Abstract—The base-metal (70–75 wt %) and tin–sulfide (10–15 wt %) deposits are the main indium suppliers in the world. However, the causes and conditions of In accumulation in the ores of these deposits are still unclear. To shed light on this problem, we simulated the physicochemical conditions of formation of base metal and tin–sulfide ores with elevated indium content. For this purpose, the average composition of ore–bearing hydrothermal solutions and parameters of ore precipitation at these deposits were determined using available literature data. Based on these data, obtained standard thermodynamic characteristics $$\Delta G_{{\text{f}}}^{0},$$$$\Delta H_{f}^{0},$$$$S_{f}^{0},$$$$V_{f}^{0},$$$$C_{p}^{0}$$ of chloride indium species ($${\text{InCl}}_{2}^{ + },$$ InCl3, InClOH+), coefficients required for calculations at elevated temperature and pressure, the formation of elevated indium contents in these ores was numerically simulated using “Gem–Selektor-3” and “Chiller” softwares. The results of thermodynamic modeling of the formation of quartz–cassiterite and tin–sulfide ores show that the higher In contents in tin–sulfide ores are related to their formation from acid (pH 4.3), high–chloride (6.6 m) solutions, which contain In (0.002 m) in form of (InCl3aq). The quartz–cassiterite ores were formed from near–neutral (pH 5.3), low–chloride (1.02 m) solution, in which In occurred as hydroxocomplexes InO2H and $${\text{InO}}_{2}^{ - }$$ in concentrations no more than 0.00004 m, which, respectively, determined its low contents in these ores. Computer modeling of the formation of indium–bearing sulfide-base metal and barite-base metal deposits shows that they were formed form high–temperature chloride (1.3–4.3 m) hydrothermal solutions of near–neutral composition (pH 5.8–6). The main In speciations are hydroxocomplexes InO2H and $${\text{InO}}_{2}^{ - }$$, which provide In concentrations of 5–9 × 10–5 m). However, due to the low indium concentrations in hydrothermal solutions, the forming sulfide minerals (sphalerite, pyrite, and chalcopyrite) differ in the lower indium contents compared to the minerals of tin–sulfide ores.

Thermodynamic modeling was carried out for the formation of Mo–W ores at the Kalguty deposit (Gornyi Altai). The modeling was based on the physicochemical conditions of Mo–W ore formation estimated from fluid inclusion data. Quartz–wolframite veins of the deposit were formed under the influence of homogeneous reduced carbonate–chloride fluids, which showed elevated W and Sb concentrations. Pyrite–chalcopyrite–molybdenite mineralization was formed under the influence of heterogeneous oxidized sulfate–carbonate–chloride fluids enriched in Cu, Mo, W, Bi, and S. The economic combined greisen–vein Mo–W (Be) mineralization of the Kalguty deposit was formed by the superposition of molybdenite–chalcopyrite mineralization on the mineral assemblages of earlier quartz–wolframite veins. Ore forming processes were modeled for the scenarios of isobaric cooling and rock–solution interaction in the presence of oxidized and reduced model solutions corresponding to the natural ore-forming fluids of the Kalguty deposit. The results of thermodynamic modeling allowed us to conclude that rock interaction with oxidizing acid solution enriched in Cu, Mo, Bi, W, and S is the most plausible model for the formation of the greisen Mo–W ores. The interaction was accompanied by the inversion of the Eh–pH parameters of oxidizing ore-forming fluid and changes in its metal content, salt composition, and gas components. The chalcopyrite–molybdenite mineralization was formed during cooling of hot (>400°C) metalliferous oxidizing acid fluids before the inversion of their Eh–pH parameters. Wolframite ores could be deposited from the same portion of ore-forming fluid after the Eh–pH inversion and cooling. The combined Mo–W mineralization of the Kalguty deposit could result from at least two hydrothermal rhythms characterized by similar physicochemical parameters of ascending ore-forming fluids. The level of ore formation of each successive hydrothermal rhythm moved upward. This resulted in the telescoping of the high-temperature chalcopyrite–molybdenite mineralization by the earlier wolframite mineralization. The obtained data indicate the significance of probable vertical movement of the ore formation zone during the multistage mineralization process for the development of certain sequences of formation of mineral assemblages observed in ore deposits.

Проведено обобщение результатов изучения состава металлоносных флюидов собственно кобальтовых месторождений гидротермального генезиса, формировавшихся в различных геодинамических обстановках в связи со становлением щелочных и щелочно-базитовых интрузивов и даек. Для определения физико-химических параметров рудоотложения по флюидным включениям в минералах использовались как традиционные, так и новые инструментальные методы термобарогеохимии: термо- и криометрия, КР-спектроскопия; концентрации рудных и петрогенных элементов в индивидуальных флюидных включениях оценивались методом LA-ICP-MS. Полученные результаты послужили основой исследования, главной задачей которого являлось термодинамическое моделирование условий совместного переноса и отложения Co, Ni, Cu, Fe, Mg, Ca, Ag, Au, Bi, U, Pt и Pdc расчетом ряда равновесных состояний гидротермальной системы, по составу близкой к природным рудообразующим флюидам. Выявлены физико-химические факторы отложения самородных – золота, серебра, платины и палладия в рудах таких месторождений. Полученные данные могут послужить базой для разработки корректных генетических моделей рудообразующих систем собственно кобальтовых месторождений и содействовать решению проблем их поиска.

The paper reports generalized investigation data on the composition of metal-bearing fluids at hydrothermal cobalt deposits, which formed in different geodynamic settings during the development of alkali and alkali-basic intrusions and dikes. To determine the physicochemical parameters of ore deposition from fluid inclusions in minerals, both traditional and new instrumental thermobarogeochemical methods were used: thermometry, cryometry, and Raman spectroscopy; the concentrations of ore- and rock-forming elements in individual fluid inclusions were evaluated by LA-ICP-MS. The results served as the basis for a study focused on thermodynamic modeling of joint transport and deposition of Co, Ni, Cu, Fe, Mg, Ca, Ag, Au, Bi, U, Pt, and Pd; the number of equilibrium states of the hydrothermal system similar in composition to the natural ore-forming fluids was also calculated. The physicochemical factors of native Au, Ag, Pt, and Pd in the ores at such deposits were revealed. These data can be used to develop correct genetic models for the ore-forming systems of the cobalt deposits proper and to solve the problem of searching for them.

Purpose is to carry out computer thermodynamic modeling of gold and mercury behaviour in the context of their common occurrence and formation of mercuric gold in hydrothermal solutions Cl- - HCO3- - Na+ and Cl- - Na+ - Ca2+ with the use of "Chiller" programme. Methods. Physical and chemical parameters of ore-forming solutions have been used as the initial data for the modeling. They were obtained relying upon the analysis of fluid ore inclusions in the neighbourhood of surface Au-Hg deposits; fluid inclusion studies (i.e. thermometry, cryometry, RS-spectroscopy, ICP-MS-LA) were applied. High metal-bearing hydroterms according to Au (I) within 200 - 100 degrees C temperature interval is determined by means of hyperalkalinity of hydrothermal solutions as well as stability of dihydrosulphide (i.e. Au(HS)(2)(-)) complex under the conditions providing transport of gold to low-temperature (150 - 100 degrees C) ore deposition typical for Au-Hg deposits. Findings. Relying upon the previously obtained data of fluid inclusion studies and thermodynamic modeling, basic geological and geochemical conditions of occurrence have been identified; physical and chemical factors defining gold deposits with different mercury content have been determined. Originality. Computer thermodynamic modeling of common Au and Hg behaviour in hydrothermal process made it possible to demonstrate specifics of physical and chemical parameters of formation of complex gold-mercury ores. For the first time, uniqueness of free gold composition for various types of Au-Hg deposits has been determined on the basis of proper data and data by scientific sources. The results, obtained in the process of the studies, made it possible to expand substantially available concepts of their genesis to be important for the development of genetic models of ore-forming systems of Au-Hg deposits. Practical implications. Composition of gold and its mercury content may be used practically in the process of prospecting activities as a criterion to determine the occurrence of one of prospective industrial types of gold ores (Carlin-type) - finely disseminated gold and mercury ore grade mineralization - as well as formation depth and estimation of erosion level of ore bodies.

New data about the ages of the mercury-silver (Ag-Hg) mineralization and Mesozoic magmatism at the Imiter deposit and around (Anti-Atlas, Morocco) have been obtained. According to the Ar-40/Ar-39 dating, age of 40 A. the Ag-Hg mineralization is about 254.7 +/- 3.2 Ma. Ar-40/Ar-39 dating of two biotite and potassium feldspar samples from microsyenite dikes indicates 204.5 +/- 2.5 and 199.5 +/- 2.4 Ma (both of Triassic age). The age of Ag-Hg mineralization and magmatic rocks coincides with stage of development of Early Mesozoic rifting and magmatism in the Anti-Atlas. Fluid inclusion study in minerals of silver ores from the Imiter deposit shows that quartz-silver veins were formed at the temperature from 220 to 114 degrees C from hydrothermal fluid, which consists of concentrated (26 wt%) chloride solution and N-2-CH4 gas phase. Dolomite-polysulfide veins deposited at temperatures <250 degrees C from the solution with concentration from 15 to 5 wt% containing CO2 gas phase.

The physicochemical modeling of mineral formation processes at the Badran subthrust gold-quartz deposit was performed, based on a study of fluid inclusions in quartz by Raman spectroscopy, gas chromatography, thermometry, and freezing. The results show that at stage I, highly productive gold-bearing quartz veins (gray quartz) of the deposit formed from heterogeneous fluid at <320 ºC and 2.0–0.1 kbar with the active participation of CO2, N2, and CH4; the salinity of this solution reached 10 wt.% NaCl-equiv. At stage II (Au-productive), milky-white quartz was produced from the homogeneous medium-chloride-sulfide solution which remained after the heterogenization of the initial fluid, at 300–100 ºC and 0.1 kbar. At stage III (with low Au production), clear quartz formed from homogeneous chloride solutions with salinity of <4.5 wt.% NaCl-equiv. at <200 ºC and <0.1 kbar. The physicochemical conditions of Au concentration within the complex geochemical system Au–Fe–Cu–Pb–Zn–As–Sb–Hg–Ag–H2O–Cl–H2S–CO2 at the Badran deposit was modeled using the Chiller software. The following models were used: (1) solution–rock interaction and (2) condensation of gas phase (for stage I); (3) simple cooling of medium-chloride-sulfide solution (for stage II); (4) simple cooling and (5) mixing of low-chloride-sulfide solution with acid meteoric waters (for stage III). The models show the sequence of vein formation in the ore-producing system and the host-rock metasomatism in the deep horizons of the deposit.

Using the Chiller computer program, we performed modeling of the mechanisms of the joint transport and deposition of Au and Sb from various ore-forming solutions during the formation of Au-Sb deposits. Three models are considered by the example of the Uderei Au-Sb deposit in the Yenisei Ridge: (1) simple cooling (cooling only), (2) iso-enthalpy boiling (P = f(T)), and (3) solution–rock interaction (rock titration model). The behavior of Sb(III) and Au(I) in the system Au–Sb–Fe–Cu–Pb–Zn–As–H2O–Cl–H2S–CO2 under hydrothermal conditions was studied. It is shown that both weakly alkaline (near-neutral) and reduced acidic Feaq2+-enriched low-chloride high-CO2 and high-chloride hydrothermal solutions play a crucial role in the formation of gold parageneses of Au-Sb ores.

Based on data on the composition of ore-bearing hydrothermal solutions and parameters of ore-forming processes at various antimony and antimony-bearing deposits, which were obtained in studies of fluid inclusions in ore minerals, we investigated the behavior of Sb(III) in the system Sb-Cl-H2S-H2O describing the formation of these deposits.We also performed thermodynamic modeling of native-antimony and stibnite dissolution in sulfide (m(HS)-=0.0001 - 0.1) and chloride (m(CI)-=0.1 - 5) solutions and the joint dissolution of Sb-0(s) and Sb2S3(s) in sulfide-chloride solution (M-HS-=0.01; M-CI-=1) depending on Eh, pH, and temperature. All thermodynamic calculations were carried out using the Chiller computer program. Under the above conditions, stibnite precipitates in acid, weakly acid to neutral, and medium redox solutions, whereas native antimony precipitates before stibnite under more reducing conditions in neutral to alkaline solutions.The metal-bearing capacity of hydrothermal solutions (200 - 250 degrees C) of different compositions and origins has been predicted. We have established that the highest capacity is specific for acid (pH=2 - 3) high-chloride solutions poor in sulfide sulfur and alkaline (pH=7 - 8) low-chloride low-sulfide solutions. (c) 2007, IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

We report results of computer modeling of physicochemical ore formation processes at mercury deposits accumulated during the development of secondary-hydrothermal and mixed-fluid ore-forming systems. Exogenous chloride brines, oil waters of artesian basins, and petroleum pools are shown to serve as secondary mercury reservoirs and geochemical barriers.Modeling of possible mechanisms of mercury transfer and deposition in the form of cinnabar (alpha-HgS) was performed for ore-forming solutions of different compositions. Four main thermodynamic models have been constructed using the Chiller program: (1) simple cooling (cooling only), for recent thermal springs, (2) mixing of high-chloride hydrothermal solutions with cold hydrosulfuric waters (mixing model), for telethermal deposits, (3) isoenthalpic boiling (P = f(T)), and (4) solution-rock interaction (rock titration model).

Ore forming conditions for Au-Sb and Ag-Sb deposits have been estimated using thermodynamic modeling. PTX-parameters of ore-forming fluids obtained by fluid inclusion study in the minerals were used as original data for modeling. Analysis of composition of fluid inclusion solutions in the minerals of Au-Sb deposits together with mineralogical and geochemical data show that Au-Sb deposits were formed by two types of solutions: neutral–weak alkaline (C Cl < 5 wt % NaCl-eq.), and acid high concentrated chloride solution (up to 30 wt% NaCl-eq.), containing FeCl 2 and CaCl 2 besides NaCl. In low concentrated chloride solution Sb is transported as sulfide and hydroxide complexes, and Au and Ag as bihydrosulfide species. In acid high chloride solution of late superimposed stage, which contains Cu, Ag, Pb, and Zn, predominating Au and Ag species are chloride complexes, and for Sb chloride and hydroxy-complexes. The main factors determining geochemical specialization of Ag-Sb ore are high chloride concentration and pH = 3.5–4, determining low Au-bearing capacity of the solution. Unsaturated in Ag low concentrated chloride solutions took part in Au-Sb deposit forming that determines their specific composition.