On the Composition and Genesis of the Ores of the Ursk Deposits of Salair

V. K. Cherepnin

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

Introduction

This work sets forth the results of a mineragraphic study of the sulfide ores of the Ursk deposits.

The material that served as the object of the present investigations was collected mainly by the author from drill-hole cores as early as 1953. A very small part of the material from the N.-Ursk deposit was additionally delivered to the author in the spring of 1955.

The mineralogy of the Ursk deposits is not being described in the literature for the first time. Certain general data on the composition of the ores are found in the works of P. M. Lopushinsky (1935) and I. V. Derbikov (1937). This question is treated in greatest detail in the articles of G. P. Bolgov (1934, 1937), which are twenty years old. During this period a large amount of new material has been obtained at the deposits, which has made it possible to approach the solution of general questions of the mineralogy of sulfide ores in a somewhat different way.

Ore Textures

In the ores described, two main textural groups are widely developed: a) massive ores and b) disseminated ores. Naturally, it is not always possible to draw a sharp boundary between these two groups. This is explained by the fact that there is a whole series of intermediate formations belonging to the so-called rich disseminations. We quite conventionally assign to massive sulfide ores those formations that contain no more than 15% gangue material. Both among the massive ores and among the disseminated ores, banded textures are the most widespread. In both cases the banding is due to the alternation of bands of different composition. In massive ores, this pattern is most often created by the alternation of essentially pyritic bands with bands enriched in sphalerite. For the most part this banding is fairly fine (the width of individual bands is on the order of 2–3 mm).

A banded texture caused by the alternation of bands of coarse-grained and fine-grained pyrite is also not infrequently encountered. The boundary between individual bands is, as a rule, sharp. Bands composed of fine-

crystalline variety, usually wider than the coarse-crystalline bands. The latter often have the character of not quite parallel veinlets cutting the fine-crystalline pyrite mass.

In disseminated ores, banding is produced by the alternation of bands of sericite-quartz composition with bands composed of sulfides. The sulfide bands may be monomineralic, more often pyritic, or they may be polymineralic, essentially pyrite-sphalerite.

Genetically, we are inclined to regard the banding described above as relict; that is, it represents the result of successive replacement by ore-bearing solutions of laminated rocks. We see confirmation of this at every step, since the mineralization, following the lamination, literally repeats the entire structure of the host rocks, down to the platy structure (Fig. 1). The facts that small pyrite lenses are enveloped by schistosity do not in the least contradict the proposed interpretation. In our opinion, this only indicates that tectonic activity in the area had not ceased by the period of ore formation, and that later movements also took place, considerably complicating the general textural pattern in individual areas.

Fig. 1. Banded texture of disseminated sulfide ore. 1—bands with dense dissemination of pyrite; 2—sericite-chlorite schist. Natural size.

An exception to the general rule is the banding produced by the alternation of coarse- and fine-grained pyrite. There is a certain peculiarity in the formation of this texture, which will be discussed in describing the mineralogical composition of the ores.

Another very widespread texture is massive texture. It is characteristic of the pyritic portions of massive ores.

For the group of disseminated ores, a homogeneous fabric may also be distinguished. This includes areas with more or less uniform dissemination of pyrite. True, G. P. Bolgov (1937), in explaining the origin of this textural pattern, pointed out that the pyrite here formed during metamorphism at the expense of iron dispersed in the rock. It seems to us that there is no basis for resorting to such an explanation. Knowing that zones of impregnation arise during the first stages of activity of ore-bearing solutions, it is easy to suppose that these solutions, owing to their high activity, could penetrate not only along ready-made pathways,

but also to diffuse into the surrounding rocks. The result of such diffusion may be a uniform pyrite impregnation.

In addition to the textures described above, drusy and crustiform structures are sometimes encountered.

Mineralogical Composition

Among the sulfide ores of the deposits of the Ursk group, the following ore minerals have been recorded: pyrite, sphalerite, chalcopyrite, pale ore, galena, arsenopyrite, argentite, gold, bornite, covellite, chalcocite, and an unknown mineral. Of the vein minerals, the most widespread are quartz, sericite, barite, and calcite.

Pyrite is the predominant ore mineral at the deposits. Its content in massive ores reaches up to 95% of the area of a polished section (Novo-Ursk deposit).

The mineral described occurs in three forms: 1) fine-crystalline pyrite, 2) coarse-crystalline pyrite, 3) pyrite of the impregnation zone.

Fine-crystalline pyrite is the predominant variety among the massive ores. It is usually represented by an allotriomorphic-granular aggregate with individual grains on the order of the first hundredths to thousandths of a millimeter in size. Entire fields or bands in massive ores are composed of this variety. This mineral is manifested in a particularly distinctive way in rich disseminated ores. When observed at low magnification, it is always represented as structureless masses with highly irregular outlines, on the whole approaching rounded forms. Among these forms, aggregates with a radial-radiating structure are occasionally encountered (Fig. 2). This suggests that the indicated variety of pyrite originally represented a colloidal formation and subsequently underwent recrystallization. All the described formations among the disseminated ores are often concentrated in bands.

Fig. 2. Pyrite with a radial-radiating structure. Gray—sphalerite. Magn. 150×

Fig. 3. Veinlet of coarse-crystalline pyrite in fine-crystalline pyrite. Gray—chalcopyrite. Magn. 20×

Coarse-crystalline pyrite develops in the form of patches, bands, or veinlike formations among the first variety. The massive patches of this pyrite are allotriomorphic-granular aggregates with grain sizes from 0.3 to 1.0 mm. Most characteristic are thin, straight, veinlike formations (Fig. 3). Their boundary with the enclosing fine-crystalline pyrite is rather sharp. Atten-

Attention is drawn to the fact that in the sulfur–pyrite ore containing the veinlets described, all later ore and vein minerals are especially readily concentrated within these veinlets, filling the spaces between the large grains of pyrite.

In addition to the forms of occurrence described, coarse-crystalline pyrite is sometimes encountered as isolated grains, 0.3–0.5 mm and up to 5 mm across, scattered within a mass of fine-crystalline pyrite.

By pyrite of the impregnation zone we mean a poor pyrite dissemination developing in the enclosing rocks. Grains of cubic habit have dimensions on the order of tenths of a millimeter. Crystals up to 2–3 mm on an edge are sometimes found. The pyrite described gives a more or less uniform dissemination in the enclosing rock, or is concentrated in chains, small lenses, and veinlike bodies arranged along the schistosity. This pyrite often bears traces of energetic crushing. In some places, however, it is simply smeared along the planes of schistosity. Apparently G. P. Bolgov (1934, 1937) is quite correct in regarding this smearing as the result of young post-ore movements.

The internal structure of pyrite grains is revealed fairly easily by electrolytic etching with hydrochloric acid. In this process, zonal polygons are revealed in the grains. The predominant form of these polygons is the pentagon. Squares occur in subordinate amounts, and sometimes rhombi, probably representing nothing other than diagonal sections of cubic crystals, as well as equilateral triangles with truncated vertices. The latter form may reflect a combination of cube and octahedron. In individual cases the structure of pyrite grains is revealed in the form of almost perfectly regular hexagons. This form most likely represents a section of cubic crystals perpendicular to a third-order axis. As a result of structural etching, patterns similar to those described by S. N. Ivanov (1950) for pyrite deposits of the Urals are often revealed.

Sphalerite is second only to pyrite in abundance. Its average content in polished sections is 11%. However, in individual polished sections it is often the dominant ore mineral.

The mineral described occurs as crosscutting veins, bands, or small inclusions in the mass of pyrite. The dimensions of these inclusions usually do not exceed 0.5–0.6 mm along the long axis. An especially close association of sphalerite with fine-crystalline pyrite is observed. At low magnifications such areas seem to resemble mutual intergrowth of these two minerals. At high magnifications, however, it is clearly visible that there is no intergrowth here, but simply a dense scattering of fine pyrite grains, intensively corroded by sphalerite, to the point of the formation of skeletal forms. The mineral described is very closely associated with galena. Sphalerite is encountered rather often together with chalcopyrite and gray copper ore. In this case they not infrequently jointly compose the inclusions mentioned above in the pyrite aggregate, producing a poikilitic structure of the ore. Much more rarely can an association of sphalerite with arsenopyrite be observed. In every case, however, the latter is distinctly corroded by sphalerite. In places, though very rarely, isolated small inclusions of argentite occur within the mineral described. Among secondary minerals, covellite readily develops after sphalerite. No relationships of sphalerite with gold, bornite, or chalcocite were observed.

All that has been described above characterizes the occurrence of sphalerite in massive-

ores or in rich disseminations. As for the poorer disseminations, here this mineral develops in the form of inclusions arranged in chains along the schistosity of the enclosing rock.

Under these conditions, among the sulfides sphalerite is usually associated only with pyrite. On the other hand, it is very closely associated with barite, developing along the boundaries of grains of the latter (Fig. 4).

Upon structural etching of sphalerite areas, an allotriomorphic aggregate of grains is revealed. The sizes of individuals range from 0.018 to 0.14 mm along the long axis. The sphalerite grains bear no distinct traces of deformation.

Fig. 4. Loop-like structure of replacement of barite (gray) by sphalerite (white). Magn. 45×

Fig. 5. Relationships of sphalerite (3) with chalcopyrite (2) and pyrite (1). Magn. 77×

Chalcopyrite is also a fairly widespread ore mineral. Quantitatively, it is sharply subordinate to the minerals described above. In the overwhelming majority of cases it makes up only a few percent of the area of the polished section. The mineral most often develops among bands or areas of coarsely crystalline pyrite, filling the spaces between its grains and corroding the latter (Fig. 3). Sometimes in such places a rather branched network of chalcopyrite veinlets is formed. In the cases described, chalcopyrite almost always is most closely associated with fahlerz. Here, however, the mineral described quite often is also associated with sphalerite. The true relationships of chalcopyrite and sphalerite can be observed only in structurally etched polished sections. In this case it is clearly visible how chalcopyrite, developing along the boundaries of sphalerite grains, vigorously corrodes the latter (Fig. 5). In addition to the described forms of occurrence, chalcopyrite is also encountered as a decomposition product among bornite (Fig. 6) and in the form of rare isolated inclusions in vein minerals.

Among secondary minerals, covellite is often associated with chalcopyrite, and in only one polished section—chalcocite. No relationships with other ore minerals were observed.

Fahlerz, like chalcopyrite, occurs in almost every polished section, being considerably inferior to the latter quantitatively. The average content of the mineral described in the polished sections is 3.7%.

The closest association of the mineral described is observed with chalcopyrite, together with which it composes small inclusions of the most irregular form in the pyrite aggregate. Upon structural etch-

it is clearly seen that the fahlores develop along the boundaries of chalcopyrite grains, vigorously corroding them (Fig. 7). As was indicated above, the mineral described readily develops also within sphalerite. In this case it forms small worm-like intergrowths and short sinuous veinlets confined to the boundaries of sphalerite grains. In isolated cases the fahlore is very closely associated with galena and argentite; however, it was not possible to establish clear interrelations between these minerals. In one polished section the joint occurrence

Fig. 6. Inclusions of bornite (with a lattice structure of chalcopyrite breakdown) among pyrite. Magn. 77×

Fig. 7. Relations of chalcopyrite (3) with fahlore (2). 1—pyrite. Magn. 150×

of the mineral described with bornite could be observed. This association will be discussed in greater detail in the characterization of the latter. Among the secondary minerals, covellite develops very readily after fahlore. No relationships with arsenopyrite, gold, or chalcosine were observed. In places, areas of fahlore are cut by a rather dense network of small cracks, along which barite develops.

Microchemical investigation showed that the mineral described belongs to the antimony variety of the fahlores.

Galena in the ores described is a rather rare formation. It is most often encountered at the Novo-Ursk deposit. In the ores of the Samoilov deposit, galena was identified in 2 polished sections. At the Beloklyuchevsk deposit this mineral was recorded in only one polished section.

It develops as irregularly shaped inclusions among the more widespread minerals. The size of the inclusions ranges from the first hundredths to 0.2 mm.

Galena is especially closely associated with sphalerite, in which it usually occupies the interstices between the grains of the latter, intensely corroding them. Often the inclusions of galena have a worm-like form. The structure of such areas approaches a subgraphic one.

In two places it was possible to observe cases in which inclusions of fahlore were intersected by thin veinlets of galena. In one polished section a close association of galena with argentite was observed; this will be described in greater detail below.

Sometimes small inclusions of galena occur among chalcopyrite. In this case they are quite clearly confined to the grain boundaries of the latter. Finally, there are rare cases of corrosion of pyrite grains by galena.

No relationships with other primary minerals could be observed. As for secondary minerals, a fine dusting of covellite was observed in places within the mineral described.

Among the vein minerals, galena is at times associated with barite, forming rare inclusions in it. In addition, barite, in the form of extremely thin veinlets, sometimes cuts galena.

Arsenopyrite, contrary to the assertion of G. P. Bolgov (1934), is a fairly widespread mineral in the ores of the Ursk deposits. It is true that it occurs for the most part as isolated grains, scattered either in the enclosing shale or among the pyritic portions of the ore. More rarely it is found among inclusions of the vein mineral, and still more rarely among sphalerite.

The mineral described appears in different conditions in different ways. In those cases where it develops as sporadic disseminations within the enclosing shale, it is characterized by the most regular crystallographic outlines. The crystals of arsenopyrite occurring within the vein mineral look approximately the same. Observations show that the outlines of the crystals most often have a prismatic, rhombic, or wedge-shaped character. However, these forms can in no case be regarded as the result of a change in the habit of the crystals. They are simply the result of different sections. Under the conditions described, the largest individuals are encountered, reaching 2 mm along the long axis. In the enclosing rocks they are almost always oriented according to the schistosity.

As for arsenopyrite developing within the pyritic aggregate, here two varieties of the mineral described can be clearly distinguished. The first variety is represented by isolated grains, on average 0.3–0.4 mm across, scattered in the mass of fine-grained pyrite. In most cases they have regular crystallographic outlines, but almost always are sharply corroded by the surrounding pyrite. The second variety is expressed as very small (thousandths of a millimeter) crystals, usually gathered in clusters. At low magnification such arsenopyrite concentrations have the appearance of a dusting. Observations show that the fine-grained arsenopyrite aggregate tends to develop along the boundaries of pyrite grains. In other places it can be clearly seen how, from the periphery, it replaces pyrite grains, as if overgrowing them in the form of a rim (Fig. 8).

Arsenopyrite occurring among sphalerite has grains 0.1–0.3 mm across, rarely smaller. The outlines of the grains are usually idiomorphic. Often they are very intensely corroded by sphalerite, to the point of forming skeletal structures. No relationships of arsenopyrite with other sulfides were observed.

Large grains of the mineral described bear traces of rather intense crushing. Moreover, along these weakened directions, quartz and barite penetrate into the arsenopyrite crystals.

Argentite (?) was found in only one polished section from the ores of the Samoilov deposit. It develops as inclusions of varied form. The average size of the inclusions is 0.06 mm along the long axis. The color of the mineral is light—grayish-yellowish. Bireflection is not observed. In crossed nicols, in oil, anisotropy is manifested. The change in color ranges from brownish to dark bluish-gray tones. The mineral is soft, softer than galena. After polishing, its surface bears many scratches. Diagnostic etching: HNO₃—turns brown and blackens; HCl—practically has no effect; HgCl₂—turns brown; FeCl₃—turns brown; KOH—has no effect. The negligible size of the inclusions does not permit microchemical tests to be carried out.

The most frequently described mineral is associated with galena. In this case the boundary between the two minerals is always smooth. Somewhat less often argentite occurs in association with fahlerz. The character of the relationships is usually the same as in the preceding case.

Fig. 8. Relationships of pyrite (1) with second-generation arsenopyrite (white). Black—the vein mineral. Magn. 115×

Fig. 9. Paragenesis of sphalerite (1), argentite (4), and gold (5). White—unknown mineral; black—barite; 2—chalcopyrite; 3—fahlerz. Magn. 360×

However, in one place a thin veinlet of the mineral described was encountered, cutting an inclusion of fahlerz. Finally, very rarely the described mineral is found in association with gold and sphalerite (Fig. 9). Relationships with other ore minerals are not observed.

Gold was also found only in the same polished section from which argentite was described. Its largest inclusion, worm-like in outline, has a length of 0.015 mm. In the case described, the gold is closely associated with argentite, forming a veinlet-like body in quartz (Fig. 9). No structural relationships between the two minerals could be observed here. In other places in the same polished section, isolated droplet-like inclusions of gold up to 0.0019 mm along the long axis were found among the argentite. No other associations of gold were observed.

Bornite was encountered in two samples from the Novo-Ursk deposit and in one sample from the Samoilov deposit. Its quantity in the polished sections rarely exceeds 1–2%. By the character of its occurrence, two varieties of the described mineral may be distinguished.

The first variety occurs as inclusions of various shapes and small areas among pyrite, sphalerite, and galena. The average sizes of these inclusions range from 0.36 to 0.61 mm. In the first two cases, bornite inclusions are situated in the interstices between the grains of the enclosing minerals, distinctly separating them. In the last case, because of the very small size of the inclusions of both minerals, clear relationships between bornite and galena could not be observed.

Most of the mentioned bornite inclusions bear a lattice structure of chalcopyrite exsolution (Fig. 6). In addition to the fact that bornite contains chalcopyrite in the form of exsolution products, these two minerals sometimes develop together, composing the same inclusions. Under these same conditions, fahlerz also often associates with bornite, appearing

in the form of vein-like segregations cutting both bornite and chalcopyrite. Covellite develops very readily after bornite, and in places also chalcocite.

The second variety of the mineral being described was encountered among covellite developing as crusts on the parting planes of collomorph ore (Novo-Ursk deposit).

None of the inclusions of the described variety of bornite contains chalcopyrite breakdown products. Here the bornite is very vigorously replaced by covellite. In all probability, unlike the first variety, this bornite is already an exogenous formation.

Covellite occurs fairly often in the ores described, but almost always in negligible amounts. It develops not only after copper-bearing minerals (chalcopyrite, tetrahedrite, bornite), but also after sphalerite and galena. Most often, perhaps, it is found among chalcopyrite. In this case covellite forms thin rims along the periphery of chalcopyrite inclusions. These rims arise more readily when the chalcopyrite occurs among non-ore material. In addition to rims, rare thin covellite veinlets or irregularly shaped patches composed of a needle-like aggregate arise in chalcopyrite. Tetrahedrite is replaced by covellite more intensively. Here reticulate, loop-shaped, and even cementation replacement structures often develop. In sphalerite covellite is observed more rarely, but when it occurs, it is present in much larger amounts than in chalcopyrite. The replacement of bornite proceeds especially vigorously. In areas with a breakdown structure, covellite first appears along the boundary between the chalcopyrite lamellae and the bornite; then the replacement process develops toward the bornite. Ultimately, the chalcopyrite lattice proves to be entirely enclosed in the covellite mass. Covellite develops much less readily after galena. Here it sometimes forms a very fine dissemination and thin isolated veinlets. Overall, the study of polished sections showed that the mineral described, even at its maximum development, scarcely constitutes 2% of the area of the section.

As an exception, the following fact may be noted: examination of several unpolished sections from a mass of massive ore (borehole 51, depth 150 m) showed a complete absence of secondary sulfides. Macroscopically, however, rather abundant crusts of bluish-black material were noted on the parting surfaces of this ore. In a polished section prepared from this material, it was established that the latter consists of covellite with a metacolloidal structure, among which relics of bornite occur.

Chalcocite is a very sparsely distributed mineral in the ores described. It was found in only a few polished sections and in negligible amounts. All cases of its occurrence are confined to chalcopyrite. Here it develops either as independent thread-like veinlets, or is present in veinlets composed of covellite, concentrating in the near-selvage parts of the latter.

Unknown mineral. In one case, among argentite, three very small inclusions of some more yellow mineral, possessing a somewhat higher hardness, were encountered (Fig. 9).

A characteristic feature of this mineral is the presence of distinct bireflectance, which becomes sharp in oil. At the same time, lamellar twins are very clearly manifested. It is very difficult to form a definite idea of the relation of the mineral described to one or another reagent, owing to the fineness of its inclusions and the considerable chemical activity of the surrounding argentite. It is only striking that this

the mineral disappears after etching with nitric acid, and it cannot be revealed afterward by polishing.

The material at our disposal does not make it possible to determine the mineral precisely. However, the presence of strong reflection pleochroism, lamellar twins, and also the fact that the mineral disappears after the action of nitric acid compel us to suppose that we are dealing with some telluride of silver or, less probably, of gold. The paragenesis of the mineral described also speaks in favor of this.

As for the vein minerals, as indicated above, the most widespread among them are: quartz of two varieties (fine metasomatic quartz and stalk-like quartz growing on the faces of pyrite and arsenopyrite crystals), sericite, barite, and calcite. Being sharply limited by the scope of the article, we are unable to give their description here.

Paragenesis and Order of Deposition

Study of the mineral complex described has shown that the following five paragenetic associations may be distinguished in its composition: 1) pyrite–arsenopyrite; 2) sphalerite–barite; 3) chalcopyrite–bornite; 4) galena–argentite; 5) an association of secondary sulfides.

The first association includes two varieties of pyrite and arsenopyrite. Investigation of extensive material carried out recently has shown that, apparently, it is more correct to regard both varieties of pyrite as independent generations separated by a deformation break.

As for the pyrite of the impregnation zone, we do not consider it possible to assign it to an independent generation that arose at the expense of the iron present in the rocks themselves. We are convinced that this pyrite represents a normal hydrothermal formation, apparently contemporaneous with the first—fine-crystalline—variety.

In arsenopyrite we are also inclined to distinguish two generations. The first should include all the coarser-crystalline arsenopyrite developed both in the enclosing rocks and in the ore body itself. Fine-crystalline arsenopyrite, developing in the form of aggregates along the boundary of pyrite grains of the first generation and replacing them from the periphery (Fig. 8), belongs to the second generation. Unfortunately, the relationships of this arsenopyrite with coarse-crystalline pyrite were not observed. Therefore we only quite provisionally regard the second generation as a later formation than the first.

The sphalerite–barite association is fairly widely distributed in the ores studied. It is a distinctly later formation in relation to the association described above. Of this pair, barite is the earliest. Sphalerite, in its development, is usually confined to the boundaries of its grains, often forming a mesh-like replacement structure (Fig. 4).

The chalcopyrite–bornite association, in addition to the minerals indicated, also includes pale ore. The earliest member here is chalcopyrite. At the end of the period of chalcopyrite deposition, apparently, deposition of primary bornite occurred, containing the decomposition structure of chalcopyrite. Pale ore is a distinctly later formation than chalcopyrite (Fig. 7). A case was also observed in which primary bornite was cut by a veinlet of pale ore.

The galena–argentite association, apparently, is the most

a young member of the entire paragenetic series of primary ore mineralization.

From the characterization of galena given above, we see that it is a distinctly later formation than sphalerite and chalcopyrite, and also, probably, than the pale ore. In this same association we include the gold that occurs together with it and the unknown mineral described above. The material at our disposal did not make it possible to reveal the true picture of their age relationships. There is no doubt that all of them are very close in time of formation and, for the time being, may be regarded without detriment as contemporaneous.

Of the complex of secondary sulfides, the earliest is bornite; this is followed by chalcocite and, finally, by covellite.

As for the accompanying non-ore minerals, for example, we distinguish both varieties of quartz as independent generations. The fine-crystalline quartz of the first generation precedes ore deposition, whereas the quartz of the second generation follows pyrite and arsenopyrite (Fig. 10).

Fig. 10. Relationships of quartz (1), sericite (2), and pyrite (black). Enlarged 70×

The main mass of sericite apparently arose simultaneously with the quartz of the first generation, through the decomposition of the feldspars of the enclosing rocks under the action of hydrothermal solutions. However, a considerable part of it undoubtedly formed later than pyrite and arsenopyrite. This is indicated by the growth of sericite scales on the faces of crystals of the minerals mentioned. In addition, it is possible that there is still later sericite, confined to zones of young movements.

The main mass of barite formed between the pyrite–arsenopyrite association and sphalerite. An insignificant amount of it arose somewhere near the end of the period of ore deposition, after galena. The possibility is not excluded that, throughout the interval of time from sphalerite to galena, deposition of a small amount of barite was taking place.

Calcite is the latest member of all the primary mineralization of the Ursk deposits, forming cross-cutting veinlets in zones of disseminated ore.

In general, the sequence of mineral deposition in the ores studied is illustrated by the following scheme (Fig. 11).

Fig. 11. Scheme of the sequence of mineral formation.

Labels in the figure: Minerals; Epochs of mineral formation; hypogene; I stage; II stage; hypergene. Minerals listed: pyrite; sericite; pyrrhotite; arsenopyrite; barite; sphalerite; chalcopyrite; bornite; fahlore; galena; argentite; gold; calcite; chalcosine; covellite.

CONCLUSIONS

The investigations carried out on the sulfide ores of the Ursk deposits permit the following conclusions to be drawn.

1. The banded textures most widespread in the ores are relict textures that arose through the successive replacement of disseminated rocks by ore-bearing solutions. An exception is the banded texture produced by the alternation of bands of coarse- and fine-grained pyrite. Here the former represents a later generation, confined to weakened directions that developed within the mass of the latter.

2. The constantly observed gradual transitions from massive ores to disseminated ones do not permit us, following G. P. Bolgov, to accept different points of view on the genesis of the main mass of the ores and of the rare pyrite dissemination in the enclosing rocks.

3. In mineralogical composition, the deposits studied belong to the pyritic type and are very similar to analogous deposits of the Urals (Amiraslanov, 1937). In addition to the ore minerals described by previous investigators, we were able to establish the presence of hypogene bornite, argentite and telluride, gold or silver.

4. The deposition of ore matter during the formation of the deposits of the group took place from true solutions. At certain moments, in various places, owing to a sharp increase in concentration and an increase in the number of crystallization centers, colloidal systems arose with gel structures typical of them.

1. Processes of secondary sulfide enrichment in the ores described are very weakly developed. By contrast, oxidation processes manifested themselves very intensively, leading to the formation of an entire complex of new mineral formations.

REFERENCES

Amiraslanov A. A.—Mineralogical characteristics of pyrite deposits of the Urals and secondary processes in them. ONTI NKTP USSR, 1937.

Bolgov G. P.—Mineralogical investigations of polymetallic ores of the Salair deposits. Materials on the Geology of the WSK, issue 15, 1934.

Bolgov G. P.—Sulfides of Salair. The Ursk group of polymetallic deposits. Proceedings of the Tomsk Industrial Institute, vol. 58, issue III, 1937.

Derbikov I. V.—The Novo-Ursk polymetallic deposit of Salair. Materials on the Geology of the WSK, issue 42, 1937.

Ivanov S. N.—Experience in studying the geology and mineralogy of pyrite deposits. Transactions of the Mining-Geological Institute, Ufa Branch of the Academy of Sciences, issue 8, 1945.

Ivanov S. N.—Study of pyrite growth zones in the pyrite deposits of the Urals. Notes of the All-Union Mineralogical Society, No. 2, 1950.

Corrections and Noted Misprints

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