ON THE ROLE OF HOST ROCKS IN THE FORMATION OF VEIN DEPOSITS: THE CASE OF THE SARALINSKY ORE FIELD

V. I. BAZHENOV

(Presented by the scientific seminar of the Department of Mineralogy, Petrography, and Geology and Exploration of Mineral Deposits).

On the history of the question

As early as the middle of the last century, during the mining of deposits of various metals, it was observed that ore bodies, passing from one rock into another, change their composition and the content of the useful component. Along with this, changes in their form and thickness were also often noted. Therefore, for various deposits some rocks were regarded as favorable, whereas others were regarded as unfavorable. These facts served, to a certain extent, as evidence for the lateral-secretion theory.

The influence of host rocks on the formation of vein deposits was noted in the works of a whole series of authors. Thus, A. Grodek [36], K. I. Bogdanovich [10], F. Beischlag, P. Krusch, J. H. L. Vogt [32], V. A. Obruchev [20] cite a considerable number of examples of deposits in which the chemical action of the host rocks, which acted as precipitants of metals from ore-bearing solutions, is manifested quite clearly. It is pointed out that bituminous rocks often play the role of precipitants. Therefore, in the Annaberg, Marienberg, and other deposits, areas enriched in metals are confined to places where veins intersect rocks rich in carbonaceous matter [32]. In a number of deposits of the Ore Mountains, rich cobalt-nickel mineralization is localized in places where veins intersect horizons of bituminous cupriferous shales. But along with the chemical influence, the authors listed note that in some cases the host rocks may also exert a galvanic effect. As an example, the Kongsberg deposit is usually cited, where rich silver mineralization is confined to the intersection of the veins with fahlbands. In a number of cases, the influence of the physico-mechanical properties of rocks is established, determining changes in the thickness of ore bodies, their branching, and pinching out.

E. J. Dunn [34], in his survey work on the geology of gold-ore deposits of South Africa, Australia, and New Zealand, gives a whole series of examples of the chemical influence of host rocks on the deposition of gold. In this, the role of “indicators”—favorable rocks—is often played by various bituminous rocks, which act as reducers of gold from solutions. In some cases, other types of host rocks serve as “indicators”: pre-ore dikes, sandstones, etc.

The association of rich gold mineralization with places where horizons of carbonaceous-argillaceous shales are intersected in the deposits of southeastern Australia is also noted in the works of F. H. Stillwell [40, 41] and N. R. Junner [37].

But in the works of geologists of the American school, the question of the role of host rocks in the process of ore formation was developed somewhat differently. On the basis of the study of ore deposits of the western states of the USA, which possess many specific features of genesis, American geologists came to the conclusion that structures play the leading role in the process of ore formation. And thanks to the numerous valuable works of V. Lindgren, C. D. Hulin, and other representatives of the American geological school, this trend was successfully developed in the form of the doctrine of structural control and became widely disseminated in many countries. At the same time, it was usually pointed out that host rocks exert a definite influence on ore-forming processes, but in this case the leading role is played not by the chemical but by the physico-mechanical properties of the rocks. As an example one may cite the views of W. H. Newhouse [39]. In his survey work there is a list of deposits in which a dependence of mineralization on the composition of the host rocks is established, with rocks differing in composition and physico-mechanical properties proving favorable. He considers the cause of such influence to be the different response of rocks to mechanical stresses, their unequal ability to fracture and to produce well-sustained cracks, etc. Therefore, in the author’s opinion, the more favorable rocks are most often hard, brittle varieties, whereas soft, plastic rocks, as a rule, do not produce well-sustained large fractures and therefore are regarded as unfavorable. Entirely analogous views on the role of host rocks were expressed by A. M. Bateman [13], who believed that earlier ideas about the chemical influence of rocks were exaggerated, and also by a number of researchers who studied the ore deposits of Canada [35, 36]. Only in extremely rare cases are examples of chemical precipitation of metals from gold-bearing solutions noted [33].

Such mechanical views of geologists of the American school exerted a great influence on the methodology of studying hydrothermal deposits and on the development of the theoretical foundations of the doctrine of mineral deposits in all countries in the first half of the present century. In analyzing the regularities of distribution of endogenous mineralization, attention was paid only to structural control. At the same time, the question of the chemical influence of host rocks on endogenous ore formation ceased to be considered, and its treatment disappeared from the pages of textbooks and manuals for courses on mineral deposits published in the last 20–25 years in our country [9, 14, 26].

Only in 1949 did K. N. Ozerov [21] again raise the question of the influence of host rocks. He cited a number of examples of deposits in which this phenomenon is clearly established. On the basis of statistical processing of the data, he came to the conclusion that the most...

less favorable for the localization of epigenetic deposits of hydrothermal origin are acidic igneous rocks, as well as arkosic sandstones and feldspathic quartzites.

Considerably more attention began to be paid to the question of the influence of host rocks in Soviet literature from the beginning of the 1950s. P. M. Tatarinov [27] believes that the development of this question proceeds in three main directions, which reflect the diverse influence of wall rocks: a) influence on the deposition of matter, b) influence of the host rocks on the form of ore bodies and the conditions of their occurrence, c) influence of host rocks on the composition of ore-bearing solutions.

At various times, cases of lithological control of mineralization for deposits of different postmagmatic ore formations have been noted in the literature. Characteristic examples were given for vein deposits of the quartz–scheelite formation [24, 30]. In both cases, rich scheelite mineralization is confined to rocks rich in lime: in the first case—to amphibolites, in the second—to marbles. In both cases it is recognized that the formation of scheelite-rich ores is caused by a chemical reaction between tungsten-bearing solutions and the wall rocks, rocks rich in lime.

The influence of host rocks on the localization of rich uranium ores in vein deposits was noted by G. A. Pelymskii [22], and by E. M. Yanishevsky and V. M. Konstantinov [31]. Among the rocks favorable for uranium deposition they include (in order of favorability): skarns, banded amphibolites, graphitized schists, etc.

N. G. Sergiev and M. V. Tashninina [25] pointed out the important role of carbonaceous-clayey schists in the localization of a number of polymetallic deposits of Rudny Altai. M. G. Khisamutdinov [29] gave a number of examples from among the deposits of Southern Altai. They occur both in carbonate and in silicate rocks and, depending on this, have different ore-body forms and differ in the mineral composition of the ores. A. G. Betekhtin [8] notes that lithological control of mineralization is manifested comparatively often. In this, the interaction of solutions with the wall rocks plays an important role. The absence of lithological control, in his opinion, is characteristic of deposits of the near-surface facies, because colloidal solutions play a noticeable role in their formation. Along with chemical influence, the physicomechanical properties of rocks (their porosity, permeability, etc.) also play a noticeable role.

A whole series of examples of the influence of host rocks on the localization of enriched zones and the form of ore bodies is given in the works of A. S. Velikii [15] and F. I. Wolfson [16].

Cases are sometimes noted of changes in the composition of vein minerals where quartz veins pass from one kind of rock into another [23].

Another direction in the development of this question is found in the works of Kh. M. Abdullaev and a number of other authors [1, 2, 3, 17]. In their opinion, postmagmatic solutions are enriched in those components that were assimilated by granitoid magma. Thus, assimilation of wall rocks determines the metallogenic specialization of granitoid magmas. But at present this question has not been developed sufficiently fully; a whole series of propositions remains debatable.

Brief Geological Characterization of the Saralinsky Ore Field

The Saralinsky ore field is located in the axial part of the Kuznetsk Alatau Range, in the upper reaches of the Srednyaya Sarala River. It is one of the oldest gold-bearing districts of Western Siberia.

The main features of the geological structure of the ore field have been covered in a number of published works [7, 11, 12]. Therefore, here we shall confine ourselves to a brief account of this question.

The basis of the geological structure of the Saralinsky ore field is a thick effusive-sedimentary sequence, which has a complex structure (Fig. 1). At its base occur various sedimentary rocks:

Fig. 1. Diagram of the geological structure of the Saralinsky ore field (dikes are not shown).
1 — bituminous limestones; 2 — quartz-sericite, chlorite-sericite, and other schists; 3 — clayey, carbonate-clayey, and carbonaceous-clayey schists, sandstones, intermediate effusives; 4 — basic effusives and their tuffs; 5 — clayey and carbonaceous-clayey schists, sandstones with limestone lenses; 6 — felsites, felsite-porphyries and their tuffs, limestones, carbonaceous-clayey schists; 7 — gabbro; 8 — gabbro-diorites; 9 — diorites; 10 — plagiogranites; 11 — faults; 12 — quartz veins. Quartz veins: 1 — Andreevskaya, 2 — Kaskadnaya, 3 — Vstrechnaya, 4 — Ivanovskaya.

clayey, carbonate-clayey, carbonaceous-clayey schists, sandstones, conglomerates with limestone lenses and individual flows of effusives of intermediate composition and their tuffs. This essentially schistose sequence is overlain by a comparatively thick sequence composed predominantly of basic effusives (diabases, diabase porphyrites, mandelsteins) with thin interbeds of tuffaceous and sedimentary rocks. Higher in the section lies a predominantly schistose sequence consisting of clayey, carbonaceous-clayey, and carbonate-clayey schists and sandstones with thin lenses of carbonate rocks. The uppermost part of the section is made up of a sequence of acid effusives (felsites and felsite-porphyries) and their tuffs. In its very upper parts there are po-

are various types of sedimentary rocks: limestones, clayey and carbonaceous-clayey shales, etc.

The age of the rocks of the effusive-sedimentary sequence, according to various investigators, is considered debatable: Cambrian or Precambrian.

From the east, adjoining the area of distribution of the rocks of the effusive-sedimentary sequence along a tectonic contact, there is a belt of bituminous limestones containing numerous remains of algal colonies of Sinian age.

The rocks of the effusive-sedimentary sequence within the ore field form an anticlinal fold with an axis plunging to the north. In form it is asymmetric. Its limbs are complicated by additional folding. The geological structure of the ore field is also complicated by numerous disjunctive disturbances. Among them, by spatial orientation, three principal groups are clearly distinguished: submeridional, sublatitudinal, and diagonal.

The first group of tectonic disturbances includes the oldest disturbances, which break the ore field into a series of tectonic blocks elongated in the meridional direction. Their age is pre-ore. The amplitude of displacement along these disturbances reaches several hundred meters. Disjunctive disturbances of sublatitudinal and diagonal trends occur frequently in different parts of the ore field. As a rule, they are characterized by an insignificant displacement amplitude and therefore are recorded only on large-scale plans. Their age is pre-ore, partly post-ore.

The rocks of the effusive-sedimentary sequence are cut by small intrusive bodies having a varied petrographic composition. Among them are distinguished rocks of the gabbro, gabbro-diorite, diorite, granodiorite, and plagiogranite types. The largest intrusive body (the Ararat intrusion) is situated in the northern part of the ore field. All intrusive bodies exposed in the ore field belong to the Martaiga magmatic complex, widely developed in the Kuznetsk Alatau, with which the gold mineralization of the Sarala ore field is genetically associated.

A characteristic feature of the ore field is the wide development within it of vein rocks. Among them, dikes of acidic and basic composition are distinguished. The former have a limited distribution. In composition they are most often represented by albitites. The strike of the dikes is latitudinal. They are usually subjected to noticeable hydrothermal alteration. Therefore their age is undoubtedly pre-ore.

Dikes of basic composition have the widest distribution within the ore field. According to V. M. Lyakhnitsky, they make up on average about 35% of the area. In places, however, their abundance reaches 45–50%. The thickness of the dikes varies within wide limits: from several centimeters to 60–70 m. Their strike is submeridional, and their dip is steep to the west or to the east. In petrographic composition the basic dikes correspond to diabases, diabase porphyrites, gabbro-diabases, etc. On the basis of the criterion of intersection of mineral formations of different ages, six successive generations of dikes are distinguished here, differing from one another in petrographic composition and in textural-structural features. There are also some differences in chemical composition, with the later generations being characterized by a somewhat elevated alkali content.

Quartz veins are cut by dikes of basic composition. Nevertheless, the dikes of the first two generations, which include

the largest and most numerous dikes are undoubtedly pre-ore [4]. Dikes of later generations are post-ore or intra-ore.

Features of the Distribution of Quartz Veins

The only genetic type of gold mineralization in the Saralinsky ore field is gold-bearing quartz veins. The total number of quartz veins known at present is more than 200. They are confined to various fracture systems in the rocks. With respect to their orientation relative to the bedding of the host rocks, two types can be distinguished among the quartz veins: 1) bedding-parallel veins and 2) crosscutting veins. The former occur parallel to the bedding of the host rocks, whereas the latter are confined to various systems of normally and obliquely crosscutting fracturing.

Within the area of the ore field the quartz veins are distributed extremely unevenly. Some areas are characterized by the presence of a large number of quartz veins, whereas others contain practically none at all. Such an uneven distribution cannot be explained by unequal degrees of study or by unequal accessibility of the various areas. Analysis of the distribution of quartz veins permits one to state that this phenomenon is due, on the one hand, to the unequal lithological composition of individual areas of the ore field and, on the other, to the peculiarities of their geological structure.

Thus, it is established that more than 70% of all veins known at present are confined to the belt of distribution of basic effusives (Fig. 1), which in plan has a horseshoe-like shape, repeating the outlines of the closure of an anticlinal fold. In individual areas this belt is literally saturated with a large number of quartz veins. Almost exclusively crosscutting veins, confined to various fracture systems, are distributed here. Bedding-parallel veins are encountered extremely rarely.

Less favorable for the localization of quartz veins are thick, essentially schistose strata. No more than 20–22% of the known veins are situated in them. It is important to emphasize that these strata are especially characterized by the occurrence of bedding-parallel veins, whereas crosscutting veins are almost unknown.

Still less favorable for the localization of quartz veins are areas composed of acid effusives and their tuffs. In them only isolated veins are known (no more than 2–3% of their total number).

The least favorable for the formation of quartz veins in the Saralinsky ore field proved to be thick horizons and strata of carbonate rocks. Quartz veins are completely unknown in them.

A characteristic feature of the ore field, in comparison with other gold-ore fields of Khakassia and the Mariinsk taiga, is the extremely weak saturation of the intrusive rocks of the Martaigin magmatic complex with quartz veins, with which the gold mineralization is genetically associated. Thin, isolated quartz veins occur here only in the endocontact of the intrusion.

Thus, the lithological composition exerts a distinct influence on the spatial distribution of the various types of quartz veins. The reason for such an influence is apparently explained by differences in the physico-mechanical properties of the rocks. The most favorable for the formation of quartz veins were the most brittle, hard rocks—basic effusives. In them broad, extended, persistent fractures could develop, filled with crushed and re-

a crumpled material that facilitated the processes of metasomatism. On the other hand, the thick schist horizons were unfavorable for the formation of extended fractures. Tectonic stresses in such soft and plastic rocks were relieved through partial squeezing-out and flow of these rocks, through their boudinage. Therefore they were considerably less favorable for the localization in them of crosscutting quartz veins. This is confirmed by the fact that some thick and persistent quartz veins of the ore field (Ivanovskaya, Shchegolevskaya, Sentyabrskaya, and some others), occurring among basic effusives, upon entering thick schist horizons branch into a multitude of small quartz veinlets, each of which soon pinches out. By contrast, the development of bedding veins is extremely characteristic of schist sequences. They are usually confined to the planes of interstratal movements that passed along the boundaries of rocks with different physico-mechanical properties.

As was noted, limestones proved to be the least favorable rocks in the ore field. The reason for the absence of quartz veins in them, too, apparently lies in the difference between the physico-mechanical properties of silicate and carbonate rocks. In the latter, the formation of any relatively large, gaping fractures is impeded by the ability of the rocks to recrystallize and heal fractures. Some veins (for example, Veselaya), even when entering comparatively thin limestone horizons, pinch out very quickly; and along their continuation only a band of recrystallized limestone can be traced.

It is somewhat more difficult to explain the weaker development of quartz veins in the intrusive rocks of the Martaitinsky complex. Probably it is likewise due to the difference in the physico-mechanical properties of the intrusive rocks and the rocks of the effusive-sedimentary sequence at the time of ore formation. The latter, owing to their greater fracturing and dislocation, proved to be a more favorable medium for the localization of quartz veins than the massive, weakly fractured intrusive rocks.

Observations made in various parts of the ore field make it possible to say that pre-ore dikes played a significant role in the localization of quartz veins. Their role is especially great in the localization of bedding quartz veins. Most of them (the Andreevskaya, Kaskadnaya, Nenastnaya, and other veins) are confined to the hanging wall of sills or gently dipping dikes of acidic and intermediate composition. As a detailed study of these veins shows, their formation occurred mainly through selective metasomatism of the crushed mass of the dikes. At the same time it is established that the morphology of such veins (their extent, thickness, etc.) is directly dependent on the morphological features of the dike, as well as on the degree of its crushing, the thickness of the zone of crushed rocks, i.e., in other words, on the tectonic preparedness of the dike. Those dikes in which the processes of crushing were weakly manifested, even with intense hydrothermal alteration, bear only insignificant silicification in the form of veinlets and irregular spots of white barren quartz. In the Kaskadnoye deposit, the confinement of swells of the quartz vein to those parts of the vein fracture that lie in contact with a gently dipping dike is clearly evident (Fig. 2). Where the dike pinches out, the vein pinches out simultaneously as well. Segments of the vein fracture occurring among schists contain only thin quartz veinlets that do not carry commercial mineralization.

The role of dikes in the localization of crosscutting veins has been studied less well, because the workings driven along such veins are at present inaccessible for inspection. But in some cases there is noted an associ—

Fig. 2. Projection of the Kaskadnaya vein onto the horizontal plane. Scale: 0–250 m.

1 — outcrop of the vein at the ground surface; 2 — areas of distribution of porphyrite sills in the footwall of the vein; 3 — pinches of the vein; 4 — swellings of the vein; 5 — basic dikes; 6 — fault disturbances; 7 — mine workings; 8 — elements of the vein attitude.

the confinement of quartz veins to low-thickness pre-ore dikes (the Ivanovskaya and Yubileinaya veins), which thus evidently played the role of an ore-controlling factor.

Along with the noted lithological control in the distribution of quartz veins in strata of differing lithological composition, within the ore field there is a clear confinement of clusters of quartz veins to the crests of anticlinal and subsidiary synclinal folds. These parts of the folded structures proved to be the most fractured and, because of this, the most favorable for the localization of quartz veins. Probably the confinement of certain clusters of quartz veins to areas adjoining the zones of some major tectonic disturbances is connected with the same cause.

Brief characterization of the process of ore formation. Distribution of gold in the veins and the causes of the formation of ore shoots

Ore formation was a complex process, repeatedly interrupted by tectonic movements. Therefore, on the basis of the criterion of crosscutting relations among mineral associations of different ages in the ores of the Saralinsk deposits, it is customary to distinguish four successive stages of mineralization: 1) quartz-scheelite, 2) quartz-pyrite-arsenopyrite, 3) quartz-polymetallic, and 4) quartz-calcite.

With the first of these, the quartz-scheelite stage of mineralization, is associated the formation of gray and dark-gray, locally black quartz, calcite, scheelite, and apatite. This mineral association is rather widespread and is known in many quartz veins of the ore field.

The mineral associations of the second, quartz-pyrite-arsenopyrite stage of mineralization are the most widespread. They are known in practically all quartz veins of the ore field. This stage is associated with the deposition of light-gray to milky-white coarse-grained quartz, albite, ankerite, pyrite, arsenopyrite, a small amount of chalcopyrite, and also native gold, which is distinguished by a comparatively high fineness (750–780).

The mineral associations of the quartz-polymetallic stage of mineralization are represented by white or light-gray quartz containing pyrite, sphalerite, galena, chalcopyrite, fahlores, gold, silver, and other minerals. The gold of this stage of mineralization is usually fine and is paragenetically closely associated with sulfides, forming inclusions in them up to several tenths of a millimeter in size. In comparison with the earlier gold, it is of lower fineness (600–650). The distribution of the mineral associations of the stage of mineralization described is less extensive than that of the preceding one. They are most widely developed in a number of bedded veins occurring in the arch part of the anticlinal fold (the Andreevskaya, Kaskadnaya, Vstrechnaya, and other veins), and also in some crosscutting veins (Ivanovskaya, Shchegolevskaya, and some others).

The quartz-calcite stage of mineralization in the Saralinsk ore field manifested itself as the final stage of mineralization. It is represented by quartz-calcite veins and veinlets composed of well-bounded crystals of water-clear quartz and a granular aggregate of white calcite. In some parts of the veins they contain open cavities, the walls of which are coated with strongly elongated crystals of calcite of scalenohedral habit. Along with quartz and calcite, such veins contain epidote, actinolite, zeolites, chlorites, and, in rare cases, pyrite, sphalerite, and galena. The mineral associations of this stage of mineralization, in one quantity or another, are distributed in practically all veins.

Mineral associations of different ages in ore bodies are usually isolated from one another, forming independent bodies which, in mining practice, have been termed veins or bands. Thus, for example, in the Andreevskoe deposit the Annensko-Nikolaevskaya and Sulfidnaya veins are distinguished, and in the Kaskadnaya deposit—the Hanging and Footwall bands. They are composed of mineral associations corresponding, respectively, to the quartz–pyrite–arsenopyrite and quartz–polymetallic stages of mineralization. Spatial superposition of mineral associations of different ages is observed less often.

As A. M. Khazagarov notes [28], the localization of individual mineral associations is confined to those parts of vein fissures which, as a result of tectonic movements, became slightly opened. The extent of such sectors is determined by the morphological features of the ore-hosting fissures.

The individual minerals included in one or another mineral association are distributed unevenly. In this connection, the association of certain minerals with definite types of enclosing rocks attracts attention. This association is clearly established for a number of non-ore minerals.

As the mineralogical study of the ores shows, albite occurs only in those quartz veins or vein sectors that lie in contact with effusives of basic composition. In these sectors albite often forms large accumulations. Quartz veins, or their sectors, lying in contact with other types of rocks do not contain albite.

A study of the mineralogy of the Bratskaya, Marshalovskaya, Novo-Tumannaya, Obruchevskaya, and Kaskadnaya veins shows a very close confinement of various chlorites, zeolites, prehnite, actinolite, and epidote to those sectors of carbonate veins that lie in contact with pre-ore dikes of basic composition. With increasing distance from them, these minerals gradually disappear, and the veins become purely carbonate.

Such a relationship between the mineralogical composition of quartz veins and the lithological composition of the wall rocks must undoubtedly be explained as the result of their chemical influence on the ore-bearing hydrothermal solutions. The confinement of albite to alumina-rich rocks, and of chlorite, epidote, and actinolite to pre-ore dikes characterized by a rather high content of iron and magnesium, makes it possible to say that in the cases described the wall rocks served as a source of the material necessary for the formation of these minerals. It was shown earlier that the formation of zeolites and prehnite in carbonate veins is also connected with the removal of alumina from the wall rocks in the course of their near-ore alteration [6].

Of particular importance is the question of studying the distribution of gold in the ores and elucidating the conditions of formation of ore shoots. The solution of these questions undoubtedly plays a major role both from the theoretical point of view and for practical investigations.

Gold, which is the principal valuable component of the ores of the deposits of the Saralinsky ore field, is distributed extremely unevenly in the quartz veins. Against the general background of low and medium metal contents, sectors enriched in gold—ore shoots—stand out. They have various sizes and forms. In some cases, gold-rich pockets measure up to several meters across; in other cases, the ore shoots extend for as much as several hundred meters along the strike and dip of the vein. The concentration of the metal in the ore shoots varies.

It was noted earlier that the ore shoots are confined to those sectors of the gold-bearing quartz veins which lie in contact with carbonaceous—

...or carbonaceous-clayey schists [5]. Thus, a lithological control of the gold mineralization is clearly established. Along the way, we note that a richer sulfide mineralization is also confined to these same sectors, represented by densely disseminated, in places almost massive, ores of polymetallic composition. Mineralogical studies also show that native gold is confined to bands and inclusions of carbonaceous matter in vein quartz.

With a more detailed study of the distribution of gold mineralization in the quartz veins, certain new characteristic features of the noted lithological control were established. Thus, for example, in various parts of the Kaskadnaya vein, as well as in some other veins (Andreevskaya, Uglistaya, Moshchnaya, etc.), those sections of veins that occur among carbonaceous and carbonaceous-clayey schists are distinguished by very low, noncommercial gold contents. They are composed of milky-white, sulfide-free quartz. The ore shoots in the Kaskadnaya and Andreevskaya veins, however, occur where the vein lies in contact between carbonaceous or carbonaceous-clayey schists and other rock types, most often with a sill of porphyritic composition.

A comparison of the conditions of occurrence of ore shoots in crosscutting veins also shows that sections of quartz veins cutting only a thickness of carbonaceous-clayey schists do not carry commercial gold mineralization. Rich ore shoots occur where the veins cut horizons composed of carbonaceous schists interbedded with other rock types: sandstones, thin flows of basic effusives and their tuffs (the Ivanovskaya, Spyashchaya, Shchegolevskaya veins, and others). Under these conditions, very rich ores are often formed.

The facts noted make it possible, with some confidence, to speak of the nature of the influence exerted by carbonaceous schists on the processes of ore deposition. Quite naturally, the facts cited completely exclude the possibility of chemical precipitation. On the other hand, these same facts compel one to agree with the opinion of N. G. Sergiev and M. V. Tashchinina [25] concerning the electrochemical effect of carbonaceous schists. In this case, the carbonaceous schists play the role of one of the electrodes of a natural galvanic cell, in which the second electrode is an aluminosilicate rock, and the electrolyte is the ore-bearing solution. The electric current arising in this process promotes the precipitation of gold and other heavy metals from solutions. Apparently, an electromotive force of greater magnitude arises where the ore-hosting fracture cuts a sequence consisting of carbonaceous-clayey schists interbedded with other rock types. By the nature of the origin of the electric current in it, such a sequence resembles a “voltaic pile.” Therefore ore shoots occurring in contact with such sequences are often distinguished by a very high gold content.

In conclusion, we shall briefly consider the role of structural control in the distribution of gold mineralization in quartz veins and in the localization of ore shoots. In the past, decisive importance was attributed to structural control in the process of formation of ore shoots. Thus, for example, V. M. Kreiter [19], on the basis of data from G. M. Kaikova, notes that ore shoots in the quartz veins of the Saralinsky ore field are confined to sectors where the veins pinch and swell.

In the course of work in various parts of the ore field, we repeatedly observed various structures which, according to existing concepts of structural control, should be regarded as favorable for the formation of shoot-like mineralization. These include, for example, swellings, which are known in practically every vein. Phenomena of intersection of quartz veins with different spatial orientations were repeatedly observed. In the Andreevskaya

In the Kaskadnaya veins, branching of veins is often encountered. Sometimes a certain enrichment in gold is observed in steeply dipping segments as compared with gently dipping ones. It is characteristic that in some cases a clearly expressed structural control is manifested, and in the noted structures a noticeable enrichment in gold is observed. In other cases, however, despite the presence of favorable structures, there is no enrichment in gold. Comparison of these and other examples shows that enrichment in gold in favorable structures appears only when these structures occur among carbonaceous or carbonaceous-argillaceous shales. In these cases, enrichment in gold takes place against the background of the generally high content characteristic of segments of veins lying in contact with carbonaceous-argillaceous shales. Thus, in other words, structural control in the cases described develops against the background of lithological control, which also played the decisive role in the formation of ore shoots.

Conclusion

In describing the factual material, the influence of the host rocks on the processes of hydrothermal ore formation has been noted repeatedly. It was indicated that the host rocks exert a substantial influence on various aspects of the hydrothermal process.

1. The composition of the host rocks largely determines the spatial distribution of quartz veins. The overwhelming majority of them are confined to the sequence of basic effusives, which are undoubtedly the most brittle rocks. In the case described, the dominant role was undoubtedly played by the physical-mechanical properties of the rocks: their brittleness, hardness, ability to create open cavities, etc. Depending on these properties, particular rocks may be either favorable or unfavorable.

2. The morphology of bedded veins is largely conditioned by the morphology of a sill or dike of acid or intermediate composition to whose contact the vein is confined. As was noted above, this is explained by the greater capacity of porphyrites to be replaced by vein quartz in comparison with the shales enclosing them.

3. The distribution of certain minerals in quartz veins depends on the composition of the host rocks, which probably served as the source of the material necessary for their formation.

4. Deposition of gold and the formation of ore shoots proceeded with a predominance of lithological control. In this process, carbonaceous and carbonaceous-argillaceous shales undoubtedly acted as an electrochemical precipitant of material from ore-bearing solutions.

Thus, in the process of ore formation, both the physical-mechanical properties of rocks and their chemical composition play a noticeable role. They exert a very important influence on the entire process of ore formation, determining the distribution of gold mineralization in space.

Nevertheless, the significant role of structural control cannot be denied. As was noted in the description of the Saralinsky ore field, it, together with lithological control, influences the distribution of quartz veins in space, the distribution of mineral associations of different ages in quartz veins, and also the localization of gold-enriched segments developing against the background of larger ore shoots.

The example presented shows that the host rocks take an active part in the process of ore formation, and their possible influence must be taken into account in geological investigations. Co-

quantitative ratios of lithological and structural control in different ore fields can undoubtedly vary. Evidently, the rather pronounced manifestation of lithological control in the Saralinsky ore field was promoted by the complex lithological composition of the enclosing sequence.

REFERENCES

1. Kh. M. Abdullaev. The role of assimilation and hybridism in the concentration of metals in postmagmatic ore solutions. Dokl. AN UzSSR, 1949, No. 8.

2. Kh. M. Abdullaev. The influence of the composition of the enclosing rocks on the formation of postmagmatic deposits. Jubilee collection dedicated to the 25th anniversary of the UzSSR. Tashkent, Publishing House of the Academy of Sciences of the UzSSR, 1949.

3. Kh. M. Abdullaev. The influence of the process of assimilation and hybridism on the composition of postmagmatic solutions. Izv. AN SSSR, geological series, 1950, No. 3.

4. V. I. Bazhenov. On the question of age relationships between dikes and ores in the Saralinsky ore field (Kuznetsk Alatau). Tr. Inst. Geol. Geof. SO AN SSSR, 1960, issue 4.

5. V. I. Bazhenov. On the influence of enclosing rocks on the localization of ore shoots in the Saralinsky ore field. Geologiya i geofizika, 1960, No. 5.

6. V. I. Bazhenov. On zeolitization of the enclosing rocks in contact with gold-ore quartz veins in the Saralinsky ore field. Zap. Vost.-Sib. Otd. Vsesoyuzn. Miner. Obshch., 1962, issue 4.

7. L. S. Bernstein. Structure of the Saralinsky ore field. Tr. NIGRIZoloto, 1947, issue 16.

8. A. G. Betekhtin. The role of the enclosing medium in processes of endogenous ore formation. Zap. Vses. Min. Obshch., part 86, issue 2, 1957.

9. A. G. Betekhtin, S. P. Ershov, V. N. Zverev et al. A Short Course on Mineral Deposits. Gostoptekhizdat, 1946.

10. K. I. Bogdanovich. Ore Deposits. St. Petersburg, 1913.

11. A. Ya. Bulynnikov. Basic features of gold mineralization in the Saralinsky district. Gorn. zhurn., 1929, Nos. 6–7.

12. A. Ya. Bulynnikov. Gold-Ore Formations and Gold-Bearing Provinces of the Altai–Sayan Mountain System. Tomsk, 1948.

13. A. M. Bateman. Industrial Mineral Deposits. Foreign Literature Publishing House, 1949.

14. S. A. Vakhromeev. Deposits of Mineral Resources. Gosgeoltekhizdat, 1961.

15. A. S. Velikii. Structures of Ore Fields. Leningrad University Press, 1961.

16. F. I. Wolfson. Problems in the Study of Hydrothermal Deposits. Gosgeoltekhizdat, 1962.

17. Ya. D. Gotman. On the role of enclosing rocks in the formation of magmatogenic deposits. Izv. AN SSSR, geological series, 1953, No. 2.

18. A. V. Korolev. On the significance of enclosing rocks in the formation of postmagmatic deposits. Tr. Inst. Geol. AN UzSSR, issue 6, 1951.

19. V. M. Kreiter. Structures of Ore Fields and Deposits. Gosgeoltekhizdat, 1956.

20. V. A. Obruchev. Ore Deposits. Part 1, 1928.

21. K. N. Ozerov. On the role of enclosing rocks in the localization of epigenetic mineral deposits of pneumatolytic-hydrothermal origin. Vest. Leningrad. Gos. Univ., 1949, No. 5.

22. G. A. Pelymskii. On the influence of enclosing rocks on processes of ore deposition in hydrothermal deposits of the Urals. Geol. Rudn. Mestorozhdenii, 1959, No. 6.

23. N. V. Petrovskaya. On certain cases of spatial coincidence of different types of endogenous mineral formations. Zap. Vses. Min. Obshch., part 85, 1956, issue 3.

24. A. V. Pek. A case of a clearly expressed dependence of the degree of mineralization on the lithological composition of the enclosing rocks. In: Collection “To Academician D. S. Belyankin on the 70th Anniversary of His Birth and the 45th Anniversary of His Scientific Activity”. Publishing House of the Academy of Sciences of the USSR, 1946.

25. N. G. Sergeev, M. V. Tadinina. On the possible role of carbonaceous-argillaceous shales in the localization of polymetallic deposits of Altai. DAN SSSR, vol. 92, No. 3, 1953.

26. P. M. Tatarinov. Conditions of Formation of Deposits of Ore and Non-Ore Mineral Resources. Gosgeoltekhizdat, 1955.

27. P. M. Tatarinov. On the question of the role of enclosing rocks in the process of forma-

...of the formation of endogenous mineral deposits. “Geology of Ore Deposits,” 1959, No. 2.

1. A. M. Khazagarov. Staging of mineralization of gold deposits of the Saralinsky ore field. “Exploration and Protection of Mineral Resources,” 1957, No. 5.

2. M. G. Khisamutdinov. On the influence of host rocks and the temperature of ore-bearing solutions on the composition and place of formation of ores, using certain Altai deposits as examples. “Soviet Geology,” 1959, No. 50.

3. P. M. Khrenov. On one case of lithological control of tungsten mineralization. Reports of the Academy of Sciences of the USSR, 1955, vol. 100, No. 5.

4. E. M. Yanevsky and V. M. Konstantinov. On the influence of tectonic and lithological factors on the localization of hydrothermal uranium mineralization in the Ore Mountains. “Geology of Ore Deposits,” 1960, No. 6.

5. Beyschlag F., Krusch P., Vogt J.— Die Lagerstätten der nutzbaren Mineralien und Gesteine.— Stuttgart. 1921. Bd. 2. zauflage.

6. Buffam B. S. W.— Moneta Porcupine Mine.— Structural geology of Canadian ore deposits. Symposium. Montreal. 1948.

7. Dunn E. J.— Geology of gold. London. 1929.

8. Gill J. H.— The Canadian precambrian shield.— Structural geology of Canadian ore deposits. Symposium. Montreal. 1948.

9. Groddeck A. V.— Die Lehre von den Lagerstätten der Erze. Leipzig. 1879.

10. Junner N. R.— The geology of gold occurrences of Victoria. Econ. geol. 1921, pp. 80—120.

11. Lang A. H.— The Cordilleran region of Western Canada. Structural geology of Canadian ore deposits. Symposium. Montreal. 1948.

12. Newhouse W. H.— structural features associated with the ore deposits described in this volume. Ore deposits as related to structural features. Princeton, New Jersey 1942.

13. Stillwell F. L.— Replacement in the Bendigo quartz veins and its relation [[unclear: end of title not visible]].

14. Stillwell F. L.— Victorian gold occurrences.— Econ. geol. 1922, No. 1.