Atach-Kurgon River, which flows into the Sakmara River near the village of Kuvatskoye. Dark- to black-green, massive or schistose, they are rarely pure in their composition. Some quantity of epidote, zoisite, serpentine, calcite, sericite (?), chromite, and magnetite is always admixed with them. Of great interest is a magnetite-chlorite schist of nodular structure, taken in the serpentinite mass along the Atach-Kurgon River. Magnetite develops in the form of well-defined crystals, which creates a picture outwardly close to a porphyroblastic structure. Formations of the same character were observed by B. Krotov^2) in chlorite-garnet rocks of the Miass dacha (36, 185). It must be assumed that magnetite is a metasomatically included mineral and that the processes which deposited it served as the cause of the development of chlorite rocks in the serpentinites. Some indirect confirmation of this proposition is furnished by chalcedonies found in individual specimens of chlorite-garnet rocks, which are connected by gradual transitions with the chlorites described.

More often than chlorites there occur mica-chlorite rocks, usually of massive or irregularly schistose structure. In composition they differ from the preceding ones only by the abundant occurrence of light mica, to which are added, in small quantities, metasomatic quartz, talc, titanite, and albite. They are also encountered among massive varieties of green schists.

Chlorite-garnet rocks usually occur together with the formations described above. They differ from other chlorite rocks by the development of garnet and amphibole. The garnet is pink, anomalous, close to almandine. The amphibole, in bluish tones of pleochroism, is close to actinolite.

Somewhat approaching in external appearance the amphibole chlorite-garnet rocks of various composition are glaucophane schists and hornfels, widely distributed in the upper reaches of the right tributaries of the Sakmara River, the Savalair River, and the Talapty River (near the village of Temyasovskoye). A finely schistose glaucophane schist with an admixture of epidote and chlorite was encountered in an outcrop

^1) In this respect, Slavik’s indication (104) is of interest; he noted the development of tremolite asbestos as a result of the uralitization of diallage in the gortonolites of South Africa.

^2) B. Krotov draws a parallel between the process of formation of chlorite-garnet rocks and saussuritization. The difference, in his opinion, consists only in the intensity of the process and in some difference in the final mineral formations (36, 191).

on the left bank of the B. Yulyk River, somewhat below the mouth of the Bigash River. In all three cases the rocks alternate with green schists, even with distinctly developed micaceous injection quartzites (Talapty River), and often themselves contain quartz in appreciable quantity. No connection with serpentinites was found. It is most probable that these rocks should be regarded as the most intensely metamorphosed green schists, or as formations transitional from them to injection quartzites. Of interest in this respect are the considerations of Levinson-Lessing, expressed by him concerning the genesis of glaucophane schists in the vicinity of Denezhkin Kamen in the Northern Urals. Without denying Rosenbusch’s opinion regarding the connection of glaucophane formations with gabbroid rocks, Levinson-Lessing notes that, according to chemical analysis of these rocks, they contain too much sodium, and therefore alkaline gabbros must have served as the original material for the glaucophane schists (41, 89, 90). Taking into account the injectional character of the metamorphism of the crystalline schists of the Urals, it seems more natural to us to suppose, for the formation of glaucophane, and partly also of albite, the introduction, together with quartz, of a certain amount of sodium.

In composition, the glaucophane rocks vary very sharply. The constant minerals are: albite, actinolite, quartz, garnet, glaucophane, titanite, epidote, and light-colored mica. Albite and garnet are often sieve-like, penetrated by amphiboles, quartz, epidote, and garnet and albite. The poikiloblastic structure is often very sharply expressed. The poikiloblasts are usually represented by garnet or albite. Amphiboles often pass into bright-green chlorite. The process goes so far that we have chlorite-garnet rocks completely identical with those described above. The difference lies in the character of the chlorite, which in the serpentinite formations is distinguished by a dirty brownish-green coloration and is almost isotropic (pennine).

In some varieties of these rocks there is so much quartz that the rock becomes, in its character, closer to amphibole schists transitional to injection quartzites, together with which they were described above. It is interesting to note, for some glaucophane rocks, the appearance of a bluish coloration of the pyroxene, with constants somewhat unusual for these minerals. The extinction angle ($CN_g$) varies from 35° to 45°, $2V = +75^\circ$. It is very probable that in this case we are dealing with a manganese or jadeite type, perhaps a chromium-bearing diopside (99, 472, 496).

Marbles are encountered comparatively rarely in the rocks of the metamorphic series. Small outcrops of these rocks occur in the vicinity of the village of Yulyk, the village of Itkulovo, the village of Chingiz, and especially large outcrops at the headwaters of the Shulka River, which flows into the Zilair River. At the last locality the marble is quarried and burned for lime. In all cases the marbles either come into direct contact with serpentinites or are situated near these rocks. These dark-gray, coarse-grained rocks (with grains up to 6 mm in diameter) consist essentially of calcite of mosaic structure. The rocks are often strongly shattered, with numerous slickensides, and are only slightly penetrated by quartz veinlets. Penetration by quartz is especially strong in the marbles of the Chingiz village and Itkulovo village area. Their stratigraphic position is as yet undetermined. It is quite possible that these rocks constituted interbeds in porphyrite formations that served as the original material for the green schists of the Ural-Tau.

In concluding the description of the rocks composing the metamorphic series, one cannot pass over in silence the numerous quartz veins, sometimes several meters thick, which so often cut through all the rocks of this formation and are remarkably persistent along strike for great distances. The usual type of vein quartz of these formations contains no traces of sulfides. According to a report by the technical director of the trust, mining engineer L. I. Shamansky, sampling of these veins did not reveal gold in them. Cutting across various formations, they cause, depending on the composition of the rock, chloritization,

staling, or the appearance of sericite and of radiating, sometimes anthophyllite, amphibole. Quartz veins are sometimes encountered that contain smoky quartz. The gray-colored bands of quartz create the impression of separate veinlets penetrating the main body of white massive quartz. Under the microscope the simultaneous formation of these bands is clearly revealed by the complete uniformity of structure and by the absence of any traces of injection. Thus, evidently, we are dealing with comparatively low-temperature formations, poor in sulfides¹.

Thick quartz veins, similar in character to those described, apparently occur often in the Urals. A. V. Nikolaev (54, 149) notes thick quartz veins devoid of gold, occurring in the gneisses of the Kyshtym district and extending, conformably with the gneisses enclosing them, for a considerable distance (up to several versts). In the Southern Urals, in the Aidyrlya area, P. P. Gudkov (9, 26 and 36) notes thick quartz veins devoid of pyrites, occurring in serpentinites, porphyries, and porphyrites. The formation of these veins, in P. P. Gudkov’s opinion, is in some cases connected with the intrusion of gneisso-granite and is confined to tectonic fissures.

The formations described must be distinguished from the albite-quartz veins rich in calcite, discovered by me in work at the Yuluk mines². These latter are still younger formations and accompany the processes of formation of pyrite lenses.

From the preceding description of the rocks composing the metamorphic series, the complexity of the genesis and mutual relations among the individual elements of this formation becomes sufficiently evident. It is quite possible that the present work in many respects does not give sufficient illumination to certain questions; nevertheless, the material at our disposal permits us to arrive at the following main propositions.

1. Within the metamorphic series it appears possible to distinguish two stratigraphically different groups of rocks: a) the series of mica and green schists, and b) phyllites. The latter group is represented in the area very weakly and belongs to the upper horizons of the metamorphic series.

2. The series of rocks described is complexly metamorphosed. As we shall see below, the conglomeratic graywackes occurring in the Middle Devonian horizons contain pebbles of crystalline schists, especially phyllites. P. P. Gudkov (9, 9) indicates, in the composition of Carboniferous (?) sandstones, pebbles of gneisses distinct from the gneisses that cut this series. Finally, Nalivkin (52, 77), in Devonian deposits not younger than \(D_2^1\), notes pebbles of crystalline schists. Thus, by the Middle Devonian the rocks described had already been metamorphosed. We do not possess reliable material on the character of these first alterations, since the features of the first metamorphism may have been considerably obscured by the effects of powerful acid intrusions that followed at the end of the Paleozoic, with which the alteration of serpentinites included in the metamorphic series is probably connected³, as well as by those alterations that bear the character of injection metamorphism. Finally, the processes of ore metasomatism, which probably followed one of the last acid

of intrusions, produced in the mass of metamorphosed rocks fairly significant changes, expressed in the formation of talc, chlorite, fibrous amphiboles (anthophyllites), sericite, and carbonates.

It is very probable that the thick quartz veins and, probably, the later formations—albite-quartz veins, rich in calcite—played no small role in the processes of alteration of the latter order.

1. The rocks of the metamorphic series become less altered toward the east, with approach to the porphyrites and serpentinites of the Sakmara belt; conversely, with movement westward we observe the most strongly altered formations. This consideration does not apply to the later alterations, often connected with ore metasomatism, which are equally well expressed both in the phyllites and in the mica-quartz series. The intensification of the general character of metamorphism toward the north is, very probably, connected with more intensive processes of erosion, which exposed deeper horizons.

2. A striking feature of the rocks of the metamorphic series is the unusual abundance of albite, the amount of which is abnormal even for green schists, which, apparently, originate at the expense of erupted rocks. This circumstance is readily explained if one takes into account that the processes of alteration of the rocks were accompanied by the introduction of a greater quantity of alkalies and silica, which, as is known, are the most readily migrating elements (89; 78, 219 and 87). It is interesting to note that among the alkalies sodium predominates; this is fully consistent with Chirvinsky’s statement (82, 48) that under normal conditions the rate of diffusion of sodium is greater than that of potassium. Usually indications of the migration of potassium are easily explained by the fact that the intensive development of micas in metamorphosed series of argillaceous schists more often attracted the attention of investigators. But albite also appears not infrequently in argillaceous rocks. Of interest in this respect are I. K. Bazhenov’s descriptions of the metamorphic series of the Sayan Mountains (1, 14–15), where intensive albitization of peridotites and even of argillaceous rocks in contact with granites is observed.^1 Subsequent changes in the rocks are characterized by the development of carbonates, amphibolitization, and talcization, and are evidently likewise connected with the injection of an acid magma (103), rich in water and carbon dioxide (105). It is quite possible that the intrusive bodies responsible for all the described alterations have not yet been exposed by erosion, and that we are dealing with upper horizons rich in quartz veins.^2

3. The primary character of quartzites and phyllites is established easily, i.e., the rocks of this group possess sufficiently clear psammitic and pelitic relict structures. The matter is somewhat more difficult with the green schists of the mica-quartz series.

The green schists of the Urals have long attracted the attention of investigators. In composition they are entirely identical with Spurr’s prasinites (101), which originated through alteration of gabbroid rocks. Closely akin to them are the green schists of Steiermark, described by Angel (87, 177), as metamorphosed diabases. Chernyshev (80, 145), L. Nikolaev (55, 653), Krasnopolsky (35, 55), Vysotsky (3, 56), Duparc (11, 45 and 90, 34), Krotov (36, 200), and Zavaritsky (26, 54) point (for various regions of the Urals) to a definite connection between green schists and porphyritic rocks. There is no doubt whatever that our rocks, too, had eruptive material as the basis for their origin, and it is very probable that their most massive varieties correspond to altered diabase intrusive—

^1 The presence of acid plagioclase in injected schists is described by V. N. Lodochnikov (45, 431).

^2 Nikitin (53, 128) connects the development of mica and talc in serpentinites and the formation of listwanites from uralite porphyrite with pneumatolysis.

rocks (101). No direct transitions from the diabasic porphyrites of the Sakmara River to green schists were observed, although these porphyrites, in contacts with felsites, yield rocks similar to green schists.

2. Porphyrites, tuffs, and jaspers.

Porphyrites are rocks that are extremely widespread and occur in Ural formations of various ages. According to Vysotsky’s investigations in the N.-Tagil district (3, 22—23), rocks of this composition were extruded throughout the entire Devonian. For the Southern Urals, the lower part of the Paleozoic, older than \(D_2^2\), is, according to Nalivkin (52, 73, and 76), the most abundant in exposures of “greenstone rocks, causing intense metamorphism and the formation of jaspers and hornfels.” Since in our district porphyrites occur in exclusive association with jaspers, I shall permit myself to dwell somewhat on the small amount of literary material available on this subject.

As early as Murchison (51, 213 and 232), attention was drawn to the association of jaspers, “greenstone porphyries,” and copper-ore deposits in the Southern Urals. Analyzing the composition of the rocks of the Irendyk Range, Karpinsky (28, 325) notes the close connection of porphyritic tuffs and jaspers. The same is noted by Chernyshev (80, 145, 81, 206) for the regions of the Central Urals. In the Miass dacha, Krotov B. (36, 220, 239, 361—364) describes dense tuffs, siliceous slates, and jaspers and considers these formations to be derivatives of tuffs and limestones (36, 364). The works of Vysotsky, Zavaritsky, and Pyarn for 1912—14 in the Southern Urals repeatedly establish an association of jaspers and porphyrites (62, 126—127; 63, 33; 64, 40—42 and 46). At the same time, on the one hand there are indications of interbedding of jaspers and porphyrites (62, 126—127), and on the other of the “cutting through” of jaspers by porphyrites and tuffs (63, 33; 64, 40—42). The association of jaspers and porphyrites can be discerned from the reports of Churakov and Tikhonovich (66, 35 and 42) on investigations in the districts of the town of Verkhneuralsk and the Irendyk Range. In the Irendyk region Tikhonovich notes the interbedding of siliceous shales, porphyrites, and their tuffs. Moreover, this entire complex of rocks is overlain by jaspers of the Middle Devonian and by higher-lying formations of the Upper Devonian.

In the subsequent works of A. N. Zavaritsky in the Southern Urals, the connection between jaspers and porphyrites is established quite definitely (17, 375; 20, 6; 21, 37; 23, 378; 25, 104; 26, 4); moreover, in almost all his works A. N. Zavaritsky emphasizes that the porphyrites are younger than the jaspers, and only in one instance indicates interbedding of these rocks (25, 104). For the region of Verkhneuralsk, Magnitnaya, and Baimak (23, 373 and 376), porphyrites of this type are the oldest of the erupted rocks. It is interesting to note that the joint occurrence of jaspers and porphyrites also proves characteristic of the Mugodzhar Mountains. Prigorovsky repeatedly notes (72, 895, 901—902) that the main mass of porphyrites of the Mugodzhar cuts through the jaspers. At the same time, observing in the lower parts of the jasper-bearing sequence pebbles of porphyrites, he advances the supposition that there also existed an older phase of eruptions (72, 912), no later than \(D_2\).

Thus, the majority of investigators, establishing the joint occurrences of jaspers and porphyrites, note the younger age of the erupted rocks. Only in rare cases is interbedding of these formations indicated, and only Tikhonovich (66, 42) and Prigorovsky (72, 912) provide some material that permits one to suppose the existence of porphyrites older than the jaspers.

Porphyrites and their tuffs within the area studied occur at the following points: a) the Sakmara River, where the porphyrites occur together with serpentinites at the boundary with the phyllite horizon of the metamorphic series, and b) the Irendyk Range.

Considering the relationship between jaspers and porphyrites, it must be noted that the most significant masses of jasper within the area studied are situated at the boundary of the greywacke series and the porphyrites of the Irendyk Range and the Sakmara River, thus corresponding to the uppermost horizons of the formation described. On the other hand, within the thick series of porphyrites and tuffs of the Irendyk Range one also observes thin interbeds of altered green jaspers, often impregnated with chalcedony. Finally, a thick band of strongly fractured jaspers separates the rocks of Irendyk from the “lower green suite,” which, according to the investigations of L. S. Librovich (44, 74), belongs to the upper horizons of the Middle Devonian; and the black siliceous shales of this suite, in the area of our investigations, are in composition very close to jasper formations, since under the microscope they reveal, in their composition, oval concretions of quartz and chalcedony characteristic of radiolarians. All these observations allow one to note that jaspers are formations characteristic of the entire Middle Devonian series, but they are most strongly developed in the upper horizons of the formation, where in some cases they are closely interbedded with tuffaceous formations.¹ Moreover, since the greater part of the tuffs contains fragments of augite porphyrites, in the present case it will perhaps be more correct to consider that a large part of the porphyrites belongs to deeper horizons than the jaspers. Leaving aside the green schists of the metamorphic series, the original material for which may have been formations of this kind, the augite porphyrites within the area studied are, as was noted for the Southern Urals by A. N. Zavaritsky (23, 373), the oldest of the eruptive rocks, whose age in this case does not extend beyond the limits of the Middle Devonian.

a) The porphyrites of the Sakmara extend in an almost continuous belt along the eastern boundary of the crystalline schists through the entire district. In places they come into contact with jaspers, but more often they are separated by intrusive bodies of gabbro-peridotite magma. The relations between the porphyrites and the gabbroid rocks are unclear. It is very probable that the diabase dikes cutting the porphyrites are derivatives of the gabbro-peridotite magma. The relations of the rocks are greatly obscured by the similarity of the marginal facies of the gabbro and the diabase porphyrites.² In some cases it is entirely impossible to distinguish whether we are dealing with an effusive or an intrusive rock, especially if one takes into account that both types of formation along this belt have undergone strong milonitization and are penetrated by quartz feldspathites, whose injection was accompanied by silicification phenomena and by impregnation of the country rocks with chalcedony.

Usually dense, with a weakly expressed porphyritic structure, colored in various shades of green, the Sakmara porphyrites are rarely more or less well preserved. The greater part of them is sharply milonitized and penetrated by thin quartz veinlets with albite and calcite. Milo-

nitization and subsequent metamorphism alter these rocks so much that they become somewhat similar to the green schists of the metamorphic sequence.

In composition the porphyrites are very uniform. The porphyritic segregations are represented by pyroxene and plagioclases. In very rare cases amphibole is observed, and the rocks containing this mineral are distinguished by a lighter, slightly yellowish color. The groundmass is more often of pilotaxitic, more rarely of ophitic structure, and consists of the same components.

Pyroxene in the porphyritic segregations rarely exceeds 0.8 mm in diameter, and sometimes is altogether absent; in the groundmass the size of its grains decreases to 0.04 mm in diameter and less. In a fresh state it is encountered comparatively rarely. Usually it has been altered into serpentine-chlorite, which in turn is replaced by calcite and quartz. Alteration into serpentine is accompanied by the separation of leucoxene, often as a fine dust penetrating the whole rock. As a result of these processes we often have a pseudomigdalostone structure. \(2V = +56^\circ,\ CNg = 46^\circ—55^\circ\). In some cases it is altered into uralite.

The porphyritic segregations of plagioclase attain, in individual cases, up to 2 mm in diameter. More often it predominates over pyroxene. Usually it has been altered into saussurite, more rarely into one clinozoisite or sericite. Twinning is visible rather distinctly, but zoning is not preserved. In composition it varies from No. 35 to 52. Complex twinning laws are often observed.

In places variolitic rocks occur, close in character to the variolites of Boktybai of the Mugodzhary Mountains described by Levinson-Lessing (12, 141—146 and 42, 220). Varioles from 1.5 to 2 mm in diameter are round formations of radial-fibrous structure, consisting of pale-green amphibole and plagioclase. The groundmass consists of amphibole alone.

Mylonitization of the porphyrites is very widespread and is accompanied by a large number of quartz, quartz-albite, and calcite veinlets. In the groundmass of the mylonitized rocks the primary minerals can rarely be discerned. Ordinarily we have dense rocks, sharply schistose, with a patchy dirty-green coloration. Under the microscope the finely comminuted material of the porphyritic segregations of plagioclase and pyroxene appears immersed in a complex aggregate of albite, clinozoisite, epidote, sericite, quartz, leucoxene, chlorite, and pale-yellow serpentine predominating over all these components, characteristic of mylonitized serpentinites (76, 82—83). The filling of cracks by quartz veinlets is often accompanied by amphibolitization, development of epidote, impregnation by pyrites, and silicification of the rock. The same changes are observed in porphyrites in contact with felsitic porphyries. This time the changes are so intense that we have green rocks, rich in a finely disseminated dust of radiating amphibole and albite, very reminiscent in composition of certain varieties of amphibole green schists of the metamorphic sequence.

The processes of silicification accompanying the injection of quartz-albite veinlets are expressed in an extremely interesting way. Numerous observations on mylonites indicate that usually we are dealing with intersecting veinlets of different composition. The earliest in age, straight quartz veinlets are always broken and cut by capriciously winding albite-quartz veinlets (Figs. 4—5), accompanied by strong swellings and rapidly wedging out¹. In some cases the rock is so densely penetrated by thin quartz veinlets of this composition that it takes on a gneiss-like appearance. Usually such rocks are noticeably impregnated with pyrites (environs of the village of Yumasheva). It is often observed that impregnation by quartz

is limited by the alteration of the porphyritic segregations of the rock (Fig. 6). In such cases the quartz is often accompanied by calcite and chlorite. Finally, the penetration of the rock by quartz is sometimes so fine that the entire rock has a gray interference coloration of a basic tone, with a radiating structure, caused by the finest threads—veinlets—of quartz.

Taking into account the sharp milonitization, strong alteration, and weakly expressed porphyritic structure, it is more correct to call the Sakmara porphyrites diabase porphyrites.

Tuffs of diabase porphyrites occur in the region of the Sakmara River comparatively rarely. Their outcrops have been noted in the vicinity of the village of Iskakovo on the Sakmar River and at the head of the Belekéi River, which enters the Sakmara from the right somewhat above the village of Muldabaevo. Usually these are dark rocks with a greenish tint, consisting of angular porphyritic fragments cemented by limonite-chlorite-serpentine, more rarely calcitic or ferruginous, material. In some cases these formations are difficult to distinguish from broken porphyrites.^1) Together with these rocks there are observed jaspers and tuffaceous sandstones, very similar in character and composition to the graywackes of the Upper (?) Devonian. Finally, in the same places small outcrops of micaceous quartz sandstones were encountered, in whose composition, among grains of quartz, there occur rounded grains of tourmaline and flakes of mica^2). The outcrops of all these formations represent areas of strongly shattered—milonitized—rocks surrounded by serpentinite.

b) Porphyrites and tuffs of the Irendyk Range. Insofar as the diabase porphyrites of the Sakmara River are poor in tuffs, the augite porphyrites of the Irendyk are rich in them. The entire northern part of the investigated area, crossed by the road from the Tubinsk mine to the village of Kuseevo, is composed almost exclusively of epidotized and impregnated with pyrites tuffs of augite porphyrites, containing here and there thin interbeds that have taken on a green color, often impregnated with cubes of pyrite, of uniformly colored or banded jaspers.

In composition and structure the effusives of the Irendyk are more varied than the rocks of the Sakmara River. Augite porphyrites with a sharply expressed porphyritic structure predominate. Somewhat more rarely there occur porphyrites whose phenocrysts are represented only by plagioclase and, finally, in some cases quartz-bearing keratophyric-type formations are encountered^3). All the rocks have undergone strong alteration, expressed in sharp epidotization, accompanied by the deposition of quartz and pyrites.

In some varieties pyroxene reaches 1 cm in diameter and in this case has an oval, almost round form. It is remarkably well preserved both in the tuffs and in the porphyrites. Twins are very common. \(2V = +60^\circ - 59^\circ\), \(CN_g - 45^\circ\). Augite. Just as in the diabase porphyrites of the Sakmara River, pseudomorphs of quartz after augite are often observed. Epidote and serpentine are very often added to the quartz.

Plagioclase is either sharply sericitized or proves to be albite. Evidently, in this case we are dealing with decalcified plagioclase, a phenomenon very characteristic of the Devonian porphyrites of the Urals (36, 208—209).

The main mass is almost always pilotaxitic and only in the more acidic varieties becomes felsitic or andesitic, with a noticeable fluidal arrangement of the plagioclase laths. Often the alteration of the rock proceeds so far that—

^1) Leviason-Lessing draws attention to the very same circumstance (41, 85) in investigations in the South-Zaozerskaya dacha.

^2) The rocks closely resemble the sericite sandstones of the phyllite series of the Southern Urals, described by E. K. Vysotskii (3, 74).

^3) In the vast majority of cases these rocks have the character of vein effusives and are completely identical with the quartz albitophyres described below. It is most likely that in the present case we are dealing with formations younger than the augite porphyrites.

that the bulk of the rock is a continuous felt of epidote, chlorite, serpentine, and leucoxene. Quartz, in the overwhelming majority of cases, is secondary.

The most highly developed of the secondary minerals is epidote, occurring in the rock in the form of accumulations—aggregates or veinlets. In some cases its amount is so great that we have a rock composed almost entirely of epidote. In the vast majority of cases epidote, like quartz, is a metasomatic mineral.

The tuffs of augite porphyries are extremely uniform in composition, but vary greatly in the size of the fragments, which in some cases reach 5–10 cm in diameter, forming flow breccias described by Zavaritskii (20, 6). Psammitic varieties occur more often than pelitic ones. A common component of the tuffs is the numerous angular fragments of the porphyries described, most often augitic ones. The groundmass retains no traces of its primary composition and has been entirely transformed into a complex aggregate of epidote, actinolite, chlorite, albite, and leucoxene. There is very much metasomatic quartz and epidote. A characteristic feature is the presence, in large quantity, of fragments of augite, striking in their freshness. No fragments of jasper were observed.

Jaspers. Rocks of this type are very widespread in our district and do not differ in any way from the radiolarian jaspers described by Chernyshev (81, 207) and Zavaritskii (15, 60; 16, 222; and 21, 42–44) for various districts of the Southern Urals and assigned by E. Ya. Perno (64, 51) to the upper division of the Middle Devonian. They form narrow ridges of hills of meridional strike. Often along the strike they pinch out and pass into siliceous-clayey rocks. Usually the thickness of the jaspers is not great, but sometimes reaches 1000 m. Probably in this latter case we are observing an exaggerated thickness caused by the gentle bedding of the jaspers. In the vast majority of cases these are dense rocks with an even fracture, colored in various colors. Red and black jaspers are encountered most often, more rarely pinkish, yellowish, gray, and banded ones. On weathering they break up into angular parallelepipedal rubble. Under the microscope the chief mineral is quartz, with grain size varying according to the degree of recrystallization of the rock. In the most recrystallized rocks, dentate-bordered quartz forms a structure close to a mosaic one; among little-altered rocks there occur varieties consisting of a fine siliceous-clayey, almost isotropic material. Secondary components are clayey material, calcite, and flakes of colloidal material that color the rock. In some cases the latter is replaced by hematite. Judging from the frequent presence of manganese in the jaspers, this element too probably plays no small role in the coloration of the rocks.

The most characteristic feature of these rocks is the presence of oval, almost round bodies, filled, depending on the degree of alteration of the rock, with quartz, chalcedony, or clayey isotropic material. The diameter of these bodies is remarkably constant and ranges from 0.06 to 0.1 mm. In mylonitized jaspers these inclusions are also deformed and strongly flattened; in the most recrystallized varieties of jasper they are very faintly visible, and then only with crossed nicols. Finally, in several well-preserved siliceous rocks it was possible to observe, in some such bodies (Fig. 7), appendages resembling needles. There is no doubt that in these cases we are dealing with material of organic origin, identical with the radiolarian jaspers common in the Southern Urals.

In the process of metamorphism the jaspers first of all recrystallize. A large number of quartz veinlets appear, sometimes tracing a very intricate pattern. Then sericite appears, especially in the clayey varieties, and, finally, within the altered porphyries and tuffs of Irendyк there occur

colored green diabase rocks containing large quantities of pyrite, chlorite, epidote, and titanite. And in these altered varieties the oval radiolarian bodies are clearly visible. The altered diabases are especially well manifested on the left bank of the Sapsal River, near the road from the Tubinsky mine to the village of Kuseevo.

3. Siliceous shales and tuffites of the Middle (?) Devonian.

On the eastern slope of the Irendyk Range the described porphyrite sequence is replaced by a belt of diabases, upon which lies a suite of closely interbedded tuffaceous sandstones and siliceous shales. These rocks occur conformably with the diabases, dipping eastward, and wedge out toward the east¹). In comparison with the tuffs of the Irendyk Range, the rocks of this sequence are less affected by metasomatic processes, and only the lower horizons of the suite, directly adjoining the diabases, are distinctly altered.

In composition and character the suite described occupies an intermediate position between the sequence of the Irendyk Range and the Upper Devonian greywackes described below. The siliceous shales are usually dense blackish-gray rocks, composed of fine tuffaceous material to which siliceous (sometimes amorphous) material is admixed in varying amounts. Calcite and oval quartz-filled formations are often observed, entirely identical with those of the radiolarian diabases. The tuffaceous sandstones usually consist of very poorly rounded or angular fragments of porphyrites, albitophyres²), and diabases, cemented by clayey material and often permeated throughout by chlorite—serpentine. Occasionally large fragments of quartz are encountered, resembling phenocrysts of albitophyres.

In the upper horizons of this suite, near the pond on the Sultanka River (one kilometer east of the village of Kuseevo), there occur comparatively fresh tuffs of pyroxene porphyrites. The horizontal thickness of the tuffs does not exceed 400 meters, and these rocks extend in such a narrow band far northward, along the western margin of a small meridional ridge of hills. Throughout their entire extent the tuffs are accompanied by fragments of strongly dislocated and altered diabases. In addition, small lenses of indeterminate occurrence of dark-gray stromatoporoid limestones³) are associated with them. In composition and structure these rocks differ from the tuffs of the Sakmara River and the Irendyk Range. Usually we have dirty-greenish coarse- or medium-grained rocks, consisting of angular fragments of porphyrites and, in some cases, diabases. In the latter case calcite appears as the cement, sometimes predominating in the composition of the rock. In the finer-grained varieties an ellipsoidal shell-like jointing is often observed. In the coarse-grained varieties individual fragments reach 5 or more centimeters and at first glance strongly resemble flow breccias in the porphyrites of the Irendyk Range. The rocks are often entirely unmetamorphosed and consist of extremely varied porphyritic material. Diabase and augite porphyrites predominate, but very often more acidic varieties are added to them, close in composition to felsitic porphyrites and even quartz albitophyres.

Both in lithological composition and in position (lying upon the diabases), the sequence of these rocks is very close to the “lower green suite” described by L. S. Librovich (44, 74), which lies upon the diabases of the southern part of the eastern slope of the Irendyk Range and was assigned by him to the upper horizons of the Middle Devonian. Sim—

¹) In the area of the Suvarsky mine one can often observe an almost horizontal occurrence of the rocks.
²) Fragments of these rocks often predominate.
³) They resemble the dark limestones with a pelicipod–gastropod fauna described by L. S. Librovich for the lower horizons of the Upper Devonian (44, 75).

This is further exacerbated by the presence in the upper horizons of our series of stromatoporoid limestones, whose occurrence, according to the studies of E. Ya. Chern (74, 350), is characteristic of the very lowest horizons of the Upper Devonian¹. Proceeding from these considerations, I have provisionally assigned on the map to the Upper Devonian the tuffaceous sandstones and shales adjoining from the east the belt of tuffs with outcrops of jasper and limestone, cut through by diorites and similar in composition to the rocks of the grauwacke series described below.

4. The Grauwacke Series of the Upper Devonian.

The series described takes a fairly considerable part in the structure of the region studied. All the lowered, plain-like areas between Ural-Tau and Irendyk, as well as some parts of the gently rising steppe east of Irendyk,² are composed predominantly of grauwacke sandstones and clayey shales. Belts of these rocks extend far to the south, and already beyond the limits of our survey, on the river Ziryan-agach, which enters the Tanalyk from the right near the village of Yulbarsovo, the grauwackes contain interbeds of coal and are overlain by crinoid limestones of the Lower Carboniferous \((C^1_1)\), containing an abundant fauna, in which, according to preliminary determinations by Prof. P. M. Ryzhkov of the Siberian Technological Institute, the following forms have been recorded: Reticularia lineata Mart., Spirifer bilobatus Janich, Spirifer cf. duplicicosta Phill., Spirifer cf. crassus Kon., Productus mesolobus Phill., Productus plicatilis Sow., Productus pustulosus Phill., Orthis resupinata Mart., Pugnax triplex M’Coy. The grauwackes containing coal beds are connected with the series described by imperceptible transitions, but are distinguished by an extraordinary abundance of concretions of varied form, among which spherical ones predominate, in individual cases reaching up to 0.5 m in diameter. The rocks of the eastern belt are entirely identical with those of the western,³ but are distinguished by a large number of sill-like bodies of augite diorites cutting through them, and do not contain, in any noticeable quantity, fragments of rocks of the metamorphic series.

In character, the suite described is very close to similar Upper Devonian formations noted by various investigators (60, 257; 61, 147; 62; 127, 70, 226–228; 74, 366–368) for regions of the Southern Urals near our own. It must be supposed that the main mass of these rocks, especially in the northern parts, is of greater age than in the south. It is very possible that the grauwackes of the Ziryan-Agach River belong to the horizon of sandstones referred by Librovich (70, 226) to the base of the Lower Carboniferous. But it is also quite possible that some parts of the rocks directly adjoining the jaspers belong still to the upper parts of the Middle Devonian, and consequently correspond approximately to the “lower green suite” noted on the eastern slope of the Irendyk Range. The following circumstances speak in favor of this view. In the great majority of cases, direct contacts between the jaspers and the rocks of the grauwacke series cannot be observed, since fine jasper rubble covers considerable areas, usually concealing the outcrops of rocks adjacent to the jaspers. Nevertheless, in some areas of both the western and eastern belts of jaspers it was possible to note, between the jaspers and the grauwackes, although of small thickness, outcrops of porphyrites or

their tuffs. Minor outcrops of porphyrites were observed in the western belt of pits, 1 km to the SW from the village of Tavykaeva. In the eastern row of pits, in the extreme northern part of the mapped area, 2–3 km north of the village of Tabeidullina, small outcrops of tuffs were observed between the pits and the gravel pits.

It is interesting to note the find of fusuline limestone in the area of the wide development of grauwackes. The limestone was taken from the spoil of a pit dug for a dugout amid a plowed field, 5–2 km west of the village of Voskresenskoe, situated at the headwaters of the Belekëi-Buzuluk River. No bedrock outcrops were observed, since in this place the grauwackes are covered by deposits. In a thin section of this rock the sections of individual shells are clearly visible. On the eastern slope of the Irenyk Range L. S. Librovich (44, 84) notes the presence of foraminifers in Lower Carboniferous limestones. It is possible that in this case also we are dealing with a formation of the same age.

Dirty-gray grauwackes with a greenish or yellowish tint, and with a well-expressed platy jointing, are rocks which vary greatly in grain size. Near the pit belt of the Sakmara River, especially in the vicinity of the village of Iskakova, one observes coarse conglomerates, passing gradually through conglomeratic grauwackes into closely alternating beds of grauwacke sandstones and clay shales. The pebbles of the conglomerates reach up to 25–30 cm in diameter.

The chief peculiarity of the composition of the grauwackes is the large amount of slightly rounded eruptive material, together with well-rounded pebbles of quartz, quartzites, phyllites, diabase porphyrites, epidote, garnet, jasper, and other rocks characteristic of the rocks of the metamorphic series and of the Middle Devonian. Angular or slightly rounded fragments of effusives always occur in very large quantity; they predominate in grain size over the rounded components and give the rock a structure reminiscent of tuffites. Among the unrounded eruptive material, acidic, quartz-bearing albite-porphyry rocks predominate. Diabase porphyrites usually occur in the form of well-rounded pebbles, and the serpentine-chlorite material characteristic of them often enters into the composition of the cement. The presence of a large number of fragments of quartz-bearing rocks is the main distinction of these formations from the porphyrite tuffs of the Irenyk Range. Among the quartz-bearing rocks, besides acidic effusives, an important role is played by fragments of jasper and crystalline schists, especially quartzites. Coarse pebbles of phyllites enter in large quantity into the composition of the conglomeratic grauwackes. Pure quartz pebbles are entirely absent from the conglomerates. It must be supposed that the individual pebbles or angular fragments of quartz, sometimes noticeable in the fine-grained varieties, had as their original material eruptive rocks or the quartzites of the metamorphic series. The absence of pebbles of vein quartz becomes especially significant in comparison with the Tertiary conglomerates, in which, together with pebbles of crystalline schists, pebbles of vein quartz occur in very large quantity. Evidently, a large part of the quartz veins of the metamorphic series formed after the Upper Devonian.

In the composition of the fine-grained rocks the predominant material is clayey substance, together with which there is always a certain quantity of fragments of quartz, feldspars, flakes of sericite, calcite, epidote, and leucoxene. This same material is often also the cement of grauwacke-tuffite formations.

Besides clayey cement, calcite is a very widespread binding material. Sometimes the rocks are so enriched in calcite that they pass into formations close to limestones; calcareous grauwackes are especially well developed in the southern part of the area, in the outcrops of the Belekëi-Buzuluk River. Some enrichment in lime is observed generally in the grauwacke series with increasing distance from the pits underlying it. It is very possible that the calcareous

formations characterize the younger upper horizons of the graywacke-tuffite sequence.

Coarse-grained or conglomeratic graywackes, more often confined to the lower parts of this formation, are characterized by an abundance of fragments of jasper and diabase porphyries. In such cases the cement of these rocks is the same finely comminuted diabase material, immersed in a lemon-yellow aggregate of serpentine-chlorite material. In such cases the rocks become very close in composition to the tuffs of augite porphyries of the Sakmara River, and they can be reliably distinguished only by the rounded pebbles of porphyries and phyllites, which, it should be noted, owing to their fine schistosity, rarely show abrasion surfaces that are clearly visible under the microscope.

Considering the composition of this sequence, one is inevitably led to note that its chief distinctive feature is the presence of well-rounded pebbles of porphyries, jaspers, and phyllites, together with weakly rounded fragments of quartz albite porphyries, often standing out by their size relative to the other components.

Thus there is reason to suppose that, by the time of the formation of our sequence, jaspers and porphyries had undergone considerable erosion; that by the same time rocks of the metamorphic sequence had been exposed by denudation; and, finally, that eruptions of quartz albite porphyries had already occurred. The question now arises: when did these eruptions of acid rocks take place? It seems to me, judging from the presence in the “lower green formation” of tuffaceous formations rich in fragments of albite porphyries, that the main phase of their eruptions belongs still to the upper parts of the Middle Devonian. Probably, by the time of deposition of the graywacke sequence, volcanic activity had almost ceased, or, if it did manifest itself, did so only very weakly and at times corresponding to the formation of its very lowest horizons.

Within the studied region, albite porphyries of an undoubtedly effusive type were not observed. At best, the quartz albite porphyries occurring in the rocks of the Irendyk Range belong to the type of the so-called “vein effusives” (76, 277—282) and are apparently more often associated with augite diorites. It is highly probable that the source of the tuffaceous material was eruptions of felsitic rocks, usually transformed into greenstones, so widespread in the southern parts of the T. Baimak district, within the main sulfide deposits, where they are often completely indistinguishable from intrusive quartz albite porphyries.

4. Intrusive rocks.

The intrusive rocks of the studied region are naturally divided into the following three groups: 1) ultrabasic intrusive rocks of gabbro-peridotite magma, very widespread in the area of the Sakmara River; 2) augite diorites, forming small intrusive bodies in almost all formations of the district, but occurring most abundantly among the graywackes of the Upper Devonian east of the Irendyk Range; and 3) quartz or felsitic albite porphyries, occurring as small intrusive bodies in the peridotites and among metasomatically altered rocks of the Irendyk Range.

Peridotites of the Sakmara River form an almost continuous series of small intrusive bodies, having an ellipsoid-like form, the minor axis of which rarely exceeds 2 km, while the major reaches 7—10 km. In mineralogical composition the rocks described belong to the group of pyroxene peridotites, characteristic, according to the indications of Vysotsky (4, 212), of the eastern slope of the Urals, and occupying the last place in platinum content among the olivine rocks of the Urals. Within individual intrusive bodies the pyroxenites vary rather considerably in mineralogical composition. Nor-

normally the peripheral parts of the bodies consist of gabbro, whereas the central parts are represented by pyroxene peridotites of varying composition, often almost completely transformed into serpentinites.

The gabbroic rocks are rather uniform in mineralogical composition, but vary greatly in grain size. Alongside coarse—or even very coarse—grained rocks, medium- and fine-grained varieties are often encountered, lying at only a very slight distance from the former. In general it should be noted that the marginal gabbroic zone of the peridotite bodies is of insignificant thickness and is often entirely absent. The chief components of these rocks are pyroxene and plagioclase in a typical gabbroic association; in the fine-grained varieties ophitic and porphyritic textures are observed. Quartz gabbros were encountered rarely.

In a fresh state, gabbroic rocks are not found. The best-preserved specimen taken was one of quartz gabbro¹, in which it was possible to determine the number of the plagioclase, which proved to be andesine No. 38. (The mode of occurrence of this rock is uncertain; it is very possible that it represents a vein in pyroxene peridotite.) Usually the plagioclase has wholly passed into saussurite, and the pyroxene into uralitic hornblende. In the fine-grained varieties the only mineral often best preserved is uralitized pyroxene of porphyritic segregations. In some cases the colorless uralite has delicate polysynthetic twins, which give it a striking resemblance to plagioclase, especially in a thin section². The main mass, however, is a continuous felt of chlorite, serpentine, titanite (more often leucoxene), and saussurite. In this latter case, especially if the rock is milonitized, we have a formation extremely difficult to distinguish from altered diabase porphyries. Milonitization is often accompanied by injection of thin albite-quartz veinlets.

The gabbroic rocks should also include amphibolites, which often replace normal uralitic gabbros, especially along the contact of the albitophyres cutting the bodies of pyroxene peridotites. These rocks are particularly well expressed in the western part of the intrusive body in the area of the village of Sharmaevo. Normally these are black or mottled banded rocks of gneiss-like texture, consisting essentially of amphibole and plagioclase, to which garnet, mica, epidote, and titanite are often added as accessory constituents. The amphibole is more often in brown pleochroic colors; sometimes, apparently as a result of alteration, it assumes a green coloration. With \(N_g = 14^\circ\), \(2V = -76^\circ\). It approaches grünerite. The plagioclase is not preserved in a fresh state.

Since the amphibolites accompany the albitophyres, it is most probable that these formations should be regarded as metamorphic rocks, the original material for which was the gabbroic varieties of pyroxene peridotites. It is interesting to note that the amphibolites themselves are often strongly deformed and altered. In such cases the rock becomes green; slickenside surfaces are often observed; cracks are sometimes filled with albite-quartz veinlets, and chlorite, epidote, leucoxene, serpentine, saussurite, and talc develop.

The main mass of the pyroxene bodies consists of diverse rocks that are varied combinations of monoclinic and rhombic pyroxenes, to which a certain amount of olivine is always added. Chromite and spinel sometimes appear as accessory minerals, in considerable quantity. Pure olivine rocks are not encountered. Usually we have a wehrlite–harzburgite series of rocks passing into almost pure pyroxenites—diallagites. Monoclinic pyroxenes generally predominate over rhombic ones. The latter are more often represented by enstatite, whose presence in the rock—

... is always accompanied by monoclinic pyroxene and olivine. In varieties rich in olivine, rhombic pyroxene predominates. The structure is most often poikilitic. Usually we have large (not more than 3 cm) pyroxene crystals, poikilitically penetrated by olivine in the form of small oval grains. Among secondary minerals, uralite, bastite, chlorite, talc, and serpentine play a large role. With intense serpentinization the rocks take on a black coloration; the latter acquires bluish and green tones when all the components of the rock are altered. In such cases, in the thin section, besides serpentine, only bastite is often observed, emphasizing the primary nature of the rock. Unlike the serpentinites of the metamorphic sequence, the serpentine of the rocks described more often has a typical mesh, rather than antigorite, lattice structure. In the rocks richest in olivine (vicinity of the village of Sharmaevo), thin (1 cm) veinlets of chrysotile are often encountered among the black serpentinized harzburgites.

The relationship between the pyroxenites and the enclosing country rocks is extremely uncertain. Above, the striking similarity between the marginal gabbroid facies and the diabase porphyrites bordering them has already been mentioned more than once. Moreover, the entire belt of pyroxenite rocks and diabases is strongly mylonitized. In the very body of the serpentinites, typical serpentinite schists are very often encountered, consisting of material so finely crushed that under the microscope it does not affect polarized light¹. Crushing of the rock is often accompanied by silicification, as a result of which under the microscope we have complete replacement of serpentine by quartz, with preservation of the structure characteristic of the former. Mylonitization and metamorphism associated with the injection of albitophyres and the post-volcanic processes that followed them greatly obscure the phenomena of contact action of the gabbro-peridotite magma upon the country rocks, which in the present case are represented in the west by porphyrites that differ little in composition, and at the eastern contact by jaspers.

Observations on the contacts of serpentinites with jaspers and graywackes of the Upper Devonian provide extremely ambiguous material. Alteration in the jaspers is observed only in connection with the sharp mylonitization of these rocks. Such ocherous and silicified, strongly fractured jaspers are found near the village of Temyasovo, at the village of Chingiz (the steep hill opposite the village of Itkulovo), and in other places that have attracted the attention of prospecting parties². In places, in such cases, quartz veins and actinolitized broken rocks of the graywacke sequence are observed. We do not consider it possible to ascribe these phenomena of metamorphism to the influence of the gabbro-peridotite magma³, since observations in the calmer parts of the eastern contact indicate the complete preservation of the jaspers and even of the limy graywackes. Of interest in this respect is the contact of the peridotites and jaspers on the northern margin of Lake Murzakaeva. At this point the serpentinized peridotites are separated from the limy graywackes by a small pinching-out interbed of jaspers, the thickness of which here does not exceed 5–6 meters. Microscopic study established the striking freshness of these and other rocks. In the jaspers, for example, the quartz material composing them is almost completely unrecrystallized. The absence of noticeable signs of metamorphism can be explained by the mechanical contact of these formations, by the extremely weak manifestation of metamorphism characteristic of ultrabasic rocks, or by its complete absence. Thus, observations on the contacts do not provide material for establishing the age relations of the jaspers, porphyrites, and serpentinites; however, taking into account the extensive literature on this

question, one may for the time being conditionally accept the prevailing opinion on this matter. With the exception of Fedorov (77, 90), who associated the time of formation of the ultrabasic rocks of the northern Urals with the Lower Paleozoic, all the other investigators, in the persons of Vysotsky (3, 35; 4, 194; 63, 31; 64, 40–42), Zavaritsky (23, 383–384), Krotov (36, 400), Baklund (2, 95–96), and others, regard the beginning of the Hercynian folding as the earliest time of intrusion of the olivine rocks of the Urals¹. Therefore, in further geological constructions we shall have in mind the probable Lower- or Middle Carboniferous age of intrusion of the gabbro-peridotite magma, i.e., we shall regard the diabase porphyrites and the jasps as more ancient formations.

Augite diorites. By this name are understood typical hypabyssal rocks, strongly varying in composition, structure, and size of intrusive bodies, which occur in almost all the formations of the district. Within the metamorphic series, near Lake Algazina on the Malyi Yuluk River, there are exposures of quartz augite diorite; the strong development of loose formations does not permit the form of the intrusive body to be established. In the area of the Tubinskii mine, on the left bank of the Sapsal River, there are exposures of augite diorites of indefinite outline, noted already by Zavaritsky (20, 13). On the northwestern margin of Lake Tolkach, augite diorites have been found lying as a meridionally elongated intrusive body. In both cases these rocks occur at the boundary of the Irendyk tuffs and the Upper Devonian graywackes, and noticeably metamorphose the latter². A large number of vein-like masses of diorites, whose thickness varies from 500 to 1 meter, is observed in the area of the Sunar mine and Lake Sultan.

The rocks described rarely have a porphyritic structure. More often they are even- and medium-grained, mottled formations. Dark varieties also occur, with a strong development of dark-colored components, among which amphibole always predominates. A taxitic structure is very often observed; it is expressed in the segregation of small schlieren rich in quartz and albite, distinguished by a larger grain size than the enclosing rock. Sometimes within a single intrusive body one may observe all the varieties of these rocks, forming a complete gamut from quartz mangerite to hornblendites; but there are cases when the latter form independent bodies.

The diorites usually contain the following minerals: pyroxene, plagioclase, amphibole, albite, sphene, apatite, and ilmenite; in the most acid formations—quartz and biotite. Pyrites and calcite are extremely widespread, their appearance being accompanied by the development of sericite, chlorite, serpentine, prehnite, and epidote. In some cases, within the diorite body, there is development of thin calcite-quartz veins that have been the object of exploitation for gold.

Pyroxene is almost always pinkish in color, very rarely colorless; \(2V = +62^\circ\), \(CNg = 39^\circ\)—\(40^\circ\). It is often overgrown by amphibole and sometimes is almost wholly replaced by it. It alters into serpentine and chlorite. Amphibole, with pleochroism in reddish-brown to yellow tones, is an indispensable member of these rocks. Its optical constants are extremely variable. The extinction angle varies from \(2^\circ\) to \(40^\circ\), \(2V = -60^\circ\) to \(-87^\circ\). In one case \(2V = +86^\circ\). Evidently we are dealing with a series of transitional members from basaltic hornblende to kataphorite. Basaltic hornblende with a small extinction angle is more often encountered in hornblendites, whereas in the more acid rocks rich in quartz and albite a typical kataphorite appears.

The tendency of the rocks to differentiate is most sharply expressed in the composition of the plagioclase. Within a single thin section it is almost always possible to observe two generations of this mineral. The first separates out soon after the pyroxene and ranges in composition from No. 50 to No. 10. The second is represented by albite and, in time of formation, belongs to the later stages of the rock’s consolidation. The formation of albite immediately precedes the appearance of quartz and—possibly—of biotite. In the most acid varieties, albite is not inferior in amount to plagioclase, which in these cases is more often represented by oligoclase. In the basic rocks it occupies narrow, angular interstices between the plagioclase prisms or rims them with a thin border. In quartz-rich varieties antiperthite and sometimes alkali feldspar were observed.

Quartz is typically residual; it more often occupies triangular interstices between plagioclase prisms in the form of fine micropegmatitic aggregates. Occasionally quartz crystals free from feldspar are observed. In such cases biotite is strongly developed in the rock.

Ilmenite and sphene are closely connected with one another in their appearance. The separation of ilmenite is constantly associated with the appearance of hornblende. In places a mutual intergrowth of these minerals is observed.

Calcite and pyrites¹ belong, in time, to processes following rapidly after the last stages of formation of the rock. The rocks in the vicinity of the Sunar deposit and Lake Sultaevo are especially rich in these minerals. In these cases a strong alteration of all components is noticeable. The dark-colored minerals usually change into chlorite; in the hornblendites, uralite, serpentine, and talc also develop; the plagioclases pass into sericite, and sometimes prehnite and epidote develop.

Thus, the formations described, as was already noted by A. N. Zavaritsky (20, 13), in their most acid varieties approach syenitic rocks, with sodium predominating over potassium in the chemical composition. The appearance in such cases of residual quartz and the hypabyssal character of the rocks make it fully justified to call them quartz monzonites. On the other hand, along the Sultanka River, near the village of Kuseevo, along with ordinary diorites there were observed outcrops of hornblendites consisting almost exclusively of amphibole, among the crystals of which islands of relict pyroxene are preserved, producing the impression of a poikilitic structure. Quartz monzonite and hornblendite are, for the dioritic rocks, extreme members connected with one another by a close series of transitional formations.

Normally, the contact effects of diorites on the country rocks are manifested rather weakly² and are reduced to phenomena of contact metasomatism. Usually the graywackes undergo noticeable silicification. Feldspars in fragments of porphyrites pass into sericite or prehnite. In the area of the Sultanka River, where there is a dense network of dioritic bodies, phenomena of contact metamorphism are completely obscured by metasomatic processes, as a result of which we have black massive hornfelses, rich in zoisite albite, epidote, calcite, and ores. The latter apparently account for the dark coloration of these rocks. Sometimes prehnite, epidote, leucoxene, and fibrous amphibole develop in the country rocks.

Albitophyres. In our region, outcrops of albitophyric rocks are often associated with augite diorites and follow tectonic lines³.

¹ Pyrite and chalcopyrite.
² It proved possible to trace only the contacts of diorite with graywackes, since the contacts of diorites with the Irendyk rocks in the area of the Tubinsky mine are covered by a large swamp.
³ The same is indicated by Vysotsky (3, 64) for the Southern Urals, where “quartz keratophyres” mark faults as narrow bands.

Three belts of these formations are discernible. The first belt is confined to the diabasic porphyrites and serpentinites of the Sakmara River. The albitophyres of this belt, in contact with the serpentinites, are marked by the development of amphibolites. The second belt runs along the western boundary of the porphyrites and jasper of the Irendyk Range with the graywacke sequence. In this case the albitophyres are associated with diorites, which are often in contact with the graywackes. Clear contacts between the albitophyres and the graywackes were not observed. The enclosing rocks are more often the tuffs of the Irendyk Range. In most cases we are dealing quite clearly with intrusive formations resembling “vein effusives” (36, 277–284). Finally, small outcrops of quartz albitophyres were observed along a narrow belt of tuffs and jaspers running approximately 1 km west of the Sunar mine.

There is not sufficient material concerning the age of these rocks. Since the albitophyres cut the peridotites of the Sakmara River, we are entitled to regard them as among the youngest formations in our area (if the Carboniferous age of the basic rocks is accepted). But, as has already been mentioned, we have sufficient grounds to believe that rocks of approximately the same composition may also have been present in the upper horizons of the Middle Devonian. The rocks of the second belt are the most doubtful in this respect, since their enclosing rocks are the tuffs of the Irendyk Range. However, since some of these bodies clearly follow tectonic lines that also include the graywackes, there is more reason to suppose that in this case as well (at least for the greater part) the albitophyres are formations younger than the graywackes.

No direct connection between the diorites and the albitophyres was observed, but since both mark by their appearance the zones of one and the same disturbances, a genetic connection between these formations becomes very probable. In favor of this same circumstance are the well-expressed phenomena of metasomatism accompanying the injection of both kinds of rocks. In both cases the metasomatic processes, differing in intensity, are extremely similar in the composition of the minerals deposited, of which the most frequently encountered are quartz, epidote, pyrites, and carbonates¹.

The albitophyres are dense, quartz-rich rocks, sometimes with a weak porphyritic structure, and of varied coloration. Most often they are light-colored, with yellowish, pinkish, or greenish tints, but there are also dark, almost black, or black-green rocks. The green coloration is usually connected with secondary alteration: mineralization and propylitization.

In the porphyritic segregations there are usually quartz and albite, more rarely one of these minerals. The groundmass consists of the same components, to which is added chlorite, developing at the expense of an indistinct dark-colored mineral. As accessories, sphene and magnetite occur. Secondary minerals are quartz, pyrite, sericite, chlorite, epidote, and, perhaps in some cases, sphene may also be secondary. The structure of the groundmass is very varied. In the more basic rocks poor in quartz, we often have structures approaching trachytic or andesitic. In the acidic varieties, microfelsitic, microgranitic, and spherulitic structures are very widespread.

The quartz of the porphyritic segregations rarely exceeds 1 mm in diameter; it is sometimes very regularly bounded by crystallographic faces, often strongly corroded by the groundmass and surrounded (especially in the spherulitic varieties) by a sharply expressed rim consisting of a parallel-fibrous aggregate (quartz-feldspathic), characteristic of the spherulites of the groundmass. In the groundmass

In the rock mass, quartz occurs in an extremely varied manner, depending on its origin. Primary quartz is usually associated with feldspars in the structural relationships indicated above. Spherulitic formations deserve some attention. In size, the spherulites rarely exceed 0.15 mm in diameter, but they are usually much smaller. In form they approach the spherical, but their sections rarely attain regular circular outlines. This circumstance is evidently explained not only by compression from the surrounding medium during the growth of the spherulite. It is observed that the material of the spherulite is completely identical in structure with the border that clothes the porphyritic segregations of quartz. Sometimes, at the center of the spherulite, there is a small quartz crystal that has not yet dissolved (sometimes sphene). In these latter cases the shape of the spherulite is especially irregular, being apparently determined by the outlines of the mineral undergoing resorption. The most widespread among the spherulites is a radial-fibrous structure (Fig. 8), but in some cases (together with normal spherulites) ellipsoidal quartz aggregates of concentric—crustiform structure are encountered (Figs. 9–10). The individual zones of these formations differ from one another in grain size.

Secondary quartz is very often encountered in albitophyres in the form of veinlets, separate accumulations, or rims around pyrite grains (Fig. 11). Sometimes quartz appears in such considerable quantity that it completely obscures the primary structure of the rock. In some cases it is quite impossible to distinguish silicified felsites from silicified jaspers and graywackes.

Feldspar is normally represented by albite, but in some rocks plagioclases are also encountered together with albite. Unfortunately, in such cases we are dealing with strongly destroyed phenocrysts, in which only the outer albitic border has been preserved, while the inner part is filled with a brown serpentine-chlorite material with admixtures of flakes of mica, epidote, and clayey (perhaps poizitic) substance. Usually, in rocks where plagioclases occur, they form phenocrysts of greater size than the accompanying albite.

The intrusion of albitophyres was accompanied by intense metasomatic processes, as a result of which we have propylitization of the albitophyres themselves and pronounced phenomena of metasomatism in the country rocks. The processes of mineralization are expressed chiefly in epidotization, silicification, and impregnation with pyrite ores¹. In the area of the felsite belt passing through Lake Tolkach and the Tubinsk mine, the rocks most affected by metasomatic processes are the porphyrites and tuffs of Irendyk, which dip to the east and thus constitute, as it were, the hanging wall of the albitophyre veins. In the area of the serpentinite belt of the Sakmara River, apart from the usual phenomena of silicification and pyritization, the injection of albitophyres is accompanied by a strong development in the country rocks of albite-calcite-quartz veinlets. This circumstance is of considerable interest, especially if one takes into account that on the eastern slope of Irendyk, calcite-quartz veins accompany the intrusion of diorites.

5. Tertiary deposits.

In concluding the description of the formations of the investigated area, mention should be made of the comparatively rare occurrences of gravels and even conglomerates. Formations of this character were encountered along the Sakmagush River, 1.5 km north of the village of Iskakovo, where they occur rather high above the river valley in the form of small accumulations—remnants preserved from the modern

of washout. The pebble, which makes up these rocks, is excellently rounded and consists chiefly of vein quartz and rocks of the metamorphic series. Apparently, our pebble beds are entirely identical with formations of the same kind described by Vysotskii (59, 163) for the Krinka Ridge on the eastern slope of the Southern Urals, where they are remnants of a Neogene basin. It is very possible that the quartz and jasper pebble, as if scattered over the plain between Ural-Tau and the Irendyk Range, has as its source Tertiary formations almost completely destroyed by present-day erosion.

TECTONICS AND STRATIGRAPHY.

The Verkhneuralsk district was called by Murchison (51, 252) a “nest of disorders.” Analyzing the stratigraphy of the Southern Urals, this scholar (51, 251—252) notes that “among strata uniformly strongly fractured and altered, it is fruitless labor to seek the order of beds according to their superposition,” i.e., he goes on to say, “the sequence is often in an inverted position, with the younger beds dipping beneath the older.” In the subsequent literature on the Urals, especially on its southern part, we constantly encounter indications of the development of isoclinal folding (86, 424; 34, 48; 30, 277; 64, 48—49), accompanied in some cases by intrusions of acid magma (86, 424—425). The same picture is noted by Prigorovskii (73, 530) for the region of the Mugodzhar Mountains. A. N. Zavaritskii (22, 55—58), in his general work on the tectonics of the Urals, definitely emphasizes the coexistence of inclination and overturning of folds with ruptures of the overthrust type. The same tectonic relationships of formations on the western slope of the Southern Urals are noted in recent works by Nalivkin (70, 224—225), who points out, among other things, the intense dislocation of the nappe type for the lower Paleozoic (52, 73).

Dislocation processes of this type, at least in the Southern Urals, extend to all formations of the Paleozoic (63, 34) and are assigned in time, chiefly, to the Middle Carboniferous. But the orogenic processes of the Urals are not limited to this. The most recent work of E. A. Kuznetsov and E. E. Zakharov clearly indicates the existence of Tertiary-age disturbances of the thrust type on the eastern slope of the Urals (40, 23). The superposition of just these two systems of disturbances, the existence of which for the time being cannot be doubted,¹ must create a rather complicated picture of the tectonics of the Urals. However, in the literature on the Urals there are indications of the existence of an even more ancient phase of orogenic movements, preceding the main mountain-building process of the Urals. Fedorov (77, 86) believed that the ancient meridional folding of the Northern Urals was associated with the Lower Devonian transgression. For the northern Urals, Vysotskii admits the existence of plicative dislocations, accompanied by faults, along which eruptions of augite porphyrites of the beginning of the Upper Devonian took place (3, 23 and 64). Finally, Tikhonovich (67, 43) presents extremely interesting considerations for the tectonics of the southern Urals. Establishing, within the Irendyk, a lithological group “of the Middle and, perhaps, Lower Devonian, represented by extraordinarily thick deposits of clayey and siliceous shales, interbedded with porphyrites and their tuffs,” Tikhonovich² expresses the supposition of the existence in the region of the southern Urals of “a special phase of orogenic movements that long preceded the main Ural mountain-building process.”

¹ On the Ufa plateau, in the Krasnoufimsk region, Frediarksom (79, 527) recorded Tertiary-age step faults of meridional strike.

² Relying on the indication of E. Ya. Parr of a discordance in the bedding of the Upper and Middle Devonian in the Verkhneuralsk region.

Thus, in approaching the question of studying the tectonics of our district, we must remember the probable complexity of the tectonic relations of the individual formations. This year’s material is not exhaustive, and the schemes given below resolve the questions only in a first approximation. It is very likely that in reality the questions under consideration will prove much more complex, but they can hardly be presented more simply than they are set forth here. In proceeding to describe the stratigraphy and tectonics of the formations composing the district, I shall, for convenience of description, begin with the oldest formations by age.

The oldest formations in the district are crystalline schists. There are no direct indications of their age, unless one counts the presence of their pebbles in the conglomerates of the Upper Devonian. In any case, by age they are older than the Middle Devonian jaspers, and the rocks composing them, by the beginning of the Upper Devonian, had not only been metamorphosed but also laid bare by denudation. Within the investigated district the crystalline schists form an anticlinal fold, especially well expressed in the south. The dip of the beds is gentle, but the western limb is noticeably steeper than the eastern. Usually the angle of dip in the western limb varies from \(20^\circ\) to \(25^\circ\), and in the eastern from \(10^\circ\) to \(18^\circ\). Toward the north the dip increases markedly. In the eastern limb, folds of the second order are often observed, accompanied by dislocations. The axis of the fold is apparently plunging to the north.

Along the eastern contact of the metamorphic series there lies a broad belt of serpentinites and diabase porphyries cut through by albitophyres, to which are always joined fragments of jaspers, micaceous and tuffaceous sandstones, sometimes completely identical in composition with the rocks of the grauwacke series. All the rocks entering into the composition of this broad belt bear signs of strong crushing, which does not spare even the albitophyres. Widely developed phenomena of crumpling greatly obscure the mutual relations of the porphyries, serpentinites, and crystalline schists. It may be asserted with a high degree of probability that the albitophyres follow a tectonic line, probably formed in the epoch of Hercynian folding. As for the intensive phenomena of crushing, which even the albitophyres did not escape, one can only suppose that they are connected with later movements.

On the basis of the material at our disposal, it is difficult to say with certainty whether in this latter case we are dealing with vertical block displacement of masses or with dislocations of the thrust type. The presence of a block-fault dislocation at the boundary of the porphyries and crystalline schists perfectly explains the contact of the ancient western series with the younger formations of the downthrown eastern block. But if attention is paid to the wide development of phenomena of mylonitization affecting the peridotites and the various rocks included in them, then the presence also of dislocations of the thrust type becomes sufficiently probable and is even confirmed by certain observations. In the region of the village of M. Algazin there is an old abandoned copper deposit occurring in grauwackes (Fig. 12). To the west, the grauwackes are separated by a small bed of strongly shattered jasper from gabbroic rocks transformed into amphibolites. The grauwackes, like the jaspers, are also strongly mylonitized. The old workings, sunk in the grauwackes, have partly caved in, but in their dumps there is a large quantity of serpentinite rubble. The presence of this latter becomes still more noteworthy if one takes into account that, to the west at this latitude, the belt of ancient rocks is represented only by amphibolites. Such a phenomenon is most easily explained by the overlapping of the basic rocks by jaspers and grauwackes, which agrees perfectly with the absence, noted above, of contact changes in the jaspers and grauwackes at the boundary with the peridotites. Apparently, in this belt we are dealing with a complex assemblage of different ages and different types of dislocation,

it being quite probable that the movements occurred more than once and in different epochs, approximately within the limits of the same surfaces, so that the albitophyres, perhaps following thrust-type disturbances of the Hercynian folding, were themselves subsequently broken by displacements of the same character, the latest of which was the horst uplift of Ural-tau (Figs. 17 and 18).

The Middle Devonian series of the Irendyk Range lies exclusively with an easterly dip. It is most likely to be assumed that the uniform dip of the beds is connected with the presence, along the western margin of the Irendyk Range, of thrust disturbances (Fig. 17). On the western slope of the Irendyk two lines of disturbance can be traced rather well, bounding a wedge composed of jasper and grauwacke, extending from the Tubinsk mine southward to the Shakarada River, a right tributary of the Tanalyk River. The eastern margin of this wedge is splendidly marked by intrusive bodies of diorites and quartz albitophyres, and the western one by a discontinuous belt of silicification, often including gold-bearing quartz veins. The disturbance evidently continues southward as well, as may be judged from outcrops of strongly brecciated and mineralized jaspers, often associated with small bodies of quartz albitophyres. It is possible that mineralization belts of meridional strike observed on the eastern slope of the Irendyk Range coincide with disturbances of the same type. Such a line of mineralization passes along the eastern boundary of the porphyries and the adjacent, strongly brecciated and silicified jaspers and porphyries. On this trend, among other things, lies the Ishberda gold-ore deposit. Finally, it is quite possible that the indicated mineralized belt, passing one kilometer west of the Sugarsky mine, coincides with a disturbance of a similar type. The tectonic lines described belong to one age of formation, since they are always connected with the appearance of diorites and the metasomatic phenomena accompanying their injection. In the present case we are dealing with ancient disturbances (probably of Hercynian age), the planes of which were healed by subsequent injections of igneous rocks and by metasomatic processes.

The grauwackes of the Upper Devonian usually do not give good sections, since they are covered by a large quantity of loose deposits. A traverse along the Sapsal River, which cuts across almost the entire thickness of the grauwackes, indicates that the prevailing direction of dip is easterly. The occasional westerly dips are always connected with the presence of small folds of the second order. These latter are quite clearly visible on the banks of the Sakmara River, near the village of Tavlykaevo. The rocks here, as everywhere, are strongly cleaved. The strike of the schistosity usually deviates little from meridional and is always with an easterly dip, rarely exceeding 60°. Tracing of the bedding distinctly indicates the presence of small folds with minor disturbances of an evidently thrust character. No less interesting is the section along the Sapsal River within the limits of the Tubinsk mine, where a small eastern ridge of jaspers lies definitely with a thrust disturbance upon the grauwackes. The overthrust block of grauwackes lying upon the jaspers sometimes has a gentle attitude and is folded into small folds of the second order. It must be supposed that the rocks of the grauwacke suite are folded into comparatively gentle folds, perhaps complicated by disjunctive disturbances, which possibly have not been exposed solely because of poor outcrop.

Taking into account the material set forth, one may conceive the following scheme of the stratigraphy of the area studied. The metamorphic series includes, chiefly, formations of pre-Devonian age (52, 72), and perhaps in part also Lower Devonian formations (phyllites). During the Middle Devonian we have an epoch of intense volcanic activity, recorded by deposits of jasper, effusive rocks, and their tuffs, during which the composition of the igneous rocks underwent certain changes. The main mass of effusives is represented by augite porphyrites and

only at the end of the Middle Devonian (within the “Lower Green Series”) do we encounter tuffaceous formations of acidic albitophyric rocks, often quartz-bearing.

In the composition of the rocks of the graywacke sequence we already observe rounded fragments of all formations of the Middle Devonian and even of rocks of the metamorphic sequence. The presence, at certain points in the district, of conglomerates at the base of this series, and also the almost complete absence of rocks of the Lower Green Series in the western limb of the Irendyk anticline (a phenomenon not satisfactorily explained by tectonic displacements), compel one to think of a significant continental hiatus between the deposits of these formations. It is quite possible that the indicated hiatus was preceded by an ancient phase of folding assumed by Tikhonovich (71, 43).

Among intrusive rocks the oldest are the ultrabasic rocks of the Sakmara River. Albitophyres cut these rocks and are younger formations; likewise, the aegirine diorites genetically connected with the albitophyres, which metamorphose the graywackes of the Upper Devonian, are probably younger as well. It is most correct to connect with this same complex of rocks the processes of intense metasomatism affecting the rocks enclosing the albitophyres and diorites of the formations.

If one takes into account that the overwhelming majority of investigators assign a Carboniferous age to the olivine rocks of the Urals—the beginning of the Hercynian folding—then one may suppose that the appearance of the described complex of igneous rocks was preceded by a period of Hercynian dislocations, during which the formation of folds was accompanied by a series of various disturbances that subsequently served as pathways for the penetration of magmas. It is very probable that these injections occurred more than once, timed to moments of weakening of tangential stresses. The enormous masses of quartz veins, which additionally metamorphose the crystalline schists of the district, may mark an intrusion of this character, the bodies of which have not yet been exposed by denudation.

During, probably, the greater part of the Mesozoic, a continental regime prevailed in the territory of the district. The sea reappeared only in the Tertiary epoch, as is evidenced by the remains of Tertiary pebble deposits. It is difficult to say when the overthrust of the graywacke sequence and the Middle Devonian rocks onto the serpentinites of the Sakmara River occurred. In any case, this disturbance is younger than all the Paleozoic rocks of the district, but apparently older than the quite recent uplift of the Ural-tau Range (Figs. 17 and 18).

MINERAL RESOURCES

A detailed study of the ore deposits was not included in the program of work for 1926. Therefore the material on copper deposits presented below is insufficiently complete and may suffer from certain inaccuracies, since, out of necessity, too little time was devoted to its collection and processing. But since the geological material on these deposits is of great importance for illuminating the geology, tectonics, and ore-bearing character of the district, I consider it necessary to dwell upon it.

1. Copper deposits.

Among the mineral resources of the district investigated, copper deposits play a prominent role. Within the area covered by the investigations of this year are located the following deposits: 1) the Tubinsky mine, which is at present being worked; 2) the Yulubsky mines, not being worked; 3) the Suvar-uzyak deposit, which is under exploration; and, finally, 4) along the serpentinite belt of the Sakmara River there are here and there abandoned small, weak deposits of oxidized copper ores.

The Tubinskoye deposit is located approximately 3.5 kilometers north of Lake Tolkach. The deposit was described in general terms by A. N. Zavaritsky (20, 24), at the time of whose visit the mine was not in operation. In the work of recent years the pyrite lens of the deposit has been opened down to the 79-meter level; therefore, as a supplement to Zavaritsky’s material, I shall allow myself to say a few words characterizing this deposit.

In the area of the Tubinsky mine there are no good natural sections. The material on which the appended geological sketch map (Fig. 13) is based was obtained mainly from observations of surface outcrops of rocks. The best exposures are encountered along the route on the Sapsal River, which cuts across the strike of the rocks and in some places along whose course there are small natural sections. Since this route exposes the main sequence of sedimentary formations, I shall begin the geological description with it.

In the northwestern part of the map the Sapsal River flows among graywackes, the beds of which dip eastward at an angle varying from 45° to 60°. Moving upstream, as one approaches the western jasper belt, we observe in the rocks certain signs of compaction¹. Near the jaspers the graywackes are strongly fractured, as are the jaspers themselves, which are also fractured and folded. There is no doubt that the jaspers in this place lie upon the graywackes with a disturbance of the thrust-fault type. It is very probable that the previously noted line of intense silicification, found south of the Tubinsky mine between two belts of jaspers and including their western ridge, is a continuation of this thrust.

Farther eastward, up to the very eastern margins of the pond, we encounter numerous surface outcrops of graywackes, striking from NW 320° to meridional and with an easterly dip varying within the limits of 30° to 60°. Westerly dips of the beds were not observed.

South of the pond, among the graywackes, outcrops of clayey jaspers are found. These jaspers are a continuation of the eastern jasper ridge, and there is every reason to suppose that to the north they pass beneath the graywackes, thus forming the closure of an incipient anticlinal fold whose axis plunges northward. In the very upper reaches of the Sapsal River, as one approaches the diorites, compaction and, finally, silicification are again observed in the graywackes. It is probable that the presence in this area, on the right bank of the Sapsal, of an excellent exposure is connected with this circumstance; there, over a distance of 150 meters, the graywackes form a series of small folds with the axes plunging northward. The schistosity, beautifully expressed in the graywackes throughout the entire route, most often does not coincide with the bedding and has a strike of NE 25° with a steep dip to the east. It is extremely interesting to note that at the northern end of the eastern jasper ridge, at the place of the most intense bending of these rocks, the schistosity (NE 25°) in the graywackes is oriented almost at a right angle to the strike of the jaspers (NW 280° with a gentle dip to the north). Exactly the same bedding elements are shown by the graywackes on the right bank of the Sapsal River, near the contact with the diorite. In this latter case the graywackes, having a strike of NW 285°, possess a very gentle dip to the north².

The appearance of albitophyres in the intervals between the two belts of jasper is accompanied by intense phenomena of ore metasomatism. All the rocks of this area constitute a sharply expressed zone of mineralization, which, besides jaspers and albitophyres, includes strongly kaolinized tuffaceous sandstones and shales, occurring chiefly in the hanging wall of the intrusive body. Small wedges of these rocks are also encountered within the body of the albitophyre—

porphyry. The primary character of these rocks is strongly obscured by phenomena of silicification, impregnation with pyrites, and sericitization. However, in their main part these rocks, by their character, come closest of all to graywackes. It is very possible that, together with the latter, in the process of thrust movement the tuffs originally lying below them were also ground down¹. The albitophyres themselves were also subjected to the action of metasomatic processes. The metasomatic minerals, as for the entire Irenyk sequence, are quartz, epidote, and pyrites, causing intense sericitization of the rocks. In the areas of rock closest to the ore lenses, the phenomena of mineralization are strongly obscured by kaolinization, as is often the case (85, 784), connected with the process of secondary sulfide enrichment, which is expressed at this deposit with unusual sharpness.

Within the limits of the Tubinsk mine there are three spatially separated ore bodies: northern, middle, and southern. The northern one has been opened only in the oxidation zone by open workings and a shaft. The iron hat, as is usual for Ural deposits (97), is rich in barite in the lower horizons and is worked for gold. The gold is almost white in color, with a faint yellowish tint, always with a large admixture of silver. Judging by the open workings, the length of the deposit does not exceed 40 meters. In the hanging wall lie jasperites; in the footwall—a felsitic quartz albitophyre. This latter also occurs in the hanging wall.

The middle lens has been reached by small surface workings of an exploratory character only in the oxidation zone and has not been sufficiently traced along the strike. From the appended geological sketch it is easy to see that this lens, like the southern ore body, is confined to the contact of the albitophyres and a wedge of tuffaceous sandstones.

The southern, main lens, on which the principal exploitation workings are at present based, lies in the hanging wall of the albitophyre (quartz). In the hanging wall of the lens, along a horizon of 40 m, occur tuffaceous sandstones, which lower down are replaced by albitophyre. The lens has an irregular form and pinches out both along the strike and along the dip, with the formation of branches. Of interest is the branching on the 73 m horizon, where we have three small lenses, uniting higher up, on the 63 m horizon, into one ore body branched to the south and to the north (fig. 14). The maximum length of the deposit does not exceed 140 m, with a normal thickness of not more than 20 m. With increasing depth the pyrite deposit, apparently, likewise pinches out, decreasing in thickness. The general character of this change is readily seen from the appended sections.

The ore body in its main mass should be divided into two parts: 1) the zone of oxidized ores, reaching the 55 m horizon, and 2) the ores of the zone of secondary sulfide enrichment. Primary ores, entirely unaffected by the processes of sulfide enrichment, were almost not observed within the workings. The boundary between the zones is indistinct and uneven,² which is in complete agreement with Schneider, who indicates that in poorly permeable rocks (such as the jasperites) the boundaries of the zones are usually expressed very irregularly (100). Often, among typical barite sands, there occur pockets of pyrite ores—though, in the overwhelming majority of cases, of the sulfide-enrichment zone. The oxidized ores are represented by brown iron ores and barite. The zone of oxide enrichment is weakly developed. Among the minerals characterizing it, cuprite is encountered chiefly. The zone of sulfide enrichment is developed with unusual sharpness. The residual primary ore minerals are: pyrite, chalcopyrite, zinc blende, tennantite, and galena. The last occurs only in the upper horizons of the ore body. Zinc blende and

chalcopyrite appear most abundantly at the 63-meter level. In ore samples from the 79-meter level, pyrite predominates, while zinc blende and chalcopyrite are only weakly manifested. Of the minerals of the zone of secondary sulfide enrichment, covellite is developed exclusively, to which there is always added a certain amount of chalcocite. Both minerals replace in the same way chalcopyrite, zinc blende, and even pyrite. The richest ores consist almost of pure covellite. Covellite is encountered noticeably at all the working levels. Ores poor in covellite from the deeper levels of the ore body are also poor in copper, which, evidently, is connected with the primary impoverishment of the ores in chalcopyrite (90).

In conclusion it is necessary to note disturbances, often well expressed in certain places of the ore lens. Unfortunately, no record of such disturbances was kept during exploitation, and it is quite impossible to establish their connection with the form of the lens. It is very probable that the sharp change in the dip of the lens, noted already by Zavaritskii (20, 24), is connected with such disturbances. One such disturbance was observed by me at the 63-meter level in working No. 14, which was driven along the NW branch from the main lens. The ore of the branch is strongly crushed. Especially mylonitized areas are sharply enriched in covellite. It should be noted that, in general, the ores of this branch were distinguished by a high copper content. At the end face the ore is cut off by a line of disturbance, apparently passing along the entire extent of this lateral lens in a plane close to the plane of dip of the ore body itself. It is quite possible that disturbance fissures, favoring the circulation of ground waters, contributed to the intensive development of the zone of sulfide enrichment. In this respect the character of the microstructure of the ore from the 63-meter level is of interest. Deformations are clearly observed only in etched polished sections rich in sphalerite. The latter consists of an aggregate of small grains (from 0.02 to 0.05 mm in diameter). Usually no bending is observed in twins of sphalerite, but sometimes, in areas where covellite especially strongly replaces this mineral, the bendings are quite distinctly noticeable and appear only in the grains adjoining the covellite.

The present level of the ground waters lies considerably above the boundary of the oxidation zone (Fig. 14). This circumstance to some degree agrees with the considerations of Nox (97), concerning the influence of climatic changes on the surface alteration of the Kyshtym ore deposits, and also, very probably, depends on movements of the lithosphere, especially if one takes into account the comparatively recent uplift of the Ural-Tau.

The Yuluk deposits are not being worked at the present time. At the time of my visit I found them in exactly the same state as did A. N. Zavaritskii (20, 36 and 37).

The Northern deposit, situated 5 km south of the village of Yuluk, as noted by Zavaritskii (20, 36) and in the reports of Kensbury¹, has been worked out completely. Therefore, without dwelling on its characterization, excellently given by A. N. Zavaritskii (20, 36), I shall permit myself to note only the following circumstances. The country rocks of this deposit are represented by sharply chloritized green schists of the metamorphic series. The development of chlorite is connected with the deposition of metasomatic quartz, as was indicated above for the nodular albite schists. In addition, strong carbonatization of the rocks is observed; most often the carbonates replace the albite of the green schists. Finally, in the dumps from the adit there are observed pieces of coarse-grained albitic rock, apparently constituting a vein in the green—

schists. Here, too, fragments of a rock consisting of albite and biotite, with the latter predominating, were observed. Apparently, in the present case we have a vein formation close to pegmatites.

The South Yuluk deposit is located 1.5 m to the north of the village of Algazinaia on the Yuluk River. Judging from the old English plans (see the section in Fig. 15), it consists of a series of thin pyrite veins occurring conformably with the schists of the metamorphic sequence and having a gentle westerly dip. The country rocks are chloritized green schists; moreover, graphite varieties of these are developed in the hanging wall of the deposit. The oxidation zone is represented by ironstones and schists impregnated with oxides and carbonates of copper. At times the process of this replacement has gone so far that the result is massive ore formations consisting entirely of copper oxides and carbonates; the primary nature of the rock is revealed only by the preserved thin-schistose texture. Apparently, in contrast to the Tubinsk mine, on the Yuluk we have a sharply expressed zone of oxidized enrichment. Pyritic ores were taken from the dumps of the prospecting shaft. The principal minerals are pyrite and chalcopyrite; sphalerite occurs in small quantities. Among the secondary sulfides, covellite is developed. In outward appearance the ores of Yuluk are considerably poorer in chalcopyrite and sphalerite than those of Tubinsk.

It is of great interest to note the quartz–albite–calcite veins often observed in the dumps of the main shaft, whose thickness reaches 50 cm. Sometimes the albite and calcite disappear, and we are dealing with excellent pseudomorphs of quartz after calcite¹. Finally, to the south of the village of Algazinaia, at approximately 200–300 meters, outcrops of quartz augite diorites are observed. The rocks are fractured and have a green coloration. The alterations consist of a strongly developed pelitic coating on the feldspars and chloritization of pyroxene and amphibole. In composition the rocks are entirely identical with the augite diorites of the Tubinsk mine and the eastern slope of the Irendyk Range.

The Sunarskoe deposit is located 3.5 kilometers west of Sultanskoe Lake, in an area of strong development of diorite veins. The deposit was exposed by prospecting in the oxidation zone. The ore body is situated at the contact of diorites and tuffaceous schists. The form of the deposit is very indefinite and irregular. The richest ores occur at the contact itself, but nevertheless the vein mass is formed by the body of the diorite, not by the schists. It often happens that the ore is a kaolinized diorite impregnated with copper oxides, in which numerous pseudomorphs of brown iron ore after pyrite are still visible. Typical ocherous ores are connected with the described series of transitions and in most cases even preserve the structure of the erupted rock. Apparently, the ore body represents a chalcopyrite-enriched portion of the diorite. The ordinary oxidized ores are represented by finely porous ironstones with powdery limonite, forming the angular patterns so characteristic of ironstones produced from primary sulfide ores rich in chalcopyrite (92, 613–618). In most cases cuprite and copper carbonates, often filling fine cells, are admixed with the limonite in appreciable quantity. In places sulfide ores occur, represented chiefly by chalcopyrite. Microscopic examination of this ore revealed, in small quantities, pentlandite, pyrrhotite (?) and magnetite. Pentlandite is usually observed in the form of small relict grains surrounded and corroded by chalcopyrite. In some cases there occur sulfide grains, surrounded by limonite of a pinkish color, similar to pentlandite, but turning brown from nitric acid (50%). I have named this mineral pyrrhotite.

Magnetite occurs here and there in idiomorphic crystals. It is difficult to establish the order of deposition of the minerals, since the secondary covellite, cuprite, and especially limonite very much obscure the primary character of the boundaries and forms of the mineral grains. One can say definitely only that chalcopyrite was deposited later than pentlandite and, probably, later than magnetite. Plant analyses of the ores give the following fluctuations in the content of the principal metals: Ni—from 1% to 2.2%; Fe—from 19% to 35%; Cu—from 2% to 9%, and Zn—from 1.5% to 3.5%¹.

The peculiar composition of the ore and the close association of the ore body with augite diorite sharply distinguish this deposit from the ordinary sulfide deposits of the Tanalyk–Baimak district. In the present case we are probably dealing with a magmatic ore formation, approaching, according to A. N. Zavaritsky’s classification (24, 69), the type of fusible deposits arising in the process of crystallization differentiation².

Finally, there is a whole series of weak deposits of oxidized copper ores in the serpentine belt of the Sakmara River. The most interesting is the formerly worked deposit of such ores near the village of Algazinskaya on the Sakmara River, one kilometer north of the mouth of the Laimberda River. The deposit consists of thin veinlets of malachite ores situated in cracks of graywacke, occurring together with jasper outcrops at the contact with the amphibolites of the serpentine belt (Fig. 12). Both the jasper and the graywackes are strongly fractured. Microscopic study of the mylonitized graywackes reveals intense silicification. Albite-quartz veinlets, accompanied by the deposition of sulfides, are often observed. The amphibolites become more sharply expressed as one approaches the jaspers. A decrease in metamorphism is observed toward the west. In the dumps of workings laid in the graywackes, serpentinites and brown ironstones occur, resembling those of the Yulukskii deposits. Evidently in the present case we have a tectonic boundary between jasper-graywackes and serpentinites.

Efflorescences of copper salts are often encountered in the rocks of the serpentine belt. Near the village of Yaratovaya, on its southern margin, strongly silicified diabase porphyrites with copper oxides are encountered. In this case we have a clear connection between the deposition of pyrites and quartz albite-porphyries, which metamorphose the serpentinites into amphibolites and are themselves penetrated by albite-quartz veinlets.

Near the village of Yumashevskii, whole zones of diabase porphyrites are observed, so densely penetrated by albite-quartz veinlets that the rocks assume a gneiss-like appearance. In this case as well, the injection of these veinlets is accompanied by deposition of pyrites. Shafts had been sunk in some parts of these formations. Evidently, a deposit of the same type is encountered in serpentinites on the bank of a small brook southeast of the village of Aminova, 400 meters west of the jasper hills. Deep shafts have been sunk in the serpentinites; in their dumps there are fragments of vein material with coatings of copper green. Since albite-porphyries are often (the villages of Sharmaevo and Tubinsk) accompanied by quartz veins that cause noticeable mineralization in the country rocks, it is very probable that in the present case as well we are dealing with a formation of the same kind.

Concluding the description of the copper deposits of the district studied, the following principal points should be noted.

1. The overwhelming majority of deposits, regardless of the age of the enclosing formation, are associated with the appearance of intrusive bodies of augite diorites or albite-porphyries.

1. The appearance of ore deposits is closely associated with the intense development of metasomatic processes, which are probably the chief factor in the greenstone alteration of the tuffs and porphyrites of the Irendyk Range. The metasomatic minerals are usually quartz, epidote, pyrites, calcite, and possibly albite. An interesting indication in this respect is provided by the calcite-quartz veins, sometimes with albite, which are often associated with the ore bodies. These formations are equally well developed both in the area of exceptional development of albitophyres (the Sakmara River belt), and in areas where augite diorites are almost the only igneous rocks (Yuluk and the district of the Sultan River).

2. In the composition of their ore minerals, the ores of Yuluk do not differ fundamentally from the Tubinsk ores. Moreover, in the Yuluk ores, according to the analyses cited by Zavaritskii (20, 36–37), barite is present, though in small quantities. The Sudar deposit occupies a somewhat special position, since pentlandite enters into the composition of its ore.

3. Thus, all the copper deposits of our district are genetically connected with the intrusion of augite diorites, and also of albitophyres, which probably represent an additional injection of the former. The differences in the composition of the ores are most naturally to be connected, as is often the case (91), with different degrees of manifestation of the separate stages of the mineralization processes.

2. Gold and platinum.

The gold deposits of the district investigated are to a considerable extent only of historical interest, since the enormous majority of them have by the present time been worked out. Just as with the copper deposits of the district, the gold-bearing placers are associated with the areas of development of the same augite diorites and albitophyres.

Near the village of Sharmaeva, on the Sakmara River, within the broad serpentinite belt at this place, at the mouths of small streams—left tributaries of the Sakmara River—prospecting works discovered gold placers of the “headwaters” type. According to Bashkir prospectors, the gold occurred, as is usual for the Southern Urals (26, 85; 46, 328), directly in the chernozem. The study of this belt revealed that the placer gold¹ was confined exclusively to a narrow belt of amphibolites, separated on the east from the rest of the serpentinite mass by albitophyres. The albitophyres are accompanied by silicification and pyrites. The pyrites are weakly developed; usually only pyrite is observed, and copper pyrites is encountered rarely. To the north the albitophyres wedge out, and in their place there appears a large number of irregular quartz veins. The apices of such quartz veins north of the village of Sharmaeva, opposite the village of Itkul, were worked for gold by prospectors. Since the stretches of the streams east of the albitophyre belt contain no gold, there remains no doubt that the source of the small placers of gold on the Sakmara River is the belts of silicification and the quartz veins accompanying the injection of the albitophyres.² It is very possible that formations of the same kind may also be encountered in the district of the Savalair River and its tributaries, where albitophyres make up fairly thick bodies.

Taking into account the connection of albitophyres with the placers, it is not difficult to imagine the genesis of the notorious “coating” veins, sometimes encountered among talcose serpentinites. Formations of this kind usually represent gold-bearing bands of talc; sometimes in the latter thin

veinlets of quartz and pyrite, and in places quartz is almost absent and the “vein” is marked by an ocherous stripe in talc serpentinites. Depending on whether quartz veinlets are present or not, local gold miners distinguished “primazkovye” or “semiprimazkovye” veins, emphasizing in the latter case transitional formations toward normal quartz veins¹. Probably the true “primazkovye” veins are rich calcite-quartz veinlets². The introduction of such carbonate-rich formations was naturally accompanied by talcification of the serpentinites, and subsequent weathering processes first of all destroyed the calcite, which was highly favorable for the formation of gold-rich pockets so characteristic of “primazkovye” veins.

On the eastern slope of the Irendyk Range, along the Sultanka River, which flows into Lake Sultanskoe, rich gold placers were once worked; their dumps are still being rewashed by prospectors. As already indicated above, the area of these placers is penetrated by a large number of vein-like bodies of augite diorites, which often make up the bedrock of the placers. The diorites and their varieties always contain a large quantity of pyrites and are in places cut by calcite-quartz veins. The latter at times were distinguished by a high gold content (the Tukai mine). Their occurrence varies within broad limits, but more often is confined to the quartz diorite of Tukan as a separate feature, with a westerly dip. It is quite possible that, in addition to these veins, the sources of the placer gold of the Sultanka River were the diorites themselves, as well as iron caps of deposits of this kind, such as Sunar.

Platinum is encountered rarely within the area studied. In the area of the described Sharmaevo placers, platinum was also found in the washing scoops. Since the schistless rocks of the Sakmara River belong to the group of pyroxenite peridotites—rocks least characteristic of platinum deposits (4, 151 and 633; 106)—it is difficult to count on serious platinum deposits in the region of the Sakmara belt. The genetic setting closely resembles the platinum-poor deposits with predominance of gold in the Baranchinskaya dacha (66, 28–29).

Moreover, according to Vysotsky (4, 634–635), platinum occurred in the placers of the Sultansky and Tadalshinsky mines. Since serpentinites are absent in the area of these deposits, the genesis of this platinum is apparently connected with a different type of igneous rocks. These may prove to be either diorites, which occur in both areas, or the augite porphyrites of the Irendyk Range³.

3. Magnesite, asbestos, and chromite.

In the serpentinite belt of the Sakmara River, near the village of Sharmaevo, there is the Sharmaevo deposit of magnesite known in the literature (18, 4, 56, 314). The magnesite occurs as small nests in serpentinites, on the floor of a deep basin bounded on the west by a ridge of albitophyres and on the east by jasper. The nests vary considerably in size, but ordinarily do not exceed 30 meters in diameter at the surface and 5 meters in depth. Such nests are very easy to find, since they usually form small hillocks rising above the low hills of the serpentinite basin. South of the serpentinite—

of the stock, near the village of Murzakaevo, in serpentinized pyroxenites of the werlite type, one can often observe a dense network of magnesite veinlets. Small nests of magnesite, crowning the tops of small serpentine hills, may also be observed in the northern part of the serpentine stock, in the area of the village of Kinzebulatovo and of the road from the village of Itkulovo to Baimak. In one of the magnesite nests magnificent radiating aggregates of aragonite were found.

The genesis of magnesites associated with serpentines is not interpreted in the same way by different investigators. Karpinsky (28, 328), as early as 1884, suggested that “probably, the magnesite originated as a result of the action on this rock (serpentine) of water containing carbonic acid, while silica supplied the material for the siliceous accumulations accompanying the magnesite”; moreover, at times this process proceeds so intensively that it “promotes the transformation of serpentine into a quartz porous mass.” Kuznetsov (39, 8–9), in analyzing the processes of silicification of portions of serpentines associated with the proximity of quartz and pegmatite veins, establishes the decomposition of serpentine with the formation of opal and magnesium carbonate. Bain (88) believes that changes in serpentines occur under the action of carbonated magmatic waters depositing MgCO₃ in the form of veinlets and accumulations. Finally, Geisler (5, 34) believes that the Khalilovo magnesites (Southern Urals), in their formation, are connected “with processes of surface weathering of serpentine and are confined chiefly to the most disintegrated parts of the enclosing rock.”

The magnesite nests in the Sharmayevo area, as in the Khalilovo district, are situated in the surface parts of serpentine bodies, and from this standpoint the genetic connection of magnesite with processes of surface weathering seems the simplest and most natural. However, the association of magnesite nests at Sharmayevo with parts of serpentines most mineralized by albite rocks¹ and the presence of aragonite in the magnesite (19, 18)² make it possible to suppose that the formation of magnesite may be connected with temperatures higher than those of surface weathering.

It is highly probable that the intrusion of albite rocks was accompanied by the formation, in the serpentines, of the thin magnesite veinlets often observed,³ while its accumulation in the form of nests in lowered parts of the surface was a subsequent stage connected with processes of surface weathering. It should be noted here that the mode of occurrence of these nests (the tops of small hills) indicates that present-day denudation processes cannot have been involved in the formation of the magnesite, but merely prepare outcrops of formations of some preceding epochs.

Asbestos is often encountered in the serpentines of the metamorphic series and of the Sakmara River. Since the promising asbestos deposits in the Urals are associated, in the overwhelming majority of cases, with the injection of acid rocks into olivine peridotites or dunites (38, 59; 48, 154–155; 71, 5; 75, 6–7), it is difficult to count on promising deposits of it within the limits of our comparatively poor olivine pyroxenitic rocks. All the asbestos occurrences registered so far are weak and devoid of industrial significance.

According to the character of manifestation of these occurrences, they may be divided into two parts: 1) asbestos deposits of the serpentines of the metamorphic series, and 2) chrysotile veinlets in the most olivine-rich peridotites in the area of the village of Sharmayevo. In the first case we usually have veins of tremolite asbestos,

often associated with quartz veins that transform serpentinites into talc-tremolite rocks. An asbestos vein of this kind in the vicinity of the village of Yuluk was explored by the trust’s manager Gabitov by means of a small adit, in which even now one can see a thin (from 3 to 5 cm) pinching-out veinlet of asbestos. According to the local resident M. Adigamov, the vein was first discovered in the lower part of the bank of the Bolshoi Yuluk River, by the water, and had a thickness of as much as 1 meter. By order of the Trust, samples were sent for testing, but the results are not available. In addition to this occurrence, coarse fibrous asbestos is found in serpentinites along the Tuganu River north of the village of Yuluk, and irregularly fibrous asbestos has been encountered in serpentinites of the middle course of the Yarma-elga River, west of Chingizskaya. All these occurrences either possess asbestos of decidedly low grade or contain only small reserves of it.

In the serpentinites of the Sakmara belt, asbestos was observed only in the form of thin veinlets, several millimeters thick, associated chiefly with olivine-rich varieties of pyroxenitic peridotites. No industrial significance of the occurrences was observed. Considering the limited distribution of olivine rocks, there is no particular reason to expect the discovery of large asbestos deposits.

In the middle course of the Shulka River, near quarries of marble for lime, nests of chromite occur in serpentinites, resembling the deposits of the Kaiprakty district described by Geisler (6, 33—34). Large nests were not observed.

4. Coal.

Within the limits of the area investigated, no coal deposits were observed. The deposits described below are situated beyond the limits of the geological survey; however, since these deposits have a certain significance, I shall allow myself to set out the factual material available in this regard. Two deposits were examined: 1) the Ziryan-Agach River, a right tributary of the Tanalyk River between the villages of Old and New Yulbarsovo, and 2) the Ayuly River, 5 kilometers upstream from the village of Ayuly-Tomak.

Outcrops of coal seams on the Ziryan-Agach have been mentioned more than once by Tikhonovich (58, 75; 67, 241; 68, 165); in this connection he indicates exposures of two coal seams, the thickness of which reaches 1½ arshins. I succeeded, by means of small trenches, in uncovering a seam of carbonaceous shale lying on the right bank of the Ziryan-Agach River and not exceeding 20 cm in thickness. The enclosing rocks are calcareous sandstones with a large number of spherical concretions, reaching 0.5 meter in diameter. Upon the sandstones lies Lower Carboniferous limestone ($C_1^1$) with a rich fauna. The strike of the rocks is NW 300°—310°, with an eastward dip of 45°—60°. The entire sequence is traversed by a fault of overthrust character. The breccias that mark it consist of fragments of sandstone, carbonaceous shale, and limestone. Along its strike the coal seam rapidly pinches out. In the nature of the formations present, the Sukholozhskoye coal deposit on the eastern slope of the Urals, described by V. Golubyatnikov (7, 640), most closely approaches ours; there the sandy-clayey coal-bearing deposits gradually pass into formations of the Upper Devonian.

The coal deposits on the Ayuly River differ considerably from the preceding one in the character of the formations composing them. The deposit was indicated to me by the resident of the village of Yuluk, M. Adigamov. At the place indicated by him, no direct outcrops of coal were observed. Fragments of coal were found in large quantity on a broad, beach-like area at the place where a small spring falls into the Ayuly River from the left side. The area is covered by a rather thick layer of loose soil formations, during the plowing of which about 3 poods of coal were plowed up. Fragments of coal were also observed in this soil in large quantity at the time of my visit. Their form is always angular and entirely

bears no signs of having been reworked by water. Several abandoned pits exposed aleuritic sands, sometimes passing into sandstones. In places along the stream colored clays are observed. Upstream, a few meters away, the grauwackes of the Upper Devonian crop out. It is very likely that the thickness of the sands here is insignificant, but the strong influx of groundwater prevented the pits from being sunk down to the grauwackes. It is possible that, in the present case, the source of the fragments of coal was a coal seam in loose rocks. Formations of this character on the eastern slope of the Urals are associated either with rhaetic coals of the Chelyabinsk type (43, 15) or with formations of Neogene age (70, 227), to which belong the Yakovlevskie workings, situated 50–60 km east of Baimak. Since the enterprises of Baimak are in great need of fuel, and since deposits of coals of this age usually have a quiet mode of occurrence, the deposit on the Ayuly River deserves light drilling exploration.

GENERAL CONCLUSIONS.

1. The following formations take part in the structure of the area investigated: a) a metamorphic sequence; b) deposits of the Middle Devonian; c) a sequence of argillaceous shales and grauwacke sandstones of the Upper Devonian; d) pyroxene peridotites, augite diorites and albitophyres; and, finally, e) Tertiary gravels, encountered comparatively rarely.

2. Within the metamorphic sequence it appears possible to distinguish two stratigraphically different groups of rocks: a) a sequence of mica and green schists, and b) phyllites. The rocks of the latter group are represented in the area very poorly and—possibly—belong to younger formations.

3. The rocks of the crystalline belt are complexly metamorphosed formations. By the time of deposition of the grauwacke suite of the Upper Devonian, they had already been metamorphosed. We have no reliable material on the character of these first changes, since the features of the first metamorphism may have been considerably obscured by the action of the powerful acid intrusions that followed at the end of the Paleozoic, with which the alteration of the serpentinites included in the metamorphic sequence is probably connected, as well as those alterations that have the character of injection metamorphism. Finally, processes of ore metasomatism, probably following one of the last acid intrusions, produced in the sequence of metamorphic rocks fairly significant changes, expressed in the formation of talc, chlorite, fibrous amphiboles, sericite, and carbonates.

4. In the composition of the Middle Devonian deposits two suites are indicated. The lower of them is represented chiefly by augite porphyrites and their tuffs, interbedded with thin beds of jasper. The upper—according to Librovich (44, 74), the “lower green suite”—is separated from the preceding by a thick bed of jasper and represents a close alternation of siliceous shales and tuffaceous sandstones, in the composition of which, besides fragments of porphyrites, a large amount of angular material of albitophyres, often quartz-bearing, is frequently observed.

5. The grauwacke sequence is most developed in the depressed plain belt between the Ural-tau and Irendyk ranges. It is probable that the sandstones and shales of the Sunar mine area, close in composition to its rocks, represent formations of the same age. In the first case, thick beds of jasper most often serve as the lower boundary of this suite; in the second, the suite of these rocks lies on the “lower green suite” of the Middle Devonian, being separated from it by small interbeds of stromatoporoid limestones. The upper boundary of these rocks is formed by Lower Carboniferous limestones \((C^1_1)\), observed in the south, in the area of the Ziryan-Agach River, where the western belt of grauwackes imperceptibly passes into calcareous sandstones and shales containing interbeds of coal.

1. The grauwackes include a large amount of unrounded eruptive material, in which acidic, quartz-bearing albitophyres predominate. The finer and rounded material consists of fragments of diabase porphyrites, crystalline schists, and jasper. Quartz pebbles are not encountered. Thus, by Upper Devonian time not only had the metamorphic series been formed, but the latter had also been exposed to a considerable extent by denudation. In addition, the almost complete absence of rocks of the “lower green suite” on the western limb of the Irendyk anticline, as well as the presence, at certain points in the district, of conglomerates at the base of the grauwacke suite, compels one to think of a possible break between the Middle Devonian deposits and the grauwackes. It is possible that the incipient break was preceded by the phase of folding presumed by Tikhovich.

2. The intrusive rocks of the district are divided into three groups: a) ultrabasic intrusive rocks of gabbro-peridotite magma, distributed in the area of the Sakmara River; b) augite diorites, forming small intrusive bodies in almost all formations of the district, but occurring most abundantly among the Upper Devonian grauwackes east of the Irendyk Range; and c) quartz or quartz-free albitophyres, occurring as small intrusive bodies following tectonic lines. The oldest in age are the gabbro-peridotites, whereas the augite diorites and albitophyres represent the youngest formations in the area studied (excluding Tertiary deposits).

3. In mineralogical composition, the rocks of the gabbro-peridotite magma belong to the group of clinopyroxene peridotites, characteristic (4, 212) of the eastern slope of the Urals and occupying the last place in platinum content among the olivine rocks of the Urals.

4. The predominant rocks in the composition of the peridotite bodies are formations of the wehrlite–harzburgite series, passing into nearly pure pyroxenite-diallagites. The marginal zone of the clinopyroxene peridotites, represented by gabbroid rocks, is of insignificant thickness and at times is even entirely absent.

5. The relationship between the pyroxenites and the enclosing country rocks is uncertain. Phenomena of contact metamorphism either are not observed at all, or the study of this phenomenon is extremely hampered by the sharp milonitization and contact metamorphism of the quartz albitophyres that cut the serpentinites and pyroxenites.

6. The augite diorites are typical hypabyssal rocks, strongly varying in composition, structure, and size of the intrusive bodies. Quartz mangerite and hornblendite are, for the dioritic rocks, extreme members connected with one another by a close series of transitional formations.

7. Vein-like bodies of diorites occur in all formations of the district. Contact effects are usually weak and amount to contact metasomatism expressed in silicification and serpentinization. But in the area of the Sultan River, where there is a dense network of dioritic bodies in the grauwackes, the phenomena of contact metasomatism are unusually strongly expressed, as a result of which we have black massive hornfels, rich in sieve-like albite, epidote, calcite, and ores. In addition, in the rocks of the grauwacke series there are almost always present, in one quantity or another, grenite, sphene, and radiating amphibole.

8. The albitophyres of the district should, by age, be divided into two groups. The oldest, usually felsitic-looking rocks form part of the upper horizons of the Middle Devonian. The quartz albitophyres of intrusive character belong to younger formations.

9. The injection of intrusive albitophyres is usually accompanied by intensive contact-metasomatic processes, as a result of which we have alteration both of the albitophyres themselves and of the enclosing country rocks.

The processes of mineralization are expressed chiefly in epidotization, silicification, and impregnation by pyrites. The rocks most affected by the processes of metasomatism are the porphyrites and tuffs of the Irendyk Range, which compose the hanging wall of the albitophyre veins.

1. No direct connection between the diorites and the albitophyres has been observed; but, since both mark by their appearance zones of the same disturbances and are accompanied by identical metasomatism, the genetic connection of these formations becomes very probable.

2. Tertiary deposits are very weakly developed and are represented by gravels of Neogene age.

3. The rocks of the district have repeatedly undergone the action of dislocations of various ages. The rocks of the metamorphic sequence probably underwent an even more ancient meridional folding noted by Fedorov (77, 86), associated with the Lower Devonian transgression. Possibly the next phase of folding occurred at the end of the Middle Devonian; and, finally, in the Carboniferous we have a distinctly manifested Hercynian epoch of dislocations. As a result of such complex influences, we nevertheless observe a Paleozoic folded in comparatively gentle folds—a circumstance readily explained by the presence of thick interbeds of jasper and porphyrites, at times difficult to bend.

Disjunctive forms of dislocation appear much more intensely and sharply. The oldest of these, of overthrust character, still belong to the time of the Hercynian folding and are marked by belts of mineralization and by intrusions of augite diorites and quartz albitophyres. In the area of the Sakmara River we have younger disturbances of the overthrust type, to whose action the albitophyres themselves were subjected; and, finally, perhaps quite recently, the Ural-tau Range was uplifted along a fracture separating the rocks of the metamorphic sequence from the porphyrites of the Middle Devonian.

1. Within the limits of the investigated district there are various mineral resources. The most important role is played by deposits of copper and, in part, gold, genetically connected with the intrusion of augite diorites and quartz albitophyres. In addition, the magnesite deposit in the serpentinites of the Sharmayeva Valley deserves serious attention. Deposits of platinum, asbestos, chromite, and coal are in the great majority of cases insignificant, or at most can have only local importance.

LIST OF LITERATURE

1. Bazhenov, I. K. Preliminary report on geological investigations in 1924 in the southwestern Sayan Mountains.—Izv. Sib. O. G. K., vol. IV, no. 5, 1925.

2. Baklund, O. O. Petrographic provinces of the Ilmen Mountains.—Geol. Vestn., vol. III, 1917.

3. Vysotsky, N. K. Platinum deposits of the Isovsk and Nizhne-Tagil districts in the Urals.—Tr. G. Kom.; new series; issue 62, 1913.

4. Ego-zhe. Platinum and the districts of its extraction.—Committee for the Study of the Natural Productive Forces of Russia, Petrograd, 1923–25.

5. Geissler, A. Magnesite in the Khalilovo district.—Vestn. Geol. Kom., No. 4, 1925.

6. Ego-zhe. New chromite districts in the Southern Urals.—Vestn. Geol. Kom., No. 4, 1925.

7. Glubtnikov, V. The Sukholuzhskoye coal deposit on the eastern slope of the Urals.—Gorn. Zhurn., No. 8, 1925.

8. Gordienko, M. Magnesite deposits in the Sysert and Nizhne-Iset dachas. Gorn. Zhurn., 1924, Nos. 11–12.

9. Gudkov, P. P. The district of the gold placers of A. S. Antonov and O. P. Vishnevskaya in Orsk Uyezd, Orenburg Governorate.—Izv. Tomsk. T. I., vol. XXXIX, No. 3, 1915.

10. Derviz, V. M. On geological investigations in the Goroblagodatsky district in 1923–24.—Izv. G. K., vol. 43, No. 10, 1924.

11. Dupark, L. and Sigg, G. Copper deposits in the Sysert dacha in the Urals.—Tr. Geol. K., new ser., issue 101, 1914.

1. Eremenko, E. V. and Levinson-Lessing, F. Yu. Materials for the petrography of the Mugodzhar Mountains.—Trans. St. Petersburg Soc. Nat., vol. XXXIII, no. 5, 1905.

2. Zavaritsky, A. N. Some rocks from the environs of the Tsarevo-Aleksandrovsky mine in the Miass dacha.—Proc. Mining Inst., vol. III, 1912.

3. The same. On the investigation of Mount Magnitnaya in 1911.—Ibid.

4. The same. Petrographic observations in the environs of the Miass plant.—Ibid.

5. The same. Geological investigations in the environs of Mount Magnitnaya in the Southern Urals. Bull. Geol. Com., vol. XXXI, 1912.

6. The same. Geological investigations in the Southern Urals carried out in 1913. Bull. Geol. Com., vol. XXXII, 1914.

7. The same. Magnesite.—Natural productive forces of Russia, vol. IV; minerals, Petrograd, 1917.

8. The same. Results of the investigation of magnesite deposits in the Satka district in 1918.—Mining Journal, nos. 2–3, 1920.

9. The same. The Tanalyk-Baimak copper-ore district.—Mining Journal; supplement no. 4, Moscow, 1920.

10. The same. Mount Magnitnaya and its deposits of iron ores.—Trans. Geol. Com., new series, issue 122, 1922.

11. The same. On the tectonics of the Urals.—Bull. Geol. Com., vol. 42, no. 2, 1923.

12. The same. The principal features in the development of the volcanic cycle in the Urals.—Bull. Geol. Com., vol. 43, no. 3, 1924.

13. The same. On the classification of magmatic ore deposits.—Bull. Geol. Com., vol. 45, no. 2, 1926.

14. The same. Descriptive Petrography, Part II. Sedimentary Rocks.—Leningrad, 1926.

15. The same. Materials for the study of the gold-bearing districts of the Urals.—Materials on General and Applied Geology, issue 16, 1926.

16. Zolotko, I. The past and present of the Tanalyk-Baimak district on the lands of the Bashkir Republic. Mining Journal, no. 6, 1921.

17. Karpinsky, A. Geological investigations carried out in the Southern Urals in the summer of 1884.—Bull. Geol. Com., vol. IV, 1885.

18. Karpinsky, A. and F. Chernyshev. General geological map of European Russia, sheet 139.—Trans. Geol. Com., vol. III, no. 2, 1889.

19. Karpinsky, A. Fossil-coal deposits on the eastern slope of the Urals.—Publ. Geol. Com.; Essay on the fossil coals of Russia, 1913.

20. The same. On the origin of accumulations of fluorite in the deposits of the Moscow stage of the Carboniferous system and on certain other geological phenomena.—Bull. Imp. Acad. Sci., 1915.

21. Kolenko, B. Z. Petrographic sketches. Rocks of the exposures on the Circum-Baikal railway, between the stations Baikal and Kultuk. I. Peridotite of Krutaya Guba.—Notes Min. Soc., second series, part 61, issue 1, 1918.

22. Krasnopolsky, A. Perm—Solikamsk.—Trans. Geol. Com., vol. XI, no. 1, 1889.

23. The same. Geological sketch of the environs of the Lemezinsky plant.—Trans. Geol. Com., new series, issue 17, 1904.

24. The same. Geological sketch of the environs of the Verkhne- and Nizhne-Turinsky plant and Mount Kachkanar.—Trans. Geol. Com.; new series, issue 52, 1909.

25. Krotov, B. P. Petrographic investigations of the southern part of the Miass dacha.—Trans. Soc. Nat. at Kazan Univ., vol. 47, no. 1, 1915.

26. Krotov, P. Geological investigations on the western slope of the Cherdyn and Solikamsk Urals.—Trans. Geol. Com., vol. VI, 1888.

27. Kryzhanovsky, V. I. A serpentine-asbestos deposit in the Berezovskaya, Kamenskaya, and Monetnaya dachas in the Urals.—Trans. Geological Museum named after Peter the Great of the Imp. Acad. Sci., vol. I, no. 3, 1907.

28. Kuznetsov, E. A. Rocks of Lake Uvildy of the Kyshtym dacha.—Trans. Inst. Applied Mineralogy and Petrography, issue 2, 1923.

29. Kuznetsov, E. A. and E. E. Zakharov. On the tectonics of the eastern slope of the Urals.—Bull. Moscow Soc. of Naturalists; new series, vol. XXXII, 1926.

30. Levinson-Lessing, F. Yu. Geological sketch of the Yuzhno-Zaozerskaya dacha and Denezhkin Kamen in the northern Urals.—Trans. St. Petersburg Soc. Nat., vol. XXX, issue 5, 1900.

31. The same. Advances in petrography in Russia.—Petersburg, 1923.

32. Librovich, L. S. The Chelyabinsk brown-coal deposits.—Materials on General and Applied Geology, issue 60, 1923.

33. The same. Geological investigations on the eastern slope of the Southern Urals in 1925.—Bull. Geol. Com., vol. 46, no. 2, 1927.

34. Lodochnikov, V. N. Several interesting rocks from different spurs of the Altai.—Notes Min. Soc., second series, part 51, no. II, 1923.

35. Meglicky and Antipov. Geognostic description of the southern part of the Ural Range.—St. Petersburg, 1858.

36. Meister, A. K. Gold.—Survey of the mineral resources of the U.S.S.R.; Geol. Com. issue 18, 1926.

1. Mikheev, N. S. On the question of the structure of asbestos deposits in the Urals.—G. Zh., vol. 4, 1909.

2. Moldavantsev, E. P. Geological investigations of Denezhkin Kamen in the Northern Urals in 1923.—Izv. G. K., vol. 43, no. 9, 1924.

3. The same. On the presence of platinum in diabases and pyroxene porphyrites of the Northern Urals.—Bull. Geol. Com., no. 5, 1925.

4. Murchison, R. I. Geological description of European Russia and of the Ural Range.—St. Petersburg, 1849.

5. Nalivkin, D. V. On the geological structure of the Southern Urals.—Notes of the Mining Institute, vol. VII, 1926.

6. Nikitin, V. V. Geological investigations of the central group of dachas of the Verkh-Isetsk Works, the Revdinsk dacha, and the Murzinsk district.—Trans. Geol. Com., new series, issue 22, 1907.

7. Nikolaev, A. V. An outline of the kyanite deposits in the Kyshtym mining district.—Notes of the Mineralogical Society, second series, pt. 61, issue 1, 1918.

8. Nikolaev, D. Geological investigations carried out in the Southern Urals in 1901 and 1902.—Izv. Geol. Com., vol. XXII, 1903.

9. Replies to inquiries from institutions and individuals, communicated by the Moscow Department of the Geological Committee.—Izv. G. K., vol. 37, 1918.

10. Report on the state and activity of the Geological Committee for 1902.—Izv. G. K., vol. 22, 1903.

11. The same. For 1907.—I.G.K., vol. 27, 1908.

12. The same. For 1909.—I.G.K., vol. 29, 1910.

13. The same. For 1910.—I.G.K., vol. 30, 1911.

14. The same. For 1911.—I.G.K., vol. 31, 1912.

15. The same. For 1912.—I.G.K., vol. 32, 1913.

16. The same. For 1913.—I.G.K., vol. 33, 1914.

17. The same. For 1914.—I.G.K., vol. 34, 1915.

18. The same. For 1915.—I.G.K., vol. 35, 1916.

19. The same. For 1916.—I.G.K., vol. 36, 1917.

20. The same. For 1917.—I.G.K., vol. 37, 1918.

21. The same. For 1918.—I.G.K., vol. 38, 1919.

22. The same. For 1919.—I.G.K., vol. 39, 1920.

23. The same. For 1925.—I.G.K., vol. 45, 1927.

24. Preobrazhensky, P. I., and Churakov, A. N. Asbestos.—Natural Productive Forces of Russia, vol. IV; Mineral Resources; Petrograd, 1917.

25. Prigorovsky, M. M. A brief geological sketch of the Mugodzhar Mountains and adjacent parts of the Turgai and Ural steppes.—Izv. G. Kom., vol. 33, 1914.

26. The same. On certain sedimentary strata west and east of the Mugodzhar Mountains.—Izv. G. K., vol. 31, 1912.

27. Perna, E. Ya. The Paleozoic of the eastern slope of the Urals between the town of Verkhneuralsk and the Magnitnaya station.—Izv. G. K., vol. 31, 1912.

28. Tatarinov, P. M. On the geology of the Bazhenov asbestos district.—Bull. Geol. Com., no. 5, 1925.

29. Usov, M. A. Description of rocks (the Border Dzhungaria).—Izv. Tomsk. Technol. Inst., vol. II, issue 1, 1911.

30. Fedorov, E. S., and V. V. Nikitin. The Bogoslovsk mining district.—St. Petersburg, 1901.

31. Fersman, A. E. Precious and colored stones of the U.S.S.R. Part II.—Publ. of the Commission for the Study of the Natural Productive Forces of the U.S.S.R. under the Academy of Sciences of the USSR, 1925.

32. Frederiks, G. A trip to Krasnoufimsk uyezd in the summer of 1915.—Izv. G. K., vol. 34, 1915.

33. Chernyshev, F. Geological investigations carried out in the Urals in the summer of 1884.—Izv. Geol. Com., IV, 1885.

34. The same. Description of the central part of the Urals and its western slope.—Trans. Geol. Com., vol. III, no. 4, 1889.

35. Chirvinsky, P. N. The parent magma of the deep-seated rocks of the Ilmen Mountains.—Notes of the Russian Mineralogical Society, pt. IV, issue 1, 1925.

36. Stuckenberg, A. Geological investigations in the Southern Urals.—Izv. G. K., vol. 15, 1886.

37. The same. Geological investigations carried out in the Southern Urals in 1898.—Izv. G. K., vol. 18, 1889.

38. Yagovkin. Secondary enrichment of sulfides.—G. Zh., nos. 1, 2, 3, 4–5, 1924, and no. 12, 1923.

39. Yakovlev, N. Geological sketch of the ore-bearing region of syenites in the Nizhne-Tagil district in the Urals.—Izv. G. K., vol. 25, no. 6, 1906.

40. Angel, F. Gesteine der Steiermark.—Graz, 1924, B. 60, der Mitteil. des Nat. Vereins für Steiermark.

41. Bain, G. W. Types of Magnesite Deposits and Their Origin.—Econ. Geol., no. 5, 1924.

1. Becke, F. Stoffwanderung bei der Metamorphose.—Tsch. Min. Petr. Mitt., XXXVI, 25, 1923.

2. Behaghel, G. Die Kupfererzvorkommen im Uralischen Bergrevier von Sissertsk.—Zeitschr. f. prakt. Geol., Heft 4, 1923.

3. Berg, G. Genetische Beziehungen vulkanischer Erzmetasomatosen.—Zeitschr. f. prak. Geol., 33, 1925.

4. Blanchard, R. and P. F. Boswell. Notes on the oxidation Products Derived from Chalcopyrite.—Econ. Geol., Vol. XX, No. 7, 1925.

5. Fergusson, H. G. The Limestone Ores of Manhattan, Nevada.—Econ. Geol., 1921, Ref. N. J. Bd. II, Abt. A, 1925.

6. Idem. Geology and Ore Deposits of The Manhattan Districk, Nevada.—U. S. Geol. Suw. Bull., 1924, 723.

7. Holden, E. F. The Temperature—pressure Conditions During The Formations of Smoky Quartz and Amethyst.—Amer. Miner. 10, 1925. Ref. N. J Bd. I, 1926.

8. Kalb, G. Kristalltracht, Vorkommen und Bildungstemperatur der Mineralien.—Centr. f. Min., 1923.

9. Knox, H. H. An Effect of Climatic Changes On The Superficial Alteration of Ore Deposits.—Econ. Geol., XVII, 1922.

10. Parker, R. L. Serpentin und Talk von Disentis—Surrhein.—Schw. Min.—Petr Mitteil., 1921. Ref. N. J. Bd. I, 1926.

11. Rosenbusch—Mügge. Mikroskopische Physiographie der Mineralien und Gest—Bd. 12. 1926.

12. Schneiderhöhn, H. Die Oxydations und Zementations—Zone sulfidischer Erzlagerstätten.—Fortschr. der Min., Kristall. und Petr. 9, 1924. Ref. N. J. Bd. II, 1925.

13. Schnell, J. R. Les roches basiques des nappes penniques.—Schweiz. Min. Petr. Mitteil., 1921. Ref. N. J. Bd. I 1926.

14. Schrader, F. C. The Jarbidge Mining District, Nevada.—U. S. Geol. Surv. Bull., 1923. Ref. N. J. 1925. Bd. II, Abt A.

15. Schwartz, G. M. The Contrast in the Effect of Granite and Gabbro Intrusions on the Ely Greenstone.—Journ. of Geol., 32, 1924.

16. Slavik, Fr. Über zwei anchimonomineralische Fazies des Westbohmischen Gabbromasivs.—Rozpravy České Akademie 31, Ref. N. J., Bd II, Abt. A. 1925.

17. Spurr. Ore Injection at Edward.—Eng. Min. Journ., 1924. 684.

18. Wagner, P. A. and E. F. Mellor. On Platinum-bearing Hortonolite Dunite of The Lydenburg District.—Trans. Geol. Soc. S. Africa. 28, 1925. Ref. N. J. Bd II, 1925.

Description of figures and drawings.

Fig. 1. Inclusion of glaucophane in an albite crystal. a — albite, b — glaucophane.

Fig. 2. Form of occurrence of metasomatic quartz in nodular albite-chlorite schists. a — albite, Q — quartz.

Fig. 3. Overgrowth of sphene by chromite in serpentinites of the metamorphic sequence. a — sphene aggregate; b — chromite.

Figs. 4–5. Forms and relationships of quartz and albite-quartz veinlets in mylonitized diabase porphyrites of the Sakmara River. I–J — quartz veinlet, II–II — albite-quartz veinlets.

Fig. 6. Form of a quartz aggregate, apparently representing a pseudomorph after a phenocryst of pyroxene in diabase porphyrite.

Fig. 7. Remnants of radiolarian skeletons in jasper.

Figs. 8–10. Forms of spherulites in quartz albitophyres.

Fig. 11. Overgrowth of pyrite by metasomatic quartz. Qu — quartz, Py — pyrite.

Fig. 12. Scheme of the distribution of rocks at the mine near the village of M. Algazha.

Fig. 13. Geological map of the Tubinskii mine.

Fig. 14. Plan and sections through the pyrite lens of the Tubinskii deposit.

Fig. 15. Plan and section of the Yuzhno-Yuluk deposit.

Fig. 16. Geological map of the Tanalyk-Baimak district.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 7.

Fig. 6.

Fig. 5.

Fig. 8.

Fig. 4.

Fig. 9.

Fig. 10.

Fig. 11.

To the article by Engineer F. N. Shanov.

Diagram of the distribution of rocks at the mine near the village of M. Algazina

(Reconnaissance sketch survey)

Legend:

• Microdiabase
• Jasper
• Graywacke
• Mine
• Prospect pits

Fig. 12.

Scale: 0–200 meters.

Geological Map of the Tuba Mine.
Tanalyk–Baimak Copper-Ore District
in the Southern Urals.

Fig. 13.

Scale: 100, 0, 100, 200, 300, 400, 500 meters.

Visible map labels include:
r. Tuba; Lake Bannoe; Bezymyannoe Lake; Lake Gorkoe; [[unclear: several smaller handwritten locality labels]].

Legend

• Albitophyres.
• Diorites.
• Clayey and hornfelsic sandstones, siliceous shales, and clay shales.
• Metamorphosed ore-bearing rocks: [[unclear: Turonian?]] sandstones and clay shales.
• Jaspers.
• Jasper rubble.
• Ancient ponds.
• Actual boundaries of rocks.
• Possible boundaries of rocks.
• Ore lenses.

Fig. 14.

Plan and sections of the copper-pyrite lens of the Tubinsky deposit.

Scale: 0–75 m.

Conventional symbols:

• Oxidized ores
• Massive ores

Section along 1–1, trench III

Labels visible in the section:

• surface
• present groundwater level
• borehole 5
• level 145 m
• level 154 m
• level 164 m
• level 170 m

Section along 2–2

Label visible:

• borehole 1

Section along 3–3

Plan

Labels visible on the plan:

• section along 1–1
• section along 2–2
• section along 3–3
• borehole 1
• borehole 5
• trench III
• level 120 m
• level 145 m
• level 154 m
• level 164 m
• level 170 m

To the article by Eng. F. N. Shatov.

Cross-section along the prospecting line

Kapit. sh.                      Prospecting shaft

Skv. 7   Skv. 5

horizon 200′

Fig. 15.

Plan of the 200-foot level

Kapit. sh.

Prospecting shaft

Skv. 7.

Skv. 5.

South–Yultanskaya prospecting line

N
S

0 10 20 30 0 50 100 150 200 250 300 fathoms.

For the article by Engineer F. N. Shanov

Geological Map

of the Tanalyk–Baimak Copper-Ore District

in the Southern Urals

Scale: kilometers.

Legend

Symbol	Explanation
—	Metamorphic series with predominance of mica schists and quartzites.
—	Metamorphic series with predominance of green schists.
—	Graywacke series of the Upper (?) Devonian.
—	Jaspers.
—	Siliceous schists and tuffites of the Middle Devonian \((D_1)\).
—	Marbles and limestones.
—	Peridotites and serpentinites.
—	Porphyrites and their tuffs.
—	Listvenites.
—	Quartz and quartz-free albite diorite.

Fig. 16.

To the article by Eng. F. N. Shtanov.

Fig. 17.

Schematic latitudinal section of the Zinc Mine
(Tuba Mine)

Labels visible on the section: [[unclear: shaft name]], R. Sakmara, [[unclear: “Tukan…”]], [[unclear: “No. Urendy”]].

Legend

• Metamorphic strata
• Jaspers
• Porphyrites and their tuffs
• Siliceous shales and tuffs
• Primary suite
• Pyroxenites and serpentinites
• Granodiorites
• Disjunctive disturbances

Fig. 18.

Schematic latitudinal section through the M.-Aleksandrovskoe deposit

Labels visible on the section: [[unclear: “sh. Ivanov”]], R. Sakmara, Alexandrovsky stream.

Scale: 0–10 km.

1. The gold placers described above were discovered during the working of magnesite. ↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩

2. Although Rosenbusch-Mügge (199, 293) indicates that aragonite in certain exceptional cases may form at 70° and lower. ↩↩↩↩↩↩↩↩↩↩↩↩↩

3. From this point of view of the origin of magnesite, the observations of Gordienko (8, 11–12) in the areas of the Sysert and N.-Isetsk dachas are of some interest; there he notes the occurrence of magnesite in serpentines in four parallel bands. ↩↩↩↩↩↩