MINERALOGY AND CONDITIONS OF FORMATION OF COLUMNAR MINERALIZATION AT THE ANDREEVSKOYE DEPOSIT

V. I. Bazhenov

(Presented by Professor, Doctor F. N. Shakhov)

The Andreevskoye deposit is one of the largest and most thoroughly studied deposits of the Sarala ore field and is situated in its northern part. The ore body of the deposit is represented by a quartz vein extending almost in a latitudinal direction, with a strike azimuth of 75–105°. The dip of the vein is northerly, at an angle of 45–60°. In the upper horizons of the deposit the dip of the vein is considerably gentler, reaching 35–37°.

The quartz vein lies conformably with the enclosing rocks, being confined to a fracture passing along the contact between effusive porphyries and a thin unit of carbonaceous shales. Thus, the footwall of the vein is represented by porphyries, and the hanging wall by carbonaceous shales. However, such conformable occurrence of the vein is not always maintained. Cases are observed where, over small intervals, the vein deviates from conformable occurrence, and then clayey shales, sandstones, and so forth appear in the footwall.

The ore body of the Andreevskoye deposit is rather complex in its structure. Within it are distinguished the so-called Annensko-Nikolaevskaya and Sulfide veins. These veins differ in their mineralogical composition, the Sulfide vein being enriched to a considerable degree in sulfides in comparison with the Annensko-Nikolaevskaya vein. Usually the Sulfide vein occurs in the footwall of the Annensko-Nikolaevskaya vein, but occasionally cases of intersection of the latter are observed; i.e., the Sulfide vein is a younger formation than the Annensko-Nikolaevskaya.

In the upper part of the deposit a spatial separation of these two veins takes place. The upper boundary of the joint occurrence of the two veins is an extremely irregular line (Fig. 1), and at the same time a general tendency is evident for this boundary to plunge eastward. The Sulfide vein passes into the footwall of the Annensko-Nikolaevskaya vein and, not far from the ground surface, pinches out completely.

The structure of the ore body is further complicated by the presence of a whole series of apophyses, the dimensions of which are for the most part small. Sometimes, at some distance from the main vein, in its footwall and hanging wall, there occur stringers, which are quartz veins, usually small in thickness and relatively limited in strike.

formation. Such formations apparently include the so-called Mariinskaya vein, known in the upper levels of the deposit, as well as a number of short vein segments known at deeper levels.

DIAGRAM
of the distribution of ore columns of the Andreevskoye
deposit

Projection onto a vertical plane (without crosscut adits)

Fig. 1

The thickness of the ore body is variable. Pinches of the vein alternate with swells, where the thickness of the ore body decreases to 0.05–0.10 m, and in places the vein pinches out completely and only a barren fracture—the conduit—remains. In general, it may be noted that with depth the average thickness of the vein increases. Whereas in the upper levels its thickness was 0.30–0.50 m, in the lower levels the vein thickness averages 0.90–1.10 m, at times reaching even 2.0 m. Taking into account the arc-shaped form of the ore body, it should be noted that the pinches of the vein are confined to the bend of the arc, while the swell portions are situated on its limbs.

The vein of the Andreevskoye deposit is cut by a large number of meridional post-ore dikes of basic composition, which are known here under the general name—proterobases.

The number of dike formations in the deposit is enormous. In places they account for up to 30–35% of the total length of the workings.

Mineralogical composition of the ores

The ores of the Andreevskoye deposit are composed chiefly of quartz, in which admixtures of other minerals, both ore and non-ore, are noted. Among the vein minerals composing the ore body, the following have been found: quartz, calcite, sericite, albite, apatite. The ore minerals are represented by pyrite, sphalerite, galena, pyrrhotite, scheelite, arsenopyrite, chalcopyrite, tennantite, gold, marcasite, pyrargyrite, native silver, famatinite, cuprodescloizite (?) and smithsonite.

Pyrite is the most widespread ore mineral. Its amount constitutes no less than 50% of the ore minerals.

As a result of the study of the ores, three different-age generations of pyrite were identified.

Pyrite of the first generation occurs in comparatively small amounts. It is a fine impregnation of small cubic crystals up to 1–2 mm across in quartz of the second generation, which makes up the main part of the Anne–Nikolaevskaya vein.

Under the microscope it is observed that pyrite of the first generation forms small euhedral grains in quartz, while the latter is always corroded by pyrite. At the same time there is distinct replacement of pyrite by later arsenopyrite. With such replacement, more or less large, scattered relics of pyrite grains with strongly corroded outlines remain inside large arsenopyrite crystals.

Pyrite of the second generation is the most common ore mineral. It occurs as rather large cubic crystals up to 1.0–1.5 cm in size, which usually, together with other sulfides, are arranged as bands parallel to the vein selvages, producing a banded texture of the ore. Very often the pyrite is confined to bands of carbonaceous shales in quartz, which is also characteristic both of pyrite of the first generation and of other sulfides.

Spectral analysis establishes in pyrite of the second generation an insignificant admixture of As in an amount up to 0.001%.

Under the microscope pyrite is observed as isometric grains with square outlines. The grains are distinctly corroded by sphalerite, galena, and other sulfides. As a result, pyrite grains acquire swollen and even skeletal forms. Sulfides not infrequently penetrate the pyrite along fine cracks, likewise corroding it.

Pyrite of the third generation was not encountered macroscopically. Under the microscope it also occurs very rarely. It forms veinlets up to 0.02 mm wide. Such pyrite veinlets, often accompanied by calcite, cut most of the minerals noted: pyrite of the second generation, sphalerite, chalcopyrite, and others; that is, the formation of these veinlets took place during the final stage of mineral formation.

Sphalerite is also one of the most widespread minerals in the ores of the Andreevskoye deposit.

It forms veinlets and impregnations in the ore, and sometimes composes fairly large monomineralic accumulations.

Macroscopically it has a reddish-brown color. Zoning is sometimes observed, caused by the presence of zones of different density and brown coloration.

Spectral analysis of the sphalerite establishes rather high contents of Ag, Cd, Sb; Ga, In, Bi, and Mn are established in small amounts (less than 0.005%).

When sphalerite is etched with $\mathrm{KMnO_4} + \mathrm{H_2SO_4}$ for 30′, the granoblastic structure of the aggregate is revealed. The form of individual grains is isometric or elongated. Grain boundaries are uneven and serrated. In some cases a cataclastic structure of the aggregate appears.

Near the contact with post-ore dikes, recrystallization of sphalerite takes place with the formation of a granoblastic aggregate, which is composed of isometric grains with even, smooth outlines. During recrystallization the emulsion impregnation of chalcopyrite disappears in the sphalerite, but emulsion impregnation of pyrrhotite often appears in it.

Similar recrystallization phenomena are manifested at a distance of up to 60–80 cm from the contact with the dikes. The size of individual grains in the granoblastic aggregate averages 0.2–0.4 mm. Individual grains, as a rule, have fine polysynthetic twins.

In studying the ores it is noted that, with respect to such minerals as pyrite of the first and second generations and scheelite, sphalerite behaves as a later mineral, developing in them along cracks, filling the interstices of the grains of these minerals, and penetrating along the boundaries of individual grains.

Galena, together with the minerals described above, belongs among the most widely distributed minerals. Galena, like sphalerite, forms disseminations in the ores. It not infrequently, together with other sulfides, fills bands parallel to the selvages of the vein. Sometimes galena cements fragments of quartz, creating a breccia-like texture of the ore.

Spectral analysis establishes a rather high content of Ag and Bi in galena. The presence of these elements is apparently due to the presence of fine inclusions of Ag and Bi minerals, which are quite often observed in galena.

When galena is structurally etched with HCl 1 : 1 for 2–3 minutes, the panidiomorphic-granular structure of the aggregate is revealed. The sizes of individual grains do not exceed 0.6 mm.

Galena usually fills cracks and cavities in quartz, and penetrates along cracks and along grain boundaries in pyrite and sphalerite.

Arsenopyrite occurs comparatively rarely in the ores of the Andreevskoye deposit. Two generations of this mineral are distinguished.

The first, earlier generation is closely associated with quartz of the second generation. It sometimes fills cracks in quartz, composing veinlets. Sometimes it replaces inclusions of carbonaceous shales, developing as bands parallel to the selvages of the vein.

Spectral analysis establishes in arsenopyrite an insignificant admixture of Co and Ag.

Arsenopyrite forms coarse grains up to 3 mm in size. The grains are rhombic in shape. It often forms granular aggregates with a panidiomorphic-granular structure. Under the microscope it is clearly observed that arsenopyrite replaces pyrite of the first generation and, in turn, is intersected by veinlets of pyrrhotite of the second generation.

Arsenopyrite of the second generation occurs in considerably smaller amounts. No macroscopically visible segregations of it are encountered. In its development it is closely associated with pyrrhotite. It is observed in it as small grains, 0.005–0.02 mm in size, of rhombic or irregular shape. These grains are usually arranged as clusters, or are drawn out as chains inside, or more rarely along the periphery, of pyrrhotite grains. Some grains are distinctly corroded by pyrrhotite.

The formation of arsenopyrite of the second generation is apparently connected with the contact action of post-ore dikes.

Scheelite occurs comparatively often. It forms separate nests or veinlets in the eastern part of the western ore column. The areas richest in scheelite were noted both on the middle and on the lower levels of the deposit.

In its development scheelite is closely associated with the earliest quartz composing the Anisisko-Nikolaevskaya vein. As already noted, scheelite often fills veinlets. Not infrequently it fills drusy cavities in vein quartz, creating more or less large nests.

Macroscopically, scheelite is represented by a brownish-yellow variety. Spectral analysis establishes in it an insignificant admixture of In.

In polished section scheelite is structurally etched by HF for 3–4 minutes. Etching reveals an extremely unevenly granular structure of the aggregate. The sizes of individual grains range from 0.02 to 3 mm. During

In this case the larger grains are, as it were, immersed in a more fine-grained aggregate. Occasionally a zonal structure is observed in individual scheelite grains. It is characterized by typical growth zoning.

The association of scheelite with the earliest quartz of the pre-sulfide stage of mineralization also determines the spatial separation of scheelite from areas with rich sulfide mineralization. In other words, sulfides occur together with scheelite only very rarely and in insignificant amounts. Sometimes it can be established that scheelite is cut by veinlets of later quartz. Chalcopyrite, sphalerite, and galena are also observed; they penetrate along the boundaries of scheelite grains and along fractures.

Pyrrhotite is a widely distributed mineral of the ores and is observed in considerable quantity during their macroscopic study. Like the other sulfides, pyrrhotite forms nests and veinlets in the ore, cutting the quartz.

Spatially, pyrrhotite in the ores of the Andreevskoye deposit is confined to the exocontact of post-ore dikes. This regularity was first noted by A. M. Novoselov (1939) for a number of Sarala deposits and was confirmed by later observations. A. M. Novoselov believes that pyrrhotite in the ores of the Sarala deposits could have formed: a) by dissociation of pyrite, b) by introduction of iron sulfide from basic magma, and c) by a hydrothermal process during ore formation.

According to our data, pyrrhotite in the Andreevskoye deposit could have formed by both the first and the second methods.

In favor of the first method is the decrease in the amount of pyrite as the contact with the dike is approached, up to its complete disappearance. In favor of the second method of pyrrhotite formation is the presence of pyrrhotite in the dikes, as well as a certain admixture of nickel, established by spectral analysis, which is characteristic of pyrrhotite associated with basic magma.

Spectral analysis reveals an admixture of arsenic in the pyrrhotite, as well as traces of nickel. The arsenic admixture is readily explained by the fine inclusions of second-generation arsenopyrite, which, as noted earlier, occur inside pyrrhotite grains. The traces of nickel are probably due to an isomorphous admixture of this metal to the iron of pyrrhotite.

Under the microscope, the granular structure of the pyrrhotite aggregate is clearly revealed; in monomineralic areas it has a uniformly granular, allotriomorphic-granular structure. The size of individual grains averages 0.3–0.5 mm.

Within the pyrrhotite aggregate, individual, comparatively rare pyrite grains are occasionally encountered, by which the corrosion and replacement of pyrite by pyrrhotite can be established. Often the interstices of pyrrhotite grains are filled by sphalerite or galena, and sometimes by chalcopyrite. Such relationships of these minerals with pyrrhotite are characteristic of parts of the vein located in exocontact with post-ore dikes, i.e., in those parts of the ore body where recrystallization of sulfides took place. With increasing distance from the contact with the dikes, entirely different paragenetic relationships of pyrrhotite with other sulfides are observed; here pyrrhotite fills the interstices of sphalerite grains and often also penetrates it along fractures, i.e., it is later than the unrecrystallized sphalerite aggregate.

Chalcopyrite is observed rather rarely during macroscopic study of the ores, mainly in areas with abundant sulfides, in the form of small, irregularly shaped segregations.

Chalcopyrite is very widely distributed as a fine emulsion-like dissemination in sphalerite, forming small, rounded segregations oriented along crystallographic directions in the sphalerite. But some part of the chalcopyrite occurs in the ores as larger, irregular grains that penetrate along the boundaries of galena and sphalerite grains.

Gray copper ore is represented by tennantite. In the form of segregations visible macroscopically, it occurs very rarely in areas with intense sulfide mineralization. In microscopic study, tennantite is noted comparatively often, usually in the form of small segregations irregular in shape. These grains, as a rule, develop on the boundary of a galena aggregate; sometimes elongated inclusions of gray copper ore are situated along the boundaries of galena grains and, more rarely, sphalerite.

In some cases, penetration of chalcopyrite is observed along the boundaries of grains of gray copper ore.

Gold is the principal useful component in the ore, determining its industrial value.

Two generations of native gold are clearly distinguished in the ores. Gold of the first generation is associated with the quartz–pyrite–arsenopyrite stage of mineralization. It is represented very often by coarse gold disseminated in the quartz of the Annensko-Nikolaevskaya vein. Assay analyses performed show that it is high-grade (fineness 750). In the ores this gold occurs without association with sulfides.

It forms irregular intergrowths, very often penetrating along quartz grains. It is often noted that deposition of the first generation of gold is confined to inclusions of carbonaceous matter in vein quartz. Gold develops on these inclusions by means of evident metasomatism.

Gold of the second generation is associated with the later quartz-sulfide stage of mineralization. It occurs in close association with various sulfides: galena, sphalerite, gray copper ores, chalcopyrite, and others.

Chemical analysis of gold of the second generation shows that it is of lower grade (fineness 650); it contains a considerable amount of impurities of Ag and Cu and other metals. The gold is usually fine, invisible macroscopically. Its distribution is closely connected with the manifestation of sulfide mineralization. The size of individual gold particles does not exceed 0.4 mm and, as a rule, is considerably smaller. A large part of the gold occurs in a finely dispersed state in sulfides. The form of the gold particles is usually rounded, oval. They occur as inclusions and intergrowths most often in galena, tennantite, and chalcopyrite. Sometimes dendrite-like intergrowths of gold were noted in sphalerite.

Pyrargyrite occurs very rarely in sulfide ores, being established only by microscopic study. Its development is closely connected with areas of galena development. It occurs as small inclusions in galena, often situated along the boundaries of grains of the latter. Sometimes pyrargyrite forms small grains located in quartz; very often they are surrounded by a rim of famatinite. The size of individual grains and inclusions of pyrargyrite does not exceed 0.02–0.03 mm.

Famatinite occurs very rarely in the sulfide ores of the Andreevskoye deposit. The development of famatinite grains is confined to pyrargyrite grains, around which it grows as a thin rim.

Native silver occurs very rarely in the ores. It is usually found in the form of rounded, elongated, or wormlike ...

intergrowths in galena. The size of individual intergrowths averages 0.008–0.01 mm. The presence of inclusions of silver and pyrargyrite apparently accounts for the rather high silver content in galena, as determined by spectral analysis.

Marcasite is encountered rarely during microscopic examination. Under the microscope it appears as fine-grained aggregates rimming grains and aggregates of pyrrhotite along their periphery. Not infrequently it penetrates along the boundaries between pyrrhotite grains or along cracks cutting the pyrrhotite.

The formation of marcasite at the expense of pyrrhotite is associated with the oxidation of pyrrhotite in the mine working.

Cuprodescloizite (?) is encountered very rarely. Under the microscope it has low reflectivity. Its color is gray, close to that of sphalerite, but somewhat darker. Its hardness is medium. It is distinctly anisotropic in air. It polarizes in gray tones. A brownish-red or yellowish-red internal reflection is characteristic. The internal reflection is so intense that it sometimes completely masks the anisotropy of the mineral.

Microchemical tests showed the presence of copper and zinc.

In a polished section, cuprodescloizite forms elongated, curved, or worm-like grains up to 0.04 mm in size, occurring in a carbonate-sericite mass. This entire mass, together with the cuprodescloizite, in the form of veinlets cuts earlier mineral associations.

Smithsonite is encountered very rarely in old mine workings, in the form of white coatings or thin crusts covering the surface of sphalerite.

Vein Minerals

Quartz is the principal mineral composing the ore bodies of the Andreevskoye deposit. The amount of quartz in the ore bodies is 90–98%.

In the study of the ores, several generations of quartz of different ages were identified.

Quartz of the first generation is encountered very frequently. It is represented by dark-gray, locally almost black quartz with a characteristic resinous luster.

Under the microscope it shows a coarse-grained structure. The size of individual grains reaches 20–30 mm. The quartz is xenomorphic and prismatic. In transmitted light it is evident that very fine, opaque inclusions up to 0.001 mm in size are disseminated in it; these inclusions are probably carbonaceous or graphitic matter, which gives the quartz its dark color. No ore mineralization is associated with this quartz.

In this form, quartz of the first generation is encountered rarely, usually in those areas that were not affected by later mineralization. Here the dark quartz composes more or less large portions of the Andreevsko-Nikolaevskaya vein.

In the remaining parts of the vein, this dark-gray quartz underwent intense recrystallization with the formation of gray or light-gray quartz. Against the general background, rounded spots of darker, dark-gray quartz with a resinous luster are often preserved; these represent relics left from recrystallization.

Sometimes the formation of small drusy cavities is observed in the quartz; their walls are covered with well-formed prismatic crystals of milky-white quartz up to 1 cm in size.

The central parts of drusy cavities are usually filled with scheelite, to which calcite is sometimes added.

Quartz of the second generation is also encountered very frequently. Together with quartz of the first generation, it takes part in the composition of the Annensko-Nikolaevskaya vein.

Macroscopically it is represented by a light-gray or white variety. The structure of the quartz is usually coarse-grained; not infrequently the quartz is parallel-fibrous. The size of individual grains sometimes reaches 2–3 cm. The quartz has a sharply expressed cloudy extinction. Large crystals are often subject to recrystallization, breaking down into a fine-grained aggregate of elongated grains. In other cases a granoblastic medium- or coarse-grained structure is manifested, with the quartz forming more or less isometric grains, which likewise undergo recrystallization.

Sulfide mineralization is associated with this generation of quartz, represented by pyrite of the first generation, arsenopyrite of the first generation, and gold.

Quartz of the third generation composes mainly the Sulfide vein. Macroscopically it is represented by a coarse- and medium-grained dull-white variety. The size of individual grains reaches 5–6 mm. The form of the grains is most often prismatic. It has cloudy extinction; not infrequently it undergoes recrystallization, breaking down into a fine-grained aggregate.

Quartz of this generation is accompanied by a considerable amount of various sulfides.

Quartz of the fourth generation occurs as a fine-grained aggregate that cuts, in the form of thin veinlets, often together with calcite and sericite, all earlier mineral associations.

Quartz of the fifth generation was encountered in a veinlet of quartz–feldspar composition cutting the Annensko-Nikolaevskaya vein. In this veinlet the quartz, in the form of well-formed crystals, grows on the wall of the fissure, forming incrustation crusts on it. The quartz is water-clear, transparent, and free of inclusions.

Calcite is a rather widely distributed mineral. It is observed in the form of two generations.

Calcite of the first generation is represented by large crystals of light-gray color, which in coloration are very close to quartz of the second generation.

Calcite of the first generation not infrequently fills cavities in quartz of the first generation. Not infrequently it fills drusy cavities in quartz of the first generation, while clearly replacing both quartz and scheelite, which also fills these cavities.

Calcite of the second generation is much more widespread. Macroscopically it is represented by a white, often translucent variety. Not infrequently it forms comparatively large, well-bounded crystals.

Calcite of the second generation, together with quartz of the fourth generation, fills thin veinlets, the thickness of which on average does not exceed 2–3 cm and only in rare cases reaches 15–20 cm.

Such calcite–quartz veins and veinlets cut all earlier mineral associations composing the ores of the Andreevskoye deposit.

Sericite is often encountered as greenish accumulations located along fractures in the quartz of the Sulfide and Annensko-Nikolaevskaya veins. Very often it develops in quartz–calcite veinlets.

Under the microscope it appears as individual small flakes.

and flakes, and also in the form of the finest scaly aggregates filling the spaces between grains of quartz and calcite.

Feldspar (albite?) occurs very rarely in the ore of the Andreevskoye deposit. It was encountered in the form of a thin quartz–feldspar veinlet cutting a quartz vein parallel to its selvages. The appearance of such a veinlet is confined to the exocontact of a thick post-ore gabbro-diabase dike, the formation of which A. Ya. Bulynnikov (1928) connects with the removal of material from a basic magma.

The feldspar has a reddish coloration, caused by the presence of brownish products of decomposition of this mineral.

Under the microscope it is seen that the feldspar occupies the central parts of the veinlet. In the form of tabular or irregular grains it fills the space between idiomorphic crystals of second-generation quartz.

The feldspar is rather intensively destroyed and in transmitted light has a brownish coloration. Indistinct fine polysynthetic twins are sometimes visible in it.

The spaces between feldspar grains are filled with pyrrhotite.

Apatite occurs extremely rarely. It was found in the form of small hexagonal prisms, up to 1 mm in size, of bluish-green color. It is closely associated with second-generation quartz.

Fig. 2. Paragenetic scheme.

Distribution of gold and the causes of formation of columnar mineralization

The distribution of gold in the ores of the Andreevskoye deposit is extremely uneven. Along with enriched areas, there are parts of the vein where the metal content is measured in units or even fractions of a gram per tonne, or which are completely devoid of gold.

The character of the distribution of gold in the ores is clearly seen in Fig. 1, where the outlines of areas enriched in gold are shown on the vertical projection of the ore body.

Here two main types of mineralization are clearly distinguished: bush-like and columnar, which, in general, correspond to two different-age stages of gold deposition.

The first type of mineralization is confined to the upper horizons of the ore body. The gold-enriched areas are small nests and clusters. The gold, as a rule, is visible and of high fineness. This is gold of the first generation.

Such clustered mineralization is characteristic of the Annensko-Nikolaevskaya vein in areas located above the upper boundary of the joint occurrence of both veins.

It has not been possible to establish the cause of the localization of individual ore nests and clusters in the vein, since the upper horizons of the deposit were mined out long ago and the workings are now completely inaccessible for inspection. Archival materials for this part of the deposit have scarcely been preserved.

Columnar mineralization, by contrast, is confined to the lower horizons of the Andreevskoye deposit. The gold-enriched areas have the form of columns, comparatively large in strike length and persistent down dip.

The ore columns are located on the limbs of an arc, being confined to areas where the vein swells. At the deposit two ore columns are clearly distinguished, which may be designated as western and eastern.

In plan, both ore columns are bodies of elongated form, whose lower boundary has not yet been exposed. The ore columns have a distinct easterly dip at an angle of \(35—40^\circ\). Their occurrence fully corresponds to the occurrence of the swollen portions of the vein to which they are confined.

With regard to the causes of the localization of columnar mineralization, it should be noted that it was conditioned by a whole series of factors which, to one degree or another, influenced the position and shape of the ore columns.

In studying the causes of columnar mineralization at the Andreevskoye deposit, first of all, the confinement of the ore columns to the areas of vein swelling is very clearly revealed, whereas the pinches of the vein are devoid of sulfide mineralization and, with respect to gold content, are almost completely barren. But even in the areas of swelling, the concentration of gold is not uniform. The richest areas are confined to the eastern parts of the swellings, which lie below the pinches, if one takes into account their rather gentle easterly dip.

T. M. Kaikova was the first to draw attention to the connection between the ore columns and the vein swellings; according to her data, V. M. Kreiter (1956) considers the columnar mineralization of the Andreevskoye deposit to be ore columns of the first type, confined to areas of opening during relative movement of the fracture blocks. Such a connection of the columnar mineralization with the vein swellings, of course, cannot be denied; it is excellently revealed when the corresponding plans are examined. It should only be added that the appearance of the richest areas in the ore columns in places immediately adjoining the pinches should be explained by the more intense fracturing of the rocks, in comparison with the other parts of the swellings, where crushing during relative movement of the walls was manifested much more weakly. Nevertheless, the factor just noted is not the only, nor even the principal, factor that played a role in the localization of columnar mineralization.

In studying the Andreevskoye deposit it is clearly revealed that the gold content in the ore columns gradually decreases with depth; that is, with depth there is a tendency for the ore columns to pinch out, although the vein shows no signs of pinching out, as—

on the contrary, the average thickness of the vein increases somewhat with depth.

The richest sectors are located in the upper part of the ore shoots, near the upper boundary of the conjoint occurrence of the Annensko-Nikolaevskaya and Sulfide veins. This coincidence is manifested very clearly in the case of the Western ore shoot and somewhat less clearly in the case of the Eastern one.

The influence of this line on the localization of columnar mineralization is still not entirely clear. It is possible that this is connected with the fact that this line of conjoint occurrence of the two veins represents a line of sharp bending of the Sulfide vein along the dip angle.

In addition, one must take into account the development, along the line of conjoint occurrence of the two veins, of considerable splitting of the Annensko-Nikolaevskaya vein and the deposition of sulfides above the line of its conjoint occurrence with the Sulfide vein. This explains the certain mismatch between the contours of the ore shoots and the noted boundary of the conjoint occurrence of the two veins.

Thus, the principal factor determining the position of the ore shoots was the sharp flattening of the Sulfide vein and the associated deposition of ore matter along this boundary. Below this boundary, the intensity of mineralization gradually weakens.

The second factor that played a significant role in the localization of gold mineralization below this line was that, at the time of deposition of the minerals of the quartz-sulfide stage of mineralization, owing to the relative displacement of the walls of the fissure, only slightly opened sectors—i.e., sectors of vein swells—were accessible for the circulation of solutions and deposition of minerals. This also determined the connection of the ore shoots with the sectors of swells.

The richest sectors among the ore shoots are observed where there is a spatial superposition of the cluster mineralization characteristic of the Annensko-Nikolaevskaya vein and the columnar mineralization of the Sulfide vein. Such sectors, as a rule, are small in size and are characterized by the presence of both visible, high-grade gold and finely dispersed gold associated with sulfides.

In conclusion it should be noted that the pinching-out of the known ore shoots in grade noticeably reduces the prospects of the deposit at depth. Nevertheless, the possibility of discovering new ore shoots, owing their appearance to some new structural factors whose character is at present still difficult to judge, is by no means excluded.

REFERENCES

1. Bulynnikov A. Ya.—The Sarala gold-ore district. Izv. Sib. Otd. Geolkom, vol. VII, no. 3, 1928.

2. Kreiter V. M.—Structures of ore fields and deposits. Gosgeoltekhizdat, 1956.

3. Novoselov A. M.—The role of Proterozoic magma in the metamorphism of gold-ore deposits of Sarala. Vestnik ZSGU, No. 3, 1939.

Corrections and Noticed Misprints

In the article by S. A. Stroitelev, “Study of the Crystallization of Epsomite and Mirabilite,” for technical reasons braces have been replaced by square brackets, for example: [100] instead of {100}, etc.