Fluid Inclusions In Ore Minerals Research Articles

Ore-Forming Fluids of the Aleksandrovskoe and Davenda Deposits (Eastern Transbaikalia)

A study of the composition of fluid inclusions in ore minerals of the Davenda Mo–porphyry deposit and the Aleksandrovskoe sulfide–quartz–gold ore deposit, as well as of fluid inclusions in minerals of igneous rocks, showed that ore-forming fluids inherit the salt and gas composition of magmatic fluids generated during crystallization of ore-bearing rocks of the Amudzhikan–Sretensky Igneous Complex, which formed simultaneously with the Au and Mo mineralization. The gold-bearing sulfide–quartz veins of the Aleksandrovskoe deposit formed with the participation of two types of hydrothermal fluids, differing in the composition of salts and the gas phase: homogeneous Ca–Na chloride fluids with CO2 and heterophasic Na–K–Fe-chloride fluids, which indicates two sources of ore-forming fluids during the formation of Au-mineralization. Na–K–Fe-chloride fluids in terms of salt and gas composition were similar to the ore-forming fluids of the Mo-mineralization of the Davenda deposit. Ore-forming Ca–Na-chloride with CO2 The fluids of the Aleksandrovskoe field are comparable in salt and gas composition with the magmatogenic fluids of quartz diorite porphyries and diorite porphyrites. Ore forming Na–K–Fe carbonate-chloride fluids of the Davenda and Aleksandrovskoe deposits show great similarity in composition to magmatic fluids of granite porphyry and emphasize the genetic identity of Mo mineralization in both deposits. The data obtained confirm the widespread opinion that a genetic relationship exists between gold mineralization and dikes of intermediate and mafic composition, and molybdenum–porphyry mineralization with granite–porphyry of the Amudzhikan–Sretensky Igneous Complex. The real agents of this genetic link are metalliferous magmatogenic fluids, the salt and gas composition of which inherit ore-forming fluids. The formation depth of productive ore mineral assemblages in veins of the Aleksandrovskoe and Davenda deposits is estimated at 7.9–7 and 8–6.3 km, respectively, which is not typical of porphyry deposits, the formation of which is characterized by shallower depths.

Physicochemical Parameters of the Origin of Hydrothermal Mineral Deposits: Evidence from Fluid Inclusions. V. Antimony, Arsenic, and Mercury Deposits

Physicochemical parameters under which hydrothermal Sb, As, and Hg deposits are formed are estimated using data from a database (which was compiled and continuously updated by the authors and includes data from more than 21 500 publications on mineral-hosted fluid and melt inclusions). The discussed parameters of the fluids are their temperature, pressure, density, salinity, and gas composition. The paper reports data on the temperature, pressure, and salinity of fluid inclusions in ore minerals (antimonite, orpiment, realgar, and cinnabar) and the calculated average composition of the dominant fluid components of natural fluids (CO2, CH4, N2, and H2S) at Sb, As, and Hg and, for comparison, at Au, Sn, W, Cu, Pb, and Zn deposits. The compositions of individual inclusions in minerals and chill glasses of rocks are utilized to calculate mean As and Sb concentrations in magmatic silicate melts of mafic, intermediate, and acid composition. Data are reported on the calculated Sb, As, and Hg concentrations in natural mineral-forming fluids.

Infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the Woxi orogenic Au–Sb–W deposit, western Hunan, South China

The Woxi Au–Sb–W deposit, hosted by the Neoproterozoic low-grade metamorphic clastic rocks, is located in a brittle-ductile shear zone within the Xuefengshan Range, South China. Orebodies are predominantly banded quartz veins, which are strictly controlled by bedding faults and display significant vertical extents (up to 2km) without obvious vertical metal zoning. Fluid inclusions hosted in quartz, scheelite, and stibnite from quartz–scheelite and quartz–sulfide–gold veins have been studied using conventional and infrared microscopy, respectively. Four types of fluid inclusions were identified based on petrography, including type I (two-phase, liquid-rich aqueous inclusions), type II (two- or three-phase, CO2-rich inclusions), type III (two-phase, vapour-rich aqueous inclusions), and type IV (single-phase aqueous inclusions). The fluid inclusions in ore minerals (scheelite and stibnite) and their coexisting quartz largely share similar characteristics in terms of their types, homogenization temperatures and salinities. This is consistent with the fact that these ore minerals are always intergrown with quartz. Microthermometric and laser Raman data indicate a low-to-moderate temperature (140–240°C), low salinity (<7.0wt.% NaCl equiv.), CO2-rich, N2-bearing aqueous ore-forming fluid. Such fluid is further identified as a deeply non-magmatic crustal fluid rather than a mantle-source fluid by the significantly low 3He/4He ratios (0.002–0.281Ra), and a small amount of meteoric water or host-rock-buffered fluid could be involved. W ore precipitation was probably associated with mixing between a deeply-originated crustal fluid and host-rock-buffered fluid based on the fluid inclusion features in scheelite and quartz-I. However, Au and Sb ore deposition probably resulted from boiling which was caused by the marked pressure drop. Geological features (such as banded structure and crack-sealing structure) also indicate that fluid pressure fluctuation induced by fault-valve mechanism occurred during ore precipitation. These characteristics of the ore-forming fluids in the Woxi deposit are in good agreement with the definition of orogenic gold deposits and the Woxi Au–Sb–W deposit is probably an atypical orogenic gold deposit for its unique ore-forming element association.

Ore-forming mechanism for the Xiaoxinancha Au-rich Cu deposit in Yanbian, Jilin Province, China: Evidence from noble gas isotope geochemistry of fluid inclusions in minerals

The Xiaoxinancha Au-rich copper deposit is one of important Au-Cu deposits along the continental margin in Eastern China. The deposit consists of two sections: the Beishan mine (North), composed of altered rocks with veinlet-dissemination sulfides and melnicovite-dominated sulfide-quartz veins, and the Nanshan mine (South), composed of pyrrhotite-dominated sulfide-quartz veins and pure sulfide veins. The isotope compositions of noble gases extracted from fluid inclusions in ore minerals, i.e. ratios of 3He/4He, 20Ne/22Ne and 40Ar/36Ar are in the ranges of 4.45–0.08 Ra, 10.2–8.8 and 306–430, respectively. Fluid inclusions in minerals from the Nanshan mine have higher 3He/4He and 20Ne/22Ne ratios whereas those from the Beishan mine have lower 3He/4He ratios. The analysis of origin, and evolution of the ore fluids and its relations with the ore-forming stages and the ages of mineralization suggests that the initial hydrothermal fluids probably come from the melts generated by partial melting of oceanic crust with the participation of fluids from the mantle (mantle-plume type)/aesthenosphere. This also corresponds to the continental margin settings during the subduction of Izanagi ocaneic plate towards the palaeo-Asian continent (123–102 Ma). The veinlet-dissemination ore bodies of the Beishan mine were formed through replacement and crystallization of the mixed fluids generated by mixing of the ascending high-temperature boiling fluid with young crustal fluid whereas the melnicovite-dominated sulfide-quartz veins were formed subsequently by filling of the high-temperature ore fluid in fissures. Pyrrhotite-dominated sulfide-quartz veins in the Nanshan mine were formed by filling-deposition-crystallization of the moderate-temperature ore fluids and the pure sulfide veins were formed later by filling-deposition-crystallization of ore substance-rich fluids after boiling of the moderate-temperature ore fluids. The metallogenic dynamic processes can be summarized as: (1) formation of fluid- and ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success-sive ascending of the ore fluids and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling.

Antimony in hydrothermal processes: solubility, conditions of transfer, and metal-bearing capacity of solutions

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–H 2S–H 2O 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 Cl − = 0.1−5) solutions and the joint dissolution of Sb (s) 0 and Sb 2S 3(s) in sulfide-chloride solution (m HS − = 0.01; m Cl − = 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 °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.

Organic Gases in Fluid Inclusions of Ore Minerals and Their Constraints on Ore Genesis: A Case Study of the Changkeng Au‐Ag Deposit, Guangdong, China

Abstract  The newly discovered Changkeng Au‐Ag deposit is a new type of sediment‐hosted precious metal deposit. Most of the previous researchers believed that the deposit was formed by meteoric water convection. By using a high vacuum quadrupole gas mass spectrometric system, nine light hydrocarbons have been recognized in the fluid inclusions in ore minerals collected from the Changkeng deposit. The hydrocarbons are composed mainly of saturated alkanes C1–4 and unsaturated alkenes C2–4 and aromatic hydrocarbons, in which the alkanes are predominant, while the contents of alkenes and aromatic hydrocarbons are very low. The σalka/σalke ratio of most samples is higher than 100, suggesting that those hydrocarbons are mainly generated by pyrolysis of kerogens in sedimentary rocks caused by water‐rock interactions at medium‐low temperatures, and the metallogenic processes might have not been affected by magmatic activity. A thermodynamic calculation shows that the light hydrocarbons have reached chemical equilibrium at temperatures higher than 200°C, and they may have been generated in the deep part of sedimentary basins (e.g., the Sanzhou basin) and then be transported by ore‐forming fluids to a shallow position of the basin via a long distance. Most of the organic gases are generated by pyrolysis of the type II kerogens (kukersite) in sedimentary host rocks, only a few by microorganism activity. The compositions and various parameters of light hydrocarbons in gold ores are quite similar to those in silver ores, suggesting that the gold and silver ores may have similar metallogenic processes. Based on the compositions of organic gases in fluid inclusions, the authors infer that the Changkeng deposit may be of a tectonic setting of continental rift. The results of this study support from one aspect the authors' opinion that the Changkeng deposit is not formed by meteoric water convection, and that its genesis has a close relationship with the evolution of the Sanzhou basin, so it belongs to the sedimentary hot brine transformed deposit.

Origin of CaCl2 brines by basalt-seawater interaction: Insights provided by some simple mass balance calculations

Modern rift zone hydrothermal brines are typically CaCl2-bearing brines, an unusual chemical signature they share with certain oil field brines, fluid inclusions in ore minerals and a few uncommon saline lakes. Many origins have been suggested for such CaCl2 brines but in the Reykjanes, Iceland, geothermal system a strong empirical case can be made for a basalt-seawater interaction origin. To examine this mechanism of CaCl2 brine evolution some simple mass balance calculations were carried out. Average Reykjanes olivine tholeiite was “reacted” with average North Atlantic seawater to make an albite-chlorite-epidotesphene rock using Al2O3 as the conservative rock component and Cl as the conservative fluid component. The excess components released by the basalt to the fluid were “precipitated” at 275° C as quartz, calcite, anhydrite, magnetite and pyrite to complete the conversion to greenstone. The resulting fluid was a CaCl2 brine of seawater chlorinity with a composition remarkably similar to the actual Reykjanes brine at 1750 m depth. Thus, the calculations strongly support the idea that the Reykjanes CaCl2 brines result from “closed system” oceanic basalt-seawater interaction (albitization — chloritization mechanism) at greenschist facies temperatures. The calculation gives a seawater: basalt mass ratio of 3∶1 to 4∶1 (vol. ratio of 9∶1 to 12∶1), in keeping with experimental results, submarine vent data and with ocean crust cooling calculations. The brine becomes anoxic because there is insufficient dissolved or combined oxygen to balance all the Fe released from the basalt during alteration. Large excesses of Ca are released to the fluid and precipitate out in the form of anhydrite which essentially sweeps the brine free of sulfate leaving an elevated Ca concentration. The calculated rock-water interaction basically involves Na + Mg + SO4 ⇌ Ca + K, simulating chemical differences observed between oceanic basalts and greenstones from many mid-ocean ridges.

The effect of salinity on the maximum thermal gradient of a hydrothermal system at hydrostatic pressure

The effect of salinity on the temperature-depth relations of a brine of constant composition, enclosed in a vein system, but freely connected to the surface, and everywhere at the boiling point for the hydrostatic head, was calculated by using a mathematical model. The Na-Ca-K-Cl brines which are found in thermal springs and in fluid inclusions in ore minerals were approximated by the available data for vapor-saturated NaCl-H 2 O solutions. In general, the results are similar to those calculated by D. E. White in 1968 for H 2 O, except that the gradients are steeper because of the increase in density and the decrease in vapor pressure caused by the dissolved salt. As a practical rule, the depth to an isotherm in a 5, 10, 15, 20, and 25 wt percent NaCl brine system is, respectively, 92, 84, 77, 70, and 63 percent (+ or -2 percent) of the depth to the same isotherm in an H 2 O system. From the data presented, the minimum depth to the growth site of crystals containing fluid inclusions which indicate boiling of the brine can be estimated. Among other applications, these results are useful toward the understanding of the behavior of brines in geothermal areas which may or may not contain compositional stratification.

Composition of fluid inclusions, Cave-in-Rock fluorite district, Illinois, and Upper Mississippi Valley zinc-lead district

This paper describes the chemical composition and relative deuterium concentration of primary fluid inclusions in ore and gangue minerals from the Cave-in-Rock and Upper Mississippi Valley districts - both of which are of the Mississippi Valley type. Compositional changes are compared to the paragenetic sequence. The fluid inclusions in the early ore minerals are nearly saturated sodium-calcium chloride brines. Fluid inclusions in late minerals are less concentrated and have a lower relative deuterium concentration. In the Cave-in-Rock district the composition of primary fluid inclusions in yellow fluorite, the earliest ore mineral, is similar to that of connate water in the Illinois basin in the same strata as the ore deposits. The change in composition of fluid inclusions in the later quartz and sulfide minerals indicates a water of different origin, possibly magmatic, was introduced. Connate and possible magmatic waters were largely flushed out during deposition of the gangue minerals in the last stages of mineralization, and the composition of the fluid inclusions in these gangue minerals trends toward that of meteoric water or a dilute mixture of meteoric and magmatic water. In the Wisconsin-Illinois-Iowa district, fluid inclusions in the ore minerals are highly concentrated sodium-calcium chloride brines that have a high relative deuterium concentration; inclusion fluid in late gangue minerals contains less deuterium and is relatively dilute.