Mineralium Deposita最新文献

In a gold deposit near Nassara, southern Burkina Faso, gold occurs closely associated with pyrite within a network of veins hosted by metavolcanic and metasedimentary rocks. Using SEM and LA-ICP-MS analyses, we identified three generations of pyrite with distinct roles in gold mineralization. Pyrite 1 (Py1) formed early during mineralization, replacing alteration minerals like ankerite in metabasalt. Pyrite 2 (Py2) developed around Py1 in pressure shadows caused by localized micro-shear zone reactivation during successive micro-seismic events. Pyrite 2 is enriched in As and Au, unlike Py1. Pyrite 3 (Py3), unrelated to mineralization, formed at a later stage. Gold occurs in pyrite as micro-inclusions (in Py1 and Py2), fracture-fillings (mainly in Py2), and within the pyrite structure as invisible gold, including nanoparticles (predominantly in Py2). Combining electron backscatter diffraction (EBSD) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis reveals that deformation-induced misorientation of pyrite facilitated the remobilization of invisible gold, which subsequently re-precipitated as colloidal particles along sub-grain boundaries and within fractures, mimicking visible inclusions. These findings demonstrate that gold perceived as inclusions (visible or invisible) often precipitates within micro/nano-fissures and sub-grain boundaries during remobilization. This highlights the critical importance of thorough ore characterization for accurately determining gold deportment. Such insights advance our understanding of mineralization processes and support the development of more efficient recovery strategies.

Stibnite is a relatively common mineral in epithermal deposits, with little known about Sb transport and efficient stibnite precipitation. The famous Kremnica Au-Ag low-sulfidation deposit and Zlatá Baňa intermediate-sulfidation Pb-Zn-Cu-Au-Ag-Sb deposit are hosted in two different Neogene volcanic fields in Western Carpathians, Slovakia. In both deposits, stibnite-rich veins occur outside of major vein structures, accompanied by illite, illite/smectite, and kaolinite alteration, and affiliated to late-stage fluids (< 2 wt% NaCl eq., < 150 °C). Sulfur isotopic composition of stibnite and sulfides is different at both deposits, likely due to a different magmatic-hydrothermal evolution of the parental magmatic chambers in the Central and Eastern Slovak Volcanic Fields. The Sb isotopes (δ¹²³Sb), however, show similar values and trends of gradual simultaneous increase with δ³⁴S values, explained by a progressive precipitation of stibnite and its fractionation with the fluid. The data were modeled by two coupled Rayleigh fractionation models, (for Sb and for S), assuming a predominant Sb transport in HSb₂S₄^– with a variable amount of S species. Higher molality ratio m_S/m_Sb of fluids was found in Kremnica (~ 3–4) than in Zlatá Baňa (~ 2). At both deposits, the heaviest δ¹²³Sb values are accompanied by a decrease in the δ³⁴S values probably due to the commencement of pyrite/marcasite precipitation. According to thermodynamic models of solubility of Sb(III) complexes and observations from active geothermal fields, stibnite precipitation was triggered by temperature decrease accompanied by mixing with a mildly acidic fluid (pH 4–5) of a steam-heated CO₂-rich condensate on margins and in the final stages of epithermal systems. The proposed model for the origin of stibnite-bearing veins in epithermal systems can be used for their better targeting and efficient mineral exploration.

Bulk rock geochemistry and SWIR reflectance spectroscopy are widely used by companies for rapid and cost-effective exploration of volcanic-hosted massive sulfide (VHMS) deposits. However, few studies have integrated bulk-rock geochemistry with hyperspectral reflectance spectroscopy in greenstone belts that have undergone high-grade metamorphism. Here we present an extensive dataset combining bulk-rock geochemistry with chlorite and white mica SWIR spectral reflectance from the amphibolite-grade King VHMS deposit of the Yilgarn Craton, Western Australia. At King, the footwall stratigraphy is dominated by tholeiitic mafic rocks overlain by a sequence of calc-alkaline intermediate-felsic metavolcanic rocks. The hanging-wall stratigraphy is characterized by a thin metaexhalite layer, overlain by thick succession of interbedded metasedimentary and metavolcanic rocks. Chlorite spectral signatures are more Fe-rich in mafic lithologies and Mg-rich in felsic rocks, particularly where intense Mg-metasomatism occurred before metamorphism. In all units, Fe/Mg ratios of chlorite are strongly tied to bulk rock Fe/Mg ratios. White mica in the footwall is primarily muscovitic, with minor amounts of phengite in deep Fe-rich mafic rocks. By contrast, the hanging-wall sequence is dominated by phengitic signatures in both the Fe-rich metaexhalite, and weakly Ca-Mg altered volcanic rocks. This study concludes that chlorite SWIR reflectance is largely influenced by the bulk Fe/Mg composition of the host rock, whereas white mica reflectance correlates with the type and intensity of hydrothermal alteration prior to metamorphism. These findings underscore the potential of using chlorite and white mica spectral signatures to understand hydrothermal alteration patterns and detect new orebodies in metamorphosed VHMS systems.

Sedimentary Fe deposits are both scientifically and economically important. As a major ore mineral of these deposits, siderite is generally assumed to have been formed via diagenetic transformation of other Fe-bearing minerals. The Devonian Daxigou sedimentary siderite deposit, Central China, contains ca. 500 Mt Fe with an average ore grade of ca. 30 wt% FeO^T but is poorly known in the literature. Different from most sedimentary Fe deposits that contain multiple generations of Fe-bearing minerals, the ore mineral in this deposit is solely siderite, and thus may provide valuable information about the processes of siderite mineralization. Stratiform orebodies of the Daxigou deposit are hosted in a turbidite sequence formed in the Devonian Zhashui-Shanyang intraplate rift basin. Orebodies are composed of interbedded ore and mudstone layers. The ore mineral is siderite and gangue minerals are quartz and clay minerals (mainly muscovite and illite). Siderite has shale-normalized REE+Y patterns with positive Eu anomalies (Eu/Eu*_PAAS = 1.19–1.59) and low Y/Ho ratios (Y/Ho = 27.5–32.6) indicative of involvement of seafloor hydrothermal fluids. Siderite separates have εNd_(t) values from − 9.9 to -8.9, suggesting that Fe was leached from underlying clastic rocks. Siderite has δ¹³C_PDB values from − 3.45 to -1.09‰ and δ⁵⁶Fe_IRMM014 values from − 0.72‰ to -0.27‰, with only limited fractionations relative to dissolved inorganic carbon in seawaters and to hydrothermally derived Fe²⁺. High resolution transmission electron microscopic images reveal that siderite grains were nucleated on the surface of clay minerals. Thus, we conclude that siderite of the Daxigou deposit was precipitated directly from ferruginous seawaters via heterogeneous nucleation on clay minerals at elevated temperatures, instead of formation through diagenetic transformation from other Fe-bearing minerals. The Daxigou deposit can be considered as a unique primary sedimentary siderite deposit. It was formed under an extensional regime of the South China Craton during the breakup of Gondwana. Our study provides new insights about the mineralization pathways of sedimentary Fe deposits in the geological past.

The Gondpipri layered mafic–ultramafic intrusion at the western margin of the Bastar Craton in Central Indiacomprises leucogabbro, gabbronorite, and websterite. The intrusion hosts both magmatic and hydrothermal Ni-platinum group element (PGE)mineralisation. In this study, we use in-situ measured trace element composition of pyrite and magnetite and zircon U–Pb geochronology to elucidate hydrothermal processes and their timing. Secondary platinum group minerals (PGMs) occur as veins and fracture fillings in sulfide and oxide minerals together with hydrothermal zircon clusters within chlorite alteration. Electron microprobe (EPMA) analysis reveals that magmatic PGMs are enriched in Pt, Pd, and Rh, whereas the hydrothermal PGMs are characterized by higher Fe, S, Te, Bi, and Ni. A semi-metal collector model (Bi-Te) is proposed for PGE in the Heti Ni-PGE prospect, where an immiscible Bi-Te melt exsolves and acts as a collector for formation of primary PGM following precipitation of Pd tellurides, tsumoite, melonite and hessite upon cooling of temperature hydrothermal fluids. Two generations of pyrite (Py-I and Py-II) and magnetite (Mag-I and Mag-II) are identified. Py-I and Py-II exhibit distinctive concentrations of Co, Se, and Au, while Mag-I and Mag-II have variable concentrations of REEs, Cr, Ti, Ga, V, Ba, and Sr. Selenium geothermometry of pyrite indicates that hydrothermal mineralisation occurred within a temperature range of 200 °C to 475 °C. The Ni-PGM-Bi-Te mineralisation is associated with an unusual cluster of megacrystic zircons, which are likely hydrothermal origin. Uranium-lead (U–Pb) dating of five zircons using LA-ICPMS yields a concordia age of 2524 ± 7 Ma, interpreted as the age of the hydrothermal sulfide-hosted Ni-Te-Bi-PGE mineralization.

Epithermal precious metal deposits are uncommon within the Archean rock record, as are detailed descriptions of their associated features and modes of formation. The Vent prospect is a Neoarchean Au–Ag occurrence within the Eastern Wabigoon Subprovince of the Superior Province in Ontario. It is hosted by aphyric, and quartz ± feldspar-porphyritic aphanitic dacitic flows that show remnants of spine-like structures within blocky flow top breccia facies that lack visible hyaloclastite, consistent with subaerial emplacement. Numerous phreatic breccia dikes containing rounded, heterolithic, fragments in a fine rock flour and locally altered matrix intrude the dacitic host rocks, supporting a subaerial setting. Discordant replacement and stringer Au- and Ag-bearing pyrite mineralization is associated with a decimeter-scale, zoned, discordant sequence of metamorphic associations consisting of a) quartz-pyrite; b) kyanite-quartz; c) muscovite-kyanite; and d) muscovite. The geochemical characteristics of these metamorphic associations reflect intense pre-metamorphic acidic alteration. These lithofacies, alteration characteristics, and mineralization styles are consistent with a subaerial volcanic edifice altered by acidic hydrothermal fluids, which periodically brecciated the edifice. We propose that the features that characterize the Vent prospect are consistent with those of Phanerozoic epithermal systems. New U–Pb zircon geochronology of the host dacites indicate formation at ca. 2720 Ma, suggesting that the Vent prospect may represent one of the oldest identified epithermal deposits preserved in the ancient rock record. The recognition of epithermal mineralization in Archean greenstone belts underlain by Mesoarchean crust, such as those of the Eastern Wabigoon, opens up the possibility of potential for gold and silver in other underexplored Archean greenstone belts.

We provide timestamps for the major zinc-lead (Zn-Pb) Mississippi Valley-type Black Angel deposit (Greenland) based on new pyrite rhenium-osmium (Re-Os) isotope geochemistry data: (1) a Re-Os isochron age 1,884 ± 35 million years ago (Ma – 2σ, 1.8%) for subhedral pyrite cemented by sphalerite ± galena in dolomitized clean limestone, and, (2) a Re-Os model age 1,828 ± 16 Ma (2σ, 0.9%) for epigenetic massive pyrite in siltstone/mudstone cap rock. Zinc-lead mineralization in evaporite-bearing carbonates in the Karrat Basin took place ca. 1,884 Ma at the time of far-field fluid flow associated with back-arc spreading ca. 1,900–1,850 Ma. Mineralization predates the development of the Rinkian foreland basin (ca. 1,850 – < 1,800 Ma) and a collisional stage (ca. 1,830 – < 1,800 Ma) in the context of the telescoping Rinkian and the Nagssugtoqidian Orogens. Replacement of clean carbonate and sustained acid neutralization led to significant sphalerite precipitation ca. 1,884 Ma. Conversely, precipitation of epigenetic massive pyrite in the cap rock ca. 1,828 Ma may signal (1) the lack of chemical reactivity of the cap rock for the pH-buffered conditions needed for Zn-Pb mineralization, and (2) the unfavorable impact of incipient regional Rinkian metamorphism (ca. 1,830–1,800 Ma) and tectonic compression on aquifer permeability and continued brine migration. The initial ¹⁸⁷Os/¹⁸⁸Os ratio (Os_i-pyrite = 1.07 ± 0.32) from isochron regression identifies a crustal origin for Os and, by corollary, other metals in the ca. 1,884 Ma Zn-Pb mineralization. Although the Rae Craton basement rocks comprise the dominant source for metals (based on our Os_i-pyrite and δ⁶⁶Zn_{pyrite/sphalerite} data), we identify a complementary contribution in Zn (maximum 12–24%) from Paleoproterozoic sedimentary carbonate. This source of Zn in sedimentary calcite is deemed possible in the context of Paleoproterozoic seawater at high Na/Cl ratio and in the absence of Zn-based eukaryotic metabolism in shallow marine environment.

Tungsten enrichment during the formation of giant W deposits is thought to be related to magmatic and hydrothermal processes. However, the mechanisms of W enrichment and their role in controlling ore formation remain unclear. Zircon is a ubiquitous accessory mineral that can provide a record of the physicochemical conditions during mineralization. Dahutang in South China is a giant W deposit (1.89 Mt WO₃ at 0.18%) associated with the late Mesozoic granites. In this study, we report new zircon morphological, geochronological, and chemical data for the most evolved Li-mica albite granite in the Dahutang deposit, in order to determine the processes of W enrichment. We classified the zircons into three types based on their appearance and composition. Type-IA and -IB zircons (ca. 145 Ma) successively crystallized from metasedimentary-derived magmas (δ¹⁸O = 8.9 ± 0.3‰) at 786–732 °C. Type-II zircons formed by interaction between volatile-rich melts and Type-I zircons at 669 ± 39 °C. Type-III zircons formed by autometasomatism of earlier Type-I and -II zircons, which involved exsolved hydrosilicate fluids. Our numerical model shows that the granitic melts have undergone > 95% fractional crystallization and experienced metasomatism by hydrosilicate fluids, during which the rare-metals (W, Nb, and Ta) were extensively enriched. Furthermore, we compiled data for ten W deposits across South China to investigate the key factors controlling the formation of giant W deposits. The strong correlation (R² = 0.79) between WO₃ tonnage and zircon Hf content indicates that an extensive and multi-stage evolution may be the key factor controlling the formation of giant W deposits.

Porphyry deposits of the Cu-Mo-Au-Re metal spectrum mainly occur in arc settings, but only some segments of the same arc host significant metal resources. The factors controlling the variable metal endowment in magmatic arcs remain unclear. Here, we conducted zircon U-Pb age, trace element, and Hg isotope studies on the ore-bearing (i.e., fertile) and coeval barren granitic rocks from the Upper Triassic Yidun arc, eastern Tibetan Plateau. The results show that the barren granites from the northern Yidun arc display normal arc magma features, and have low oxygen fugacities (ΔFMQ= -3.7 to -0.5), low water contents. Their negative Δ¹⁹⁹Hg values (-0.20 to 0.02‰) indicate that they were mainly derived from continental basement rocks. The fertile granites from the southern Yidun arc exhibit adakitic geochemical affinity (i.e., high Sr/Y and La/Yb ratios), high oxygen fugacities (ΔFMQ = 0.2 to 2.7), and high water contents. Their positive Δ¹⁹⁹Hg values (-0.07 to 0.23‰) indicate an oceanic source of the Hg and suggest that they were derived from an enriched mantle source modified by oxidizing, subduction-related fluids/melts. The contrasting characteristics of fertile and barren granites indicate that magma sources likely have a critical control on the metallogenic potential of arc magmas, with slab-derived fluids imprinting high fO₂ and volatile contents for the formation of productive intrusions in arc settings. Arc magmas derived from oxidized and water-riched magma sources have a predisposition to form porphyry Cu deposits, and should be regarded as priority targets for porphyry deposit exploration.