Mineralium Deposita最新文献

Understanding the sulfur isotope cycle is essential in developing genetic models of porphyry copper deposits. In this paper, we characterize the sulfur isotope evolution of the Duobuza deposit, a typical porphyry Cu-Au deposit, using the sulfur isotope composition of sulfides in successive hydrothermal stages. We show (1) an increase of δ³⁴S values from the inner potassic core (−4.8 to −0.4‰, n = 37) to the peripheral propylitic halo (1.2 to 4.8‰, n = 5) during the early stage; (2) an increase from the early stage potassic alteration to the transitional stage sericite-chlorite alteration (−2.6 to 0.6‰, n = 25); (3) a progressive enrichment, from the quartz-dominated veins (−3.1 to 0.5‰, n = 10), through the anhydrite-dominated veins (−2 to 0.6‰, n = 7), and to the pyrite-dominated veins (−0.7 to 2.3‰, n = 7) during the late stage. The integration of sulfur and oxygen isotope and fluid inclusion data, modeling and mineralogical evidence suggests that the ³⁴S depletion within the potassic core compared to the propylitic halo can be best explained by boiling-induced oxidation of hydrothermal fluids. The increase in δ³⁴S from potassic alteration, through sericite-chlorite alteration, to the late stage hydrothermal veins is interpreted to be related to the partial reduction of an oxidized fluid by water-rock interaction. Our findings highlight the potential of sulfur isotope data to assist exploration for Cu-Au porphyry deposits where a predictable zonation pattern is present.

This paper provides comprehensive analyses of mineral microtextures, nanoparticulate electrum, defective crystal structures of key primary hydrothermal minerals - quartz and pyrite, the bulk sulfur isotopic composition of pyrite and marcasite, and fluid inclusions in hydrothermal quartz and calcite, all aimed at characterizing ore mineralization. The study primarily focuses on samples collected from a steep normal fault and its damage zone, which formed during hydrothermal brecciation, while also incorporating samples from other thinner brecciation zones. The data utilized in this study originate from the Surnak (or Sarnak) gold deposit located in the Eastern Rhodope Mountains of Southeast Bulgaria. This deposit, characterized as low-sulfidation, offers a distinctive geological context for exploring the hydrothermal processes associated with hydrothermal brecciation, colloidal, and mesocrystal formation. The unique microtextures and mesocrystal structures observed in quartz and pyrite crystal lattices offer valuable insights into the colloidal stage that the paleohydrothermal solution experienced during hydrothermal brecciation, pressure drop, and subsequent boiling. Bladed-textured calcite crystals, containing both vapor-rich and liquid-rich inclusions, provide direct evidence of fluid boiling. Fluid inclusion data from hydrothermal quartz further suggest the involvement of two distinct fluid types, each with different temperatures and salinities. Our findings point to a causal relationship between brecciation episodes, fluid boiling, nanoparticle nucleation, the colloidal stage, and the subsequent formation of mesocrystals.

Chalcocite, bornite, and chalcopyrite are the main copper minerals in the world-class Olympic Dam Cu-U-Au-Ag deposit, South Australia. Olympic Dam is characterized by systematic, inwards and upwards zonation of Cu-Fe-sulfide assemblages, encompassing chalcopyrite-pyrite, bornite-chalcopyrite, bornite-chalcocite and chalcocite-only zones. Trace element analysis of Cu-(Fe)-sulfides (~ 3500 spot analyses) by laser ablation inductively coupled plasma mass spectrometry on samples from across the deposit identifies the role of spatial position, protolith, and the presence/absence of co-existing sulfides (sphalerite, tetrahedrite-tennantite and carrollite) in control of trace element endowment. Cu-(Fe)-sulfides host concentrations of precious metals (Ag, Au), potential value-add elements (Se, Te, Bi, As, Sb, In) and deleterious elements (Pb, Hg). Where bornite-chalcocite co-exist, Ag is partitioned into chalcocite and Bi into bornite; in the absence of either bornite or chalcocite, chalcopyrite is a significant host for both elements. Chalcocite from the chalcocite-only zone is depleted in Bi-Te-Ag-Au compared to the bornite-chalcocite zone, demonstrating the role of bornite as an initial scavenger of these elements. A distinct inherited Cr-Ni-Zn signature is identified in chalcopyrite hosted by banded iron formation derived lithologies and proximal to crosscutting dykes. Despite some variation, Cu-(Fe)-sulfides generally contain more Bi and lesser Se towards deeper levels. The concentrations of these elements in paired bornite-chalcocite assemblages show promise as ore vectors, whereas Ag/Te in brown bornite and Se/Ag in chalcopyrite are prospective lateral vectors. Results carry implications for understanding deposit evolution, provide insights towards developing reconnaissance exploration vectors, and offer guidance on trace element deportments likely to impact ore quality and geometallurgical performance.

Sunnyside is a well-preserved Miocene polymetallic vein deposit located in the Western San Juan Mountains of Colorado, USA. The steeply dipping veins extend vertically for ~ 600 m and can be traced laterally over a combined length of ~ 2100 m. Fracture-controlled fluid flow dominated during the pre-ore stage. Subsequent ore deposition along major extensional structures took place at far-from-equilibrium conditions resulting in the formation of ore mineral dendrites in a silica matrix that was originally noncrystalline. Recrystallization of the noncrystalline silica to quartz caused extensive microtextural modification of the veins during and after the ore-stage. Microtextural evidence suggests that essentially all quartz in the ore-stage veins originated from a noncrystalline silica precursor. The deposition of ore mineral dendrites and noncrystalline silica is interpreted to have occurred during repeated fluid flashing events over the lifetime of the hydrothermal system. A period of quasi steady-state fluid flow occurred during the post-ore stage resulting in the formation of gangue minerals in open spaces in the veins. Fluid inclusion evidence suggests that the veins at Sunnyside formed at the transition between the epithermal and porphyry environments at ~ 1300–1900 m below the paleowater table at temperatures ranging up to ~ 345 °C. 

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.