Bulletin of the Tomsk Technological Institute of Emperor Nicholas II.

Vol. XXI, 1911, No. 1.

P. P. Gudkov.

The “6th Berikul Area” Mine

in the Tomsk Mining District.

(Preliminary report on a summer assignment in 1909.)

With 2 tables of drawings and 3 figures in the text.

The “6th Berikul Area” mine is located in the Mariinsk district of Tomsk Province, 70 versts south of the Tyazhin station of the Siberian Railway. The mine allotment is situated in the valley of the stream Sukhoy Berikul, which flows into the Bolshoy Berikul—the right tributary of the Kiya.

The environs of the “6th Berikul Area” constitute a low (according to Professor Zaitsev’s determination—about 685 meters) plateau, which, as we shall see below, is not a primary tectonic form of relief, but owes its origin to erosional processes. This plateau is dissected by the streams Sukhoy Berikul, Bolshoy Berikul, and several small tributaries of both. The valleys of the streams are, for the most part, not fully formed, not broad, and have rather steep slopes, cut by numerous transverse hollows and small gullies. In those places where the streams cut through the thickness of limestones, the valleys have the appearance of true gorges.

In the geological structure of the area examined, the principal role is played by crystalline limestone, dioritic porphyrite, augite-biotite norite-diorite, and hornblende granite.

The limestone extends in a broad belt along the lower part of the valley of the Bolshoy Berikul and is a white or yellowish-white, distinctly crystalline rock, now medium-, now fine-grained. The character of the bedding of the limestone is, for the most part, wholly indistinct; only in one place—on the Sosnovka stream near the contact of the limestone with the porphyrite—is clear stratification observed in the former, caused by a very regular alternation of white and dark-gray thin bands; parallel to the bedding, the rock also reveals a rather regular schistosity, dipping to the SE : 96° at an angle of about 76°.

The entire middle part of the valley of the Sukhoy Berikul is occupied by dioritic porphyrite. This rock, in which, as we shall see further, there also occur and

The gold-bearing quartz veins of the mine examined occur in the form of numerous outcrops and large cliffs on the steeper and higher right-hand dump of Sukhoy Berikul. In external features the porphyrite is a dark-gray or greenish-gray, sometimes dense, sometimes fine-grained rock, in which for the most part only very rare and small laths of feldspar are distinguished; more rarely there are more distinct and larger segregations of the same mineral; in some specimens one can also see small black-green prisms of hornblende; sometimes, finally, no segregations whatever are discernible. Microscopic examination of a thin section of one specimen of porphyrite showed that the fine-grained holocrystalline groundmass of the rock has a structure close to panidiomorphic and consists of a felt-like mixture of laths of plagioclase and prisms of hornblende (with pleochroism from brownish-yellow to green), fairly abundant crystals and grains of magnetite, and a very meager quantity of small grains of quartz and flakes of biotite. Very rare segregations belong to small, considerably sericitized crystals of plagioclase and not entirely regular prisms of green hornblende. Thus, by its microscopic properties the rock may be recognized as close to malchite or—owing to the negligible content of quartz—to orbite. As for the conditions of formation of the rock, the structure of the groundmass and the presence in it of the last primary hornblende indicate that crystallization of the rock proceeded rather slowly and under considerable pressure.

The study of the conditions under which the porphyrite occurs leads to the same conclusion. In a whole series of outcrops on the slopes of the right-hand dump of the valley of Sukh. Berikul, the porphyrite is observed lying directly upon the diorite and granite described below; at the same time, very often both of the latter rocks penetrate the porphyrite in numerous and thin veinlets. In addition, these same deep-seated rocks are sometimes also encountered as independent exposures among the porphyrite outcrops, and at the same elevation as the latter (for example, on the summit of the right-hand dump of the valley of S. Berikul). All this gives grounds to suppose that the described thickness of porphyrite represents only the lower part of the cover of this rock—a cover which was once, perhaps, very thick, but in places completely destroyed by denudation.

In close connection with the injection of the porphyrite by deep-seated rocks are the contact changes¹ of the former, namely, its transition into a darker, fine-grained rock, that is, one strongly enriched in biotite. A thin section of one specimen of this rock pre—

constitutes a fine-grained aggregate of honeycomb structure, consisting chiefly of transparent plagioclase, abundant biotite (both as separate plates and in the form of small rounded inclusions in the feldspars), and numerous crystals and grains of magnetite, partly evenly scattered, partly clustered into small rounded patches; in addition there are irregular grains of green hornblende and an insignificant quantity of grains of orthoclase and quartz. On the basis of the totality of all these microscopic properties, as well as of the conditions of occurrence in the closest association with the deep-seated rocks, the described form of alteration of the porphyrite must be explained by the influence of the contact action of the diorite and granite, and may be called a biotite–feldspar hornfels.

I now turn to the deep-seated rocks—the norite-diorite and granite. The former, as has already been said, forms, among the porphyrite, as it were, separate islets (chiefly in the space between the Sosnovka stream and the lower course of the Sukh. Berikul) or² occurs in the form of outcrops covered by the porphyrite like a mantle. In the latter case the norite-diorite injects the porphyrite with numerous and thin veinlets, and itself not infrequently contains lens-shaped inclusions of porphyrite altered into the hornfels already familiar to us.

In its macroscopic properties the norite-diorite is a medium-grained hypidiomorphic mixture of colorless or yellowish crystals of plagioclase (with distinct twin striation); abundant, fairly large and regular plates of biotite; and black dull grains of augite. Microscopic investigation gave the following results: abundant fresh plagioclase, which in general habitus belongs to the andesine–labradorite series, forms partly long and narrow laths, partly broader prismatic crystals, and not infrequently reveals an indistinct zonal structure; augite has a pale greenish color and occurs predominantly in grains intersertally wedged between the laths of plagioclase, more rarely in more or less regular—idiomorphic with respect to the feldspar—individuals; biotite, subordinate in quantity to augite, forms irregular large plates possessing sharp pleochroism and containing inclusions of magnetite (rarely—apatite); in still smaller (but nevertheless noticeable) quantity there are small prismatic crystals of hypersthene with characteristic pleochroism from pale green to pale pink. The character of the plagioclase and the simultaneous presence of dark-colored elements characterizing various groups of quartz-free plagioclase rocks give grounds to call the rock under consideration an augite–biotite

² In many places on the right bank in the middle and lower parts of the valley of the S. Berikul.

norite-diorite. The indicated properties of the norite-diorite remain (so far as one may judge of this from macroscopic determination) the same in all its outcrops marked on the geological map; deviations are observed only in the exposures opposite the main mine (on the right bank of the valley of the S. Berikul), where in the veinlets extending into the mass of the porphyrite—in addition to the elements mentioned above—grains of quartz are also distinguished, and the rock itself, somewhat reducing the size of its grains, approaches in external appearance that quartz diorite which—as we shall see further on—is encountered in the face of the Eleninskaya adit.

Another deep-seated rock—granite—composes, for a considerable distance, the right slope of the upper part of the valley of the S. Berikul, and is also not infrequently exposed in the very bed of this stream. Even by outward features many specimens of the granite very much resemble the norite-diorite just described, differing from it only in a smaller content of dark-colored elements and in the presence of smoky-gray grains of quartz. The resemblance is also revealed under microscopic examination. Thus, one thin section of the granite proves to consist of: irregularly rounded grains of orthoclase (sometimes perthitic); similar or somewhat more regular individuals of plagioclase; small grains of quartz; pale-greenish crystals and grains of augite, often surrounded by green hornblende³), and fairly abundant biotite, now in small plates gathered into sinuous rows, now in larger tablets with inclusions of magnetite. In this way, the described thin section differs from the norite-diorite only by the appearance of orthoclase and quartz and the disappearance of hypersthene.

In other places, however, the granite, while continuing to retain its external properties, proves under microscopic examination to have an already different composition; namely, it represents a hypidiomorphic mixture of perthitic orthoclase, quartz, and hornblende, while biotite is present only in insignificant quantity, and plagioclase and augite are entirely absent. However, comparing the description of the thin sections of all three specimens (the norite-diorite and the two granites), one may note that the first thin section of the granite occupies an intermediate place between the second thin section of the same rock and the thin section of the norite-diorite. If, in addition to what has been said, one adds that near the northwestern boundary of the area occupied by granite there are also exposures of norite-diorite; that these exposures are connected with the granite by the most imperceptible transitions; that near the contact with the porphyrite there are found in the granite, in places, the same inclusions of altered porphyrite as in the norite-diorite, then one may suggest that both deep-seated rocks are genetically connected with one another and probably represent products of differentiation of one and the same magma.

³) Partly secondary, partly—perhaps—also primary.

The same supposition may perhaps be made also with respect to the hornblende gabbro encountered on the Nikolaev stream. At the very least, one cannot fail to note the fact that this coarse-grained rock, consisting of regular narrow laths of plagioclase and blackish-green, somewhat fibrous-looking, indivisible hornblende, on the one hand very much resembles certain specimens of hornblende diorite that occur here and there among norite-diorite; on the other hand, in its microscopic composition it appears to be, as it were, the same norite-diorite, with the difference that all the dark-colored elements have been replaced by uralite and chlorite. However, for a categorical confirmation of the assumptions expressed, more detailed microscopic investigations are necessary, and perhaps also additional observations in the field.

In concluding the geological sketch of the environs of the Berikul mine, it is also necessary to mention the rather numerous and varied veins cutting the rocks described. The most widespread of these veins are pegmatite veins, consisting of quartz, feldspar, and light mica, and occurring in the diorite porphyrite, more rarely in the granite. Possessing insignificant thickness (not more than 2–3 cm), they only here and there have a more or less regular strike²; in most cases they represent sinuous, rapidly pinching-out veinlets which, together with thin apophyses of norite-diorite, penetrate into the mass of the porphyrite.

Second place in extent is occupied by veins of a grayish-greenish rock with sparse disseminations of pyrite; by external features this rock may be called diabase aphanite. Its veins have a thickness from 1 to 12 vershoks, occur in limestone and granite, have a steep (75°–85°) dip to O and a strike of NW:32, NW:2 and NW:13°.

In addition, in various places the following were encountered in the porphyrite:

1) a vein of pink aplite, 3 vershoks thick, passing in altered hornstone porphyrite in the direction NO:26° (dip almost vertical);

2) a vein of diabase porphyrite with a cryptocrystalline greenish groundmass and fairly abundant and large segregations of narrow long laths or broad flat tablets of greenish-white plagioclase³; the strike and dip of this vein, owing to the very small dimensions of the exposure in which it was encountered, could not be determined.

3) A thick vein of a pinkish-yellow fine-grained rock, consisting of feldspar crystals and black grains and streaks

hornblende deceptive rock, in its macroscopic properties resembling vogesite; strike—close to meridional, dip not determined.

4) Finally, in some places veins of rocks were encountered which, macroscopically, are determined as felsite porphyry (in the granite outcrops in the upper part of the valley of the S. Berikul) and syenite-porphyry (in diorite porphyrite) ⁶).

Thus, concerning the geological structure of the environs of the “6th Berikul Area” mine, the following may be said: the mass of diorite porphyrite (malchite), in which the gold-bearing quartz veins of the mine occur, represents only the lower part of a destroyed denudation cover. Separating in the west from the more ancient crystalline limestone by an almost straight line, the porphyrite overlies norite-diorite, which probably represents a product of differentiation of the same magma from which the hornblende granite forming the upper part of the valley of the S. Berikul was formed. Both this latter rock and, especially, the norite-diorite either intrude into the porphyrite as a mass of thin winding apophyses, or send off a whole series of similar veinlets of pegmatite. Everywhere that such injection is observed, the porphyrite has been altered into a biotite–feldspar hornfels. Thus, the deep-seated rocks are undoubtedly younger than the porphyrite. The youngest formations in the investigated area are, on the one hand, veins of diabase aphanite and diabase porphyrite; on the other—products of differentiation of an acid orthoclase magma—aplite and vogesite. The strike of the greater part of the indicated veins is close to the meridional direction, deviating from it to one side or the other by an angle of no more than 38°.

On the appended map is also shown the distribution of rocks in the system of the B. Berikul River above the mouth of the S. Berikul; this distribution is borrowed from the “Geological Map of the northeastern part of the Tomsk Mining District,” compiled by Messrs. Zaitsev and Reutovsky. I considered it useful to supplement my map in this way, first, in order to present a broader geological picture; secondly, in order to show to what extent and in what direction the map of Messrs. Zaitsev and Reutovsky should be changed in that part of it which relates to the region of my personal investigations. To this end I have shown, among other things, how the boundary between the granite and the limestone is drawn on the map of the named authors, for it is precisely in this that the chief discrepancy lies between the data of my investigations and the map of Messrs. Zaitsev and Reutovsky: for some reason the latter did not at all note the presence of the mass of diorite porphyrite,

⁶) A microscopic determination of all the indicated vein rocks has not yet been carried out.

having such a considerable distribution and being a rock enclosing the gold-bearing quartz veins.

I now turn to the description of the deposit itself. The “6th Berikul Area” was claimed for placer gold. Its extraction was carried on from 1830 to 1900; during this time 6,627,615 poods of sands were washed and 8 poods 17 pounds 22 zolotniks 11 dolyas of gold were obtained, with an average content of 47 dolyas per 100 poods⁴. The distribution of gold in the placer (the working was carried on in the lower part of the valley of the S. Berikul, beginning approximately one and a half versts above its mouth) was uneven; individual gold particles had an angular form and not infrequently contained pieces of quartz⁵. The fineness of the gold (according to data of the Tomsk Gold-Smelting Laboratory for 1893, 1894, and 1899) ranged from 693 to 790 (per 1000), and on average was about 718 per thousand.

During the working of the placer, quartz ridges with inclusions of pyrites appeared from time to time in the bedrock of the cut. At the end of the nineties these quartzes were sampled at the Tomsk Gold-Smelting Laboratory, and—in view of the good results of the sampling—the then owner of the “6th Berikul Area” began to equip the mine. In 1900 the working of the placer was discontinued, and from 1901 in the official reports on the mining industry of Russia⁶ we find data on the extraction of vein gold alone. These data, supplemented by information supplied to me by the district engineer I. P. Beresnevich for the most recent years, are given in the following table.

P. P. Gudkov.

In addition, from 1903 through 1907 (inclusive), ore gold was mined on the allotment “Berikul Sites,” adjoining the allotment “6th Berikul Area” on the southern side. According to official data, the production of ore gold at the “Berikul Sites” was expressed by the following figures (the processing was carried out at the mill of the “6th Berikul Area”).

Thus, the total quantity of ore processed at the mill of the “6th Berikul Area” up to 1910 amounts to 3.499.800 poods; the quantity of gold obtained from this ore is 141 poods 16 funts 23 zol. 24 dol., and the general average content equals 15 zol. 48 dol.

In the form of its occurrence, the primary deposit of the mine under investigation represents a complex system of veins, the number of which, as is already evident from the plan of the underground workings, is very considerable^10). It should be noted, however, that in reality the number of separate veins is probably considerably smaller than is assumed at the mine, since it has already been established that some veins are not independent, but are merely continuations or branches of others.

Nor did all the veins attract equal attention from the owners and the mine administration; more or less significant workings exist only along the Magistralnaya, Tatarskaya, Bikul’tovskaya, Kedrovo-Petropavlovskaya, and Khotimskaya veins.

The veins (with the exception of the Khotimskaya) occur in diorite porphyrite. At first glance at the plan of the underground workings, the strike of the veins may seem very variable and irregular; however, if one looks carefully at the same plan, it is not difficult to notice that the horizontal workings follow chiefly two directions: NO:18°—43° and NW:295°—344°. If one accepts

^10) On the plan (Table 2, drawings 1 and 2) not all the discovered veins are shown; this was done so as not to complicate drawings already sufficiently intricate even without that; moreover, some veins less important in an economic respect (Prokop’evskaya, Troitskaya, Solominskaya, Mikhailovskaya, and others) are not shown on those drawings either, which were given to me by the mine administration.

if we take into account that the latter direction corresponds to those parts of the workings that have been driven along faults and displacements, then it may be said that the mean general strike of the Berikul veins has the form of a certain wave-like curve, the convexities of which in the middle part of the system of workings are directed toward the northwest, and at the margins toward the southeast.

The changes in strike with depth—as far as can be judged from the direction of the crosscuts on the Main Vein—are very insignificant.

All the veins, with the exception of the Khotimskaya, dip to the NW, making with the horizontal plane an angle, for the most part, equal to 40°–45°, more rarely 70°–80° (Kedrovaya v.) or 25°–20° (Tatarskaya). The changes in dip with depth in some veins are negligible; in others they reach considerable limits. These changes, and in general the details of occurrence of the veins and all the properties of the latter, will be considered in greater detail in the description of the individual veins, to which we shall now proceed.

We shall begin with the Main Vein, on which—as is already evident from the plans—the most considerable workings are present.

Concerning the history of the development of work on the Main Vein, I have the following information⁷. The various portions of this vein were discovered at different times and—as has already been mentioned—were at first taken for separate, independent veins. There were four such portions. Earlier than the others the portion⁸ was discovered, located at present on the surface of adit No. 1, with a depth of 24 arshins. At the place where the shaft intersected the vein, an adit was then driven along the latter, above which extraction of the vein was subsequently carried out for 20 sazhen along the strike and for 7 sazhen upward along the dip. The average thickness of the vein in these workings was approximately ¾ arshin; the average gold content was about 8–10 zolotniks⁹. At present this portion is not being worked, and shaft No. 1 appears to be flooded. Further development of the vein was carried out through shaft No. 2, sunk to 42 arshins. The thickness of the vein at the place where the shaft intersected it was 8 vershoks. The vein mass consisted of solid quartz, containing, more or less parallel to one another and to the walls of the vein, thin stringers of fine grains of arsenical pyrite, larger individual crystals of the same, rather abundant inclusions of pyrite, and a little galena; in its middle part, however, the vein had a cockade structure, due to the presence of rounded fragments of the wall rock impregnated with pyrite, bordered—

...covered first by a layer of yellowish-white calcite, and then by a thinner layer of fine-grained mispickel. The tenor of the vein was 5–6 zolotniks per 100 poods of ore.

The southern part of the Main Vein was worked by the so-called “Vydrinskaya” adit¹⁰, driven at a height of 3–3½ arshins above the bed of the stream; then eight stoping drifts were driven (directly one above another) above this adit and three drifts below it. In the adit itself the thickness of the vein sometimes was notable for its constancy, remaining for a considerable distance equal to 1–1½ arshins, and at other times, on the contrary, underwent considerable fluctuations. The vein mass consisted of solid quartz containing abundant inclusions of mispickel, pyrite, and galena. The gold content during the driving of the adit was: in 1904—from 20 to 40 zolotniks, in 1905—from 8 to 10 zolotniks per 100 poods of ore. The stoping drifts driven above the Vydrinskaya adit passed mainly through a thick clayey mass representing the product of destruction of the vein and of the country rock; in the lower stoping drifts, however, the same quartz vein was worked as in the adit itself, but its structure was different, namely: it had, in general, a banded appearance, owing to the presence of more or less parallel stringers of fine grains of mispickel; in its middle part the vein also contained cockade-like inclusions, of which some had a composition entirely analogous to the inclusions described above; others, however, contained in the center not country rock, but accumulations of pyrite crystals. The thickness of the vein in the lower stoping drifts remained fairly constant along the strike, but decreased down the dip: in the drift immediately below the adit it was equal to 10–12 vershoks, in the next one 8–10 vershoks, and in the lowest 6–8 vershoks. The gold content in the ore from the lower drifts was 6–8 zolotniks per 100 poods.

The northern part of the Main Vein, which at first had also been regarded as an independent vein, was worked by an adit still known under the name “Eleninskaya”¹¹. Here the vein was distinguished by great irregularity both in thickness and in gold content.

Regarding those properties of the Main Vein that were revealed during its further exploitation (from 1905 to 1909), I possess only the following information, kindly communicated to me by engineer A. A. Krasovskii, who was in charge of the underground workings.

1) The Main Vein is generally richer in the south-western part (from the inclined shaft) than in the north-eastern part;

2) in three places marked on the plan (Table 2, Fig. 2) with hatching, in the vein there were encountered sections distinguished by their content, having the form of steeply dipping columns, whose width in places reached 25 sazhens; in the southernmost of these columns (in the part of it marked in Fig. 2, Table 2 by cross-hatching) the vein was also distinguished by a considerable content of large gold grains weighing more than 1 zolotnik;

3) both in the area of the columns just mentioned and, not infrequently, in other parts of the vein richer in gold, its mass was distinguished, on the one hand, by an increased content of calcite, and, on the other, by an increase in the relative amount of zinc blende and galena—especially fine-grained;

4) in the vein there were observed disturbances of bedding in the form of two large (up to 25 arshins) displacements, almost parallel in strike but dipping in different directions (NW and SO) and at different angles to the horizon; in addition—especially toward the southwestern part of the works—many small (up to 1½ arshins) displacements were encountered; along the displacements the vein mass—predominantly the calcite mass of the vein—is thin and barren.

5) In the walls of the veins, slickensided surfaces were often observed, not infrequently covered as if with smeared or rubbed-in grains of pyrite.

During my visit to the “6th Berikul Area,” work on the Main Vein was concentrated in the lower levels of its southwestern part and at the lower end of the inclined shaft. But besides these working faces, I succeeded in studying the character of the vein also in the upper southwestern and all the northeastern workings, as well as at some points near the inclined shaft. I shall begin the description of my observations with the southwestern workings. The uppermost of these is the Main adit. At its terminal face the vein is absent; it had disappeared (according to Mr. Krasovsky) already at some distance from the face, having been replaced by a band of more or less soft and finely laminated rock, representing a dense muddy-greenish mass in which only here and there small grains of pyrite can be distinguished; this mass is cut by several veinlets (about 1½ cm thick) of yellowish-white calcite.

In all the other southwestern stopes there is observed a more or less regularly formed vein, the changes in whose structure and composition may be characterized as follows.

The vein mass consists essentially of quartz, now quite compact, now showing a more or less distinct crystalline structure. Sometimes calcite is added to the quartz; it either has a white color and occurs in the form of crystals closely mixed with the quartz mass, or (which is much more frequent)

has a yellowish-white color and forms small (up to 1½ cm) veinlets in the selvage of the footwall side of the vein and layers in cockade-like inclusions.

The most widespread structure of the vein is banded, due to the presence of thin parallel strings of small grains of arsenical pyrite, or darker (from an abundant content of the finest inclusions of the same pyrite) bands of quartz, or to the content of the above-mentioned calcite veinlets adjoining the selvages, or, finally, to the presence of thin layers of country rock as if clamped within the vein mass. Sometimes inclusions of other ore minerals (especially pyrite) are arranged in more or less rectilinear rows. In some stopes this banded structure is expressed more or less distinctly; in others it is combined with an irregular massive structure or (near the junctions) with a cockade structure. In the stopes described, the cockade inclusions reach up to 3 inches in length and up to 2 inches in width, and in composition and structure they scarcely differ from those already described; namely, there occur such inclusions: a core of altered country rock, containing sparse disseminations of mispickel and pyrite, is surrounded first by a layer of yellowish-white calcite, and then by a thin stringer of small grains of mispickel, to which, here and there, separate larger crystals of pyrite are attached; in other inclusions the intermediate layer of calcite is absent, and the fragment of country rock is directly enveloped by a stringer of mispickel; finally, some inclusions have yellowish-white calcite in the center and mispickel along the periphery. The relative quantity of inclusions varies within considerable limits and is sometimes so large that the quartz mass fills only small intervals between the cockades.

Of the ore minerals in the southwestern stopes of the Main vein, the most widespread is arsenical pyrite, present in all the specimens I collected; enough has already been said about the forms of occurrence of this mineral in describing the structure of the vein.

Pyrite is encountered almost as often, but its relative quantity is very variable: in specimens of the vein from the upper and lower stopes (from the 1st to the 3rd level of the adit and in stopes 5 and 6 of the adits), pyrite is contained only in the form of sparse and small grains disseminated directly in the quartz, or occurring among strings and clusters of mispickel grains; in stope 2 of the level of the adit, pyrite is completely absent; finally, in the part of the vein between the 3rd and 5th level adits it is found in appreciable quantity, forming in places (independently or with the participation of other minerals) continuous accumulations up to 2 inches long and 1½ in. wide. Zinc blende and lead-

a full luster appear only in the lower workings (beginning with the 3rd stope drift), the former forming rather large crystals occurring among fine-grained accumulations of mispickel, inside nests of pyrite or directly in quartz; while the latter is contained in small, clustered crystals, occurring chiefly in close intergrowth with mispickel and pyrite, more rarely—directly in quartz.

In the middle part of the workings along the Magistral vein, it was possible to study its structure only in the following few places, where part of the ore had not been removed: in the pillar at the 6th stope drift on the southwestern side of the inclined-shaft trunk; in the recess¹² above the same drift on the other side of the inclined shaft; and in the pillar above the 4th stope drift, near the inclined working marked on the plan (Table 2, Drawing 2) with the number 2. In addition, it was possible to examine the stope at the bottom of the inclined shaft, which by the time of my visit had been deepened to 217 arshins along the dip of the vein.

In all the first three points the vein has an almost identical thickness—from one to \(1\frac{1}{2}\) arshins—and one and the same structure, determined by the presence of more or less numerous cockade-like inclusions; but the character of the latter and the general composition of the ore mass are not everywhere the same, namely: in the first and last of the indicated points the cockade inclusions are small and in structure do not differ in any way from similar inclusions in the southwestern workings, while the ore minerals in these points are represented almost exclusively by mispickel alone; but in the recess at the 6th stope, on the northeastern side of the inclined shaft, the cockade inclusions have a diameter of up to 5 inches and are distinguished by the special feature that, between the layers of calcite and mispickel, they not infrequently contain a zone of uneven width composed of crystals of pyrite—alone or with the participation of zinc blende and galena; all three of the latter minerals are also contained here outside the cockades, forming either individual crystals embedded in the quartz mass, or large nest-like accumulations; these accumulations are always built according to one and the same scheme (zinc blende and galena among crystals of pyrite, while the latter is surrounded by mispickel) and therefore make it possible to establish with certainty the order of formation of the ore minerals, indications of which had already been encountered in the southwestern workings, namely: after the deposition of calcite, which made up the shells of fragments of the country rock, zinc blende was separated first; after it—and partly simultaneously with it—a galena lead ore, then—pyrite and, finally, mispickel.

In the terminal stope at the bottom of the shaft the vein consists of one thick (about 6 vershoks) and several thin (up to \(1\frac{3}{4}\) vershoks) veinlets,

separated by finely laminated, now dense, now more disintegrated country rock; the structure of the vein is banded, owing to the presence of numerous thin stringers of mispickel and of quartz bands stained by it a darker color. Of the ore minerals, besides mispickel, there occur only not especially abundant but, in part, scanty and coarse grains and crystals of pyrite. The gold content here is 6–8 zol. per 100 poods; in the parts of the vein with cockade structure described above, the content (according to Mr. Krasovsky) reached 20 zol. per 100 poods. Thus, in the middle part of the workings the Main Vein has almost the same properties as in the south-western faces.

The north-eastern faces present an entirely different picture. A more or less thick and normally formed vein is observed here in only one place—in a ledge near the 5th inclined working, under the 4th extraction drift. The vein mass (6–8 versh. thick) consists of continuous splintery fractured quartz, in which there are (3″ × 5) accumulations of pyrite, thin stringers of small grains of mispickel, and rare irregular inclusions and interlayers of country rock altered into a talc-like mass, containing a few inclusions of the smallest crystals of arsenopyrite and, here and there, gray pyrite.

In all the remaining north-eastern faces, instead of a vein there is observed only a fissure, having a thickness from ¼ to ¾ arsh., filled with finely laminated altered country rock, or else the entire face is occupied by rock containing only rare veinlets of yellowish calcite, quartz, or both together. These veinlets (also encountered in the altered rock inside the fissure) are almost everywhere completely barren, and the ore-bearing character is expressed only by the impregnation in the altered rock of pyrite crystals, sometimes larger and more abundant, sometimes very small and scanty; in the lower (4th, 5th, and 6th) levels a very insignificant quantity of the smallest inclusions of mispickel is added to them.

The disappearance of the vein and its replacement by the fissure just described was recorded even before reaching the present position of the north-eastern faces, namely: in the 6th extraction drift the vein ended soon beyond the north-eastern boundary of the middle stope; in the 3rd extraction drift—immediately beyond the extreme north-eastern stope; in the 1st drift—5 sazhens short of the present face; and in the 4th drift, besides the disappearance of the vein near the north-eastern face, the same phenomenon was also observed in the interval between the middle and extreme NE stopes, where, over a length of 8 sazh., instead of solid quartz the vein fissure contained only soft greenish rock with small fragments of quartz and calcite¹³.

To complete the description of the Main Vein, it remains only to speak of the character of its country rock, which everywhere is porphyrite. In comparison with the outcrops on the surface, the porphyrite in the underground workings is distinguished above all by a much greater degree of fissuring, while the surfaces of the fissures are marked by great regularity.

As regards a more detailed determination of the nature of the alteration and their confinement to one or another position relative to the vein, the preliminary study I have made of the collected suite makes it possible to note the following. On the side of the footwall of the vein, the porphyrite in most cases has a black-gray color, a dense or fine-grained (sometimes hornfels-like) structure, and on the joints here and there contains small crystals of calcite and pyrite; these same minerals (and especially the latter) also occur in the form of fine disseminations in the rock or cut it in various directions as thin veinlets.

The macroscopic properties of the porphyrite on the hanging-wall side of the vein are somewhat different: here it has predominantly a greenish-black color, on the planes of separation it possesses a greasy luster, among the coatings it contains only isolated small and thin films of calcite, and inclusions of pyrite are for the most part not at all distinguishable to the naked eye.

Microscopic examination of the corresponding thin sections shows that the described forms of alteration of the porphyrite are characterized chiefly by an increase in the relative amount of hornblende¹⁴ and magnetite, by the appearance of sparse disseminations of pyrite and, perhaps, by a somewhat greater calcitization of the plagioclase¹⁵. Thus, the rock of the hanging and footwall sides of the vein, even at an insignificant distance from the latter, in essence differs very little and, chiefly, only in external features, from the porphyrite samples from its outcrops on the surface.

The same cannot be said of the mass which sometimes makes up the selvages of the vein or is contained in the fissure replacing the vein in the NE workings. Even by its macroscopic properties this mass represents something quite special: it has a very light, almost white color, is greasy to the touch, often contains small shining flakes of a mica-like or talc-like mineral, and is almost always rich in disseminated pyrite crystals of various sizes and, in part, chalcopyrite. A thin section of this mass, as the microscope shows, consists chiefly of small, not infrequently radially fibrous aggregates, leaves of a colorless mineral with distinct cleav—

…ness, bright colors of polarization, and straight extinction; in negligible quantity, tiny grains of quartz, specks of calcite and, perhaps, serpentine are admixed with these flakes.

Almost the same character of alteration is shown by the country rock near the displacement fissures, adjacent to the selvedges just described, or in those cases when it passes as a band between the vein and its lateral branches. The rock here has a completely compact structure, a light-gray or yellowish-gray color, possesses an argillaceous odor, and contains numerous small glints or larger regular crystals of mispickel and pyrite. In its microscopic properties this rock differs from the preceding in that it consists chiefly of an aggregate of very fine grains of calcite, among which a talc-like mineral is contained in small quantity; in addition, a clayey substance is present in the form of numerous elongate-rectangular, translucent, in reflected light—cloudy-white, spots.

With the foregoing, one could conclude the description of the various alterations of the country rock of the Main Vein, were it not that the upper northeastern stopes present certain peculiarities (in the 1st, 2nd, and 3rd adit levels and in the Eleninskaya adit), in which, besides porphyrite, a quartz diorite is also found. The mutual relations of these rocks are explained by the following drawing of the end face of the Eleninskaya adit (see Fig. 1).

Fig. 1.

γ—quartz diorite;

γ—δ—porphyrite altered and injected by diorite;

δ—the same altered porphyrite, but without injection;

δ′—porphyrite altered into a soft, light-colored talcose rock;

δ″—the same rock, but harder;

c—a veinlet of calcite and quartz.

Microscopic examination of the rocks from this stope gave the following results.

A thin section of the rock near the selvedge of the hanging wall represents an aggregate of separate small fragments of more or less fresh plagioclase (and also of rare, larger and more regular crystals of it); of a small quantity of quartz grains and of rather abundant biotite, now brown, now replaced by chlorite and forming…

accumulations of small leaves and thin sinuous strings; in addition, there are small areas of calcite and fine grains of sphene. Finally, here and there areas of an evenly granular structure are observed, consisting chiefly of plagioclase. In general, the appearance of the thin section confirms the supposition that the rock is an injected porphyrite.

This character is much more distinctly expressed in the rock from the footwall side (at a distance of ½ arshin from the vein): the thin section from that part of the rock, which has a coarser-grained structure, may be said to differ not at all from the thin section of the light-colored granitoid rock “g” from the edge of the face on the hanging-wall side. The latter represents a hypidiomorphic mixture of plagioclase crystals of different sizes, some fresh, others thickly dusted with the finest sericite-calcite dust; lath-shaped grains and more or less regular transverse sections of pleochroic green-brown hornblende, often containing inclusions of plagioclase crystals; plates of biotite—fresh or, to a greater or lesser degree, replaced by chlorite and likewise carrying inclusions of feldspar; small grains of quartz squeezed between individuals of plagioclase; very rare rounded grains of pale greenish augite, passing at the edges into hornblende; and abundant grains and crystals of magnetite. Thus, the rock must be called a hornblende-biotite quartz diorite; at the same time, one cannot fail to note the great similarity in the mineralogical composition of this rock with those granite specimens which—as was indicated above—are transitional members between normal hornblende granite and biotite-augite norite-diorite. On the other hand, the quartz diorite of the Eleninskaya adit (at least in macroscopic features) is almost completely analogous to the apophyses of the latter norite-diorite observed in outcrops, intruding into the mass of porphyrite.

All the observations stated, since, of course, they may be trusted without verification by more detailed microscopic studies, make it possible to advance the following assumptions regarding the extent of the Main vein. In view of the fact that at the northeastern ends of the upper underground workings along this vein the disappearance of the vein is observed and, together with it, the replacement of the porphyrite by quartz diorite; on the other hand, in view of the fact that this latter quartz diorite apparently represents the same rock that is exposed at the surface from beneath the porphyrite mass—it may be thought that, with further driving of the indicated workings, they would cut into the very massif of the deep-seated rock, and that the band of foliated and altered porphyrite now observed in the existing workings would then disappear in them. In the field-

This latter supposition is supported by the fact that the indicated zone shows a tendency to pinch out.

Now we shall leave the Main Vein for a time and proceed to the description of other veins, of which we shall consider only two in greater detail: the Tatarskaya and the Khotimskaya.

The Tatarskaya vein is characterized above all by an extremely irregular mode of occurrence. As is seen from the horizontal projection of the workings along this vein (see Table 2, Drawings 1, 2, and 3), its strike in the south-western part (adit No. 7) almost coincides with the strike direction of all the other veins, whereas the north-eastern workings make a much greater angle with the line of the magnetic meridian, trending toward ONO. The dip of the Tatarskaya vein is likewise variable. In the exposure on the dump the vein had a very gentle, almost horizontal occurrence, but after only 10–12 arshins the angle of dip began rapidly to increase, and adit No. 5, driven there, passed into a working inclined to the horizon at an angle of about 15°. The same dip is now observed in the end face of adit No. 5 and in the working marked on the plan by the letters aa. But besides this general dip to the NW, in various workings the vein also shows an inclination to the horizon in other directions; thus, in workings branching off toward ONO from adit No. 5, a dip of the vein in the same direction is also observed; and beginning from the fault shown on the plan (west of adit No. 4), the workings gradually descend toward adit No. 7; finally, an even sharper change in dip was found in the workings driven somewhat south of adit No. 7 and now already caved in (see Table 1, Drawing No. 3 and 3′); namely, between adit No. 1 and small shaft No. 3 the vein bent steeply downward (toward WSW at an angle of about 45°), and in place of quartz, in this steeply dipping part there appeared a white, loose clayey mass, with a thickness of up to 10 arshins. Farther west—in shaft No. 3 and adit No. 7—a quartz vein was again encountered, with a more or less normal mode of occurrence.

Another characteristic feature of the Tatarskaya vein is the frequent disturbance of its occurrence in the form of faults. Besides the two faults marked on drawings No. 3 of Table 1 and No. 2 of Table 2, quite a few others were encountered; moreover, along the dip, chiefly normal and diagonal faults were observed, and along the strike—upthrows. The height of these, as of the other faults, is usually 1–1½ arshins, and more rarely reaches 1 sazhen.^20)

It is very possible that both of the indicated features of the Tatarskaya vein (sharp changes in dip and frequent disturbances of occurrence) represent—

^20) All the information cited concerning the conditions of occurrence of the Tatarskaya vein is taken from the notes of A. I. Kozlov.

although the phenomena are closely connected with one another; thus, the change in the angle of dip in adit No. 5 may be explained by the crumpling and overturning of the destroyed upper part of the vein under the influence of downslope movement of material from the slopes; the change in occurrence between adit No. 1 and shaft No. 3—by a fault of the south-western part of the vein, etc.

The thickness of the Tatar vein fluctuates within considerable limits. Having, in the outcrop from which adit No. 5 was laid out, a thickness of about 1 arshin, as the adit was driven forward the vein at first decreased its thickness to 4–5 vershoks, and then (with the change of occurrence from gentle to more steeply inclined) again became more massive and, at the end face of adit No. 5, reached 12–14 vershoks. In the other workings the thickness of the vein was:

In the workings extending to the E from adit No. 5, the vein broke up into several separate thin veinlets.

In the composition of the Tatar vein¹⁶, in comparison with the Main vein, the principal difference observed is that in the former sphalerite and—especially—galena occur much more often and in much greater quantity; pyrite also plays, perhaps, a somewhat larger role than in the Main vein; but, prevailing in places over mispickel in relative amount, pyrite—as in the Main vein—yields to arsenopyrite in extent of distribution.

The structure of the vein is in most cases banded, owing to the arrangement of inclusions of ore minerals in more or less rectilinear rows. In connection with this it is interesting to note that in some workings¹⁷ a considerably greater ore content of the vein is observed on the side of the footwall.

The vein rock is everywhere quartz, but not infrequently calcite is admixed with it in small quantity; the latter either has a yellowish coloration, a less distinct crystalline structure, and forms a thin (up to 1/2–3/4 cm) veinlet passing along the footwall side of the vein and separated from the quartz by a thin stringer of fine-grained mispickel; or it has a white color, a clear coarse-crystalline—

...with a crystalline structure and occurs either as small patches among the quartz, or in the form of an original pegmatite-like intergrowth with the latter.

The average gold content in the Tatarskaya vein ranged from 8 to 19 zolotniks (per 100 poods), but in some places (for example, in adit No. 5) individual samples showed 40 zolotniks and even 47 zolotniks.

In the country rocks, as compared with those of the Main vein, no other peculiarities are observed; all the specimens at my disposal belong to one or another of the forms of alteration of porphyrite described above. The only thing that may be noted is a somewhat more intense calcitization and pyritization of the country rock of the Tatarskaya vein, with pyrite occurring both as separate scattered crystals and in thin veinlets. Dissemination of mispickel is encountered comparatively rarely.

The Khotimskaya vein was worked by an adit driven at a distance of 40–45 sazhens lower (downstream) than the Petropavlovskaya adit, on the left side of the valley of the S. Berikul. The plan of this adit is given in Fig. 2, Table 1. For the first 20–25 arshins the adit followed a fissure, the right wall of which consisted of crystalline limestone, the left of porphyrite; the fissure itself was filled with a breccia-like mixture consisting of large fragments of limestone and pieces of porous quartz cemented by an ocherous mass. Then, instead of the fissure, a pyritous vein appeared, along which a western (left from the mouth of the adit) drift was driven. The purpose and character of the subsequent workings along the vein are explained by the following figure.

Fig. 2.

I–I — part of the adit driven along the fissure;

b–b — working driven along a veinlet of quartz that pinched out where it met a calcite veinlet (c)

d–d — drift along the pyritous vein (the view of the end face is shown in Fig. 3)

e–e — drift driven along a calcite veinlet observed in the end face

x — place where an accumulation of pieces of cavernous quartz cemented by an ocherous mass was encountered.

δ — porphyrite; K — crystalline limestone; Cl — pyrite.

An examination of the faces of the workings indicated in Fig. 2 gave the following results. In the face of the left (western) drift (d) the following picture is observed:

P—an accumulation of pyrite crystals, cemented by a very small amount of gray and white cryptocrystalline calcite mass.

Br.—a breccia-like mixture of irregular patches of yellowish-white calcite and altered pale greenish and bluish porphyrite; the mixture is permeated by abundant disseminations of pyrite in the form of small accumulations of fine grains.

c—a veinlet (¾″ thick) of yellowish-white, clean, coarse-crystalline calcite.

δ—dense black-gray porphyrite.

K—yellowish-white fine-grained limestone.

Fig. 3.

In the small working a (see Fig. 2) the entire face is filled with the same pyritic mass as occupies the left side of the just-described face.

In the face of working b there is observed chiefly porphyrite, fairly fresh, in places somewhat hornfels-like, and cut by several parallel thin veinlets of calcite; near the latter—in the lower part of the face—the porphyrite shows alteration into a dense dark-gray rock. Disseminations of pyrite are observed neither in the porphyrite nor in the calcite veinlets.

Finally, the face (e) of the eastern (right) drift lies entirely in yellowish-white limestone, containing very sparse disseminations of small pyrite crystals; the latter are somewhat more abundant in the middle part of the face, where there passes an almost vertical (2″–3″ thick) veinlet of coarse-crystalline calcite, and adjoining this veinlet is a rather thick band, distinguished from the rest of the limestone mass by the presence of separate patches¹⁸ of more or less fresh porphyrite and of thin veinlets of pale-green mass.

Thus, in comparison with the Magistralnaya and Tatarskaya veins (and, as will be seen below, also with the other Berikul veins), the Khotimskaya vein is distinguished by the following features:

1) it occurs mainly at the contact of the limestone with the porphyrite, and sends only small apophyses into the latter;

2) having the same NNO strike as all the other veins, it dips not to the NW, but to the OSO at an angle of about 52° (see Fig. 3);

3) in its vein mass the chief role is played by coarse-crystalline yellowish-white calcite (similar to the calcite occurring in the other veins in the form of veinlets along the hanging-wall side and in the form of coatings on fragments of country rock in cockade inclusions); quartz, however, was contained in separate cavernous pieces only in the destroyed part of the vein near its outcrop on the ridge;

4) among the ore minerals in the vein the dominant importance belongs to pyrite, which at times forms—as we saw—almost continuous accumulations across the entire thickness of the vein; arsenopyrite, on the contrary, is almost entirely absent; finally, a fifth peculiarity of the Khotimskaya vein is that, despite its composition (almost entirely pyrite), it was distinguished by a rather considerable gold content, namely: in the destroyed part it contained from 20 to 40 zol. per 100 p., and in the pyritic part it yielded 2–3 zol. of mechanical and 5–6 zolotniks of chemical gold¹⁹; whereas, as will be shown below, in the other veins the pyrite apparently contains almost no gold.

Finally, for completeness in the description of the Khotimskaya vein, the following must also be noted: along the continuation of the Khotimskaya vein in the allotment of the Decadent placer (parallel to the “6th Berikul Area” and situated 1/2 verst south of the latter), near the contact of limestone with porphyrite, a belt of crushed limestone was discovered, containing inclusions of sphalerite and pyrite.

With regard to the other veins, occurring in the porphyrite and—as was indicated—having an NNO strike and a dip to the NW, I shall confine myself to indicating the composition and structure of their vein mass. A specimen from the end face of the lower adit on the Bikul'tovskaya vein belongs to quartz of a dense, indistinctly crystalline structure, containing on one side a fairly thick (1 1/2 mm wide) band of small grains of arsenopyrite. A specimen from the rich part of the Struzhkovskaya vein—from the end face of the adit after the sharp turn of the latter—represents a quartz mass with rather abundant but small accumulations of pyrite, thin veinlets of galena, and a small quantity of mispickel. In the country rock of this part of the Struzhkovskaya vein, the numerous winding veinlets of pyrite deserve attention; they contain here and there separate crystals of sphalerite, and there are several somewhat thicker veinlets of calcite, which cut across and in places seem to offset the pyrite veinlets. The chemical vein, insofar as one may judge from the specimens of it that I have, consists of quartz having a banded structure, owing to the arrangement of the grains of mispickel in thin parallel cords. Of the other ore minerals cont—

encountered only pyrite in the form of small, irregular crystals. The content²⁰ of gold in the Chemical vein was 3–5 zol.; the thickness, as the adit was extended, increased to 1½–2 arsh., and, moreover, increased from the lower to the upper part of the adit.

The Petropavlovsk vein is interesting because, in one of the adits driven along it, it had a swelling up to 13 sazh. wide and 15 sazh. long; it consisted of quartz colored greenish, an insignificant amount of calcite, and abundant inclusions of pyrite, arsenopyrite, and galena, to which separate crystals of zinc blende were occasionally added. The gold content ranged from 6 to 10 zol., sometimes reaching 15 zol. per 100 pud.²¹

The Kedrovye veins are steeply dipping branches of the Petropavlovsk vein, but richer than it, especially the steepest one.

Among the other veins, which have much less economic interest, we should note the Mikhailovsk, Prokopievsk, and Troitsk veins. All of them were discovered on the right side of the valley of the S. Berikul and were worked by adits for a very insignificant distance.

The Mikhailovsk vein is not being worked because of its very insignificant thickness; the vein mass consists of quartz with a comparatively large participation of calcite and rare disseminations of individual grains of galena and pyrite; the gold content was rather high, but irregular.

The Prokopievsk vein was distinguished by directly opposite qualities: with its substantial thickness (reaching 2 arsh.), this vein was extremely poor (1–2 zol. per 100 pud.). At present, in the end face of the adit only a broad—approximately about 1 arsh.—crack is visible, filled: at the hanging wall, with thinly laminated yellowish-brown, strongly decomposed rock with abundant and fine dissemination of pyrite; in the middle part, with a band of almost solid pyrite, cut by winding quartz veinlets; and on the footwall side, with a dense white clayey mass, also containing veinlets and accumulations of pyrite.

In the end face of the adit along the Troitsk vein there is observed a band 2 vershoks thick, having at the footwall a thin selvage of the same white clayey mass that was just mentioned in the description of the Prokopievsk vein, only here in this mass, besides pyrite, there are also crystals of arsenopyrite; the upper part of the band consists of porous, ocherous quartz on the surface, with inclusions of individual rare crystals and accumulations of pyrite.

Thus, acquaintance with the composition and structure of the Berikul veins leads us to the following conclusions.

The vein mass consists predominantly of quartz alone; calcite—if it is sometimes associated with the quartz—always plays a very insignificant role, although it is of interest in that it occurs in two different forms of manifestation. The first is characterized by a yellowish-white coloration, resembling the coloration of the limestone occurring in the lower reaches of the S. Berikul; in this form the calcite is found as coatings on fragments of barren rock, as rounded nuclei rimmed with mispickel, or as small veinlets occurring on the footwall side of the vein. The other form is characterized by a pure white color and is peculiar to that calcite which is found directly within the quartz mass (whereby at times a regular, as it were granophyric, intergrowth with quartz is observed).

In the faces of workings driven along the displacements, and in the northeastern faces of the Main vein, where the quartz mass disappears completely, as well as in the vein mass of the Khotim vein, exclusively the first form of calcite manifestation is found.

The most widespread structure of the vein mass is banded; moreover, the banding is in part caused by the arrangement of small grains of mispickel in the form of thin parallel vein-like strings along the vein. Other ore minerals—pyrite, zinc blende, and galena—are often arranged in the same direction, forming either separate disseminations in the quartz or nest-like accumulations of various size (in the gently dipping parts of the veins these accumulations are found chiefly near the footwall). In addition, in some places a true lenticular (monosymmetrical) structure is observed, caused by the presence of the above-mentioned calcite veinlets (on the footwall side), separated from the quartz mass by a thin string of mispickel. Finally, near displacements and faults (in particular, in those places of the Main vein that are marked on the plan by hatching), the veins, while retaining a generally banded character, contain more or less numerous cockade inclusions; the composition of the latter is as follows:

1) a fragment of altered country rock (often containing a sparse impregnation of small crystals of mispickel, or of mispickel and pyrite) is surrounded first by a layer of yellowish-white calcite, then by a thin string of mispickel; modifications of this category of cockade inclusions are those in which the intermediate layer of calcite is absent and the rock is directly enveloped by mispickel, and those in which, between the layers of calcite and mispickel, there is also a zone of uneven width made up of crystals of pyrite, zinc blende, and galena.

2) a nucleus of yellowish-white calcite surrounded by mispickel;

3) a nucleus of crystalline pyrite surrounded first by calcite, then by mispickel.

Of the ore minerals, the most widespread in the Berikul veins is mispickel, absent only in the Khotim vein; second place belongs to pyrite, which occurs not as often as arsenical pyrites, but at times exceeds the latter in relative quantity. On the contrary, zinc blende and galena have, in general, a limited distribution, occurring chiefly near faults and slips; in fact, as is evident from the preceding, these minerals are contained in the Tatarskaya, Struzhkovskaya, Petropavlovskaya, Kedrovo-Petropavlovskaya, and Khimicheskaya veins, and in those parts of the Main vein which constitute “pillars”; but the Tatarskaya vein, as was indicated, is distinguished by the most frequent disturbances of bedding; the Struzhkovskaya, Khimicheskaya, and Petropavlovskaya are broken by slips (this may already be judged from the sharply curved workings along these veins—see drawing 2, table 2); finally, the “pillars,” i.e., the parts of the Main vein outstanding in richness, are characterized, first, by a breccia-like structure, and, second, are likewise confined either to slips or to abrupt changes in strike (see the same drawing No. 2, table 2). Free gold, which—according to Mr. Krasovsky—is sometimes encountered in the quartz mass of the Berikul veins, was not observed by me personally in any of the specimens collected.

In conclusion to the description of the Berikul veins, and in order to clarify the question of the gold content in the various ore minerals of these veins, I shall give the following data from analyses carried out by the student (now engineer) V. N. Chelpanov.

Analysis of pure coarse-crystalline galena showed a very high content of silver (per 100 poods—10 lb. 57 zol. 57 dol.) and a very insignificant content of gold (in one assay—traces, in another—2 zol. 29 dol. per 100 poods).

A general analysis of one of the typical samples of the Main vein showed the following composition:

\[ \begin{aligned} \mathrm{SiO_2} &— 65.52\% \\ \mathrm{CaCO_3} &— 27.66\% \\ \mathrm{MgCO_3} &— 1.82\% \\ \mathrm{FeS_2} &— 3.25\% \\ \mathrm{FeSAs} &— 1.75\% \end{aligned} \]

The gold content in the same sample proved to be 5 zol. 73 dol. per 100 poods; the fineness of the gold—857 per 1000.

From these data it is evident that mispickel and zinc blende are distinguished by the greatest gold content; but since, as was indicated above, zinc blende occurs only locally, while mispickel, on the contrary, is the most widespread, it may be said that it is precisely mispickel that determines the gold-bearing character of the Berikul veins, and therefore these veins may be assigned to the arsenopyrite quartz-gold formation.

However, the question of the formation may also be resolved in another form, if one takes into account that the deposit described contains a considerable quantity of silver. This is evident, first, from the analysis cited of galena, which—as it turned out—contains more than 10½ lb. of silver per 100 poods; secondly, from data on the fineness of gold obtained at various times from the veins of the “6th Berikul area.” These data were obtained by me from the Tomsk Gold-Smelting Laboratory and, for greater clarity, are enumerated in the following survey.

From this table it is evident that the metal obtained at the factory of the “6th Berikul Area” is an alloy of gold and silver—an alloy in which the ratio Ag : Au averages 1 : 2.21, and sometimes reached a value of 1 : 1.25. In short, in those 141 poods 16 pounds 23 zolotniks 24 dolyas which, in the form of “gold,” were extracted at the “6th Berikul Area” and the “Berikul Cliffs” from 1901 to 1909, there is contained about 44 poods 15 pounds of silver. This quantity is so considerable that it seems possible to assign the Berikul veins to the formation of gold and silver ores.

A comparison of the deposit described with typical representatives of each of the indicated formations leads to the following conclusions.

Among deposits of the arsenical formation, the Berikul veins show similarity with the mines near Zwickenberg in Carinthia, Santa Cruz in the province of Santa Barbara in South America, and Culera in Catalonia²³ (in the eastern part of the Pyrenees); however, the similarity concerns only the composition of the vein mass, while the surrounding rocks in the indicated mines are different: in Carinthia—quartz schists; at Santa Cruz—banded gneisses and crystalline schists²²; at Culera—dislocated Paleozoic schists.

All the other deposits of the arsenical formation described by Beck²⁴ differ from the Berikul deposit not only in the character of the surrounding rocks (which are, for the most part, metamorphic schists), but also in the content of certain minerals absent at Berikul—most often sulphide compounds of antimony and copper, and sometimes manganite, pyrrhotite, and tourmaline.

Among deposits of the silver-gold formation, the Botes-Muszari deposits in Zibenbürgen and Boisza in the Brad region (Hungary) approach the Berikul veins (but do not contain mispickel). Most of the other known deposits of this formation, although also associated with rocks more or less close to the Berikul porphyry (Tertiary and Mesozoic trachytes, dacites, rhyolites, and especially andesites), are characterized by the presence of telluride compounds and rich silver ores, which do not occur at Berikul²⁵.

The genesis of the Berikul veins, after the general processing of the collected material that has so far been carried out, cannot be considered fully clarified; however, certain assumptions may already be made.

Thus, one may think that the fissures, the result of the filling of which are the Berikul veins, belong to tectonic (exokinetic) fissures. In favor of this speak:

1) the coincidence of the strike and dip of the ore veins, on the one hand, with the strike and dip of the veins of eruptive rocks, and, on the other, with the direction of the western boundary of the granite massif (see the geological map);

2) the phenomenon noted above of the replacement of ore veins by a band of stratified, altered, and sulfur-compound-impregnated enclosing rock (a band of porphyrite in the NE workings of the Magistral vein; a band of limestone along the continuation of the Khotimskaya vein).

As for the mode of formation and the time of deposition of the various ore minerals composing the veins, the conditions of occurrence of these minerals described above and the composition of the cocarde inclusions make it possible to reconstruct the history of vein formation as follows.

After the formation of the first tectonic fissures (parallel to the veins of eruptive rocks and to the margins of the granite massif), pyrite and mispickel were probably deposited in them in connection with the eruption of the granite; these now occur as inclusions in fragments of country rock forming the nuclei of the cocardes.

Then the already existing fissures widened, were broken up by faults and dislocations (in a direction parallel²⁶ to the veins of eruptive rocks and perpendicular²⁷ to them), and, in places of greatest destruction, were filled with fragments of rock. Immediately after these processes²⁸ there occurred the deposition of that yellowish-white calcite which forms veinlets on the side of the footwall of the veins and shells around fragments of country rock. Such conditions of occurrence of the calcite compel one to assume that the solutions containing CaCO_3 flowed down along the walls of the fissures from above downward, i.e., that this calcite is of vadose origin and was probably leached from the thickness of the limestone.

The next stage of vein filling consisted in new emanations of sulfurous metals (zinc blende, galena, pyrite, and mispickel); the emanations probably accompanied the eruption of the veins of the granite series and proceeded with particular intensity in the places of greatest destruction, which explains the outstanding richness of the parts of the vein adjacent to the faults and dislocations.

Finally, these latter emanations, as volcanic activity died out, were gradually replaced by thermal waters, which—while the deposition of sulfurous metals continued—led to the deposition of quartz and white calcite.

The features of the Khotimskaya vein indicated above may be explained by the fact that this vein was completed in its formation during the first gas emanations and the deposition of vadosic calcite. The considerable richness of this vein, inconsistent with its composition (on the basis of the analyses by G. Chepchanov cited above), suggests that only the pyrite of the second generation²⁹ is devoid of gold and, conversely, that the pyrite of the first generation is gold-bearing.

Clarification of this question by assaying the pyrite constituting the cores of the cockades, as well as a general, detailed study of the distribution of gold among the various ore minerals of the Berikul veins, and verification of all the hypotheses expressed concerning the genesis of the deposit described, should form the task of further treatment of the material collected.

In concluding the description of the mine “6th Berikul Area,” I consider it a pleasant duty to express my sincere gratitude to Messrs. G. S. Stepanov, A. A. Krasovsky, M. A. Stepnov, and to my closest collaborator A. I. Kozlov, who assisted me in my investigations; to Messrs. I. P. Beresnevich and P. I. Pokrovsky, who supplemented the materials I had collected with data on the production of gold and its assays; and to the owner of the mine, A. D. Rodyukov, for the hospitality shown.

Geological Map

of the environs of the mine of the “6th Berikul Area.”

Compiled by A. Karpinsky on the basis of the survey by [[unclear: initials/name]]
Scale: 1 verst to an English inch \((1:42000)\).
Plate I.

For the article by P. B. Butusov: “The Mine of the 6th Berikul Area.”

Designations

• beds of [[unclear: rock name]]
• outcrops of limestones “b” and “b-[[unclear]]”
• line of strike of the limestones
• line of strike of the [[unclear: rock name]]
• line of occurrence of clayey [[unclear: schists/slates]]
• occurrence of [[unclear: rock name]]
• [[unclear: limestone]] and crystalline schists
• old gold-washing workings and quartz veins
• ancient workings
• porphyries
• granite—gneiss
• diorites
• gold-bearing sands
• trap rocks
• springs

Map annotations

• Boundary between limestones and granites according to the map of Zaitsev and Remezovsky.

Plan

of the talc vein
(according to the survey by D. I. Kordov)

Scale 1:1000.

Drawing 2.

Visible labels on the drawing:

• talc along the Berikul vein
• quartz
• N

Schematic representation of the workings on the Matrosskaya vein

according to the plan of the Matrosskaya mine
by D. I. Kordov, 1905.

Scale: 1/100 sazhen.

Drawing No. 3.

Visible labels on the drawing:

• quartz
• Matrosskaya vein
• shaft No. 2
• shaft No. 3
• talc along the Berikul vein
• ore
• vein No. 3
• [[unclear: several handwritten labels within the mine workings]]
• N

Plan of underground workings at the mine of the “6th Berikul Area.”
Scale 1:1000
(10 sazhen in 1 inch)

Drawing 2.

Conventional signs:

— drifts — 9th level
— drifts — 8th level
▧ — mined-out stopes on the 7th level
▧ — drifts to be driven in the 6th level
▧ — ore bodies proposed for extraction
▧ — ore bodies proposed for exploration, or for driving along the vein
[[unclear: several symbols and explanatory notes in the legend]]
■ — shaft
▰ — sump
[[unclear: final legend item]]

Visible inscriptions on the plan include:

• Shaft no. 1
• Shaft no. 2
• Alexandrovskaya shaft
• Ivanovskaya shaft
• old adit
• [[unclear: mine-working names and level labels repeated throughout the plan]]
• I, II, III, IV, V, VI, VII, VIII — level or section designations marked on the workings
• N — north arrow
• B — east
• C — north
• Ю — south
• З — west

[[unclear: Numerous handwritten labels on individual galleries, shafts, and crosscuts are too small or blurred to read reliably from the visible page image.]]

Underground Berikul mines.
“6th Berikul area”

In axonometric projection.
On plane \(C D\).
\(\alpha = 45^\circ;\ \beta = 60^\circ;\)
Scale 1:1000.
Drawn by L.

Visible labels in the drawing: I, II, III, IV, V, VI; shaft No. 1; shaft No. 2; cross adit; adit [[unclear]]; river [[unclear]] Berikul.

Table II.
For the mine of P. P. Bartenov.

Visible labels in the inset drawing: \(55\), \(56\), \(57\), \(m_1\), \(m_2\), B.

Plan of the underground mining workings at the “Nikolaevskaya Mine.”

Scale 1:1000 (10 sazhens in 1/100).

Fig. 2.

Legend for plans Nos. 1 and 6:

Visible labels on the plan include: “Level I,” “Level II,” “Level III,” “Level IV,” “Level V,” “Level VI,” “Alexandrovskaya Shaft,” “Kundusuyul River,” “adit along an ore-bearing vein,” “adit along a barren vein,” and several numbered shafts and workings.

Projection of the geological part of the underground workings onto the vertical plane ASS

Scale 1:1000.

Labels and annotations visible in the drawing:

• Bindukovskaya adit
• Sobolevskaya adit
• Magistralnaya adit
• Exploratory adit
• Dmitrievskaya adit
• Paraskovya adit
• Bindukovskaya adit
• Petro-Pavlovskaya adit
• Petrovskaya adit
• Fatimskaya adit
• Shaft No. 2
• I
• II
• III
• IV
• V
• VI
• 28 arshins
• Drawing 4
• [[unclear: handwritten note beginning “Convergence …”]] on the mine [[unclear]].

1. These changes of the porphyrite (as well as its injection by deep-seated rocks) occur so frequently that it is quite impossible to mark them on the map. ↩

2. Indicated on the geological map. ↩

3. This rock probably cuts the limestone as well, since its pebble is fairly widespread in the bed of the B. Berikul. ↩

4. According to data presented to me by district engineer I. P. Beresnevich. ↩

5. This information is taken from a very detailed report on the summer practical work of student A. I. Kozlov, which was handed over to me. ↩

6. Collections of statistical information on the mining industry of Russia, published annually by the Mining Department. ↩

7. Drawn from the already mentioned note by A. I. Kozlov. ↩

8. Indicated on the plan above the 1st crosscut, near shaft No. 1 (Table 2, drawing 2). ↩

9. The note by A. I. Kozlov contains no information on the structure and composition of the Main Vein in this portion. ↩

10. Now known under the name Main and marked on the drawings (Table 2, Drawings 1, 2, 4) by the letters M₁, M₂, and M₃. ↩

11. On the drawings this adit is marked by the letter E (Table 2, Drawings 1, 2, 3). ↩

12. In this recess there is a pump for pumping water from the shaft. ↩

13. All these data were communicated to me by A. A. Krasovsky. ↩

14. Especially in samples from the hanging wall. ↩

15. In samples from the footwall. ↩

16. So far as I can judge of this from personal observations and on the basis of examination of samples delivered by Messrs. Kozlov, Mochalov, and Verevkin. ↩

17. In the lateral eastern working from adit No. 5 and in the lower working connecting adits No. 5 and No. 7—near the fault marked on the drawing. ↩

18. These porphyrite patches probably represent apophyses intruded into the limestone, appearing in the wall of the face in cross section. No microscopic study was made of rock specimens from the Khotimskaya adit. ↩

19. According to data from the note of A. I. Kozlov. ↩

20. According to data from the note by A. I. Kozlov. ↩

21. I was unable to enter the workings along the Petropavlovsk vein, because at the time of my visit to the mine they were almost filled to the roof with ice. ↩

22. J. M. Maclaren—“Gold: its geological occurence and geographical distribution,” p. 610, London—1908. ↩

23. Beck—“Lehre von den Erzlagerstätten” Dritte Auflage, I B., S. 456. ↩

24. l. c. SS. 457—459. ↩

25. Beck, l. c., S. 461. ↩

26. Dislocations in the southwestern part of the lower workings of the Magistral vein. ↩

27. Dislocations encountered by the adits: Magistral, Struzhkovskaya, Kedrovo-Petropavlovskaya, and Petropavlovskaya. ↩

28. However, the occurrence of cocardes, whose nucleus is calcite, indicates that mechanical destruction of the fissures continued even after the deposition of calcite. ↩

29. G. Chepchanov, as we know well, subjected to processing only the pyrite enclosed directly in quartz, i.e., pyrite of the second generation. ↩