Ore-forming Solutions Research Articles

Geological setting, lead-zinc mineralization characteristics and its potential prospects in the Na Bop - Pu Sap area, Cho Don, Northeastern Vietnam

The Lo Gam structural zone is recognized as a crucial area for the occurrence of lead-zinc deposits in Northeast Vietnam, encompassing the distinguished territories of Cho Dien and Cho Don. Specifically, within the Cho Don area, the Na Bop-Pu Sap area emerges as particularly noteworthy owing to the considerable scale and quality of its lead-zinc ore deposits. In order to comprehensively investigate the geological attributes and lead-zinc mineralization phenomena prevalent in Na Bop-Pu Sap, a suite of analytical techniques including petrographic analyses, mineralogical examinations, scanning electron microscopy (SEM), and ICP-MS were employed. Furthermore, stable isotope investigations and single mineral sphalerite analyses were conducted to assess the origin of metal constituents and the physicochemical conditions conducive to ore genesis. The Na Bop-Pu Sap area is under the influence of the NW-SE fault system, with the ore structure predominantly manifesting as bands and veins aligned parallel to the foliations of hosted rock. This configuration suggests a close association between the formation of lead-zinc ore and the foliation processes occurring within the shear zones. The assemblage of ore minerals within the region primarily comprises galena, sphalerite, pyrite, pyrrhotite, and arsenopyrite. Integration of S and Pb isotopic analyses alongside single mineral sphalerite assessments reveals that the ore-forming solutions emanate from both magmatic activity and sedimentary sources, with lead-zinc ore deposition occurring at temperatures ranging from low to medium. Projections suggest that the Na Bop-Pu Sap mining area may exhibit relative degrees of erosion extending to depths of approximately 600 meters below the existing terrain surface. This comprehensive examination of the ore characteristics in the Na Bop-Pu Sap mine area yields invaluable insights, thereby advancing our understanding of the potential for deep-seated lead-zinc mineral resources within the Northeastern Vietnam.

Mathematical model of the formation of barite-lead mineralization of the Ushkatyn III deposit (Central Kazakhstan)

The genesis of stratiform deposits of lead and barite in sedimentary rocks is of great interest from the point of view of replenishing reserves of polymetallic ores. The aim of the work is to establish the regularity of the hydrogenic formation of ores in limestones, taking into account the influence of the nanosurface of pores and cracks based on a mathematical model of the movement and characteristics of ore-bearing solutions in the pores. The thicknesses of the surface layer of limestones and minerals included in the ore-containing strata and sulfide minerals are calculated. The results indicate that they are nanostructures with special physical properties different from the rest of the substance, which is confirmed by the regularity of the formation of a heavy sulfur isotope in ores of various textural types. The influence of hydrotherms with different densities, kinematic viscosity, and velocity on the intensity of mineralization formation in cracks and pores of limestone, as well as the occurrence of new feathering cracks around the fractures of dismemberment, is estimated. The dependence of the hydrothermal flow density on the diffusion of the liquid is established. The equation of kinematic viscosity is derived from the pressure in the solution flow, the velocity of its movement, the mass of particles of ore-forming elements, and sulfur isotopes under thermodynamic conditions of determined Gibbs energies. The relationship of the viscosity of the solution with the surface tension of the nanolayer of limestone particles in cracks and pores is shown, indicating that the greater this energy, the greater the velocity of movement of ore-forming solutions, the fewer branches of newly formed cracks around the dissection crack. The mathematical model is applicable for the numerical analysis of the regularity of mineralization in cracks, taking into account the influence of the nanostructural layer of cracks and pores of limestone in the thermodynamic conditions of the occurrence of an ore-bearing formation.

Distribution and Cocrystallization Coefficients of a Wide Range of Typomorphic Elements in Magnetite, Hematite, and Sphalerite in Hydrothermal Systems

Abstract —Distribution of a wide range of elements in the systems with magnetite, hematite and sphalerite is studied by the method of thermogradient hydrothermal synthesis combined with internal fluid sampling at 450 °C temperature and 100 MPa pressure. The distribution and cocrystallization coefficients are determined; the literature and original data on these coefficients are summarized. The possibility of obtaining the reproducible data on elements distribution in the mineral − solution system in the occurrence of many typomorphic elements is substantiated. This considerably increases the experiment efficiency. A significant advantage of using cocrystallization coefficients rather than “conventional” distribution coefficients expressed by the ratio of the element concentrations in crystal and solution (fluid) is shown. The features of behavior and occurrence of elements in hydrothermal systems are provided with physico-chemical evidence, through application of cocrystallization coefficients. The examples of the behavior of typomorphic trace elements in sphalerite are considered, which support the theoretical analysis. The major (Fe, Mn, Zn and possibly Cu) and secondary (Ti, V, Al, and Co) components of ore-forming solutions are estimated according to the compositions of magnetite and hematite from hydrothermal ore deposits of various types. The similarity in compositions of magnetite and hematite does not prove their coformation from a single fluid, quite the reverse, and this fact indicates different compositions of fluids from which the minerals were deposited.

The mineral composition and formation conditions of quartz-beryl mineralization of the Pervomaiskoe molybdenum deposit, Dzhida ore field, Southwestern Transbaikalian region

The article is devoted to determination of the mineral composition, physicochemical parameters, and sources of the substance of quartz-beryl mineralization of the Pervomaiskoe ore deposit, that is distinguished as an independent stage of the mineral formation. The main minerals are quartz and beryl; phenakite has first been identified for the Pervomaiskoe deposit. Ore minerals are represented by molybdenite, pyrite, and rare grains of cassiterite, chalcopyrite, rutile, aikinite, wulfenite, columbite, monazite, and xenotime. Results of studying the fluid inclusions have showed that homogenization temperatures of the fluid inclusions in the beryl vary in the range from 265 to 191°C. The ore-forming solutions are characterized by a low salinity of 5.9-8.6 NaCl equiv. Homogenization temperatures of fluid inclusions in the quartz correspond to 281-250°C. Data on the isotopic composition show the participation of meteoric waters in the ore-forming process.

Mineralogy of the ores on the southern flank of the Mutnovskoe gold-silver-polymetallic deposit (Southern Kamchatka)

The Mutnovskoe deposit is one of the largest and most prospective ore deposits in South Kamchatka. The northern and southern flanks within the main veining zone Opredelyayushchaya, composed of low-sulfi (goldsilver) and sulfide-polymetallic (gold-silver-polymetallic) types of ores, respectively, are distinguished. The paper presents the results of the complex mineralogical and geochemical studies of the gold-silver-polymetallic ores of the southern flank of the deposit. Features of textures and structures, mineral, chemical compositions and genesis of the ores, as well forms of precious and base metals occurrences are shown. Typomorphic features of pyrite, sphalerite, galena, chalcopyrite, tennantite-tetrahedrite, Au, Ag, Pb and Bi tellurides, native gold, Bi, Se and Ag sulfosalts are characterized. The pyrite-sphaleritequartz, sphalerite-galena-quartz, and chalcopyrite-tennantite-tetrahedrite mineral associations are distinguished. The temperatures and composition of ore-forming solutions are shown.

Geology, molybdenite Re-Os age, H-O-S-Pb isotopes, and fluid inclusion features of the Maodeng Mo-Bi-Sn-Cu deposit, Inner Mongolia

Maodeng deposit is a large-sized Mo-Bi-Sn-Cu deposit located in the Xinlinhot of Inner Mongolia in the southern segment of the Great Xing’an Range. The ore-forming elements in the deposit are found in the volcanic breccia of Lower–Middle Permian Dashizhai Formation and granite porphyry of the Alubaogeshan complex, constituting distinct regional mineralization zones such as hydrothermal vein-type of Sn-Cu orebodies in the upper parts and stockworks, veinlets and disseminated-type of Mo-Bi orebodies in the lower parts. This paper has conducted an integrated study using a comprehensive field survey, molybdenite Re-Os age, fluid inclusion, and isotopic (O, H, S, and Pb) analyses. The mineralization in the deposit can be divided into four stages, which are molybdenite-native bismuth-quartz (stage I), cassiterite-wolframite-topaz-quartz (stage II), chalcopyrite-sphalerite-galena-fluorite-sericite-quartz (stage III) and stibnite-pyrite-quartz-fluorite (stage IV). The Re-Os isochron age of four molybdenite samples was estimated as 139.2 ± 3.9 Ma, indicating the deposit was formed during the Early Cretaceous. The Maodeng deposit is characterized by three kinds of fluid inclusions (FIs): liquid-rich two-phase, vapor-rich two-phase, and daughter mineral-bearing three-phase FIs. The homogenization temperatures for the FIs of stages I through IV are 292–387 °C, 222–333 °C, 172–252 °C, and 122–197 °C, with calculated salinities of 4.2–43.6 wt%, 2.1–38.9 wt%, 1.9–33.6 wt% and 0.7–5.1 wt% NaCl equiv., respectively, showing the gradual reduction in temperature and salinity of hydrothermal fluids. Hydrogen and oxygen isotopic data of quartz indicate that the dominant origin of the ore-forming solutions from deep granitic intrusions followed by their dilution by limited meteoric water. The sulfides have δ34S values ranging from − 6 ‰ to − 0.49 ‰, and have 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios similar to those of K-feldspars from the Alubaogeshan pluton, suggesting the primary origin of ore-forming materials of the Maodeng deposit are magmatic. Molybdenite and native bismuth may precipitate primarily by fluid boiling, chalcopyrite could deposit mainly by fluid mixing, and cassiterite precipitate mainly through fluid boiling and mixing.

Garnet trace element geochemistry of Yangla Cu deposit in NW Yunnan, China: Implications for multistage ore-fluid activities in skarn system

Garnet is a common hydrothermal mineral in skarn-type deposits, and is useful for constraining the ore-fluid composition. Based on the mineralogy and geochemical features of different types of garnets from the Yangla Cu deposit, we discuss the factors and mechanism of rare earth elements (REE) incorporation into skarn-type garnet, together with the skarn-forming environment. Garnet from Yangla belongs to the grossular–andradite solid solution series, and can be divided into two types (i.e., zoned and unzoned). Early garnet (Grt I) aggregates (avg. And84.96 Gro9.62 Spe + Pyr + Alm5.42) in the proximal skarn is clearly oscillatory-zoned, whilst most of late garnet (Grt II) (avg. And96.26Gro0.58Spe + Pyr + Alm3.16) in the diopside skarn is unzoned. Grt I is slightly LREE-enriched and HREE-depleted with positive Eu anomalies, whereas Grt II is obviously LREE-enriched and HREE-depleted with positive Eu anomalies. Grt I has higher total REE, Y and HFSE contents than Grt II. We suggest that fluid composition and physicochemical conditions greatly controlled the REE incorporation into garnet. The Grt I oscillatory zoning was likely formed by self-organization under relatively low growth rate, leading to Al/Fe fluctuation in the fluid related to the change of external factors (such as fluid boiling). Based on the differences of microscopic texture and geochemical characteristics between Grt I and Grt II indicate that Grt I was likely formed under a mildly acidic and reducing environment and low W/R ratios, whereas Grt II may have formed in a more acidic and oxidizing environment with higher W/R ratios. The changes in redox, pH and W/R ratios cause the compositional variation from Grt I to II during the ascent of the early hydrothermal fluid. During the process of the crystal formation, the oxygen fugacity increased, and the mildly acidic to acidic ore-forming solution shifted from a low W/R ratios condition to a high W/R ratios condition, causing the precipitation of metal sulfide. The fissures of Grt II are infilled by pyrrhotite, chalcopyrite and pyrite, showing that the garnets form prior to the mineralization of copper and can provide space for the precipitation and enrichment of metals.

THE ROLE OF ENDOGENOUS FACTORS IN HYDROGENIC ORE FORMATION

Processes in hydrogenic ore formation by groundwater and does not explicitly associated with the magmatism, possible participation of deep fluids and thermal solutions are of endogenous origin, which is the cause of non-equilibrium physico-chemical condition of the host rocks, mineralization of underground waters and their transformation into ore-forming solutions. The ore-bearing fluid has a predominantly aqueous composition. The behavior of hydrocarbons in hydrothermal solutions of vadose origin obeys the laws of joint solubility of H2O, CO2, CH4 and liquid bitumoids at various pressures and temperatures. Epiplatform activation of geotectonic structures of different ages and types that have a sedimentary cover leads to a combination of ore-forming processes in time and often in space caused by descending infiltration waters and ascending hydrothermal solutions. Such ore-forming processes on the territory of Ukraine can be traced in the Don-Dnipro structural-metallogenic zone and the Volyn-Podolsk metallogenic region. In the Don-Dnipro structural-metallogenic zone during the Cimmerian metallogenic epoch (late Triassic – early Cretaceous), fault zones and tectonically complicated salt-dome anticlines served as discharge centers for both ascending hydrothermal solutions and pressure infiltration waters. As a result, a group of polygenic deposits of uranium-bitumen-mercury composition was formed, including the Adamovskoye uranium-bitumen deposit and the Slavyanskoye mercury ore occurrence, located within the same structure. On the territory of the Volyn-Podilsky metallogenic region, Cimmerian-era ore occurrences are formed by ascending low-temperature carbon dioxide-hydrocarbon chloride solutions of deep (metamorphic or metagenetic) origin, which were diluted by underground meteor waters before the completion of ore formation. This led to the redistribution of uranium and associated ore elements during the lithogenesis of sedimentary rocks and regeneration during the late Paleozoic-early Mesozoic tectonic activation involving both exogenous and endogenous processes. The result was the formation of hydrothermal-regenerative uranium ore occurrences, which are characterized by their proximity to zones of discontinuous faults, veined-interspersed mineralization, its presence not only in sedimentary rocks, but also in zones of foundation fracturing, association of uranium minerals (coffinite, nasturane) with the release of solid black bitumen and ore occurrences of the barite-fluorite-polymetallic formation.

First Data on Isotopy and Mineralogical Features Ores Kumirnogo Silver Deposit (Russia, Primorsky Region)

Lockated in the noth part of Primorsky region, the Kumirnoe silver deposit is very interesting object from a geological point of view. Data about isotopic mineralogical characteristics of its ore mineralization was first presented in this essay. More than 80 ore bodies are known at the deposit. They mostly contain quartz, hydromica, sericite, adularia, chlorite, montmorillonite and kaolinite. Ore mineralization is represented by silver-bearing minerals: acanthite, pyrirargyrite, polybasite, stephanite, freibergite, selenium-containing aguilarite and eletrum. The obtained isotope data indicate that sulfur composition is close to meteorite standard, this is indicated by the narrow positive interval of its sulfur ratios (2,0-2,8‰). It gives the reason to assume that homogeneous hydrothermal ore-forming solutions participated in its formation. Its comparison with isotopic data of gold-silver deposits located in the continental marginal volcano-plutonic belts (Ducat, Mnogovershinnoe, Sergeevskoye) shows that the formation of the Kumirnoe deposit was at the same time: Cretaceous- Paleogene, it’s possible it was under similar geological conditions. This is confirmed by the age data obtained by us earlier for Kumirnoe deposit (it matches Cretaceous- Paleogene).

Micro-Nanoscale Characteristics of Pyrite and Its Implications for Gold Mineralization: Two Cases of Gold Deposits in the Youjiang Basin and Southwestern Tianshan Mountains.

The mineralogical and compositional characteristics of gold-bearing minerals and the occurrence of gold are not only of great significance to exploring the sources of ore-forming materials and their formation mechanisms but also helpful for designing reasonable beneficiations and smelting schemes and achieving remarkable economic benefits. This paper presents an integrated study on the crystal characteristics, elemental composition and distribution of pyrite (the main gold-bearing minerals), on the basis of electron probe microanalysis (EPMA), scanning electron microscopy (SEM), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and nano-secondary ion mass spectrometry (NanoSIMS). The occurrence of gold in the Shuiyindong gold deposit and Ashawayi gold deposit has been studied by means of microscopy, SEM, and EPMA images, elemental correlations, S-Fe-As ternary diagrams, logAs-logAu diagrams and Au/As ratios. The gold in pyrite of the Shuiyindong deposit is in the form of nano gold inclusions and lattice gold. The gold in pyrite of the Ashawayi deposit dominantly exists in the form of nano gold inclusions or is present as micro-nano gold particles in the cracks or edges of pyrite, some of which can exist as lattice gold. The ore-forming hydrothermal solution of the Shuiyindong gold deposit is mainly underground hot brine, but it may be reformed by a deep magmatic hydrothermal solution or volcanic-subvolcanic hydrothermal solution. The ore-forming hydrothermal solution of the Ashawayi gold deposit is mainly derived from the metamorphic hydrothermal solution formed during the orogenic process, and the ore-forming process or post-mineralization process may be reformed by the leaching of underground hot brine. Finally, the characteristics of ore-forming fluids and evolution of the two types of deposits are determined via pyrite element surface scanning. This paper shows that micro-nanoscale study of gold-bearing pyrite is of great significance to understanding the gold mineralization process and is worth further study.

Mineral composition and formation conditions of the Inkur tungsten deposit ores (Dzhidinsky ore field, South-Western Transbaikalia)

The aim of the study is to clarify the mineral composition and determine the conditions of the formation of the quartz-hubnerite veins of the Inkur stockwork tungsten deposit (the Dzhidinsky ore field, South-Western Transbaikalia). The research methods include a mineralogical and petrographic description of the ore quartz-hubnerite veins; an electron microprobe analysis of the mineral associations; thermometry, cryometry, and Raman spectroscopy of the individual fluid inclusions in quartz, fluorite, hubnerite, and muscovite. The mineralogical and petrographic studies has made it possible to clarify the mineral composition of the Inkur deposit ores and determine the mineral paragenesis formation sequence. The fluid inclusion studies have established that the ore deposition was occurring in the relatively low-salinity (~5.7–14.6 wt. % eq. NaCl) homogeneous solutions due to a decrease of the temperature. The study of the salt composition of the solutions has identified Ca chloride as a prevailing component, with NaCl, KCl, and MgCl as admixtures. CO2 and N2 have been identified in the gas phase of inclusions. Two stages of mineral formation have been defined: high-temperature (≥300 °С) and low-temperature (≥2.00–300 °С). The conducted studies allow qualitative estimation of the chemical composition of the ore-forming solutions. It has been established that one of the main factors of the hubnerite deposition is a temperature factor.

3D geophysical modeling of the Alberton-Mathinna section of the “Main Slide,” northeast Tasmania

We have developed a high-resolution 3D model of the Alberton-Mathinna section of the “Main Slide,” northeast Tasmania. This geological model expresses a new synthesis based on mapping and structural interpretation on multiple cross sections. We have refined this model by 3D geophysical inversion constrained by gravity and magnetic survey data coupled with drilling and rock physical property databases. Our modeling incorporates statistically generated sensitivity characterization metrics into 3D model products that map confidence in the geometry of geological units at depth. The results include a granitoid surface that is considerably more detailed than earlier versions based on 2D modeling. Among the new features to emerge is a cupola 1.6 km below and slightly west of the Mathinna goldfield. At the Ringarooma United deposit located within the Alberton goldfield, we seethat the fault network underpinning the deposit was intruded by granite to a depth of approximately 400 m. Ore-forming solutions for both deposits have been interpreted as metamorphic in origin, but our results suggest the possibility of a role for magmatic fluids (i.e., granite related) in the gold-mineralizing system, particularly for the Ringarooma United deposit.

Geology, geochemistry, fluid inclusions and O–H stable isotope constraints on genesis of the Lake Siah Fe-oxide ± apatite deposit, NE Bafq, Central Iran

The Lake Siah iron ± apatite deposit is situated in the Bafq Mining District (BMD), Central Iran. The iron ± apatite orebodies are hosted by a succession of rhyolite, rhyolitic tuff, trachyandesite, and andesite of Lower Cambrian age. The host rock has undergone widespread alteration and mineralization stages including Na (albite–quartz), followed by Na–Ca (albite–calcite–amphibole–magnetite ± quartz ± epidote), magnetite–apatite, K (biotite ± K-feldspar), hydrolytic (sericite–quartz), and argillic (kaolinite–montmorillonite ± dickite), respectively. Electron microprobe analyses (EPMA) from magnetite and hematite show significant variations of trace elements. Based on Ni/Cr + Mn and Ca + Al + Mn versus Ti + V diagrams, the majority of magnetite samples belong to Kiruna-type deposits. At least, three generations of fluid inclusions, including solid-bearing (L + V + S) (Type I), liquid-rich (L + V) (Type II-A), vapor-rich (L + V) (Type II-B), and liquid or vapor mono-phase (Type III), are recognized in quartz and apatite. The solid-bearing fluid inclusions in quartz completely homogenized at temperatures of 150 to > 530 °C with salinities of 30–58 wt% NaCl equiv. Liquid-rich fluid inclusions in apatite homogenized to a liquid phase at 175–210 °C, whereas the vapor-rich fluid inclusions homogenized to a vapor at 335–350 °C. Oxygen isotope analysis was carried out on quartz and magnetite. The hydrogen and oxygen isotopic compositions of quartz (δ18Ofluid values of 7.57–11.04‰) show that with progress in time the ore-forming solutions gradually evolved from a magmatic to meteoric-dominated source.

Composition of minerals from the skarn deposits Väster Silvberg (Sweden) and Tumurtijn-ovoo (Mongolia): Indications of different element supply in submarine hydrothermal-sedimentary ore genesis

We compare chemical compositions of the main minerals from two submarine exhalative sulfide-bearing manganiferous iron-ore deposits, i.e.Väster Silvberg in Sweden (VS) and Tumurtijn-ovoo in Mongolia (TO). At VS, much Al is present in garnet (Fe-spessartine) and biotite, whereas at TO the ore-associated garnets are Al-poor (andradite) and minerals not associated with ore minerals are Al-rich (grossular, vesuvianite). The low-Al of andradite at TO agrees with the low-Al of volcanic ore-forming solutions from the modern oceans. The Al-rich minerals at both TO and VS indicate the assimilation of Al-rich volcanic material in both deposits. The elements Ca and Mg show opposite distributions: at VS much Mg is incorporated in kutnahorite, knebelite, biotite, and Mn-actinolite, Mg-rich minerals are absent at TO; in contrast, the garnets at TO contain more Ca than the garnets at VS. We explain these differences by the different carbonate minerals constituting the accompanying carbonate rocks at the two deposits, namely calcite and dolomite at VS, and only calcite at TO. These minerals primarily resulted from evaporation of seawater. Also during times, when they did not form massive carbonate rocks, they settled to the seafloor in minor amounts. There, they were partially combined with volcaniclastic Al-rich input. When the ore solutions spread on the seafloor and percolated through the bottomset they mixed with the seafloor mud producing ore-bearing sediments as precursors of Al-rich, Mg-rich skarn ores at VS and Al-poor, Mg-poor, Ca-rich skarn ores at TO. As a result, three sources supplied elements for the skarn-ore formation at the investigated deposits: volcanic ore solutions, Al-rich volcanic material and evaporitic carbonates of different composition.

Geology and Geochemistry of Carbonate Hosted Pb-Zn Deposit on North-east Part of Kahramanmaraş (Helete) in Engizek Belt

The aim of this study is to reveal the geological and geochemical properties of Pb-Zn mineralizations associated with carbonate rocks along the Helete (Kahramanmaraş) district in Taurus Orogenic belt. The Paleozoic Malatya metamorphics and Eocene sedimentary rocks are present in the Helete region within the area defined as Engizek Belt (North of Kahramanmaraş) in the Eastern Taurus Orogenic belt. In the Gümüşbanı region, there are bariteed Pb-Zn mineralizations in the Paleozoic Malatya metamorphic rocks. Epigenetic mineralization observed in fractures and cracks is vein-type and disseminated. The thickness of the veins varies between 1 cm and 10 cm. The ore paragenesis contains barite, galena, sphalerite, chalcopyrite, fluorite and covellite. In geochemical analysis of samples taken from ore zone, Pb reaches maximum 50.21%, Zn maximum 51.99% and BaO 52.13%.  In geochemical analysis, the ore zone has a maximum of 50.21% Pb and Zn a maximum of 51.99%. In the isotope geochemistry study, the value of δ34S was determined between 10.92 and 11.24‰. As a result of the field and laboratory studies, it was determined that the mineralization was limited to the fractured lines and Paleozoic aged carbonate rocks, and S in the ore-forming solution pointed out to the continental origin. 

Age, Conditions of Formation, and Fluid Composition of the Pervomaiskoe Molybdenum Deposit (Dzhidinskoe Ore Field, South-Western Transbaikalia, Russia)

The article discusses the composition of studied ore-forming solutions and the P-T conditions of molybdenum mineralization in the Pervomaisky stockwork deposit which is situated within the Dzhidinsky ore field (South-Western Transbaikalia, Russia). New geochronological data of zircons from granites, muscovite, and molybdenite from the ore zones indicates the association of the granite formation and ore deposition processes which occurred 119–128 million years ago. Quartz-molybdenite veins of the Pervomaisky deposit were formed at the temperature of ≥314–186 °C with some boiling periods. Fluid inclusions in these veins have total salt concentration of 6.3–12.7 wt. % NaCl equivalent (eq. NaCl). The salt solution is composed of chlorides of Na, Ca, K, and Fe. The gas phase contains CO2, CH4, and N2. A series of elements were determined in fluid inclusions by laser ablation (LA)-ICP-MS: Li, Be, B, F, Na, Mg, Al, Cl, K, Ca, Mn, Fe, Cu, Zn, Nb, Mo, Ag, Sn, La, Ce, Ta, W, Au, Pb, Th, U. The Mo content reaches 559 ppm (average of 228 ± 190 ppm) in high-grade quartz-molybdenite veinlets, whereas Mo content is up to 212 ppm (average of 25 ± 29 ppm) in the low-grade veinlets. High-grade veinlets were formed by near-neutral solutions with a higher content of Mo, S, and F, while relatively low-grade veinlets were deposited from alkaline solutions. Our results demonstrate the pH of the solutions as one of the key factors for ore deposition.

How to form a giant epithermal precious metal deposit: Relationships between fluid flow rate, metal concentration of ore-forming fluids, duration of the ore-forming process, and ore grade and tonnage

Economic metal deposits associated with hydrothermal systems represent the end product of a series of complex processes the are related to the amount of ore fluid that flows through the system, the concentration of metal in the ore fluid, the depositional efficiency, and the duration of the ore-forming process. These factors, in turn, largely control the size (tonnage) and grade of the deposit that forms. Of these factor, the duration of the mineralizing event is one of the least understood aspects of ore genesis. We have used ore tonnage (produced + reserves) and grade information from a large number of epithermal precious metal (Au ± Ag) occurrences, combined with simplifying assumptions related to the metal solubilities and precipitation efficiency, to estimate the amount of fluid required to deposit the amount of the metal observed in the deposit. Total gold tonnage for 279 epithermal veins, prospects and deposits ranges from 0.0002 T (6 troy oz; Wharekirau-ponga, New Zealand) to 1089 T (35 million troy oz) in the giant Pueblo Viejo deposit, Dominican Republic, with a median value of 5.93 T Au (191,000 troy oz). Total silver tonnage for 246 epithermal deposits ranges from 0.0004 T (12 troy oz; Wharekirau-ponga, New Zealand) to 62,207 T (2.0 billion troy oz; Cerro Rico de Potosi, Bolivia), with a median value of 40.8 T (1.31 million troy oz) Ag. The median gold grade, based on 246 deposits, is 5.29 g/T, and the median silver grade for 216 deposits is 93.3 g/T. The reported metal content and grade data suggest that about ~1012 kg of fluid is required to transport and deposit the amount of Au or Ag observed in a median size deposit, and that the largest deposits may require 1014 to 1015 kg of metal-transporting fluid. The median reported flow rate compiled for 693 modern continental geothermal systems, representing modern analogs of the ore-forming environment for the epithermal deposits, is about 5.78 kg/sec with the highest reported flow rate of ~3000 kg/sec. Based on the median flow rate, the time required to form a median-sized epithermal Au deposit is ~12,900 years, and that required to form a median sized Ag deposit is ~7800 years. The largest “giant” deposits could have formed in ~105 years assuming the median flow rate, or in ~104 years at the maximum reported fluid flow rate of 3000 kg/sec.Results of this assessment of the relationship between precious metal grades and tonnage, combined with reasonable fluid flow rates and metal contents of the ore-forming solutions, indicate that the active mineralization event need not be longer than ~104 years to form a median-sized deposit, assuming continuous deposition. Field and laboratory data suggest, however, that mineralization in epithermal deposits is episodic rather than continuous and is associated with discrete pulses, perhaps triggered by hydrothermal eruption events that lead to fluid immiscibility and the concomitant quantitative precipitation of all metal in solution. As such, gold and/or silver deposition likely occurred over only a small fraction of the total lifetime of the hydrothermal system, as evidenced by discrete bands of high-grade ore separated by barren or lower grade bands within mineralized quartz veins. Results of this study suggest that giant deposits do not necessarily require ore-forming fluids with exceptionally high metal contents, but rather may simply represent hydrothermal systems that were active for longer periods of time or were characterized by higher fluid flow rates, or both, resulting in greater amounts of metal-bearing fluid flowing through the ore horizon.

Physicochemical Conditions of the Existence of Early Cambrian Chemotrophic Microbiota in the Zone of Influence of Sulfide Ore-Forming Hydrothermal Solutions

Complex studies of the Early Cambrian Kyzyl-Tashtyg pyrite deposit (East Tuva) allowed us to reconstruct the paleohydrothermal systems, to understand the physicochemical conditions of hydrothermal processes, and to study the patterns of existence of ancient hydrothermal biota in the zone of activity of solutions participating at all stages of the formation of ore-bearing structures starting from the influence of postmagmatic fluids and up to low-temperature hydrotherms. The data on the biota reported were obtained during study of the objects occurring in the zone of influence of relatively low-temperature hydrothermal systems. In some cases, microorganisms were found in basaltic complexes hosting ore bodies; in other cases, fauna was related to the ferrous–siliceous deposits. It was found that microorganisms in basaltic amygdules were formed at temperatures of ~110–140°C under the influence of hydrothermal solutions of the Kyzyl-Tashtyg deposit. Much lower temperatures (up to 100°C) existed during the evolution of microfossils in the quartz–hematite hydrothermal structures of the Kyzyl-Tashtyg deposit.

He-Ar Isotopes and Trace Gas Compositions of Fluid Inclusions in Massive Sulphides from the Yushui Copper-Polymetallic Deposit, South China: Metallogenic Implications

The Yushui ore deposit, located in the middle section of the Yong’an-Meixian Hercynian depression, is a medium-sized Cu-polymetallic massive sulphide deposit in Eastern Guangdong Province, South China. This deposit is characterized by unusually high copper grade (up to 50–60 wt. % Cu). Other metallic elements, such as lead, zinc and silver, are also economically important in the Yushui ore bodies. The aim of this study was to apply N2–Ar–He systematics, together with organic gases (light-hydrocarbon tracers), to constrain the origin and evolution of ore-forming fluids. The helium-argon isotopes and trace gas compositions of fluid inclusions trapped within metal sulphide minerals were measured for a number of bonanza ores from the Yushui deposit. The noble gas concentrations in the studied samples vary over one to two orders of magnitude (4He: 2.27–160.00 × 10−5 cm3 STP g−1; 3He: 0.53–34.88 × 10−12 cm3 STP g−1; 40Ar: 6.28–37.82 × 10−7 cm3 STP g−1; 36Ar: 1.25–10.40 × 10−9 cm3 STP g−1). Our data show a narrow range of 3He/4He ratios from 0.006 to 0.056 Ra (~0.026 Ra on average, n = 8), which are considerably lower than the modern atmospheric end-member value; whereas the 40Ar/36Ar ratios (ranging from 333.76 to 501.68, with an average of 397.53) are significantly greater than that of air-saturated water. Most of the bornite samples have somewhat higher 3He/4He ratios of trapped fluids when compared to chalcopyrite. Overall, these He-Ar results are well within the range of crustal reservoir, thus implying a predominantly crustal source (originated from Caledonian basement) for ore-forming solutions, with little contribution from mantle-derived fluids. Analysis of the N2–Ar–He composition in Cu-rich sulphides indicates that the Yushui ore-forming fluids were probably derived from formation water (or basinal hot brines). Moreover, organic gas species identified in sulphide-hosted fluid inclusions are mainly composed of C1–C4 alkanes, while the concentrations of unsaturated olefins and aromatic hydrocarbons are very low. In particular, most chalcopyrite samples with relatively low 3He/4He ratios (0.006–0.016 Ra) and 40Ar*/4He values (0.0002–0.0012) are generally characterized by very high CO2/CH4 ratios (~60–102). All these suggest that main-stage Cu-Ag metallogenic processes might have not been affected by high-temperature magmatic activities or superimposed by strong metamorphic overprinting, although some chalcopyrite-rich ores appear to be influenced by later stage hydrothermal processes. In summary, neither magmatic input nor convecting seawater has played an important role in the formation of Yushui copper-polymetallic deposit. The massive sulphide ore bodies were products of water–rock interaction between metal-bearing basinal brines and the host sedimentary strata.

Ore Formation Conditions of the Aunik F-Be Deposit (Western Transbaikalia)

The paper presents the results of studying of the ore composition, ore-forming solutions, formation conditions, and sources of Be mineralization based on the example of the Aunik F-Be deposit, which is part of the Western Transbaikalia beryllium-bearing province; the main factors responsible for the beryllium mineralization are also assessed. The ores of the deposit are represented by feldspar-fluorite-phenakite-bertrandite metasomatites that formed after carboniferous limestones during its metasomatic replacement by hydrothermal solutions bearing F, Be, and accompanying admixture elements. It is established that the early phenakite-fluorite assemblage formed from high-fluoride CO2-bearing solutions with high alkalinity and a salinity of ~10.5–12 wt % NaCl eq. in the temperature range ~370–260°C at pressures from 1873 to 1248 bar. Later fluorite and bertrandite were formed by solutions with a salinity of 6.4–7.7 wt % NaCl eq. in the temperature range of ~156–110°C and pressure range of 639–247 bar. Isotopic composition studies of the ore assemblage minerals have confirmed the apocarbonate nature of the main ores at the deposit, making it possible to establish the igneous nature of the ore-forming paleohydrothermal solutions, the source of which were subalkaline leucogranites. The main factors controlling the formation of F-Be ores were the decrease in F activity in solutions owing to bonding of Ca and F in fluorite and the reduction in temperature during ore deposition. The increased alkalinity of the ore-forming solutions controlled the low solubility of Be complexes, which resulted in a low Be content in ores and a relatively small-scale mineralization at the deposit.