Ore Geology Reviews最新文献

Ion-absorption rare earth element (REE) deposits in South China are the world’s most important source of heavy REEs (HREEs). These deposits were formed by the weathering of granitic rocks whose formation involved primary HREE enrichment. Previous studies have identified the key role of late-stage magmatic evolution, especially the magmatic–hydrothermal transition stage played in HREE enrichment, but the detailed processes need further investigation. Garnet is a common HREE carrier in parent rocks and also a main contributor of these elements in formation of ion-absorption HREE deposits. Here, we investigate textural and compositional variations in garnets from parent rock (muscovite granite) of the Dabu ion-absorption HREE deposit to constrain the primary HREE enrichment of the parent rock during late-stage magmatic evolution. Mass-balance calculations reveal that garnet accounts for ∼67 % of the Y and 64 % of the REEs in the Dabu muscovite granite. The garnets can be classified into three types: i) magmatic garnets (Grt-1A) are intergrown with plagioclase, K-feldspar, and quartz, host both melt and mineral inclusions, and have high REE + Y contents (6488–19,215 ppm); ii) magmatic–hydrothermal garnets (Grt-1B) occur as overgrowths on Grt-1A, host both melt and fluid inclusions, and have intermediate REE + Y contents (2681–8683 ppm); and iii) hydrothermal garnets (Grt-2) are intergranular with quartz and altered biotite, host primary fluid inclusions, and have the lowest REE + Y contents (476–1247 ppm). The texture and composition of the three types of garnet indicate that the magma have undergone a transition from a volatile-undersaturated to a volatile-oversaturated aqueous system. The fluid, from which some REE minerals precipitated, present in the magma system was derived from the magma itself rather than from an external source, as evidenced by the similarity in Nd isotopic composition between the REE minerals and the whole-rock samples. During this transition, the presence of high-HREE garnet prevents the HREE partitioning into refractory minerals (e.g., zircon, REE-bearing phosphate) or extracting from the magma system by the fluid. Our findings show that granites containing high-HREE garnet have high potential for forming ion-absorption HREE deposits and that garnet can reliably record their magmatic evolution.

Volcanogenic massive sulfide (VMS) deposits are widely distributed both geographically and temporally, occurring from ancient Archean cratons to modern submarine volcanic environments, with a notable surge during the Paleozoic era. The North Qilian orogenic belt in China is a prominent Paleozoic VMS metallogenic province, shaped by complex geological processes such as the opening of the Qilian Ocean, oceanic subduction, and arc-continent collision. Previous research has constrained the timing of VMS mineralization in the North Qilian to between 440 and 470 Ma, identifying two primary deposit types: Kuroko-type and Cyprus-type. However, ongoing debates persist regarding the classification and geodynamic framework of these VMS deposits. The recent surge in international research on VMS deposit classification and tectonic settings has prompted a reassessment of VMS mineralization within the North Qilian belt. This study revisits the geological and geochemical characteristics of VMS deposits in the region, identifying two distinct types: Mafic VMS deposits and Bimodal-Felsic VMS deposits. Furthermore, the metallogenic dynamics of the Shijuli, Jiugequan, and Baiyinchang deposits have been re-evaluated in the context of the structural evolution and contemporary interpretations in this area.

Massive sulfides and sulfide-bearing breccia were collected from the Forecast vent field in the southern Mariana Trough. These samples exhibit varying degrees of hydrothermal alteration and/or mineralization, with the former type having significant enrichments in Au (up to 101 ppm). In this study, detailed analyses of mineralogy, geochemistry, S isotope, and fluid inclusion were conducted to understand the unusual Au-rich mineralization. Mineralogical investigations and geochemical analyses (LA–ICP–MS and EPMA) of dominant sulfide minerals indicate that electrums, the main phase of Au mineralization, are characterized by two different generations based on mineralogical relationships and fineness. Early-stage high fineness electrums (930–981 ‰) are associated with sphalerite under relatively high-temperature fluid conditions, whereas galena is main host mineral related to late-stage low fineness electrums (773–868 ‰). Sphalerite geothermometry (231–264 °C), the occurrence of colloform textured sulfides, and microthermometric characteristics of fluid inclusions (T_h = 220–304 °C; Salinity = 1.4–6.6 wt% NaCl equivalent; a general trend of decreasing salinity with decreasing T_h) indicate that significant decreases in H₂S activity, attributed to seawater dilution and rapid precipitation of sulfide minerals, facilitated the efficient destabilization and deposition of Au transported as sulfide complexes from hydrothermal fluids. In particular, the lower ³⁴S values (+0.2 ‰ to + 1.3 ‰) of sulfides compared to those of arc/back-arc lavas (δ³⁴S = +5‰ to + 11 ‰), along with the prevalence of CO₂ in the vapor phase of fluid inclusions, reflect that the significant contribution of magmatic volatile influx supplied most of the sulfur and metals (including Au) to the Forecast hydrothermal fluids. Additionally, the abundance of montmorillonite and varying proportions of sulfide and gangue minerals observed in hydrothermal samples suggest that the chemical buffering of fluids by associated substrates and/or sediments could be another significant factor in promoting Au-rich mineralization. Therefore we conclude that the combination of magmatic fluid–seawater mixing and host rock alteration plays an important role in the formation of Au-enriched massive sulfides in the Forecast vent field.

Yongping copper deposit is a large-scale polymetallic mine that contains 1.6 Mt of proven Cu metal reserves with an average grade of 0.74 % and contributes significantly to China’s production of copper. This deposit is situated in the eastern part of the Qin-Hang Metallogenic Belt (Jiangxi province, SE China) at the contact zone between the Yangtze Cu–Mo metallogenic belt and the Jiangxi W–Sn–REE metallogenic belt. The thick stratiform and lenticular-shaped orebodies are hosted in the Carboniferous Yejiawan Formation, consisting of sandstone, limestone, mudstone, and chert-rich clastic rocks. Dominant metal-bearing minerals are chalcopyrite and pyrite with a minor amount of sphalerite, tetrahedrite, galena, molybdenite, pyrrhotite, magnetite, hematite, and scheelite. Although intensive research has been done on its geological setting, geochemical characteristics, and geodynamic evolution over the past thirty years, the origin and depositional environments have remained controversial. In the current research, in situ trace element geochemistry and sulfur isotope analyses, coupled with microscopic investigation, were conducted on sulfide minerals using the LA-ICP-MS technique. The results display that Yongping pyrite rich in Co, As, Ni, Zn, Cu, and Te and deplete in other trace elements. Sphalerite rich in Fe, Mn, Cu, and Cd, followed by In, Co and Ga. The calculation results of formula T(°C) = (Fe/Zn + 0.2953)/(0.0013) reveal that sphalerite was formed in medium–high temperature conditions (262 °C–377 °C). The δ³⁴S_V-CDT values of studied sulfides (pyrite, chalcopyrite, sphalerite, and tetrahedrite) varied from −1.52 ‰ to 5.13 ‰ with an average of 2.36 ‰, which are highly consistent with those recorded from porphyritic biotite granite stock of Shizitou (from 2.20 ‰ to 4.5 ‰), suggesting a dominantly magmatic origin. Collectively, trace element compositions of analyzed sphalerite and pyrite from the Yongping area exhibit characteristics of typical skarn deposits. Combined with previous studies, we can conclude that the Yongping Cu deposit is a skarn deposit that was most likely formed by contact metasomatism after the intrusion of the Jurassic Huoshaogang-Shizitou granitic stock into the Carboniferous Yejiawan Formation.

The West Junggar in Xinjiang, western China, represents a significant gold mineralization belt hosting over 200 gold deposits, with the Hatu gold deposit being the largest among them. In this study, ore geology and fluid inclusion assemblages of quartz samples from the Hatu gold deposit were investigated in an effort to clarify the mineralization process and its relationship with the geodynamic settings. The mineralization process is delineated into early (pyrite-albite-quartz veins), middle-a (quartz-ankerite veins), middle-b (quartz-ankerite-sulfide-native gold veins), and late (quartz-calcite veins) stages. The early stage veins suggest a compressional setting while the middle-a and middle-b stage veins suggest a tensional shear setting. The late stage veins are typically filled fissures cutting through earlier veins. Scanning electron microscope-cathodoluminescence (SEM-CL) reveals that early stage quartz (Q1) exhibits concentric CL-oscillatory growth zoning, while middle-a stage quartz (Q2a) displays unidirectional zoning and ranges from CL-bright to CL-dark, middle-b stage quartz (Q2b) is CL-bright and weakly zoned, and late-stage euhedral quartz (Q3) shows sector zoning transitioning from CL-gray to CL-dark. Quartz that formed in these stages developed three types of fluid inclusions: pure CO₂ (PC-type), CO₂–H₂O (C-type), and H₂O–NaCl (W-type). The early stage quartz contains C- and W-type fluid inclusions homogenizing at 309–345 °C, while the late stage quartz contains only W-type fluid inclusions with homogenization temperatures of 164–229 °C. Microthermometry of fluid inclusion indicated the evolutionary of the metallogenic fluid from a high-temperature, CO₂-rich, and minor CH₄ metamorphic fluid to a low-temperature, CO₂-poor meteoric fluid. From the early to middle-a stages, fluid boiling caused the unloading of ore-forming elements whereas fluid mixing led to the precipitation of polymetallic sulfides and gold in the middle-b stage. Trapping pressures in the middle-b stage were estimated using C-type inclusions, illustrating that gold mineralization took placed at depth of 8.0 km. We propose classifying the Hatu gold deposit as an orogenic deposit, originating from the collisional orogenesis between the Yili-Kazakhstan and Siberian continents in the Late Carboniferous.

Marine cobalt-rich (Co-rich) crusts are submarine critical metal resources with high economic value. In this study, detailed in-situ fine-scale morphological, mineralogical, and geochemical analyses were conducted on Co-rich crust from the Western Pacific. The Co-rich crust can be divided into three layers: (1) Layer 1 is the oldest anthracite layer and contacts with the substrate, showing a very dense laminated/columnar texture. Layer 1 can be further divided into two distinct sublayers: a lower black, massive, dense sublayer (Layer 1–1) and an upper black-to-brown sublayer (Layer 1–2). (2) Layer 2 is porous and locally vuggy, and its pore space is filled with a large amount of silicate detrital minerals and clay minerals. (3) Layer 3, on the top, is black and dense, with a dendritic, columnar/laminated texture. Co is very unevenly distributed throughout the whole crust, with three distinct Co-rich areas. Layer 3 is a typical hydrogenetic crust and has not undergone late alteration. The main processes for Co enrichment are specific adsorption-oxidation on Mn-oxides and the structural incorporation of Co³⁺ into Mn-oxide phases. The average Co content of the Layer 3 is much higher than that of the other two layers. The presence of abundant detrital and clay minerals, along with high levels of Al, Si, and Ti in Layer 2, indicates the incorporation of terrigenous material, resulting in a high average growth rate. However, these processes are not conducive to Co enrichment. In the phosphatized Layer 1, fluctuations in element content are significantly greater than in the upper, non-phosphatized layers. Phosphatization has resulted in the partial decomposition of the initial Co-rich micro-layers, which may have reactivated and migrated Co, contributing to secondary Co enrichment.

The Xilaokou gold deposit with ca. 50 t of gold reserve @ 2.7 g/t represents a novel type (carbonate-sulfide vein type) of gold mineralization within the Jiaodong gold province. However, its mineralization age and metallogenic mechanism remain poorly constrained, hindering a comprehensive understanding of the ore-forming processes in the Jiaodong gold province. In this study, we employ syn-ore stage hydrothermal monazite in situ U-Pb geochronology to determine the ore-forming age of the Xilaokou gold deposit. Additionally, we conduct in situ LA-(MC)-ICP-MS elemental mapping and sulfur isotope analysis in ore-related pyrite to unravel the sulfur source(s) and provide new insights into the ore-forming processes of the Xilaokou gold deposit. Our findings reveal the following key points: (1) U-Pb dating of hydrothermal monazite in Au-bearing pyrite yields an ore-forming age of 119.9 ± 3.0 Ma. This age is consistent with the mineralization ages (around 120 ± 5 Ma) of other gold deposits in the region, including Liaoshang-, Jiaojia-, and Linglong-type deposits. (2) Gold in pyrite primarily occurs as micro-grains (5–20 μm) within pyrite fissures associated with sphalerite and galena. (3) Elemental mapping and sulfur isotope analysis indicate that major Au mineralization is linked to elevated concentrations of As, Sb, and Tl, along with heavy sulfur isotope values (δ³⁴S∼24.7 ‰). (4) Early-stage Au mineralization is characterized by enrichment of As, Cu, and Bi, with normal sulfur isotopic composition (δ³⁴S∼8 ‰). We propose that the carbonate-sulfide vein type gold deposits represented by the Liaoshang and Xilaokou gold deposits in the Jiaodong gold province are genetically linked to quartz-sulfide vein and disseminated type deposits. The major ore-forming stage involved the addition of S and Au from a metamorphic massif at slightly lower temperatures. These findings highlight a new exploration direction within the North China Craton. In summary, the Xilaokou gold deposit provides valuable insights into gold mineralization processes in Jiaodong, emphasizing the importance of considering diverse deposit types and their genetic relationships in the region.

The Skouries Au-Cu porphyry deposit is located in northern Greece and hosted by quartz monzonites and monzogranites of early Miocene age (∼20 Myr). The host rocks show geochemical similarities to other mafic to felsic intrusions in the district that have a similar strike direction, but which are 6 Myr older and lack evidence of economic mineralization. The Skouries magmas probably formed by fractional crystallization of mafic mantle-derived melts, from which the ore-forming fluids were released during second boiling accompanied by massive feldspar crystallization at ∼65 wt% SiO₂. Drill core samples record the dominant potassic alteration with A- and B-type veins, which are locally overprinted by chlorite-sericite alteration and related C-type veins, transitioning into sericitic alteration assemblages and D-type veins. The ore mineralization is characterized by chalcopyrite, bornite, pyrite, magnetite and accessory minerals, such as tellurides and PGE minerals. Incompatible trace element ratios of the host rocks, that are commonly used as tracers of magma fertility (e.g., Sr/Y, La/Sm), vary between the alteration-types and may therefore not generally provide a record of magmatic processes. Fluid inclusion and Ti-in-quartz thermometry yielded a temperature range of 520 to >600 °C for the A-type veins and 420 to 500 °C for the B-type veins. Decreasing fluid inclusion entrapment pressures suggest relatively rapid uplift of the hydrothermal system during the early- to main porphyry stage. Fluid inclusion compositions indicate that early K- and Cl-rich fluids caused the potassic alteration resulting in a strong mobilization of REEs, following a decrease in fluid salinity and temperature with proceeding porphyry evolution. Systematic variations in trace element contents (e.g., As, Ag, Pb) and ratios (e.g., As/Sb, Zn/Pb) of pyrite record fluid temperature changes and suggest early phase separation as a major ore-forming process. The common occurrence of native Au as inclusions in pyrite and chalcopyrite are indicative of early Au oversaturation in the fluid, which we relate to sulfide precipitation and phase separation, destabilizing the AuHS⁰ or Au(HS)₂^- complex, leading to the accumulation of Au particles. The formation of such Au colloids in fluids may thus reflect an important step towards the hydrothermal enrichment of Au in porphyry environments.

Bauxites are an excellent indicator of tropical palaeoclimate and subaerial exposure in the geologic record, where the study of their structures, textures, mineralogy, geochemistry, and cover deposits can provide invaluable insight into the palaeoclimatic and palaeoenvironmental conditions during their formation. The present study focuses on these aspects of the bauxite and its cover from the Rovinj-1 deposit with the aim of reconstructing the evolution of the palaeoclimate and palaeoenvironments during its formation.

The Rovinj-1 deposit formed during the early Kimmeridgian to late Tithonian subaerial exposure phase on the Istrian part of the Adriatic Carbonate Platform (AdCP). The bauxite formation can be divided into two phases: (1) the formation of pelitomorphic bauxite under humid tropical climate, and (2) the erosion and redeposition of bauxite at the end of its formation due to climatic aridification. The climate aridification also led to increased iron oxide formation, which scavenged numerous trace elements, especially light and middle rare earth elements, causing their increase in the upper part of the deposit. The upper part also exhibits negative Ce anomalies, while the lower part displays high Ce anomalies. The bauxite formation was followed by an internal transgression during which a karstic lake formed above the bauxite. At the beggining of the transgression, the deposition of the alternation of limestones and clays started under anoxic to euxinic conditions, and equivocal to oxic conditions towards the end of the transgression, indicating the shift in lake conditions from restricted to open which is also supported by the presence of glauconite as this reflects the increasing marine influence. This sequence was interpreted as a blue hole sequence. The clays/marls of the cover sequence also reflect climatic aridification as they show a gradual increase in mixed-layer illite–smectite and illite content and a decrease in kaolinite content. The end of this regional subaerial exposure phase and the restoration of full-marine carbonate deposition is marked by the deposition of the limestones of Kirmenjak unit covering the bauxite deposit. Overall, this study enabled a detailed palaeoclimatic and palaeoenvironmental reconstruction of the Istrian part of the AdCP, expanding the current knowledge of the conditions at the AdCP during the Late Jurassic.