Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Formation in the Black Shale-Hosted Gold Deposits, Bodaybo Ore Region, Russia

Journal of Earth Science, Vol. 31, No. 3, p. 514–522, June 2020 ISSN 1674-487X Printed in China https://doi.org/10.1007/s12583-019-1024-4

Natalia N. Ankusheva *1, 2, Ekaterina E. Palenova1, Svetlana N. Shanina3 1. Institute of Mineralogy, South-Urals Federal Research Center of Mineralogy and Geoecology, Urals Branch, Russian Academy of Sciences, Miass 456 317, Russia 2. Geological Department, South-Urals State University, Miass 456 300, Russia 3. Institute of Geology of the Komi Science Center, Urals Branch, Russian Academy of Sciences, Syktyvkar 167 982, Russia Natalia N. Ankusheva: https://orcid.org/0000-0003-4142-5606

ABSTRACT: The P-T conditions of auriferous and barren quartz veins from Kopylovsky, Kavkaz and Krasnoye gold deposits in Proterozoic black shales of Bodaybo ore region are presented the first time in this study. Fluid inclusions trapped in auriferous quartz are aqueous Na±K-Mg chloride with salinity of 6

wt.%–8.8 wt.% NaCleqv. Homogenization temperatures vary from 260 to 350 ºС, and calculated trapping pressures are 1.2–1.6 kbar. The fluids trapped in barren quartz have more complicated compositions with

Na, K, Mg and Fe chlorides, salinity up to 13 wt.% NaCleqv, and homogenization temperatures ranging between 140 and 280 ºС. The volatiles in fluids are dominated by H2O, followed by CO2 with minor amounts of CH4 and N2. We suppose that auriferous and barren quartz veins have been formed due to the basic metamorphogenic fluid as evidenced by the close slat and gas fluid composition. KEY WORDS: Bodaybo, black shales, gold deposits, gold-bearing quartz, barren veins, fluid inclusions, P-T conditions.

0 INTRODUCTION whereas smaller gold occurrences in the Bodaybo region are The Bodaybo gold-bearing region is one of the largest studied poorly. But many features to understand the genesis of gold provinces in Russia. Situated in the eastern part of Russia gold mineralization could be better defined by small deposits in the Lena River Basin, this region belongs to the Baikal oro- rather than the giant deposits, which are characterized by poly- genic belt. It hosts the well-known giant Sukhoi Log Deposit genic and polychronic ore-forming processes (Rundqvist, 1997). (2 956 t Au and 1 541 t Ag, Migachev et al., 2008) as well as Therefore, the small-scaled deposits Kopylovsky, Kavkaz, and several smaller deposits (Verninskoye, Golets Vysochayshiy, Krasnoye were studied in this work. etc.). All gold deposits of the Bodaybo region are hosted by The study focuses on characterizing P-T conditions of the Upper Proterozoic black shales. formation of the gold-bearing and barren quartz veins and fluid There are two major hypotheses for the formation of the volatile composition of the Kopylovsky, Kavkaz, and Krasnoye deposits in the Bodaybo region: magmatic hydrothermal and deposits, on the basis of previous studies of our colleagues whi- metamorphic hydrothermal. According to the first hypothesis, the ch aimed to describe mineralogical-geochemical features of main stage of gold concentration in the ore is related to post- these deposits and host rocks (Palenova et al., 2015a, b, 2013). metamorphic intrusions, including granitoid and hypothetical deep-seated mafic complexes (Yudovskaya et al., 2011; Laverov 1 GEOLOGICAL SETTING et al., 2007; Distler et al., 2004). According to the metamorphic The Bodaybo region is the part of the Mamsko-Bodaybinsky hydrothermal hypothesis, ore-forming fluids result from the re- District and composed of Upper Proterozoic carbonaceous- gional metamorphism of initially metalliferous carbonaceous terrigenous sediments folded and intruded by Late Paleozoic sequences (Large et al., 2007; Buryak and Bakulin, 1998). granitoids (Fig. 1). Granitoid stocks and large batholiths of the Many papers have been focused on the Sukhoi Log Deposit, Mamsko-Oronsky (about 420 Ma, Gerasimov et al., 2007) and which is the typical of the aforementioned genetic models, Konkudera-Mamakan (2 phases, 325 and 270 Ma, Bukharov et al., 1992) complexes intrude terrigenous sequences in the southern *Corresponding author: [email protected] part of the region. Also there are Late Paleozoic thin lamprophyre © China University of Geosciences (Wuhan) and Springer-Verlag dykes. The sedimentary rocks are greenschist facies metamor- GmbH Germany, Part of Springer Nature 2020 phosed with increasing grade from chlorite-muscovite subfacies in the central part to biotite subfacies at the margins (Ivanov, 2008). Manuscript received February 13, 2019. The gold deposits in the Bodaybo region consist of two Manuscript accepted May 30, 2019. large ore clusters: Kholmolkhyn, with the largest known deposits

Ankusheva, N. N., Palenova, E. E., Shanina, S. N., 2020. Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Forma- tion in the Black Shale-Hosted Gold Deposits, Bodaybo Ore Region, Russia. Journal of Earth Science, 31(3): 514–522. https://doi.org/10.1007/s12583-019-1024-4. http://en.earth-science.net Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Formation in the Black Shale-Hosted Gold Deposits 515

Figure 1. Simplified geological scheme of Bodaybo ore region (after Ivanov, 2008).

(Sukhoi Log, Verninskoe) located in the north and Artemovsky in the Vasilievsky anticline, Kavkaz Deposit is located. the south (Ivanov, 2008); Kopylovsky and Kavkaz (Dogaldyn The Krasnoye Deposit is situated in 75 km north from

Formation (Vdg3) and Krasnoye (Vacha Formation) deposits Bodaybo Town at the watershed of Krasny and Tjoply streams (Palenova et al., 2015b). and confined to the complicated anticline upper bend (Kuz- The Kopylovsky Deposit is located 45 km NE from Bo- menko, 2013). The deposit is hosted by carbonaceous quartz daybo Town and confined to the homonymous near-latitudinal and quartzitic metamorphosed sandstones and siltstones, and anticline—a tight asymmetric fold with gently dipping northern less, interbedded carbonaceous shales. Gold mineralization is (42º–50º) and near-vertical southern limbs. The curved hinge of confined to the dispersed and lens-shaped pyrite dissemination the fold dips gently to the southwest and east. Quartz veins, zones, and fewer quartz veins with sulfide mineralization. Gold stockworks and NE-trending strike-slip-normal faults are devel- has formed inclusions and growths in pyrite (Ankusheva et al., oped at the hinge curvature (Palenova et al., 2015b). The host 2019; Palenova et al., 2013). rocks are sandstones and siltstones, and carbonaceous shales of All studied deposits are characterized by sulfide mineraliza- the Dogaldyn Formation metamorphosed to sericite-chlorite tion in the form of layers and disseminations in carbonaceous greenschist facies (Palenova et al., 2013). In addition, rare thin shales and metamorphosed sandstones and siltstones; quartz- lamprophyre dykes are developed at Kopylovsky Deposit. The pyrite veinlets in stockwork zones; nest-shaped and poor dis- nearest granite pluton is located 40 km east (Aksenov, 2004). semination in quartz veins (Fig. 2) (Palenova et al., 2015a, b). Gold ores are located in the core and north limb of the Kopy- Gold formed inclusions and growths with pyrite and native grains lovsky anticline and predominantly hosted in carbonaceous shale in quartz veins. At the deposits, ores are divided into gold- intercalated with metamorphosed sandstones and siltstones. sulfide-quartz (quartz veins and stockwork zones in anticlinal The Kavkaz Deposit is located 35 km north from Bodaybo fold core) and Au-sulfide (mineralized zones in host rocks) types. Town in the central part of the Vasilievsky ore field which con- Quartz veins are divided into 3 types: (1) thick (1–8 m) selli- tains a 200 to 800 m wide ‘belt’ of quartz veins. This belt is con- form in curves of folds and flexures; (2) concordant thin quartz- trolled by the Millionny and Korolkovsky oblique-slip faults pyrite veinlets (from several millimeters to 5 cm thick); (3) the which are complicated by the northern limb of the Kairo-Lenin youngest veins of different thicknesses (from 1 cm to tens of cm). anticline and conjugated with higher order folds, in one of which, Quartz (rare quartz-carbonate) veins at Kopylovsky Deposit

516 Natalia N. Ankusheva, Ekaterina E. Palenova and Svetlana N. Shanina

Figure 2. Photographs showing the quartz veins of deposits. (a) Sample 358-2 with Au, and (b) sample 504-80.2, barren from Kopylovsky; (c) sample 258-2, squares are visible Au from Kavkaz; (d) sample 141425-135.6, galena-quartz vein with Au from Krasnoye. include galena and chalcopyrite. At Kavkaz Deposit, quartz veins 514 nm emission line (10 mW); the lateral resolution was better contain chalcopyrite, sphalerite, galena, chalcocite, secondary than 2 μm; acquisition time was equal to 30 s; accumulation covellite, and visible gold. And at Krasnoye Deposit, quartz veins number was equal to 10 (Pankrushina et al., 2019). The nitro- contain galena, chalcopyrite, and tennantite. gen peak area from the inclusions was calculated by subtracting

atmospheric N2 peak area from the measured one when focused 2 ANALYTICAL METHODS in the gas phase. Microthermometric studies were performed using double- polished sections on TMS-600 (Linkam) stage at the Thermo- 3 RESULTS barogeochemistry Laboratory of the South-Urals State University 3.1 Characteristics of Fluid Inclusions (Miass). The temperatures within -20 to +80 ºC range are meas- At Kopylovsky Deposit, quartz was sampled in gold- ured with a precision of ±0.1 ºC and out of this range, ±1 ºC. The bearing vein from a trench (sample 358-2). According to the fluid composition was determined according to Davis et al. (1990) atomic adsorption analysis, Au content in this vein is 0.73 ppm and Spencer et al. (1990). Salinities were calculated using the (after acid dissociation) and 1.40 ppm (after alkali dissociation). temperatures of final ice melting of fluid inclusions according to Quartz formed non-zoned anhedral grains up to 3 mm size. Bodnar and Vityk (1994). The pressures of trapped fluids were Fluid inclusions are bi-phase (VL) isolated, and groups unre- examined using CO2 inclusions. The fluid density was calculated lated to healed fractures. According to the classifications of using H2O-CO2-CH4 system, CO2 homogenization temperatures Roedder (1984) and Van den Kerkhof and Hein (2001), these and molar volumes of fluid inclusions (Thiery et al., 1994; inclusions are primary and pseudosecondary confined to the Brown, 1989). Microthermometric measurements were obtained fractures cracked during the quartz formation. Inclusions have about 300 individual fluid inclusions. irregular, rounded and sometimes ‘negative crystal’ shapes with The bulk chemical composition of volatiles trapped in inclu- 15–20 m in size (Figs. 3a–3c). sions was determined by gas chromatography using Tsvet 800 The barren quartz of Kopylovsky Deposit was sampled (GS-Q station, 30 mm0.53 mm40 mm) with pyrolytic adapter from the core (sample 504-80.2), and two types of fluid inclu- and precolumn in Geonauka, Center of Collective Sharing (Syk- sions have been analyzed. Type 1 is bi-phase (VL) inclusions tyvkar). The carrier gas is helium, and quartz samples were heated with 15–20 m in size and large vapor bubbles up to 50%–60% in quartz reactor at 500 ºС according to the technique of Mironova bulk. Sometimes vapor bubbles are moving but there is no liq- et al. (1992). Chromatographic signals were calculated by uid CO2. These inclusions are often located according to the TWS-MaxiChrom software. The measuring inaccuracy is 16%. growth zone of quartz grains why they are classified as primary In addition to the gas chromatography, we calculated the inclusions. Type 2 is presented by isolated dark bi-phase (VL) gaseous phase composition by Raman spectroscopy analysis of fluid inclusions with size about 40 m and large vapor bubbles fluid inclusion composition from auriferous and barren quartz (Figs. 3b, 3c). They are confined to fractures formed during the (on the sample of Krasnoye Deposit) using spectrometer quartz formation and classified as pseudosecondary inclusions. LabRam HR800 Evolution equipped with Olympus BX-FM As for Kavkaz Deposit, we studied the quartz vein with 2 optical microscope. Raman spectra were excited using the Ar mm visible Au located in goethite cavities (sample 284-5). The

Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Formation in the Black Shale-Hosted Gold Deposits 517

Figure 3. Microphotographs showing fluid inclusions in quartz. (a)–(c) Kopylovsky Deposit: (a) auriferous quartz, (b) and (c) barren quartz, (b) Type 1, (c)

Type 2; (d) auriferous quartz from Kavkaz Deposit; (e) CO2-rich fluid inclusion in quartz from Krasnoye Deposit. V. Gaseous; L. liquid.

Table 1 Microthermometric data of quartz from the black shale-hosted gold deposits, Bodaybo region

Deposit Veins n Teut (ºC) Tfm (ºC) C (wt.% Thom (ºC)

(salts) NaCleqv) Kopylovsky Auri* 65 -23…-24 -3.7…-5.7 6.1–8.8 300–350 (P, VL) (NaCl-KCl)

Barren 45 -21…-23 -3.3…-5.7 5.5–6.8 200–240 (P, VL) (NaCl±KCl) -36…-37 -4.5…-5.7 7.5–8.8 260–280

(PS, (NaCl-FeCl2±

VL) MgCl2)

Kavkaz Auri 45 -21…-23 -4…-5.8 6.5–8.8 212–280 (P, VL) (NaCl±KCl) Krasnoye Auri 100 -35…-36 -3.6…-7.6 6–10 260–330

(P, VL) (MgCl2-NaCl)

CO2rich 15 -31…-33 -4…-7 5.3–8.2 311–330

(VLL) (KCl-MgCl2)

Barren 105 -21…-23 -4.6…-10 7.3–13.9 140–280 (P, VL) (NaCl±KCl)

Teut. first melting temperature; Tfm. final melting temperature; C. salinity; Thom. homogenization temperature; n. number of measurements.

Auri*. auriferous quartz; fluid inclusion associations: P. primary; PS. pseudosecondary; CO2-rich. tri-phased inclusions; VL. bi-phase;

VLL. tri-phase CO2 inclusions.

bi-phase (VL) fluid inclusions are rounded, elongated, and rarely inclusions of 5–25 m in size and tri-phase CO2-rich inclusions angular shapes. They formed zones or groups of 3–4 inclusions (VLLCO2) with about 20%–50% liquid CO2-phase of the inclu- of 10–20 m in size (Fig. 3d). sion bulk (Fig. 3e). They are elongated, rounded and isometric, The investigated fluid inclusions in quartz from auriferous and sometimes ‘negative crystal’ shapes. and barren quartz from Krasnoye Deposit were collected from In all veins, in both auriferous and barren quartz, secon- different depths in carbonaceous schists and aleurolites con- dary fluid inclusions are small (not exceed 5 m) and marked fined to the folded black shales of Vacha and Aunakit suites of fractures in quartz. Also we observed small monophase dark Patomsky Complex. In quartz from the auriferous galena-quartz (gas) and light (liquid) inclusions (not exceed 3–5 m) which vein (sample 141425-135.6), we observed bi-phase (VL) fluid are co-genetic to primary bi-phase inclusions.

518 Natalia N. Ankusheva, Ekaterina E. Palenova and Svetlana N. Shanina

3.2 Composition and Salinity of Inclusions temperatures range between -3.3 and -4.3 ºС, corresponding to

Fluid inclusion data are shown in Table 1 and Figs. 4 and 5. a salinity of 5.5 wt.%–6.8 wt.% NaCleqv. Microthermometric measurements were obtained from about The eutectic temperatures of the Type 2 inclusions from 400 individual inclusions. barren quartz vein of Kopylovsky Deposit range between -36.7

The eutectic temperatures measured in fluid inclusions from and -37.0 ºС, suggesting the presence of FeCl2 (and possible auriferous quartz vein of Kopylovsky Deposit range between MgCl2) in fluid. The final ice melting temperatures range be- -23.0 and -23.8 ºС (n=11). These temperatures are marked by the tween -4.5 and -5.7 ºС. Salinity is 7.5 wt.%–8.8 wt.% NaCleqv. NaCl-KCl-H2O fluid. For most inclusions, the final melting tem- For inclusions in quartz from the auriferous vein of peratures of ice range between -3.7 and -5.7 ºС corresponding to Kavkaz Deposit, eutectic temperatures range between -21.8 and salinities between 6.1 wt.% and 8.8 wt.% NaCleqv. -23.9 ºС, indicating NaCl-KCl-H2O fluid. The final ice melting Fluid inclusions of Type 1 from barren quartz vein of temperatures range between -4.0 and -5.8 ºС and correspond to

Kopylovsky Deposit show the eutectic temperatures range be- a salinity of 6.5 wt.%–8.8 wt.% NaCleqv. tween -21.7 and -23.9 ºС, suggesting a simple NaCl-H2O sys- The eutectic temperatures and salinities of bi-phase fluid tem with KCl presence. In most inclusions, the final ice melting inclusions in auriferous and barren veins of Krasnoye Deposit are

50 50 (a) n=250 n=150 25 25 (b) 1 14 14 2 12 12 3 10 10

n 8 8

6 6

4 4

2 2

220 260 300 320 340 360 140 180 220 260 Homogenization temperature (ºС) Homogenization temperature (ºС)

Figure 4. Homogenization temperatures of fluid inclusions in quartz from auriferous (a) and barren (b) quartz veins. Deposits: 1. Kopylovsky; 2. Kavkaz; 3. Krasnoye.

1 2 3 12 4 5

) 10

eqv

Salinity (wt.% NaCl 8

7 2

150 200 250 300 350 400 Homogenization temperature(С) º

Figure 5. Homogenization temperature vs. salinity plot of fluid inclusion in quartz. 1, 2. Kopylovsky Deposit: 1. auriferous quartz, 2. barren quartz; 3. auriferous quartz of Kavkaz Deposit; 4, 5. Krasnoye Deposit: 4. auriferous quartz, 5. barren quartz.

Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Formation in the Black Shale-Hosted Gold Deposits 519 different. For auriferous veins, they range from -35 up to -36 ºC, the range of 1.2–1.6 kbar (Brown, 1989). which identifies MgCl2-NaCl-H2O fluid; and for barren veins, they range from -22 to -23 ºC, which specifies NaCl-KCl-H2O 3.5 Bulk Gas Composition of Fluid Inclusions fluid. In auriferous quartz the final melting temperatures vary According to gas chromatography analysis of 4 samples, from -3.6 to -7.6 ºC and salinity is 6 wt.%–10 wt.% NaCleqv with fluids are dominated by H2O and CO2 (Table 2). The total con- the peak 6.5 wt.%–8 wt.%. In barren quartz the final melting tents of volatiles in auriferous quartz from Kopylovsky and temperatures are -4.6 to -10 ºC, salinity is 7.3 wt.%–13.9 wt.%, Kavkaz deposits reach 400 ppm–500 ppm, and in barren quartz and NaCleqv with peak 10 wt.%–12 wt.%. from Kopylovsky and Krasnoye deposits, they do not exceed 280 ppm. The CO2 contents in inclusions from auriferous quartz 3.3 Homogenization Temperatures range between 196 ppm and 240 ppm. The N2 contents are be- All studied fluid inclusions are homogenized to a liquid tween 0.56 ppm and 4.4 ppm; CH4 amount does not exceed 0.37 phase. Fluid inclusions in quartz from gold-bearing quartz vein of ppm and H2O content range between 45 ppm and 300 ppm. In- Kopylovsky Deposit are homogenized between 300 and 350 ºС clusions in auriferous quartz of Kavkaz Deposit contain 0.28 with multimode frequency. Fluid inclusions in auriferous quartz of ppm H2. The ratios of СО2/(СО2+Н2О) range between 0.39 and Kavkaz Deposit are homogenized between 212 and 280 ºС, with 0.61 and СО2/СН4 is from 643 to 2 051. The correlations of vola- the peak between 260 and 270 ºС on the distribution plot (Fig. 4). tiles are CO2>H2O>N2>CН4 for Kopylovsky Deposit, and The homogenization temperatures of Type 1 fluid inclusions H2O>CO2>N2>CН4 for Kavkaz and Krasnoye quartz. in quartz from barren quartz of Kopylovsky Deposit range be- The primary fluid inclusions of different shapes reaching the tween 200 and 240 ºС, with peak of homogenization between size of 40 μm have been found in each of the quartz samples. 210 and 230 ºС. Homogenization temperatures of the Type 2 Their Raman spectra are presented by the superposition of sev- inclusions in barren quartz of Kopylovsky Deposit range between eral narrow bands corresponding to CO2 and N2 molecule spectra. 260 and 280 ºС, with the peak between 270 and 280 ºС on the Using the expression from Burke (2001) it was determined that distribution plot (see Fig. 4). the variations of CO2 mole fraction in fluid inclusion in aurifer- The temperatures of fluid inclusion homogenization of ous quartz are equal to 96.9%–98.6% mol and in barren quartz, auriferous quartz from Krasnoye Deposit are 260–330 ºC with the 88.3%–98.0% mol. Thus, both Raman spectroscopy and gas peak 300–320 ºC on the distribution plot (see Fig. 4). The chromatography are consistent excluding СН4 which has not temperatures of homogenization show weakly positive correla- been detectable upon Raman spectroscopy because the level is tion with salinity of fluid. The temperatures of fluid inclusions below the detection limit of Raman spectrometer. homogenization of barren quartz from Krasnoye Deposit range between 140 and 280 ºC showing bimodal distribution with small 4 DISCUSSION AND CONCLUSION peak 160–180 ºC and high peak 240–260 ºC. The temperatures of The composition and origin of ore-bearing fluids during homogenization show weakly negative correlation with salinity the formation of gold deposits in black shales have been dis- of fluid (see Fig. 4). cussed in many publications (Yudovskaya et al., 2011; Laverov The secondary fluid inclusions are too small in size therefore et al., 2007; Goldfarb et al., 2005; Distler et al., 2004; Groves et we have determined only temperatures of homogenization rang- al., 2003; Rundqvist, 1997; etc.). In this study, we first studied ing between 130 and 180 ºC. P-T conditions of productive auriferous and barren quartz veins for small deposits of Bodaybo ore region—Kopylovsky, 3.4 Pressure of Mineral Formation Kavkaz, and Krasnoye. They are similar in structural and geo- Trapping pressures of fluid inclusions have been determined logical and mineralogical peculiarities. As shown by Budyak et using CO2-rich inclusions in quartz from the galena-quartz vein al. (2018) and Chugaev et al. (2014) and references therein, of Krasnoye Deposit. The temperatures of CO2 melting range these deposits are confined to the same suits as giant Verninsky between -56.7 and -57.1 ºС. The temperatures of CO2 homog- and Sukhoi Log deposits, which implies the prospects of large enization to liquid phase range between 16.1 and 21.3 ºС. The reserves therefore it is important to study the condition of ore total homogenization temperatures of these inclusions range formation of these deposits. between 311 and 330 ºС. The CO2 densities range between 0.78 Our data highlighted that auriferous and barren quartz of and 0.85 g/cm3; molar volumes are 57–58 cm3/mol (Thiery et al., Kopylovsky, Kavkaz and Krasnoye deposits have been formed 1994). The pressures at temperature of 300 ºС are calculated in due to fluids with different compositions, temperatures and

Table 2 Bulk gas chromatography data of fluid inclusions in quartz

Point Sample No. H2O CO2 N2 CH4 H2 H2O CO2 N2 CH4 H2 No. (ppm) (mol%) 1 358/2 151 240.58 4.44 0.374 - 59.76 38.95 1.13 0.167 - 2 504a/80.2 45 69.42 0.56 0.062 - 60.95 38.47 0.49 0.094 - 3 284/5 308 196.95 1.54 0.096 0.28 78.53 20.54 0.25 0.028 0.643 4 141425/135.6 201 85.04 0.94 0.045 - 85.01 14.71 0.26 0.021 -

1, 2. Kopylovsky Deposit: 1. auriferous quartz; 2. barren quartz; 3. auriferous quartz from Kavkaz Deposit; 4. auriferous galena-quartz vein from Krasnoye Deposit.

520 Natalia N. Ankusheva, Ekaterina E. Palenova and Svetlana N. Shanina salinities. The mineral-forming fluids responsible for auriferous Sukhoi Log Deposit (see Fig. 1). The Р-Т conditions of barren and barren quartz veins are both water-chloride but differ in quartz and quartz-sulfide veinlets of Sukhoi Log Deposit are chloride composition. The fluid of auriferous quartz predomi- 185–385 ºC, 130–2 450 bars and 130–385 ºC, 190–2 290 bars, nantly contains Mg and Na+K chlorides, and barren quartz respectively (Distler et al., 2004). According to Gavrilov and comprises K and Na followed by Mg+Fe chlorides. Mg and Fe Kryazhev (2008), the auriferous and barren quartz was formed in fluids are borrowed from the host rocks containing iron- at 300–350 ºC (primary fluid inclusion data) and at 190–290 ºC magnesia carbonates. Probably, Mg (±Fe) may be crystallized (secondary fluid inclusion data) and pressures of 0.8–1 kbars. during the temperature decreasing in the form of carbonates Similar temperatures and pressures were obtained by Rusinov which occurred in thick saddle-shaped quartz veins. In spite of et al. (2008) for deposits of Lena gold-bearing area as follows: low MgO contents in the rocks of Krasnoye Deposit (0.17 200–355 ºC and 0.8–1 kbars. The salt composition of fluids + 2+ 2+ - - wt.%–1.14 wt.%), it reaches 2 wt.% in the sample units. In contains Na , Ca , Mg , HCO3 , and Cl (Gavrilov and Kavkaz and Kopylovsky deposits, MgO contents are signifi- Kryazhev, 2008; Rusinov et al., 2008). The gas phase is com- cantly higher (3.06 wt.%–6.27 wt.% and 3.53 wt.%–4.85 wt.%, posed of CO2, N2, and CH4 (Gavrilov and Kryazhev, 2008; respectively) (Palenova, 2015). Rusinov et al., 2008; Distler et al., 2004) with a dramatic

The auriferous quartz of Kopylovsky and Krasnoye depos- prevalence of CO2 and equal amounts of N2 and CH4. its was formed when temperatures decreased from 350 to 260 According to geological location and fluid inclusion data, ºС and pressures 1.2–1.6 kbars. These pressures correspond to quartz veins on the examined deposits were formed consistently. the latest productive assemblage with Ag selenides and tellu- We suppose that auriferous and barren quartz veins have been rides and electrum (Palenova, 2015). But this association is not formed due to the basic metamorphogenic fluid as evidenced typical for the Kopylovsky and Kavkaz deposits. The salinity of by the close slat and gas fluid composition. Auriferous quartz the fluid is 6 wt.%–10 wt.% NaCleqv. has been formed earlier at higher temperatures, whereas barren The fluid was water-rich (up to 300 ppm) and contained quartz has been formed later when the temperatures decreased significant amount of СО2 (up to 240 ppm), and N2 (up to 4.4 in the environment of plastic and breakable deformations as ppm) and a few CH4 that might be released due to fluid/rock testified by cutting location of barren veins in fold hinges. The interaction when host black shales destruction included organic similar temperature decreasing from 380–447 ºС to barren matter (Xu et al., 2011; Bottrell and Miller, 1990). This is con- veins 154–87 ºС is identified at Chertovo Koryto Deposit con- firmed by a carbon matter of host rocks of Krasnoye Deposit fined to Tonodsky uplift of Lena ore region in the Early Pro- including chloroform and alcohol benzene bitumoids (Budyak terozoic carbon terrigenous rocks of the Mikhailovsky suit et al., 2018). The assemblage of N+S+O indicates their organic (Tarasova and Budyak, 2017). This suit is subdivided into two genesis. The presence of nitrogen in fluid can have a catalytic metamorphic stages as follows: high temperature stage up to effect on the leaching rate of heavy metals (Au, Ag, and PGE) epidote-amphibolite facies and retrograde green shale stage from the host rocks during metamorphic and metasomatic al- (Yudovskaya et al., 2016). Probably, in Chertovo Koryto De- teration and the following deposition on the reduced geo- posit, the higher temperatures of auriferous quartz formation chemical barriers (Budyak et al., 2018). The coexisting mono- were cause of that. In addition, Chertovo Koryto Deposit is phase gas and liquid fluid inclusions and more concentrated bi- characterized by the CO2 percentage reduction from auriferous and tri-phase inclusions indicate the heterogeneous fluid (Pro- to barren veins (from approximately 100% up to ½). As men- kofiev et al., 1994 and references therein) that may result in the tioned earlier (Laverov et al., 2007), at Sukhoi Log Deposit, gold deposition (Bowers, 1991). The CO2/CH4 ratios indicated two stages of gold formation were distinguished. The first stage oxidized fluid type. The H2 determined in fluid inclusions in is about 450 Ma and close to the age of the regional metamor- auriferous quartz of Kavkaz Deposit may be a result of pyroly- phism corresponding to streaky-disseminated gold-sulfide ores sis of organic material from host metamorphosed sedimentary and metasomatites. The second stage is about 320 Ma that close rocks during OH- groups dissociation (Kulchitskaya and to the Konkudera-Mamakan granitoid complex formation and Chernish, 2012). corresponds to barren quartz deposition. By analogy with Suk- During the ore formation, carbon compounds can form hoi Log Deposit, these stages are supposed for other deposits of metal-organic substances including with Au or be a sorption Bodaybo region including Kopylovsky, Kavkaz, and Krasnoye barrier (Yudovich and Ketris, 1988). Moreover, the carbon deposits that resulted from a long geological history of the re- material is sensitive to the processes of temperature and pres- gion and polychronic ore formation. sure increasing and can indicate metamorphic transformations. The barren quartz veins were formed at lower temperatures ACKNOWLEDGMENTS varying between 280 and 140 ºС. The fluid salinity is higher up This study was partially supported by the State Contract of to 13 wt.% NaCleqv. In fluid inclusions H2O and CO2 are also the Institute of Mineralogy, South-Urals Federal Research prevalent. But barren fluid is reduced in volatiles compared with Center of Mineralogy and Geoecology, Urals Branch, Russian auriferous fluid (bulk contents 115 ppm and 507 ppm, respec- Academy of Sciences (Project for 2019–2021) and the Basic tively). The higher salinity and decreased volatile amounts in Research Foundation of Russia (No. 16-05-00580). Sincere thanks barren hydrothermal fluid may be caused by the mixing with go to the reviewers and the editors for their suggestions. The final metamorphic fluids often accompanied by dehydration of the publication is available at Springer via https://doi.org/10.1007/ fluid (Prokofiev et al., 1994; Shepherd et al., 1991). s12583-019-1024-4. Our results were compared with similar data of the unique

Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Formation in the Black Shale-Hosted Gold Deposits 521

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