Using modern thermobarogeochemical methods (thermo-and cryometry, Raman spectroscopy, and LA-ICP-MS), we studied fluid inclusions in quartz from ores formed at the quartz-fluorite, pyrite-chalcopyrite, pyrite-molybdenite, and polysulfide stages of evolution of the Samolazovskoe gold deposit. We have established the fluid regime of the ore formation processes, the gas and liquid composition, main solid phases (metal sulfates, carbonates, and chlorides), homogenization temperatures of the inclusions, and the eutectic temperatures of their solutions. The obtained data helped to estimate the fluid temperatures during the formation of ores at each stage and to determine the contents of major salt components. Based on the substance solubility values given in the reference-book by V.B. Kogan, we have first constructed a phase diagram of the system Na2SO4-NaHCO3-H2O (Na2SO4 < 35 wt.%) at temperatures below 40 degrees C. The metal contents and geochemical specifics of solutions at each stage of the ore formation were determined by LA-ICP-MS. At the quartz-fluorite stage, the solutions were enriched in B, V, Co, Ni, Zn, As, Te, Cs, Ba, and Mg; at the pyrite-molybdenite stage, they had high concentrations of Ti, Ni, Nb, and Mo; and at the polysulfide stage, the solutions were rich in Ca, As, Pb, Sb, Te, Ag, Rb, Ba, and Sr. Native sulfur found along with sulfate and sulfide sulfur in the inclusions impelled us to study the sulfur isotope composition. The research has shown a light sulfur isotope composition (delta S-34 = -2.5 to -13.4 parts per thousand). We believe that sulfide sulfur in the Samolazovskoe deposit formed from a fluid during high-temperature (>500-700 degrees C) sulfate reduction. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Contents of major impurities (Ag, Cu, and Hg) have been studied in gold from ore deposits of various types: (1) associated with skarns and black shales (Altai-Sayan folded area (ASFA) and North Vietnam), (2) pluton-related porphyry Cu-Mo (ASFA), and (3) volcanic pyritic (Rudny Altai, the Urals, and North Vietnam). Analysis of gold ore mineralization in deposits of these types reveals diverse gold compositions along with diverse compositions of productive mineral assemblages. Silver is the most abundant impurity in gold from all fields studied, but its contents vary broadly even within a field type. The content of silver in gold depends not only on its abundance in hydrothermal solutions but also on other independent solution parameters: sulfur fugacity, temperature, salt composition, and pH. The regular decrease in native gold fineness from early to late generations in sulfide ore deposits is related to temperature decrease and large-scale sulfide formation. These processes reduce sulfur fugacity in the solutions and favor silver deposition in native gold rather than in sulfides. Gold of later generations is enriched in mercury in many deposits studied, whereas copper gravitates to earlier, high-temperature ones. In addition to deposition temperature, the contents of copper in gold are determined by its content in hydrothermal solutions, as evidenced by the association of copper-rich gold with basic-ultrabasic, skarn, and porphyry copper deposits. The processes causing the deposition of gold of various chemical compositions are complex. They correlate, to an extent, with gold mineralization temperature, whereas the spectrum of impurities often depends on the belonging of a gold deposit to a certain igneous complex. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

We present the results of a study of the geologic structure and age sequence of formation of the Late Neoproterozoic-Early Paleozoic plagiogranitoid and gabbroid associations in the Bumbat-Hairhan intrusive area of the Lake Zone in Western Mongolia. The petrogeochemical characteristics of the plagiogranitoids provide information about the conditions of formation of their parental melts at the island-arc and accretion-collision stages of the regional evolution. They also help to establish the main magma-generating sources as well as the major mechanisms of large-scale formation of granitoid melts and their relationship with ore generation processes. According to the trace-element and REE patterns and indicative ratios of these elements, the plagiogranitoids are subdivided into high-and low-alumina ones. Among the island-arc plagiogranitoids (551-524 Ma) of the Bumbat-Hairhan area, high-alumina varieties are the most widespread. They resulted from the partial melting of metabasites in equilibrium with garnet-containing restite at >= 15 kbar during their subsidence into the subduction zone. In geochemical features these plagiogranitoids are similar to high-Si adakites of different world regions. Island-arc low-alumina plagiogranitoids are scarcer. Their geochemical characteristics indicate that the parental melts were generated through the partial melting of metabasites in the lower part and/or in the basement of the island-arc system in equilibrium with amphibole-containing restite at <= 8 kbar. Plagiogranitoid associations of the accretion-collision stage (511-468 Ma) are the most widespread in the Bumbat-Hairhan area. They are subdivided into high-and low-alumina ones. According to the contents of trace elements and their indicative ratios, the low-alumina plagiogranitoids resulted from the partial melting of metabasites in equilibrium with plagioclase-containing restite at <= 8 kbar in the upper part of the collisional structure, and the high-alumina ones were generated through the melting of metabasites in the basement of thick crust in equilibrium with garnet-containing restite at >= 15 kbar. Geochronological studies in the Bumbat-Hairhan area revealed two stages of ore-generating processes spatially and temporally related to the formation of low-alumina plagiogranitoids. The early stage (518 +/- 5 Ma), development of vein Cu (Au) mineralization, coincided in time with the formation of island-arc low-alumina plagiogranitoids of the Darbi massif (similar to 524 Ma). The late stage (456 +/- 4 Ma), formation of porphyry Cu-Mo (Au) mineralization, was synchronous with the formation of the low-alumina plagiogranites at the accretion-collision stage (similar to 468 Ma). (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The Pb-Zn deposits in the Lo Gam structure, northeastern Vietnam, account for >80% of all the Pb and Zn resources of Vietnam. All the deposits make up four isolated ore districts (Thai Nguyen, Cho Don, Cho Dien, Na Son), which can be combined in one metallogenic zone extending for >100 km from southeast to northwest. The Pb-Zn deposits in all the ore districts show some similarity to stratiform (Mississippi-type) deposits: confinement to Devonian carbonate sediments; localization at the intersection of faults of different orientations; vein and stockwork (pocket-vein-disseminated) morphology of the mineralized zones; evidence for hydrothermal-metasomatic formation (carbonate-rock marbleization, quartz-carbonate veins, etc.); and low and moderate mineralization temperatures (<250 degrees C). On the other hand, some differences from stratiform deposits are observed: widespread occurrence of Permo-Triassic igneous rocks in the above ore districts; absent tabular orebodies, which are typical of stratiform deposits; large set of trace elements (In, Bi, Sb, Au, Ag, Cu, Cd) not typical of stratiform deposits; and an endogenic primary source, as evidenced by the isotope composition of sulfur (delta S-34 = 2.68%), which is close to meteoritic, and the set of trace elements, which are mainly of deep genesis. All this indicates that the above Pb-Zn deposits within the carbonate units are low-and moderate-temperature hydrothermal-metasomatic products associated with active magmatism which took place in this region in the Permo-Triassic.The differences in the mineral composition of the deposits, as well as in the trace-element set and contents at different deposits, clearly indicate an intricate ore formation process and the relation of the deposits with magmatism of different compositions. The simple mineral composition and the limited set of trace elements (Cd, Ag, Sb, As) at the Lang Hich deposit are closer to the characteristics of stratiform deposits. Also, manifestations of magmatism are almost absent here. On the contrary, unusually high (ppm) In (75.8), Sn (307.5), Cu (1080), Ag (157.7), Bi (99), and As (13,650) contents were observed at the deposits of the Cho Don and Cho Dien districts, with widespread granitoid magmatism in the Phia Bioc complex. Rare-earth mineralization (orthite) and high Mo, Re, and Rb contents at the deposits of the Na Son district are probably due to the widespread occurrence of stratified alkaline volcanics and their subvolcanic analogs, which belong to the Pla Ma complex (xi gamma PZ(2) pm). (C) 2012, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B. V. All rights reserved.

The Sin Quyen Cu–Fe–Au–REE deposit is localized in the Proterozoic deposits of the Phan Xi Pang zone, northern Vietnam. The mineralization is formed by lenticular and sheet-like bodies occurring concordantly with the host rocks. Seventeen orebodies have been recognized in the deposit, which form an ore horizon up to 140 m in total thickness, about 2 km in strike, and up to 350 m in dip. The ores are of simple mineral composition: Au-rich copper and iron sulfides (chalcopyrite, pyrite, pyrrhotite) and iron oxides (magnetite, hematite). Gold and silver are distributed unevenly in the ores: Their contents vary from hundredths and tenths of ppm to 1.8 ppm. Copper sulfide ores are the main concentrator of gold and silver. All ores are characterized by high REE contents, tens and hundreds of times exceeding the element clarkes. The highest contents have been revealed for Ce and La. Orthite is the main carrier of REE. No correlation between REE and ore elements of sulfide-oxide ores has been revealed, which points to the independent formation of the mineralization. Orebodies together with the host rocks underwent metamorphism at 500–600 to 630–685 °C and 3–7 kbar. The spatial association of the mineralization with amphibolites (metamorphosed basites) and the mineral composition of ores suggest that the Sin Quyen deposit is of Cyprian volcanogenic type.

The investigation of melt inclusions in the minerals of volcanic rocks from the massive sulfide deposits of Siberia and the Urals revealed some specific features in the development of their magmatic ore systems. It was shown that the petrochemical and rare earth element compositions of melt inclusions reflect the geodynamic conditions of their formation: island arc conditions for the massive sulfide deposits of Rudny Altai, eastern Tuva, and the Salair Range and a back arc basin environment for the Yaman-Kasy deposit. The silicic melts of inclusions from the volcanic rocks of massive sulfide deposits show some specific features with respect to the contents of volatile components. In all of the ore deposits studied, fluorine content was always low (0.03–0.08 wt %), whereas chlorine content (0.13–0.28 wt %) was higher than the average value for silicic melts (0.17 wt %). There is a strong differentiation of water content in melt inclusions, both between deposits and between various volcanics from a single deposit. Ore-bearing melts show the highest water contents of 3.34–4.07 wt %. High Cu contents in the silicic melts of the Yubileinoe and Kyzyl-Tashtyg deposits (up to 7118 and 3228 ppm, respectively) may indicate the affinity of some ore components to particular silicic magmas. This is supported by the elevated contents of Cu in the porphyry Cu deposits of Romania (Valea Morii), Mongolia (Bayan Ula), and Bolivia. On the other hand, the silicic melts of inclusions from the molybdenum-uranium deposit of the Strel’tsovka ore field show high contents of another group of ore components (U and F).

Gold mineralization of the Tardan deposit is of different spatial occurrences and is related to different hydrothermal-metasomatic formations, the main ones being skarn-magnetite bodies, metasomatites of mineralized crush zones, and metasomatites of argillizitic-rock association. The formation of gold mineralization was a multistage process related to the repeated magmatism of the Tannu-Ola complex. It took place in a wide temperature range (400–150 °C), which determined the diversity of produced mineral assemblages. The gold mineralization associated with magnetite bodies shows a spatial correlation with magnesian and calcareous skarns and is localized in plagiogranites and gabbro-diorites of the Tannu-Ola complex intruded in the Late Ordovician. Gold mineralization that occurs in crush zones and along the fault sutures in moderate- and low-temperature hydrothermal-metasomatic rocks (propylites, beresites, serpentinites, and argillizites) formed somewhat later than skarns as a result of the intrusion of granite dike bodies. Comparative analysis of different types of gold mineralization showed both a change of mineral assemblages of the gold mineralization during the ore formation and some geochemical difference between gold and gold-bearing ores. In passing from early to late occurrences of native gold, its fineness decreases, the contents of admixtures correspondingly increase, and the gold composition changes. Gold of high-temperature rocks is rich in Cu (up to 17%), and gold of low-temperatures rocks has higher contents of Ag and Hg.

As inferred from melt inclusions in minerals of volcanogenic rocks, the ore-magmatic pyrite systems of Rudny Altai and Tuva had quite a specific history. Volcanism manifestations in these regions have both similarities and differences. The chemical composition of melt inclusions in quartz of acid volcanic rocks from the pyrite deposits of Rudny Altai is close to the chemical composition of the rocks, and in REE content they correspond to island-arc magmas. At early stages of development of a magmatic system, acid melts formed, which had high temperature (1230-1250 degrees C), were dry (0.19-0.77 wt.% H2O) and rich in copper (844-7118 ppm). The copper enrichment was evidently due to the mantle gas flows containing chloride complexes of Cu. In the process of further development of the system, the dry melts gave way to water-saturated melts (1.54-4.30 wt.% H2O) and the Cu content in the silicate melt decreased (124-1393 ppm), which was possibly consequent on the fact that the highly water fluid phase was isolated and some copper from the melt was extracted into it. At the final stages of development of the magmatic system, magmas depleted in fluid and ore components were formed. Studies of melt inclusions in minerals from volcanogenic rocks of pyrite deposits of eastern Tuva have shown that in REE contents the melts correspond to island-arc conditions of formation. Acid rocks of the ore-bearing member and acid melts of inclusions in quartz of andesite are residual products of crystallization differentiation of the initial basalt magma, whereas elevated copper contents in melts (325-1028 ppm) are possibly related to its accumulation in residual melts at the expense of elevated clarke of this element in the initial basic rocks. Low concentrations of water (0.41-0.87 wt.%) in this melt seemed to promote higher contents of Cu in the silicate melt at this stage of evolution of the magmatic system.

The high gold potential of Cu-ore (Cu-skarn, porphyry Cu-Mo, and pyrite-polymetallic) deposits widespread in the Altai-Sayan folded area is shown. The ore formation processes at these deposits included multistage mineralization with the gradually decreasing temperature of ore-forming solutions. At the early high-temperature stages, mainly the profile ores (often, of zonal structure) of the deposits were produced. Their mineral composition is closely related to the composition of the corresponding ore-magmatic system and is regularly repeated in ore objects of different sizes and ages. At the final stages, low-temperature mineral assemblages formed, which often have a similar set of ore and vein minerals. A distinctive feature of these assemblages is the presence of Ag, Pb, and Au tellurides, Bi minerals, native bismuth, and Hg-containing minerals. Gold in the minerals is of varying fineness; the main trace elements in it are Ag and Hg. The low-temperature mineral assemblages are close to ores of epithermal deposits (including Carlin-type ones) developed in the same areas. These ores might be the products of the final-stage evolution of the ore-magmatic systems.

Volcanogenic pyrite-polymetallic deposits widespread in southern Siberia (Rudny Altai, eastern Tuva, northern Baikal region, and western Transbaikalia) are divided into two groups according to their formation mechanism: volcanogenic hydrothermal (VHMS-type) (Kyzyl-Tashtyg deposit in Tuva; Korbalikhinskoe, Zolotushinskoe, Yubileinoe, and other deposits in Rudny Altai) and volcanosedimentary (SEDEX-type) (Kholodninskoe deposit in the northern Baikal region and Ozernoe deposit in western Transbaikalia). Comparison of major ores and ore minerals during the volcanosedimentary and volcanogenic hydrothermal formation of pyrite-polymetallic deposits showed their significant difference in the spectrum and contents of trace elements. Ores of the VHMS deposits have high concentrations of trace elements as they formed under drastic drop in temperature (as a result of boiling-up of solutions and their mixing with sea water), which caused mass deposition of ore matter and coprecipitation of accompanying elements, including their sorption by crystallizing sulfide minerals. The poorer spectrum and lower concentrations of trace elements in ores of the SEDEX deposits are, on the contrary, related to the rhythmic formation of chemogenic ores from sea-floor brine pools. The reduced amount of endogenic sulfur and gradual reduction of sea water sulfur and its involvement in sulfide formation prevented rapid mass deposition of sulfides and, accordingly, coprecipitation of accompanying elements.