Prof. P. P. Gudkov

The District

of the Gold Placers

of A. S. Antonov and O. P. Vishnevskaya

in Orsk Uyezd

of Orenburg Governorate

Tomsk
Printing House of the House of Diligence
1918.

The District of the Gold Placers of A. S. Antonov and O. P. Vishnevskaya in Orsk Uyezd of Orenburg Governorate

Prof. P. P. Gudkov.

In the summer of 1912, I and mining engineer M. A. Usov (now professor at the Tomsk Technological Institute), on assignment and at the expense of the Russian Gold-Mining Society, carried out a geological examination of the gold placers of A. S. Antonov and O. P. Vishnevskaya, situated on the lands of the Kvarken stanitsa in Orsk Uyezd of Orenburg Governorate. Since in the existing literature there is no more or less detailed geological description of this district, and since our investigations in it, like many other geological works carried out by Prof. V. A. Obruchev, M. A. Usov, and myself, were undertaken by the Russian Gold-Mining Society to a considerable extent thanks to the initiative of the late Prof. L. L. Tove, I am inclined to think that the present article will be of some interest and, at the same time, will serve as suitable material for the issue of the Proceedings of the Institute dedicated to the memory of L. L. Tove.

The principal group of the placers of A. S. Antonov and O. P. Vishnevskaya is situated, as already mentioned above, near the Kvarken stanitsa in Orsk Uyezd of Orenburg Governorate, and lies between the rivers Baituk and Aidyrlya, which flow into the left tributary of the Ural—the river Suunduk.

The beginning of gold mining in this district—namely, the working of placers—dates, judging by the Collection of Statistical Information on the Mining Industry of Russia, to 1882; the first of the placers worked were the Ioanno-Krestitel’sky Vishnevsky and (from 1884) the Elizavetinsky. The extraction of lode gold, according to the data of the same Collection, began (on the Novgorodsky, Nachal’no-Nikol’sky, Petropavlovsky, and Skuchny allotments) in 1900, and continued until March 1, 1906, by the company of A. S. Antonov and

O. P. Vishnevskaya, from March 1, 1906, to September 17, 1908—the Orsk Goldfields Ltd company, and then—again by the owners themselves. Already in the second year of working the primary deposits, the quantity of vein gold amounted to 12 poods 25 pounds, and by 1908 it had increased so much that the firm of A. S. Antonov and O. P. Vishnevskaya occupied ninth place among all gold-mining firms in Russia and second place among firms extracting mechanical vein gold.

But, despite the long-standing exploitation of the placers and the successful development of the extraction of vein gold, in the geological literature up to 1912 there was not only no special description of the gold deposits in the basin of the Suunduk River, but, in general, only scanty and fragmentary geological information about this district was available. Such, for example, are: Helmerssen’s article*) in vol. IV of the Mining Journal for 1835, in which, among other things, a brief description is given of the route from the Urust-Kinskan River to the Aderlya River (on the newer maps—Adyrlya or Aidyrlya); Barbote-de-Marny’s article in No. 6 of the Mining Journal for 1857, from which it may be learned that placer development along the Suunduk River was already taking place in the fifties of the last century;**) P. V. Eremeev’s article in vol. III of the Mining Journal for 1887, containing “A Description of Certain Minerals from Gold-Bearing Placers on the Lands of the Orenburg Cossack Host and on the ‘Bashkir Lands,’” including gold in a quartz conglomerate from the Happy Creek on the Suunduk River; several data on the rocks in the lower course of the Suunduk River in the “Report on the State and Activity of the Geological Committee in 1907,”*** etc. And only in 1915, i.e., already after our expert examination, did the district of the Antonov and Vishnevskaya claims enter the sphere of systematic work by the Geological Committee, namely, it was investigated by Messrs. Voznesensky, Vysotsky, and Zavaritsky. In the brief report on these investigations, printed in No. 1 of vol. XXXV of the Proceedings of the Geological Committee, there is already given a concise characterization of the relief of the locality, the rocks composing the district are enumerated, the geological interrelations of these rocks are indicated in general outline, and a condensed description is given of the gold-bearing veins in allotments situated in the system of the Aidyrlya River and in the vicinity of Mount Sinii Shikhan. But, I repeat, in 1912 almost nothing was known about the district subject to our expert examination, and we had not only to study in detail all the accessible and rather numerous workings, but also to carry out a detailed geological survey of the entire locality, depicting—

*) “Orographic and Geognostic Description of a Part of the Kirghiz Steppe, Lying between the Ural and Uem Rivers and the Rivers Flowing from the Left Side into the Tobol River.”

**) “A Geognostic Sketch of Certain Remarkable Placers of the Ural Range.”

***) Proceedings of the Geological Committee, 1907, XXVII, pp. 62–75.

shown on the accompanying map (No. 1). We were able to complete all this work in a comparatively short period (from May 12 to June 15) not only thanks to the special character of the terrain, which permits free and rapid travel almost everywhere by carriage, but also to the constant and kindly assistance of the manager of the mines, P. P. Novgorodov, to whom I take this opportunity with pleasure to express our gratitude.

Orographic Sketch

The locality occupied by the principal group of claims of A. S. Antonov and O. P. Vishnevskaya is a small and low plateau. Its most elevated part coincides with the serpentinite stock shown on the general geological map (No. 1) and consists of a series of hills, separated by the valley of the Aidyrlya River—an irregular basin, elongated along the northern boundary of the serpentinite massif—and by several narrow transverse ravines. The relief of all the remaining part of the area investigated is very smoothed, and its plain-like character is disturbed only by the general gradual lowering toward the Suvunduk River, by rare isolated hills in the NW part of the Antonov placer, by sharply expressed ridges on the Rossiya and Spassky claims and in the middle part of the Ofitsersky placer, and by the small hill Siniy Shikhan, situated amid an extensive plain.

If one takes into account that all the hills and ridges just enumerated are composed of very hard, siliceous jasper-like rocks, while Mount Siniy Shikhan consists in its chief mass of vein quartz, then the district under consideration may confidently be regarded as a peneplain—almost a plain—and the existing slight irregularities of its surface as conditioned by an as yet unfinished cycle of erosion and by the unequal hardness of the rocks composing the district. These same factors probably also explain the topographical peculiarities noted above in the part of the district near the mouth of the Aidyrlya: the serpentinite stock occurring here evidently once formed, and still forms at the present time, a natural barrier to the waters flowing from the central part of the plateau occupied by the claims; therefore the upper level of intense erosion has retreated from the Aidyrlya River fairly far to the north (almost to the latitude of the Troitsky and Belinsky placers) and has caused the formation of an elongated basin along the northern boundary of the serpentinite stock and of narrow ravines connecting this basin with the valley of the Aidyrlya.

Owing to the fact that the erosion cycle of the district has not yet ended (as is evidenced by the considerable dissection of the relief in the lower course of the Aidyrlya River), the bedrocks in many places …

in places they emerge at the day surface, while the number of outcrops that are generally eroded and, for the most part, covered is closely connected with the intensity of denudation. Hence it is evident that the completeness of geological investigation of the district in its various parts could not have been the same: whereas in the southern workings of the Aidyrlya group the outcrops were observed by us almost in abundance, to the north and east the material for compiling the geological map was supplied chiefly by artificial excavations. Perhaps this is why gold mining appeared and developed in the southern part of the district: here the quartz gold-bearing veins, like other rocks, often come to the surface, manifesting themselves in the form of low ridges or of eluvial placers.

Geological Sketch

Of the various rocks composing the district of Antonov’s and Vishnevskaya’s gold placers, the chief interest is presented by the igneous rocks: they have here the greatest relative development; they determine the principal features of the geological history of the district; and to them the primary deposits of the noble metal owe their origin.

Among the igneous rocks, first place, by their share in the geological composition of the locality, is occupied by the intrusive rocks of the granite-diorite formation. To these belong chiefly granites and granodiorites, forming several separate geological bodies.

The most significant of these bodies is situated on the Suvunduk River, northwest of the main group of placer allotments, and extends beyond the limits of the map (No. 1). It is composed, in its main mass, of oligoclase–microcline biotite granite, colored a light yellowish-gray. This granite represents a typical normal granite; among its morphological features one may note only that microcline often forms porphyritic segregations in it, while quartz and oligoclase usually occur in aggregates. No traces of later mountain-building pressure are observed in this granite, but near the southern contact it becomes gneiss-like and contains a little garnet and muscovite, i.e., minerals indicating crystallization of the rock under conditions of slight lateral pressure. The structure and composition of the Suvunduk granite remain constant throughout the part of it examined, and only granulite and pegmatite veins and veinlets are encountered in abundance in it, most of them having a NW strike; quartz gold-bearing veins, on the contrary, have not yet been found at all.

Another, perhaps equally significant massif, constituting the sub—

the soil of the entire area of the Sinii Shikhan mine and extending from here far to the southeast, consists of pink microperthitic hornblende-biotite granite. It was impossible to determine the facies varieties of this granite, or to find any vein rocks belonging to its massif, since the area studied by the latter presents an almost completely level plain covered by an enormous layer of eluvium, and the more or less fresh specimens of granite we took come from the deep excavations present here. On the other hand, many quartz gold-bearing veins were found in this massif, extending in a fairly broad belt for about 8 versts to the southeast. The isolated mountain Sinii Shikhan mentioned above, which gave its name to the mine on which it is located, also consists of such veins, strongly widening in one place.

Noticeably different from the two granites described is a small stock situated not far to the southeast of the mouth of the Aidyrla River. It belongs to rocks composed of the same components as the granite of the Suvunduk River, but containing, in addition, hornblende and possessing more significant traces of protoclase, namely—a fairly distinct gneiss-like structure, the constant presence of a certain quantity of almandine and muscovite, and—the presence of cloudy extinction, and sometimes also bands of crushing, in the quartz. The pressure that caused these features of the rock evidently continued even after its complete crystallization, for it was reflected not only in the gneiss-granite itself, but also in the products of the latter’s differentiation encountered here and there—pegmatite veins consisting of gray microcline-microperthite, poor white mica, and rather abundant parallel veinlets of quartz showing, under the microscope, distinct cloudy extinction. Quartz veins in the gneiss-granite under consideration were also found in places, and some of them were even explored and apparently are gold-bearing to one degree or another.

The greatest significance in respect to gold content belongs to a granodiorite forming an irregularly elliptical body (with axes of 6 and 2½ versts) in the central part of the main group of allotments and to four small stocks so far exposed in the immediate vicinity of the first. The central body in its southern half consists of typical granodiorite. This is a fine-grained rock with porphyritically projecting prisms of plagioclase; in fresh specimens obtained from underground workings it is light gray, and in weathered specimens pinkish. In its composition, as is seen under the microscope, the principal share is taken by plagioclase (for the most part close to Nos. 35–40), common hornblende, and quartz; subordinate quantities include potassium feldspar*) and biotite,

*) It often forms, with quartz, a fine micropegmatitic intergrowth filling the interstices between the plagioclase and hornblende.

and, as accessory minerals, apatite and ores. A very characteristic feature of the granodiorite is the frequent occurrence of small schlieren, distinguished from the general mass of the rock by a more fine-grained texture and an increased content of hornblende. In the rock composing the northern part of the body under consideration, a noticeable enrichment in quartz is observed, together with the appearance of somewhat more frequent and larger grains of microcline-microperthite; conversely, the relative amount of dark-colored components decreases, and biotite assumes the principal role among them. The transition from one rock to the other is detectable over a short distance, but with clear gradualness, so that the rock of the northern part, although in its composition it approaches normal granite, must be regarded merely as a facies variety of the granodiorite of the southern part, indicating that, in the formation of the latter, both crystallization differentiation (the above-mentioned schlieren) and magmatic differentiation took place. The products of differentiation of the granodiorite magma should also include: the coarse-grained feldspathic hornblendite replacing the principal rock in the western part of the Petro-Pavlovsk allotment; the veins, observed here and there, of diopside-hornblende spessartite; and the rock composing the small stocks mentioned above (in the Lermontov and Troitsk allotments and to the west of the Antonov allotment). The latter differs from the granodiorite of the southern part of the central body by a higher content of femic minerals (usually strongly chloritized), by the almost complete absence of potash feldspar, and by the smaller grain size of its principal mass, for which reason—given a certain porphyritic character of the plagioclase individuals—the texture sometimes approaches a granite-porphyry texture.

Both the granodiorite and the facies varieties listed above are everywhere accompanied by quartz gold-bearing veins, and moreover by those richest in this district. To these same veins belong also those which, up to the present, have alone been subjected to intensive working.

The second group of intrusive rocks, occupying, in terms of its relative development in the district studied, the place following granites and granodiorites, is represented by serpentinites and gabbroid rocks.

The serpentinites compose a large massif in the lower course of the Aidyrlya River and, apparently, an isolated body in the eastern part of the Feodosievsky and Georgievsky allotments; the size and form of this body, owing to the absence of outcrops, have remained undetermined. Microscopic study shows that all the serpentinites belong to the antigorite type, displaying, for the most part, a typical mesh structure, which—depending on the size and shape of

individuals of antigorite—it may also be termed sometimes prismatic, sometimes acicular-prismatic, sometimes scaly*). Fairly often in serpentinite thin sections there occur larger porphyritic, indivisible bastite grains, sometimes preserving the outlines of pyroxene crystals. Conversely, neither mesh structure nor any traces whatever of olivine could be established anywhere, and in only two thin sections were thin and rare veinlets of chrysotile encountered. As fairly constant admixtures in the serpentinites there are separate grains, skeletal accumulations, or dots of ore arranged in sinuous rows (often in the form of clear chromite), and irregular porphyritically projecting grains of calcite. The latter in some thin sections is so abundant as to give grounds for calling the corresponding specimens ophicalcites.

The gabbroid rocks, which, like the pyroxenites (from which the serpentinites probably formed), represent products of differentiation of a gabbro-peridotite magma, occur as numerous veins in the serpentinites and form a rather large group of outcrops in the southern part of the Aidyrlya serpentinite massif, composing—perhaps—the whole central part of the latter. In petrographic terms they may be characterized as dark-gray and dark greenish-gray, medium- or fine-grained gabbro-diorites, containing, as their principal components, saussuritized labradorite and, to varying degrees, a decolorized brownish-greenish or uralite-like hornblende, and, as accessory admixtures, titanite, magnetite, and, in some thin sections, scanty quartz filling small interstices.—The genetic connection of the gabbro-diorites with the serpentinites, apart from the indicated conditions of occurrence, is also proved by the fact that the gabbro-diorites, while displaying clear traces of contact metamorphism—namely, transition into amphibolites—near the gneissogarnite cause no changes in the serpentinites, even where they are in immediate contact with them.

Also in an obvious, but probably not genetic, only spatial, connection with the just-described representatives of the gabbro-peridotite group are porphyritic rocks, forming veins among the gabbro-diorite–serpentinite massif of the Aidyrlya River and surrounding this massif on the north-eastern side. They are represented by two varieties, connected with one another by gradual transitions. One of these varieties is characterized by the presence of porphyritic segregations of albite and quartz and by a microgranitic or granophyric structure of the groundmass; in short—it should be termed a quartz keratophyre; the other contains, in a fine-grained allotriomorphic groundmass, porphyritic segregations of oligoclase, chloritized biotite (rarely—together with likewise chloritized hornblende)

*) Cf. B. P. Krotov, “Petrographic Investigation of the Southern Part of the Miass Dacha,” Proceedings of the Society of Naturalists at Kazan University, vol. XLVII, issue 1, p. 98.

and scanty quartz; i.e., it belongs to the quartz porphyrites. In their outward habitus both varieties resemble granite-porphyries, and owing to this, as well as in view of the conditions indicated and the absence of tuffs associated with them, they should be regarded not as typical effusive, but rather as hypabyssal formations.

Quartz veins occur fairly often in all the rocks just described, although it should be noted that in the gabbro-diorites and serpentinites they are confined chiefly to those places where porphyries appear. Within the area of Antonov’s and Vishnevskaya’s allotments, veins of this category have been almost entirely unprospected, but it may be supposed that to some extent they contain gold, for at the Rameev mine, situated south of the Georgievsky allotment within the limits of the northeastern serpentinite body, quartz veins have been subjected to fairly deep working.

The typical effusive rocks are represented in the district chiefly by porphyrites, which form a more or less continuous mass, surrounding on the southern and eastern sides the central body of granodiorite and enclosing small apophyses of the latter. Among these porphyrites, dense greenish aphanitic varieties are especially widespread; they contain small calcite amygdules and, under the microscope, reveal an intersertal or pilotaxitic mixture of calcitized plagioclase, chlorite, and abundant carbonaceous grains of ore; but occasionally porphyrites in the proper sense of the word are also encountered, differing from aphanites in the absence of amygdules and in the presence of scanty, small phenocrysts of calcitized plagioclase. However, all the porphyrites preserve the properties just indicated only in comparatively few places; over most of the area occupied by them they show changes caused by intense mountain-forming pressure—namely, considerable chloritization and, to varying degrees, complete schistosity, usually trending in a northwestern direction. Here and there, such changes also bring about the transition of porphyrites into dense chloritic schists.

Quartz veins are also encountered in the porphyrites and in part have even been subjected to some working, but nearly all of them occur near the margins of granodiorite apophyses.

Among other effusive rocks one may also mention felsites, which, together with the corresponding tuffs, enter into the composition of the siliceous formations described below. But everywhere these rocks have undergone such silicification and have so lost their individual properties that their primary nature can be inferred only from a few minor features.

Sedimentary rocks are distributed very unevenly in the district of the investigated mines, composing almost entirely the eastern

half of this district; within the claim areas of the Aydyrlinskaya group proper they play a subordinate role, yielding the principal place to igneous formations. The latter, of course, have disturbed the more or less calm bedding of the sedimentary formations, which have a meridional strike approximately common to the entire Urals, and in some places have produced contact-metamorphic changes in them. Lithologically, among these sedimentary formations one may distinguish a sandy-clayey facies, siliceous formations, and carbonate rocks.

The sandy-clayey facies is most highly developed in the district in general and especially in its eastern half, where it probably composes the entire area between the Sineshikhansky granite, the serpentine body of the Georgievsky and Feodosievsky claims, and the complex of igneous rocks of the Aydyrlinskaya group of placers proper (see the map in Table No. 1). It is composed of quartz-rich sandstones, sandy-clayey-micaceous and sandy shales, clayey and carbonaceous-clayey shales containing here and there thin interbeds of coal. These carbonaceous rocks occur mainly in the eastern part of the indicated area and, judging by the conditions of occurrence, represent the upper division of the sequence under consideration. However, under the microscope a small amount of carbonaceous matter—usually in the form of thin, sinuous-parallel veinlets—is observed in all the enumerated members of the sandy-clayey facies. As for the other results of the microscopic study of these rocks, only the following features observed in sandstone thin sections deserve mention: a considerable crushing of the coarser quartz grains, forming, as it were, small lenses encircled by the above-mentioned carbonaceous veinlets, and a relatively abundant content of flakes of light mica. The first feature shows that mountain-building pressure not only disturbed the bedding of the sedimentary rocks but also affected their internal structure; the second compels one to suppose that the original material for the formation of the sandstones was supplied by some gneisses, among which the gneisses occurring in the district studied could not as such have been included, for they exerted here and there upon the shales and sandstones a more or less evident metamorphosing influence.

With respect to gold content, the sandy-clayey formation is of some interest only near the Sineshikhansky granite massif and to the northwest of the serpentine body exposed within the claim areas of Feodosievsky and Georgievsky. In both places many quartz veins were discovered, and many of them were worked, although at the time of our visit to the district work was being carried out only at the Nikolai-Elizavetinsky placer.

Siliceous rocks, in terms of their relative distribution within the district, occupy a rather modest place. They crop out in many places on different sides around the central core of igneous rocks, and occur here and there among the latter in the form of small islets (not shown on the map). Having repeatedly undergone the action of gases and vapors rising from the igneous formations, and—together with this—having experienced much-varied pressure, the siliceous rocks almost everywhere recrystallized and yielded quartzitic and jasper varieties of massive breccia-like structure. They are colored most often brownish-gray or brown, somewhat more rarely (the jasper varieties) red and dirty green, and under the microscope they present a dentate-honeycomb quartz aggregate, which in the quartzitic modifications usually has unequal grain size in different parts, while in the jasper-like ones it is uniformly fine-grained; in all cases it contains more or less abundant fine veinlets and irregular spots of limonite, sometimes rare grains of red iron ore and magnetite, and here and there also scattered flakes of chlorite. The iron oxides, limonite and red iron ore, were probably formed from pyrite, which in some specimens—for example from the outcrops on the Ofitserskii allotment—is discernible even with the naked eye.

As has already been indicated, obscure felsitic formations enter into the mass of the siliceous rocks. They are encountered especially near the Uspenskii and Kachkarskii mines, and are distinguished macroscopically by a lighter coloration, and under the microscope by the presence of areas resembling finely recrystallized microfelsite, with rare small porphyritically projecting individuals of quartz.

Despite their proximity to the gold-bearing rocks, the siliceous formations, apparently, are not accompanied by gold-bearing veins. True, there are rather many quartz veins in them, but all such veins must be regarded as secondary, formed from the substance of the siliceous rocks themselves. Such veins are especially interesting in contact with the limestones of the Turgenevskii mine, where druses and brushes of rock crystal are frequently encountered.

Limestones, for the most part dolomitized and in many places marble-like, were encountered in the western part of the area studied. They too have almost everywhere undergone considerable recrystallization, owing to which they acquired a massive structure and proved devoid of organic remains; only in a few places was it possible to find in them scanty columnals of crinoids. The contact-altered varieties of carbonate rocks are generally discolored; in general, they are colored light or dark gray, with—

than in either of the other cases; when struck with a hammer, they emit a strong odor.

In gold-bearing respects the limestones appear, evidently, to be unpromising. Only in proximity to the altered sandy-clayey deposits—for example, on the allotments of Dedushka Kroger and Sonechkin—are quartz veins found in the limestones; these have in places been slightly prospected and may perhaps, like the veins in the siliceous rocks, be secondary.

For completeness in the petrographic characterization of the area under study, and in order to clarify the geological relationships indicated below, it is necessary to dwell also on the contact-metamorphic rocks. Contact metamorphism was manifested chiefly in the rocks occurring adjacent to the intrusive bodies of the granito-diorite formation already known to us. The degree of this metamorphism is in more or less clear dependence on the size of the body of the active rock, and—perhaps—also on the composition and structure of the latter. Thus, the contact metamorphism produced by the Suvunduk and Aydyrlya granite massifs is revealed in the country rocks very sharply and can be traced for a great distance; meanwhile, the contact belt of the central body of granodiorite is not very clearly expressed and has little thickness, while around small stocks of granodiorite it was not noticed at all, at least in the outcrops that could be observed here. As for the dependence between the intensity of metamorphism and the structure of the active rock, it is clearly attested by the difference, noted below, in the strength of the contact alterations produced by the gneiss-granite of Aydyrlya and by the almost structureless granite of Suvunduk.

Let us now turn to the description of the contact-metamorphic formations themselves, considering them by contact belts, since in this way it will be most convenient to confirm the observations made in the preceding lines.

The contact belt of the central granodiorite body is almost entirely represented by altered porphyrite rocks. As has already been mentioned, contact metamorphism is here, for the most part, weakly expressed. It is true that microscopically it can always be observed that the amygdaloidal and aphanitic varieties of the porphyrites, as well as the groundmass of the porphyrites proper, become very hard in the contact zone, acquire a hornfels-like fracture, and lose the schistose structure characteristic of these rocks. However, the changes observed under the microscope in thin sections of such specimens are usually limited only to the saussuritization or zoisitization of plagioclase and to the neoformation of epidote, clinozoisite, pale-green fibrous hornblende, and quartz, which compose, now partly—

... rocks, then mixed with one another: abundant small areas of fine-grained honeycomb structure. And only in a few places, in direct contact with the granodiorite, is there observed in the porphyrites an insignificant injection and a more or less typical hornfelsing, manifested under the microscope in the abundant development of small flakes of biotite, for the most part replaced by chlorite and also accompanied by epidote, quartz, and secondary hornblende.

Under the influence of the magma of the granite massif of the Suvunduk River there proved to be limestones, siliceous rocks, and sandy-clayey deposits.

The limestones underwent a rather intense alteration, but one exclusively structural: in their place white marbles were formed, devoid of any contact minerals and even retaining the smell of the primary rocks. The grain size of the marbles increases as one approaches the granite massif, so that in the Troitsk mine, for example, varieties occur which may be called coarse-grained and which consist of fairly idiomorphic crystals of calcite, almost unbound by cement, and—for this reason—are readily subject to desquamation. Conversely, medium- and fine-grained marbles are sufficiently dense and may be used for facing.

The siliceous rocks of the contact belt under consideration were observed at very few points; they have passed into white or light-gray quartzites, which under the microscope reveal a honeycomb, uneven-grained aggregate of quartz, among which occasional small grains of pyrite occur.

As for the sandy-clayey deposits encountered over a considerable extent along the left bank of the Suvunduk River and at a comparatively great distance from the boundaries of the Suvunduk granite body established by observations, they underwent alteration very unevenly. Thus the sandstones—especially the conglomerate-like varieties of the latter—have almost preserved their primary macroscopic properties, and only the microscope reveals that the cement of these rocks has been transformed into a fine-grained allotriomorphic quartz-feldspar aggregate with sparse narrow flakes of muscovite, while, as new formations, there have appeared a small number of hornblende needles, fine scaly accumulations of chlorite, and separate, larger plates of colorless mica. Conversely, the finer the grain of the rocks was, the greater the alterations observed in them; and in place of clayey shales there arose typical dark-brown or black dense hornfels shales with a mass of uniformly distributed nodules. The latter, as is seen under the microscope, are sheaf-like and radially fibrous intergrowths belonging, judging by their optical properties (the rather noticeable...

refraction; weak pleochroism from colorless to pale greenish-blue; weak birefringence; a sandy-hourglass structure of individual individuals and a large angle between the optical axes—one of the varieties of brittle micas.*) The main mass, among which these intergrowths stand out, resembles the cement of altered sandstones, but is distinguished by a much higher content of muscovite needles and a very meager content of quartz.—Since the described hornfels schists were also found in the versts at 6 from the Suvunduk massif, it must be supposed that this massif extends along the right bank of the river rather far to the south, or else that there is here an independent outcrop of the same intrusive rock.

In the contact belt of the gneiss-granite lying to the southeast of the mouth of the Aidyrlya stream, metamorphism manifested itself very intensely. Within the sphere of its influence, as is evident from the geological map, there proved to be chiefly gabbroid rocks, from which, as a result of contact effects, amphibolites and amphibole schists were formed, in the immediate vicinity of the gneiss-granite strongly injected by it. In external appearance the amphibolites are rather varied, resembling now saussuritized gabbro, now massive or indistinctly schistose fine-grained rocks composed, as it were, entirely of amphibole alone. Under the microscope, however, it is seen that the differences among specimens least similar in macroscopic properties are not so great: in all thin sections, as the principal components, there are observed very turbid saussuritized individuals of plagioclase; separate grains of zoisite and irregular prisms of pale greenish or brownish**) hornblende; and only the relative content of these minerals in the different thin sections varies appreciably; in addition, more or less abundant grains of titanite, apatite crystals, and, here and there, small druses of epidote appear. The injected amphibolites always possess a clear schistosity, and under the microscope reveal a regular alternation of narrow layers, of which some are usually composed of an almost continuous aggregate of short prisms of dirty-greenish hornblende, others—of an aplitic mixture of fresh plagioclase and quartz, or of these same minerals with separate grains of zoisite. In some thin sections, however, this picture is modified by the fact that in the darker layers plagioclase, zoisite, and diopside are observed in approximately equal quantities, while in the lighter layers—plagioclase with a negligible admixture of dirty-greenish hornblende.

*) Dr. Ernst Weinschenk, Gesteinbildenden Mineralien, 2nd edition, Freiburg im Breisgau, 1907, pp. 141–143.

**) Sometimes—with a bluish-greenish rim.

The serpentinite did not, evidently, enter directly into the zone of the contact under consideration, but it may be noted that the outcrops of this rock, encountered at a short distance from the northern boundary of the gneisso-granite, are characterized by an especially dense structure and, perhaps, by a greater than usual development of chrysotile veinlets. Finally, for characterizing the contact influence of the gneisso-granite it is very important to note that—despite the comparatively very intense metamorphism of the gabbroid rocks—the alterations of the limestones occurring on the western side of the gneisso-granite body are expressed extremely weakly; and, for example, in the limestone outcrops between this body and the Suvunduk River, for the most part no macroscopically visible recrystallization is even observed.

As for the western contact belt of the Shikhansky granite, one must form an idea of it (owing to the absence of outcrops) only from a few specimens taken from the dump of the shaft at the Voskresensky mine of the Rossiya Partnership*). All these specimens represent a sandy-clayey carbonaceous formation,—and judging by them—the sandstone varieties of this formation underwent changes of the same qualitative kind, but less intense, as the analogous rocks near the Suvunduk River, while the carbonaceous matter entering these rocks as an admixture or forming independent thin interbeds was converted into graphite.

As regards the contact metamorphism produced by other rocks, it is so weak that it is almost not amenable to observation. It is true that one may say that the rocks of the serpentinite contact belt underwent a certain silicification and opalization; but in view of the fact that in the investigated parts of this belt siliceous rocks occur everywhere, it is permissible to explain the indicated opalization not by the contact influence of the serpentinite, but by a partial extraction of substance from the material of siliceous formations. The effect of porphyritic rocks upon serpentinites is established with greater certainty: almost everywhere, where outcrops of these rocks were encountered at a short distance from one another, dense siliceous-ferruginous masses were observed in place of serpentinites; these consist, as the microscope shows, of a fine-grained allotriomorphic quartz aggregate with unevenly distributed patches of carbonates and with abundant irregular quartz-hematite or quartz-limonite veinlets, the arrangement and structure of which seem to make it possible to discern in them former chrysotile veinlets. However, here too it must be stipulated that traces of silicification, in the form of the formation of pseudomorphs of a fine-grained mixture of quartz after crystals of feldspar,

*) This mine is located 3 versts to the southwest of the Siniy Shikhan mine.

are observed under the microscope also in specimens of the porphyries themselves, taken near the outcrops of the serpentinite; and therefore the indicated alteration may possibly be regarded as the result of post-volcanic processes that accompanied the eruption of the porphyries.

Finally, it will not be superfluous to note that many slightly ore-bearing jasper-like formations, such as those in the hills of the Ofitsersky and Antonovsky mines, owe their character, perhaps, to the influence of those eruptions which brought forth the porphyrites.

Let us now proceed to clarify the stratigraphic relations of the rocks composing the area under investigation.

The oldest formations must, of course, be considered the rocks of the sedimentary formation, since they are everywhere cut through and often metamorphosed by the eruptive rocks; the only exception among the latter is the felsites with their tuffs, which alternate with, and are of approximately the same age as, the siliceous rocks.

The thickness of the sedimentary formations, as we have seen above, is divided rather definitely into three facies: siliceous, sandy-clayey, and carbonate (limestones with dolomites). The stratigraphic relations between these facies, on the basis of the bedding elements measured where this was possible and marked on the geological map, appear as follows: the sandy-clayey rocks, in their main mass, constitute the uppermost division of the sequence and, apart from this, in the form of more or less hornfelsed varieties, form interbeds among the limestones; the siliceous rocks occupy, in the overall succession, an intermediate position, conformably overlying the limestones and also conformably underlying the sandy-clayey deposits. However, in this form the question of stratigraphic relations is resolved with sufficient definiteness only in the part concerning the siliceous rocks and the main mass of the sandy-clayey facies of the general sedimentary sequence lying to the east of the group of the Aidyrlya allotments proper. As regards the question of the stratigraphic position of the limestones, besides the supposition stated above, another assumption is also permissible. In fact, in describing the contact-metamorphic rocks it was mentioned that the altered sandy-clayey schists of the right bank of the Suvunduk differ from the same rocks forming part of the western contact belt of the Sineshikhan granite only by a greater intensity of metamorphism. If to this we add that the hornfelsed sandstones and schists on the right bank of the Suvunduk River are especially developed in the immediate vicinity of the Suvunduk River (between Kudryavtsev’s mill and the Kvarzhen stanitsa), and that here they form, perhaps, an entirely independent horizon, unrelated to the belt that passes between Sonechkin and

With the adjacent allotments, it will be quite permissible to recognize the limestones as the very uppermost division of the entire sedimentary sequence, overlying the sandy-clayey deposits. The absence of limestones in the eastern part of the area investigated may be explained, under this assumption, by a longitudinal fault, by which they were brought into contact with the very lowest division of the sequence—the siliceous rocks—and, owing to downthrowing, escaped the denudation that destroyed them to the east. Of course, both of the interpretations given for the relations among the rocks of the sedimentary formation, like almost all stratigraphic constructions, are only hypothetical—the more so since we have very little data of a stratigraphic character, owing to the absence of fossils and of sufficiently extensive outcrops of the rocks. Still, if attention is paid to the fact that in the western part of the area the sedimentary rocks are bounded on three sides by bodies of igneous rocks and display more or less frequent and sharp changes in the elements of their attitude, while in the siliceous formations traces of the action of thermal waters are often observed (in the form of recrystallization and drusy quartz veins), then the supposition of a fault having occurred here must be considered highly probable. On the other hand, it should be noted that the superposition of limestones upon the sandy-clayey rocks was discovered by N. N. Tikhanovich in the lower course of the Suunduk River) (to the southwest of the settlement of the Kvarken stanitsa and almost directly on the strike line of the sedimentary suite discovered by us near this settlement); and that, according to the geological investigations of Mr. Voznesensky, on the right bank of the Suunduk River in the Kvarken stanitsa there are developed sedimentary rocks, represented chiefly by sandy-clayey shales,*) which, it must be thought, belong to the same sequence that we encountered in the outcrops of the left bank of the Suunduk River between Kudryavtsev’s mill and the settlement of the Kvarken stanitsa.

In addition to the fault discussed above, and undoubtedly earlier than its formation, the sedimentary rocks throughout the entire area investigated underwent a plicative dislocation of an approximately meridional strike, common to the whole Urals. To determine, even approximately, the number of folds accommodated within the limits of the area shown on the map was impossible, owing to the lack of outcrops, the absence of fossils, and the more or less homogeneous lithological composition of the individual facies; but since in almost all cases known to us the dip of the beds is not very steep, it will not be risky to assert—

*) Izv. Geolog. Komit., XXVII, art. “Report on the State and Activity of the Geological Committee in 1907,” p. 71.

*) Izv. Geolog. Komit.*, XXXV No. 1, “Report on the Execution of Work Provided for by the Program of 1915,” p. 48.

that the plicative dislocation was not among the especially strong ones. *) For this reason, perhaps, this part of the Urals has at the present time proved to be almost leveled by denudational processes, whereas both the Middle and the Northern Urals, where more significant folds arose, have still retained the character of a mountain chain.

As to the relative age of the rocks under consideration, in view of the absence of determinable fossils, one must speak, of course, only conjecturally and chiefly on the basis of published data on the geology of other districts close to that investigated by us. Such data are: 1) the indications of P. N. Tikhonovich that east of the Ural River, between Tanalykskaya Station and the town of Orsk, there occur rare outcrops of presumably Devonian siliceous shales and crystalline limestones, as well as Lower Carboniferous limestones, sandstones, and shales with interbeds of thin coal; moreover, as was already noted above, P. N. Tikhonovich established Lower Carboniferous limestones (lying upon a sandstone-conglomerate sequence) in the lower course of the Suunduk River ); 2) the results of the investigations of B. P. Krotov, who established that along the eastern half of the Miass dacha there extends a belt of limestones of Lower Carboniferous age, and along the western half of the dacha—a belt of limestones of Middle Devonian age; ) 3) the remark of Academician A. P. Karpinsky that “up to the present no traces whatever of intrusions of deep-seated rocks within the limits of the Upper Carboniferous and in the more recent deposits of the Paleozoic (in the Urals) have been observed.” ) If, bearing these data in mind, one recalls that coal-bearing formations are included in the sandy-clayey facies of our district, that in stratigraphic position the sandy-clayey facies, as was indicated above, probably occupies an intermediate position between the siliceous rocks and the limestones, and that the latter, together with other members of the sedimentary sequence, have been altered in contact with granites, ) then the sandy-clayey rocks and limestones may be assigned either to the Lower or to the Middle Carboniferous, and the siliceous formations—to the Lower Carboniferous or to the Devonian. ****)

*) Mr. Voznesensky also arrives at the same conclusion; according to him, the sedimentary rocks of the western part of the area he investigated are gathered into broad folds of northwestern and northeastern trend.—Izv. Geol. Committee, vol. XXXV, No. 1, p. 18.

**) Ibid., p. 71.

***) Ibid., p. 490.

****) “On the Origin of Deposits of Fluorspar in the Deposits of the Moscow Stage of the Carboniferous System and on Certain Other Geological Phenomena,” Izv. Imp. Acad. Sci., 1915, series VI, p. 1545.

*) Consequently—according to Karpinsky’s remark—they cannot belong to the Upper Carboniferous.

**) I note, at the same time, that on the geological map of European Russia (2nd ed. of the Geological Committee), both in the system of the Suunduk River and over a considerable area to the east and to the north, only Lower Carboniferous deposits are shown.

Among the igneous rocks, if the above-mentioned felsites are not taken into account, the serpentinites and porphyries must be recognized as the most ancient; these appeared, however, only after the formation of the sedimentary rocks. Indeed, the material of the serpentinites and porphyries seems nowhere to enter into the composition of the sedimentary deposits, and their schistosity has an entirely different—northwestern—strike. Moreover, it must be taken into consideration that the denuding erosion has already, undoubtedly, carried away a fairly thick mass of porphyritic formations, while the latter—nevertheless—still consist to a considerable extent of vesicular varieties; this means that outpourings of porphyritic lava took place repeatedly over a prolonged period of time, and—if they were contemporaneous with the sedimentary rocks—then the latter would have had to be interbedded with porphyries or with porphyry tuffs. *)

The relation of the serpentinites to the porphyries cannot be precisely determined, since no contact between these rocks was found. However, in view of the considerable analogy in the geological structure of the district under consideration and of the southern part of the Miass dacha, it may be assumed with sufficient probability that the serpentinite is older than the porphyry; for in the Miass dacha B. P. Krotov established in many places that the magma of the porphyries broke through the serpentinites along fissures, flowed out onto their surface, and partly covered the serpentinites with masses of loose volcanic products. **) Such an assumption is important for us, among other things, also in that it allows us to speak with greater confidence of the less ancient age of the serpentinites in comparison with the sedimentary rocks. In fact, the serpentinites represent altered pyroxenites, i.e., basic deep-seated rocks which, at the time of their formation, were separated from the surface by some thick mass, now completely washed away; and this latter mass, once we have concluded that the porphyries are younger than the serpentinites, consisted, in all probability, precisely of sedimentary rocks.

Intrusive rocks of the granite-diorite formation belong, undoubtedly, to younger formations, since they break through and, to a greater or lesser degree, metamorphose all the rocks just considered. However, the intrusions of granite-diorite magma, which created several independent bodies in our district, pro—

*) N. N. Tikhanovich and B. P. Krotov observed such interbedding in the districts they investigated; but this still does not prove the incorrectness of our supposition regarding the relative age of the Aydyrlya porphyries, for—according to A. P. Karpinsky—the porphyries, like many other effusive rocks, erupted in the Urals repeatedly, beginning with the Lower Devonian epoch up to the Permian period and even later (op. cit., note on p. 1544).

**) Op. cit., p. 377.

did not proceed simultaneously. This is indicated by manifestations of lateral pressure which occurred during the formation of certain intrusive bodies.

Indeed, we have seen that the Aydyrlya massif is composed of gneiss-granite, in places passing into thin-schistose orthogneiss; i.e., it was formed, evidently, under conditions of strong lateral pressure. This pressure, which in the given massif produced a schistosity of northwestern strike, continued also during the formation of the accompanying gneiss-granite pegmatites, manifested itself rather far to the north on the serpentinites and porphyrites, which acquired schistosity of the same strike, and was also reflected in the sedimentary rocks, which in places exhibit cleavage.

The Suvunduk microcline granite, as was said in the description, in its principal mass has a massive structure and is only slightly gneiss-like in its peripheral parts; this gives undoubted grounds for supposing that it was formed already toward the end of the formation of the Aydyrlya gneiss-granite body, when the lateral pressure began to diminish and could be reflected only on the margins of the massif and on the strike of the pegmatite veinlets cutting the latter.

Finally, in the Shikhan granite and in the rocks of the granodiorite family, which compose several small bodies in the area occupied by the central group of the Aydyrlya claims, no traces of protoclase are observed any longer; therefore the formation of these bodies must be assigned to the time of the complete cessation of that lateral pressure of which we have just been speaking. However, here too it must be noted that the Shikhan granite may be considered to have formed somewhat earlier than the granodiorite bodies and soon after the intrusion of the Aydyrlya and Suvunduk granites: in it, as was noted above, there passes a long belt of quartz veins of the same northwestern strike that is characteristic of the first period of intrusion; in the granodiorite stock, however, the disposition of the quartz veins shows dependence only on the outlines of this stock, and is by no means tied to any single particular direction.

As for the quartz porphyries and quartz porphyrites, from the description given of the conditions of their occurrence—and perhaps simply from examination of the geological map—the more southerly age of these rocks in comparison with the serpentinites and porphyrites is established with sufficient certainty. But if one takes into account the absence of manifestations of dynamometamorphism*) in the quartz porphyries,

*) This shows that the eruption of the porphyries took place after the cessation of the lateral pressure that accompanied the intrusion of the gneiss-granite and granites, but was not reflected on the granodiorite.

and their hypabyssal habitus, it may be supposed that these rocks are approximately contemporaneous with the granodiorites and—perhaps—constitute the suite of the latter.

Description of the Quartz Gold-Bearing Veins.

From the geological sketch given above it is evident that the quartz veins of the district described may be divided into three groups, according to their conditions of occurrence: veins occurring in granodiorite; veins occurring in other igneous rocks; veins occurring in sedimentary rocks. We shall describe each of these categories separately.

1) Veins occurring in granodiorite.

As has already been said above, and as is evident from the appended map No. 2, the greatest number of veins discovered in the district belongs to the group under consideration. Some of them—the Novgorodovskaya, Miasskaya, Safonovskaya I, and Krasnaya Gorka I—have been worked to a depth below the level of the ground waters; others have been mined only down to the level at which water appears; a third group has been subjected only to prospecting by surface trenches, or has not even been prospected at all, but has been discovered by natural outcrops, which usually appear in the form of low ridges of various lengths. The strike of all these veins is rather diverse, but for the most part follows three directions, corresponding at the same time to the outlines of the central granodiorite body; namely: meridional, north-northeastern, and close to latitudinal. Changes in the strike of each individual vein are observed rarely and, for the most part, are insignificant. The dip angle of the majority of veins is \(80^\circ\)–\(90^\circ\), less often \(60^\circ\)–\(70^\circ\), and in very few*) \(27^\circ\)–\(30^\circ\). The direction of dip in veins with meridional and NNO strike is, with very rare exceptions, westerly; while in veins with a strike close to latitudinal it is sometimes northerly, sometimes southerly. The magnitude of the dip angle, both along the strike and at depth, is preserved by all the veins with great constancy.

No disturbances of occurrence are observed in any of the veins examined by us, and—judging from the miners’ reports—nor in all the other more or less prospected veins. The rare bends of the stopes that may be seen on the plans of the workings along the Novgorodovskaya and Miasskaya veins are explained not by any displacements of parts of the veins, but by a peculiar coulisse-like structure of the vein fissures and by their very widespread branching, or—by

*) The Novgorodskaya Poperechnaya II, Raduzhnaya, and Belaya Gora; moreover, the last three probably represent one vein.

in the local terminology—by its capacity to “yield marks.” It should be noted, however, that, owing to the weak development of underground workings, in many cases it has not been possible to determine whether these “marks” are branches of some vein or represent parts of a new, independent vein cutting the first. Likewise, for lack of data, the question had to be left open as to whether two veins of different strike freely intersect each other, or whether one of them blocks the continuation of the other. Thus, in particular, with regard to the Novgorod vein it can only be said hypothetically that it continues northward beyond the Miass vein. In favor of this supposition are, first, the absence of any indications that the Miass vein is an offsetter of the Novgorod vein; second, the presence of a rather long series of quartz outcrops along the line of strike of the Novgorod vein in the area between the Kazan and Petropavlovsk allotments (north of the latter); third, the directly observed (according to the words of the mine foreman M. G. Eroshkin), in one of the prospectors’ pits, intersection of the Novgorod and Miass veins. Finally, it must be borne in mind that the spread of prospecting work along the Novgorod vein northward only as far as the Miass vein cannot be regarded as contradicting the supposition under consideration, since north of the Miass vein there are no workings at all, including even small prospectors’ “diggings”; and therefore, with regard to the northern continuation of the Novgorod vein, it must be said not that it was not found, but simply that it was not sought.

Turning to a detailed description of other properties of the quartz veins occurring in the granodiorite, it should be stipulated that these properties could be studied more or less thoroughly only in the workings on the Novgorod, Miass, and Krasnaya Gorka veins; the workings on all the remaining veins were, at the time of our investigations, flooded or caved in. Therefore, the information given below on the character of these veins, worked almost exclusively by prospectors, has been drawn by us from interviews with old employees of the Antonov and Vishnevskaya company.

The thickness of the Novgorod, Miass, and Krasnaya Gorka veins, in general, may be called very constant. True, as is evident from the transverse “cuts” given (see Table No. 3), in the Miass vein there are sections of rather varied thickness; but it should be noted that the length of the sections on which the thickness remains almost the same—that is, is very considerable—and the changes in thickness are usually very gradual.

As to the thickness of the remaining veins occurring in the granodio-

The following figures, communicated to us by the mine surveyor M. G. Eroshkin, may give an idea of the thickness of the veins:

Vein	Claim	Average ore-bearing constant thickness
Gomzhin’s vein	Pushkin	0.33 sazhen
Netkachev’s	Gogol	0.25 sazhen
Novikov’s	Siberia	thickness in the mine—1.00 sazhen, to N from the mine—0.3 sazhen
Zmeinaya	Siberia	thickness = 0.17–0.42 sazhen
Shvedkov’s	Siberia	0.33 sazhen
Pryamaya	Siberia	0.33–0.66 sazhen; rarely—0.25 sazhen
Srednyaya	Siberia	0.33 sazhen
Shevchenkov’s	Siberia	0.40 sazhen
At the western boundary of the claim	Voskresensky	up to 0.82 sazhen
Olginskaya	Voskresensky	up to 0.66 sazhen
Zhaginchin’s S.	Voskresensky	0.25 sazhen
Zhaginchin’s N.	Voskresensky	0.25 sazhen
Minkhailov’s	Voskresensky	0.33 sazhen
Egorov’s	Voskresensky	in the NE working—0.08 sazhen; in the SW one—0.40 sazhen
Nikolaev’s	Lermontov	0.28 sazhen
Krasnaya Gorka II	Novgorod	0.10–0.12 sazhen
Belaya Gora	Nach.-Nikolsk	to W—0.25 sazhen; to E—0.6 sazhen
Elizavetinskaya	Nach.-Nikolsk	0.25 sazhen
Krasavitsa	Nach.-Nikolsk	0.33 sazhen

Sharp changes in thickness in the majority of the veins listed here, according to the same M. G. Eroshkin, were not observed.

In the composition of the veins of the category under consideration, and likewise in the composition of the vast majority of all veins generally in the district investigated, the principal, or even exceptional, part is played by quartz. It has now a white, now a yellowish, and occasionally a pinkish coloration, and very often possesses not a solid but a drusy structure—that is, it contains miarolitic cavities with druses of crystals of the same quartz or rock crystal, often of considerable size.

After quartz, the most widespread constituent of the veins may be considered the inclusions of altered granodiorite. They usually have the form of thin and short interlayers, pinched within the mass of quartz and arranged parallel to the salbands of the veins, though they are sometimes of quite irregular shape. Their dimensions, with the exception of certain stopes in the workings along the Krasnaya Gorka veins, are very small.

An even more subordinate role in the composition of the veins described is played by sulphides, of which pyrite is most often encountered; [[unclear: word continues on next page]]

somewhat less often—galena, accompanied here and there also by zinc blende and chalcopyrite. The first two of these minerals occur either in the form of thin and short stringers, or as separate crystals and small (2–8 cm in diameter) nests; the others occur exclusively as small inclusions and accumulations.

The products of oxidation of the pyrites, ochres, are observed almost everywhere, but in small quantity, so that even in the very upper horizons they never foul the quartz to any considerable degree. It should be noted, however, that both the ochres and the pyrites, without anywhere attaining a high content, are distributed rather unevenly.

The veins are very rich in freely visible gold, and one may even say that it appears everywhere where its total content increases more or less noticeably. In the near-surface parts of the veins, and especially in the eluvial placers formed from these parts, gold is often encountered in the form of nuggets, having a more or less distinct crystalline structure and reaching a weight of up to half a pound. But in these same surface parts of the veins it is not rare to observe gold also in the form of thin plates, forming, as it were, little shelves between the walls of cavities lined with ochre and produced as a result of the removal of pyrite crystals. In deeper workings the forms in which visible gold appears are different: here it everywhere forms either thin and short veinlets in the quartz, or separate small grains and leaflets confined to fine cracks (in the same quartz).

But however often gold may be observed even with the unaided eye, the overall gold-bearing character of the veins under consideration and their industrial significance are determined by the content of such particles of the precious metal as are completely inaccessible to recognition; and therefore, in order to judge the gold-bearing character and its connection with one or another feature of the composition or structure of the veins, one has to turn to the data of special sampling and to the results of processing the ore extracted from the various workings. On the basis of the study of materials of this kind, supplied to us by the mine management during the examination, it is possible, with greater or lesser confidence, to establish the following:

1) Gold is distributed in the veins, in general, very unevenly, but the degree of this unevenness is not the same not only for different veins, but also for different parts of one and the same vein; thus, in the Miass vein, often over a distance of five, or even fewer, sazhens, the gold content changes by 10–20–50, or even by 90 times; conversely, the gold-bearing character of the Safonovskaya, Krasnaya Gorka, and Novgorodskaya veins fluctuates within considerably smaller limits, while part

of the same Miass vein, adjoining the roll-back adit of the second horizon, preserves its gold-bearing character almost constant over a fairly large distance.

2) Changes in the content in all the veins, and especially in the Novgorod vein, are markedly sharper and more considerable along the dip than along the strike; to this it must also be added that the surface horizons, being on the whole richer, as compared with the lower horizons, differ from the latter also by a greater irregularity in the distribution of gold.

3) Parts of veins with increased gold content (10 zolotniks or more per 100 poods) have an irregular form, elongated now along the strike, now along the dip, now in some intermediate direction.

4) With regard to the dependence between the gold content and particular features of the veins, comparison of direct observations in the workings with the results of assaying permits one to say with confidence that an increase in gold content coincides, first, with places of the greatest mechanical destruction and the strongest decomposition of the granodiorite, and, secondly, with an increase in the relative quantity of sulphides, especially galena.

5) Despite the considerable inconstancy of the gold content, the general average gold content in almost all the veins, according to the results of washing the ore from each vein at the factory, proved to be identical and equal to from 4 to 4.3 zolotniks per 100 poods.

The structure of the veins, as is already partly evident from the foregoing, is massive, only rarely—thanks to the parallel arrangement of pyrite stringers and lenses—showing a tendency toward banded structure; in general it is very simple and uniform (see Table No. 3, sections through the Miass and Novgorod veins). Among the observed structural features worthy of mention are: the presence of the above-mentioned interbeds of country rock, which cause the appearance of parallel selvage cracks, on the planes of which rather coarse and sharp slickensides are often observed; the tendency of the veins to give off to both sides thin, so-called parallel to the vein, apophyses—“companions”; the coulisse-like structure of the Miass vein, which in many places appears to consist of separate parts with the same strike but not situated on one straight line, and wedging out toward one another.

More or less sharply expressed selvages are observed in all veins only in very few places, and always possess a very insignificant thickness.

Changes of the granodiorite in connection with the veins, insofar as one can judge from observations in the crosscuts, extend to the sides of the veins for a very small distance (1–2 sazhens), and macro-

manifest themselves macroscopically in a more or less complete discoloration of the rock. In thin sections of the corresponding specimens it is seen that the feldspars have been completely replaced by a fine-scaly sericite-calcite aggregate; that, in place of the dark-colored components, only accumulations of ore specks remain; and that, as new formations, scanty crystals of pyrite have appeared among the products of decomposition of the feldspars, together with rather large grains of calcite among individuals of primary quartz, which shows*) a b. ch. strong cloudy extinction, and sometimes also small zones of crushing. In the immediate vicinity of the veins, the changes in the granodiorite are more significant: here there is observed almost everywhere (and especially in the surface workings), instead of granodiorite, a clayey or ocherous-clayey bluish-white, yellowish, or brownish mass, which has completely lost all signs of its primary structure.

Concerning the influence of the veins on the chemical composition of the granodiorite, an idea may be formed from the following data of two analyses, carried out in the laboratory of the Tomsk Technological Institute by the student F. O. Lysenko.

	SiO₂	Al₂O₃	Fe₂O₃ + FeO	MgO	CaO	K₂O	Na₂O	Loss on ignition	Σ
Fresh granodiorite	66.89	16.17	4.99	0.78	4.57	2.53	3.98	1.20	100.01
Altered granodiorite near the vein	63.50	16.24	4.17	0.83	4.73	4.75	1.38	6.20	101.80

Thus, the principal changes in the chemical composition of the granodiorite during its decomposition near the veins consist in an increase in loss on ignition, an increase in the relative content of K₂O, as if at the expense of a noticeable decrease in the content of Na₂O, and—in some degree—a decrease in SiO₂; the remaining chemical components of the rock remain, in their relative quantities, almost without change.

II. Veins occurring in porphyries, serpentinites, and porphyrites

The greater part of these veins—comparatively far less numerous than the preceding ones—had been very poorly explored by the time of our visit to the district. Many of them, for example, all the veins in the porphyries and serpentinites, had only just been cleared in several places at their natural outcrops; on many, only shallow prospecting works had been carried out; and in all, on five veins only,

*) In contrast to the quartz in specimens of unaltered granodiorite.

occurring in porphyries—Il’inskaya, Kolchedannaya, Diamantnaya, Vodyanaya, and Shkol’naya—have more substantial workings, though these are inaccessible for inspection. Therefore, naturally, our information about the veins of this second category is rather scanty and amounts to the following.

The strike of these veins is either the same as that of those occurring in granodiorite, or else northwesterly; the dip is steep (\(60^\circ\)—\(70^\circ\)—\(80^\circ\)) and directed southward or southwestward. The greatest extent over which the veins occurring in porphyries have been traced (from natural outcrops) is 100–140 sazhens, while the established extent of veins in serpentinites and porphyries is no more than 10–20 sazhens. The thickness of the veins, so far as can be judged from the information communicated to us, is for most veins 0.25–0.33 sazhens, and only at Kolchedannaya does it reach 0.68 sazhens. The gold content in individual samples was determined at 3–4 zolotniks per 100 poods; in samples from Kolchedannaya it reached up to 9 zolotniks per 100 poods, but on average it was probably very low, for otherwise we would have had to find far more substantial workings on many of these veins. This same weak auriferousness is also indicated by the fact that pyrites, in any considerable quantity, were observed only in the quartz of the Kolchedannaya vein, while the quartz of the other veins appears either quite clean or only faintly ocherous. However, according to the words of the steiger M. G. Eroshkin, visible gold was encountered fairly often in the Vodyanaya vein.

In conclusion to this brief description I shall add that—as already mentioned in the general geological sketch—the veins in the porphyries are found chiefly in close proximity to the boundaries of the granodiorite bodies, while the veins in the serpentinites are always clearly associated with the outcrops of porphyries cutting through these serpentinites.

III) Veins occurring in granites and sedimentary rocks.

In the description these veins may be combined into one category on the grounds that the most important of them, to which we shall confine our characterization, despite the difference in the enclosing rocks, are located close to one another and possess many common features. Namely, this group includes: the veins of the Nikolo-Elizavetinsk allotment—Faizulin’s, Gogolevskaya, and Pavlov’s—and the veins of the Sinii Shikhan allotment—Arapov’s, Vasil’evskaya, and Spornaya. The first of these occurs in argillaceous-sandy shales, the second and third in a band of the same shales injected by granite, while the veins of Sinii Shikhan occur in granite. The aforementioned similarity of all the veins is manifested above all in the character of the alteration of the country rocks, which in the vicinity of the veins are uniformly transformed into a clayey or ocherous-clayey mass, often having so completely lost all traces whatsoever of the structure of the original rock that, as to the character of the latter,

one must judge only on the basis of certain indirect considerations. Thus, in the faces of the workings along the Gogolevskaya and Pavlovaya veins, the enclosing rock appears partly as a destroyed sandy-clayey schist, and partly as a clear-grained clayey mass, formed either from feldspathic sandstone or from granite; but since the entire area north of the veins under consideration is composed of fine-grained sandy-clayey schists, and to the south of granites, while feldspathic sandstones have been encountered absolutely nowhere, it must be thought that the indicated granular mass represents destroyed granite,*) and that the veins in question occur in a belt of schists injected by this granite. The similarity of all types of wall rocks is further increased by the fact that the granite near the veins acquires a distinct schistosity, which is observed especially clearly near the Vasil’evskaya vein in the allotment and Sinii Shikhan: study of the dumps extracted along the course of this vein near the southern boundary of the allotment makes it possible to trace all transitions from pink medium-grained biotite-hornblende granite through greenish milonite of the same granite into a yellowish-light-gray kaolinized mass with sharply expressed schistosity. To complete the characterization of the enclosing rocks, it remains to note that all the rocks—and especially the schists—are rather abundantly permeated with ocher, probably formed from pyrite formerly contained in the rocks.

Let us now turn to the veins themselves. The strike of all of them is northwesterly (see the drawing in the lower left corner of Table No. 3), while for the veins of the Nikolo-Elizavetinskii allotment and Sinii Shikhan it should more precisely be called north-northwesterly; the dip is directed to the northeast and makes with the horizon an angle, in the case of the Faizulinova, Gogolevskaya, and Pavlovaya veins, of 65° (in places 70° and 77°), and in the case of the Vasil’evskaya vein—81°.

With respect to structure, for the Gogolevskaya and Pavlovaya veins a very characteristic tendency is to split into several separate veinlets; the thickness and number of such veinlets vary within very wide limits, and therefore the appearance of the veins in the faces is quite varied. Thus, for example, in the western wall of a small winze below the adit horizon, 56 arshins, the vein (Gogolevskaya), with a total thickness of 1 sazhen, consists of several thick branches separated by thin interbeds of schistose ocherous-clayey mass; in the eastern face of the same adit there are observed three more or less thick veinlets, and between them—a dense network of numerous—

*) In favor of such a solution to the question speaks, to a certain extent, also the fact that the granite, as indicated in the general geological sketch, is younger than the schists, whereas the presence in the body of the latter of feldspathic sandstones would be more probable only under the opposite relation, when these sandstones could be regarded as formed from products of the weathering of granite.

thin veinlets; in the eastern stopes the stopes above the indicated drift show only abundant, thin, branching veinlets; in one of the western stopes of the same series a rather thick branch with thin lenses of ocher-clayey mass near the footwall, and several thin, branching veinlets in the rock of the hanging wall, pass through the stope; in the eastern stope of the lower drift level, 47 arshins (from the Aleksandrovskaya mine), the Pavlovskaya vein represents a combination of one veinlet, widening upward, on the side of the hanging wall, and several thin veinlets parallel to the first—on the side of the footwall, etc. (see the drawings of the stopes in the lower right-hand corner of Table No. 3).

The quartz in the Gogolevskaya and Pavlovaya veins, unlike the veins in the allotments of the Aidyrlinskaya group, always has a dense “massive” structure, but is often broken by numerous fissures, the planes of which are covered with thin films of black-brown iron oxides or with equally thin sericite coatings. The gold content in this quartz is distinguished, one may say, by exceptional irregularity: with the general poverty of both veins, extraordinarily rich sections were encountered in them. The dimensions of such sections, judging from the accounts, are almost always very small, so that the distribution of the gold must be called not even patchy but nest-like. Whether there is any regularity in the arrangement of the enriched nests cannot be said, for during our visit to the mines all the workings were in the poor parts of the veins; but, according to the statements of employees who had observed the operations, it may be considered more or less established that the nests are chiefly confined to those parts of the veins that reveal the greatest mechanical destruction.

On all the remaining veins of the Nikolo-Elizavetinsky and Sine-Shikhansky allotments, no work whatever was being carried out in our presence, and only on the basis of inquiries, and of a study of the dumps near the mines, can it be said that the Vasilievskaya vein had a thickness of up to 12 arshins, but was worked either only along the central strip or near the hanging wall; that the quartz in it was formerly “massive,” at times somewhat translucent at the edges, i.e. pure, more rarely with small spots of malachite and azurite, and on the whole poor in gold. Likewise, apparently, the numerous prospecting workings scattered along the continuation of the Vasilievskaya vein for a distance of almost 10 versts from the northern boundary of the Siny Shikhan allotment, as well as the shallow pits and trenches encountered over a considerable area to the northwest of the Nikolo-Elizavetinsky allotment, in the area of exceptional development of sandy-clayey shales, did not yield any notably favorable results.

Genesis of Quartz Gold-Bearing Veins

To determine the genesis of a deposit means to ascertain as the result of what geological process it was formed and by virtue of what causes it acquired the properties now inherent in it—its form, composition, and structure. To answer all these questions constitutes the final and principal task of the theoretical study of a deposit, which, like any other geological formation, must not only be described but, so far as possible, interpreted by the investigator. But it is no less important to clarify the genesis in a geological appraisal as well, i.e., in such an investigation as must provide a basis for judging the continuation of the deposit along its strike and at depth, the probable changes in the properties of the deposit beyond the parts of it exposed by workings, and—in particular—the extent to which one may count on further development of the deposit justifying the costs of purchasing it at the price set by the seller, or the costs of the proposed expansion of exploitation, the construction of new technical installations, and so forth.

The opinion, widespread and supported, strange as it may seem, even by many mining engineers, that the practical questions just enumerated can be resolved by prospecting alone must be recognized as entirely incorrect. Quite apart from the fact that detailed prospecting (and only such prospecting is to be kept in view in the present case) in itself requires considerable expenditure, which can be undertaken only with a certain hope of favorable results, the prospecting data furnished by individual pits and boreholes are always fragmentary, scattered, and can be correctly interpreted only if there is a clear conception of the form and properties of the deposit and of the general geological structure of the locality in which the deposit occurs.

Conversely, if, on the basis of a careful study of the deposit, its genesis is more or less definitely established, and the dependence is noted and explained between the content in it of the given metal or metallic compound—on the one hand—and the form, structure, and composition of the deposit, the character of the surrounding rocks, and the entire geological history of the given place—on the other hand, then it becomes possible not only to design prospecting expediently (i.e., to plan such prospecting works, each of which would answer a quite definite question and which, with the smallest number of them and the least expenditure on their execution, would make it possible to obtain a sufficiently complete idea of the deposit), but also to predict with some probability the results of prospecting, and together with that—the prospects for further development of the deposit.

After this brief digression, made by me, incidentally, because the views expressed on the significance of scientific geological expertise were shared and defended by the late L. L. Tove, to whose memory the present article is dedicated, I shall now turn to clarifying the genesis of the auriferous veins, beginning with those that are of chief interest—namely, the veins occurring in the granodiorite and its modifications.

With regard to these veins, we now know that they are far more numerous than the veins occurring in other rocks, and that among them are found all the richest veins worked during our study. We also know that, while having a varied but in general parallel outline to the main contour of the granodiorite stock and strike, these veins often intersect one another, are distinguished by a fairly constant thickness and a great tendency to give off apophyses, in many places contain band-like or irregular inclusions of altered granodiorite, and, as a rule, do not have sharply expressed salbands. On the other hand, from the geological sketch we know that granodiorite is the youngest rock in the district studied; after its formation there occurred neither volcanic eruptions nor any disjunctive dislocations. All this, one may say, involuntarily leads us to the thought that the veins under consideration represent the result of the filling of fissures formed owing to the contraction in volume of the granodiorite body during its cooling, i.e., endokinetic fissures, and at the same time compels us to regard the granodioritic magma as the primary source of the substances now found in the composition of the veins, and likewise as the primary source of the gold. In connection with the latter conclusion, and partly in confirmation of it, it should be noted that granodiorite and certain intrusive rocks close to it, of intermediate acidity, such as quartz diorite, quartz monzonite, the so-called sienit Grő’ba Typus, play an entirely exceptional role in the formation of the most varied ore deposits created by contact metamorphism and post-volcanic processes. Indeed, it is enough to leaf through any more or less detailed course on ore deposits—for example, K. I. Bogdanovich’s Ore Deposits, or Beischleg and Krusch’s Die Nutzbaren Mineralien und Gesteine—Vogt, or, still better, Lindgren’s Mineral Deposits, to see how many known deposits of the two categories just mentioned are genetically connected with granodiorite and quartz monzonite, or with rocks which, although named differently in the description, by their indicated mineralogical composition must be assigned to the same granodiorite. Especially striking is this exceptional, so to speak, ore-creating role of the rocks under consideration.

rocks, will appear before us if we focus attention on the deposits of the Urals. Here, if one takes into account that the “hornblende granite,” to the contact of which with the Lower Devonian rocks the Bogoslovsk deposits of copper and iron are confined, consists chiefly of andesine, hornblende, and quartz; orthoclase occurs only in rare cases, in the form of small grains between plagioclase and quartz, and chemically it is characterized by an SiO₂ content of about 63%); that the augite and hornblende granites, as well as the augite syenites and diorites of Mount Magnitnaya, are connected by transitions with granodiorite and are probably products of the differentiation of the magma of this latter); and, finally, that—according to Bogdanovich’s remark)—certain common features bring the rocks of the Bogoslovsk district and the rocks of Blagodat’, Vysokaya, and Magnitnaya closer together, then it may be said that granodiorite, its modifications, and other varieties of intrusive rocks of intermediate acidity, as active rocks of ore deposits, have very few rivals in a considerable part of the Urals. And the number of these rivals will, in my opinion, diminish still further in the future, since at present in some descriptions we have a not quite exact determination and an insufficiently detailed description of rocks; in some, we find mention of such granites and diorites which, undoubtedly, should be regarded merely as partial products of differentiation of granodioritic magma**).

In addition to the considerations adduced, our view of granodiorite as a rock whose magma was the primary source of the gold of the veins under consideration may be further confirmed by the following. In recent times geological investigations have been establishing ever more frequently that ore deposits regarded as the result of post-volcanic processes are connected with the apices and roofs of intrusive masses and with intrusive bodies of small dimensions,

) E. S. Fedorov and E. D. Stratanovich, “Genesis of augite-granite rocks according to new data,” Transactions of the Mining Institute of Empress Catherine II, vol. II, no. 1, 1909, pp. 63 and 66.—K. I. Bogdanovich, Ore Deposits, vol. I, p. 206.
) K. I. Bogdanovich, l. c., pp. 195 and 200.
) K. I. Bogdanovich, l. c., p. 206.
) For a characterization of the analogous role of these same rocks in the history of the formation of the deposits of the Kuznetsk Alatau, it is enough to refer to the following descriptions of the best-known mines of this range: 1) P. P. Gudkov, “The Bogomdarovanny Mine in the Achinsk Mining District,” Proceedings of the Tomsk Technological Institute, vol. XX, no. 4, 1910; 2) V. A. Obruchev and P. P. Gudkov, “Report on the geological examination carried out by order of the Russian Gold-Mining Society of the Bogomdarovanny Mine and the mines of the Mariinsky group of placer mines,” St. Petersburg, 1911; 3) P. P. Gudkov, “The Mine, 6th Berikul Area, in the Tomsk Mining District,” Proceedings of the Tomsk Technological Institute, vol. XXI, no. 1, 1911; 4) P. P. Gudkov, “The Telbess Iron-Ore District,” Ore Herald, 1916, no. 3; 5) M. A. Usov, “The Saralinsk Gold-Ore District,” Bulletin of the Society of Siberian Engineers, 1917, no. 9–10. I note, moreover, that the granite and norite-diorite indicated by me as the parent rocks of the deposits of Bogomdarovanny and of the 6th Berikul area, after detailed processing of the collections made and after broader acquaintance with various parts of the Kuznetsk Alatau, should be considered varieties of granodiorite, very close to the granodiorites of the Telbess and Saralinsk districts.

representing apophyses of larger and more deeply embedded masses; this connection has also received a theoretical explanation, namely, it is supposed that the upper parts and apophyses, or projections, of massifs should naturally be chiefly associated with emanations, which then lead to the deposition of metal-bearing minerals). Turning now to our geological map, we may with great probability assume that the small stocks within the limits of the Tsarevo-Nikolaevsky, Lermontov, Troitsky, and westward from the Antonovsky allotments represent lateral apophyses, while the large central stock represents the upper part of a massif whose main body has not yet been exposed by denudation. This assumption is in full accord with the abundant schlieren observed in the large stock, frequent changes in structure and mineralogical composition, etc. All these manifestations of differentiation are highly characteristic precisely of the upper marginal parts of intrusive masses, where—as is believed—the chemical equilibrium of the magma may be disturbed under the influence of partial melting of the roof rocks*).

Thus, we shall consider it proven that the primary source of the gold and other substances found in the composition of the veins under consideration was the granodiorite magma, and that these substances were carried out of it by deep-seated fumaroles and deposited in fissures that arose in the upper parts of the granodiorite stocks, owing to the contraction of the latter during cooling. It remains now to clarify,

) M. A. Usov, “The District of the Mines of the Rudnoe Delo Society of the Tushetukhanovsky and Tsetzenkhanovsky Aimaks in Mongolia, its geological structure and conditions of gold content”—Mining and Gold-Industry News, 1914, Nos. 14–18.—M. Korovin, “New Data on the Question of the Genesis of Gold Deposits in the Vitim Upland”—Journal of the Society of Civil Engineers, 1914, No. 11;—V. A. Obruchev, “Geological Survey of the Gold-Bearing Districts of Siberia,” part II, issue II, pp. 31–34;—B. Butler, “Relation of Ore Deposits to Different Types of Intrusive Bodies in Utah”—Economic Geology X, 1915;—A. Knopf, “The Tourmalinic Silver–Lead Type of Ore Deposit”—Econ. Geology VIII, 1913;—F. Noetling, “Beiträge zur Kenntnis der Zinnerzlagerstätten in Tasmanien”—Neues Jahrb. für Mineralogie etc., B. Bd. XXXIX, 1914. (All the articles listed, except those by M. Korovin and V. A. Obruchev, are abstracted in Bulletin of the Society of Civil Engineers* for 1916 and 1917.)

) R. Daly, Igneous Rocks and Their Origin, New York, 1914, pp. 109, 205; also M. A. Usov, l. c., p. 59, and his “Orography and Geology of the Kentei Range in Mongolia,” Proceedings of the Geological Committee, vol. XXXIV, No. 297, pp. 946, 948. Here it should be noted, by the way, that sharp manifestations of differentiation, in themselves, also constitute a very characteristic feature of intrusive bodies to which emanation deposits are confined; moreover—in Daly’s opinion—this is explained by the fact that the melting of the roof rocks not only disturbs the chemical equilibrium of the magma, but also enriches it with gaseous substances (l. c., pp. 213, 361, 401; also “Discussion of paper by B. Butler”—Econ. Geology, 1915, Vol. X, No. 5, pp. 471–472). However, one may think that even if such borrowing of gases from the surrounding rocks did not take place, and if, in general, the differentiation of the magma were caused not by the melting of the surrounding rocks but by some other causes, then it (differentiation) by itself may lead to more intense emanations, for during differentiation the acidic portions of the magma are always segregated, and with them—as is known—the main mass of gases is associated. And since complex magmas, to which the magmas of granodiorite and monzonite belong, possess a special capacity for differentiation, the now sufficiently known and above-noted exceptional role of these rocks in the creation of emanation deposits becomes understandable.

by what means and under what physico-chemical conditions the deposition itself of the vein minerals took place, and for what reasons the uneven distribution of gold in them, noted in the description of the veins, resulted.

To answer the first question we must turn to the peculiarities of the structure of the veins. The rather considerable thickness of the veins—in any case greatly exceeding the width that open fissures in granodiorite could have had—the usual absence of sharp selvages, the intense alteration of the granodiorite adjacent to the veins, and the very widespread band-like or irregular inclusions in them of likewise altered granodiorite—all this hardly permits any doubt that the given veins are not filled broad fissures, but, so to speak, bands of granodiorite replaced by vein minerals along narrow fissures that served as channels for the circulation of emanations. In other words, one must think that the deposition of the vein minerals took place chiefly by means of metasomatism.*)

As to the conditions under which the process of vein formation proceeded, indications are given by the character of the chemical alteration of the granodiorite adjacent to the veins, the structure of the aggregate resulting from such alteration, and the mineralogical composition of the veins. Indeed, both on the basis of a priori theoretical considerations and on the basis of experimental investigations, and—the results of detailed study of rocks and ore deposits—there is increasingly greater confidence in the supposition that every lithogenetic (or lithometamorphic) process is governed to a very substantial degree by temperature and pressure, and leads to the creation of mineral combinations that are the most stable under the given conditions.**) Hence—conversely—each

*) Some readers, on the basis of the indication by K. I. Bogdanovich (“Ore Deposits,” vol. I, p. 53), may perhaps object to me that the assumption of metasomatic deposition of the vein minerals contradicts the above-mentioned prevalence of drusy structure in the quartz of the veins under consideration; but on this point it must be said that 1) metasomatism excludes the possibility of formation only of large cavities, and that, according to the same K. I. Bogdanovich (l. c., p. 373) and W. Lindgren (“Mineral Deposits,” New York, 1913, p. 163), drusy structure is not infrequently encountered in metasomatic deposits (for in metasomatism in many cases a reduction of volume must take place); 2)—alongside metasomatism, part of the quartz in the Aidyrlya veins (especially near the surface) was also deposited directly from solution in open cavities.

**) K. I. Bogdanovich, l. c., vol. II, pp. 355 and 456. Besides the literature indicated here by K. I. Bogdanovich, it may be noted that the ideas in question have found a fairly complete expression in the “Mineralogy” of Prof. V. I. Vernadsky (lithographic ed., issues I and II, Moscow, 1910), in the second part of the book “The Inorganic Life of the Earth. The Life of Rocks” by I. D. Lukashevich (St. Petersburg, 1909), and especially in the already cited and below-cited book by W. Lindgren, “Mineral Deposits.”

the assemblage of minerals which, by their structural interrelations, we may recognize as having formed as the result of the action of one and the same process, indicates to us the physico-chemical conditions that obtained during that process. True, at the present moment we are still far from possessing factual material sufficiently complete to express the indicated dependence in a consistent scheme; but something has already been done in this direction, and in Lindgren’s book Mineral Deposits we find a fairly well-constructed classification, in which each category of deposits is characterized by definite limits of temperature and pressure on the one hand, and by a definite combination of minerals on the other. And so, if we turn to this book, we must admit that the veins under discussion belong to deposits arising at medium depth under rather high pressure (140–400 atmospheres) and at temperatures ranging from 150° to 300°. In fact, among the features by which Lindgren characterizes this category of deposits, we find, among others, the following,*) mentioned in our description: quartz takes a strong part in the composition of the veins, and among the sulfides there occur pyrite, galena, sphalerite, and chalcopyrite; in the granodiorite near the veins there is observed replacement of the feldspars by a sericite-calcite mixture and of the dark-colored components by iron oxides, formed, probably, from pyrite that had been preserved here and there; chemically, the alteration of the granodiorite consists in a decrease in the content of SiO₂ and Na₂O and in an increase in loss on ignition (probably in connection with an increase in the content of H₂O and CO₂).

As regards the unevenness in the distribution of the gold, here the chief cause should be recognized as secondary alterations of the veins, for—as was indicated in the description—such unevenness is manifested especially sharply in the upper horizons, while changes in the gold content are more considerable and frequent along the dip than along the strike of the veins. However, it must be thought that, to a certain extent, the same unevenness was inherent in the veins immediately after their formation as well, being the result partly of an uneven distribution of the dark-colored components, by whose replacement the gold-bearing sulfides were deposited,**) and partly of more intense mechanical destruction of the granodiorite in some places, owing to which a larger mass of metalliferous emanations could have been directed there.

) See pp. 514, 515, and 520.
*) As occurs, for example, in the Butte veins in Montana (K. I. Bogdanovich, op. cit., vol. II, pp. 36–37).

The conclusion we drew above, that the granodiorite stocks represent the upper parts and apophyses of a large massif hidden at depth, also makes it possible at once to resolve the question of the genesis of the veins occurring in the porphyrite. Since these veins are found almost exclusively in the space between the granodiorite stocks and, consequently, also above the large massif mentioned,* it is natural to regard them as the result of the action of the same process to which the veins in the granodiorite owe their origin. The difference between the former and the latter consists only in the fact that the metalliferous emanations penetrated the porphyrite chiefly along the direction of the schistosity inherent in it (as is shown by the NW strike of the greatest, in established extent, veins—Shkolnaya and Melnikova), and that—judging by the weak alteration of the porphyrite—metasomatism did not play here so essential a role as in the formation of the veins in the granodiorite. From this it may, incidentally, be concluded that the veins occurring in the porphyrites should be distinguished (insofar as this does not depend on secondary processes) by a more uniform distribution of gold; but, on the other hand, if our supposition concerning the confinement of the principal mass of emanations to the upper protrusions of the massif is correct, it follows that these veins should, in general, be less rich.

Let us now turn to the veins of the eastern part of the district. In resolving the question of their genesis, the following must be borne in mind: these veins have a rather constant northwestern (coinciding with the direction of the former dislocations) strike and have been traced over a very considerable distance; moreover, over the greater part of their extent they occur in the Shikhan massif of hornblende-biotite granite. A very characteristic feature of the veins is their tendency to branch, so that in the faces of workings along the veins one observes now a single thick branch, now several such branches, sometimes accompanied by various quantities of thin veinlets, and now, finally, as it were a band of rock mottled with a mass of fine veinlets and branches of quartz. Both the granite and the other rocks near the veins are more or less clearly schistose, strongly decomposed, and abundantly penetrated by ocher, and in places transformed into a completely structureless ocherous-clayey mass; the gold content in the veins is distinguished by exceptional irregularity. On the basis of these data it may at once be acknowledged with sufficient confidence that

* It is quite possible that a vertical geological section through the central one of the small granodiorite stocks might present a picture similar to that depicted by V. A. Obruchev in Figs. 1c and 2c in his “Geological Survey of the Gold-Bearing Districts of Siberia,” in issue II of part II, pp. 32 and 33.

the fractures that determined the position of the veins under consideration have a tectonic character; that the formation of the veins was effected by emanations issuing from the granite; and that all the workings examined by us expose only the upper part of the deposit, i.e., they have not yet emerged from the sphere of influence of eluvial processes, or the so-called iron-hat zone. The question of genesis is thus reduced to ascertaining what the primary ore minerals containing gold were, and what causes conditioned the extraordinary variability in the richness of the veins. To the first question one can, of course, answer only hypothetically: that among the sulphides in the veins and in their wall rocks there was chiefly pyrite, for neither copper oxides (with very rare exceptions), nor lead ochres, nor any other secondary minerals characteristic of the iron hat of polymetallic deposits are observed anywhere. As for the irregular distribution of gold in the veins, this—as was already indicated in the description—should be connected with the unequal degree of mechanical destruction of the wall rocks; moreover, it must be added that the variable structure of the vein fractures, which arose during dislocation and caused an uneven distribution of metalliferous emanations, may then also have determined the unequal degree of secondary mechanical destruction caused by eluvial processes, as well as, in general, the unequal intensity of these processes in the various parts of the veins.

The remaining veins, discovered in the southwestern corner of the area investigated, as I said in the description, were observed by us only in small and scattered natural outcrops. The data from such observations are, of course, very scanty and compel us to confine ourselves to the remark that the veins occurring in serpentinite near the stock of gneiss-granite were probably created by post-volcanic processes that accompanied the intrusion of this gneiss-granite and are confined to the same tectonic fractures as the veins of the eastern allotments; while the veins in the strip of allotments between Sirotsky and Rossiya are, most likely, connected with the eruption of porphyries.

Turning to the practical conclusions from all the results set forth of the investigation of the Aydyrlinsky district, let us first address the question of the continuation of the veins.

From what has been said regarding the genesis of the veins and, in particular, regarding the character of the vein fractures, it is natural to suppose that the veins occurring in granodiorite probably continue only to the boundaries of the stocks of this rock; while the veins in the Shikhansky and Aydyrlinsky granites (as well as the veins in the serpentinites) have chances of a more considerable and, generally speaking, indefinite extension in space, although their properties, upon passing from one

rocks into another may reveal significant changes. In depth, all the veins, as having arisen owing to volcanic activity, must of themselves pass beyond the limits within which underground workings are still possible. But, of course, in practical terms what is of interest is not how deep the veins continue, but to what depth they retain an ore-grade—that is, permitting profitable exploitation—gold content. An exact answer to such a question can undoubtedly be given only by exploration; nevertheless, certain assumptions may also permissibly be expressed on the basis of the results of geological investigation. Namely: 1) the forms of occurrence of free gold indicated in the description of the veins of the central group of claims make one think that the deepest of the workings inspected by us are situated in the so-called cementation zone and, perhaps, only in the upper part of this zone; consequently, a sharp and rapid decrease in the gold content with further deepening of the workings is, in any case, unlikely; the same may be said also with respect to the veins of the Nikolo-Elizavetinsky claim, where the workings described have not yet even passed beyond the zone of the iron cap, and where at greater depth one may expect, even if less rich in individual pockets, nevertheless a less variable content; 2) by analogy between the geological structure of the district studied (at least as regards the character of the rocks composing it) and the Kochkar district, situated in the same Southern Urals, where operations are being conducted at a depth of 100 and more sazhen, there is reason to count on the preservation, down to this depth, of an ore-grade gold content in the Aidyrlinsky veins as well.

The second practical conclusion ensuing from our views on the genesis of the veins concerns their comparative evaluation and amounts to the following: the greatest industrial interest is presented by the veins occurring in granodiorite, and especially those of them around which the granodiorite shows noticeable mechanical disturbances; the veins in porphyrites and the veins of the eastern claims of the district deserve less attention—the former because, according to our conclusions, they are in general less rich; the latter because of the extreme variability in gold content, which excludes the possibility of their proper and systematic exploitation until such time as the laws governing the distribution of enriched pockets are more definitely established and it is clarified that the relative number and degree of auriferousness of these pockets are sufficient to cover the unproductive expenses of extracting poor ore from the sections between the pockets. All this should be borne in mind when planning exploration work in the Aidyrlinsky district.

Geological Map

of the district of the gold mines of A. S. Antonov and O. P. Vishnevskaya in Kvarkenskaya Stanitsa, Orsk Uyezd.

To the article by P. P. Prudkov. Plate No. 1.

Scale: 1 verst to an inch.
0 — 1 — 2 — 3 versts.

North: N

Visible map inscriptions:

• Mount Ishanova
• River Suunduk
• River Buruktal
• River Kamenka
• Mill
• Mill
• Mill of Sokolov
• Antonova Stanitsa
• Inoselkov
• Zaison
• Vladimirovsky
• Nadezhdinsky
• C
• Saratov
• Petrovsky
• Mikhailovsky
• Babai
• Stepan
• Saratov
• Alexandrovsky
• Konstantinovsky
• Lyubovsky
• Sakharinsky
• Kotov
• Dmitrovsky
• Nikolsky
• Pyatnitsky
• Pugachevsky
• Ilinsky
• Bogoslovsky
• Vasilyev
• Pavlovsky
• Bogoslovsky
• Voskresensky
• Skatinsky
• Antonov Stanitsa
• Panteleevsky
• Mikhailovsky
• Bogdanov
• [[unclear: vertical mine name at far right]]
• [[unclear: vertical mine name at far right]]

Visible map inscriptions

• Kvarkenskaya Station
• Kuznetsov’s Mill
• Pudovikov’s Mill
• Aidyrlya River
• Zolotarev’s Mill
• Sukhorechka
• Sergeevsky
• [[unclear: small handwritten mine/property name]]
• [[unclear: small handwritten mine/property name]]
• Antonovsky
• Paninsky
• [[unclear: “Gintovo Lyadovo” or similar]]
• Shumilinsky
• Kazarin
• Ostrovsky
• Troitsky
• Komarovsky
• Spassko-Voskresensky
• Pavlovsky
• Mikhailovsky
• Borisovsky
• Aleksandrovsky
• Sofievsky
• Konstantinovsky
• Elizavetinsky
• Nikolayevsky
• Spassky
• Petrovsky
• [[unclear: mine/property name]]
• [[unclear: mine/property name]]
• [[unclear: mine/property name]]
• [[unclear: mine/property name]]
• S
• C
• C

Visible map labels:

• “Western” [[unclear: handwritten label at upper left]]
• “Mikhailovsky” [[unclear: handwritten label within the gridded area at upper left]]
• “Kornev” [[unclear: label inside a rectangular plot near the upper center]]
• “Solonchanka River”
• “Kitai” [[unclear: label inside the central polygon]]
• “Gorshkovsky” [[unclear: label inside the right-hand elongated polygon]]
• “Orlovsky” [[unclear: label inside the adjacent right-hand polygon]]
• “road” [[unclear: dashed road label]]
• “Pavlovsky Settlement”

Legend

• Granites
• Gneiss-granites
• Conglomerates and porphyry-porphyrites
• Granodiorites (where there is more dark rock—granite; where less—granodiorite)
• Serpentinites
• Amphibolites, hornblende gabbro (epidiorites)
• Porphyries
• Porphyrites, amygdaloidal porphyrites, and tuffs
• Contact-altered porphyrites, porphyrites, and porphyroids
• Gneiss-clayey schists, sandstones
• Contact-altered sandy-clayey schists and sandstones
• Siliceous sedimentary rocks
• Limestones
• Strike and dip of schistosity and bedding of rocks
• Geological boundaries, more or less precisely established
• More or less presumed geological boundaries

Visible map labels include: “Russia”; “Ilyaso-Vishnevsky mine”; “Siniy [[unclear]] gold”; “Ilyinsky”; “Semenovsky”; “Left [[unclear]]”; and other partially legible handwritten mine or locality names.

Pushkin

Alexandrovka

Lev

Dmitro

Natalyev

Olgov

Pavlovsky

Zimin

Sibir

Sakhalin

m. Pryamoy

[[unclear: vertical settlement/mine name]]

[[unclear: name ending in “-skaya”]]

Tsarevo-Nik[[-]]

m. Alexandrovka

Kadom

Karaatinsky

N

S

Turgenev

[[unclear: partly cut-off name at lower left]]

Bogotinsky

Kozya [[unclear: second word]]

Kasandrov [[unclear: second word]]

m. Ivanov

[[unclear: vertical name near m. Ivanov]]

Visible map labels:

• [[unclear: partial label at upper left]]
• Vodyanoy
• [[unclear: partial label at left edge]]
• Voskresensky
• Yelizaveta
• Mikhailov
• Yegorov
• Orenburgskaya
• Vladimiro-[[unclear]]
• Kostromskoy
• Ofitsersky
• Arkhangelsky
• [[unclear: labels inside circled area]]
• [[unclear]] K.
• [[unclear: partial label at left edge]]
• [[unclear]]sky
• Lermontov
• Budarsavsky
• Ostrovsky
• [[unclear: partial label at lower left]]
• Kanavsky
• Neputevy
• [[unclear: partial polygon label at bottom edge]]

Visible map inscriptions

• Maksimovo
• Semenovsky
• Petro-Pavlovsky
• Vishnevsky
• Plesovsky
• Koshkar
• Mitkino
• Sokurtoy
• Safronovsky
• Zasteno-Krivtsovsky
• Bogorodsky
• Bogorodskaya ravine
• Bystraya Aidyrlya

Scale: 0, 100, 200, 300, 400, 500, 600 sazhen.

Mining allotments / workings and other labels in the northeastern part of the map

• Zimin mine
• Miass mine
• Mikhailovskaya
• Nikitinskaya
• [[unclear: label resembling “Savinskaya”]]
• Novogorodsky
• [[unclear: label beginning “Kordon…”]]
• Ivanovo-Nikolsky
• Preobrazhenskaya
• Elizavetinskaya
• Rich Mountain
• Razumnaya
• Poteryannaya
• Mine Nikolai
• Mine Anton
• Mine Balagan
• Mine [[unclear: name resembling “Khlotnaya”]]

To the article by P. P. Fedorov, Table No. 2.

Location of gold-bearing veins discovered in the central group of allotments of A. S. Antonov and O. P. Vishnevskaya in the Kvarken stanitsa, Orsk Uyezd

Map labels

• Mikhailo-Aleksandrovsky
• Factory
• [[unclear: partially cut-off label ending in “-Kozinikskaya”]]
• Matyushin
• Vinogradovsky
• Elizavetinsky
• Smolensky
• Leo Tolstoy
• Antonovsky
• Vnezapny
• [[unclear: “Pantino” or similar]]
• Anton Chekhov
• Maloputinsky

Legend

— Boundaries of intrusive bodies of the granodiorite formation.

…… Veins discovered by outcrops or prospected only by surface workings.

– – – Veins worked down to the level of groundwater.

—— Veins worked below the level of groundwater.

⋯ Placers.

Lith. Sib. Assoc. of Printing, Tomsk.

Horizontal projection of the Miass vein.

W — O

Level 80 arshins, 33–37.8 sazhens W of the Miass shaft.

W — O

Level 80 arshins, 18.6–22.4 sazhens W of the Miass shaft.

W — O

Level 80 arshins, 1–4.8 sazhens W of the Miass shaft.

W — O

Level 120 arshins, 89–92.8 sazhens E of the Miass shaft.

W — O

Level 120 arshins, 80.5–84.3 sazhens E of the Miass shaft.

W — O

Level 120 arshins, 37.2–41 sazhens E of the Miass shaft.

W — O

Level 160 arshins, 24.2–28 sazhens E of the Miass shaft.

Drawing 15. Dubenovka, plate No. 3

Vertical section of the north-eastern vein of the Malachite group, 80 sazhens.

Legend

○ — Ferruginous quartz
— — Nests of conglomerates
⋯ — Limonitic outflow from altered quartzites
▱ — Selvage of altered granodiorite

Scale: 5 cm = 1 sazhen
0 — 0.20 — 0.40 — 0.60 — 0.80 — 1.00 sazhen

Quartz gold-bearing veins at the mines of the Spasitel’skaya group.

Scale: 1:1400.

Scale bar: 0 — 100 — 200 — 300 — 400 — 500 sazhens.

Labels visible on the plan:

• Nikolaevo-Vladimirsky
• Orlovka
• Bogatyrsky
• Solov’eva
• [[unclear: name near the short vein, possibly “Trekh bratov”]]
• [[unclear: “Sestro…” or similar]]
• Spasitel’sky mine
• Dmitrieva
• Vasil’evskaya
• Plastovaya
• Dmitrievskaya / Dmitrieva [[unclear: handwritten ending]]

Schematic drawing of a typical occurrence of gold-bearing quartz disseminated along the Glagolevskaya vein of the Nikolae-Elizavetinsky mine (Stanislavsky group).

Legend

• Quartz vein and veinlets
• \(\gamma\) — Granites altered into a secondary clayey mass

Scale: 4 cm = 1 sazhen

0.00 | 0.25 | 0.50 | 0.75 | 1.00 sazhen

[[unclear: lithographic imprint]], Tomsk.