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Scheelite of the Kekura gold deposit in the Western Chukchi Peninsula is reported for the first time. Three generations of the mineral have been identified. According to the LA–ICPMS data, the Mo content in scheelite does not exceed 0.2 ppm and the total REE ranges from 20 to 150 ppm. The REE distribution patterns of all three scheelite generations have a strong positive Eu anomaly (Eu/Eu* = 4.4–55.6), which is typical of scheelite from intrusion-related and orogenic gold deposits. The high Sr concentration (1300–12 000 ppm) is characteristic of the hypabyssal intrusion-related Au deposits. According to the fluid inclusion data, the minimal crystallization temperature of scheelite and associated quartz is 200–250°С.

The Peschanka deposit and Nakhodka ore field occurring in the Baimka Cu-Mo-Au porphyry-epithermal trend in the western Chukchi Peninsula, Russia are spatially related to monzonitic rocks of the Early Cretaceous Egdykgych Complex. Tetrahedrite solid solution (Tts) was recognized at the deposit and within the ore field in the following assemblages: (1) porphyry stage bornite, chalcopyrite, and molybdenite, (2) transitional (subepithermal) stage sphalerite, galena, chalcopyrite, and As-free pyrite, (3) HS epithermal stage enargite, chalcopyrite and high-fineness native gold, and (4) IS epithermal stage As-rich pyrite, galena, sphalerite, and low-fineness native gold and electrum. The porphyry and subepithermal Tts crystals are oscillatory zoned because of variable contents of Sb and As. The literature data show that similar zoning has been recognized in the Tts crystals in the other porphyry Cu-Mo-Au and transitional assemblages and differs from the other type deposits. Therefore, such a zoning is considered to be a guide to these two mineralization types. No zoning was found in Tts referred to the HS and IS epithermal assemblages within the Baimka trend. The porphyry stage Tts evolves from Fe-rich tennantite ((sb = Sb/(Sb + As) below 0.01, fe = Fe/(Fe + Zn) 0.60–0.80) through oscillatory zoned tennantite enriched in Sb and Zn (sb 0.19–0.37, fe 0.56–0.66) to tetrahedrite enriched in Zn (sb 0.51–0.70, fe 0.39–0.66). This trend is caused by the Sb accumulation and increased fS2. The review of published data shows that such trend is typical of the other porphyry deposit worldwide. Therefore, it is considered to be a guide to distinguish porphyry deposits from the other type deposits containing fahlores and to distinguish porphyry-stage fahlores. The composition of the transitional stage Tts evolves from Zn-rich tetrahedrite (sb 0.56–0.82, fe 0.03–0.05) through Zn-rich tennantite (sb 0.03–0.19, fe 0.11–0.13) followed by Zn-rich oscillatory zoned solid solution (sb 0.03 to 0.69, fe 0.09 to 0.11) to goldfieldite. This evolution testifies to increased fTe2 to the end of transitional stage. The HS stage Tts corresponds to Fe-rich tennantite (sb below 0.05, fe 0.65–1.00) containing high Cuexcess (1.43 apfu). The IS stage Tts evolves from Zn-rich tennantite (sb = 0, fe = 0.44) to Zn-rich tetrahedrite (sb = 0.97, fe = 0.03). The latest Zn-rich tetrahedrite of this assemblage is enriched in Ag (up to 4.1 wt.%) testifying to increasing Ag activity to the end of mineralizing process. The review of literature data shows the similar trend for the transitional and IS Tts in the other porphyry-epithermal systems. Therefore the Tts evolution trend is a criterion to separate porphyry, transitional, IS, and HS Tts.

The Tumanny Au-Ag-Te-Hg epithermal prospect, Chukchi Peninsula, Russia is located in the near contact zone of the large Vuknei pluton, part of the Early Cretaceous Egdykgych Complex, which is related to the Peschanka porphyry copper deposit and the Nakhodka porphyry-epithermal ore district located 45 km north of Tumanny. Mineralization at Tumanny is characterized by an early carbonate-base metal and a late gold-silver-sulfosalt mineral assemblage. Pyrite of the first assemblage is unzoned and As-poor, and tennantite-tetrahedrite solid solutions (Ttrs) are characterized by a weak oscillatory zoning caused by variable contents of Sb and As, low Ag content, and the widely variable Sb/(Sb + As) values. Pyrite of the second assemblage is zoned and As-rich (up to 5.2 wt%) and Ttrs is weakly zoned and Ag-rich (up to 10.35 apfu) and has a comparatively narrow range of Sb/(Sb + As) value. Electrum, Au-Ag alloy (“kustelite”), Au-Ag-S phases, hessite, polybasite, and imiterite recognized at the prospect belong to the second mineral assemblage. The homogenization temperature of primary fluid inclusions in quartz ranges from 340 to 210 °C and decreased during the mineralizing process; fluid salinity varying from 0.8 to 5.2 wt% NaCl equiv is not evolved during the process. Cores of quartz crystals formed from a boiling fluid, whereas crystal rims appear to have formed from a lower temperature non-boiling liquid. LogfS2 decreased from −8 at the formation of carbonate-base metal assemblage to −16 at the deposition of gold-silver-sulfosalt assemblage as temperature decreased from 340 to 200 °C. Bulk ICP-OES analysis of mineralized samples indicated up to: 38 ppm Au, 908 ppm Ag, 154 ppm Mo, 106 ppm Te, 53 ppm Se, 9246 ppm As, 1284 ppm Sb, and 23 ppm Bi. Cluster analysis of the data obtained identified three geochemical associations corresponding the carbonate-base metal the gold-silver-sulfosalt, and to the overlapped mineral assemblages. The whole-ore composition is controlled by mineralogy of these assemblages. Taking into account the geological setting, mineralogy, composition of minerals, and fluid inclusion data, the Tumanny Au-Ag-Te-Hg prospect is characterized as intermediate sulfidation epithermal style.

The Kekura gold deposit in Western Chukotka, Russia is spatially related to the granitic rocks of the Early Cretaceous Gvardeisky Complex. The deposit was formed during five mineralization stages: (1) cassiterite-scheelite-chalcopyrite-bornite-arsenopyrite, (2) molybdenite, (3) chalcopyrite-gold-bismuth tellurides, (4) arsenopyrite-gold-scheelite, and (5) stibnite-gold-silver. The tetrahedrite group minerals (Ttgs) were identified in stages 2, 4, and 5. In the molybdenite stage Ttgs are associated with digenite, bornite, chalcopyrite, molybdenite, and arsenopyrite. Ttgs from the arsenopyrite-gold-scheelite stage are associated with scheelite, chalcopyrite, sphalerite, galena, and native gold with fineness of 800–850. Along with tetrahedrite, stibnite-gold-silver mineralization includes Ag-Au and Au-Ag-Hg alloys, native silver, sphalerite, stibnite, boulangerite. The molybdenite stage Ttgs display a wide range of the Sb/(Sb + As + Bi) ratio (sb) 0.06–0.85 and a narrow range of the Fe/(Fe + Zn) ratio (fe) 0.78–1.00, and are enriched in Cu (up to 5.767 apfu Cu at the M(1) site); the Ag content does not exceed 0.080 apfu. Ttgs of the arsenopyrite-gold-scheelite stage have the Cu-free at M(1) site, but are highly variable in the sb and fe values, ranging from 0.24 to 1.00, and from 0.14 to 1.00, respectively; the Ag concentration is higher than that in the molybdenite stage Ttgs, reaching 0.365 apfu. The stibnite-gold-silver tetrahedrite has high Ag (up to 3.442 apfu) and sb and fe ranging from 0.68 to 1.00 and from 0.10 to 0.84, respectively. Some Ttgs compositions of the molybdenite and stibnite-gold-silver stages are Bi-bearing that is caused by the replacement of previous Bi-minerals.

The concentration of the Al and Ti paramagnetic impurity centers in pre-ore and ore-stage quartz at the Peschanka porphyry copper–molybdenum–gold deposit in the Western Chukchi Peninsula, Russia were determined using electron paramagnetic resonance spectroscopy (EPR). The [AlO 4 - /h+]0 concentration in pre-ore and ore-stage quartz varies from 29 to 124 and from 13 to 101 at. ppm, respectively. The contents of the [TiO 4 - /Li+]0 and [TiO 4 - /H+]0 centers reach 20 and 6.3 at. ppm, respectively. Pre-ore quartz associated with the formation of biotite–potassium feldspar–quartz alteration and ore-stage quartz associated with the formation of quartz–sericite rocks followed by the ore deposition differ considerably in the Ti center content, especially the [TiO 4 - /H+]0 center. The [TiO 4 - /H+]0 concentration is much higher in the pre-ore quartz (>2 at. ppm) than that in the ore-stage quartz related to copper mineralization (

Mineralogical, fluid inclusion, and geochemical studies of precious metal mineralization within the Baimka trend in the western Chukchi Peninsula have been preformed. Porphyry copper–molybdenum–gold deposits and prospects of the Baimka trend are spatially related to monzonitic rocks of the Early Cretaceous Egdygkych Complex. Four types of precious metal-bearing assemblages have been identified: (1) chalcopyrite + bornite + quartz with high-fineness native gold enclosed in bornite, (2) low-Mn dolomite + quartz + sulfide (chalcopyrite, sphalerite, galena, tennantite-tetrahedrite) ± tourmaline with low-fineness native gold and hessite, (3) rhodochrosite + high-Mn dolomite + quartz + sulfide (chalcopyrite, sphalerite, galena, tennantite- tetrahedrite) with low-fineness native gold, electrum, acanthite, Ag and Au–Ag tellurides, and Ag sulfosalts, and (4) calcite + quartz + sulfide (chalcopyrite, sphalerite, galena) with low-fineness native gold, Ag sulfides and selenides, and Ag-bearing sulfosalts. Study of fluid inclusions from quartz, sphalerite, and fluorite have revealed that hydrothermal ores within the Baimka trend precipitated from fluids with strongly variable salinity at temperatures and pressures ranging from 594 to 104°C and from 1200 to 170 bar, respectively. An indicator of vertical AgPbZn/CuBiMo geochemical zoning is proposed. The value range of this indicator makes it possible to estimate the erosion level of the porphyry–epithermal system. The erosion level of the Baimka deposits and prospects deepens in the following order: Vesenny deposit → Pryamoi prospect → Nakhodka prospect → Peschanka deposit → III Vesenny prospect.

Tourmaline-supergroup minerals are proposed as efficient indicators of porphyry-style Cu, Au and Sn deposits and therefore are considered as useful for both the prospection and exploration of these important mineral deposits. The tourmaline-supergroup minerals from the porphyry deposits exhibit some general features: (1) sector and oscillatory chemical zoning of crystals; (2) presence in several generations; (3) Fe → Al coupled substitution; (4) evolution from Fe-rich to Mg-rich varieties resulting from sulphide deposition at the late stage; (5) Li concentration ranging from a few to ~30 ppm. On the other hand, there are distinguishing features for tourmalines from different deposits: (1) total Mg content is ~2 apfu for tourmaline in the Cu deposits, 1–2 apfu in the Au deposits, and 0–1 apfu in Sn deposits; (2) maximum Fe tot ~3 apfu (Cu, Sn) and ~5 apfu (Au), (3) maximum F content up to 0.1 apfu (Cu, Au) and up to 0.5 apfu (Sn); (4) Fe 3+ /Fe tot ~0.5–0.8 (Cu, Au) and ~0.2 (Sn).

The Nakhodka ore field located 220 km south of the Bilibino town, Chukchi Peninsula, Russia comprises Cu-Mo-porphyry (Malysh and Vesennii) and Mo-Cu-porphyry (Nakhodka, III Vesennii) deposits. The late epithermal mineralization with native gold of low fineness (498–766) of the first group deposits refers to the IS (intermediate sulfidation) type, which is characterized by the occurrence of petzite; stutzite; acanthite; pearceite; and minerals of the Pb-Bi-Ag-Se-Te, Ag-Te-Se, and Ag-Bi-Se systems, as well as by native tellurium. The epithermal mineralization forms at fTe2(−19...−18) and fS2(−14...−13) and temperatures

A thermochemical study of natural aluminum hydroxosulfate Al2[(OH)4SO4] · 7H2O, aluminite (Nakhodka deposit, West Chukotka, Russia) is performed on a Tian-Calvet “Setaram” high-temperature heat-conducting microcalorimeter (France). The enthalpy of aluminite formation from simple compounds is obtained via the melt calorimetry of dissolution, ΔfH○(298.15 K) = −4986 ± 21 kJ/mol.