SOME PROBLEMS OF THE PETROGRAPHY OF THE CHANYSH MASSIF

(Gorny Altai)

V. I. YARYGIN

(Presented by the scientific seminar of the GRF)

The Chanysh massif is situated within the interfluve of the Andoba, Chanysh, and Kaurchak rivers (right tributaries of the Lebed River), at the junction of the mountain systems of the Kuznetsk Alatau (Gornaya Shoria) and Gorny Altai.

The geology of the region has been studied by many investigators. The first serious work on the geology of the region was the research of A. M. Kuzmin [3]. Later the region was visited by A. P. Lebedev [4], V. A. Kuznetsov, and G. P. Nagorskii, who provided a summary of the magmatism and stratigraphy of the entire Lebed region. In 1952–1960 geological investigations were carried out here by E. S. Shinkarev, V. I. Fominskii, V. N. Konovalov, and V. I. Zinov'ev. As a result of these works, all the intrusions of the region, including the Chanysh massif, were studied in detail. In the summer of 1962, the staff of the Department of Petrography of the Tomsk Polytechnic Institute carried out thematic work on the study of the petrography of the Chanysh massif; the results of this work are set forth by the author in the present article.

The development of ideas concerning the petrography of the Chanysh massif is important from the standpoint of assessing its prospects with respect to ore minerals, in particular gold.

The geological structure of the Lebed region may briefly be characterized as follows. The central part of the area of distribution of the intrusion, by its structural features, may be assigned to the Uimeno-Lebed synclinorium, which in the north passes into the Kondoma-Lebed synclinorium. In essence, they represent a single structure of interregional character. This structure is complicated by local structures of plicative and disjunctive character. Within the region, among the latter, the Upper Kondoma anticline of northwestern strike, plunging to the southeast, and the Andoba graben of submeridional strike are distinguished. In the axial part of the Upper Kondoma anticline there occurs a Lower Cambrian sequence of metamorphic schists, augite porphyrites and their tuffs, with interbeds and lenses of sandstones and tuffs of acid effusives. Its limbs are composed of two Middle Cambrian sequences. The lower sequence is represented by plagioclase, augite, and diabase porphyrites, coarse-fragmental tuff breccia, more rarely diabases and amygdaloidal rocks. The upper sequence is composed of tuffs of acid effusives, tuffites, tuff breccias, sandstones, conglomerates, and thin lenses of limestones. Among the Cambrian effusive-sedimentary forma-

...Lower Devonian red-colored sandstones and conglomerates are developed, which compose the Andoba graben.

The Chanysh massif occurs in the upper part of the Middle Cambrian in the southwestern limb of the Verkhnekodom anticline. In plan it has a lens-like form elongated in a northwestern direction, with a width of about 2 km and an area of about 20 km². This form is caused by a local weakened zone of the fracture type, which at the same time served as a feeder channel and chamber for the emplacement of the magmatic melt. This tectonic zone existed, being repeatedly renewed, for a long time—presumably from the Lower Cambrian to the Devonian. Tectonic movements manifested themselves again already in postmagmatic time, being expressed in a longitudinal fault that divided the massif into a southwestern part and a northeastern part thrust over the former.

The position of the massif in space is determined by the character of its relations with the enclosing rocks and by its prototectonic anatomy.

The boundaries of the massif are poorly expressed in the area of the northeastern part, where there are gradual transitions into the country rocks. These transitions are caused by the broad zones of hornfelsing and skarnization developed here. In the most exposed part, along the right side of the Kaurchak River, many veins of plagiaplites, aplites, and microdiorites occur. The southwestern contact has fairly clear and sharp boundaries. Hornfelses are almost absent; zones of skarnization are of low thickness and are manifested only owing to the presence of lenses of actively skarnized limestones. From all the foregoing it follows that the southwestern and northeastern contacts of the intrusion dip to the northeast, since hornfelsing, skarnization, and vein magmatism were intensively manifested in the northeastern exocontact, whereas on the southwestern one they are poorly developed or altogether absent. In addition, in outcrops of granites along the Chanysh River a planar orientation of dark-colored minerals and porphyritic segregations is observed, dipping to the northeast at an angle of 70°, which indicates the direction of magma flow to the northeast.

Thus, in general outline the massif has the form of a large dike, occurring in the limb of the anticline and plunging in a northeastern direction. Its structural position is discordant.

The petrographic varieties of the intrusion are represented by three groups of rocks: 1) hornblendites, gabbro-diorites, and quartz monzonites; 2) porphyritic biotite–hornblende granites and their varieties; 3) aplites–malchites. The first have a subordinate significance in the intrusion, being exposed on the northeastern margin in the form of a narrow discontinuous belt. It extends from Mt. Shorba in the north to the Kaurchak River in the southeast.

We shall proceed to brief petrographic descriptions of the rocks composing the massif.

Hornblendites have been encountered in three places along the right side of the Kaurchak River and in the area of Mt. Shorba, in the form of belts or lens-shaped bodies. They are connected by gradual transitions with the more widespread gabbros and diorites, which likewise form belt-lenses. The hornblendites are dense, medium-grained rocks of almost black color in fresh fracture; on weathered surfaces they have a brownish tint. Under the microscope they show a panidiomorphic-granular, commonly sideronitic structure. Their mineralogical composition is uniform. Quantitative counts in thin sections by the planimetric method show that their freshest varieties are composed of 80% ura-

with lithic hornblende. Plagioclase is present in an amount of 15%, rare grains of potassium feldspar, and ore minerals—up to 5%. Secondary minerals occur in insignificant amounts: epidote, pelite, and saussurite. The hornblende occurs as broad plates with rectilinear boundaries. Sometimes it forms rims around grains of monoclinic pyroxene or replaces it with the formation of complete pseudomorphs. Its color is dark green along $Ng$ and yellowish-green along $Np$. Almost all individuals are simple twins on (110), $cNg = 19^\circ$, $2V = -80^\circ$. The monoclinic pyroxene is salite with a hedenbergite molecule content of about 30% ($Ng = 1.718$; $Nm = 1.694$; $cNg = 40$–$41^\circ$; $2V = +58^\circ$). Plagioclase is very strongly replaced by a saussurite aggregate and therefore is closer to indeterminate. Potassium feldspar occurs very rarely. It is characterized by its xenomorphic grains, gravitating toward cataclastic areas, and by abundant brown films of pelite. In small quantities there occur prismatic and columnar grains of apatite, continuous aggregates of fine-grained magnetite, and, rarely, sphene.

Hornblendites contain nodules and vein-like bodies of rocks of giant-crystalline pegmatoid aspect. The contacts between the hornblendites and them are gradual. The named veinlets pass between fragments of hornblendites, sometimes penetrate along a series of fractures, seize and assimilate small fragments of hornblendite. Depending on this, hornblende develops in them, predominantly along gulfs, causing a gradual transition into hornblendites. Under the microscope, in them there is observed an identical idiomorphism of plagioclase and hornblende. The plagioclase in composition corresponds to oligoclase-andesine No. 28–30, strongly replaced by epidote and sericite. Hornblende is replaced by chlorite and biotite. Very rarely grains of potassium feldspar occur with a characteristic gigantic microcline lattice. Of the accessories, sphene, apatite, and magnetite are present.

Gabbros occur in the same places as the hornblendites, in the form of elongated bands and lens-shaped bodies arranged parallel to the contact of the massif. In external appearance they are medium-grained, dense rocks of dark-gray color and a somewhat indistinct trachytoid texture. Under the microscope the structure is gabbroic; sometimes mutual poikilitic intergrowths of plagioclase and dark-colored minerals are observed. The mineralogical composition, calculated by the planimetric method, is as follows: plagioclase—50%, hornblende and monoclinic pyroxene—43, accessories—5%. In small quantity there are secondary minerals: epidote, biotite, saussurite, and rarely chlorite.

Plagioclase forms short-columnar grains of idiomorphic form. It is almost completely replaced by an aggregate of saussurite and gray pelite. In some individuals, fresh areas have been preserved with polysynthetic albite and complex-axis twins. In such grains, diaphthorization of plagioclase has proceeded to the formation of peripheral rims of acidic composition. In composition, in the cores of grains it corresponds to labradorite No. 60–62 ($Ng = 1.568$; $Np = 1.561$; $2V = -78^\circ$), and at the periphery to andesine-labradorite No. 49–50 ($Ng = 1.564$; $Np = 1.557$; $2V = -72^\circ$). Monoclinic pyroxene is observed only in the form of sieve-like relics or corroded cores in amphibole grains. In composition it corresponds to salite with a hedenbergite molecule content of about 30% ($Ng = 1.716$; $Np = 1.683$; $cNg = 38^\circ$; $2V = 58^\circ$). Hornblende forms complete homoaxial pseudomorphs after pyroxene with preservation of its primary structure. The habit of the crystals is compact. Its color is dirty green with a bluish tint; pleochroism along $Ng$—dirty green, $Np$—bluish-green; $Ng = 1.773$; $Np = 1.655$; $cNg = 18^\circ$; $2V = -88^\circ$. Horn-

hornblende, in turn, is intensively replaced by biotite, i.e., the replacement proceeds according to the scheme monoclinic pyroxene—hornblende—biotite. Accessory minerals are represented by magnetite in the form of xenomorphic inclusions in the interstices of hornblende, sphene in the form of isometric envelope-shaped crystals, and apatite in columnar-prismatic crystals.

Diorites and quartz monzonites are developed along the entire belt of basic rocks from the Kaurchak River to Mount Shorba. They are especially well exposed on the right bank of the Kaurchak River and in plan have the form of elongated lenses. In all probability, these are hybrid rocks of an acid melt that intruded along a tectonic zone and of rocks of the gabbro group. This is demonstrated by the presence, among these diorites, of xenoliths of gabbro which, in composition and chemistry, correspond to the gabbro described above.

Fresh diorites are dark-gray, dense, medium-grained rocks, weakly gneissose parallel to the strike of this belt. Under the microscope they show a hypidiomorphic-granular texture with signs of cataclasis. The mineralogical composition of the rock is not strictly constant, varying within the following limits: plagioclase—58–68%, hornblende—20–30, potassium feldspar—1–5, quartz—1–8%, and accessory minerals. Secondary minerals are present in small amounts and are represented by biotite, muscovite, prehnite, tremolite, actinolite, and saussurite.

Plagioclase forms large prismatic grains of idiomorphic habit, which are intensively replaced by a fine-grained aggregate consisting of scales of sericite, chlorite, and rounded grains of zoisite. In composition, the plagioclase corresponds to andesine No. 32–40 with an optic-axes angle of 85°. Almost all individuals have undergone cataclasis, as a result of which open cracks are formed, in which epimagmatic minerals appear: muscovite with a 20% content of the phengite molecule \((2V = -42^\circ\), elongation positive, extinction straight, \(Nm = 1.593)\) and prehnite with an iron molecule content of about 9% \((Ng = 1.656;\ Np = 1.623;\ 2V = 68^\circ\), elongation negative, extinction straight). Potassium feldspar occurs in the interstices of plagioclase grains. It is covered by a continuous coating of clayey secondary minerals, through which cleavage on \((001)\) is visible. Its optical-crystallographic properties \((\angle Nm : \perp (001) = 7^\circ,\ 2V = -72^\circ)\) identify it as orthoclase. Plagioclase at the boundary with orthoclase has zigzag outlines, indicating replacement of the former by microcline. Hornblende, as in the gabbro, forms homoaxial pseudomorphs after monoclinic pyroxene. The habit of its grains is compact prismatic. In relation to plagioclase it is somewhat xenomorphic, adapting to the interstices of the latter and partially replacing it. The monoclinic pyroxene is diopside-salite \((cNg = 40^\circ,\ 2V = 58^\circ)\). The amphibole is ordinary hornblende (pleochroism: \(Ng\)—dark green, \(Np\)—light green, \(2V = -66^\circ,\ cNg = 16^\circ\)). Hornblende is replaced by chlorite-pennine with a 42% content of the amesite molecule and 10% of the ferroantigorite-daphnite molecule \((Nm = 1.577\), optical sign positive, \(Ng - Np = 0.002)\), by fibrous actinolite, and by biotite, the flakes of which have undergone bending deformation to the formation of gentle arcs. Accessory minerals are represented by magnetite in the form of a fine-grained aggregate tending toward dark-colored minerals, sphene, apatite, and zircon.

Quartz monzonites are spatially associated with bodies of diorites. The boundaries between them are gradual. In external appearance they are...

differ sharply from the diorites described above in their flesh-red color. Under the microscope the rock has a typical monzonitic texture. The mineral composition is as follows: andesine—44%, microcline—25, quartz—20, hornblende—8, accessory minerals—1%. Biotite is present in variable, but usually very small, quantities (about 2%). In some specimens, sericite, epidote, and chlorite (pennine) become considerably developed, forming mainly after plagioclase and hornblende. Plagioclase individuals show zonal structure, expressed in a saussuritized central part, corresponding in composition to andesine No. 30, and a relatively fresh peripheral rim (oligoclase No. 17). Microcline ($\angle Nm : \perp (001) = 14^\circ$, $2V = -68^\circ$) is observed as xenomorphic grains, with respect to plagioclase often twinned according to the Carlsbad law [001]. The accessory minerals are magnetite, sphene, apatite, spinel, and zircon.

Porphyritic biotite-hornblende granites compose the southwestern part of the massif, formed during the second phase of intrusion. They occupy an extensive area, represented in plan by a broad lens-shaped belt extending from the Kaurchak River to Mt. Shorba. Macroscopically, these are rocks of porphyritic texture and light-pink color. A feature of the porphyritic granites is a barely perceptible planar orientation of the dark-colored minerals, and, less often, of the K–Na feldspars. Under the microscope the rock has a granitic texture. The mineral composition, calculated by the planimetric method, is as follows: plagioclase—30%, orthoclase—30, quartz—19, hornblende and biotite—10, accessory minerals—3%.

Plagioclase forms prismatic grains of idiomorphic form, twinned according to the albite and Carlsbad laws. Almost all crystals have zonal structure. Secondary minerals—sericite, epidote, zoisite—develop as a fine-grained aggregate in the central parts of the grains, which in composition correspond to albite-oligoclase No. 17, while the peripheral rim is represented by fresh albite No. 10. Orthoclase is observed in porphyritic segregations and in xenomorphic grains. The phenocrysts have idiomorphic rectangular forms and are intergrown with albite (microperthite) parallel to the cleavage directions (1502) and (001). Inside they contain inclusions of quartz of isometric form, zonal plagioclase, chloritized hornblende, and apatite. At the periphery, as a rule, they have uneven zigzag boundaries, either projecting in the form of tongues into the surrounding quartz-feldspar medium-grained aggregate, or being resorbed themselves in the form of embayments and cavities. In composition it belongs to sodic orthoclase ($\angle Ng : \perp (010) = 0$, $2V = -70^\circ$). Hornblende ($cNg = 21^\circ$, $2V = -64^\circ$) has crystals of pyramidal form, twinned according to simple laws. It is intensely replaced by chlorite (pennine) and biotite, which sometimes entirely replace the hornblende. Accessory minerals are represented by apatite in prismatic columnar grains, sphene, zircon, and magnetite.

Porphyritic plagiogranites are localized along the longitudinal cataclased zone of the massif as a belt with indistinct outlines. In outward appearance these are leucocratic rocks of coarse- and medium-grained texture. Under the microscope the rock is of porphyritic texture with areas of strong cataclasis. Porphyritic segregations of plagioclase and partly orthoclase occur among a fine-grained aplitic groundmass consisting of quartz and orthoclase. The mineral composition, calculated by the planimetric method, is as follows—

zoned plagioclase—59%, quartz—20, orthoclase—15, biotite and hornblende—4, accessory minerals—2%. Secondary minerals are present—pelite, sericite, chlorite.

In composition, plagioclase in the central zones corresponds to albite-oligoclase No. 20, and in the peripheral zones—to albite No. 12. Orthoclase ($\angle Nm : \perp (001) = 3^\circ$, $2V = -63^\circ$) is rarely encountered as phenocrysts. All crystals are fresh in appearance and are intergrown with cryptoperthite along (001). They usually contain small grains of zoned plagioclase, hornblende, and quartz, and along the periphery are surrounded by a rim consisting of a fine-grained aggregate of hornblende, biotite, and chlorite. Hornblende is primary relative to biotite, which develops along cleavage and cracks. The fine-grained mass of aplitic texture consists of isometric grains of quartz and orthoclase. Its total content relative to the rock is 40%. Among the accessory minerals, sphene is present in envelope-shaped crystals; magnetite occurs as disseminated grains.

Granosyenites occur in the field of the intrusion as spots of various configuration. In appearance, this is a dense flesh-red rock consisting of orthoclase (40%), quartz (25%), albite No. 10 (30%), and biotite (2–3%). Accessory minerals are rare (1–2%) and are represented by apatite, magnetite, and leucoxene. Secondary minerals develop after albite (sericite), after biotite (pennine), and after orthoclase (pelite).

Aplitic granites occur in the marginal parts as lens-shaped bodies. Macroscopically these are light-pink rocks of fine-grained texture. Under the microscope their texture is aplitic, conditioned by a panidiomorphic-granular aggregate of plagioclase (20–50%), potassium feldspar (30–54%), and quartz (25–30). Biotite and accessory minerals are rare and amount to 1–2%. In composition, plagioclase corresponds to oligoclase No. 22–24, along which sericite and gray pelite develop. Orthoclase ($\angle Nm : \perp (001) = 3^\circ$, $2V = -60^\circ$) is replaced by albite to the formation of microperthite. Accessory minerals are represented by magnetite, zircon in small grains with pleochroic halos, sphene, and leucoxene.

Rocks belonging to the vein facies have a limited distribution. Such rocks have been encountered within the endocontacts of the intrusion and very little in its exocontacts. In the endocontacts of the intrusion there are veins of plagioaplites and deluvial dumps of malchites. The thickness of the veins ranges from several centimeters to a meter.

Plagioaplites have been encountered in the western endocontact and in the eastern exocontact. These rocks have a fine-grained texture and a pink coloration, owing to the predominance of potassium feldspar. The microscope shows a typical aplitic texture. The grain shapes are isometric (irregularly polygonal and irregularly rounded). The mineralogical composition, calculated by the planimetric method, is as follows: plagioclase—15%, potassium feldspar—39, quartz—49, hornblende and muscovite—1.5, magnetite—0.5%. Secondary minerals—fine disseminations of epidote, sericite, brown pelite, chlorite—occur in negligible amounts, with the exception of pelite, which completely clogs the potassium feldspar. Plagioclase forms short-prismatic crystals twinned according to the albite law. In composition it belongs to albite-oligoclase No. 12.

Malchites have been encountered in one place near the confluence of the Chanysh and Vaginskii rivers. Macroscopically this is a fine-grained, dark-gray rock of uniform composition. Under the microscope its texture is microdioritic. The mineralogical composition is as follows: plagioclase—60%, hornblende—35, quartz—4, accessory minerals are rare—1% and rep—

are represented by sphene and magnetite in the form of inclusions in hornblende. Plagioclase forms isometric grains with resorbed outlines. Twinning is distinct according to the albite–Esterel law. According to determination, it belongs to andesine-labradorite No. 43. Hornblende occurs as short-columnar and prismatic crystals of compact habit (pleochroism: \(N_g\)—bluish-green, \(N_p\)—light yellow-green, \(cN_g = 18^\circ\), \(2V = -72^\circ\)).

The rocks in the contact area underwent considerable changes with the formation of hornfelses. Along the southwestern contact of the intrusion the width of the hornfelsing belt is very small and is expressed in weak hornfels recrystallization, always, apparently, accompanied by slight metasomatism.

Skarns in contacts with the massif are encountered rarely and are developed chiefly in areas where limestones and conglomerates are present. Here skarns were observed that form relatively small nests and sheet-like bodies. They are comparatively simple in mineralogical composition—dark-green monoclinic pyroxene predominates in the form of columnar aggregates, and brown garnet of grossular-andradite composition. Epidote, radiating amphibole, and carbonates are less widespread. Of ore minerals, pyrite, chalcopyrite, and hematite are present. Locally the skarns are purely garnet, but more often mixed—pyroxene-garnet. In a number of cases garnet and pyroxene are completely replaced by actinolite and epidote, with the formation of amphibole-epidote skarns.

Hybridism and autometasomatism manifested themselves especially intensively in the field of development of ultrabasic and basic rocks, accompanied by a considerable alteration of the latter. This led to the formation of hybrid and autometasomatic rocks, among which the above-described diorites, quartz monzonites, and hornblendites are distinguished. The previously characterized gabbros are relics of the primary rocks. The xenoliths of gabbro encountered in diorite once again confirm this proposition.

S. S. Il’enok (1) believes that the disintegration of rocks of the gabbro type is associated with the penetration of mobile alkaline material, which deposited orthoclase, hornblende, and possibly plagioclase of andesine composition. Apparently, the introduction of alkaline solutions was accompanied by the transition into a mobile state and partly by the removal of iron-magnesium silicates. Thus, the penetrating solutions had the composition of aplite and grano-syenite. This is also indicated by the composition of the vein rocks, in which rocks of quartz-syenite composition predominate. The penetration of the solutions apparently took place along a tectonic microfracture zone for a long time, continuously changing their composition.

Judging from the ubiquitous development of hybrid rocks, it may be assumed that microfracturing extended throughout the entire belt of basic rocks, also affecting the enclosing rocks—intensely in some areas, weakly in others. This caused gradual transitions between hybrid rocks and primary magmatic rocks, as well as between magmatic and enclosing effusive rocks.

The process of autometasomatism is later and superimposed with considerable intensity on primary-magmatic and hybrid rocks. In the biotite-hornblende porphyritic granites, the typical autometasomatic process of albitization of microcline with the formation of perthite is widely developed. At the same time, the plagioclase of the rock undergoes desanorthitization under the influence of autometasomatic introduction of sodium. These phenomena indicate progressive enrichment of the residual solutions in \(Na_2O\), partly in \(Al_2O_3\). The manifestation of iron-magnesium autometasomatism encompasses the conditions of epidotization,

chloritization and biotitization. During chloritization, amphiboles become unstable, entirely passing into chlorites. During epidotization the mobility of the epidote molecule increases. As noted above, epidote first replaces plagioclase grains. Then veinlike segregations of epidote arise, enclosing crystals of epidotized plagioclase. Here, too, replacement of hornblende by biotite is observed, with the introduction of magnesium, while potassium is assimilated in the course of the reaction between microcline and hornblende.

Autometasomatic processes are strongly manifested among gabbro-pyroxenites and hybrid rocks. In them the uralitization of monoclinic pyroxene is especially strongly developed; it occurs as a result of reaction between pyroxene, plagioclase, and magnetite, with the introduction of a certain amount of magnesium. As a result, hornblendites are formed from pyroxenites, and hornblende gabbro from normal gabbro. Other processes, such as de-anorthitization, epidotization of plagioclases, biotitization, and chloritization, develop according to the same schemes as in the granites. It should be emphasized that the autometasomatism of the rocks probably took place under continuously decreasing temperatures. Associated with this is the breakdown of early minerals and the formation of low-temperature stable minerals. An illustration may be provided by the alteration of minerals, leading to the paragenetic series: monoclinic pyroxene—green hornblende—biotite—actinolite—chlorite.

Thus, in terms of the character of the structure and texture of its rocks, and of the character of autometasomatism and contact transformations, the intrusive massif has a clearly expressed hypabyssal character.

In order finally to be convinced of the above-listed features of the intrusion, it is necessary to dwell in detail on its petrochemical characteristics. For more graphic petrochemical comparisons of the various rocks of the intrusion, a summary table of the chemical compositions of the magmatic rocks is proposed. All analyses were performed by the chemical laboratory of the Tomsk Complex Expedition of the NTGU.

The vector diagram of the chemical compositions of the rocks (Fig. 1), obtained from the above summary table of chemical compositions, clearly illustrates the petrochemical features of the intrusion. On this diagram, the rocks of each phase are characterized by a definite position, orientation, and size of the vectors.

The rocks of the gabbro-pyroxenite phase (vectors 10, 11, 16, etc.) occupy the extreme lower position on the diagram, differing sharply from the others by high values of \(b\) and \(c\). The magnitude and orientation of the vectors on the \(asb\) plane indicate the high magnesian character of the corresponding rocks. And the direction of the vectors on the \(csb\) plane indicates a low potassium content relative to sodium. The rocks of the granite phase are represented by a group of vectors (1, 2, 3, 5, etc.) regularly situated in the upper part of the diagram.

The diagram reflects the following features of the rocks of the intrusion:

1. All rocks of the intrusion are characterized by a high silica content, because all the vectors are situated comparatively close to the vertex \(S\).

2. In its chemistry, the intrusion should be assigned to typical calc-alkaline rock series. This is indicated above all by the position of the variation line: on the \(asb\) plane it is situated close to the \(sb\) line, which indicates a moderate alkalinity of the rocks of the intrusion. On the \(csb\) plane it is situated far from the \(sb\) line, which indicates a relatively high calcium content in the rocks. The configuration and direction of the variation line also correspond to calc-alkaline series.

Summary table of analyses of intrusive rocks. Table 1

Continuation of Table 1

Explanations for Tables 1 and 2: albite granite, 3 and 4—plagiogranite, 5 and 6—porphyritic plagiogranite—potassium biotite-hornblende granite, 8—quartz monzonite, 9—diorite, 10 and 11—gabbro, 12—diorite, 13—pyroxene gabbro-diorite, 14 and 15—diorite, 16—hornblendite, 17—malchite.

1. Rocks of phase 3 (vectors 1, 4) are characterized by a significant oversaturation with alumina, as indicated by the rotation of the vectors on the \(asb\) plane to the left.

2. The granitoid rocks have a relatively high content of potassium alkali, as indicated by the gentle orientation of vectors 1, 2, 5, 6, 0, and others on the \(csb\) plane. Judging from the position and direction of the projections of the variation line, as well as from the magnitude and direction of the vectors, the final derivatives of the Chanysh intrusion approach alkaline rock series with a potassium trend. The steep inclination of the variation line

Fig. 1. Diagram of the chemical compositions of rocks of the Chanysh intrusion (after A. N. Zavaritskii).

on the \(asb\) plane and the sharp, characteristic turn of the upper end of the line toward the vertex \(s\) indicate that this intrusion possesses a clearly expressed pantelleritic tendency, very characteristic of alkaline series. On the \(csb\) plane the variation line comes very close to the \(sb\) line, which indicates the poverty in calcium of the final products of magma crystallization.

1. The ratio FeO : MgO in the rocks always lies within the limits of 1, which testifies to the granitoid character of the original magma.

2. The group of hybrid rocks occupies an intermediate position on the diagram between normal basic rocks and granitoids (vectors 9, 14, 18).

Thus, all the factual material on the structural-geological position, petrography, and petrochemistry of the Chanysh intrusion makes it possible to draw interesting conclusions concerning petrogenesis. In our opinion, the intrusion was formed in 3 stages, separated by a long interval of time. In the first stage, which manifested itself in the Middle Cambrian, rocks of chiefly gabbroic composition were formed; in the second—granites and plagiogranites. In the third stage, rocks of a dike series were formed.

In the initial stage of formation of the intrusion, undifferentiated basic magma was injected into fissure zones, at the expense of which bodies of gabbro and pyroxenites were formed; subsequently, these were partly assimilated by later phases.

The magma of the 2nd stage was emplaced along renewed fissured zones. At the contact of rocks of the 2nd phase with rocks of the 1st phase, a process of hybridization is manifested. Later, alkaline metasomatism took place, which led to the appearance of new metasomatic formations, at times resembling magmatic ones (porphyritic segregations of potassium feldspar). The rocks of the 2nd phase are characterized by a potassium specialization of the alkalies; moreover, the increasing role of potassium is characteristic of the final products of the magmatic chamber, which are then replaced by postmagmatic metasomatic and hydrothermal solutions rich in ore components, in particular gold. Thus, the 2nd phase of the Chanysh intrusion is of considerable interest metallogenically. Gold mineralization in the district is genetically associated with it, in the form of quartz, quartz-barite veins and quartzites.

The intrusion described has numerous analogues in the Lebed district, which may also be considered promising for gold mineralization.

REFERENCES

1. S. S. Il’enok. The relation of magmatic replacement phenomena to ore formation. In the collection of articles “Basic Ideas of M. A. Usov in Geology,” Publishing House of the Academy of Sciences of the Kazakh SSR, 1960.

2. Yu. A. Kuznetsov. Magmatic formations. Regularities in the distribution of useful minerals. Vol. 1, Publishing House of the Academy of Sciences of the USSR, 1958.

3. A. M. Kuz’min. Brief report on geological investigations in the upper part of the Lebed River, right tributary of the Biya River. Proceedings of the Siberian Department of the Geological Committee, 1924.

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