This study evaluates epidote chemistry as a discriminator of and vector to skarn mineralization, based on LA-ICP-MS analyses of epidote from the Devonian Dolphin Tungsten (W) skarn and Neoproterozoic mafic volcanic rocks (up to 6.5 km northeast from the deposit) on King Island, Tasmania. Epidote from the mafic volcanics has distinctive compositions relative to skarn epidote and metamorphic signatures and records a distal footprint of magmatic-hydrothermal fluids > 4.5 km from Dolphin. Exoskarn epidote, replacing garnet during retrograde alteration, has low Fe/Al ratios (< 0.5) and high Sn (mean > 100 ppm) and Bi (mean > 10 ppm). Endoskarn epidote, replaced feldspar phenocrysts and/or occurs in veins, and is enriched in B, Li, As and Sb (mean > 5 ppm). U-Pb dating of exoskarn epidote yielded a 356.7 ± 8.9 Ma age, which is within uncertainty of the Sandblow Granodiorite ( 351 Ma), whereas the City of Melbourne Bay Volcanics epidote yielded a 394 ± 65 Ma age consistent with the emplacement of the Tabberabberan‑orogeny intrusions in western Tasmania. A comparative analysis, involving a compilation of 6,008 analyses from previous studies, confirms that epidote compositions vary significantly between magmatic-hydrothermal and metamorphic systems. Arsenic is higher in porphyry epidote, Bi is a distinctive tracer of skarn epidote and elevated Sn is characteristic of W-skarn systems. The LREE/HREE ratios in metamorphic epidote (< 5) are typically lower than in magmatic-hydrothermal epidote (> 5). Additionally, the Sn/HREE ratio discriminates epidote associated with W systems (> 25), Cu deposits (1–25) and metamorphic environments (< 1). Our findings confirm that epidote chemistry is a robust tool for evaluating ore potential and distinguishing skarn from porphyry and metamorphic systems.
The Triangle orogenic gold deposit (Val-d’Or, Canada) offers a well-constrained setting to investigate shear-hosted gold-bearing quartz–tourmaline–carbonate veins developed across contrasting volcanic, volcanoclastic, and intrusive host rocks. SEM–CL and BSE imaging of veins from two main shear zones (C2 and C4), reveal four types of quartz with variable degrees of deformation and recrystallisation, contrasting with tourmaline that preserves primary oscillatory or irregular zoning defined by subtle Fe–Na variations. In situ SIMS oxygen and boron isotopic analyses of texturally constrained quartz–tourmaline pairs show similar isotopic variability at sample and deposit scales: δ18Oqz = 11.8–14.1‰ (excluding two outliers), δ18Otur = 8.2–11.1‰, and δ11Btur = − 12.6 to − 7.8‰ (excluding two outliers). Quartz–tourmaline geothermometry yields apparent local equilibrium temperatures of ca. 196–417 °C (mean = 321 °C). Calculated fluid compositions range from 1.3‰ to 9.9‰ for δ18Owater and − 8.6 to − 3.6‰ for δ11Bwater. The spread of δ18Owater values and the broad negative correlation between δ18Owater and δ11Bwater are best explained by binary mixing between isotopically distinct fluid components: a metamorphic component represented in the model by δ18Owater ≈ 10‰ and δ11B ≈ − 9‰, and an upper-crustal pore-fluid component represented by δ18Owater ≈ 2‰ and δ11B ≈ − 3‰. These results provide evidence consistent with fluid mixing at both the sample and deposit scales at Triangle, suggesting that interaction between isotopically distinct fluid components controlled fluid evolution during fault-valve cycling and QTC vein formation.
Ore districts in orogenic belts can record polyphased geological histories integrating both pre‑ and syn‑orogenic processes. The F–Ba–Pb–Zn–(Ag) mineralization of the Grand‑Châtelard district, located within the external crystalline massifs of the Western Alps, exemplifies such complexity and results from two distinct superimposed hydrothermal events. The first, dated to the Mesozoic, is linked to the circulation of moderately saline brines during the rifting of the Western Tethyan margin. These fluids, trapped at [140–175 °C] and low pressures [0.35–0.85 kbar], precipitated fluorite–barite–galena–sphalerite veins filling normal faults affecting both the Variscan basement and its sedimentary cover. The mineralizing system involved basinal brines [22–25 eq. wt
Apatite is a widely distributed accessory mineral in igneous and hydrothermal systems. Here we integrate cathodoluminescence (CL) imaging, in situ REE geochemistry, and oxygen and strontium isotope analyses of apatite from 43 samples spanning 16 European deposits representative of diverse magmatic to magmatic–hydrothermal settings, including carbonatites, alkaline complexes, lamproites, layered intrusions, IOA–IOCG deposits, granite-pegmatite systems, and hydrothermal and metasomatic veins. The combined dataset reveals systematic chemical and isotopic trends that distinguish primary magmatic apatite from magmatic–hydrothermal transition and hydrothermal–metasomatic generations, while also providing diagnostic criteria for different classes of phosphate-bearing deposits. Primary magmatic apatite is commonly characterized by LREE-enriched patterns, low δ18O values (generally 3–9‰), relatively low to moderate radiogenic Sr(i) signatures (0.701–0.707), and oscillatory CL zoning. Progressive fluid interaction with primary magmatic apatite is typically expressed by partial REE depletion, increasing δ18O values, more radiogenic Sr(i) compositions, and the development of dissolution–reprecipitation textures. Granite–pegmatite systems are distinguished by strong intra-REE fractionation expressed by tetrad effects (> 1.1), radiogenic Sr isotopic compositions, and pronounced negative Eu anomalies. Apatite from hydrothermal and metasomatic deposits exhibits the strongest modification of primary signatures, including marked REE depletion, elevated δ18O values, radiogenic Sr(i) ratios, and commonly turbid or microcrystalline CL textures. This study therefore highlights the analytical and interpretative power of integrated in situ methodologies for resolving the evolution of economically and geologically significant P-rich systems.
Two types of crystallised melt were identified as tiny, sharply bounded, ellipsoidal inclusions (typically 20–80 µm) in metamorphosed massive pyrrhotite ore (12–14 kbar, 530–550 °C) from the VMS Besshi-type Tisová deposit. The Pb-Bi-S melt is more abundant than Pb-Bi-(Sb)-S melt. Many inclusions exhibit complex internal eutectic-like intergrowths with enclosing sulphides. Electron-backscatter diffraction revealed crystallographic continuity of pyrrhotite/chalcopyrite across the boundaries of the inclusions, indicating that the Fe-(Cu)-S sulphides enclosed within the blebs were formed by the replacement and recrystallisation of the host sulphides, rather than by the direct crystallisation of the melt. Micro-computed X-ray tomography confirmed the dominance and random distribution of smaller inclusions. It also showed a strong, unidirectional preferred orientation of the longest axis of the inclusions within the metamorphic foliation plane, which is consistent with their ductile deformation shortly after melt crystallisation. Larger and more irregular inclusions are often oriented at an acute angle to the foliation, suggesting their link to the onset of brittle deformation. The estimated bulk compositions of the Pb-Bi-S inclusions are shifted towards galena relative to the experimentally constrained melt fields. We interpret this as selective bismuth loss during a phase of enhanced late metamorphic fluid activity. Our observations support the formation of melts at or near peak metamorphic conditions during the climax of the Variscan orogeny, followed by fluid-related modification(s) during the post-orogenic uplift phase. Our results show that melts may represent an important mechanism for the redistribution of Bi, Pb, Sb during metamorphism of sulphide ores.
Fluorite (CaF2) is a potential pathfinder to critical mineral and rare earth element (REE) deposits but its application has been limited to a narrow range of mineralization types. I show that fluorite is a robust recorder of mineralization fertility by applying statistical and machine-learning methods to a new global fluorite geochemical database. Distinct median rare earth and trace element patterns are observed among deposit types and genetic environments. Fluorite associated with carbonatites and REE deposits are relatively enriched in Sr and have minimal Eu anomalies. These characteristics define new bivariate discrimination diagrams that correctly identify 78
Metasedimentary rocks of the Mesoproterozoic Belt Supergroup in the United States and correlative Purcell Supergroup in Canada contain diverse types of mineral deposits with a variety of commodities including base metals, precious metals, and critical metals. The economically most important deposits (≥ 10 Mt past production + reserves + resources) are stratabound Pb–Zn–Ag ores at the Sullivan mine in southeastern British Columbia, Ag–Pb–Zn–(Cu) veins of the Coeur d’Alene district in northern Idaho, stratabound sediment-hosted Cu–Ag deposits of the Spar Lake, Montanore, and Rock Creek deposits in western Montana, stratabound Co–Cu–Au–(Bi–Y–REE) ores of the Idaho cobalt belt, and stratiform Cu–Co–Ag at the Black Butte deposit in western Montana. Minor deposits in the region, also hosted in strata of the Belt and Purcell supergroups, are stratabound Pb–Zn–Ag deposits in southeastern British Columbia, and Th–REE–(Cu) veins of the Lemhi Pass district in northern Idaho and western Montana. Small prospects and occurrences include gold-quartz veins, Ag–Pb–Zn veins, Fe–(Cu–Au) deposits, and a variety of rare metals (Th, REE, Nb, Be, Sn) in pegmatites and carbonatites. High-precision geochronology of ore and gangue minerals, like in the Sullivan deposit, has yielded only Mesoproterozoic ages, but other deposits (Blackbird, Rock Creek, Coeur d’Alene, Lemhi Pass) have U–Pb and/or Re–Os ages that suggest Neoproterozoic, Paleozoic, and/or Mesozoic to Tertiary overprinting of older Mesoproterozoic mineralization, possibly linked in some cases to fluid flow during reactivation of deep basement structures. Some of the Paleozoic and younger ages are also attributed here to dissolution-reprecipitation of dated minerals and not to new metal introduction. An integrated assessment of the geochronological data reveals growing evidence for previously underappreciated roles of major mineralizing events occurring during the East Kootenay orogeny (1379 − 1325 Ma) and the Grenvillian orogeny (1150 to 980 Ma), with important implications for mineral exploration in many parts of the Belt-Purcell Basin.
The Shankaraghatta Complex in the Dharwar Craton (Southern India) hosts highly serpentinized komatiites containing minor disseminated nickel-sulfides as blebs of millerite–pyrite–violarite ± chalcopyrite, locally enriched in a range of semi and precious metals. This study shows that these rocks, yielding a Sm-Nd age of 2718 ± 107 Ma, are broadly coeval with the highly nickel-sulfide mineralized komatiites of the Yilgarn Craton (Western Australia), but significant mineralization is absent in the Shankaraghatta Complex and across the Dharwar Craton. This discrepancy is addressed through systematic multiple sulfur isotope characterization of the sulfides, which reveals a predominant mantle-like signature that rule out significant crustal assimilation during komatiite emplacement in the complex. It is proposed that sulfide saturation was unlikely achieved through dynamic processes typical of economically mineralized komatiite systems, such as, turbulent magma flow and interaction with sulfur-rich crustal reservoirs. Instead, sulfide formation is attributed to fractionation within a cooling magmatic system, with subsequent serpentinization-driven remobilization locally enhancing semi and precious metal concentrations, as supported by detailed sulfide trace-element geochemistry, and study of platinum-group minerals and their textures. In addition, review of regional radiogenic isotope data suggests the absence of significant lithospheric structures capable of channelizing and focussing magma flow during emplacement, indicating a stable, partially cratonized crust that hindered widespread komatiite emplacement in the Dharwar Craton. This study therefore suggests that although Dharwar komatiites may be unfavourable for nickel-sulfide mineralization, widespread serpentinization may have remobilized and locally concentrated a range of metals, leading to previously unknown styles of non-conventional mineralization.
Seafloor massive sulphide (SMS) deposits are potential sources of Cu, Zn, Au and Ag, however, how seafloor weathering affects the content of these metals in the deposits remains poorly understood. Key sulphide weathering products, i.e. Fe-oxyhydroxide and atacamite, can provide insight into metal mobilisation during and after oxidation of sulphides. Ten Fe-oxyhydroxide and three massive sulphide samples from the Semenov hydrothermal cluster (13°30′N, Mid-Atlantic Ridge) were studied; five Fe-oxyhydroxides and all sulphides were analysed by LA-ICP-MS with one sulphide sample analysed by LA-TOF-ICP-MS mapping. Additionally, a sequential leaching study comprising nine Fe-oxyhydroxide samples was performed. Copper is mainly sequestered into the sulphide weathering products atacamite ( 60
The Youjiang Basin in southwestern China is the world’s second-largest province of Carlin-type gold deposits, yet its exploration potential remains underexplored compared to its counterpart in Nevada, USA. A primary challenge has been the lack of robust, data-driven metallogenic models to guide the search for deeper, concealed orebodies. This study addresses this critical knowledge gap by conducting a comprehensive geochemical investigation of the Lannigou deposit, the largest fault-controlled Carlin-type gold deposit in the basin. In this work, we integrated large, spatially matched geochemical datasets from deep drill-core rock (n = 449) and surface soil (n = 2,280) samples. Through comprehensive statistical analyses, mass transfer calculations, and innovative three-dimensional spatial visualization, we successfully (1) identified distinct ore-related (Au-As-Hg-Sb-Ag-Tl-W-Mo) and diagenetic (Bi, Co, Cu, Ni, Zn, Pb) elemental suites, delineating their controlling geological mechanisms; (2) established a robust vertical geochemical zonation pattern (Mo → Tl → Sb → W → As → Au → Ag → Hg), which serves as a powerful vector for assessing the erosional level of mineralizing systems; and (3) revealed the critical role of a deep-seated, bedding-parallel detachment fault (F1) as a master conduit, channeling ore-forming fluids from basement structures into shallower, ore-hosting reverse faults. Based on these findings, we propose a new metallogenic model wherein ore-forming fluids ascended from depth, migrated laterally along this major detachment fault, and subsequently precipitated gold within structurally favorable traps, such as secondary reverse faults on anticlinal limbs. Our metallogenic model and the identified geochemical vectors offer robust and actionable criteria for targeting concealed Carlin-type orebodies in the Youjiang Basin and analogous terranes worldwide.
The Jiama porphyry–skarn system in the Gangdese belt, Tibet, hosts bornite-rich skarn ores with visible Au–Ag minerals and the newly recognized Bi-rich bornite-related mineral juxingite (Bi₆Cu₁₄₀Fe₃₀S₁₂₅). This study investigates the redistribution of Au–Ag–Te–Bi during the cooling of bornite-bearing Cu–Fe sulfides, using integrated microanalytical and nanoscale techniques. Two assemblages are identified: a Cu-rich bornite-I + digenite assemblage with wittichenite, and a bornite-II + juxingite + chalcopyrite assemblage. Matrix Au contents in the analyzed Cu–Fe sulfides are low, with quantifiable values generally ≤ 13 ppm, whereas Ag and Bi commonly reach concentrations of hundreds to thousands of ppm. In the bornite-I + digenite assemblage, ordered digenite-related domains exsolved coherently from bornite-I and locally transformed into anilite, producing Bi-rich segregation domains enriched in Ag, Au, and Te. In the bornite-II + juxingite + chalcopyrite assemblage, juxingite records Bi-rich ordering during coherent to semi-coherent exsolution. The concentric zoning of bornite-hosted telluride inclusions, from Au–Ag cores through hessite to Cu–Te-rich rims, records progressive Au–Ag–Te segregation and reorganization during cooling. These observations suggest different redistribution behaviors of Bi and Te during cooling: Bi was stabilized in juxingite and Bi-rich Ag–Au–Te-bearing segregation domains, whereas Te was concentrated in telluride-bearing domains closely associated with Au–Ag minerals. Thus, visible Au–Ag minerals at Jiama are interpreted to have formed, at least in part, through cooling-driven internal redistribution rather than solely by late-stage fluid overprinting. This finding suggests that cooling-driven internal redistribution may be an important control on visible Au–Ag mineralization in bornite-rich skarn and porphyry Cu–Au systems.
Rare-metal pegmatites are important sources of lithium and other critical metals essential for green-energy technologies. In the Musha–Ntunga area of Rwanda, spodumene-bearing lithium–cesium–tantalum (LCT) pegmatites intrude Mesoproterozoic metasedimentary rocks of the Karagwe–Ankole Belt. This study integrates petrography, mineral chemistry, and whole-rock geochemistry to investigate pegmatite crystallization, the magmatic–hydrothermal transition, and host-rock metasomatism related to pegmatite-derived fluid migration. Drill cores intersect pegmatite dykes up to 100 m thick, with reported lithium concentrations locally reaching 20700 ppm (4.5 wt
Fluorite mineralization in the AGS deposit occurred in an epithermal setting from fluids exsolved from the associated St. Lawrence Granite and mixed with meteoric water. Veins of the deposit cut Cambrian sedimentary rocks, and sills and a massive variant of the granite. The mineralization is characterized by banded, colloform and breccia textures, and is divided into three stages: Early, Main and Late. The magmatic origin of the fluorite is supported by the Nd-Sm age of 361 Ma, ƐNd values (1.7 to 2.9), strong negative Eu anomalies and REY contents ( 5 to 1000 times chondrite values) of the fluorite, all comparable to the associated granite. Interaction of a vapour-rich magmatic fluid with oxidized surface-derived fluids formed an acidic fluid that led to greisenization and fracturing of the overlying rocks prior to fluorite precipitation. Fluorite precipitated between 130 and 180 °C from H2O-NaCl-CaCl2±FeCl2±MgCl2 fluids with salinities of 9.7–27.5 eq. wt
The albite–lepidolite–topaz Beauvoir granite of the Western European Variscan Belt hosts economic concentrations of rare metals (Li, Sn, Nb, Ta, and Be) associated with magmatic–hydrothermal processes, particularly in unit B1 at the top of the intrusion. The phosphate mineral assemblage indicates that amblygonite-group minerals (AGMs) constitute a subordinate Li-bearing phase in addition to lepidolite, whereas Be-phosphates (beryllonite and hurlbutite) represent the main host for beryllium. Magmatic apatite in exceptionally rare in the B1 unit, suggesting very low Ca activity in the melt. Compared with other peraluminous and perphosphorous granites and pegmatites, the crystallization of Be-phosphates together with the absence of beryl indicates persistently high phosphorus activity during advanced fractional crystallization. LA-ICP-MS analyses of AGMs indicate high but heterogeneous Li, Na, and F contents reflecting solid-solution between montebrasite and amblygonite, as well as AGM replacement by lacroixite. During subsequent hydrothermal stage, both primary Li- and Be-phosphates are progressively replaced by Ca-rich phosphates: morinite and crandallite-group minerals replace AGMs, whereas herderite, loomisite, and secondary apatite successively overprint Be-phosphates. These mineral sequences record significant Ca and Sr inputs from external fluids during early subsolidus evolution of the granite, a process also reflected in the whole-rock geochemical signatures. During muscovitization of albite and lepidolite, dissolution of Be-phosphates by circulating fluids induces significant Be loss, whereas AGM breakdown also releases some lithium. The evolution of the phosphate assemblages, therefore records the transition from highly fractionated magmatic conditions to hydrothermal alteration associated with muscovitization. Overall, the Beauvoir granite represents a distinctive rare-metal system characterized by a lepidolite–Be-phosphate association and the absence of beryl, indicating that the Li–Be endowment was essentially established during the magmatic stage and subsequently modified by hydrothermal redistribution.
The Falchani Lithium Project, a volcanogenic sedimentary deposit in the Neogene Macusani Volcanic Field (Puno, Peru), hosts > 5.5 Mt Li₂CO₃ resources and represents a significant potential complementary source for South American lithium production, currently dominated by Andean salar deposits of the Lithium Triangle. The ore comprises volcanogenic tuff and breccia subdivided into the Lithium-rich Tuff and stratigraphically overlying and underlying Upper and Lower Breccia units, respectively. Primary minerals include quartz, feldspars, and trioctahedral Li-F micas (zinnwaldite and lepidolite). Secondary minerals define a vertical mineralogical zonation. The Lithium-rich Tuff is characterized by abundant kaolinite and the preservation of Li-F micas, whereas the Upper and Lower Breccia are dominated by dioctahedral smectites (beidellite–montmorillonite series) with scarce, corroded relict micas. Zeolites locally occur as the predominant secondary phase in brecciated Lithium-rich Tuff samples. Lithium contents peak in the Lithium-rich Tuff (3000–4200 ppm Li), with the bulk hosted by Li-F micas, and only 7
Structural and geochronological studies of the San Albino orogenic gold deposit, NW Nicaragua within a micro- to macroscopic framework can constrain mechanisms of deposit formation and the overarching tectonic context. High-grade, gold-bearing vein sets formed during three stages of hydrothermal activity: early shear vein emplacement (stage 1), episodic reactivation and progressive deposition of sulfides with minor gold (stage 2), and localized recrystallization with precipitation of galena and most free gold (stage 3). Subvertical dikes cut the ore zones and are themselves cut by younger faults. Thus, the age of these dikes places an absolute timing constraint on earlier mineralization and later events. Zircon dating of the dikes by U-Pb LA-ICP-MS yields an emplacement age of 96 Ma and provides a minimum mineralization age. Based on this and current understanding of the regional geology, mineralization occurred between 115 and 96 Ma, being triggered by large-scale tectonic reconfigurations associated with formation of the Caribbean plate. Post-mineral structural overprint includes a Laramide ( 70–55 Ma) shortening event and extensional to transtensional activity since the mid-Tertiary.
Lower Cretaceous strata of the Eastern Cordillera of Colombia host some of the world’s premier emerald deposits, yet the timing of mineralization—and its relationship to the tectonic evolution of the Cordillera—remains poorly constrained. We present high-resolution in situ U–Th–Pb petrochronology of monazite and xenotime from both the Eastern and Western Emerald Belts, revealing at least three stages of mineral growth: (1) authigenic crystallization during early burial and diagenesis ( 140–120 Ma, Eastern Belt; 125–100 Ma, Western Belt) (2) metamorphic recrystallization at 120 Ma (Eastern Belt) and 99 Ma (both belts) associated with peak basin temperatures; and (3) prolonged hydrothermal overprinting initiated by a major fluid pulse at 85 Ma and persisting until 37 Ma. Emeralds (± euclase) and associated REE minerals formed during this final stage in at least two distinct episodes. Our results document a multistage, episodic history of emerald mineralization, with REE redistribution closely linked to polyphase tectonothermal processes rather than a single mineralizing event. These findings refine the temporal framework for Colombian emerald formation, highlight the potential for REE recovery as a by-product of emerald mining, and underscore the importance of non-magmatic hydrothermal systems in sedimentary basins as potential sources of critical minerals.
The McDermitt caldera (Oregon–Nevada, USA) hosts the largest volcano-sedimentary (VS) Li resource globally. This study presents an integrated geological, mineralogical, and isotopic investigation of the McDermitt deposit in Oregon, with the aim of constraining the processes responsible for Li enrichment in clay-type VS Li mineralization. Our study reveals that Li mineralization occurs in stratiform lacustrine units composed of hectorite-bearing claystones interbedded with siliceous–carbonate beds and altered ash fall units. Lithium enrichment is mainly controlled by the formation of Mg–Li smectites (hectorite) associated with hydrous silica, and locally by zeolitization of tuffaceous precursors – a pathway that can be explained by devitrification of volcanic glass under near-neutral to slightly alkaline conditions. Geochemical and isotopic data indicate that mineralization formed through fluids at average temperatures of 133 °C and δD values of − 107‰, consistent with heated meteoric waters in a geothermal setting. Unlike the nearby Thacker Pass deposit, illitization of smectite did not occur, reflecting differences in the total amount of Li available and in the pH chemistry of deeper fluids circulating on a caldera-scale.
Marvel Loch (63 t Au) represents a group of high-P (300–400 MPa) gold deposits spatially associated with 2.65–2.62 Ga, garnet-muscovite and spodumene pegmatites in the 3.0 Ga Southern Cross greenstone belt, Yilgarn Craton. The ore bodies terminate at 650–800 m depth at pegmatitic granite. Structural relations, mass-balance calculations, 87Sr/86Sr and 206Pb/204Pb in scheelite and galena, and the δ13CPDB of CO2 (-4.8‰) in the calcite-depositing fluid implicate the I-type granite below as the source. Magnesian olivine-calcite-chlorite-phlogopite, quartz-diopside, and calcic diopside-hornblende skarn (4–15 g/t Au), and low-grade biotite-anorthite-microcline gneiss occur in a 1.5 km long foliated zone bound to the contact meta-komatiite / meta-gabbro. Garnet-biotite and Ti-in-biotite thermometry indicate a peak temperature of 650 –550 °C during calcic skarn and biotite-anorthite-microcline replacement in meta-gabbro, and cooling to about 400 °C during retrograde alteration of anorthite to phengite + prehnite + clinozoisite, confirming estimates for magnesian skarn. The fluid (log fO2 = -18 bar at 650 °C) became reduced during cooling and progressive replacement, as suggested by Fe3+/Fetotal ratios in whole rocks, CH4 in fluid inclusions, and positive Eu-anomalies in scheelite. At a sulfur fugacity of 10− 7-10− 9 bar, cooling is reflected in pyrrhotite + Ni-loellingite (600 –500 °C) in calcite-rich magnesian skarn, arsenopyrite + pyrrhotite + base-metal sulfides ± bismuth (550 –400 °C) in quartz-diopside skarn, and retrograde pyrrhotite + pyrite ± marcasite (450 –350 °C) in metasomatic gneiss. Marvel Loch is a gold skarn deposit formed at 11–15 km depth in a batholith environment. Reduced tungsten skarns (7–10 km) share the W-Au-As-Bi signature, and the reduction of a magmatic H2O-CO2 fluid during cooling and replacement of ferrous or graphitic host rocks.
Sedimentary rock-hosted copper-cobalt deposits of the Central African Copperbelt (CACB) supply over 70
