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Article

The Gold Mineralization of the Baranyevskoe Au-Ag Epithermal Deposit in Central Kamchatka

by
Nadezhda Tolstykh
1,*,
Daria Bukhanova
2,
Maria Shapovalova
1,
Andrey Borovikov
1 and
Maksim Podlipsky
1
1
Sobolev Institute of Geology and Mineralogy of SB RAS, 630090 Novosibirsk, Russia
2
Institute of Volcanology and Seismology FEB RAS, 683006 Petropavlovsk-Kamchatsky, Russia
*
Author to whom correspondence should be addressed.
Minerals 2021, 11(11), 1225; https://doi.org/10.3390/min11111225
Submission received: 11 October 2021 / Revised: 31 October 2021 / Accepted: 2 November 2021 / Published: 4 November 2021
(This article belongs to the Special Issue Gold Deposits in Russia: Geology, Mineralogy and Ore Genesis)
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Abstract

:
The Baranyevskoe Au-Ag epithermal deposit of low-sulfidation (LS) type is located on the Kamchatka Peninsula in the Neogene-Quaternary Central Kamchatka Volcanic Belt, where Au-bearing quartz veins are usually accompanied by veinlet stockworks. Two economic associations are typical of the Baranyevskoe deposit. The first corresponds to gold-pyrite-quartz association with low-grade native gold (521–738‱) intergrown with pyrite. Some accessory Au-Ag minerals within the early association were also identified: acanthite AgS2, hessite AgTe2, lenaite Ag(Fe,Cu)S2, petzite Ag3AuTe2, utenbogardite Ag3AuS2 and unnamed Ag-Sb-As sulfosalts. The former Au-Ag minerals were most likely formed in the temperature range of 320–330 °C based on the study of arsenopyrite thermometers and fluid inclusions. The second, a gold-sulfosalt-quartz association, includes high-grade native gold (883-941‱) in intergrowth with chalcopyrite. Cuprous phases (bornite, chalcocite, heerite, native copper, Cu-Zn solid solutions), Bi-rich sulfosalts (aikinite PbCuBiS3, emplectite CuBiS2, witticenite Cu3BiS3), stannoidite Cu8Fe3Sn2S12, mawsonite Cu6Fe2SnS8), Au-bearing galena, Te-free and Bi-rich tetrahedrite-tennantite represent this association. Fluid inclusions in gold-sulfosalt-quartz association are characterized by homogenization temperature ranging from 226 to 298 °C, and salinity from 0.4 to 1.2 wt. % NaCl eq.

1. Introduction

Epithermal Au-Ag deposits on the Kamchatka Peninsula are important sources of precious metals. These deposits are located in volcanic belts extending along the subduction zone [1,2], and occur in a geodynamic setting of island arc [3]. Among the aforementioned deposits stand out Asachinskoe, Ametistovoe, Ozernovskoe, Aginskoe, Rodnikovoe, Mutnovskoe, Maletoyvayam and others [4,5,6,7,8,9,10,11].
All these Au-Ag deposits, according to the classification of Corbett [12], belong to the low-sulfidation (LS) or quartz-adularia type, except for the recently described Maletoyvayam deposit, which belongs to the high-sulfidation (HS) or quartz-alunite type [13,14,15]. The Baranyevskoe Au-Ag epithermal deposit is of the LS type and estimated to be formed by near-neutral pH fluids [16,17]. It is located in the Kamchatka Peninsula, on the left bank of the Baranye stream (right tributary of the Balkhach River), approximately 60 km from the Milkovo village. The deposit was discovered in 1972 and, ever since, it has been explored by geologists of different mining companies (Koryakgeoldobycha CJSC, Kamchatka Gold OJSC, Kamchatka Gold Exploration LLC, etc.). The reserves of gold at the Baranyevskoe deposit are reported to be greater than 30 metric tons with an average grade of about 9 g/t [18]. The composition of ores has been studied previously, and three main mineral associations were described: gold-quartz-carbonate-adularia, gold-ore stockworks and quartz combs or “brushes” [19]; the composition of gold was compared with other deposits of the Balkhach ore cluster at Central Kamchatka [20]. It was also identified three stages of ore formation corresponding to the (1) early gold-pyrite-quartz association in altered rocks located in the central part of the deposit, (2) gold-sulfosalt-quartz association, developed in the northeastern part of the deposit, and (3) gold-poor sulfide-quartz associated with late veins [18]. The Baranyevskoe deposit is considered to be the prototype model for the abovementioned deposits of Kamchatka [18]. Therefore, further studies on identification of typomorphic features of Au-Ag mineralization in different zones, compositions of noble metals and associated unusual minerals is suggested, in order to contribute to a better understanding of the genetic processes and ore formation mechanism of one of the leading gold deposits in the Central Kamchatka mining region. This study aims to investigate in more detail the mineralogical and geochemical features of the two main profitable associations (gold-pyrite-quartz and gold-sulfosalt-quartz) belonging to different stages of ore formation within different zones of the Baranyevskoe deposit. These features are generally considered very important aspects of gold metallogeny in constraining genetical-ore processes [3].

2. Materials and Methods

The composition of the minerals was studied in the “Analytical Center for Multielement and Isotope Research” at the Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences (analyst M. Khlestov) both, in heavy concentrates of crushed samples mounted into polished sections and thin section of rocks. Microanalyzer Mira 3 (Tescan, Czech Republic) with an energy dispersive X-Ray (EDS Oxford X-Max 80) spectrometer was used for this purpose. Operating parameters were as follows: accelerating voltage 20 kV, probe current 1.6 nA, spectrum acquisition time on samples 20 s. The resolution of the X-ray spectrometer was 126–127 eV on the Mn Kα line, and the probe size was 12 nm. The beam diameter during the analyses varies within 2–5 microns, depending on the average atomic number of the sample and the wavelength of the characteristic X-ray radiation. The detection limit for most elements is within the range 0.2–0.3 wt. %. All analyses in the tables are given according to the detection limits of elements. The equivalence between measurements of EDS and WDS methods is given in [21].
Analysis of Au was performed at the Testing laboratory of AO SGS Vostok Limited, (Chita city) from a 30 g sample by means of assay analysis with NexIO 300D Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) ending; accreditation scope: Au—0.02 ppm–20,000 ppm. All other elements were analyzed by a combined method including decomposition of the sample in a mixture of acids. After decomposition, the solution was analyzed by either Optima 8300 Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) or Inductively Coupled Plasma Mass Spectrometer (ICP-MS) (Perkin Elmer, Shetlon, Connecticut, USA).
Temperatures of homogenization and melting of solid phases in fluid inclusions were determined out using a Linkam THMSG-600 microthermal chamber (Linkam Scientific Instruments, Tadworth Surrey, United Kingdom, https://www.linkam.co.uk/, 11 October 2021 visited) with a measurement range of −196 to + 600 °C. The salinity of fluid inclusions and classification into a water–salt system were determined from cryometry data [22,23,24,25]. When assessing the pressure of ore formation according to the study of fluid inclusions, the computer program “AqSo_NaCl” was used [22].

3. Geological Settings

The Balkhach volcano-tectonic structure is located within the Neogene-Quaternary Central Kamchatka Volcanic Belt (CKVB), which extends for 800 km along the Main Kamchatka fault, striking north-east at its junction with the Sredinno-Kamchatka uplift composed by metamorphic rocks of different composition [26]. The formation and development of the circular Balkhach volcano-tectonic structure, with a diameter of 22 km, is discussed in detail in [18]. The ore cluster of the same name within this structure combines four deposits: Baranyevskoe, Zolotoe, Kungurtsevskoe and Uglovoe. The Aginsk volcano-tectonic structure, which includes the Aginskoe gold deposit, is located to the northwest of the Balkhach volcano-tectonic structure (Figure 1). The Baranyevskoe deposit belongs to the Baranyevskoe ore field and the Kungurtsevskoe and Zolotoe deposits to the Zolotoe ore field (Figure 2).
The stratigraphy of the Baranyevskoe ore field includes tuff of intermediate and mafic composition, basalt, trachyandesite, tuffaceous sandstone, tuffaceous siltstone (lower stratigraphical level); and effusive rocks and tuff of intermediate and mafic composition, andesite, basalt (upper structural level) (Figure 2). Ages of deposits of the Zolotoe ore field are: Kungurtsevskoe—21 Ma [20], Zolotoe—in the interval of 21.3–17.0 Ma, whereas the Baranyevskoe deposit, located in Late Miocene-Pliocene rocks, has an age interval of 3.9–2.4 Ma according to the K-Ar method [27].
The Baranyevskoe deposit consists of a system of vein-veinlet and stockwork (veinlet-disseminated) ore-bearing structures in the zone of deep northeastern faulting (Figure 3). The Rusty ore zone is located along the central fault NE-SW and is accompanied by zones of abundant apophyses: the “Central”, “Southern” and “Hanging”, along with others branches from the axial fault in the hanging wall [18].
Quartz veins are accompanied by veinlet-disseminated stockworks, on top of which there is a 200-m interval of rocks with high profusion of weakly mineralized (less than 1 ppm Au) veinlets of carbonate and zeolite-carbonate compositions. On the other hand, the stockwork includes the rich vein-disseminated gold mineralization with an Au concentration up to 20 ppm, accompanied by metasomatic associations: pyrite-hematite-magnetite-sericite (alunite)-quartz in the central part of the stockwork and pyrite-sericite-illite-quartz at the periphery. Vuggy silica is common at deeper levels of stockworks [18]. The proportion of mineralized veinlets overlapping disseminated mineralization increases to the southwest. Quartz veins in the hanging wall are also accompanied by Au-bearing metasomatites comprising quartz, adularia, hydromica, carbonate and clay minerals. Thus, the main ore bodies (zones) of the Baranyevskoe deposit, up to 20 m thick, are composed of: (a) thick quartz veins, (b) disseminated-vein halos, and (c) sulfidized hydrothermal-metasomatic rocks. Consequently, the ore bodies exhibit a ribbon-like shape with a length up to 1500 m, in which gold is unevenly distributed.

4. Results

4.1. Samples

The rock samples for this study were collected from an open pit in the Rusty, Central and Hanging zones, the underground tunnels of the Northern Zone and outcrops of the Southern Zone. Most of the samples gathered are characterized by the gold-pyrite-quartz association, which is the most widespread in the Central zone where metasomatic rocks are superimposed onto the gold-pyrite-quartz bearing veins. The most abundant mineral within this assemblage, pyrite, is sometimes replaced by hematite, whereas native gold may be found intergrown with pyrite. The role of the gold-sulfosalt-quartz association increases toward the northeastern direction of the deposit, and is more representative for the Northern zone. The gold-sulfosalt-quartz association is formed by samples of sericite-adularia-quartz composition with fragments of host-rock andesites, which are characterized, as a rule, by crustified-breccia textures (Figure 4a). Disseminated sulfides tend to form ribbon-like areas, due to the irregular flow of hydrothermal solutions. Additionally, native gold is found in paragenetic intergrowths with chalcopyrite (Figure 4b).

4.2. The Basic Ore Minerals

Pyrite is the most abundant sulfide at the Baranyevskoe deposit. Some analyses of pyrite (more than 30%) contain As as a minor element. As-bearing pyrite forms intermittent growth zones with As-free pyrite grains (Figure 5a,b). This oscillatory zoning observed in some pyrite grains and sulfosalts of epithermal deposits [28,29] is due to fluctuations in the characteristics of the hydrothermal fluid during the growth of minerals. The concentration of As in pyrite varies from grain to grain, reaching up to 7.4 wt. % (Figure 5c) while no other trace elements have so far been identified in the pyrite of the Baranyevskoe deposit (Table 1).
Two hundred grains of gold from different zones and areas of the Baranyevskoe deposit were analyzed. The complete Au-Ag solid solution are subdivided, according to [30] into native gold—up to 30 atomic (at.) % of Ag (fineness 1000–700‱), electrum (fineness 700–300‱), “küstelite” (mineral not approved by International Mineralogical Association) with fineness 300–100‱, and Au-containing silver (fineness 100–0‱).
The composition in non-oxidized samples varies from low-grade to high-grade gold with a gap in the isomorphic series in the range of Au 74–88 at. %. Some gold grains from the Rusty and Central zones, most of the grains from the Hanging zone and half of the gold grains from the Northern zone consist of native gold and electrum with a range of fineness of 521–738‱ (Figure 6, based on data in Table 2), which are characteristic of the gold-pyrite-quartz association of the early ore-forming stage. A significant part of gold grains from the Northern zone and some grains from the Hanging zone correspond to high-grade native gold (883–941‱) (Figure 6, based on data in Table 2), typical of the gold-sulfosalt-quartz association. Electrum, “küstelite”, and the high-grade native gold are representative in the Southern zone from sediments below of quartz veins and in oxidized ores. Oxidized ores of Southern and Central zones also contain the finest gold (920–280‱) (Figure 7, Table 3). Thus, Au-Ag solid solutions of different compositions are involved in the formation ores in different-stage in almost all zones of the Baranyevskoe deposit.

4.3. Mineral Associations of Ore-Forming Stages

4.3.1. Gold-Pyrite-Quartz Association

The gold-pyrite-quartz mineralization is more widespread in the central part of the deposit (Rusty zone), where metasomatites are overprinted on veinlets of gold-pyrite-quartz veins. The low-grade gold (electrum), as a rule, was found as individual grains in concentrates of crushed sample. Such gold grains are inclusions in pyrite, and associated with acanthite Ag2S, petzite Ag3AuTe2 and uytenbogardtite Ag3AuS2 (Figure 8a). In the Central zone, this mineral assemblage is characterized by inclusions of pyrite crystals in gold (Figure 8d,e). Gold is associated with hessite Ag2Te and galena PbS (Figure 8b). The gold-pyrite-quartz mineralization in the Southern zone is featured by the development of unusual composition in acanthite, with traces of Sb, As and Se, and sometimes Au: (Ag, Au)2(S,Sb,As,Se), which is found as individual grains in ocher-clay samples (Figure 8h). The silver sulfosalts Ag10(Sb,As)S5 and Ag17(Sb,As)2(S,Se)10 composition are found both in the Southern and Central zones in the gold-pyrite-quartz mineralization (Table 4). The replacement of acanthite by lenaite Ag(Fe,Cu)S2 occurs (Figure 8i). Sulfides in intergrowth with gold are sometimes replaced by Fe-oxide (Figure 8c).

4.3.2. Gold-Sulfosalt-Quartz Association

Native gold, belonging to this association, is intergrown with chalcopyrite, which is by far the most common mineral. Sample Bar-5–2 collected from underground mines of the Northern Zone is a typical example of a gold-sulfosalt-quartz association (Figure 9). The main mineral phase associated with gold is emplectite CuBiS2 (up to 50 μm), which occurs intergrown with gold or included in chalcopyrite in their joint paragenesis (Figure 9b,c,e–g,). Native gold within this mineral assemblage is always high-grade with a concentration of Ag no greater than 12 at. %.
For the Northern and Hanging zones, emplectite is characterized by containing Pb around 2–3 wt. % and sometimes Sb up to 1.81 wt. %. Mawsonite Cu6Fe2SnS8 is also often found within this association (Figure 9a,e,g). Additionally, there is tetrahedrite of unusual composition, in which the Bi concentration either prevails over As—(Cu,Fe,Zn)12(Sb,Bi,As)4S13—or completely replaces it (Table 5, No. 31, 32). The tetrahedrite in Bar-5–2 sample contains more than 4 wt. % of Zn. Secondary minerals replacing the chalcopyrite are typically covellite CuS and geerite Cu8S5 (Figure 9c–d). Aikinite PbCuBiS3 is as well a normal-assemblage mineral of the gold-sulfosalt-quartz association in the Northern and Hanging zones (Table 5). The gold-sulfosalt-quartz association in the Rusty zone (Figure 10) is distinguished by the presence of copper-bearing (4.93 wt. % of Cu) electrum, the composition of which corresponds to the formula Au0.70Ag0.17Cu0.13, or more simply, Au7Ag2Cu, as well as bornite (Figure 10a,b). The tetrahedrite in Bar-2-1 sample is also Bi-rich (Table 5), but its concentration is lower than that of As. Another typomorphic Bi-rich mineral, wittichenite Cu3BiS3, instead of emplectite (CuBiS2), is characteristic of this association in the Rusty zone (Figure 10e–h).

4.4. Concentration of Ore and Chalcogenic Elements

The concentration of ore and chalcogenic elements in samples from different zones of the Baranyevskoye deposit were obtained. The concentration of precious metals is unevenly distributed: tenths of ppm Au in the Southern zone, units of ppm in the Rusty and Central zones, tens of ppm in the Hanging zone, whereas the highest concentrations of hundreds of ppm occur in the Northern zone (Table 6). In general, Au prevails over Ag in all zones (Au/Ag ratios are 2.80–9.91 and Ag/Au ratios are 0.10–3.72) except for the Southern zone, in which the Au/Ag ratios vary in the range of 0.16–0.52 for the quartz vein, and reaches up to 2.35 in the metasomatitic host rock (sample BAR-6-5). Thus, the samples from the tunnels (BAR-5) of the Northern Zone are the richest in Au. Sample BAR-5-1 represents the gold-pyrite-quartz association, while sample BAR-5-2 represents the gold-sulfosalt-quartz association, in which the concentrations of Pb, Sb, Se are increased by one order of magnitude, Cu and Sn by two orders of magnitude, and Bi by four orders of magnitude compared with the content of these elements in samples from other zones. At the same time, the As concentration is not high compared to its anomalous values (1030 ppm) in the gold-pyrite-quartz association of the same zone. The aforementioned distribution of elements is consistent with mineralogical features: As-bearing pyrite in one association and the presence of many Bi-rich and Sn-bearing sulfosalts included in chalcopyrite in another.

4.5. Study on Fluid Inclusions

Fluid inclusions were investigated only for the gold-sulfosalt-quartz association. Small (15–20 µm) primary gaseous and two-phase gas-liquid inclusions contained in quartz were identified. In the central parts of translucent crystals of quartz, there are mainly groups of isometric two-phase inclusions (Figure 11a) whereas gas and two-phase fluid inclusions, on the growth zones of quartz crystals, have an irregular shape (Figure 11b).
Homogenization temperature of fluid inclusions varied in the range of 226–298 °C (Figure 12a). The ice melting in cooled fluid inclusions appeared at temperatures from –0.8 to −0.2°C (Table 7). The salinity of fluid inclusions was estimated from 0.4 to 1.2 wt. % NaCl eq. Melting of eutectic in frozen fluid inclusions occurred in the temperature range of −49 to −25 °C.
Fluid inclusions in quartz from the gold-sulfosalt quartz association are characterized by eutectic melting at range of −45 to −27 °C. The fluid inclusions in the quartz of this ore association contain NaCl and KCl. Low melting temperatures of eutectics from −49 to −27 C° are characteristic of fluid inclusions in quartz of the gold-sulfosalt-quartz association with high-grade gold (Table 7). With regard to the composition of fluids at the latest stage, in addition to NaCl, there could be admixtures of CaCl2, MgCl2, FeCl2, FeCl3, K2CO3, which may lower the melting point of the eutectic of fluid inclusions [24]. The composition of gas inclusions, apparently, is dominated by water vapor.
The wide range of temperature of homogenization in the fluid inclusions (298–226 °C) along with a narrow range of salinity (0.4–1.2 wt.% NaCl eq.) (Figure 12b) may be explained by processes of mixing of hot magmatogenic fluids with cold fresh meteoric waters. The presence of primary gaseous and two-phase fluid inclusions on the growth zones of quartz crystals indicates boiling of the ore-forming fluid. The calculated pressure of homogenization of fluid inclusions in quartz from the late stage of mineralization of the Baranyevskoe deposit varies from 2.6 to 8.3 MPa, and it is mostly close to the pressures of ore formation in the near-surface volcanic-hydrothermal mineral systems. If we take these values for hydrostatic pressure, then we can assume that these ores from the Baranyevskoe deposit were formed at a depth of 260 to 530 m.
The temperature and salinity of ore-forming fluids of the late gold-sulfosalt-quartz association varied over a narrow interval; however, an even more complex composition of salts in the ore-forming fluids is assumed at the final stage of gold-sulfosalt-quartz associations: salts that may be expected to be present: NaCl, CaCl2, MgCl2, FeCl2, FeCl3, K2CO3, compared to the composition of fluids (NaCl and KCl) at the initial stage of formation of this association.

5. Discussion

Gold from the Baranyevskoye deposit is subdivided into two classes: the first includes a series of compositions related to low-grade gold and electrum with a fineness of (52–74 at. % Au) (Figure 13). Sufficiently large grains (50–100 microns) are, as a rule, in association with pyrite and are characteristic of the early high-temperature stage. Similar compositions have been described for hypogenic gold at the Aginskoye deposit [11]. The second class corresponds to high-grade gold (88–94 at. % Au) (Figure 13), which, together with chalcopyrite and Bi-rich sulfosalts, compose the mineral association of the lower-temperature stage. However, it should be noted that high-grade gold is also rarely found in the early gold-pyrite-quartz association, being represented there only by thin worm-like veins included in low-grade gold (Figure 8g).
Similar textures were previously described at the Aginskoye deposit [11]. According to the authors, such high-grade gold is secondary in origin, formed during the oxidation of hypogenic gold by meteoric waters at the stage of hypergenesis. However, we consider that the formation of high-grade gold in the Baranyevskoe deposit is mainly due to a change in the physicochemical conditions and the composition of hydrothermal solutions. Andreeva and Kudaeva [20], who previously studied the typomorphism of gold in the Balkhach ore cluster, noted that the grain size and fineness increase within the transition from quartz-carbonate-adularia stockwork rocks to carbonate rocks and quartz-carbonate-adularia veins. On the other hand, silver content in gold is considered as an indicator of the temperature regime during the formation of ores [31]. The composition of native gold evolves from very high-grade gold to electrum and Hg-bearing gold in the Western Tuva deposits (Russia) [32] as opposed to what is described in this study. Electrum is associated with pyrite at the Valunistoye deposit (Chukotka), and high-grade gold is found in the form of rims and veins in electrum, occurring later in the paragenesis [33], as in our case. The Au-Ag-Cu system with reference to [34] is shown in [35]. Composition-temperature ranges in this isotherm reflect metastable equilibria. On one side of the triangle, there is a wide row of Au-Ag solid solutions below 300 °C isotherm. That is, alloys of different compositions can crystallize at the same temperature. Therefore, at temperatures corresponding to hydrothermal conditions, opposite trends of the variation in Ag content, in gold grains, are observed for different deposits.
Pyrite is one of the most important indicator minerals in studying the features of the genesis in ore deposits. The As concentration in the pyrite of the Baranyevskoe deposit (7.37 wt. %) exceeds the As in pyrite of numerous deposits, including the values in the Kumroch deposit, where pyrite contains up to 6.79 wt. % As [36]. For instance, the content of As in pyrite at the Zaozigou Gold Deposit (Central China) is 4.1 wt. % [37], it is 4.5 wt. % in pyrite of the Roudný deposit, Bohemian Massif [38], while As in pyrite from El Valle gold deposit (Spain) is the most abundant (up to 9.5 wt. % As) [39]. Therefore, it becomes evident that the solid solution of Au is dominated by arsenian pyrite in all these deposits. However, high As concentrations are characteristic only for certain areas of zoned pyrite. Compositional zoning of pyrites in gold deposits reflects the chemical evolution of ore bearing fluids. The relatively high activity of As and Au during crystallization of the early generation of pyrite allowed As-bearing pyrite to be precipitated as a consequence. This is consistent with the extremely high As concentration in the samples of the gold-pyrite-quartz association in the Northern Zone (Table 6). The As-bearing pyrites were formed at temperatures of at least 320–330 ºC, based on arsenopyrite thermometers and fluid inclusion data [38]. The variable amount of As in grains of pyrite reflects changes in physicochemical conditions (T, fS2, fO2, pH) and the composition of fluids, which, at the same time, determine the appearance of a concentration gradient on the pyrite growth surface [40]. Pyrite and gold of low-grade composition in the early association are genetically linked with the Ag-Au minerals: acanthite, hessite, lenaite, petzite, utenbogardtite and Ag-sulfosalts: Ag10(Sb,As)S5 and Ag17(Sb,As)2(S, Se)10.
An increase in copper concentration during the development of the ore-forming system led to the formation of a later gold ore association with the leading role of chalcopyrite, as well as other cuprous phases (bornite, chalcocite, geerite, native copper and Cu-Zn solid solutions). Simultaneously, there was an increase in the fineness of gold from 700–800‱ in the early association up to 900–950‱ in the late one, as well as an increase in the concentration of bismuth (leading to the formation of emplectite CuBiS2 or wittichenite Cu3BiS3); the concentration of tin in the ore-forming system was also increased, forming mawsonite Cu6Fe2SnS8.
Primary galena from hydrothermal deposits has been shown to contain anomalous and significant levels of Bi, Ag, Te, Se, Sb, Cu, Tl and Zn [41]. Increased concentrations of Bi and Ag indicate the dissolution of the proportion of AgBiS2 in galena [42]. At the Baranyevskoe deposit, galena contains only traces of Au (up to 2.02 wt. %), and no other minor elements were found. It is assumed that a gold-bearing variety of galena contains probably microscopic or nano-inclusions of gold or gold-bearing-minerals (https://www.mindat.org/min-26564.html, 11 October 2021). Au-bearing galena from the Baranyevskoe deposit is, however, found as inclusions in Au-Ag alloys. Then, it could be argued that gold content was measured from the matrix during the analysis. Firstly, however, the galena inclusions are large enough (10–20 microns) for correct analysis; secondly, they look absolutely homogeneous (Figure 8b); and thirdly, Ag is absent in the analysis of galena, and it should have been captured together with Au. Therefore, Au-containing galena is a feature of the gold-pyrite-quartz association.
The tetrahedrite (Cu10(Fe,Zn)2Sb4S13)–tennantite (Cu10(Fe,Zn)2As4S13) solid-solution series (fahlore) is common, and widespread in Au-Ag epithermal ore deposits around the world [43]. The role of sulfosalts in gold deposits is significant, since they are closely associated with native gold, and their study is considered to be very important in identifying the nature of gold mineralization. The rather significant variability in composition makes fahlores a useful indicator of ore-forming processes and fluid compositions during their development [44].
Tetrahedrite of the Baranyevskoe deposit contains significant amounts of bismuth, which in some cases may dominate over arsenic Cu12(Sb,Bi,As)4S13. A similar and even richer in bismuth (up to 22.17 wt. % Bi) tetrahedrite was described earlier in Schwarzwald ore district with 1.83 atoms per formula unit (apfu) Bi [44] compared to Baranievskoye, where 0.20–1.10 apfu Bi, based on 4 total apfu (Sb+As+Bi) was established. However, the Bi-richest sulfosalts are also Pb-bearing [45], whereas, in the herein investigated association, it lacks Pb-Bi fahlores. Only one grain of sulfosalt containing lead (Cu3Fe3PbS7) was found. A feature of the gold-sulfosalt-quartz association of the Baranyevskoe deposit is the presence of the Te-free tetrahedrite-tennantite series, while Te-rich fahlore (goldfieldite) is characteristic in numerous epithermal deposits [46], including the gold-forming stages of the Ozernovskoe and Aginskoe epithermal deposits in Kamchatka. Moreover, at the Aginskoe deposit, the Te-rich minerals (AuTe2, PbTe, Ag2Te, Ag3AuTe2) are rather common, while pyrite is subordinate [8,9,11]. The presence of Bi-rich and, simultaneously, Te-poor varieties of sulfosalts is considered a typomorphic feature of the gold-sulfosalt-quartz association.
The increasing role of bismuth at the late gold stage (gold-sulfosalt-quartz association) expressed by the crystallization of bismuth-rich minerals—emplectite CuBiS2, wittichenite Cu3BiS3, tetradymite Bi2Te2S, sulfosalt (Cu,Fe)Bi5Te5S3—is consistent with the data of the chemical analysis of the ores from this association (Table 6). Sulfosalts of copper, iron and tin—mawsonite Cu6Fe2SnS8 and stannoidite Cu8Fe3Sn2S12—are also characteristic of the gold-sulfosalt-quartz association. These minerals indicate some enrichment in tin at a late stage in the development of the ore-forming system. Mawsonite Cu6Fe2SnS8 has been identified in association with pyrite and tetrahedrite in a vein orebody, and its formation is related to interactions during the substitution of the tin-bearing famatinite by tetrahedrite [47]. The gold-sulfosalt-quartz association identified in this study is in many respects similar to that from the Kairagach gold deposit, Uzbekistan, which is characterized by a Au-Sn-Bi-Se-Te geochemical profile; namely, it is comparable to the third generation of ore mineralization of Kairagach gold deposit: Bi-sulfosalts as well as native gold of high fineness, tetrahedrite-annivite series. These are characterized by high (up to 9 wt. %) content of Bi [48].
The microthermometry study on fluid inclusions in quartz with the most abundant dissemination of chalcopyrite and sulfosalts grains (gold-sulfosalts-quartz association) revealed in the quartz aggregate, temperatures corresponding to a range of 299–226 °C. Similar temperatures of homogenization of primary inclusions were reported for the quartz of the Aginskoe deposit (LS type) 230–280 °C [9], and were also established for the Rodnikovoe and Asachinskoe deposits in South Kamchatka [6,49,50]. In addition, at the IS type field (Cesme Hafez, Iran) [51], homogenization temperatures of primary inclusions are within the same range (140–280 °C). At the same time, it is well compatible with many HS type deposits, e.g., Maletoyvayam (255–245 °C) [15].
The salinity range can be strongly influenced, on one hand, by mixing with meteoric water (dilution), or, on the other hand, by boil-off (concentrating) [52,53]. In general, the salinity of LS type deposits shows a wide range of values. The mineralization in LS type crystallizes, as a rule, from relatively dilute brines <5 wt. % NaCl eq. Aginskoye deposit is no greater than 2 wt. % NaCl equiv. [9], as in the Juliet field (LS type), at the Okhotsk-Chukotka volcanic belt, the salinity of the inclusions is around 1.2–5.6 wt. % NaCl eq. [54]. However, data from fluid inclusions, in quartz, associated with the main gold stage in HS type deposits—Mt Carlton, Lepanto, Agan, Mt Carlton, NE Australia, Danchenkovskoe, and Maletoyvayam [15,55,56,57,58]—similarly indicate salinities up to 4.5 wt. % NaCl eq. In this respect, it becomes clear that the salinity of fluid inclusions is not necessarily related to the type of deposit, but rather depends on the conditions of ore deposition [15].
Metallogenic specialization and Au/Ag Index of ore is fundamentally related to the host environment in which ore is formed [59]. High values of this index (<50) are typical for deposits related to oceanic island arcs: Central Kamchatka—1.7; Fiji—4.9; Solomon Islands—2.6. The high ratios of Au/Ag (2.80–9.90), which characterize the Baraneyvskoe deposit, are a promising economic feature in predicting epithermal gold deposits [59].

6. Conclusions

Two Au-forming associations are characteristic of the Baranyevskoye deposit:
1. Early gold-pyrite-quartz, characterized by the presence of low-grade gold and electrum (660–820‱) in association with pyrite, the grains of which often exhibit oscillatory zoning with As concentrations up to 7.37 wt. % in some areas. Accessory Au-Ag minerals: acanthite AgS2, hessite AgTe2, lenaite Ag(Fe,Cu)S2, petzite Ag3AuTe2, utenbogardite Ag3AuS2, Au-bearing galena and Ag-Sb-As sulfosalts of unusual composition are found within this association, which is estimated to be formed in the temperature range of 320–330 °C according to [38] based on arsenopyrite thermometers and fluid inclusions.
2. Late gold-sulfosalt-quartz association includes the high-grade gold (930–970‱) intergrown with chalcopyrite and tetrahedrite-tennantite solid-solutions, which are rather common. The specific compositions of the associated minerals are due to an increase in Cu, Bi and Sn in the primary ore-forming solutions: this assemblage is characterized by cuprous phases (bornite, chalcocite, heerite, native copper, Cu-Zn solid solutions), Bi-rich sulfosalts (aikinite PbCuBiS3, emplectite CuBiS2, witticenite Cu3BiS3) and also stannoidite Cu8Fe3Sn2S12 and mawsonite Cu6Fe2SnS8. Te-free and Bi-rich tetrahedrite-tennantite series of fahlores are, as well, typomorphic minerals of this association.
3. Fluid inclusions in quartz from the gold-sulfosalt-quartz association are characterized by homogenization in the temperature range of 226–298 °C, and salinity from 0.4 to 1.2 wt. % NaCl eq. The calculated pressures and depths of the gold-sulfosalt-quartz association formation were 2.6–8.3 MPa and 260–530 m, respectively.

Author Contributions

Conceptualization, methodology, writing, project administration, N.T.; sampling, general geology on the field, D.B.; microthermometric study, A.B.; preparation and description of samples, M.S. and M.P. All authors have read and agreed to the published version of the manuscript.

Funding

The studies were carried out within the framework of the state assignment of the IGM SB RAS financed by Ministry of Science and Higher Education of the Russian Federation. This research was funded by the Russian Foundation of Basic Research project No. 19-05-00316.

Data Availability Statement

The authors would like to thank N. Karmanov and M. Khlestov (IGM SB RAS) for assisting during analytical procedures.

Acknowledgments

In this section, you can acknowledge any support given which is not covered by the author contribution or funding sections. This may include administrative and technical support, or donations in kind (e.g., materials used for experiments).

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study, collection, analyses, or interpretation of data; nor in the writing of the manuscript, or in the decision to publish the results.

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Figure 1. Location of the Au-Ag deposits on the geological map of the Central Kamchatka ore region modified after [18,26] (a) and their position on the Kamchatka Peninsula (red square) in the contours of the Central Kamchatka volcanic belt (b).
Figure 1. Location of the Au-Ag deposits on the geological map of the Central Kamchatka ore region modified after [18,26] (a) and their position on the Kamchatka Peninsula (red square) in the contours of the Central Kamchatka volcanic belt (b).
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Figure 2. Geological-structural diagram of the Balkhach volcano-tectonic structure and respective A-B cross-section modified after [18,26].
Figure 2. Geological-structural diagram of the Balkhach volcano-tectonic structure and respective A-B cross-section modified after [18,26].
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Figure 3. Geological scheme of the mineralization (a) and section I–I’ (b) of the Baranyevskoe deposit, modified after [18]; vertical scale mean the absolute height above sea level (m).
Figure 3. Geological scheme of the mineralization (a) and section I–I’ (b) of the Baranyevskoe deposit, modified after [18]; vertical scale mean the absolute height above sea level (m).
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Figure 4. Sample of sericite-adularia-quartz composition with crustified-breccia texture containing disseminated sulfide and sulfosalts (a) and visible gold on an enlarged fragment of the sample (b) (sample Bar_2-1, Rusty zone).
Figure 4. Sample of sericite-adularia-quartz composition with crustified-breccia texture containing disseminated sulfide and sulfosalts (a) and visible gold on an enlarged fragment of the sample (b) (sample Bar_2-1, Rusty zone).
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Figure 5. Back-scattering electron mode (BSE)–scanning electron microscope (SEM) images of As-containing pyrite grains (a,b) and the negative correlation S versus As in pyrite of Baranyevskoe deposit (c).
Figure 5. Back-scattering electron mode (BSE)–scanning electron microscope (SEM) images of As-containing pyrite grains (a,b) and the negative correlation S versus As in pyrite of Baranyevskoe deposit (c).
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Figure 6. Variations in the composition of Au-Ag solid solutions from different ore zones of the Baranyevskoe deposit (data from Table 2).
Figure 6. Variations in the composition of Au-Ag solid solutions from different ore zones of the Baranyevskoe deposit (data from Table 2).
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Figure 7. Variations in the composition of Au-Ag solid solutions from argillaceous-ocher sediments under mineralized outcrops of the Central and Southern zones. Southern _1 (samples BAR-6-2)—from sediments below quartz veins; Southern_2 (samples BAR-6-4)—under outcrops of oxidized ores (data from Table 3).
Figure 7. Variations in the composition of Au-Ag solid solutions from argillaceous-ocher sediments under mineralized outcrops of the Central and Southern zones. Southern _1 (samples BAR-6-2)—from sediments below quartz veins; Southern_2 (samples BAR-6-4)—under outcrops of oxidized ores (data from Table 3).
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Figure 8. Microparagenesis of the gold-pyrite-quartz association: (a)—low-grade gold intergrown with pyrite FeS2 in assemblage with akantite Ag2S and uytenbogardite Ag3AuS2, Rusty zone; (b)—low-grade gold in intergrowth with galena PbS, hessite Ag2Te and petzite Ag3AuTe2, Rusty zone; (c–e)—low-grade gold in intergrowth with chalcopyrite and pyrite replaced by Fe-oxide, Central zone; (f)—hessite with vein-like inclusions of low-grade gold; (g)—low-grade gold with vein-like inclusions of high-grade gold, South Zone; (h,i)—grains of Sb,As,Te-bearing akantite (Ag,Sb,As,Se)2S sometimes replaced by lenaite Ag(Fe,Cu)S2, the poorly compacted argillaceous-ocher rocks underneath the ore bodies, Southern zone.
Figure 8. Microparagenesis of the gold-pyrite-quartz association: (a)—low-grade gold intergrown with pyrite FeS2 in assemblage with akantite Ag2S and uytenbogardite Ag3AuS2, Rusty zone; (b)—low-grade gold in intergrowth with galena PbS, hessite Ag2Te and petzite Ag3AuTe2, Rusty zone; (c–e)—low-grade gold in intergrowth with chalcopyrite and pyrite replaced by Fe-oxide, Central zone; (f)—hessite with vein-like inclusions of low-grade gold; (g)—low-grade gold with vein-like inclusions of high-grade gold, South Zone; (h,i)—grains of Sb,As,Te-bearing akantite (Ag,Sb,As,Se)2S sometimes replaced by lenaite Ag(Fe,Cu)S2, the poorly compacted argillaceous-ocher rocks underneath the ore bodies, Southern zone.
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Figure 9. Au-Ag solid solutions from the gold-sulfosalt-quartz association, sample Bar-5-2, Northern zone in intergrowth with chalcopyrite CuFeS2, sometimes partially replaced by covellite CuS (c) or geerite Cu8S5 (d), mawsonite Cu6Fe2SnS8 (a,b,e), emplectite CuBiS2 (b,c,e,f), and bismuth-rich tetrahedrite Cu12(Sb,Bi,As)4S13 (a).
Figure 9. Au-Ag solid solutions from the gold-sulfosalt-quartz association, sample Bar-5-2, Northern zone in intergrowth with chalcopyrite CuFeS2, sometimes partially replaced by covellite CuS (c) or geerite Cu8S5 (d), mawsonite Cu6Fe2SnS8 (a,b,e), emplectite CuBiS2 (b,c,e,f), and bismuth-rich tetrahedrite Cu12(Sb,Bi,As)4S13 (a).
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Figure 10. Microparagenesis of the gold-sulfosalt-quartz association, polished section of the Bar-2-1 sample, Rusty zone: (a,c)—in reflected light; (b,d–h)—SEM image. Intergrowth of chalcopyrite, bornite Cu5FeS4 and tetrahedrite (Cu,Fe)12(Sb,As,Bi)4S13 including the hessite Ag2Te grain; (c,d)—Cu-bearing electrum intergrown with chalcopyrite, bornite and tetrahedrite; (e–h) Intergrowths of chalcopyrite with sulfosalts of different composition: tetrahedrite (e–g), wittichenite Cu3BiS3 (e,g,h); tetradymite Bi2Te2S (f) and mawsonite Cu6Fe2SnS8.
Figure 10. Microparagenesis of the gold-sulfosalt-quartz association, polished section of the Bar-2-1 sample, Rusty zone: (a,c)—in reflected light; (b,d–h)—SEM image. Intergrowth of chalcopyrite, bornite Cu5FeS4 and tetrahedrite (Cu,Fe)12(Sb,As,Bi)4S13 including the hessite Ag2Te grain; (c,d)—Cu-bearing electrum intergrown with chalcopyrite, bornite and tetrahedrite; (e–h) Intergrowths of chalcopyrite with sulfosalts of different composition: tetrahedrite (e–g), wittichenite Cu3BiS3 (e,g,h); tetradymite Bi2Te2S (f) and mawsonite Cu6Fe2SnS8.
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Figure 11. Microphotographs of quartz from the gold sulfosalt-quartz association: (a)—two-phase inclusions of isometric shape in the center of a transparent quartz crystal (sample Bar-5_2/1). Gaseous and two-phase inclusions of irregular shape on the crystal growth zone are shown in the inset; (b)—paragenesis of quartz, chalcopyrite and sulfosalts (dark) in a quartz vein (sample Bar-5_2/1). Primary two-phase fluid inclusions in a quartz crystal are shown in the inset.
Figure 11. Microphotographs of quartz from the gold sulfosalt-quartz association: (a)—two-phase inclusions of isometric shape in the center of a transparent quartz crystal (sample Bar-5_2/1). Gaseous and two-phase inclusions of irregular shape on the crystal growth zone are shown in the inset; (b)—paragenesis of quartz, chalcopyrite and sulfosalts (dark) in a quartz vein (sample Bar-5_2/1). Primary two-phase fluid inclusions in a quartz crystal are shown in the inset.
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Figure 12. Results of the fluid inclusion study: (a) histogram of homogenization temperatures of fluid inclusions in quartz of the gold-sulfosalt-quartz association from the Northern Zone of the Baranyevskoe deposit; (b) temperature of homogenization of inclusions versus their salinity. Bar-5-2/1 to Bar-5-2/3 are different sample Bar-5-2 areas of the gold-sulfosalt-quartz association.
Figure 12. Results of the fluid inclusion study: (a) histogram of homogenization temperatures of fluid inclusions in quartz of the gold-sulfosalt-quartz association from the Northern Zone of the Baranyevskoe deposit; (b) temperature of homogenization of inclusions versus their salinity. Bar-5-2/1 to Bar-5-2/3 are different sample Bar-5-2 areas of the gold-sulfosalt-quartz association.
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Figure 13. Compositions of Au-Ag alloys (at. %) in both associations of the Baranyevskoye deposit.
Figure 13. Compositions of Au-Ag alloys (at. %) in both associations of the Baranyevskoye deposit.
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Table
Table 1. Composition of the main sulfides of the Baranyevskoe deposit, wt. %.
Table 1. Composition of the main sulfides of the Baranyevskoe deposit, wt. %.
No. ZoneSampleFeCuBiAsSTotalFormula
1RustyBar-2-161.27 38.6799.94Fe0.95S1.05
2RustyBar-2-160.73 39.1099.83Fe0.94S1.06
3RustyBar-2-144.98 4.9049.7499.62Fe1.00(S1.92As0.08)2.00
4CentralBar-3-146.29 0.7752.7499.80Fe1.00(S1.92As0.08)2.00
5CentralBar-3-145.87 2.2551.4499.56Fe1.00(S1.96As0.04)2.00
6HangingBar-445.32 1.1252.3898.82Fe0.99(S1.99As0.02)2.01
7NorthernBar-5-146.19 0.8252.7399.74Fe1.00(S1.99As0.01)2.00
8NorthernBar-5-145.85 1.6251.7599.22Fe1.00(S1.97As0.03)2.00
9NorthernBar-5-145.72 2.3151.7999.82Fe1.00(S1.97As0.04)2.01
10NorthernBar-5-145.81 2.3551.5599.71Fe1.00(S1.96As0.04)2.00
11SouthernBar-6-545.36 3.9650.98100.30Fe0.99(S1.94As0.06)2.00
12SouthernBar-6-546.65 0.8452.98100.47Fe1.00(S1.98As0.01)1.99
13SouthernBar-6-545.15 4.3550.62100.12Fe0.99(S1.94As0.07)2.01
14SouthernBar-6-544.76 5.2150.13100.10Fe0.99(S1.93As0.09)2.02
15NorthernBar-5-144.61 7.3748.95100.93Fe0.99(S1.89As0.12)2.01
16NorthernBar-5-144.65 6.0948.6199.35Fe1.00(S1.90As0.10)2.00
17NorthernBar-5-229.9334.39 34.8799.19Cu1.00Fe0.99S2.01
18NorthernBar-5-230.2133.96 34.8298.99Cu0.99Fe1.00S2.01
19NorthernBar-5-230.0933.67 34.7898.54Cu0.98Fe1.00S2.02
20NorthernBar-5-230.0333.91 34.6198.55Cu0.99Fe1.00S2.01
21NorthernBar-5-229.733.91 34.598.11Cu1.00Fe0.99S2.01
22RustyBar-2-130.2834.38 34.5899.24Cu1.00Fe1.00S2.00
23RustyBar-2-130.9534.5 34.5299.97Cu1.00Fe1.02S1.98
24RustyBar-2-111.6761.022.01 25.78100.48Cu4.84Fe1.05Bi0.05S4.06
25RustyBar-2-111.6960.782.36 25.81100.64Cu4.83Fe1.06 Bi0.06S4.06
26RustyBar-2-111.9855.467.35 25.66100.45Cu4.54Fe1.12 Bi0.18S4.16
27NorthernBar-5-211.1563.05 25.6299.82Cu4.98Fe1.00S4.01
28NorthernBar-5-211.1862.90 25.1999.27Cu5.01Fe1.01S3.98
Note: 1–2—Pyrrhotite FeS; 3–16—Pyrite FeS2; 17–23—Chalcopyrite CuFeS2; 24–28—Bornite Cu5FeS4.
Table
Table 2. Composition of Au-Ag solid solutions from different zones of the Baranyevskoe deposit, wt. %.
Table 2. Composition of Au-Ag solid solutions from different zones of the Baranyevskoe deposit, wt. %.
No.ZoneSampleAuAgTotal No.ZoneSampleAuAgTotal
1RustyBar-2-177.8723.43101.3081HangingBar-479.4120.2999.70
2RustyBar-2-177.6322.62100.2582HangingBar-478.6419.9398.57
3RustyBar-2-176.6622.2398.8983HangingBar-479.8120.1599.96
4RustyBar-2-176.9921.4898.4784HangingBar-479.2519.4398.68
5RustyBar-2-178.0320.3798.4085HangingBar-479.2718.7798.04
6RustyBar-2-178.4519.8898.3386HangingBar-479.6918.7998.48
7RustyBar-2-178.5319.8998.4287HangingBar-482.2319.15101.38
8RustyBar-2-179.9520.10100.0588NorthernBar-5-165.7633.1498.90
9RustyBar-2-179.6319.9999.6289NorthernBar-5-166.7732.6699.43
10RustyBar-2-179.8419.1598.9990NorthernBar-5-167.1032.4099.50
11RustyBar-2-181.5219.14100.6691NorthernBar-5-167.1331.0698.19
12RustyBar-2-181.3518.5099.8592NorthernBar-5-169.5431.54101.08
13RustyBar-2-182.2218.10100.3293NorthernBar-5-170.1230.55100.67
14RustyBar-2-177.4221.2198.6394NorthernBar-5-170.1130.33100.44
15RustyBar-2-179.5721.54101.1195NorthernBar-5-170.2630.29100.55
16RustyBar-2-180.2420.88101.1296NorthernBar-5-170.1029.8299.92
17RustyBar-2-178.6420.1398.7797NorthernBar-5-170.2029.80100.00
18RustyBar-2-179.7420.1599.8998NorthernBar-5-169.7129.3299.03
19RustyBar-2-178.5819.8398.4199NorthernBar-5-169.1329.0198.14
20RustyBar-2-179.6120.0899.69100NorthernBar-5-170.8229.1299.94
21RustyBar-2-179.5919.8899.47101NorthernBar-5-170.428.7999.19
22RustyBar-2-180.5819.84100.42102NorthernBar-5-171.3328.95100.28
23RustyBar-2-181.5620.00101.56103NorthernBar-5-171.829.10100.90
24RustyBar-2-181.7820.00101.78104NorthernBar-5-171.5228.55100.07
25RustyBar-2-179.8519.1699.01105NorthernBar-5-171.5628.55100.11
26RustyBar-2-179.2518.9998.24106NorthernBar-5-172.4628.51100.97
27RustyBar-2-180.0119.0999.10107NorthernBar-5-171.8228.0099.82
28CentralBar-367.1433.05100.19108NorthernBar-5-170.5727.4698.03
29CentralBar-375.2424.88100.12109NorthernBar-5-171.5427.4899.02
30CentralBar-375.4923.8399.32110NorthernBar-5-175.7724.0399.80
31CentralBar-376.1323.91100.04111NorthernBar-5-177.1622.7499.90
32CentralBar-375.6523.4199.06112NorthernBar-5-270.4730.21100.68
33CentralBar-376.6023.2399.83113NorthernBar-5-270.6229.64100.26
34CentralBar-376.4723.1699.63114NorthernBar-5-270.0929.1299.21
35CentralBar-376.4922.9499.43115NorthernBar-5-270.1828.6198.79
36CentralBar-377.6422.59100.23116NorthernBar-5-270.5928.6099.19
37CentralBar-375.9021.9497.84117NorthernBar-5-271.0828.4999.57
38CentralBar-378.1822.48100.66118NorthernBar-5-271.9028.35100.25
39CentralBar-377.7322.35100.08119NorthernBar-5-271.3028.0799.37
40CentralBar-375.1921.0396.22120NorthernBar-5-273.7828.44102.22
41CentralBar-3-168.9129.2598.16121NorthernBar-5-292.617.2199.82
42CentralBar-3-171.0929.74100.83122NorthernBar-5-293.046.7699.80
43CentralBar-3-170.8928.6499.53123NorthernBar-5-293.676.79100.46
44CentralBar-3-170.9628.5599.51124NorthernBar-5-293.766.40100.16
45CentralBar-3-170.7928.1998.98125NorthernBar-5-293.806.25100.05
46CentralBar-3-171.6628.3399.99126NorthernBar-5-293.156.1799.32
47CentralBar-3-171.8827.3799.25127NorthernBar-5-291.426.0597.47
48CentralBar-3-175.8424.1199.95128NorthernBar-5-290.415.9696.37
49CentralBar-3-174.1123.2397.34129NorthernBar-5-293.566.0399.59
50CentralBar-3-177.1023.29100.39130NorthernBar-5-293.705.8799.57
51CentralBar-3-177.9523.24101.19131NorthernBar-5-293.475.7799.24
52CentralBar-3-175.9921.7997.78132NorthernBar-5-295.255.80101.05
53CentralBar-3-177.8222.28100.1133NorthernBar-5-293.935.6499.57
54CentralBar-3-178.6921.93100.62134NorthernBar-5-292.815.5098.31
55CentralBar-3-179.0720.4499.51135NorthernBar-5-295.735.50101.23
56CentralBar-3-179.6719.9099.57136NorthernBar-5-292.605.2397.83
57HangingBar-469.8529.5499.39137NorthernBar-5-292.835.2398.06
58HangingBar-470.2727.5297.79138NorthernBar-5-293.594.7898.37
59HangingBar-472.2127.6199.82139NorthernBar-5-294.284.6298.90
60HangingBar-475.0425.34100.38140NorthernBar-5-293.884.5498.42
61HangingBar-475.4924.79100.28141NorthernBar-5-296.584.13100.71
62HangingBar-482.0318.76100.79142NorthernBar-5-295.204.0099.20
63HangingBar-493.654.6598.30143NorthernBar-5-294.983.8798.85
64HangingBar-493.654.5998.24144NorthernBar-5-296.273.86100.13
65HangingBar-492.784.5197.29145NorthernBar-5-295.013.7198.72
66HangingBar-493.644.4198.05146NorthernBar-5-296.793.48100.27
67HangingBar-496.344.26100.60147NorthernBar-5-295.153.2998.44
68HangingBar-468.1932.11100.30148SouthernBar-6-168.4131.1699.57
69HangingBar-474.0825.4599.53149SouthernBar-6-170.3629.79100.15
70HangingBar-473.4524.7898.23150SouthernBar-6-278.4716.2194.68
71HangingBar-476.4323.5199.94151SouthernBar-6-280.7616.6697.42
72HangingBar-478.3422.27100.61152SouthernBar-6-279.6815.5095.18
73HangingBar-477.3221.9599.27153SouthernBar-6-277.0124.30101.31
74HangingBar-477.7022.0199.71154SouthernBar-6-276.1023.6699.76
75HangingBar-477.5120.7598.26155SouthernBar-6-276.0621.9898.04
76HangingBar-477.6520.7498.39156SouthernBar-6-277.4220.2097.62
77HangingBar-478.6820.9999.67157SouthernBar-6-276.2819.5495.82
78HangingBar-479.7721.00100.77158SouthernBar-6-278.0520.1098.15
79HangingBar-478.8320.6399.46159SouthernBar-6-279.6620.2699.92
80HangingBar-477.9920.1298.11160SouthernBar-6-280.1420.75100.89
Table
Table 3. Composition of Au-Ag solid solutions from argillaceous-ocher rocks underneath outcrops, wt. %.
Table 3. Composition of Au-Ag solid solutions from argillaceous-ocher rocks underneath outcrops, wt. %.
No.ZoneSampleAuAg Total No.ZoneSampleAuAg Total
1CentralBar-3-1a97.04 1.73 98.77 20CentralBar-3-1a76.86 21.04 97.90
2CentralBar-3-1a78.01 21.78 99.79 21SouthernBar-6-280.77 17.74 98.51
3CentralBar-3-1a75.48 24.02 99.5022SouthernBar-6-260.76 39.20 99.96
4CentralBar-3-1a75.04 24.26 99.30 23SouthernBar-6-257.28 41.95 99.23
5CentralBar-3-1a77.94 22.08 100.02 24SouthernBar-6-239.98 57.67 97.65
6CentralBar-3-1a77.92 21.30 99.22 25SouthernBar-6-225.48 75.53 101.01
7CentralBar-3-1a76.29 20.81 97.10 26SouthernBar-6-280.08 20.02 100.10 0
8CentralBar-3-1a75.84 20.77 96.61 27SouthernBar-6-277.41 19.80 97.21
9CentralBar-3-1a74.57 24.17 98.74 28SouthernBar-6-256.68 43.77 100.45
10CentralBar-3-1a78.04 20.63 98.67 29SouthernBar-6-277.98 20.63 98.61
11CentralBar-3-1a77.08 20.48 97.56 30SouthernBar-6-296.73 3.30 100.03
12CentralBar-3-1a75.64 21.54 97.18 31SouthernBar-6-294.18 4.47 98.65
13CentralBar-3-1a75.21 21.51 96.72 32SouthernBar-6-278.60 21.15 99.75
14CentralBar-3-1a76.77 21.48 98.25 33SouthernBar-6-496.63 3.28 99.91
15CentralBar-3-1a76.86 21.49 98.35 34SouthernBar-6-474.84 22.12 96.96
16CentralBar-3-1a73.33 22.53 95.86 35SouthernBar-6-496.69 2.11 98.80
17CentralBar-3-1a81.46 13.44 94.90 36SouthernBar-6-496.43 3.55 99.98
18CentralBar-3-1a79.14 21.06 100.20 37SouthernBar-6-495.53 2.92 98.45
19CentralBar-3-1a77.35 21.39 98.74 38SouthernBar-6-476.62 22.43 99.05
Note. Samples Bar-3-1a—from oxidized breccia; Bar-6-2—ochery-argillaceous highly altered rock under quartz veins, and Bar-6-4—under the outcrops of oxidized ores.
Table
Table 4. Composition of Au-Ag minerals in the gold-pyrite-quartz association from various zones of the Baranyevskoe deposit, wt. %.
Table 4. Composition of Au-Ag minerals in the gold-pyrite-quartz association from various zones of the Baranyevskoe deposit, wt. %.
NoZoneFeCuAuAgPbBiSbTeAsSeSTotalFormula
1Southern 84.69 2.5612.0699.31Ag1.97(S0.95Se0.08)1.03
2Southern 85.64 2.3612.04100.04Ag1.99(S0.94Se0.07)1.01
3Central 62.74 36.39 99.13Ag2.01Te0.99
4Southern 63.38 100.81Ag2.00Te1.00
5Rusty 63.15 99.89Ag2.01Te0.99
6Rusty 3.1661.04 100.52(Ag1.96.Au0.06)2.02Te0.99
7Rusty 63.03 100.31Ag2.00Te1.00
8Rusty 1.8262.58 101.34(Ag1.98.Au0.03)2.01Te0.99
9Rusty 62.48 99.00Ag2.01Te0.99
10Southern22.223.75 43.35 26.9596.27Ag0.95(Fe0.94Cu0.14)1.08S1.98
11Rusty 24.6842.9 100.15Ag3.07Au0.97Te1.97
12Rusty 24.6741.34 98.11Ag3.03Au0.99Te1.99
13Rusty 24.7440.47 97.36Ag2.99.Au1.00Te2.01
14Hanging 25.1261.57 10.9597.64Ag3.29.Au0.74S1.97
15Southern 78.34 7.16 11.8697.36Ag10.06Sb0.81S5.12
16Southern 79.98 2.72 3.68 12.1998.57Ag9.94(As0.66Sb0.30)0.96S5.10
17Southern 78.25 7.67 11.9497.86Ag10.00Sb0.87S5.13
18Southern 76.99 3.97 3.810.9513.4399.15Ag16.85(As1.20Sb0.77)1.97 (S9.89 Se0.28)10.18
19Central 3.24 75.14 1.97 5.531.0113.6597.30(Ag15.83Cu1.16)16.99(As1.68Sb0.37)2.05(S9.68Se0.29)9.97
20Central 2.66 73.34 9.55 1.1512.9997.03(Ag16.16Cu1.00)17.16Sb1.86(S9.63Se0.35)9.63
21Southern 3.8573.93 5.18 2.981.3312.8296.24(Ag16.51Au0.47)16.98(Sb1.02As0.96)1.98 (S9.63Se0.41)10.04
22Rusty 5.8969.1212.03 12.5699.60Ag0.98Bi1.03Pb5.97S7.02
Note: 1–2—Acanthite Ag2S; 3–9—Hessite Ag2Te; 10—Lenaite Ag(Fe,Cu)S2; 11–13—Petzite Ag3AuTe2; 14—Uytenbogardite Ag3AuS2; 15–22—Ag-sulfosalts: 15–17—Ag10(Sb,As)S5; 18–21—Ag17(Sb,As)2(S,Se)10; 22—AgBiPb6.
Table
Table 5. Composition of minerals from the gold-sulfosalt-quartz association, wt. %.
Table 5. Composition of minerals from the gold-sulfosalt-quartz association, wt. %.
NoSampleZoneFeCuZnAuSnPbBiSbTeAsSeSTotalFormula
1Bar-2-1Rusty 85.02 12.7897.80Pb1.01S0.99
2Bar-2-1Rusty 85.63 12.6198.24Pb1.02S0.98
3Bar-2-1Rusty 1.18 84.81 13.1699.15(Pb0.99Au0.01)1.00S0.99
4Bar-2-1Rusty 2.02 86.02 12.83100.87(Pb1.01Au0.02)1.03S0.97
5Bar-2-1Rusty 1.01 86.82 12.95100.78(Pb1.01Au0.01)1.02S0.98
6Bar-2-1Rusty 1.54 85.81 12.91100.26(Pb1.00Fe0.02Au0.02)1.04S0.98
7Bar-5-2Northern1.6273.92 24.0599.59(Cu7.79Fe0.19)7.98S5.02
8Bar-5-2Northern3.1173.65 24.32101.08(Cu7.64Fe0.37)8.01S5.00
9Bar-5-2Northern0.6074.09 23.5398.22(Cu7.93Fe0.07)8.00S4.99
10Bar-4Hanging 99.73 99.73Cu1.00
11Bar-4Hanging 55.4641.98 97.44Cu1.15Zn0.85
12Bar-4Hanging 64.9036.09 100.99Cu1.30Zn0.70
13Bar-5-2Northern 10.46 37.2236.78 15.3299.78Pb1.08Cu0.99Bi1.06S2.87
14Bar-4Hanging 10.24 38.3936.86 15.23100.72Pb1.11Cu0.97Bi1.06S2.86
15Bar-4Hanging 10.75 39.1234.75 15.0299.64Pb1.14Cu1.02Bi1.00S2.83
16Bar-4Hanging0.4110.15 38.8436.53 14.96100.89Pb1.13(Cu0.96Fe0.04)1.00Bi1.05S2.81
17Bar-4Hanging0.2718.69 2.0459.60 18.1898.78(Cu1.01Fe0.02)1.03(Bi0.98Pb0.03)1.01S1.95
18Bar-5-2Northern 18.55 2.4157.120.91 18.3397.32Cu1.01(Bi0.95Pb0.04Sb0.03)1.02S1.98
19Bar-5-2Northern 18.27 2.9057.341.27 18.2097.98Cu1.00(Bi0.95Pb0.05Sb0.04)1.04S1.97
20Bar-5-2Northern 18.31 2.7357.561.81 18.0998.50Cu1.00(Bi0.95Pb0.05Sb0.05)1.05S1.95
21Bar-5-2Northern 18.27 3.0358.64 17.8897.82Cu1.01(Bi0.98Pb0.05)1.03S1.96
22Bar-6-1bSouthern0.5018.38 60.13 18.5397.54(Cu0.99Fe0.03)1.02Bi0.99S1.99
23Bar-5-2Northern12.9743.71 13.81 29.4699.95Cu5.98Fe2.02Sn1.01S7.99
24Bar-5-2Northern13.0143.29 13.67 29.3699.33Cu5.95Fe2.04Sn1.01S8.00
25Bar-5-2Northern11.4642.931.43 13.36 28.8197.99Cu6.00(Fe1.82Zn0.19)2.01Sn1.00S7.98
26Bar-5-2Northern12.4242.34 13.28 1.84 28.3298.20Cu5.98Fe2.00Sn1.00(S7.93Bi0.08)8.01
27Bar-5-2Northern9.5937.783.36 17.87 28.6897.28Cu7.98(Fe2.30Zn0.69)2.99Sn2.02S12.01
28Bar-5-2Northern9.9337.462.70 17.47 2.03 27.8997.48Cu8.00(Fe2.41Zn0.56)2.97Sn2.00(S11.81Te0.22)12.03
29Bar-5-2Northern 59.34 36.16 0.814.25100.56Bi2.00Te2.00(S0.93Se0.07)1.00
30Bar-5-2Northern 58.71 36.32 0.914.29100.23Bi1.98Te2.00(S0.97Se0.08)1.02
31Bar-5-2Northern1.6638.444.37 10.4018.19 2.70 24.33100.09(Cu10.35Zn1.14Fe0.51)12.00(Sb2.56Bi0.85As0.62)4.03S12.98
32Bar-5-2Northern1.7636.734.41 1.839.8120.88 23.6299.04(Cu10.21Zn1.19Fe0.56)11.96(Sb3.03Bi0.16)4.02S13.02
33Bar-2-1Rusty3.9441.89 25.14 3.56 24.9599.48(Cu10.85Fe1.16)12.01 (Sb3.40As0.78)4.18S12.81
34Bar-2-1Rusty3.7741.76 3.3123.86 2.47 25.02100.19(Cu10.89Fe1.12)12.01 (Sb3.25As0.55Bi0.26)4.18S12.93
35Bar-2-1Rusty4.2941.93 3.3724.09 2.70 25.03101.41(Cu10.83Fe1.26)12.09 (Sb3.25As0.59 Bi0.26)4.10S12.81
36Bar-2-1Rusty3.6939.43 9.0419.69 2.16 23.7497.75(Cu10.83Fe1.15)11.99 (Sb2.82As0.50Bi0.76)4.08S12.93
37Bar-2-1Rusty3.2039.71 13.116.36 2.79 23.5998.75(Cu10.97Fe1.01)11.98 (Sb2.36 Bi1.10As0.65)4.11S12.91
38Bar-2-1Rusty3.7539.26 7.9016.13 4.29 23.8696.00 *(Cu10.77Fe1.17Ag0,13)12.07(Sb2.31As1.00Bi0.66)3.97S12.97
39Bar-2-1Rusty3.9239.46 9.2015.98 4.50 24.197.88 **(Cu10.69Fe1.21Ag0,11)12.01(Sb2.26As1.03Bi0.76)4.05S12.94
40Bar-2-1Rusty4.3040.83 9.1014.59 5.85 24.7699.43(Cu10.75Fe1.29)12.04 (Sb2.01As1.31Bi0.73)4.04S12.92
41Bar-2-1Rusty4.4741.28 10.589.93 7.97 25.2899.51(Cu10.72Fe1.32)12.05(Sb1.35As1.76Bi0.84)3.94S13.02
42Bar-2-1Rusty3.8845.25 2.779.36 12.90 26.82100.98(Cu10.98Fe1.07)12.05(Sb1.19As2.66Bi0.20)4.05S12.902
43BAR-2_1Rusty7.3011.58 15.9534.35 10.8114.19100.01 ***(Cu0.92Fe0.66Ag0.27)1.85Pb0.39Bi0.83(S2.24Se0.69)2.93
44BAR-2_1Rusty 39.45 41.130.70 19.02100.3Cu3.07(Bi0.97Sb0.03)1.00S2.93
45BAR-2_1Rusty0.9238.04 40.770.67 19.0199.41(Cu2.97Fe0.08)3.05(Bi0.97Sb0.03)1.00S2.95
46BAR-2_1Rusty0.1838.78 39.620.72 19.9399.23(Cu2.99Fe0.02)3.01(Bi0.93Sb0.03)0.96S3.04
47BAR-2_1Rusty0.2939.14 39.900.80 18.8999.02(Cu3.06Fe0.03)3.09(Bi0.95Sb0.03)0.98S2.93
48BAR-2_1Rusty0.5438.97 39.340.84 19.7299.41(Cu3.00Fe0.05)3.05(Bi0.92Sb0.03)0.95S3.00
49BAR-2_1Rusty0.4339.04 39.49 18.8097.76(Cu3.08Fe0.04)3.12Bi0.95S2.94
50BAR-2_1Rusty0.7238.76 38.940.59 18.6097.61(Cu3.06Fe0.06)3.12(Bi0.94Sb0.02)0.96S2.91
51BAR-2_1Rusty0.6737.52 40.17 18.7897.14(Cu2.99Fe0.06)3.05Bi0.97S2.97
52Bar-5-2Northern1.012.37 56.52 34.53 0.774.86100.06(Cu0.69Fe0.33)1.02Bi5.00Te5.00(S2.80Se0.18)2.98
53Bar-2-1Rusty21.6223.74 26.64 5.2725.92103.19Cu2.96Fe3.07Pb1.02(S6.41Se0.53)6.94
Note: 1–6—Galena PbS; 7–9—Geerite Cu8S5; 10—Copper Cu; 11–12—Zhanghengite CuZn; 13–16—Aikinite PbCuBiS3; 17–22—Emplectite CuBiS2; 23–26—Mawsonite Cu6Fe2SnS8; 27–28—Stannoidite Cu8Fe3Sn2S12; 29–30—Tetradymite Bi2Te2S; 31–42—Tetrahedrite Cu12(Sb,Bi,As)4S13; 43—Aikinite (Cu,Fe,Ag)PbBi(S,Se)3; 44–51—Wittichenite Cu3BiS3; 52—(Cu,Fe)Bi5Te5S3; 53—Cu3Fe3PbS7; *, ** and ***—the totals include 0.82, 0.72 and 5.83 wt. % of Ag, respectively.
Table
Table 6. Concentration of ore and chalcogenic elements in rocks of different zones of the Baranyevskoe deposit, ppm.
Table 6. Concentration of ore and chalcogenic elements in rocks of different zones of the Baranyevskoe deposit, ppm.
ZoneSampleAuAgAu/AgCuAsBiPbSbSeSnZnTe
RustyBar-2-13.770.983.8520.40240.5019.9013.30<2<0.30220.49
CentralBar-36.781.963.4688.90210.2156.4023.30<20.30950.22
CentralBar-3-16.472.312.8069.001520.1467.3026.40<2<0.30670.12
HangingBar-443.7014.103.1024.30420.4035.4011.60<20.30660.28
NorthernBar-5-113537.603.5980.9010300.2721.3056.70<20.40220.10
NorthernBar-5-211011.109.913240687800274169361161521.6
SouthernBar-6-10.221.340.1688.10110.5126.7017.00<2<0.30390.89
SouthernBar-6-20.160.430.37128380.1637.7014.10<20.40750.41
SouthernBar-6-30.361.340.2714.10190.0550.709.56<20.40430.65
SouthernBar-6-40.160.310.5234.70540.0925.006.83<20.70780.93
SouthernBar-6-50.680.292.3525.80390.0412.5012.90<20.80760.10
Table
Table 7. Summary of the microthermometric study of fluid inclusions in quartz from the gold-sulfosalt-quartz association.
Table 7. Summary of the microthermometric study of fluid inclusions in quartz from the gold-sulfosalt-quartz association.
SamplenTh °CTeu °CTm Ice °CSalinity, wt. % NaCl eq.MPa
Bar-5 2/16268–250−45−0.6…−0.81.2–1.15.3–3.9
Bar-5 2/213268–256−49−0.71.25.3–4.4
Bar-5 2/311298–226−27−0.2…−0.40.5–0.42.6–8.3
Note: n—number of analyses; Th °C—homogenization temperature of fluid inclusions; Teu °C—eutectic temperature (first melting temperature); Tm ice °C—final ice melting temperature; MPa—calculated pressure [22]; eq—equivalent.
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Tolstykh, N.; Bukhanova, D.; Shapovalova, M.; Borovikov, A.; Podlipsky, M. The Gold Mineralization of the Baranyevskoe Au-Ag Epithermal Deposit in Central Kamchatka. Minerals 2021, 11, 1225. https://doi.org/10.3390/min11111225

AMA Style

Tolstykh N, Bukhanova D, Shapovalova M, Borovikov A, Podlipsky M. The Gold Mineralization of the Baranyevskoe Au-Ag Epithermal Deposit in Central Kamchatka. Minerals. 2021; 11(11):1225. https://doi.org/10.3390/min11111225

Chicago/Turabian Style

Tolstykh, Nadezhda, Daria Bukhanova, Maria Shapovalova, Andrey Borovikov, and Maksim Podlipsky. 2021. "The Gold Mineralization of the Baranyevskoe Au-Ag Epithermal Deposit in Central Kamchatka" Minerals 11, no. 11: 1225. https://doi.org/10.3390/min11111225

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