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The Hongtoushan Cu-Zn volcanogenic massive sulfide (VMS) deposit, located in the Hunbei granite–greenstone terrane of the North China Craton, has undergone a complex, multi-stage metallogenic evolution. The deposit comprises three main types of massive ores: Type-1 ores, characterized by a sulfide matrix enclosing granular quartz and dark mineral aggregates; Type-2 ores, distinguished by large pyrite and pyrrhotite porphyroblasts and a small amount of gangue minerals; and Type-3 ores, mainly distributed in the contact zone between the ore body and gneiss, featuring remobilized chalcopyrite and sphalerite filling the cracks of pyrite. The metallogenic process of the Hongtoushan deposit is divided into three main stages: (1) an early mineralization stage forming Type-1 massive ores; (2) a metamorphic recrystallization stage resulting in Type-2 massive ores with distinct textural features; and (3) a late-stage mineralization event producing Type-3 massive ores enriched in Cu, Zn, and other metals. This study integrates sulfur isotope, trace elements, and fluid inclusion data to constrain the sources of ore-forming materials, fluid evolution and metallogenic processes of the deposit. Sulfur isotope analyses of sulfide samples yield δ 34 S values ranging from −0.7 to 4.2 (mean: 1.8 ± 1.5, 1 σ), suggesting a predominant magmatic sulfur source with possible contributions from Archean seawater. Trace element analyses of pyrite grains from different ore types reveal a depletion of rare earth elements, Cu, and Zn in Type-2 massive ores due to metamorphic recrystallization, and a subsequent re-enrichment of these elements in Type-3 massive ores. Fluid inclusion studies allowed for identifying three types of ore-forming fluids: Type-1 (avg. T h : 222.9; salinity: 6.74 wt.% NaCl eqv.), Type-2 (avg. T h : 185.72; salinity: 16.56 wt.% NaCl eqv.), and Type-3 (avg. T h : 184.81; salinity: 16.22 wt.% NaCl eqv.), representing a complex evolution involving cooling, water–rock interaction and fluid mixing. This multi-disciplinary study reveals the interplay of magmatic, hydrothermal and metamorphic processes in the formation of the Hongtoushan VMS deposit, providing new insights into the fluid evolution and metallogenic mechanisms of similar deposits in ancient granite–greenstone terranes. [ABSTRACT FROM AUTHOR]

At the Trans‐Atlantic Geotraverse hydrothermal field, metalliferous sediments cover extinct hydrothermal mounds and the surrounding seafloor. Here, we report the morphological, mineralogical and geochemical processes that deposit these sediments, remobilize their metals, and affect their preservation. We found that the initial sediment metal tenor is controlled by physical transport of hydrothermal material from its source, followed by diagenetic redistribution and potentially diffuse fluid flow after high‐temperature hydrothermal activity has ceased. We distinguished three different environments: (a) proximal metalliferous sediments on top of extinct mounds are mainly derived from oxidative weathering of primary sulfide structures and are predominantly composed of Fe oxyhydroxides with low contents of Cu, Co, and Zn; metal enrichments in specific layers are likely related to upward flow of low‐temperature hydrothermal fluids; (b) medial distant metalliferous sediments found at the base of the mounds, deposited by mass transport, contain cm‐thick layers of unsorted sulfide sands with high base metal contents (e.g., up to 28% Cu); these buried sulfides continue to undergo dissolution, resulting in metal release into porewaters; (c) distal metalliferous sediments, found in depositional basins a few hundreds of meters from the extinct mounds, include fining‐upwards sequences of thin sulfide sand layers with Fe oxyhydroxides and were deposited by recurrent turbiditic flows. Dissolved metals (e.g., Cu2+ and Mn2+) diffuse upwards under reducing conditions and precipitate within the sediment. Hence, when using hydrothermal sediments to construct reliable geochronological records of hydrothermal activity, distance from source, local seafloor morphology, mass‐transport and depositional, and diagenetic modification should all be considered. Plain Language Summary: The seafloor massive sulfide mounds at the TAG hydrothermal field (Mid‐Atlantic Ridge) are surrounded by metalliferous sediments. These sediments can be used to understand the history of the hydrothermal activity; however, the evolution of these sediments can be complex. The aim of this study is to understand the processes that lead to the accumulation and alteration of these sediments. For this, we identified the mineralogical, geochemical and physical processes that affect the sediments. Our results show that sediments found on mound tops are mainly composed of iron and manganese oxides and hydroxides, and are low in other metal contents compared to other environments. Medial distant sediments at the base of the mounds have thick beds of sulfide‐rich sediments that contain the highest concentrations of metals and are currently undergoing dissolution. In depositional channels, several hundreds of meters distal from the mounds, metalliferous sediment have accumulated in several meters thick layers that contain high concentrations of dissolved metals. This study reveals that the metal content of hydrothermal sediments is strongly controlled by their physicochemical environment and processes after deposition, and we suggest these processes should be considered when using metalliferous sediments as records of the evolution and activity of hydrothermal systems. Key Points: TAG hydrothermal field sediments have high metal contents that vary distinctly between different seafloor depositional environmentsLowest metal contents are found in sediments on top and highest in those at the base of extinct hydrothermal moundsDeposition, remobilization, and preservation of metals in hydrothermal sediments lead to distinctively different sediment characteristics [ABSTRACT FROM AUTHOR]

Many studies have proved the usefulness of Li-mica and chlorite geochemistry as indicators of the chemical and thermal evolution of magmatic systems. This study highlights the suitability of Li-micas as tracers of hydrothermal mineralizing events in world-class W-Sn deposits associated with Jurassic (190-150 Ma) granites in China through the complex magmatic-hydrothermal evolution of the Piaotang deposit (South Jiangxi). A paragenetic sequence has been established for the Piaotang deposit comprising (1) a first "silicate-oxide" stage that hosts abundant W-Sn mineralization (wolframite and cassiterite), (2) a "calcic" stage with scheelite and wolframite, (3) a "base metal sulfides" stage with cassiterite and wolframite, and (4) a late "sulfide" stage, involving for the first time a polyphase emplacement of the mineralization. Li-micas from the underlying granite, greisen, and the different stages represented in the veins, were studied. The chemistry of the micas (characterized by intermediate compositions between phlogopite-zinnwaldite-muscovite poles) demonstrates the presence of end-members representing three different fluids that were involved in the emplacement of the Piaotang deposit. These end-members can be linked to previous fluid inclusion studies conducted on this deposit. The three fluids are identified to be magmatic, meteoric (as previously reported in the literature), and also metamorphic, and are shown to have mixed throughout the different stages. Moreover, it appears that the magmatic fluids could not have been derived from the Piaotang biotite granite but instead must have originated from a more evolved rare metal granite that is presently unidentified. These fluids were responsible for the greisenization. Finally, chlorite geochemistry reveals the occurrence of a heating process (from 200 °C in stage II to 300 °C in stage III) during the post-mineralizing stages, which was responsible for the precipitation of new generations of ore-bearing minerals (cassiterite and wolframite) concomitant with a continuous gain of metals during the emplacement of the Piaotang deposit. [ABSTRACT FROM AUTHOR]

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The platinum-bearing Paleoproterozoic Vurechuaivench Massif in the Monchegorsk Pluton is made up of amphibolized and saussuritized gabbronorites, anorthosites, and norites. The geochemical features of the massif rocks are considered at four detailed areas. It was confirmed that the Vurechuaivench and Nyud-Poaz massifs are geochemically similar. The rare-earth element (REE) distribution in the rocks of the Vurechuaivench Massif is peculiar in the low total REE content (9.4-27.6 ppm), negative REE slope, significant LREE enrichment [La/Yb] = 3.7-8.7), and distinctly expressed positive Eu anomaly ([Eu/Eu*] = 1.2-2.2). The REE distribution pattern remains unchangeable throughout the entire section, including the rocks of the Pt reef, with a gradual upsection REE increase. It is suggested that the PGE reef of the Vurechuaivench Massif, as the Platinova Reef (Skaergaard massif) and Sonju-Lake Intrusion (Duluth complex), was formed during fractional crystallization in a large magma chamber without new magma influx. It is conceivable that the Vurechuaivench Massif is the allochthonous fragment of a large loppolith-like body, the lower portions of which compose the Nyud-Poaz Massif, while the middle part was almost completely eroded. [ABSTRACT FROM AUTHOR]

The axinite-bearing Gukjeon Pb–Zn deposit is hosted by the limestone, a member of the Jeonggaksan Formation, which, in turn, forms the part of the Jusasan subgroup of the Yucheon Group in the Gyeongsang Basin in the southeastern part of the Korean Peninsula. In this study, we attempted to interpret the spatial and temporal relationships among geologic events, including the mineralization of this deposit. We constructed a new 3D orebody model and suggested a relationship between skarn alteration and related mineralization. Mineralization timing was constrained using SHRIMP zircon age dating results combined with boron geochemistry on coeval intrusive rocks. Skarn alterations are restrictively found in several horizons of the limestone formation. The major skarn minerals are garnet (grossular), pyroxene (hedenbergite), amphibole (actinolite and ferro-actinolite), axinite (tizenite and ferro-axinite), and epidote (clinozoisite and epidote). The three stages of pre-skarn, syn-skarn, and post-skarn alteration are recognized within the deposit. The syn-skarn alteration is characterized by prograde metasomatic pyroxene and garnet, and the retrograde metasomatic amphibole, axinite, and epidote. Major skarn sulfide minerals are sphalerite, chalcopyrite, galena, and pyrite, which were predominantly precipitated during the retrograde stage and formed amphibole and axinite skarns. The skarn orebodies seem to be disc- or flat-shaped with a convex form at the central part of the orebodies. The vertical ascending and horizontal infiltration of boron-rich hydrothermal fluid probably controlled the geometry of the orebodies. Considering the whole-rock major, trace, and boron geochemical and geochronological results, the timing of Pb–Zn mineralization can be tightly constrained between the emplacement of boron-poor intrusion (fine-grained granodiorite, 82.8 Ma) and boron-rich intrusion (porphyritic andesite in Beomdori andesitic rocks, 83.8 Ma) in a back-arc basin setting. The boron for mineralization was sourced from late Cretaceous (Campanian), subduction-related magmatic rocks along the margin of the Pacific plate. [ABSTRACT FROM AUTHOR]

The Busang mineral prospect in Kalimantan, Indonesia, was reported to host a large Au resource until 1997 when it was revealed that drill core samples had been deliberately and systematically contaminated ("salted") with extraneous Au to falsify resource estimates. One month before the fraud was uncovered, Dr. G. Milligan, then professor emeritus of geology, visited the site to collect a suite of core samples for academic study that was deemed representative of the host rocks, alteration, and mineralization of the Busang Southeast Zone. These samples were re-examined here by optical microscopy, electron microprobe (EMPA), whole-rock geochemistry, and fluid inclusion microthermometry to characterize the subsurface geology and hydrothermal mineralization, and to assess reasons why the system is of uneconomic character. The host rocks were variably altered calc-alkaline porphyritic subvolcanic diorites, typical of the lithological units along the mineralized trend in the Kalimantan Gold Belt. Early hydrothermal mineralization with quartz-sulfide (pyrite, chalcopyrite, Cu-sulfosalts) stockwork veinlets associated with pervasive phyllic and propylitic alteration was overprinted by crudely banded quartz-carbonate-sulfide/sulfosalt (pyrite, sphalerite, chalcopyrite, galena, tennantite-tetrahedrite, bournonite-seligmannite) veins. The stockwork veins were associated with up to 140 ppb bulk rock Au, some of which was hosted by Cu-sulfosalts. Microthermometry on quartz-hosted aqueous fluid inclusion assemblages (FIA; n = 13) and single inclusions (non-FIA; n = 20) in quartz-carbonate-sulfide/sulfosalt veins yielded an overall range in homogenization temperatures (Th) between 179 °C and 366 °C and bulk salinities between 1.1 wt.% to 8.6 wt.% NaCl equivalent, with much smaller data ranges for individual FIA (e.g., FIA 3; 239.1 °C to 240.5 °C and 0.5 wt.% to 1.4 wt.% NaCl equivalent). Primary FIA along growth zones in quartz were identified, providing constraints on fluid characteristics at the time of quartz growth. Carbonate-hosted FIA (n = 3) and single inclusions (non-FIA; n = 3) in the same veins yielded Th between 254 °C and 343 °C and bulk salinities of 1.1 wt.% to 11.6 wt.% NaCl equivalent. Likewise, data ranges for individual FIA were much smaller. Many of the geological characteristics of the Busang Southeast Zone were compatible with a telescoped, intermediate-sulfidation epithermal system, having formed from diluted magmatic fluids that precipitated weak base metal mineralization. However, the system was unproductive with respect to Au and Ag, at least within the studied area. Of note, vein textures and fluid inclusion characteristics indicative of boiling or efficient fluid mixing—processes both considered critical for the formation of economic lode gold deposits—were absent in the samples. [ABSTRACT FROM AUTHOR]