Noble-metal mineralization of the Adycha-Taryn metallogenic zone: Geochemistry of stable isotopes, fluid regime, and ore formation conditions

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ScienceDirect Russian Geology and Geophysics 59 (2018) 1271–1287 www.elsevier.com/locate/rgg

Noble-metal mineralization of the Adycha–Taryn metallogenic zone: geochemistry of stable isotopes, fluid regime, and ore formation conditions G.N. Gamyanin a,b, V.Yu. Fridovsky b,*, O.V. Vikent’eva a a

b

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia Received 30 November 2017; received in revised form 18 March 2018; accepted 25 April 2018

Abstract The regional geologic setting of the Adycha–Taryn metallogenic zone, one of the areas most productive for noble-metal mineralization in northeastern Russia, is discussed. The intricate metallogenic history of the zone and the prolonged geodynamic activity of its ore-hosting structures are documented. Different types of mineralization, such as hydrothermal-metamorphogenic, gold–bismuth, gold–quartz, gold–antimony, and silver–antimony, are described. New data on the isotopic compositions of oxygen in quartz, sulfur in sulfides, and oxygen and carbon in carbonates from different mineralization types are presented. The early metamorphogenic quartz beyond the ore zones has δ18O = +20.1 ± 2.0‰. At the gold–bismuth deposits, the δ18O values of quartz are within the narrow range of +12.5 ± 0.4‰. Quartz from the gold–quartz mineralization shows much wider variation in δ18O values, from +14.2 to +19.5‰. A similar range (δ18O = +16.1 to +19.2‰) is observed for the gold–antimony mineralization. Cryptograined quartz from the silver–antimony mineralization is enriched in light oxygen isotopes (δ18O = –3.2 to +4.7‰). The following δ34S values (‰) have been established in sulfides of mineralization of different types: gold–bismuth –3.7 to –2.2 (Apy) and –6.7 to –6.8 (Py); gold–quartz –2.1 to +2.4 (Apy), –6.6 to +5.4 (Py), and –6.1 to +4.2 (St); gold–antimony –2.0 to +1.6 (Apy), –3.5 to +2.1 (Py), and –5.3 to +0.2 (St); and silver–antimony –2.0 to –1.9 (Apy), –2.2 ± 0.1 (Py), and –5.7 to –5.6 (St). The δ13C and δ18O values are contrasting in the studied types of mineralization, varying respectively from –6.9 to –5.9‰ and from +2.1 to +5.7‰ (gold–bismuth), from –9.1 to –6.1‰ and from +12.4 to 18.7‰ (gold–quartz), from –12.1 to –9.5‰ and from +15.0 to +16.3‰ (gold–antimony), from –11.6 to –11.1‰ and from +1.5 to +4.7‰ (silver–antimony). Metamorphogenic calcites are rich in both heavy C (–1.1 to –1.7‰) and heavy O (+20.3 to +20.5‰) isotopes. Microthermometric study and crush–leach analysis of fluid inclusions have revealed differences in the composition of ore-forming fluids and formation conditions for different types of mineralization. The isotopic compositions of O, C, and S of mineral-forming fluids suggest a significant input of magmatic fluids to the formation of gold–bismuth and gold–antimony deposits, the contribution of metamorphic fluids increases at gold–quartz deposits, and meteoric water is involved in the formation of silver–antimony deposits. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: Adycha–Taryn metallogenic zone; noble-metal mineralization; stable isotopes; fluid inclusions; genesis of deposits

Introduction The Adycha–Taryn metallogenic zone (ATMZ) measuring 45 km in width extends in a northwestern direction from the origins of the Malyi Taryn River for 600 km. It is one of the most productive areas in terms of both abundance and diversity of precious-metal deposits localized within the Yana–Kolyma gold-bearing belt. Metallogenic specialization of the zone is characterized by development of Au, Au–Sb, and Ag–Sb mineralization, which is primarily associated

* Corresponding author. E-mail address: [email protected] (V.Yu. Fridovsky)

there with different stages of tectonomagmatic activation. The mineral exploration in this zone has been addressed to by many publications (Amuzinsky, 2005; Amuzinsky et al., 2001; Berger, 1978; Bortnikov et al., 2010; Gamyanin, 2001; Gamyanin et al., 2001, 2003; Goryachev, 1992, 2003; Indolev et al., 1980; Fridovsky, 2002, 2017; Fridovsky et al., 2012, 2013, 2014, 2015; Tectonics..., 2001). The ATMZ area bears the evidence of several geodynamic and metallogenic events which typify the late Mesozoic history of geological evolution of the outer area of the Pacific ore belt. Therefore, mineralization types are commonly combined within the long-developing tectonic structures of different ages, which is advantageous for an in-depth study of its

1068-7971/$ - see front matter D 201 8, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.201 + 8.09.006

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spatial-temporal relationships, geological setting and localization. Given also that the polygenic and polychronic nature of mineralization is typical of large deposits, this phenomenon analysis on the example of ore objects represents an important applied task. Large placer gold deposits are widespread in ATMZ, besides the recently discovered targets with vein and veinlet-disseminated, quartz and sulfide-quartz types of gold mineralization have been intensely explored. In Russia’s northeast, to this type belong Drazhnoe, Malotarynskoe, Natalka, Nezhdaninskoe, Pavlik, Degdekanskoe, and other deposits with gold resource cumulatively accounting for 30% of all reserves of the Russian Federation (Ivanov et al., 2016). The Sarylakh and Sentachan are also large deposits within the ATMZ area whose Au–Sb reserves amount to 180,000 and 110,000 t (antimony) and to 40 and 20 t (gold), respectively (Bortnikov et al., 2010). Considering the accumulated evidence and numerous recent publications on the mineral-geochemical and geological-structural features of individual deposits within the ATMZ area (Akimov et al., 2004; Aristov et al., 2015, 2016; Bortnikov et al., 2010; Fridovsky et al., 2012, 2013, 2014, 2015, 2017),

this paper presents new results obtained by the authors from isotope-geochemical and thermobarogeochemical studies of the ATMZ ores, which allowed to analyze genetic characteristics of different ages of gold mineralization and ore-forming processes in close connection with the geodynamic evolution of the area.

Regional geological position of the Adycha–Taryn metallogenic zone ATMZ is located on the boundary between the Kular–Nera slate belt and Verkhoyansk fold-and-thrust belt, with the former being an outer zone between Kolyma–Omolon microcontinent (superterrane) and submerged Eastern margin of the North Asian craton (Fig. 1). The Kular–Nera slate belt is composed mainly by Upper Permian, Triassic and Lower Jurassic terrigenous rocks supplliued from deep-water alluvial fans and foothills of the Verkhoyansk continental margin, which were subjected to the initial stages of the greenschist facies metamorphism (Parfenov, 1984; Parfenev and Trushchelev, 1983). Its structure

Fig. 1. Position of the studied ore deposits on the schematic map of the suture zone of Kolyma–Omolon microcontinent, Verkhoyansk fold-and-thrust belt and Kular–Nera slate belt. 1, Verkhoyansk fold-and-thrust belt; 2, Kular–Nera slate belt; 3, Kolyma–Omolon microcontinent; 4, Mesozoic granitoids; 5, dacites of Taryn subvcolcano; 6, 7, ore deposits and mineral occurrences: 6, gold–quartz (gold–sulfide–quartz) (a), gold–bismuth (b), 7, gold–antimony (a), silver–antimony (b). Ore deposits: 1, Sentachan; 2, Andreevskoe; 3, Kikhtey; 4, Uzlovoe; 5, Yukhondzha; 6, Tikhoe; 7, Gan; 8, El’; 9, Rudnyi Lazo; 10, Imtachan; 11, Aulochan; 12, Motyl’; 13, Gavrikovskoe; 14, Delegenyakh; 15, Zhdannoe; 16, Tugan; 17, Tobychan; 18, Bazovskoe; 19, Dzhetan’ya; 20, Primetnoe; 21, Talalakh; 22, Nitkan; 23, Elginskoe; 24, Avgustovskoe; 25, Dirin’; 26, Kinyas’; 27, Sarylakh; 28, Ebir-Khaya; 29, Sana; 30, Maltan; 31, Malotarynskoe; 32, Pil’; 33, Drazhnoe; 34, Ergelyakh; 35, Kurdat; 36, Aid; 37, Dichek; 38, Plastovoe; 39, Sakhchan; 40, Serp; 41, Kupol’noe; 42, Klyap; 43, Sedlo. The inset shows the position of the area of works. SP, Siberian Platform; VFTB, Verkhoyansk fold-and-thrust belt; OT, Okhotsk terrane; KOM, Kolyma–Omolon microcontinent; KNSB, Kular–Nera slate belt; PDT, Polousno–Debin terrane.

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formed in several stages of deformations represents linear folds and faults of NW strike (Parfenov, 1984; Tectonics..., 2001). The Adycha–Elgin anticlinorium is characterized by the developed broad, open folds with the folding intensity increasing in proximity to the Adycha–Taryn fault. Adycha–Taryn fault (ATF) is a major tectonic structure controlling the ATMZ position, which is traced by Ten’kin fault further to the southeastern coast of the Sea of Okhotsk. In the Upper Kolyma gold-bearing region, the latter is identified with a significant portion of commercial gold deposits in the northeast of Russia (the Natalka, Pavlik, Degdekanskoe, Rodionovskoe deposits, etc.). The faults total about 1000 km in length. The Adycha–Taryn fault which separates tectonic structures of different size and differentiated geochemical signatures of igneous rocks, is a major spatial control of the deposits placement. It also affects the intensity of metamorphism, rock lithology and facies composition, and characteristics of geophysical fields. Its complex geological history of evolution, long-term geodynamic activity of tectonic structures and their permeability for fluids and magmatic melts have been discussed in detail in (Fridovsky, 2002; Sokolov, 2010; Tectonics..., 2001). These were prompted by subsynchronous late Jurassic–early Cretaceous accretion of the Kolyma–Omolon microcontinent and subduction processes in the Uda–Murgali island arc crust, which largely influenced the formation of folds and thrusts of different age, S- and I-types granitoids of the Main and Tas–Kystabyt belts dated 137–153 Ma (Akinin et al., 2009; Goryachev and Pirajno, 2014; Layer et al., 2001; Newberry et al., 2000), as well as orogenic Au, Au–Bi and Ag–Sn mineralization. Magmatism is weakly developed within the ATMZ bounds. Basically, these are small massifs of granitoid composition, except for a large Nelkan granitoid and Taryn subvolcanic dacite massifs. In addition to the granitoid massifs, the diorite-porphyrites and granite-porphyry dikes, mainly NW-, WE- and NE-oriented, were observed. In the late Neocomian, the directions of the Kolyma–Omolon microcontinent motion and of the Uda–Murgali arc subduction have changed (Tectonics..., 2001). The first developed left-lateral motions in the Adycha–Taryn fault activated early thrust faults, while Late Cretaceous postaccretion tectonic events, small granitoid stocks and subvolcanic granite-porphyry dikes, Au–Sb, Ag–Sb mineralization are associated with late Cretaceous subduction in the Okhotsk–Chukchi arc (Bortnikov et al., 2010; Nokleberg et al., 2005; Tectonics..., 2001). In the late Cretaceous and Paleogene, Adycha–Taryn fault acted mainly as a deep crustal strike-slip zone. Along the fault, shallow telethermal ore deposits tended to form in the cataclastic areas and often become superposed with preexisting gold or tin deposits, forming thereby complex polygenic deposits. Brief characterization of types of mineralization The established for the Adycha–Taryn metallogenic zone complex geological history of development, long-term geodynamic activity of tectonic structures, as well as their perme-

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ability for fluids and magmatic melts, and types differentiation of noble-metal ore deposits are listed in Table 1. The formation of the earliest, hydrothermal-metamorphogenic mineralization is associated with the collision of the Kolyma– Omolon microcontinent with the eastern margin of the North Asian craton. This mineralization is characterized by sparsely dispersed quartz–chlorite or quartz–chlorite–calcite veins (Fig. 2a). Some veins do not exceed the first tens of centimeters in thickness, while veins along strike become fairly quickly pinched out and grade into thin veinlets. Given that these veins often have layered pattern, they participate together with the host rocks in plicative deformations. In this case, their maximum thickness is reported from the joints of small folds. The composition of chlorite which is present in the form of vermicular (worm-like) grain clusters of pale greenish color is described as follows (wt.%; average of the four microprobe measurements): SiO2—25.12; Al2O3—22.05; FeO—30.68; MnO—0.15; MgO—10.86; Σ—88.86. According to the X-ray diffraction data, it belongs to the ripidolite group. Marcasite, which is rare in the veins, forms elongated polygrain anisotropic plates, locally overprinted by pyrite cubic crystals. The composition of marcasite is stoichiometric. Co and Ni admixtures (0.01–0.02%) were reported within the sensitivity range of the probe. Gold-quartz and gold–sulfide–quartz types of mineralization. The main commercial gold emplacement within ATMZ is related to orogenic type gold–quartz and gold–sulfide–quartz mineralization (e.g., the Bazovskoe, Talalakh, Drazhnoe, Levoberezhnoe, Zhdannoe, Malotarynskoe deposits). Unlike the well-known first type, the second has been the object of study since the beginning of 2000 (Akimov et al., 2004). Ore deposits are unevenly distributed throughout the ATMZ area, both across it, and along the strike, to form a broad elongate strip. Orebodies are associated with the Tithonian–Valanginian granitoids (ilmenite-series) of S- and I-type (Goryachev and Pirajno, 2014) and dykes from the Nera–Bokhapcha complex. The mineralization was emplaced later than the granitoid intrusions, which is confirmed by the results of veins dating in the Yana–Kolyma metallogenic belt (148–125 Ma) (Newberry et al., 2000). Among them, goldbearing deposits constrained by 140–130 Ma are predominant (Goryachev and Pirajno, 2014). Ore deposits are often either remote with respect to granitoid intrusions to a distance of several kilometers or have supraintrusion position. The gold–quartz and gold–sulfide–quartz deposits are structurally controlled by large elongated thrusts and less often by transverse strike-slip separating blocks with different structural architecture and tectonic evolution. Strike-slip faults are often conjugated with normal faults. The major structural-tectonic controls of mineralization placement are represented by crossing ramp: frontal and oblique, frontal and lateral (Fridovsky, 2010; Fridovsky et al., 2014, 2015). An increase in the intensity of folding observed within ore fields reaches maximum in the zones of long-term developing longitudinal ore-controlling faults. Importantly, mineralized zones of crushing commonly develop along shearing on contacts between rocks of different competency. Thrust faults are liable for the

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Table 1. Characterization of noble metal ore deposits of the Adycha–Taryn metallogenic zone Characteristic features of ore deposits

Ore deposit type Low-sulfide gold–quartz

Gold–bismuth

Gold–antimony

Silver–antimony

Geodynamic setting

Accretion

Kinematics of orecontrolling structures

Thrust

Thrust

Left lateral strike-slip

Postaccretion

Structural paragenesis

Intensely folded and thrust zone of NW strike, concentric folds with horizontal hinges, boudinage, fracture cleavage

Supra- and near-intrusion structures, mineralized crush zones

Sinistral strike-slip fault, Strike-slip fault, concentric concentric and conical folds and conical folds striking striking NE, including E–W, including axonoclines axonoclines, cleavage

Host rock

sandstones and siltstones

hornblendes, granitoids, sandstones, siltstones

sandstones and siltstones

dacites, sandstones and siltstones

Orebodies morphology

veins, vein-veinlet zones and veinlet-disseminated zones

vein-veinlet zones, zones of stockwork

veins, vein-veinlet zones

veins, vein-veinlet zones

Basic gangue minerals

quartz, carbonates (ankerite, siderite, calcite)

quartz, tourmaline, muscovite

quartz, ankerite, sericite, dickite, paragonite, pyrophyllite

quartz, dickite, calcite

Ore minerals

pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, tetrahedrite, meneghinite, boulangerite, jamesonite, chalcostibite

wolframite, arsenopyrite, lollingite, danaite, bismuthinite, tetradymite, joseite A and B, wehrlite, tellurobismuthite

stibnite, pyrite, arsenopyrite, berthierite, sphalerite, galena, chalcopyrite, tetrahedrite, jamesonite

arsenopyrite, pyrite, sphalerite, gudmundite, chalcopyrite, freibergite, pyrargyrite, berthierite, stibnite

Main productive mineral assemblage

gold–chalcopyrite–sphalerite–galena lollingite–glaucodot– arsenopyrite, bismuthinite– sulfotelluride

quartz–stibnite–berthieritic

freibergite–silver–antimony

Geochemical association of elements

Au, As, Sb, Ag, Cu, Zn, Pb, Li

Au, Bi, W, As, Te, Sn, In, Cd

Au, As, Sb, Ag

Examples of ore deposits

Bazovskoe, Drazhnoe, Zhdannoe, Malotarynskoe, Levoberezhnoe, Talalakh

Ergelyakh

Maltan, Sarylakh, Sentachan, Tan

formation of linear folds with concentric pattern revealing structural vergence dominantly towards the SW. Within the ore-bearing zones, they form tensional folding bands up to the first hundred meters in width. The largest objects are the mineralized fault zones as ore body type, which follow zones of cataclasis (the Bazovskoe, Drazhnoe and Malotarynskoe deposits), or exist as lentiform quartz veins (the Sana, Dirin’-Yuryakh, and Imtachan deposits) stratified veins in voids associated with delamination of folds (the Pil’, Talalakh, and Zhdannoe deposits). Structural types of orebodies (veined and veinlet-disseminated) of mineralized fault zones have developed in various combinations and volumes. Low-sulfide gold–quartz mineralization is common within the metallogenic zone. In terms of morphology varieties, quartz-vein orebodies are predominant, which for the most part are either obliquelycrossing, or subconcordant, and steeply- and shallow-dipping. Persisting neither along the strike, nor in thickness, they may have branchy shape or inflated parts and differently oriented apophyses, and be displaced by crosscuting structures. The highest concentration of quartz bodies is observed near the contacts between rocks with different competence. Mineralized zones of fault are characterized by more stable parameters of ore bodies and more uniform gold concentrations. Particles of vein-hosted gold are commonly bigger in veins, which may

Strike-slip

Dichek, Sakhchan, Serp

grade into nuggets of different size (Samusikov, 1990). However, both, have shown a tendency for sulfide accumulations. The mineral composition of orebodies of low-sulfide ores in gold–quartz deposits is fairly monotonous: quartz accounts for ca. 85–95%, carbonate (ankerite)—for 5–15%, ore minerals—for about 1%. However, sulfide concentrations are indicative of particularly well-endowed sections of ore bodies. The composition of vein and zones of vein-disseminated mineralization is dominated by SiO2 (51.43–87.4%), Al2O3 (4.37–17.02%), FeO (1.01–6.11%), Fe2O3 (0.44–5.67), with CaO (0.26–17.56%) and CO2 (0.47–13.00%) contents being most subject to variations. The identified ore mineral assemblages are: metasomatic pyrite–arsenopyrite–sericite– quartz; veined pyrite–arsenopyrite–quartz; gold–chalcopyrite– sphalerite–galena, and carbonate–sulfosalt (Gamyanin, 2001). Pyrite–arsenopyrite–quartz metasomatic association composes selvage (peripheral) zones of metasomatites up to 50 cm in width, with dominant development of metasomatic quartz. In metasomatic rocks, arsenopyrite which forms metacrystal “wrapped” with columnar quartz (Fig. 2b) is ubiquitously dominated by pyrite whose saturation can reach 10–20%, whereas arsenopyrite accounts for no more than 3%. Typically, prismatic arsenopyrite tends to selvage zones of veins. Although its composition is marked by the dominance of sulfur

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Fig. 2. Relationships between minerals at ore deposits of the Adycha–Taryn metallogenic zone. a, Chlorite concentrations in quartz; b, impregnation of metasomatic arsenopyrite “wrapped” with columnar quartz in near-vein-altered country rock; c, sporadic grains and crystals of arsenopyrite in quartz vein; d, intergrowth of gold and galena; e, elongated-branchy gold from assemblage with acicular sulphoantimonites; f, inclusions of minute gold particles in minerals of bismuthinite– tetradymite–joseite paragenesis; g, replacement of native gold with gold–antimony oxide; h, fine spongy gold; i, fragments of milky gold-bearing quartz are cemented by fine-grained gray quartz with Sb–arsenopyrite.

(1.05–1.12 apfu), it becomes low-sulfur in the direction opposite to selvage zones, and the gold concentration dramatically decreases from 800–950 to 20–40 ppm. In pyrite, the gold content is 0.8–12 ppm. Co and Ni are present in arsenopyrite at the level of hundredths of a percent, and Sb in the amount of the first tenths of a percent. Gangue minerals are dominated by quartz, which is present in three varieties: massive, columnar and drusy. The typomorphic features for all varieties of quartz include: two-peak thermoluminescence (TL) with higher intensity of low temperature glow peak (280 °C); average degree of crystal perfection (50–60%); low content of Li2O (5–12 ppm); the volume of a unit cell is 112.990–112.998 Å. Ore minerals present in the veins are dominated by pyrite and arsenopyrite (Fig. 2c) and their composition stoichiometry is higher, compared with metasomatic minerals. Close space–time relations are characteristic of gold with chalcopyrite–sphalerite–galena and sulfosalt associations, whose productivity is largely governed by close time of deposition with native gold (Fig. 2d), which forms intergrowths with sphalerite, and more often with galena through cocrystallizing minerals with smooth boundaries, which sometimes involves their crystals coalescence. As is the case with sulphoantimonite, a common penetration border or gold

particles coalescence with acicular aggregates of sulphoantimonite are presumable. This leaves an impact on gold morphology, which in this case is described as elongatedbranching (Fig. 2e). Lower grade gold (870–910‰) is noted for association with galena, whereas higher grade gold (930– 960‰) is associated with sulphoantimonite. Carbonate is a key mineral in the sulfosalt–carbonate assemblage where it is encountered in various amounts ubiquitously. It is interpreted as the latest mineral and tends to be localized in voids among quartz and is not tied specifically to any parts of quartz veins. By its composition, carbonate belongs to the ankerite–dolomite group with a variable ferruginous ratio and stable amounts of Mn, and sometimes Sr (Table 2, Fig. 3). Also, Amuzinsky et al. (1980) marked calcite development within ore zones, which is attributed to late Ag–Sb mineralization. Gold–bismuth type. Deposits of this type are closely tied with intrusions (“intrusion-related”) and are localized directly in small stocks of granitoids or their hornblendic halos, in dikes of variegated composition (granite porphyry, porphyry, diabases) (Gamyanin et al., 2003). Within the ATMZ bounds, the gold–bismuth mineralization is exemplified by the Ergelyakh deposit confined to the supradome zone of granitoid pluton with an area of about 50 km2 (Gamyanin et al., 2003). Granitoids and the adjacent biotite hornfels are dissected by

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Table 2. Composition of carbonates from the Adycha–Taryn metallogenic zone Ore deposit

Mineralization type

n

CaO

MgO

FeO

MnO

SrO

Dirin’

Au–Q

2

28.5

14

9.8

0.4

–

Bazovskoe

Au–Q

2

28.5

14

11.6

0.4

–

Talalakh

Au–Q

2

28.2

12.6

12.2

0.5

–

Kikhtey

Au–Q

2

30.6

15.1

10

0.6

–

Uzlovoe

Au–Q

3

28.2

14.7

9.8

0.3

–

Buyankino

Au–Q

4

29.5

12.6

12.1

0.4

–

Tikhoe

Au–Q

2

28.3

11.2

14.3

0.4

–

Gan

Au–Q

4

30.5

20.1

8

–

0.6

El’

Au–Q

2

30.4

12.5

12.5

0.4

0.3

Maltan

Au–Sb

3

27.6

13.5

11.6

0.2

0.6

Kinyas’

Au–Sb

2

28.6

14.2

13.1

0.3

0.2

Sarylakh

Au–Sb

5

30.2

14.5

15.3

0.2

0

Sarylakh*

Au–Sb

3

–

0.5

59.1

0.1

–

Sentachan

Au–Sb

4

29.1

17.7

9.6

0.3

–

Sentachan*

Au–Sb

2

0.2

0.3

59.2

0.8

–

Note. Mineralization type here and elsewhere: Au–Q is gold–quartz; Au–Sb is gold–antimony. * Regenerated carbonate.

simple lenticular steep-falling quartz veins up to 1 m thick and up to 250 m in length, occurring en echelon within E–W striking fault system. Mineralogy of gold–bismuth deposits has thus far been fairly well studied (Gamyanin et al., 1981, 2003; Rozhkov et al., 1971). The succession of mineral assemblages developed in the main orebodies is as follows: muscovite–tourmaline– quartz metasomatic, wolframite–tourmaline–quartz, pyrrhotite–lollingite–danaite–arsenopyrite, bismuth–sulfotelluride (Gamyanin et al., 1981). Native gold in sulfoarsenides is present in the form of minute impregnation (0.006–0.100 mm) in the amount of 50–150 ppm, whereas bismuth minerals are associated with free small particles of gold with the fineness ranging widely (750–960‰) (Fig. 2f). Wolframite contains 90–95% of ferberite minal. As-containing minerals are Co– Ni–loellingite, gersdorffite, Ni-danaite and arsenopyrite, representing a sequence of crystallization, from loellingite through sulfuric arsenopyrite. The late gold-bearing assemblage of bismuth minerals is represented by homological series of tetradimite, A and B joseite, tellurobismuthite with widely variable concentrations of the components causing nonstoichiometry of mineral composition. Gold–bismuth mineralization was established at the Malotarynskoe gold–sulfide–quartz deposit (Fridovsky et al., 2014), where quartz–muscovite–pyrrhotite–Co–Ni–sulpharsenides and bismuth–sulfoarsenides mineral assemblages were identified. Being not widespread, though, they attest to repeated activations of tectonic magmatism in ore-hosting structures and to probable relationship between various types of combined mineralization and intermediate magma chambers having a single deep focus. Gold–antimony type. Au–Sb mineralization is the most widespread in the axial part of Adycha–Taryn fault (the

Sentachan, Sarylakh, Maltan, Tan, Kinyas’-Yurakh, ElgiTonor deposits) (Amuzinsky et al., 2001; Berger, 1978; Bortnikov et al., 2010; Indolev et al., 1980). As such, this type of mineralization distinguishes the Adycha–Taryn metallogenic zone from other gold-bearing zones of the Yana– Kolyma belt and the entire Russia’s northeast. Geologic setting of the Sarylakh and Sentachan deposits, ore mineralogy and geochemistry, chemical composition, wallrock metasomatites have been discussed in great detail in (Amuzinsky et al., 2001), where the formation of deposits in shallow subsurface conditions from deep reducing fluid is substantiated. The authors (Bortnikov et al., 2010) emphasize that the formation of gold and antimonite mineralization at different depths was driven by geodynamic events. The superimposed stibnite and gold–quartz mineralizations lead to the formation of complex polygenic gold–antimony deposits (Bortnikov et al., 2010; Indolev et al., 1980). The example of the Maltan deposit has shown massive and intensive influence of the mineral-forming fluid of the stibnite mineralization stage on the early mineral matrix of low-sulfide gold–quartz mineralization (Fridovsky et al., 2014). At this, the existence of the same type of minerals with different typomorphic features and newly formed minerals at the same hypsometric level reflect the different level of depths of their formation, which allows to consider the formation of the Maltan deposit in two stages. For different types of mineralization, different emplacement conditions are established. Orogenic-type gold–quartz mineralization occurs in longitudinal thrusts and in their pinnate faults, as well as in quartz veins of different sizes. Roughly W–E trending oblique ramps are associated with thrusts. Antimony and gold mineralization types were emplaced in the same structures, however, anti-

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Fig. 3. Chemical composition of carbonates from the Au–quartz and Au–antimony deposits of the Adycha–Taryn metallogenic zone. * Regenerated carbonate.

mony mineralization occurred in the reactivated structures, in the left-lateral tectonic stress field (Fridovsky et al., 2014). The ore composition of gold–antimony deposits is represented by a combination of mineral assemblages noted for low-sulfide gold–quartz deposits, with superimposed bertierite–stibnite assemblage, and produced thereby the following reaction minerals: chalcostibite, ulmannite, Sb-rich pyrite, nickel-containing arsenopyrite. Native gold in these deposits is often substituted by aurostibite and mustard gold (Fig. 2g). Aurostibite has proven unstable in essentially stibnite ores and readily decomposes with subsequent formation of a subgraphic aggregate structure gold + stibnite (Gamyanin et al., 1984). During the oxidation of stibnite, such aggregates acquire spongy structure, which is often referred to by mineralogists as “spongy gold” (Fig. 2h). At this, early gold is involved first in the processes of disintegration, then dissolves and is redeposited. Gold from gold–antimony deposits is fine (<<0.25 mm) and has a large proportion of crystals. The disintegration of gold entails redistribution of its concentrations, along with the ore pillars contour widening and affiliated decrease in the elevated concentrations, culminating in its more uniform (8–12 ppm) distribution within the orebodies. Redeposition of gold leads to its ennobling and increased fineness up to 950– 1000‰. Ankerite and dolomite appear most abundant at Au–Sb deposits within the Adycha–Taryn metallogenic zone (Supletsov and Zhdanov, 1980), unlike the regenerated carbonates represented by siderite associated with the imposition of the late antimonite stage of mineral formation (Table 2, Fig. 3). Silver–antimony type. Ag–Sb mineralization was previously established by (Gamyanin and Goryachev, 1988) as an independent type and later discussed in detail in (Goryachev et al., 2011). Along with the monometal Ag–Sb manifestations, known within Taryn subvolcano, this mineralization is widely distributed in complex (polyformation) tin–tungsten and gold deposits. The maximum concentration of the silver–antimony occurrences are reported from the Dichek, Sakhchan, Serp deposits. The sulfide grade is lean in

these ore deposits. Silver concentrations in the ore bodies are associated with the prevalence of freibergite–silver–sulfoantimonite assemblage, which locally forms rich (>>1 kg/t) bonanza ores. This type of mineralization is superimposed on gold–quartz deposits. The late epithermal mineralization represented by veins and veinlets of spherolite, cryptograined or colloform-reniform quartz with poor sulfide impregnation has been identified in many Taryn ore deposits (Fridovsky et al., 2013, 2014, 2015). At the Ergelyakh deposit, it is evidenced by fairly thick (up to 1 m) veins, rhythmically zoned spherolite-cryptograined quartz containing rare impregnation of chalcopyrite, sphalerite, galena, and freibergite. These NW- and NE-oriented veins cross the roughly E–W-striking veins with gold–bismuth mineralization. At the Pil’ and Malotarynskoe deposits, the veins of dark gray to black cryptograined quartz, crosscuting and cementing the products of low-sulfide gold–quartz mineralization are saturated with Sb–arsenopyrite (Fig. 2i). Due to its typomorphic properties, this quartz (Li2O content: 700–1100 ppm; low crystal perfection (30–40%)) is similar to silver–antimony type quartz deposits developed within the Taryn subvolcano area. While cryptograined quartz from sulfides is differentiated by fairly intense impregnation of fine-grained to pulverized pyrite with rare grains of rhomboid shaped arsenopyrite. Concentration of As constantly present in the composition of pyrite is not more than 0.7%. The atomic absorption analysis has revealed elevated concentrations of Au (599 ppm) and Ag (66 ppm). Arsenopyrite from cryptograined quartz veins exhibited high levels of Sb (1.6–2.3%), which represents a typomorphic indicator for silver–antimony mineralization in the Verkhoyansk–Kolyma mesozoids (Gamyanin, 2001). Galena from veins with silver–antimony mineralization at the Ergelyakh deposit is characterized by the presence of Ag (0.7–1.2%) and Se (0.6–0.8%), whereas fahlore with Ag content up to 18% is related to freibergite.

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Geochemistry of stable isotopes Stable isotopes (O, C, and S) in minerals. Within this research, we studied isotopic composition of oxygen in quartz, carbon and oxygen in carbonates, sulfur in sulfides from different types of noble-metal mineralization of the Adycha– Taryn metallogenic zone. The measurements were carried out by the standard, mass spectrometric method at the Stable Isotope Laboratory of the Far East Geological Institute FEB RAS (analyst: T.A. Velivetskaya). Geochemistry of stable isotopes of the large gold–antimony Sarylakh and Sentachan deposits was previously discussed in detail by (Bortnikov et al., 2010). The oxygen isotopic composition of quartz from the studied deposits is presented in Table 3. Early metamorphogenic

quartz outside ore zones has δ18O values equal to +20.1 ± 2‰. δ18O values for quartz from gold–bismuth deposits vary in a narrow range +12.5 ± 0.4‰, whereas the variations are much wider (δ18O values vary between +14.2 and +19.5‰) for quartz of Au–quartz mineralization. A similar interval is typical of Au–antimony mineralization (δ18O = +16.1 to +19.2‰). The cryptograined quartz of silver–antimony mineralization is enriched with a light oxygen isotope (δ18O = –3.2 to +4.7‰). The carbon and oxygen isotopic composition of carbonates was studied for all types of noble-metal mineralization in the Adycha–Taryn metallogenic zone, as well as for calcite from early hydrothermal-metamorphogenic veins (Fig. 4, Table 4). The changes in the δ13C and δ18O values can be described as: contrasting for the studied types of mineralization from

Table 3. Oxygen isotopic composition of quartz in ore deposits of the Adycha–Taryn metallogenic zone Ore deposit

Quartz type

Mineralization type

δ18OSMOW, ‰

Assemblage

Beyond deposits

vitreous

Q

19.9; 20.3

calcite

Ergelyakh

semitransparent

Au–Bi

12.6; 12.9

sulfotellurides

Kurdat

milky

Au–Q

16.2

sphalerite, galena

Sana

milky

Au–Q

15.4; 15.9

sphalerite, galena

Dirin’

milky

Au–Q

14.2; 16.9

tetrahedrite, galena

Zhdannoe

milky

Au–Q

15.2; 16.8

sphalerite, galena

Andreevskoe

milky

Au–Q

18.1

sphalerite, galena

Uzlovoe

milky

Au–Q

18.5

stibnite

Nitkan

semitransparent

Au–Q

17.3

stibnite

Rudnyi Lazo

semitransparent

Au–Q

18.1

galenite

Yukhondzha

milky

Au–Q

18.7; 19.5

tetrahedrite

Gavrikovskoe

milky

Au–Q

16.2

sphalerite, galena

Klyap

milky

Au–Q

15.9

sphalerite, galena

Motyl’

milky

Au–Q

17.6

sphalerite, galena

Imtachan

milky

Au–Q

17.2; 18.1

tetrahedrite

Imtachan

milky

Au–Q

18.1

sphalerite, galena

Sedlo

semitransparent

Au–Q

16.3

sphalerite, galena

Aulochan

milky

Au–Q

17.8; 18.3

galena, tetrahedrite

Primetnoe

milky

Au–Q

16.3

sphalerite, galena

Ebir-Khaya

coarse-grained

Au–Q

16.6

wolframite, galena

El’

milky

Au–Sb

19.0; 19.2

berthierite, stibnite

Kinyas’

milky

Au–Sb

16.3

sphalerite, galena

Kinyas’

regenerated

Au–Sb

8.9

stibnite

Maltan

milky

Au–Sb

16.1; 16.3

sphalerite, galena

Ebir-Khaya

cryptograined

Ag–Sb

–2.7; 2.9

Ag–sulfosalts

Delegenyakh

cryptograined

Ag–Sb

–2.8; –3.2

Ag–sulfosalts

Kupol’noe

fine-grained

Ag–Sb

2.9

Ag–Sb–sulfosalts

Ergelyakh

zonal

Ag–Sb

3.1

galena freibergite

Ebir-Khaya

cryptograined

Ag–Sb

–0.3; –2.7

Kupol’noe

fine-grained

Ag–Sb

0.1; 0.3

Ag–Sb–sulfosalts

Serp

cryptograined

Ag–Sb

4.7

Ag–sulfosalts

Dichek

fine-grained

Ag–Sb

1.8; 2.4; 2.9

Ag–sulfosalts

Sakhchan

fine-grained

Ag–Sb

1.1; 2.9

Ag–sulfosalts

Note. Hereafter, mineralization types are: Q is hydrothermal-metamorphogenic; Au–Q is gold–quartz; Au–Bi is gold–bismuth; Au–Sb is gold–antimony; Ag–Sb is silver–antimony. Here and in Tables 4 and 5: Analyses were performed at the Stable Isotope Laboratory, the Far East Geological Institute FEB RAS.

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Fig. 4. Oxygen and carbon isotopic composition of carbonates from the deposits of the Adycha–Taryn metallogenic zone. Types of mineralization: 1, hydrothermal– metamorphogene, 2, gold–bismuth, 3, gold–quartz, 4, gold–antimony, 5, silver–antimony.

–6.9 to –5.9‰ and from +2.1 to +5.7‰, respectively, for ankerite from gold–bismuth deposits; from –9.1 to –6.1‰, and from +12.4 to +18.7‰ for ankerite of gold–quartz mineralization; from –12.1 to –9.5, and from +15 to +16.3‰ for ankerite of gold–antimony mineralization, from –11.6 to –11.1‰ and from +1.5 to +4.7‰ for calcite of silver–antimony mineralization. Figure 4 distinctly shows that the δ18O intervals overlap the values for gold–bismuth and silver–antimony deposits, as well as for gold–quartz and gold–antimony deposits. With respect to δ13C values, their intervals partially coincidence with the values for gold–bismuth and gold–quartz, as well as for gold– and silver–antimony deposits. Metamorphogenic calcites are enriched with a heavy carbon (–1.1 to –1.7‰) and oxygen (from +20.3 to +20.5‰) isotope. Sulfur isotopic composition of sulfides was studied for productive veins of different types of deposits (Table 5, Fig. 5). A fairly wide range of δ34S values (–6.8 to 5.4‰) were obtained for the analyzed monofractions of arsenopyrite (Apy), pyrite (Py), and stibnite (St). The different types of mineralization for which δ34S were also obtained (Fig. 5) are: gold–bismuth (–3.7 to –2.2‰ (Apy), –6.7 to –6.8‰ (Py)); gold–quartz (–2.1 to +2.4‰ (Apy), –6.6 to +5.4‰ (Py), –6.1 to +4.2‰ (St)); gold–antimony ( –2.0 to +1.6‰ (Apy), –3.5 to +2.1‰ (Py), –5.3 to +0.2‰ (St)); silver–antimony ( –2.0 to –1.9‰ (Apy), –2.2 ± 0.1‰ (Py), –5.7 to –5.6‰ (St)). The O, C, and S isotopic composition of mineral-forming fluids. The oxygen isotopic composition in the fluid is calculated using measured δ18O values for quartz and carbonates and the average homogenization temperatures of fluid inclusions in quartz and carbonate in accordance with the fractionation equations (Zhang et al., 1989; Zheng, 1999), where T is Kelvin temperature:

∆quartz–H O = δ18Oquartz – δ18OH O = 3.306 (106/T2) – 2.71, (1) 2

2

δ18O

∆ankerite–H2O = ankerite – – 4.62 (103/T) + 1.71, 18

δ18O

18

H2O =

4.12 (106/T2) (2) 6

2

∆calcite–H2O = δ Ocalcite – δ OH2O = 4.01 (10 /T ) – 4.66 (103/T) + 1.71.

(3)

18

The δ OH2O values calculated for the fluid (Fig. 6) involved in the formation of quartz are: +10.5 ± 0.2‰ (250 °C) for metamorphrogenic quartz; +6.1 ± 0.4‰ (330 °C) for quartz from gold–bismuth deposits; +7.3 to +12.3‰ (300 °C) for quartz from gold–quartz deposits; +4.9 to +8.2‰ (200 °C); for quartz from gold–antimony deposits; –13.6 to –7.3‰ (220 °C) for quartz from silver–antimony deposits. The carbon isotopic composition of carbonates from gold–bismuth and gold–quartz deposits overlaps with the interval –5 to –2‰ typical of CO2 of magmatic origin (Kerrich, 1990). Mantle carbon and carbon of granitoid magmas have values δ13C equal to –7 to –2‰ and –6 to –2‰, respectively (Jia and Kerich, 2000). It stands to reason that the carbon isotopic composition of the fluid from which the carbonates were deposited is close to these reservoirs. The fluids was enriched by light carbon isotope during the formation of gold–antimony and silver–antimony mineralization. The isotopic composition of sulfur in the fluid (δ34SH2S), which was in equilibrium with sulfides at the time of mineral formation, was calculated by the fractionation equations (Li and Liu, 2006; Ohmoto and Rye, 1979), assuming the dominance of H2S in the solutions: ∆pyrite–H2S = δ34Spyrite – δ34SH2S = 0.4 (106/T2),

(4)

∆stibnite–H2S = δ34Sstibnite – δ34SH2S = –0.75(106/T2).

(5)

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Table 4. Carbone and oxygen isotopic composition carbonates from different mineralization types of the Adycha–Taryn metallogenic zone Ore deposits

Mineralization type

δ13CPDB, ‰

δ18OSMOW, ‰

Beyond ore zones

Q

–1.7

20.5

Beyond ore zones

Q

–1.1

20.3

Ergelyakh

Au–Bi

–6.9

5.7

Pil’

Au–Q

–6.1

14.7

Dirin’

Au–Q

–6.1

14.3

Talalakh

Au–Q

–9.1

16.1

Bazovskoe

Au–Q

–7.5

12.4

Malotarynskoe

Au–Q

–7.8

18.7

Maltan

Au–Sb

–9.5

15

Kinyas’

Au–Sb

–10.4

16.3

Sarylakh

Au–Sb

–11.2

15.8

Sentachan

Au–Sb

–12.1

15.8

Dichek

Ag–Sb

–11.6

2.3

Serp

Ag–Sb

–11.1

1.5

Sakhchan

Ag–Sb

–11.3

4.7

Table 5. Sulfur isotope composition of sulfides from ore deposits of the Adycha–Taryn metallogenic zone Ore deposit

Mineralization type

Arsenopyrite

Pyrite

Stibnite

Ergelyakh

Au–Bi

–2.2; –2.8;–3.7

–6.7; –6.8

–

Avgustovskoe

Au–Q

–2.1

–1.5

–2.9

Aulochan

Au–Q

–0.4

0.7; –0.6; –1.2

–1.3

Kinyas’

Au–Q

1.3

–

–3.3; –3.6

Malotarynskoe

Au–Q

2.2; 2.4

–

–0.2; 0.4

Pil’

Au–Q

–

–1.7; –1.6; – 1.2

–

Nitkan

Au–Q

0.7

–

–3.9

Elginskoe

Au–Q

–0.7

0.9

–4.4

Dzhetan’ya

Au–Q

–

1.1

4.2

Tugan

Au–Q

–

1.2

–1.1

Uzlovoe

Au–Q

0

2.2; 4.0; 5.4

0.6; –2.0

El’

Au–Q

–

–5.7; –6.6

–0.6; –6.1

Sarylakh

Au–Sb

–0.9; –1.6; –2.0

–1.7; –3.2; –3.5

–3.5; –4.3; –5.3

Sentachan

Au–Sb

–0.6; –0.8; 1.0

0.4; 1.2; 2.1

0.2; –1.4; –2.7

Maltan

Au–Sb

1.6

–

–2.6; –3.5; –4.1

Dichek

Ag–Sb

–1.9

–2.3

–5.6

Serp

Ag–Sb

–2.0

–2.1

–5.7

For the fluid in equilibrium with arsenopyrite, we used equation (4) after (Clayton and Spiro, 2000). In gold–bismuth deposits, the δ34SH2S values for the fluid coexisting with arsenopyrite and pyrite at 330 °C vary from –7.9 to –3.3‰. The calculated values of δ34SH2S fluid for gold–quartz mineralization in equilibrium with early sulfides (arsenopyrite, pyrite) at 300 °C range from –7.8 to +4.2‰. The emplacement of late antimonite involved fluid at δ34SH2S = –1.1 to +7.6‰ (200 °C). The δ34SH2S values for the fluid involved in deposition of pyrite and arsenopyrite (gold–

antimony mineralization at 200 °C), vary from –5.3 to +0.3‰. Stibnite was crystallized at 180 °C from the fluid enriched in the heavy sulfur isotope (δ34SH2S = –1.7 to +3.9‰). The formation of the studied sulfides of silver–antimony mineralization deposited from the fluid with the δ34SH2S value equal to –5.7 to –3.5‰. Most of the δ34S values for the ore-forming fluid therefore fall within the range from –3 to +3‰, indicating magmatic sulfur participation in the ore emplacement. Besides, sedimentary rock-hosted sulfur was involved in the hydrothermal system.

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Fig. 5. Sulfur isotopic composition of sulfides from the deposits of the Adycha–Taryn metallogenic zone. Types of mineralization: a, gold–bismuth; b, gold–quartz; c, gold–antimony (data updated from (Bortnikov et al., 2010); d, silver–antimony. Minerals: 1, arsenopyrite; 2, pyrite; 3, stibnite.

Fluid inclusions. The thermobarogeochemical studies conducted for quartz of low-sulfide gold–quartz, gold–bismuth, and silver–antimony mineralization (analyst: V.Yu. Prokof’ev, IGEM RAS) were impossible for ultrafine fluid inclusions in hydrothermal-metamorphogenic quartz. Fluid inclusions in quartz of gold–quartz mineralization were analyzed on the example of the Pil’ and Malotarynskoe deposits (Fridovsky et al., 2012, 2015). The identified assemblages of primary and pseudosecondary fluid inclusions were split into two types: essentially carbon dioxide (type 1) and carbon dioxide–water (type 2), both being syngenetic, which attests to a heterogeneous state of the ore-forming fluid. Most fluid inclusions are 1–20 µm in size and have either “negative crystals” or irregular shape. The ore-forming fluids of the Pil’ deposit contained dissolved chlorides of sodium and magnesium (concentration 8.7–2.3 wt.% NaCl equiv), carbon dioxide (6.5–5.0 mol/kg solution) and methane (1.0–0.7 mol/kg solution) and were captured in the temperature range from 233 to 362 °C and fluid pressure 0.85–0.76 kbar. Ore-forming fluids of the Malotarynskoe deposit were captured by the inclusions in the 318–253 ºC temperature interval at pressure 0.76 kbar and contained dissolved sodium

and magnesium chlorides (concentration: 5.9–2.6 wt.% NaCl equiv), carbon dioxide (6.6–3.4 mol/kg solution) and methane (1.0–0.6 mol/kg solution). Secondary fluid inclusions contained aqueous solution with salt concentration 6.5–2.2 wt.% NaCl equiv and were homogenized into a liquid at 230– 169 ºC, with its density and homogenization of gas inclusions being remarkably high. Given that the mineralogical and geochemical signatures of the low-sulfide gold–quartz deposits from this zone exhibit similarity, these can be confidently interpreted as typical of other ore deposits localized within its bounds. Proceeding from the phase composition (at room temperature), the following four types of fluid inclusions are allocated in quartz from the gold–bismuth Ergelyakh deposit: (1) twoor three-phase aqueous carbon dioxide; (2) essentially gaseous, with liquid CO2; (3) two-phase gaseous–liquid; (4) three-phase fluid inclusions containing liquid aqueous solution, a gas bubble and isotropic cubic crystal identified as halite. Early quartz deposited from relatively diluted solutions containing sodium and magnesium chlorides from 4.5 to 8.6 wt.% NaCl equiv at temperatures ranging from 265 to 305 °C and a pressure of 0.2 kbar (Lykhina et al., 2003).

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Fig. 6. Oxygen isotopic composition of mineral-forming fluid from the deposits of the Adycha–Taryn metallogenic zone. Types of mineralization: 1, hydrothermal– metamorphogenic; 2, gold–bismuth; 3, gold–quartz; 4, gold–antimony; 5, silver–antimony.

The inclusions of concentrated sodium–calcium chloride solutions identified in quartz from productive gold-bearing assemblages are described as having salts concentration 32.9– 32.7 wt.% NaCl equiv and homogenizing into a liquid at temperatures of 360–255 °C; containing the inclusion of chloride Na–Mg solutions (3.7–6.9 wt.% NaCl equiv); having temperatures varying from 360 to 190 °C, and a pressure of 0.06 kbar (Gamyanin et al., 2017). Carbon dioxide–aqueous inclusions established in quartz from the galena–chalcopyrite– sphalerite assemblage, contain chloride Na–Mg solutions (4.3–2.9 wt.% NaCl equiv) and have temperature of homogenization in the range 285–250 °C, and a pressure of 1.1– 0.9 kbar. The fluid regime of the Sarylakh and Sentachan large gold–antimony deposits was previously thoroughly investigated by (Bortnikov et al., 2010). The established similarity in conditions for the formation of early gold-bearing milky quartz from bicarbonate–sodium fluid in orebodies with stibnite mineralization in the Sarylakh and Sentachan ore deposits include: a temperature range of 340–230 °C, salt concentrations at 6.8–1.6 wt.% NaCl equiv, a fluid pressure of 2.3–1.2 kbar, and overlapping fluid salinity values intervals. In late generation quartz accompanying the stibnite mineralization, fluid inclusions contained aqueous solution with salts concentration of 3.2 wt.% NaCl equiv and were homogenized into a liquid at 304–189 ºC. The syngenetic gaseous inclusions contained nitrogen with density of 0.19 g/cm3. The estimated pressure at a temperature of 189 ºC is 0.3 kbar. The numerous fluid inclusions from 25 to 1 µm in size, having either the “negative crystals” or irregular form, encountered in veinhosted quartz of the silver–antimony deposits were classified as: primary (uniformly distributed throughout the host mineral or confined to the zones of growth), pseudosecondary (confined to fractures not extending beyond the crystals) and secondary (confined to crosscutting fractures). The identified fluid inclusions were grouped into three types by their phase composition (Fig. 7): (1) carbon dioxide–

aqueous; (2) essentially gaseous; and (3) two-phase gas–liquid fluid inclusions. Gaseous inclusions, as a rule, were captured synchronously with the inclusions of the 1st and 3rd types (i.e., confined to the same zones or fractures), indicating the heterogeneous state of the ore-forming fluid (boiling). Fluid inclusions detected in quartz from ore veins of the Dichek deposit belong to type 3 (primary, gas–liquid) containing sodium chloride solutions (Teut = –37 to –32 ºC) with salts concentration of 3.6–0.8 wt.% NaCl equiv. The analysis of the chemical composition of fluid inclusions based on different methods was performed for a sample of 0.5 g of the 0.5–0.25 mm fraction in TsNIGRI (analyst Yu.V. Vasyuta) by the method published in (Kryazhev et al., 2003). Previously, the amount of water equired for calculation of concentrations of elements in the fluid was determined from the same sample. Carbon dioxide and methane were also analyzed, and Cl, K, Na, Ca, and Mg were determined by ICP-MS in the solution after the extract preparation, as well as a wide range of ore and trace elements. The composition of fluid inclusions from a number of deposits was studied (Table 6). Table 6 and Fig. 8 show that the most saturated mineralization of the fluid in the inclusions was noted for the silver–antimony and gold–antimonite type of mineralization, and the lowest—for low-sulfide gold–quartz type for quartz from the polymetallic mineral assemblage. Analysis of the content of the main components in different types of deposits allowed to establish the specifics of the ore-forming fluid. Hydrothermal-metamorphogenic mineralization (Q) suggests that the fluid has a sodium–calcium–sulfate composition with a high proportion (90%) of CO2 in the gaseous component; gold–bismuth (Au–Bi) suggests Na–Ca– Cl composition of the fluid with a high proportion of CO2 in the gases; low-sulfide gold–quartz (Au–Q) is mainly calcium– sodium–bicarbonate fluid with 80% of CO2 in the gaseous component; gold–antimony (Au–Sb) is calcium–magnesium– bicarbonate fluid with a major contribution of CO2 among

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Fig. 7. Primary fluid inclusions in quartz from silver–antimony deposits of the Adycha–Taryn metallogenic zone. a, carbon dioxide–aqueous inclusion type 1 (+20 ºC); b, essentially gaseous inclusion type 2 with carbon dioxide (+20 ºC); c, d, essentially gaseous inclusion with methane (c, +20 ºC, d, –95 ºC); e, two-phase gaseous–aqueous inclusion type 3.

gases; silver–antimony (Ag–Sb) is calcium–magnesium–sulfate–bicarbonate fluid, practically deprived of methane. Note that despite different contents of main components composing the fluid in the deposits with different mineral assemblages (arsenopyrite and polymetallic, bertierite and stibnite), both the solution type and the components’ ratio vary slightly. With regard to the contents of microcomponents, Table 7 and Fig. 8 show that these vary greatly in different types of ore deposits. It would be appropriate to set up a directed series for reducing the elements concentrations in the fluid for each type of mineralization (Table 8). These series of concentrations primarily evidence that high concentrations of any element in the fluid in no way depend on the ore mineral composition and cannot therefore be explained by “contamination”. Highly mineralized fluids of hydrothermal-metamorphogenic and silver–antimony types of mineralization bearing the minimum sulfide and other mineral load according to the visual and microscopic observations, provide a compelling evidence for this. The reason for this should be sought for primarily in the component sources. In this case, the most perytinent explanation consists in the borrowing by the ore-forming fluids (within these types of mineralization), of lithophilic and a number of ore components (Fe, As) on the long migration path through the host rocks to their discharge place. Gold–bismuth mineralization, most closely associated with the generation of fluids by shallow magma chambers, contains elements characterizing geochemistry of granitoid rocks. At the same time, the data of the

composition of fluid inclusions in quartz of different types of mineralization clearly indicate the difference and independence of ore-forming fluids determining different types of mineralization, and confirm the geological observations indicating the different ages of their formation. Conclusions This research results complete with the available published data (Amuzinsky, 2005; Amuzinsky et al., 2001; Berger, 1978; Bortnikov et al., 2010; Fridovsky, 2002; Fridovsky et al., 2012, 2013, 2014, 2015; Gamyanin, 2001; Gamyanin et al., 2003; Indolev et al., 1980; Tectonics..., 2001; and others) have shown that the several types of precious-metal mineralization revealed within the Adycha–Taryn metallogenic zone are: gold–quartz (gold–sulfide–quartz), gold–bismuth, gold–antimony and silver–antimony. The data on oxygen isotope composition of quartz, carbon and oxygen in carbonates, and sulfur in sulfides from different types of noble-metal mineralization of the Adycha–Taryn metallogenic zone bear the evidence of different sources of hydrothermal fluids involved in their formation with the following key factors identified in each: magmatogenic fluids—in the formation of gold–bismuth and gold–antimony deposits; metamorphogenic fluids—in gold–quartz deposits; and meteoric waters—in silver–antimony deposits. Sequence of the formation of different types of mineralization is distinctly associated with the region-specific geodynamic development. The onset of the collisional processes and

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Table 6. Amounts of basic components in water extracted from fluid inclusions in quarts in the Adycha–Taryn ore deposits Ore deposit

Mineralization H2O, type ppm

Main components, g/kg H2O CO2

CH4

Cl

SO4

HCO3

Na

K

Ca

Mg

Dora–Pil’

Q

–

391.9

12.5

21.2

80.1

27.7

27.2

7.1

11.9

9.4

Ergelyakh

Au–Bi grd

1686

50

15.6

26

–

0.04

10

0.87

4.07

0.03

Malotarynskoe

Au–Q

–

49.2

6.1

2.3

–

17.6

5.5

–

2.1

0.2

Sana

Au–Q

785

80.4

0.6

–

–

8.5

2

0.4

0.8

0.4

Bazovskoe

Au–Q

241

51.4

0.8

8.1

–

–

2.3

0.19

0.4

0.36

Dirin’

Au–Q

5345

95

25.6

32

–

4.50

13

1.41

7.78

0.08

Talalakh

Au–Q

665

15

0.1

–

–

13

3.5

0.2

164

2.7

Nitkan

Au–Q

918

29

0.09

–

–

15

3.48

0.29

1.19

0.25

Zhdannoe

Au–Q

1165

24

1.28

–

–

14

3.11

0.35

1.16

0.24

Imtachan

Au–Q

1187

62

0.53

–

–

30

13

0.26

0.00

0.00

Sarylakh

Au–Sb

1478

100

0.64

0.35

0.7

514

0.09

0.02

165

2.6

Sentachan

Au–Sb

1165

24

1.3

–

–

14

3.11

0.35

1.16

0.24

Ergelyakh

Ag–Sb

523

51

0.33

2.57

5.14

47

0.01

0.52

18.4

0.22

Aid

Ag–Sb

1252

11

0.63

0.55

4.49

384

0.32

2.9

126

0.43

Dichek

Ag–Sb

1856

9

0.55

0.51

2.14

576

0.14

1.13

186

1.87

Serp

Ag–Sb

744

15

1.02

0.71

1.43

387

0.38

3.35

3.3

2.25

Plastovoe

Ag–Sb

1475

7

0.55

0.35

2.16

478

0.24

0.46

0.01

0.05

Kupol’noe

Ag–Sb

196

178

1.18

2.87

5.75

13.2

0.77

0.07

7.6

0.05

Note. grd means from veins in granodiorites; from hornfelses overlying granodiorites. Analyses were performed at the Central Research Institute of Geological Prospecting for Base and Precious Metals (TsNIGRI). Analyst S.G. Kryazhev.

Table 7. Amounts of microcomponents in water extracted from fluid inclusions in quarts in the Adycha–Taryn ore deposits Ore deposit

Mineralization Microelements, mg/kg H2O type Li Rb Cs Sr

Ba

As

Sb

Ge

Cu

Zn

Cd

Pb

Au

Dora-Pil’

Q

441

28

584

124

43

5

–

37

99

–

42

–

Ergelyakh

Au–Bi

5

12

24

463

194

497

414

0.47

–

–

3.1

6.6

–

Malotarynskoe

Au–Q

38

–

–

69

–

91

26

–

27

101

–

16

1

Sana

Au–Q

3.8

0.7

–

4.6

–

27

79

0.7

1

66

–

–

0.19

Bazovskoe

Au–Q

32

0.9

1.2

7.7

6.0

5414

13.2

2.2

1.1

21

0.55

0.2

0.62

Dirin’

Au–Q

1

–

0.1

78

11

21

135

0.12

–

–

–

–

–

Talalakh

Au–Q

21

–

0.1

32

5.2

60

43

0.14

–

51

0.1

0.5

–

Nitkan

Au–Q

12

0.3

0.4

22

4

377

18

0.04

–

78

–

0.6

–

Zhdannoe

Au–Q

12

0.4

0.5

22

15

156

9

0.24

0.5

175

–

0.1

0.06

Imtachan

Au–Q

43

–

–

–

0.03

44

723

0.07

–

–

–

–

–

Sarylakh

Au–Sb

26

0.2

0.1

5

44

24

27

0.02

–

–

0.1

0.2

0.1

Sentachan

Au–Sb

29

0.4

–

7

32

18

35

0.03

–

–

–

0.3

0.1

Ergelyakh

Ag–Sb

54

0

0.3

30

152

1810

14,890

0

13.5

–

0.7

–

–

Aid

Ag–Sb

28

5.4

0.6

4

–

8577

5389

0.03

–

–

–

0.2

–

Dichek

Ag–Sb

145

1.1

0.6

87

81

487

885

0.2

–

–

–

13.5

0.8

Serp

Ag–Sb

16

7.9

1.8

256

–

635

2353

–

2.7

–

–

0.3

–

Plastovoe

Ag–Sb

22

1.6

0.4

–

0.8

200

2425

–

12.8

–

–

–

–

Kupol’noe

Ag–Sb

15

0.7

0.1

81

31.1

1834

19,422

0.01

25.9

5161

3.3

–

–

affiliated increase in the thermal gradient entail the mobilization of metamorphic waters forming hydrothermal-metamorphic mineralization in the upper crust: quartz–chlorite–calcite veins and veinlets with poor sulfide (pyrite) impregnation. As such, this type mineralization has no practical value, however, the intensity of its manifestation provides evidence of geologi-

cal and tectonic activation and the preore alteration of individual sites (tectonic blocks) in the upper crust. The research results presented in the paper have shown that the oxygen isotopic composition of the fluid in equilibrium with metamorphogenic quartz corresponds to a metamorphogenic source.

G.N. Gamyanin et al. / Russian Geology and Geophysics 59 (2018) 1271–1287

1285

Fig. 8. Distribution of the main and microcomponents of fluid in water extracts from quartz of ore deposits of the Adycha–Taryn metallogenic zone. Mineralization types: a, hydrothermal–metamorphogenic; b, gold–bismuth; c, gold–quartz; d, gold–antimony; e, silver–antimony.

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G.N. Gamyanin et al. / Russian Geology and Geophysics 59 (2018) 1271–1287

Table 8. Specific features of hydrothermal fluid composition in the Adycha–Taryn ore deposits Mineralization type

Concentration, mg/kg H2O >1000

100–1000

10–100

<10

Hydrothermal-metamorphogenic

Fe

B, Sr, Li, Mn, Ba

Zn, As, Pb, Cu, Ni, Rb, V, Sb

Se

Gold–bismuth

B, As, Se

Li, Sr, Fe, Zn, Cu

Cr, Ni, Mn, Ba, Sb

Pb, Rb

Gold–quartz

As, B

–

Zn, Li, Sr, Pb, Sb, Ni

Cr, W, Au, V

Gold–antimony

–

–

Ba, Sb, Li, As

Sr, Mo, Rb, Hg, Pb, Cs, Au, Cd, Ge, Bi

Silver–antimony

Fe, Li, B, Ba, Sr

As, Sb, Rb, Cu

Pb, V, Zn, Ni, Cr

Se

Further escalation of collision processes have prompted the formation of pockets of palingenic granitoid melts whose evolution under compression leads to the formation of goldbearing ore-magmatic systems. Shallow chambers of granitoid massifs are associated with gold–bismuth deposits, whereas the gold–quartz (gold–sulfide–quartz) deposits are suggested by intermediate chambers, which at the present time are inferred from the greater density of diorite–porphyry dikes. The role played by magmatic water in the fluid involved in the formation of quartz from the studied gold ore deposits is critical, which is evidenced by δ34SH2S values for ore-forming fluid (from –3 to +3‰). The involvement of metamorphogenic fluids in the formation of ore has also been established. Sulfur partially migrated from the host rocks into the hydrothermal system. Tectonic activation of the Adycha–Taryn fault zone in the late Cretaceous is found to be responsible for the formation of near-surface gold–antimony and silver–antimony mineralization. Cryptograined quartz of silver–antimony mineralization was crystallized from solutions enriched in light oxygen isotope, indicating the participation of heated meteoric waters in these processes. Analysis of the available data on geologic setting of the world’s largest ore deposits and those localized in the northeast of Russia, provide evidence that the development of polychronous, polyformation mineralization in the ore zones of the latter is still an ongoing process, allowing an inference that the ore-forming potential of the Adycha–Taryn metallogenic zone has yet been far from depletion. The research was carried out according to the research plan of the Diamond and Precious Metal Geology Institute SB RAS (project no. 0381-2016-0004), Program No. 48 of the Presidium of the Russian Academy of Sciences “Deposits of strategic and high-tech metals of the Russian Federation: regularities in location, formation conditions, innovative technologies for prognosis and development”, Project “Strategically important types of mineral resources and features of the geological structure of investment-attractive territories of the Republic of Sakha (Yakutia): metallogeny, tectonics, magmatism, geoecology, improvement of prospecting and forecasting technologies” of the “Program of integrated research in the Republic of Sakha (Yakutia), aimed at developing of its productive forces and social sphere for 2016–2020,” and by

the Russian Foundation for Basic Research, grant no. 18-45140040 r_a.

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