The Gaching high-sulfidation epithermal deposit in the Maletoyvayam ore field features a wide range of Se-containing minerals and selenides, as well as complex gold oxides, Au tellurides (calaverite, krennerite) and native gold typical for epithermal deposits. Pyrite included in quartzites and quartz-alunite rocks was probably formed during an early stage of the ore-forming process. During the following Au-rich stage, the $f_{{\rm S}{\rm e}_{\rm 2}}$/$f_{{\rm S}_{\rm 2}}$ increased with $f_{{\rm O}_{\rm 2}}$ being relatively high, resulting in the formation of very rare compounds that have not been previously described in nature. These include Au2Te4(Se,S)3, Se3Te2, AuSe and Au(Te,Se,S) phases. The Au2Te4(Se,S)3 compounds have some variations in composition: the complete isomorphic series between Au2Te4Se3 and Au2Te4S3 was observed. The gold and Au-minerals at the main ore stage can be stable within a range of log$f_{{\rm O}_{\rm 2}}$ of −27.3 and atmospheric oxygen (?); log$f_{{\rm S}{\rm e}_{\rm 2}}$ between −12.4 and −5.7; log$f_{{\rm T}{\rm e}_{\rm 2}}$ between −10.5 and −7.8; and log$f_{{\rm S}_{\rm 2}}$ between −12.8 and −6.8 (at 250°C). The increasing oxygen fugacity during the final stage of mineralization resulted in the formation of complex Sb,As,Te,S-bearing Au oxides. Gold-oxide formation occurs due to oxidation of Au-tellurides. The final products of this process are newly-formed secondary mustard gold and Te–Se solid solutions.

Platinum mineralization has been studied within two zoned clinopyroxenitedunite massifs of the Urals Platinum Belt. Within the Svetloborsky massif, platinum group minerals (PGM) occur directly in serpentinized dunite. The ore-forming system demonstrates the features of an early evolutionary stage: a significant portion of PtFe alloys belongs to ferroan platinum; native osmium is depleted in Ir; an isoferroplatinumosmium paragenesis is present. Within the Kamenushinsky massif, PGM are genetically related to chromitite and belong to the late-magmatic stage of the ore-forming system evolution: osmium and isoferroplatinum are rich in Ir; both isoferroplatinumosmium and isoferroplatinumiridium magmatic parageneses are present. The elevated Pt in the dunite of the Svetloborsky massif and in the chromitite of the Kamenushinsky massif is the result of two events: the primary-magmatic crystallization of PGM and later hydrothermal overprint.

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The composition and the associations of platinum-group minerals from the Salmon River placers, Goodnews Bay, Alaska, are compared with those of assemblages in other Alaskan-type complexes. Pt-Fe alloy, with an average value 25 at.% Fe, corresponds to isoferroplatinum (Pt 3 Fe). Ir concentrations in isoferroplatinum reach 15.4 wt.%, and Rh concentrations, as much as 2.27 wt.%. Tulameenite, which replaces the isoferroplatinum grains, appears as a rim with distinct boundaries. It forms a Pt 2 CuFe-PtFe series and also contains up to 2.64 wt.% Ni. Iridium and osmium occur as inclusions in the isoferroplatinum matrix and are depleted in Ru. The Ir content of osmium reaches 26 at.%, and the proportion of Os in iridium varies from 12 to 20 at.%. The concentration of Pt in iridium reaches 21.79 wt.%, which exceeds the limit of solubility of Pt in Ir at the maximum temperature of equilibration (~850°C). The composition of PGE-sulfarsenides corresponds to irarsite, with accessory platarsite and osarsite components: (Ir,Pt,Os)AsS. As predominates over S where substantial Pt exists, and excess S is present in irarsite with a high Os content. Solid solution along the erlichmanite (OsS 2)-sperrylite (PtAs 2) series is restricted. A wide range of compositions and levels of minor elements (Ir, Pd, Rh) in Pt-Fe alloys from different Alaska-type occurrences reflects geochemical features of the ore-forming system at the source. Fractionations of the PGE in the ore-forming system, from Ir-rich nuggets to Rh-rich and to Pdrich alloys, reflect the decrease in temperature of the ore-forming system. Compositional variation and temperature range of alloy genesis decrease in the order from Goodnews Bay and Inagli to Galmoenan, Fifield, Nishnii Tagil, then to Tulameen and Yubdo, and down to Pustaya and Itchayvayam occurrences.

Mineralization in the platinum-group elements occurs in lodes in the dunite-clinopyroxenite-gabbro Gal'moenan complex, in the Koryak-Kamchatka Platinum Belt of Russia, and in associated placers, namely those along the Levtyrinyvayam River and Ledyanoy and Penistiy creeks at different distances from the source. The grains of Pt-Fe alloy in lode deposits are isoferroplatinum and have Pt 3 Fe compositions, whereas those in the Levtyrinyvayam River placer range in composition from native to ferroan platinum and having iron contents generally higher than in the lodes (30-35 at.% Fe). Platinum grains from the Ledyanoy Creek placer are larger and more commonly intergrown with chromite than those from the Levtyrinyvayam River. Minor elements, which are indicators of conditions of formation of the Pt-Fe alloy, exhibit different concentrations in lodes and in the nearby placers. Platinum-iron alloy from the Levtyrinyvayam placer, the farthest from the source, represents the eroded upper apical part of the intrusion, and contains mainly Pd. The Penistiy placer receives platinum from dunite and pyroxenite of a marginal facies of the complex, and thus platinum-iron alloy bearing Rh-Ir and Pd-Rh. Placer isoferroplatinum deposited in the Ledyanoy Creek, which drains dunite and chromite-bearing rocks in the south of the intrusion, is rich in Ir (up to 6.98 wt.%), as is the Pt-Fe alloy in the Gal'moenan complex (4.34 wt.% Ir). Most grains contain also a relatively high Rh content. Isoferroplatinum + iridium and isoferroplatinum + osmium are two main primary magmatic parageneses revealed in both placers and lodes, though the first is more commonly found in lodes and in the Ledyanoy Creek placer, and the latter in the Levtyrinyvayam River placer. Lodes mostly contain laurite, RuS 2 , and the Levtyrinyvayam placer bears all varieties of (Ru,Os)S 2 , including Ru-free Rh-rich erlichmanite (Os,Rh)S 2. The irarsite-hollingworthite series predominates in lodes, and the irarsite-platarsite and osarsiteplatarsite series predominate in the Levtyrinyvayam placer. Sperrylite in lodes may contain up to 6.94 wt.% Sb, and thus differs from that in placers. The phase (Pt 0.96 Fe 0.02) ⌺0.98 (As 1.17 Sb 0.75 S 0.09) ⌺2 , a member of the sperrylite-geversite solid solution, has been found in a lode. Complete solid-solution between RuS 2 and RuAsS on one hand, and PtAsS and PtAs 2 on the other, is demonstrated. In the Gal'moenan complex, concentrations of Ir decrease, and those of Pd and Os increase, toward the upper or apical parts of the complex.

Microthermometry study of fluid inclusions in quartz veins of the Maletoyvayam deposit (Koryak Highland, Russia) was carried out. This epithermal gold deposit contains unique Au compounds including maletoyvayamite, which has not been reported anywhere else. Two paragenetic mineral associations (pyrite-quartz and maletoyvayamite-quartz) with quartz of different generations corresponding to different pulses were also described. Only early generations of quartz (Q1) include ore minerals: pyrite for the first mineral assemblage, and in Au-bearing minerals, sulfosalts, bismuthinite, and others—for the second assemblage. A study on fluid inclusions in quartz showed a salinity (mainly NaCl + KCl) range from 0.2 to 4.3 wt.% NaCl eq., increasing from the first mineral association to the second due to boiling fluids. The obtained temperature variations for quartz crystallization were 295–135 °C, the fluid pressure ranged from 79 to 4 bar. On the other hand, the range of conditions obtained for the gold productive ore association is more narrow: salinity of the fluid inclusions is 4.3 wt.% NaCl eq., the temperatures vary from 255 °C to 245 °C, and the pressure from 39 to 32 bar. These physicochemical characteristics of the Maletoyvayam ore deposit greatly coincide with other HS-type epithermal deposits; however, within the Central Kamchatka Volcanic Belt it is so far the only deposit of this type reported.

The Gaching high-sulfidation (HS) epithermal Au–Ag deposits, part of the Maletoyvayam ore field, which is located in the volcanic belts of the Kamchatka Peninsula (Russia). The main ore components are native gold, tellurides, selenides, and sulphoselenotellurides of Au and oxidation products of Au-tellurides. This study examines the different types of native gold in this ore deposit and the mechanisms and sequential transformation of calaverite (AuTe2) into mustard gold. The primary high fineness gold (964‰–978‰) intergrown with maletoyvayamite Au3Te6Se4 and other unnamed phases (AuSe, Au(Te,Se)) differ from the secondary (mustard) gold in terms of fineness (1000‰) and texture. Primary gold is homogeneous, whereas mustard is spongy. Two types of mustard gold were identified: a) Mixtures of Fe-Sb(Te,Se,S) oxides and fine gold particles, which formed during the hypogenic transformation stage of calaverite due to the impact of hydrothermal fluids, and b) spotted and colloform gold consisting of aggregates of gold particles in a goethite/hydrogoethite matrix. This formed during the hypergenic transformation stage. Selenides and sulphoselenotellurides of gold did not undergo oxidation. Pseudomorphic replacement of calaverite by Au-Sb(Te,Se,S,As) oxides was also observed.