Ore Formation Research Articles

Mineralogical and technological features of gold from placers of the southern slope of Belaya Gora (Khabarovsk Krai) and stages of its formation

The gold-placer deposit of Pokrovsky-Verny streams is formed on the southern slope of Belaya Gora (Khabarovsk Krai), where streams drain gold formations of the same-name deposit. The gold content in the waste dumps of past years often reaches commercial concentrations, which allows to be re-processed them and some of the gold goes back into the dumps. The field formed by ore and alluvial formations is a complex volcanic structure with a concentric-zone structure underlined by faults. At the initial stage of research, the goal was to determine the content of the precious metal in gravity concentrate samples from the placers, the study of the mineralogical and technological characteristics of gold going into dumps. 135 gold grains ranging in size from 10–15 µm to 3 mm were studied using an electron scanning microscope. Six main species were distinguished by composition and morphology: high-grade in the form of isometric crystals; aggregates of gold crystals with 0–29% silver admixture; dendrites with up to 41% silver admixture; grayish gold and silver amalgams; loose weishanite (Au,Ag)3Hg2 formations of gray color; aggregates of ore-bearing and nonmetalliferous minerals with gold, in which the precious metal is less than half the grain. All gold grains have a flattened shape, variably contain inclusions of clay minerals, quartz, hematite, ilmenite, magnetite, limonite. Grains of native metals and intermetallic compounds are isolated in mineral association with gold. The revealed features of gold show that the formation of the precious metal is associated with hypogenic and epithermal processes, as well as with fluid emanations coming through late deep faults. Effective gold recovery requires several stages mineral processing.

Elucidating the Role of Hydrocarbons in Cinnabar (HgS) Ore Formation: A Model for Hg Mineralization in the Terlingua Mining District, Big Bend National Park, SW Texas

Abstract The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks. The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H2S saturated. Cinnabar was deposited as a result of H2S oxidation through mixing and cooling with local meteoric water. Both Hg0(org) and Hg0(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg0 in hydrocarbons show that at cinnabar saturation, Hg0 is more than an order of magnitude more soluble in hydrocarbons (Hg0(org) = 163 mg/kg) than Hg0 in water (Hg0(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (>10–1), and alkaline conditions, with pH > 10. Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs. Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg0(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H2S produced the cinnabar-rich ores.

Spatial and genetic relationship of endogenous and exogenous gold content in the area of the Pervomaisko-Zverevsky ore cluster (Middle Urals)

Te relevance of the work is due to the need to improve the efciency of appraisal work on new and unconventional types of gold mineralization within the known ore-placer regions and clusters. Te purpose of the work is to show the results of the study of the spatial and genetic relationship between endogenous and exogenous gold content using the example of the Pervomaisk-Zverevsky ore-placer cluster (OPC). Research methodology. Mineralogical and geochemical sampling of ore bodies outcrops, chemical weathering crusts; schlicho-mineralogical studies; study of native gold on a digital basis, taking into account the shape, size and composition of particles; mapping of parameters of gold particles in the section of the crust, the upper horizon of the Mesozoic eluvium. Results. Te factors that determine the localization of gold content within the OPC are substantiated. Among the endogenous factors: structural-tectonic, magmatic, metallogenic specialization of individual blocks. In the volume of the Verkhotursky granodiorite massif (an object of prospecting), a linear substockwork with a low level of mineralization of the gold-polysulfde-quartz type was revealed. When considering exogenous factors, the confnement of ore-bearing chemical weathering crusts to smoothed relief areas, comparable with Mesozoic denudation leveling surfaces and containing dispersed gold mineralization in the basement, was established. Te profle of the weathering crust in the Verkhotursk area is complex, without a distinct vertical hypergene zonality. Tese crusts are considered as “superimposed”, fnally formed under the infuence of later low-temperature argillization processes. Te most signifcant concentrations of gold are established in the upper horizon of the crust - the zone of the Mesozoic eluvium. Based on the mineralogical and geochemical study of metal particles, a model of its accumulation, sufusion-gravity, is proposed. Under certain conditions, a gold-enriched crustal horizon can have an independent applied value. In past years, gold-bearing areal accumulations (poddernikovye placers) were successfully mined. When mapping free gold, a wide range of sample fuctuations (from low- to high-grade) was established, indicating in favor of the multi-stage processes of ore formation in the OPC area. Conclusions. Many years of experience in the geological-geomorphological, mineralogical-geochemical study of the OPC of the Ural region has been tested by the practice of forecasting and prospecting. Te approaches outlined, taking into account the close spatial relationship between endogenous and exogenous gold content, are recommended for implementation and further improvement.

Ambient Noise Tomography Using a Nodal Seismic Array Reveals Evidence for Igneous Intrusion Contributed to Ore Deposits in South China

Abstract The causes of the large-scale and intense magmatism in South China and its coeval metallogenic processes in the Mesozoic have been debated, due partly to the lack of a high-resolution crustal model. In this study, we deploy ∼500 nodal seismometers around the Nanling metallogenic belt in South China, including one linear array across the metallogenic belt and one 2D array around the Fankou ore deposit: a deposit that hosts large amounts of lead and zinc in China. The derivation of the Moho and the intracrustal structures with receiver function imaging using the linear array was conducted in a separate study. Here, we focus mainly on the shallow shear wavespeed structure in the upper crust (from the surface to about 8 km depth) using ambient noise tomography with the 2D array data. We find low-shear wavespeed anomalies (VS<2.8 km/s) associated with a basin down to about 3.0 km and several high-shear wavespeed anomalies (VS>3.6 km/s) below 6.0 km adjacent to the Fankou ore deposit, which we interpret as the crystallized igneous intrusions in the Mesozoic. Gravity modeling shows that the high density anomaly derived using the wavespeed model is required to improve the data fitting. Considering the temperature derived from a typical geothermal gradient is insufficient for mineralization, we propose that the fluid and heat brought by the igneous intrusion might contribute to the mineral concentration of the Fankou ore deposit. This observation is consistent with geochemical and petrological evidence of diabase and quartz diorite veins in the study region. The experiment shows that ambient noise tomography using dense nodal arrays has the potential in resolving the favorable conditions for ore formation and may play a role in future ore exploration.

Ore Genesis of the Lower Urgen Porphyry Molybdenum Deposit in the Northern Great Xing’an Range, Northeast China: Constraints from Molybdenite Re-Os Dating, Fluid Inclusions, and H-O-S-Pb Isotopes

The Lower Urgen molybdenum deposit (44,856 t Mo @ 0.141%), situated in the northern Great Xing’an Range, is a newly discovered porphyry molybdenum deposit. Mineralization is characterized by veinlet-disseminated- and vein-type quartz–sulfide orebodies primarily occurring in the cupola of the Early Cretaceous granite porphyry stock. In this study, we present a detailed description of the ore geology, molybdenite Re-Os dating, H-O-S-Pb isotopic compositions, and fluid inclusion (FI) analyses including petrography, laser Raman, and microthermometry to precisely constrain the timing of ore formation, the origin of ore-forming fluids and materials, as well as the metal precipitation mechanism. Molybdenite Re-Os dating yielded two model ages of 141.2 ± 1.5 and 147.7 ± 1.7 Ma, coeval with the regional Late Jurassic–Early Cretaceous molybdenum metallogenesis. The hydrothermal process can be divided into three stages: the quartz–molybdenite(–pyrite) stage, quartz–polymetallic sulfide stage, and quartz–carbonate stage. Four types of FIs were distinguished for quartz, including two-phase liquid-rich (L-type), saline (S-type), CO2-rich (C1-type), and CO2-bearing (C2-type) FIs. Microthermometric data showed that the homogenization temperatures and salinities from the early to late stages were 240–430 °C, 5.0–11.9, and 30.1–50.8 wt% NaCl equiv.; 180–280 °C and 3.0–9.1 wt% NaCl equiv.; and 120–220 °C and 0.2–7.9 wt% NaCl equiv., respectively, suggesting a decreasing trend. H-O isotopic compositions indicate that the ore-forming fluids were initially of magmatic origin with the increasing incorporation of meteoric water. S-Pb isotopic compositions indicate that the ore-forming materials originated from granitic magmas, and the mineralization is genetically related to the ore-bearing granite porphyry stock in the deposit. Fluid immiscibility and fluid–rock interaction are collectively responsible for the massive deposition of molybdenite in stage 1, whereas fluid mixing and immiscibility played a critical role in the deposition of polymetallic sulfide in stage 2.

Geology and sulphide geochemistry of the Ni-Cu-Co mineralisation of the Espedalen Complex, Norway: Constraints for the distribution of magmatic sulphides within a variably deformed anorthosite suite

The Espedalen Complex is located in the eastern portion of the Jotun–Valdres Nappe Complex, south-central Norway and comprises three main suites (jotunite-charnockite-augengneiss; main anorthosite–ultramafite–norite; and gabbronorite suites) formed between 1520 and 1500 Ma. The anorthosite-ultramafite-norite suite hosts Ni-Cu-Co mineralisations grouped as: i) ‘primary sulphides’ referring to undeformed occurrences with magmatic textures; ii) ‘deformed sulphides’ which include dismembered ore bodies; and iii) ‘remobilised sulphides’ which comprise thin sulphide veinlets indicating remobilisation. The ‘primary sulphides’ characterise the deposits of Dalen, Megrund, Trona, Veslegruva and Melgard, whereas the ‘deformed sulphides’ characterise the deposits of Stormyra, Storgruva, Andreasberg, Niccoline, Gråhøa, Jørstad and Grimstjønna. The largest mineralisations are the Dalen and Stormyra deposits, which host 5.3 Mt @ 0.29% Ni, 0.12% Cu and 0.02% Co, and 1.01 Mt @ 1.09% Ni, 0.48% Cu and 0.04% Co, respectively. This study provides the first systematic characterisation of the different Ni-Cu-Co mineralisations from the Espedalen Complex.Primary sulphides are typically hosted by medium-grained poikilitic olivine-orthopyroxenite, whereas deformed sulphides are hosted within shear zones, commonly within anorthosites. Primary and deformed occurrences comprise disseminated, net-textured and massive sulphides. The disseminated and semi-massive to massive sulphide ores from different localities comprise pyrrhotite and pentlandite with minor chalcopyrite. Post-magmatic sulphide alteration and recrystallisation (notably at Stormyra Deposit) are marked by variable (5 to 30%) development of pyrite, which replaces pyrrhotite-dominated masses. The remobilised sulphide assemblages are associated with retrograde silicates (e.g., chlorite and talc). Overall, primary and deformed sulphides can be divided into three main compositional groups based on metal tenors and the concentration of platinum-group elements (PGE): (i) Stormyra, Andreasberg (both deformed) and Megrund (primary) have the highest Ni and Cu tenors (7 to 8.5% and 3 to 3.5%, respectively) and no IPGE (Ir-group PGE) depletion relative to PPGE (Pt-group PGE); (ii) Dalen, Trona, Melgard (primary), Jørstad, Gråhøa and Grimstjønna (deformed) are similar regarding PGE distribution but have lower Ni and Cu tenors (4 to 5.5% and 1.6 to 3%, respectively); and (iii) Niccoline, Storgruva (deformed) and Veslegruva (primary) have comparable Ni and Cu tenors to group (ii), but are IPGE-depleted relative to PPGE (i.e. fractionated PGE distribution). The tenors vary from 0.3 to 2% Ni and 0.25 to 1.5% Cu in remobilised sulphides. Variations in metal tenors are interpreted to reflect a combination of different, but invariably PGE-depleted, parental magmas and variable R-factor regimes (R-factor varying from 350 to 700) during ore formation. The parental magmas can be modelled as the product of 15% mantle melting followed by approximately 2% crystallisation with sulphide removal, which lead to a PGE-depleted nature. Redistribution of sulphides during deformation of the Espedalen Complex seems to have taken place at large and small scales. Large-scale tectonic displacement has no major geochemical impact, whereas local remobilisation yielded sulphide veinlets with low metal tenors. We support that assessing if other geological domains, previously assigned to the Jotun-Valdres Nappe, are correlated or not with the Espedalen Complex is essential for further expanding this prospective area as these terrains could represent potential targets for Ni-Cu-Co deposits.

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.

Prospective assessment of the associated minerals complex in the Konksky and Bilozersky iron ore districts from the Middle-Dniprean mega-block of the Ukrainian shield

Purpose.To determine the material composition, formational types and justify the prospects for the development of metallic and non-metallic minerals complex accompanying ore occurrences and iron deposits in the Konksky and Belozersky iron ore regions of the Middle Dnieper megablock of the Ukrainian Shield. Methods.In the process of carrying out research tasks, traditional methods of studying the material composition of minerals were used - petrographic, mineragraphic, interpretation of X-ray diffraction, thermal, and chemical analyzes were carried out. An ore formation analysis of ore occurrences of minerals accompanying iron in the Konksky and Belozersky iron ore regions was carried out. Findings.The features of the geological structure, material composition, and the influence of secondary alterations of rocks and ores on the prospects for the ore content of associated minerals accompanying iron deposits and occurrences in the study areas are characterized. The ore formation types, the genesis of ore occurrences are substantiated, and the prospects for the integrated use of raw materials accompanying iron ore deposits in the Konksky and Belozersky regions are determined. The originality.The systematic generalization of factual material regarding geological and ore formations in the Konkskaya and Belozerskaya greenstone structures, the substantiation of the possibility for using the results for metallogenic forecasting, in particular, hidden ore and the substantiation of the possibility of integrated use of the subsoil of the study areas. Practical implementation is justified by the possibility of using research results in the process of exploration and development work for a complex of associated minerals within the research area. An assessment of the prospects for the use of minerals accompanying deposits of strategically important iron ore raw materials will make it possible to ensure the comprehensive use of the subsoil of iron ore areas.

Conditions of Formation of Epithermal Mineralization of the Kyplatap Volcanic Field (Central Chukotka)

The article considers the geochemical features and conditions of the formation of substantially silver mineralization of the Kyplatap volcanic field (KVF), of the Chaunsky zone, of the Central Chukchi Sector, of the Okhotsk-Chukchi volcanic belt (OChVB). New data on the composition, distribution and grade of trace elements, including REE in ores, are presented. The noticeable enrichment REE of the studied samples, the predominance of light lanthanides over heavy ones, very low Eu/Sm ratios (\( \ll {\kern 1pt} 1\)), weakly inclined near–chondrite spectra with obvious Eu minima are typical for the epithermal ore-forming system of the KVF. The Ce/Ce* vary from slightly negative to moderately positive values (from 0.81 to 1.38), and the Eu/Eu* vary from 0.28 to 0.7. This combination of Ce/Ce* and Eu/Eu* indicates the oxidative conditions prevailing during ore formation. The results of thermo- and cryometric studies of fluid inclusions in quartz allowed us to establish that the ore-forming fluid contained Na, Mg and K chlorides, epithermal mineralization was deposited by homogeneous hydrothermal fluids with salt concentrations (0.3–6.2 wt. %-eq. NaCl), fluid density – 0.60–0.87 g/cm3, at temperatures from 203 to 343°C, water vapor pressure varied from 40 to 140 bar. The obtained geochemical and thermometric data confirm the assumption put forward earlier – that the studied mineralization of KVF belongs to the intermediate sulfidation epithermal class. These data point to andesite magmas and meteoric waters as the most likely sources of fluids. The information in the article is of practical importance for regional predictive metallogenic constructions, prospecting and evaluation of epithermal Au–Ag deposits.

Geology, geochemistry, fluid inclusion microthermometry and depositional environment of the Early Cretaceous Meymeh sub-seafloor replacement sideritic-ankeritic iron deposit, Malayer-Esfahan Metallogenic Belt, Iran

Meymeh sideritic-ankeritic iron deposit in the eastern part of Malayer-Esfahan Metallogenic Belt (MEMB) is formed in the sedimentary-volcanic rocks of the Early Cretaceous sequence. Ore mineralization in the study area based on stratigraphic location and type of host rocks divided in two ore horizons. Lower ore horizon located in the dolomitic-sandy limestone (Kc3) unit, which upper ore horizon is formed in thin-bedded limestone (Km) rocks. Petrographic studies indicates that mineralization comprises three ore facies: stockwork, bedded and massive ore facies. The most important primary minerals are siderite, ankerite, ferroan-dolomite, pyrite, pyrolusite, barite and minor chalcopyrite. The most frequent textures in the ore zones include laminae, replacement, vein-veinlet, massive and banded. Dolomitization and silicification are the main wall rock alteration styles; alteration intensity increases towards the ore zones. Based on relationships between ore minerals and rock forming minerals, ore mineralization (hypogene and supergene) in the Meymeh deposit formed during three main stages: fine-grained Fe-carbonate bands are intricately interlayered with dolomite beds. Sideritic-ankeritic bands exhibit classic sedimentary textures, such as laminations and bedding, indicative of a syn-sedimentary to early diagenesis origin. Coarser-grained stage two siderites and ankerites show breccia and vein-veinlet textures, and are considered to have formed by replacement during burial diagenetic sub-seafloor fluid flow. In stage three, siderite and ankerite were converted to secondary iron oxides such as oxide/hydroxide Fe minerals during meteoric water flow through the inverted normal and thrust faults and uplift. The primary two-phase fluid inclusions in the quartz-2 and ankerite-2 minerals that have been investigated from the ore mineralization section of the Meymeh deposit are homogenized at temperatures between 110.3 to 226.9 °C. Salinities of the primary fluid inclusions range from 3.39 wt.% to 14.77 % NaCl eq. This finding suggests that hydrothermal brine fluid mixing with seawater could be the primary mechanism that prompted ore formation. The similarity of REE patterns between siderite and ankerite in different ore facies and host rock carbonates indicates their derivation from the same ore fluids. The Meymeh deposit is considered a typical case of sedimentary hydrothermal diagenetic sideritic-ankeritic mineralization, in which minerals deposited when hydrothermal fluid was released from anoxic to suboxic water columns.

Geology, fluid inclusions, and isotope signatures reveal hydrothermal evolution and genesis of the Aqishan Pb-Zn deposit in Eastern Tianshan and implications for exploration of skarn mineralization

The Aqishan deposit (1.97 Mt at 1.05 % Pb + Zn) is located in the Aqishan-Yamansu arc, on the southwest section of the Eastern Tianshan, Northwest China. Pb-Zn mineralization is mainly hosted by garnet skarn and the volcaniclastic rocks of the Yamansu Formation. To decipher the evolution of ore fluids and source(s) of ore-forming components, and constrain the ore genesis, a combination of geological work, fluid inclusions, and C-O-S-Pb isotope systematics is presented. Detailed field and microscopic observations reveal that the skarn alteration and ore formation at Aqishan could be divided into four hydrothermal stages, consisting of prograde skarn (I), retrograde skarn (II), quartz–sulfides (III), and carbonate stage (IV). Sphalerite and galena are the dominant ore minerals generally occurring as disseminations and veins with locally laminated ores in stage III. Fluid inclusion data show that the fluids responsible for prograde skarn are high-temperature (342–518 °C) and high-salinity (7.3–44.2 wt% NaCl equiv.), and recorded fluid phase separation from an intermediate-salinity supercritical fluid, which was exsolved from crystallizing granitic magma. Microthermobarometry results limit the retrograde alteration within the temperature range of 313 to 388 °C and trapping pressures of 98 to 241 bars (1.0–2.5 km), with pressure dropping from lithostatic to hydrostatic regimes associated with a phase separation event. The boiling fluid inclusions in ore stage quartz show that the Pb-Zn mineralization formed at 205–357 °C, with a decrease in temperature facilitating the precipitation of ore-forming metals from hydrothermal system. Carbon and oxygen isotope compositions of calcite indicate a predominantly magmatic source for ore fluids at Aqishan with later meteoric water involved. Bulk and in situ sulfur values of sulfides range from −6.4 to −0.7 ‰, consistent with a dominantly magmatic origin. Sulfides together with the granite porphyry and tuff, show relatively homogeneous Pb isotope compositions, indicating that abundant ore-forming metals were sourced from a magmatic reservoir with contribution from country rocks. Fluid inclusion study and available calcite C-O isotopes suggest that significant decrease in temperature and fluid-rock interactions remarkably contributed to the metal deposition at Aqishan. The skarn alteration with typical alteration assemblages of garnet–diopside is proposed as an effective mineral exploration target of skarn(–like) ores in Eastern Tianshan.

Role of volatiles in intrusion emplacement and sulfide deposition in the supergiant Norilsk-Talnakh Ni-Cu-PGE ore deposits

Abstract The Norilsk-Talnakh orebodies in Siberia are some of the largest examples on Earth of magmatic Ni–Cu–platinum group element (PGE) deposits, formed by segregation of immiscible sulfide melts from silicate magmas. They show distinctive features attributable to degassing of a magmatic vapor phase during ore formation, including: vesiculation of the host intrusions, widespread intrusion breccias, and extensive hydrofracturing, skarns, and metasomatic replacement in the country rocks. Much of the magmatic sulfide was generated by assimilation of anhydrite and carbonaceous material, leading to injection of a suspension of fine sulfide droplets attached to gas bubbles into propagating tube-like host sills (“chonoliths”). Catastrophic vapor phase exsolution associated with a drop in magma overpressure at the transition from vertical to horizontal magma flow enabled explosive propagation of chonoliths, rapid “harvesting” and gravity deposition of the characteristic coarse sulfide globules that form much of the ore, and extensive magmatic fluid interaction with country rocks.

Formation of Fluorapatite in the Equilibrium System CaO–P2O5–HF–H2O at 298 K in a Nitrogen Atmosphere

The process of biomineralization of apatite in nature has been studied by scientists from various fields of science for more than a century. Unlike the volcanogenic, hydrothermal, and other types of igneous apatites, the genesis of which is entirely clear, the formation of phosphate ores of marine sedimentary origin is still debatable. Since phosphate concentrations in water bodies are too low for the spontaneous precipitation of solid phosphates, the study of different ways for their concentration is of particular interest. In this work, phase equilibria in the system CaO–P2O5–HF–H2O at 298 K, involving fluorapatite formation, have been studied. Fluorapatite is known to be the most common phosphate mineral and the main source of phosphorus on Earth, playing an important role in the mineralization process of dental tissues in vertebrates. The equilibrium in the system defined above was studied at a low mass fraction of the liquid phase components, i.e., in conditions close to natural. It has been shown that the compounds of variable composition with the fluorapatite structure containing HPO42− ions were formed in the acid region of this system. These compounds are formed at pH ≤ 7.0 and have invariant points with monetite, CaHPO4, and fluorite, CaF2. Stoichiometric fluorapatite was formed at the lowest concentrations of the liquid phase components in a neutral and weakly alkaline medium and had an invariant point with Ca(OH)2. The composition of the resulting equilibrium solid phases was found to be dependent on the Ca/P ratio of the initial components and pH of the equilibrium liquid phase. Fluorite CaF2 was present in each sample obtained in this study.

Fe–Cu Isotope Characteristics and Geological Significance of the Yushui Seafloor Massive Sulfide Deposit in the Late Paleozoic Marine Depression, Eastern Guangdong Province

The Yong’an-Meixian Late Paleozoic Hercynian depression, located in western Fujian-eastern Guangdong, is an important metallogenic belt in China. The Yushui copper-polymetallic massive sulfide deposit from the middle part of the depression, with extremely high copper grades, has attracted considerable attention and research interest from geologists for years. In most previous research, the ore-forming material source and metallogenic process were inferred from indirect evidence (i.e., using H-O-C-S isotopic systematics as geochemical tracers). In this paper, the ore-forming process of the Yushui deposit has been studied directly by using nontraditional stable (Fe–Cu) isotopes for the first time, providing new evidence for the genesis of this deposit. The results show that there is a relatively negative Fe-Cu isotopic composition in the Yushui deposit, with δ56Fe values ranging from −0.519 to −1.063‰ and δ65Cu values ranging from −1.539 to −1.609‰, respectively. The fractionation of Fe isotopes is primarily attributed to hydrothermal leaching of the basement strata by ore-forming fluids, along with rapid precipitation of sulfides during the ore-forming process. On the other hand, the fractionation of Cu isotopes is probably controlled by the relatively low temperature of ore formation, sulfide precipitation and the involvement of organic matter in mineralization. Combining our findings with previous studies, the ore-forming materials of the Yushui deposit are likely derived from the basement ore-bearing strata (pre-Devonian strata) through leaching by hydrothermal fluids. Moreover, some of the ore bodies might have been locally overprinted by late-stage hydrothermal reworking and alteration.

Syn-tectonic fluids decoding effects of tectono-metamorphic cycles on regional metallogenic evolution of the Chinese Altai, central Asia

Despite their close temporal and spatial relationships, the effects of tectono-thermal events on ore formation remain obscure. To better understand this process, a comprehensive geochemical investigation on paleofluids from syn-tectonic felsic and quartz veins associated with the Devonian subduction and Permian collision of the Chinese Altai was conducted. We found that the Devonian fluids were organic alkanes-CO2-S-Ca-Mg-rich saline fluids with variable CO2/CH4 (0.09−5.03) and lower F−/SO42− (0.02−0.14) and Al3+/Mg2+ (0−0.11) ratios, whereas the Permian fluids were immiscible fluids including CO2-C4H10-CO-rich oxidized gas bubbles and CH4-C3H8-C2H6-Ca-Na-K-Al-S-Cl-F-rich reduced saline fluids with lower CO2/CH4 (0−1.31, mostly <1) and higher F−/SO42− (0.21−0.76) and Al3+/Mg2+ (0.10−2.56) ratios. The Devonian and Permian fluids also have similar δ13C-CO2 values of −23.8‰ to −3.5‰ and −16.5‰ to −3.7‰, respectively. These data suggest that both fluids derived mainly from devolatilization and dehydration melting of metasediments; the Permian fluids likely involve more biotite melting in the deeper crust and more mantle-derived components, whereas the Devonian fluids contain more meteoric components. Base metal-dominated Devonian mineralization occurred as deep-sourced organic matter- and S-rich fluids promoted base metal migration, whereas the relatively oxidized fluid conditions inhibited the mineralization of many other metals. By contrast, the more reduced and F-rich Permian fluids with more mantle contributions facilitated the extraction of Au and uptakes of rare metals from reworked metasediments and promoted their mineralization. These findings provide a more complete picture of how tectono-thermal events fertilize the crust and demonstrate that syn-tectonic fluids can serve as proxies for metallogenic processes during orogenic cycles in general.

Mineralization age of the Xiangshan uranium ore field, South China redefined by hydrothermal apatite U-Pb geochronology

The Xiangshan volcanic-related uranium ore field, located in the Ganzhou-Hangzhou Uranium-Polymetallic Metallogenic Belt (GHMB) in South China, has been the country’s largest historic uranium producer. Although this ore field has been intensely studied for decades, the absolute age of uranium ore formation was still debated. Conventional U-Pb dates on U-minerals (i.e., pitchblende, brannerite) and Ar-Ar dates on associated alteration minerals (i.e., illite) from different uranium deposits yield a wide range of ages (122 to 85 Ma). The uncertainty regarding the exact timing of uranium mineralization at Xiangshan has limited the development of accurate ore genesis models and precluded a better understanding of the links between metallogenesis and regional-scale geodynamics during the Cretaceous-Tertiary period in South China.In this work, we focus on applying in-situ LA-ICP-MS U-Pb geochronology to magmatic and hydrothermal apatite from two typical uranium ore deposits at Xiangshan, intending to indirectly constrain the exact timing of uranium mineralization and reconstruct the magmatic-hydrothermal history. U-Pb age determinations on magmatic zircon and apatite from the three types of ore-hosting volcanic rocks yielded precise crystallization ages of 133 to 136 Ma and 135 to 140 Ma, respectively. These results are identical within uncertainty to previously reported U-Pb dates obtained in the study area, and thereby tightly constrain the emplacement age of the Xiangshan volcanic complex that hosts uranium deposits. Moreover, the potassium feldspar-biotite Ar-Ar dating for the major volcanic rocks demonstrates that these host rocks were cooled and completely solidified through the biotite/potassium feldspar closure temperature (below 300 °C) at 133–131 Ma. Subhedral or anhedral aggregates of hydrothermal apatite ubiquitously formed in the high-grade uranium ores at the Shannan and Zoujiashan deposits and are commonly intergrown with fluorite, illite and uranium minerals. Relative to magmatic apatite from the host rocks, the hydrothermal apatite is typically characterized by much higher U and Th contents, depletion of LREEs, enrichment in HREEs and a much more pronounced negative Eu anomaly. As such, the hydrothermal apatite is unequivocal of hydrothermal origin and formed synchronously with uranium mineralization. LA-ICP-MS U-Pb dating of these hydrothermal apatite crystals yielded an absolute 206Pb/238U age of 126.7 ± 0.6 Ma for the Shannan deposit and 131.3 ± 7.2 Ma for the Zoujiashan deposit. The new ages are much older (>10 Ma) than those previously reported ages on ore or gangue minerals such as pitchblende and illite. Thus, one unidentified mineralization event likely occurred at ca. 131–127 Ma, soon after solidification and subsequent brittle deformation or faulting within the volcanic caldera. We, therefore, proposed that volcanic magmatism was highly likely to be the ‘heat engine’ driving hydrothermal fluid convection and possibly provide the essential conditions (i.e., magmatic fluids, U sources) for the formation of the U mineralization. Another implication of this study is that dating hydrothermal apatite with high U concentrations associated with uranium mineralization could be considered a complementary geochronological tool in the study of analogous hydrothermal uranium deposits worldwide.

Current actual issues of gold meniralization of the Central Kyzylkum

As a result of the analysis of the data available and collected in recent years, in contrast to the well-established ideas about the polygenic and poly-stage nature of the mineralization, it is indicated that the gold mineralization of the Central Kyzyl Kum is formed as a result of the formation of a single ore-magmatic system, which develops in the same type regardless of the composition and age of the host rocks; during the formation of deposits, the most important thing is the presence of a process that promoted ore formation, which should serve as the basis for judgements in problems of the genesis and forecasting of industrial facilities. Some problematic issues on the geology of ore deposits are noted.

The effect of platinum-group minerals on differentiation of platinum-group elements in magmatic sulfide deposits: Evidence from the Cu-Ni-PGE deposits in the Yangliuping area of the Emeishan large igneous province, SW China

Platinum-group minerals (PGM) are important host phases for platinum-group elements (PGE) in magmatic sulfide deposits. Recent studies have demonstrated that some PGM, such as sperrylite, can crystallize early from sulfide liquids. It is important to determine whether and how these PGM particles affect the enrichment and differentiation of PGE in Cu-Ni-PGE deposits. The magmatic sulfide deposits in the Yangliuping area (mainly consisting of the Yangliuping deposit and Zhengziyanwo deposit) are the largest Cu-Ni-PGE deposits in the Emeishan large igneous province, SW China. Primitive-mantle normalized PGE patterns and fractional crystallization modelling show that massive ores in the Yangliuping deposit are enriched in Pd and Pt. In contrast, massive ores, breccia ores and Cu-rich ores in the Zhengziyanwo deposit are depleted in Pt. Scanning electron microscopy (SEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), focused ion beam (FIB) and transmission electron microscopy (TEM) were used to constrain the occurrence of PGE in the massive ores from the two deposits. Mass balance calculation shows that <7% of Ir, Rh and Pt occur in base metal sulfides (BMS, mainly pyrrhotite, pentlandite and chalcopyrite) as solid solution in both the Yangliuping and Zhengziyanwo massive ores. 17% and 91% Pd are present in solid solution within BMS in the Yangliuping and Zhengziyanwo massive ores, respectively. In the Yangliuping massive ores, PtAs2 and Pd-PGM particles were commonly found within BMS crystals, and Ir-Rh-(Pt) sulfarsenides enclosed in cobaltite-gersdorffite solid solution (CGSS) are enriched in Pt. In contrast, in the Zhengziyanwo massive ores, no PtAs2 particles and fewer Pd-PGM particles were found, and Ir-Rh-(Pt)AsS particles enclosed in CGSS are poor in Pt. The distribution, mineralogy and microstructures of Ir-Rh-(Pt)AsS, PtAs2 and Pd-PGM particles in both the Yangliuping and Zhengziyanwo deposits suggest that they mainly crystallized from sulfide liquids or formed from Pd-Pt-semimetal-rich droplets. We suggest that the incorporation of Pd-PGM and PtAs2 particles into MSS cumulates led to the enrichment of Pd and Pt in the Yangliuping massive ores. In the Zhengziyanwo deposit, early fractional crystallization of PtAs2 reduced the Pt content in sulfide liquids and resulted in the formation of Pt-depleted sulfide ores and low-Pt Ir-Rh-(Pt)AsS particles, but no Pt-rich sulfide ores have been found to date. As a result, the role of PGM particles should be considered when using PGE to trace the formation process of Cu-Ni-PGE deposits. This study also provides additional evidence that the behavior of Pt in sulfide liquids is influenced by thermodynamic conditions and As, and suggests a potential for Pt-rich sulfide ores exploration in the Zhengziyanwo deposit.

Palladian Gold: Chemical Composition, Minerals in Association, and Physicochemical Conditions of Formation at Different Types of Gold Deposits

This paper reviews and summarizes the available information on the composition of palladian gold with various contents and sets of isomorphic impurities (Ag, Cu, Hg) at 50 deposits and ore occurrences with Au-Pd mineralization. It is revealed that Palladian gold is represented by the systems Au–Pd, Au–Pd–Hg, Au–Pd–Cu, and Au–Pd–Ag–Hg, but more frequently corresponds to Au–Pd–Ag, Au–Pd–Ag–Cu, and Au–Pd–Ag–Cu–Hg. Objects with palladian gold belong to different types of gold deposits and to the deposits at which the main components of ores are PGE, Cr, Cu, Ni, V, and Ti. We propose a classification of the types of deposits with palladian gold: (1) PGE ore deposits related to mafic–ultramafic magmatic complexes (two subtypes—(a) low-sulfide-grade (less than 2%–5% sulfides) Alaskan, and (b) high-sulfide-grade (more than 5% sulfides) Norilsk); (2) orogenic gold deposits (OG); (3) epithermal (porphyry) gold–copper deposits (EPGC); (4) iron oxide copper gold deposits (IOCG); (5) ferruginous quartzite deposits; (6) volcanic exhalation; and (7) gold-PGE placers of five subtypes corresponding to the types of 1–5 primary sources. Physicochemical conditions of the formation of palladian gold at some deposits of type 1 cover two areas—magmatic high-temperature and hydrothermal low-temperature. At the majority of deposits of types 2–4, its formation proceeds with the participation of hydrothermal fluids (300–60 °C) of various salinities (0.2–30 wt.% NaCl eq.). Palladian gold is mainly high-fineness (910‰–990‰), is less frequently medium-fineness, and contains Ag and Cu, but does not contain Hg at the deposits of types 1, 3, and 4. The only exception is the Au-Pd-Hg Itchayvayam ore occurrence (Kamchatka, Russia), for which two varieties of Pd,Hg-bearing native gold (fineness 816‰–960‰ and 580‰–660‰) are determined. Low-fineness palladian gold with the major content of Ag is typical of OGD deposits. Medium-fineness palladian gold occurs at ferruginous quartzite deposits and in volcanic exhalations. Hg, Ag, Cu-bearing high-fineness palladian gold is present mainly in placer deposits (type 7). The most common minerals in association with palladian gold are arsenides, stibioarsenides, sulfides, stannides, bismuthides, tellurides, and selenides of Pd and Pt. These are typical of deposit types 1 and 7. The minerals of Au, Ag, and Cu (tetra-auricupride, aurostibite, chalcopyrite, bornite, chalcocite, eucairite, etc.) are in association with palladian gold at OG, EPGC, and IOCG deposits. Hg minerals (cinnabar, tiemannite, coloradoite, potarite) are at some deposits (types 1, 2, 7-1, 7-4). Cu, Fe, and Pd oxides (tenorite, hematite, magnetite, PdO, (Pd,Cu)O) and Fe and Pd hydroxides (goethite, (Fe,Pd)OOH) occur at the deposits of the 3, 4, and 7 groups and indicate the highly oxidizing conditions of ore formation. The most common minerals among host minerals are quartz and muscovite, including fuchsite (Cr-Ms), chlorite, albite, K-feldspar, hornblende, and carbonates (calcite, siderite, etc.). The fineness, content, and set of impurities in palladian gold and minerals in association with it reflect the mineralogy of Au-Pd ores and allow them to be used as indicators for the deposit types.

Formation of Fe-Ti oxide and Ni-Co sulfide ores by concentric tube flow and hydrous metal-rich melt recharge into the cooling crystal mush: Example from the Hongge intrusion in Panxi region, SW China

The Panxi (ultra-)mafic intrusions are relatively small compared with world-class ore-related (ultra-)mafic intrusions, but they host several super-large Fe-Ti oxide deposits and few small Cu-Ni (PGE) sulfide deposits. The mechanisms that concentrate huge amounts of oxide minerals into these small intrusions and form the distinct oxide and sulfide mineralization remain poorly understood. Here, we investigate the magma dynamics that produced extensive Fe-Ti oxide and coexisting Ni-Co sulfide mineralization in the Hongge intrusion of Panxi region, based on detailed field cross-cutting relations and petrographic observations, bulk-ore/rock geochemistry, and in-situ LA-ICP-MS magnetite trace element analyses. The Fe-Ti oxide ores include magnetite-poor (<60 vol%) disseminated and magnetite-rich (>60 vol%) massive types, with the former further divided into the gabbro-hosted (GH) and (olivine-)pyroxenite-hosted (OPH) subtypes. The GH oxide ores have Cr-poor (median 86.9 ppm) magnetite and abundant apatite interstitial to silicate minerals. In contrast, the OPH and massive oxide ores have Cr-rich (median 13,956 ppm) magnetite that envelops resorbed silicate minerals. Principal component analyses of bulk-ore and magnetite elemental contents reveal genetic links between the OPH and massive oxide ores, but remarkable genetic distinction from the GH oxide ores. Considering the overall lopolith-shape orebody geometry of several branch intrusions, the GH oxide ore formation may have involved spontaneous development of concentric tube flow zones within the cooling crystal mush. However, the lower P but much higher Cr-Cu-Co-Ni contents than the GH oxide ores and the sharp intrusion of massive oxide ores into the OPH oxide ores suggests that the OPH and massive oxide ores were probably formed by upward percolation and later intrusion of hydrous Fe-rich melts from a deep-seated magma reservoir into semi-solidified and fossilized mush, respectively. In addition, sulfide ores occur mainly as irregular/lenticular aggregates in massive oxide ores and are depleted in Cu and platinum group elements (PGEs), indicating early, deep-level sulfide segregation that scavenged the Cu and PGEs from the magmas. Hence, we envisage that the assimilation of S-deficient wall-rocks into basaltic magmas may have induced the early sulfide saturation and retain the majority of Fe for later precipitation as principal oxide and minor PGE-Cu-depleted sulfide ores.