Geological-structural conditions of distribution and formation of Pyazbashi gold orefield (Lesser Caucasus, Azerbaijan).

V. G. Ramazanov¹, M.İ Mansurov¹, B. H. Galandarov¹, Mehdi Safari², U.I. Kerimli¹, A.I. Huseynov,¹

Baku State University¹

Deparment of geology Payame Noor University, İran²

The article discusses the specific features of formation of the Pyazbashi field. It is established, that the process of ore formation was long and multistage. Quartz-serisite, quartz-pyrite-molibdenite, quartz-pyrite-gold, quartz-polymetallic and carbonate stage of minera¬lization have been allocated. P-T conditions of ore formation are investigated. It happened under the temperature of 140-390⁰C and the pressure of 0,7-2,5 kbar. It is established, that ore-forming fluids were mostly of a magmatic and partly metamorphic origin.

Key words: gold, deposit, distribution regularities, isotopic content, temperature, pressure, ore, mineralization.

In endo-and exocontact zone of Meghri-Ordubad pluton (V. A. Hassanof, R. U. Hassanof, I. I.Larin, M. A. Hassanof et al) are fount out numerous gold ore deposit which spatially from on entire goldbearing zone. these are – Pyazbashi, Munundari, Bashyurt, Uchurdag, Agyurt, Shackardari and other deposits (Fig.1). Ore bearing and hosting them ore zones is these areas differ from each other in morphology, sizes and elements of bedding and often are distinguished based on testing. More often are met orebearing zones of hydrothermally altered rocks with quartz-sulfide vein and zones of quartz-sulfide veinlets in endocontacts of Meghri-Ordubad batholit intrusives (Agyurt, Bashyurt, Munundara and etc.), rarely are present vein bodies, lenses and interveins zones in exocontacts of intrusive massifs in volcanigenic-sedimentary rocks of Lower and midlle Eocene, folder into folds of NE strike (Pyazbashi, Shakardari end etc.) On some objects (Uchurdag and etc.) a small part of mineralization is related to hydrothermally altered dikes of diorite porphyries. Morphogenetic types of all these deposits first of all are caused by character of geodynamic conditions of development of Daralgez block, during the injection of Meghri-Ordubad pluton and development of the processes of mineralization, by sizes and shapes of tectonic blocks that host the granitoid intrusive and gold deposits [1,2].

Fig.1. Map showing ore deposits distribution and alteration zones at Ordubad orefield.

Among the most perspective are considered Pyazbashi ore field, that unites deposit and ore manifestations (Pyazbashi, Shakardara, Uchurdag and etc.) that have determined commercial value (Fig.2.).

Fig.2. Geological map of the Pyazbashi gold deposit

Symbols: 1 Modern sediments (loam, sandy loam, gravel); Volcanic sequences: 2. Andesitic tuff agglomerate; 3. Lavobrekchii andesites; 4. Plagioclase andesite tuffs; 5. andesitic tuffs; Volcanogenic-sedimentary sequences: 6. calcareous sandstones; 7. lime tuffites; Volcanic sequences: 8. Andesite-basalt tuffs; Intrusive rocks: 9. Diorite porphyries; 10. Porphyritic granodiorite; 11. Gabbro-diorite; 12. Quartz syenite-diorite; 13. Adamellite diorite porphyries; 14. D ranodiorit porphyries; Mineralization: 15. Alteration (silicification, sericitization, iron accumulation, pyritization); 16. Gold-bearing quartz-sulfide veins; 17. Faults; 18. geological boundaries; 19. Dip and strike.

Below is given brief characteristic of the mentioned gold mineralization field and the objects that represent this field.

Pyazbashi deposit is located on the southwestern slope of the Zangezur range between the rivers Duglanchai and Vanandchai. Shakardarine deposit is located to the southwest from Pyazbashi deposit and occupies are of southwest framing of Meghri-Ordubad batholite. The deposit is represented by goldbearing vein zones and a wide zone of goldbearing metasomatites. Goldbearing vein zones are represented by intensively silicified and Kaolinized rock with single quartz veins and veinlets with pyrite-chalcopyrite mineralization.

Gold content is irregular and varies within the limits from weak > to24g/t of silver – from 4,7 to 85,7 g/t, copper – from 0,3 to 3,0%. the zone of goldbearing metasomatites with veinlet-imprignated mineralization of pyrite and chalcopyrite contain gold from 0,4-1,0 to 2,5-3,6 g/t.

In distribution of gold mineralization on Pyazbashi deposit the dominant are endo- and exo- contact zone of granitoid massif in combination with satellites of these massifs and disjunctive structures, diversity of their systems was caused by transformation of deformational plan on different stages of ore field development. Are isolated ore transporting and ore localizing dislocations. The former have NW (300-340⁰), rarely submeridional (350-10⁰) direction and dip according to the SW with inclination of 65-80⁰ and into both direction under the angle 65-80⁰. Ore localizing dislocations as a rule are feathering due to ore transporting ones, have NE (10-50⁰), rarely sublatitudal (70-110⁰) direction and dip according to SE, rarely to NW under angles 55-85⁰ and SE and NW under angle 70-75⁰. Ore bodies and ore columns are developed on the crossing point and junction of two and more systems of dislocations or on their crossing with the contact of the intrusive.

Ore bodies are significant by their diversity and complicative shapes – veins, stockworks and columns with uneven lying elements, squeezing and blowing. In silicate rocks generate caused by fracture tectonic quartz-sulfide (gold-quartz-pyrite, gold-quartz-chalcopyrite), carbonate and quartz-carbonate-galena-sphalerite, goldbearing quartz-sericite-hematite and quartz-molybdenite veins, simple and complicated, with the length along the strike up to 1200m, along the dip 300-400m, with thickness 0,1-2,0m and more, with angles of inclination 60-90 ⁰. Vertical swing of mineralization reaches 350-450m. BY explorative drill holes on Pyazbashi deposit is determined, that characteristic for the explored horizons of geological-geochemical features of the mineralization together with productivity on gold are distributed in the range of absolute marks 2550-2260m.

Within the limits of Pyazbashi deposit are known 70 quartz-sulfide veins. The great majority of them is of gold-quartz-sulfide nature. Are seen also quartz-pyrite-chalcopyrite, quartz-carbonate-galena-sphalerite, quartz-sericite-hematite, quartz-molybdenite, quartz-carbonate barite veins. Because of spatial disconnection of the mentioned veins with various mineralization was arisen an opinion, that Pyazbashi is a complex deposit and unites gold-copper-molybdenum-lead-zinc deposit. Authors tend to consider that all in all on the deposit exists entire ore zonality. Vector of mineralogical zonality under the definite angle rises from the central part in the NW and SE direction from the deposit flank and includes as vertical so horizontal composite of an entire ore zonality. Analysis of the material of searching-explorative and thematic works (R. U. Hasanof, A. A. Mamedov, Z. M. Atakashiev, U. P. Zaruanov and etc.) shoved, that quartz-sulfide-veins are concentrated on the are and in the cross-section in a regular way. The largest scale of development and highest concentration of gold in quartz-sulfide veins is exposed on the SE flank and especially in the central part of the deposit, which northwest- ward along the strike fork info smaller zones and pinch out in the zone of NW direction, built up by lavas and lavabreccias of andesites andesites-basalts of middle Eocene age, mainly in the valley of the r. Metsget- in the core of Pyazbashi anticline of NW direction and on the flank (wings) of Metshet transversal anticline of smaller range. Trough on the NW flank in some veins, in the areas of their junction with subvolcanic andesite-dacite, transformed into secondary quartzites, are fixed high gold contents. Here is singled out wedge-shaped block, trapped between quartz-sulfide veins 1 and 5. This block contains vein with determined and hypothetical commercial gold mineralization (NN 1, 5, 36, 36_a, 38, 43). The most prolonged and rich due to gold-content from the six mentioned veins is the vein 1, investigated (R. U. Hassanof) in details from the surface and also partly opened by two horizontal ad its in the depth.

Fig.3. Photo shows vein 1 at the levels adits 1 and 15 at the Pyazbashi deposit.

We consider advisable to single-out the mentioned zone of intensive development of quartz-sulfide veins as the most perspective area of Pyazbashi deposit (Fig.3). Average length of quartz-sulfide veins is 600-800m, are followed by oxidation, leucocratization and crumpling of the rocks. Along the strike the blowing zones of quartz-sulfide veins in coulisse like way alternate with the zones of contraction, in particular, the greatest width of the quartz-sulfide veins zone is exposed in the region of the central part of the vein 1. Here, while reaching the zone of crumpling and brecciation thickness of the vein increases and are formed lenses of insignificant length and thickness, which in blowing reaches 2,5m, and in squeezing 0,1m.

Ore bodies are constructed by quartz-sulfide impregnated and intervein-impregnated ores, often oxidized, ocherous, cavernous-striped formations. For some veins (NN 1, 5 and etc.) is common breccia-like texture generated as a result of repeated, intermineralization shifts, due to which are brecciated as host-rocks so the minerals of early stages. Clasts are angular, cemented by grey finegrained quartz and massive finecrystalline pyrite. Mineral composition of ores in various. Major minerals of quartz-sulfide veins are quartz and pyrite, minerals of the second order are virgin gold, electrum, chalcozine, tetrahedrites (pole ores) and etc. Are typical impregnated, stripy, intervein and massive textures. Ore structures are complete and crystalline-grained. Among the mineral aggregates are common corrosional, crumbled, emulsive-impregnated and skeletal structures.

Due to types ores are subdivided into wretched (maybe miserable) sulfide, impregnated sulfide and complete sulfide ones. The second type of ore is dominant. In oxidation zone are developed moderately rich oxidized ores. The average depth of secondary alterations on the deposit is 40-60m from the surface along the dip of the veins. In oxidized ores are developed limonite, lepidocrocite, hydrogoethite, goethite and etc. Among sulfides, total amount of which is less than 5-10% of the ore, is strictly dominant pyrite (up to 90%). Gold in fine, related to sulfides, contains admixtures of copper up to 1,27%, silver within the limits 17,9-29,9% [10].size of gold particles is 0,001-0,01mm in diameter and coarser, their shape is irregular, isometric, sometimes oval-prolonged and dendrite-like Gold is present in all types of veins of the ore field, but mainly is met together with pyrite 2. Distribution of gold in the veins is irregular, in general it's of bushy (shrubby) type or columnar. Based on experience of explorative activities (I. I. Larin) ore columns (poles) are related to the areas of declivity of the veins. Gold content on the surface of the veins 1 varies from "weak" to 500 g/t, its average content is 18,o g/t on the traced length 1200m, at average thickness 0,66m. Here, on the level of horizone of adit N(2413m) along the traced length 465,7m, at average thickness of the vein 0,52m gold content reaches 101,4 (average 11,0 g/t). Data of superficial testing and testing of adit N1 enabled Hassanof R. U. (1970) to calculate gold reserves on vein N1 due to C₁ category in amount 0,9t.

Exposed length of mineralized zones usually comprises 60-300m, rarely reaches 500-600m, their thickness is 15-20m. Gold content in mineralized zones is significantly lower than in quartz-vein zones, but its concentrations are sustained and vary from 1 to 4 g/t, rarely reach 9 g/t.

Should be mentioned that quartz-ore vein cross-cuts different horizons of the andesitic xenotuffs and tuffs – agglomeratic xenotuffs, fine-medium-and coarse grained and lapilli, tuffs of andesites. In the underground mines, in those areas where is possible to trace quartz-sulfide veins on a significant segment permanenty is observed their forking (branching) into numerous apophysaes of the some mineral composition, mainly on the hanging wall of the veins, obliquely oriented due to the strike of the major vein and forming obtuse-angle with the shifting direction, determined along the salbands. At the some time significant part of apophizaes doesn't crop out on the surface and is blind. This feature of the vein morphology is exposed on the entire ore field, but the most well exposed is on Pyazbashi deposit including even the thinnest forkings of the veins into numerous conductions. Together with the depth on the level of the horizon of adit N15-a (2313m) vein-1 aquires clear construction with abundant blowings and squeezing and is followed by feathering and parallel veinlets related to displacements of NW and submeridional direction. It's interesting, that in those places, where the veins is located within lapilli and agglomerate andesite tuffs, its thickness decreases up to 5-15 sm, dip angles become gentle, breaks into numerous veinlets of insignificant thickness and length.

Stages of mineralization

Interrelations of different veins and minerals that construct them enable to imagine the succession scheme of hypogene mineral isolation in quartz-sulfide veins of Pyasbashi ore field in following way (from early stages to later ones) (R. U. Hassanof, A. A. Mamedov, 1971): 1 – quartz-sericite; 2- quartz-pyrite-molybdenite; 3- quartz-pyrite-gold (Fig.4. ); 4- quartz-polymettalic (Fig.5); 5- carbonate (Fig.6).

Fig.4. Hand specimen shows quartz-pyrite-gold mineralization stage. (Qz.- quartz; Py.-pyrite; Li.-limonite)

Fig.5. Hand specimen shows quartz- polymetallic mineralization stage. (Sph.- sphalerite; Gn.-galena; Py.-pyrite; Li.-limonite)

Fig.6. Photo shows the inter-relationships between the different stages of mineraliziation. (Qz.- quartz; Py.-pyrite; Ct.-carbonates)

Quartz-silicite stage constructs the major part of vein mass of ore bodies. In paragenesis with quartz are met sericite as the stripes 2-3 sm in thickness in subsalband parts of ore veins.

Quartz is whitish-grey, rarely grey, coarse crystalline, druse like and pectinate (veins 1, 1a, 4, 5, 36, 36a and etc.). Druse-like and coarse-crystalline quartz grows mainly along the walls of the cracks. Coarse crystalline character of the quartz, number of druse cavities in it, sharp boundaries of vein with neighboring rocks testify that took place an infill of open cracks in these veins, which were formed as a result of lateral stress, which in the end caused weakening along the contacts and numerous crocks along which orebearing hydrotherms were entering.

Quartz-pyrite-molybdenite stage is especially widespread on the northeastern flank of Pyazbashi deposit, close to granitoid intrusive. Intensivity of mineralization of quartz-pyrite-molybdenite stage in west-south-west direction gradually decreases. In the veins, built up by mineral assemblages of the mentioned stage, gold content varies from <weak> to 2-3 g/t. Apparently, gold in pyrite is in finedispersive condition. Milky-white quartz with thin interveins and disseminated impregnation of pyrite and molybdenite is strongly catalyzed, cross-cut by numerous quartz-gold-sulfide veinlets of the following stage of mineralization. Are observed fragments of quartz with pyrite-molybdenite mineralization, cemented by quartz of quartz-pyrite-gold ore stage (Fig.7.)

Fig.7 Cementation of quartz (white) quartz-pyrite-molybdenum stage by quartz (black) of quartz-pyrite-goldore stage adit N15 vein N5.

Pyrit-1, molybdenite and chalcopyrite from impregnations and rare thin veinlets in milky-white quartz, virgin gold forms thin impegration in unmineralizedn(ore free) mass. Lack of corrosive ration of minerals enables to unite them into one paragenetic associacion. X-ray analysis show that gold-1 contains silver (table 1) [10]. Chrystallochemical formula of the gold based on the results of three analyses accordingly are: Au₁₁₈Ag₈₂; Au₁₄₂Ag₅₈; Au₁₄₃Ag₅₇;

Table 1.

Result of chemical analyses of virgin gold of Pyazbashi ore field [10]

№ of analyze		Compozition					Formula
		Au		Ag
eight., %	at. numb.	eight. %	at. numb.	sum
1 2 3 4 5 6 7 8 9 10 11 12	82,15 79,3 82,1 80,4 78,8 75,7 82,2 79,8 82,2 75,6 80,4 70,0	0,419 0,402 0,417 0,408 0,400 0,384 0,417 0,405 0,417 0,384 0,408 0,355	17,9 29,9 18,2 19,7 22,1 24,1 18,1 21,1 18,2 25,1 19,7 30,0	0,166 0,277 0,169 0,183 0,205 0,223 0,168 0,196 0,169 0,233 0,183 0,278	100,4 99,8 100,3 100,1 100,9 99,8 100,3 100,9 100,4 100,7 100,3 100,0	Au1,43Ag0×57 Au1,18Ag0×82 Au1,42Ag0×58 Au1,38Ag0×52 Au1,32Ag0×68 Au1,27Ag0×73 Au1,43Ag0×57 Au1,35Ag0×65 Au1,42Ag0×58 Au1,25Ag0×75 Au1,12Ag0×88 Au1,42Ag0×58

In quartz-pyrite-molybdenite stage are determined molybdenite-quartz and molybdenite chalcopyrite-pyrite assemblages.

Quartz-pyrite-gold stage is characterized by precipitation of medium – and finegrained quartz with dense, but fine impregnation of pyrite, rarely chalcopyrite, gold and etc.

Before this stage took place shifts along the cracks (fractures) of NW oriented veins (300-350⁰), cracks of NE directions were corcked in favour of which overlapping of goldore stage took place mainly along the veins of NW strike. For example, along the vein 1 of Pyazbashi deposit is clearly observed how the mediumgrained quartz infills the cracks in coarsegrained quartz of previous stage, forming stripy texture (pic.8).

Should be mentioned, that onlapping of gold mineralization stage was of the same rate not on all veins of NW directions. This was depended on the rate of crack opening of different parts of the veins, Virgin gold impregnations, tiny plates or veinlets with sizes 2-3 mm paragenetically is associated with pyrites.

Fig. 8. Stripy texture of ores. White – quartz veinlet, grey – veilets and impegrantions of pyrite. (5^x) (Pyazbashi deposit).

Ground mass of gold is singled out on this stage. The major mineral of this stage is pyrite-2, which builts up nests and stripes with thickness up to some santimeters, parallel and subparallel contacts of veins and forms disseminative impregnation and thin veinlets (up to 1 sm) in quarts mass. More often pyrite is in close association with products of its oxidation by Fe oxide and hydoxides, mainly by limonite and lepidocrocide. Single grains of pyrite within quartz are rimmed by thin film of limonite along the peripheries, or are crosscut by small veins also filled by limonite (pic.9).

Fig.9. Net structure of pyrite implacement (white) by limonite (black). (100^x). (Pyazbashi deposit)

Pyrite – 2, arsenopyrite and chalcopyrite – 1 from early paragenetic association and generate idiomorphic grains. Boundaries between them are even, without any sings of corrosion and implacement, that points to their simultaneous formation. Virgin gold -2 was crystallizing in the some stage but later than sulfides as it completely fills small crocs in pyrite -2 and arsenopyrite. Gold was precipitating together with quartz as observed inclusions of this mineral captured by quartz grains during their growth. Gold, aside from virgin isolations, is present also as admixtures in pyrite, chalcopyrite and arsenopyrite. The major its concentrators is pyrite and chalcopyrite, and bearer is pyrite. In pyrite – 2 (sample4-7) gold content is less and comprises 0,03-0,08%, in chalcopyrite – 0,05% (table 2). Except gold in chalcopyrite as admixtures are present silver (0,12%) and arsenic (0,15%). Christalochemical formula of chalcopyrite-1 from Pyazbashi deposit is: (Fe_1,01Cu_1,00Ag₁₂Au_0,05)_2.18 (S_2.00As_0,15)₂₁₅. On quartz-pyrite-gold mineralization, stage are singled out pyrite-arsenopyrite and pyrite-chalcopyrite-paleore (tetrahedrite) associations.

Table 2.

Chemical composition of some ore forming minerals of Pyazbashi ore field

Minerals	№№	Composition, weight %											Sum	Formula
		Fe	Cu	Zn	Pb	Ag	Au	As	Sb	Bi	Te	S
Pyrite	1с. 2с. 3с. 4с. 5с. 6с. 7с.	46,82 45,51 45,13 45,19 46,51 45,92 46,13	- 0,23 - - - 0.03 -	0,45 - - - - - -	- - - - - - -	- - - - - - -	- - 0,15 0,08 0,08 - 0,03	- 0,18 - 0,20 - - -	- - - - - - -	- - - - - - -	- 0,02 - 0,04 0,03 - -	52,02 53,98 53,80 54,64 53,48 53,94 52,75	101,29 100,10 99,08 100,07 100,10 99,89 98,91	(Fe1,00Zn0,07)1,007S2,00 (Fe0,98Cu0,06Au0,0004)1,02 (S2,00As0,0024Te0,0001)2,0025 (Fe 0,97Au0,008)0,98S2,00 Fe0,96(S2,00Au0,08As0,0023 Te0,0033)2,011 (Fe0,995Au0,0004)0,9954 (S0,998 Te0,002)2,00 (Fe0,98Cu0,0001)0,98S2,00 (Fe1,00Au0,0001)1,00S2,001
Chalcopyrite	4c.	30,46	34,51	-	-	0,12	0,05	0,15	-	-	-	34,78	100,07	(Fe1,01Cu1,00Ag12Au0,05)2,18 (S2,00As0,15)2,15

Quartz - polymetallic stage is characterized by precipitation of finegrained Chalcedonlike quartz, pyrite, arsenopyrite-2, altait, hessite, tennatite. They are represented as veinlest, that cross-cut precipitated earlies mineral assemblages. Major ore minerals of this stage are sphalerite and galena. They are observed as nests, thin veinlest, stripes and impregnations in quartz. Before this stage latitudal and partly submeridional fractures had been opened. Onlapping of mineral association of this stage on quartz-molibdenite stage is observed on Djovuzludari manifestation of polymetallic ores. On Pyazbashi deposit (in adit.N1 - 175m of head henger-on) polymetallic vein of latitudal strike shifts gold-mineralization vein -1. Aggregates of sphalerite fill interstitials among the grains of pyrite-2 and arsenopyrite-1. Simultaneously with sphalerite were precipitating galena and tennantite, as in many cases boundaries among these minerals are clear, without traces of corrosion and emplacement. Together with galena were precipitating altait, hessite. Crystallization of sphalerite outstriped all other minerals, precipitating on this stage. This is proved by crosscutting of sphalerite by arsenopyrite veinlent of growth and by emplacement of tennantite.

Quartz-polymetallic stage also is goldbearing. Gold is found as in virgin type so as admixture. Virgin gold-3 in association with sphalerite fill interstitials among the grains of quartz and small cracks in arsenopyrite . On quartz-polymetallic stage are singled out arsenopyrite-pyrite-sphalerite, chalcopyrite-pyrite-sphalerite and quartz-galena assemblages.

To the earliest assemblage are related massive coarse-crystalline aggregates,, where pyrite and arsenopyrite have close rate of idiomorphism. The second paragenetic association of quartz-polymetallic stage is represented by aggregates of tightly accreted pyrite, chalcopyrite and sphalerite, which together fill intersfitions in coarsecrystalline aggregates of arsenopyrite without clear signs of the emplacement of the latter. This testifies later precipitation of these minerals. With them associated gold of the late generation, which differs by lower standard and also vrious in morphology grains of tetrahedrites. Galena occurs in salbands of veinlets as coarse (up to 5mm) grains, often corroding sphalerite and emplace it along cracks. Galena emplaces also pyrite, which is present here as small grains (0.1-0.2mm). Also are present arsenopyrite, altaite, hessite, tennantite. Though timing (age) interrelations of mentioned minerals are not always clear as they are rare and don't contact with each other. However, minerals that contain iron-sphalerite, pyrite, arsenopyrite are obviously earlier due to corroding them galena.

Carbonate stage is the final stage of hydrothermal process and is characterized by calcite precipitation. On this stage took place shifts along latitudal fractures as a result of which quartz-ore mass was broken and cemented by carbonate material (veins 50,51 and etc.).NW fracture systems on this stage were closed and that's why mineral assemblages of this stage are almost absent in them. Calcite, which is the final mineral of ore process, cements fragments as of hosting tuffogenic rocks of subvein space so sulfide minerals of quartz-gold-sulfide veins.

Physical - chemical conditions of the deposit formation

Physical-chemical conditions of the deposit formation was studied by means of thermobarometry. Methodology of the studies included the following. Micro inclusions were investigated in transparent - polished sections (mainly from vein quartz of different stages of ore process). Were studies sizes, shapes, phase composition and number of inclusions. Homogenization temperature of gas-liquid inclusions were determined on setting UMTK 3 [7].

As its well-known, homogenization temperature by the majority of the researchers is estimated as a mineral temperature for the mineral formation. To obtain a real temperature of mineralization is essential to insert a temperatural correction (always positive), stipulated by a pressure influence [21].

Salinity of mineral generation solutions were calculated in weighs percents of NaCl equivalent on freezing temperature of inclusions for which was taken the melting temperature of the last smallest crystal [8].

Vein quartz is characterized by micro inclusions of mineral forming solutions 2-3 to 10-15mkm in size. According to relative age are singled out primary, primary-secondary and secondary inclusions [6]. Determination of the inclusion generations of the same ages was carried out based on their morphology and homogenization temperatures. In the investigated quartz primary inclusions usually are "negative micro crystals" hexagonal singoony, distributed on the growth zones. Gas bubble within them is usually isometrical and that's why it's not transparent because of full internal reflection. Primary inclusions consist from water solution and gas. Primary-secondary and secondary inclusions are characterized by irregular flattened shape, as they as a rule are related to healed small cracks. Gas bubble in flattened inclusions has high transparency. Mineralogical characteristic of the material of plates enables to correlate temperatures of homogenization of the primary and primary-secondary inclusions in conditions of the formation of the given stage of mineral formation. Secondary inclusions were used to characterize temperature parameters of following stages. So, each quartz plate was examined as a source of information about several stages of mineral formation exposed as inclusions of different generations.

All in all were examined 40 quartz plates from Pyasbashi and Shakardari deposits. Were made 25 measurements of homogenization temperature. have been received following major results.

Pyasbashi deposit shows polimodal distribution of temperatures. Inside of wide temperatural diapason are singled out 4 major maximums, that correspond mainly to mineral formation stages. To the first quartz-sericite stage corresponds the highest temperatural interval 270-390⁰C. To, the second quartz-pyrite-molibdenite stage correspond medium temperatural interval 250-370⁰C. The third one reflects temperatural inversion during quartz-pyrite-gold ore stage - 270-320⁰C. The latest quartz-polymetallic stage is characterized lowered temperatures 140-260⁰C.

Fluid inclusions were investigated by means of thermometric methods in thermochamber. According to them were determined homogenization temperatures results of which are shown on Fig.10 and 11. Histograms of homogenization temperatures [5] in observed have polymodal character, singled out generations of inclusions corresponds to above described mineral assemblages. Is determined, that within the boundaries of Pyazbashi ore field the same assemblages are characterized by close temperatural intervals of homogenization in spite of their dominant or subordinate productivity on the given object. Presumably the temperatures of the formation of mineral assemblages are related to the level of erosive cut of the ore field. As it's determined, inclusions of the first type are almost totally homogenized in a liquid phase at temperatures 250-390⁰C with maximum in the interval 300-350⁰C (Fig.10.). Gas composite of these inclusions which mainly consist from carbon dioxide, homogenizes into liquid, rarely into gas phase. This happens at 12.0-22.8⁰C. The major of CO₂ homogenized at 4-13,5^оС. For given case density of СО₂ is estimated within the limits of 0,80 - 1,10g/sm³ . In gas phase of captured fluids aside of CO₂ are present also methane and dissoluted chlorides. Is determined that presence of methane in inclusions in general take place at the melting temperature of gas hydrate over 10^оС. Below this melting temperature they contain dissolved chlorides. Concentration of salts in the fluid, according to temperatures of gas hydrate melting (СО₂ 7,3 H₂O) comprises 1015,3 mas% NaCl - eqviv. [3] calculated according to temperatures of ice melting [19].

Temperature, ⁰C

Fig.10. Histogram of homogenization temperatures of fluid inclusions in quartz of Pyazbashi deposit:

1. inclusions of I-II types; 2. inclusions of III type.

Fig.11. gas - liquid inclusions in goldbearing quartz of Pyazbashi deposit

а) Primary 2 phase: gas-liquid (twophase); б) Substantionally gasiceous: primalry-

secondary; в) Substantionally liquid: secondary three pase; г) Liquid.

Fluid inclusions of the second type are represented by substantionally gasiceous components, which correspond in composition CO₂, homogenise at temperature from 21.5 to 23⁰C. In given temperatural interval densign of CO₂ is from 0.59- to 0.95 g/sm³.

Homogenization of fluid inclusions of the third type in liquid phase takes plave at 140-200⁰C. These solutions are characterized by relatively high concentration of salts (from 7,5 to 10,2 mas. % NaCl-eqv.). Aside of Na in the solution is dominat also Mg.

Analisic o ontained data on thermometric investigations shows, that during mineral cristallization on Pyazbashi deposit were captured thre types of fluids different in composition: 1) aqueous fluid with CO₂, CH₄ and Na and Mg chlorides; 2) gas fluids, containing CO₂ and admixtures of CH₄ ; 3) aqueous fluid of moderate salinity, containing Na and Mg chlorides. The first tub fluids are contemporaneous and obviously are derivatives of the same fluid and were formed during its exfoliation while falling of pressure and temperature or only of temperature. As temperatures of homogenization of both types of inclusions in many cases turned out to be similar, could be supposed that separation of volatite components from fluids was caused by abrupt falling of pressure, but not of the temperautre. Substationally aqueous fluid is characteristic for final stages of deposit formation. It also could form while boiling up of the fluid, which consisits of the mixture H₂O+CO₂ with chlorides.

Chemistry of ore minerals. Gold in ores of Pyazbashi ore field aside of its virgin nature, is present also in pyrite, chalcopyrite, galena, sphalerite, tennantite (see tab.2.). Standard of virgin gold is not stable and varies from high standard (82.13) to low (70.0). Is isolates as clotted, paw like, wire like, filming, scaly, dendritic, irregular table like etc. in vein quartz. Are present in paragenetic association with virgin silver, electrum. Size of gold particles varies from 1 mkm to 0.2x0.5 mm, shapes of isolation in growing's with silver is from thinnest hair like veinlets to slightly prolonged, sometimes isometric ones. Bigger isolations of gold and silver are related to mechanic features of mineral - bearings. So, veinlet shapes of isolations of virgin gold and silver are determined in tenantite, prolonged and isometric ones in chalcopyrite.

Pyrite is the major ore mineral of Piazbashi deposit. It's present in several generations. its distinctive feature is presence of admixtures of copper, gold, arsenic, zinc and tellurium, which are regularly distributed as within the limits of one grain, so in grains of different generations. Are singled out copper -, arsenic -, tellurium and gold bearing varieties. In some samples (samp. 2 c; table 2) in the composition of pyrite are simultaneously present copper, gold, arsenic and tellurium. In idiomorphic crystals of pyrite is exposed zonality apparently caused by transformation of habitus and composition.

Arsenic, tellurium and gold are characteristic for pyrites of quartz - pyrite - gold ore association, which contain maximum amount of gold - 0.08 mas%. Results of analysis of chemical composition prove high goldbearing of pyrite in association with arsenopyrite and tellurides. Concentration of arsenic in pyrite is 0.18-0.20 mas%, tellurium - 0.02-0.04 mas%.

Arsenopyrite is the mineral of minor importance in Pyazvashi ores. It's met as small shortprismatic grains. In heneral it's exposed in ores of the second and third stages in association with pyrite and sphalerite. In the first, case of association with pyrite it builts up nests and stripes parallel and subparallel to vein contacts. It formed disseminated impregnation and thin veinlets (0.5-1 sm) in secondary quartzites of Shakardari deposit. Aggregates of pyrite and arsenopyrite underwent crashing and are crosscut by veinlets of galena-sphalerite mineralization of quartz-polymetalic stage. Arsenopyrite and pyrite usually form idiomorphic grains. Boundaries among them are straight, without signs of corrosion and emplacement. This enables to suppose their almost simultaneous formation in early paragenetic association of the third stage. The main part of gold including virgin one, was crystallized on the third stage, but later than sulfides, as it fills cracks in them, in particular in pyrite and arsenopyrite.

Is investigated isotope composition of sulphur of sulfide minerals, oxygen of quartz of Pyazbashi ore field. Results are represented in tables 3 and 4 and on pic.6. Isotope composition of sulphur is determined in pyrite, chalcopyrite, sphalerite and galena. Ratio of sulphur isotopes in sulfides varies from +3.0 - +6.8 %о, in particular for pyrite +3,2-+4,1 %о, galena +3,0-+3,3%о. As is clear from the results of measuring δ³⁴S values of sulfides, precipitated on different stages don't differ a lot.

Fig 12. Isotope composition of the minerals from Pyazbashi ore field: a - isotope content of sulphur of

sulfide minerals; б - isotope content of oxygen of quartz from different stages of mineral

formation on Pyazbashi deposit.

δ¹⁸O isotopes of quartz from different stages of mineralization of Pyazbashi deposit varie from +7.5 to 16.9‰. At the same time quartz from the early qyartz-sericite stage is characterized by values of δ¹⁸O within the limits from +7.5 to 8.7‰. Quartz of quartz-molibdenite stage is characterized by δ¹⁸O values from +9.9 to 11.0‰ and from productive quartz-pyrite-goldore - +12.6 to 15‰. Quartz of the later quartz-polymetalic stage is enriched by heavy isotope of oxygen and has δ¹⁸O values from +14.9 to 16.9‰ (Fig.12.)

Table 3.

Isotope composition of the sulphur of sulfides from Pyazbashi ore field

Mineral	δ^34S%о	Mineral	δ^34S%о	Mineral	δ^34S%о
Pyrite Pyrite Pyrite Pyrite	6,8 3,5 4,2 5,4	Chalcopyrite Chalcopyrite Chalcopyrite Sphalerite	4,1 4,4 4,8 3,3	Sphalerite Sphalerite Sphalerite Sphalerite	4,1 3,2 3,1 3,0

Table 4.

Isotope composition of the oxygen of quartz from Pyazbashi deposit

δ^18О%о
Stages of mineralization
I Quartz-sericite	II Quartz-molibdenite	III Quartz-pyrite-gold ore	IV Quartz- polymetalic
+7,5 +7,9 +8,0 +8,5 +8,7	+9,9 +10,2 +10,4 +11,0 --	+12,6 +13,0 +14,1 +14,3 +15,0	+14,9 +16,2 +16,9 -- --

Correlation of gained results with literary data [3,11] shows, that δ³⁴S and δ¹⁸O values of the minerals from the Pyazbishi ore field are alike of the data, gained on numerous gold ore deposits.Distinctive feature of Pyazbashi deposit is significant change of δ³⁴S and δ¹⁸O values while in most plutonogenic hydrothermal gold deposits these values correspond to narrow intervals and are about 2-3%.

According to results of gained isotope, data might be considered the source of ore forming fluid. Water- carbon dioxide fluids with moderate salinity, which are alike of the fluid from which precipitation of described ores took place, are thought to be the products of magmatic activity [9] or of dehydration and decarbonatization reactions, that take place during the metamorphism of terrigenous rocks [15]. In case of dehydration usually is generated fluid with low concentration of salts (less than 6 mas % NaCl eqv. [16]). Formation of highconcentrated brines is possible during of fluid exfoliation, which consist of H₂O and CO₂ and NaCl, into gas and water-salt phases [12]. According to diagram of the condition of H₂O - CO₂ - NaCl system, presented by these authors (pic.13.), at content in it of 6 mas % of NaCl, exfoliation of fluid on phase enriched by H₂O - CO₂ and liquid rich in NaCl, takes place within the temperature interval from 600 to 1000⁰C at pressures 1-1.5 kbar. At higher pressures fluid slays homogenous.

.

Fig13. Phase ration in the system. Hatched area shows localization of ore formation on Pyazbashi

deposit. Phase boundaries correspond to different compositions (1-4): 1-0; 2-6; 3-12; 4-20mas%.

Exfoliation of mineral forming fluid during formation of gold veins of Pyazbashi deposit, as it was shown above, took place at different parameters P=0.7-2.5 kbar and T=140-390⁰C. Metamorphic processes, that took place in Ordubad ore field are characterized by low steps and occurred at temperatures lower than 500 ⁰C and pressures 3-4 kbar. Fluid, equilibrium with these rocks should had been characterized by the same parameters. Accordingly low temperature fluid, rich in chlorite salts, couldn't be formed as a result of exfoliation of metamorphic fluid, which was generated during dehydration and decarbonatization of the rocks. Base on above mentioned it's considerable, that chemical composition of mineral-forming fluid testifies its magmatic origin.

Involvement into ore precipitating process of components, that have various origins is proved by data about composition of stable isotopes. In favor of the fact, that impute of the components into the area of ore precipitation from the deep seating chamber, indicate similar isotope ratios of oxygen and sulphur in the veins from different flanks and horizons of Pyazbashi deposit and from the rocks of different composition. This, in our opinion, indicates that isotope exchange reactions with the host rocks didn't significantly influence on δ³⁴S_H2S and δ¹⁸О_H2O values.

Gained data about Pyazbashi deposit show, that δ¹⁸О values of water in fluid are distributed in the area of characteristic for water values, which was formed during transformation of sedimentary rocks containing organic material and is close to isotope ratio, determined for metamorphogenic waters and are lightened by isotope in comparison with primary magmatic water, values of which are accordingly in intervals from - 7 to + 20‰, from +3 to 20‰, from 5.5 to + 10‰ [18,22]. (see pic.7).

Influence of exchange isotope reactions of fluid with the rock on the ration of isotopes of oxygen in it, in mezothermal mineralforming systems is not significant [14]. That is why primary magmatic fluid (δ¹⁸О_H2O = +7 ‰) during interaction with volcanigenic host rocks, at 400 and 300⁰C could be enriched by light oxygen isotope up to 2‰. Based on this fact, couldn't be excepted involvement into ore forming system of the water of magmatic origin. It's supposed, that calculated isotope content of oxygen of the fluid is better to interpret as a result of the shifting of two fluids different in values. One of them might have magmatic origin, the second one was poor in heavy oxygen isotope and could formed during formation of waters as a result of disintegration of organic material. In this case are well explained δ¹⁸О_H2O values and its lowering to - 1‰.

Sulphur, as well as oxygen, during the ore precipitation could have different origin, especially in that case, when its isotope content is distributed within the limit of the values from +7 ‰. As possible sources are regarded mantle and magmatic systems and sedimentary host rocks. δ³⁴ S_H2O values (+2) - (-7)‰ are related to fluid, generated from granitoid melt where isotope ratio of sulphur changes from -3 to +7‰ [17]. Based on this is supposed, that sulphur, which took part in formation of Pyazbashi deposit, was extracted from magmatic source. There's also possibility of participation in the ore precipitation process of mantle sulphur, and also of the sulphur borrowed from host rocks, isotope content of which is accordingly within intervals from -3 to +3‰ and from less than +10 to +20‰. That's why it's different to simply answer the question of the sulphur impute into ore forming system took place together with fluid which separated during crystallization of granitoid magma or it was borrowed from the rocks hosting ore bodies.

So, it's possible to suppose, that while formation of the deposit, fluids were of different nature. They contain products of magmatic and metamorphogenic origin, shifting of which was rather quick in the area of ore precipitation or near it. The dominant apparently was fluid of magmatic origin.

Conclusions

Results of investigations enable to make following conclusions:

1. The ore precipitation process was long and multistage. Are singled out 5 stages of mineralization: quartz-sericite, quartz-pyrite-molibdenite, quartz-pyrite-gold ore, quartz-polymetallic, and carbonate, for which are determined molibdenite-quartz, molibdenite-chalcopyrite-pyrite, pyrite-arsenopyrite, pyrite-chalcopyrite-tetrahedrite, arsenopyrite-pyrite-sphalerite, quartz-galena mineral associations;

2. Temperature of ore formation, studied by method of homogenization of gas-liquid inclusions in transparent minerals (quartz) of different mineral associations, varies in interval from 140⁰ to 390⁰C. mineral associations of early stages (I-III) were crystallizing at temperature 250-390⁰C, later (IV-V) - at 140-300⁰C. Pressure of ore forming environment (medium) determined on crossing of isotherm in system H₂O - CO₂ and isochrore CO₂ [13] was 0.7-2.0 kbar. Precipitation of minerals of quartz-pyrite-gold ore stage took place at pressure 0.8-2.5 kbar, of quartz-polymetallic - 0.7 - 2.0 kbar.

3. Taking into account that quartz veins carry fragments of the host rocks, almost fully emplaced by quartz-sericite aggregate, could be supposed that at temperatures 250-400⁰C and pressures 0.5-3.0 kbar they might be formed in balnce with fluid with pH from 5.45 to 6.1. In conditions of quartz-sericite-potassium-feldspar metasomatose fluids will be in balance with surrounding medium ar pH from 5.2 to 6.1.

So gold mineralization of Pyazbashi ore field was formed within the temperature interval from 390 to 140⁰C, pressure - 0.7-2.5 kbar, pH=5±1. Activity of sulphur at the beginning was increasing due to mineral precipitation, and was decreasing at the end of ore forming process. Volatility of oxygen and hydrogen dioxide was lowering during precipitation of later mineral associations.

4. based on investigation data of isotope composition of oxygen and sulphur in ore forming fluids, might be supposed, that fluids have different nature, they contain products of magmatic and metamorphic origin, where dominant were fluids of magmatic origin.

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