Mineralium Deposita最新文献

Cuba contains the largest number of ophiolitic chromite deposits throughout the Americas. Most of these deposits are found within the mantle section of the Eastern Cuba and Camagüey ophiolitic massifs, which contain four different chromite mining districts (Camagüey, Mayarí, Sagua de Tánamo, and Moa-Baracoa). In addition to their potential as economic resources, chromite deposits are also excellent petrogenetic indicators to interpret the nature of ancient upper mantle, processes of melt formation in the mantle, and large-scale geodynamic processes. In this sense, major and trace elements of unaltered Cr-spinel cores together with chromitite whole-rock PGE composition reveal that high-Al Camagüey and Moa-Baracoa chromite districts were formed in equilibrium with forearc basalts (FAB)-like magmas during the incipient intra-oceanic subduction of the proto-Caribbean lithosphere underneath the Caribbean lithosphere, in a subduction-initiation process. Conversely, the high-Cr Mayarí chromite district was formed in equilibrium with more hydrated melts of boninitic affinity, typical of a more advanced stage of the subduction-initiation process. Nonetheless, the shift from FAB-like to boninite-like magmatism in an intra-oceanic subduction is gradual. This progressive change is well-recorded in the Sagua de Tánamo district that contains both high-Al and high-Cr chromitites. Thus, the studied ophiolitic chromitites allow tracing the complete magmatic evolution of an intra-oceanic subduction-initiation process. Furthermore, our data exhibits that accessory Cr-spinel composition of peridotites surrounding chromitites can be used as a prospecting indicator to anticipate the composition of ophiolitic chromitite bodies. Systematically, Cr-spinel from dunites associated with high-Al chromite deposits have lower Cr# values compared to the accessory Cr-spinel from the associated harzburgites. On the contrary, Cr-spinel from dunites of high-Cr chromite deposits show higher Cr# compared to the accessory Cr-spinel from the host harzburgites.

The Late Triassic to Early Jurassic (ca. 220 to 190 Ma) Dahongliutan pegmatite belt, located in the Western Kunlun orogenic belt, NW China, is a newly discovered, large Li-Be ore district comprising > 320 individual rare-metal pegmatites. The pegmatite belt was emplaced in a post-orogenic setting in relation with a ductile shear zone related to the Dahongliutan detachment fault, which is spatially and temporally related to post-orogenic exhumation. Deformed spodumene pegmatites, mostly striking NW with dip angle of 50 ~ 80°, occur within or adjacent to the NW-striking detachment fault. We present new field observations, mineralogical, geochemical and geochronological results from the Dahongliutan pegmatite belt, which lead to the following conclusions: 1) High-medium temperature/middle-to-low pressure metamorphic rocks and granitoids were intruded by ductile-deformed spodumene-bearing pegmatites during development of the gneissic domes; 2) Spodumene pegmatites from the Aktas, Kalaka, Bailongshan and Longmenshan deposits record two age groups, a first one during the Upper Triassic at ca. 212–205 Ma, and a second one during the Lower Jurassic at ca. 195–193 Ma, as revealed by in-situ Rb–Sr dating of micas and U–Pb dating of columbite-group minerals; 3) Textural observations and geochemical analyses of coexisting quartz and spodumene further indicate that ductile deformation provided favorable conditions for enrichment of Li and Be in pegmatites. The Western Kunlun-Songpan Ganzi rare-metal pegmatite belt shows a close spatial and genetic relationship with ductile shear zones induced by detachment faulting, making it a potential proxy for exploration targeting of Li-Be-mineralized occurrences at the regional scale as well as in other metallogenic provinces worldwide.

The Ransko (ultra)mafic massif, Bohemian Massif, Czech Republic, hosts several Ni–Cu–(PGE) deposits and peculiar Zn–Cu–Ba ores. Geochronology integrated with petrography, bulk-rock, and mineral compositions together with Sr–Nd–Pb–Hf–Os–O isotopic systematics of barren and variably mineralized (ultra)mafic lithologies as well as massive ores reveal a complex evolution of the Ransko massif and its mineralizations. The Sm–Nd and U–Pb ages obtained for gabbros and cross-cutting granite porphyry, respectively, overlap with Re–Os ages of Ni–Cu–(PGE) and Zn–Cu ores and limit the formation age of (ultra)mafic rocks and metal accumulations to ~ 370–345 Ma. Compositional variations indicate derivation of parental melts of the Ransko massif from metasomatized, Variscan sub-arc mantle and underscore the importance of assimilation–fractional crystallization and crystal accumulation processes. The Ni–Cu ores were emplaced through the gravity-driven percolation of dense sulfide liquids along previously weakened structures associated with the downward crystal fractionation. The orogenic and arc-related nature of the Ransko Ni–Cu–(PGE) mineralization shares some remarkable similarities with some other Ni–Cu deposits in the European Variscan Belt highlighting the significance of these deposits emplaced in arc-related crustal domains. Yet, the variable nature of these mineralizations indicates complex processes that happen during the emplacement and evolution of the parental magmas driving their favourable metal contents.

The structurally controlled, vein-hosted copper deposit of the Frontier Mine is distinct from the vast majority of sediment-hosted, stratiform Cu(-Co) deposits of the Zambian Copperbelt. Successively emplaced vein sets document the close interplay between the progressive structural evolution of the deposit, recording northeast-southwest shortening, and associated hydrothermal fluid flow and alteration (albitization). The deposit is hosted by greenschist-facies metasedimentary rocks of the Mwashya Subgroup in the first-order hinge zone of a regional-scale, refolded, recumbent fold (F₁/F₂). Early bedding/S₁-parallel veins (Vein Set 1) formed during layer-parallel shearing and the onset of recumbent folding (F₁). This early vein generation is relatively poorly mineralized, but was associated with a near-pervasive, bedding-parallel albitization and replacement of the mainly metapelitic wall rocks. The reaction hardening process promoted brittle deformation during the subsequent upright refolding (F₂) of the rocks and the formation of a second generation of highly mineralized, saddle-reef type veins (Vein Set 2) in the hinges of particularly upright F₂ folds (F₁/F₂). The controls of Vein Set 2 by fold hinges defines the overall shoot-like geometry of the orebody, parallel to the SE-plunging folds. The subhorizontal orientation and brecciated textures of a subsequent Vein Set 3 underline the formation of veins through continued northeast-southwest shortening of the brittle wall rocks during the lock up of the refolded first-order fold. The overprinting and structural relationships between vein sets, alteration and the regional fold structures signify a syn-tectonic, long-lived, multi-phase mineralization history during the Lufilian Orogeny. 

Granite-related mineral deposits are major primary sources of the critical metals tin (Sn) and lithium (Li). The utility of accessory minerals such as zircon and apatite as pathfinders to these ore deposits has been a subject of great interest in recent years, with a number of geochemical discriminants having been developed to distinguish barren from metal-fertile and mineralised intrusions. Here, we study the potential of apatite as an indicator mineral for tin and lithium mineralisation using a compilation of published apatite trace element data as well as new data for the mineralised Cornubian batholith and barren Bhutanese leucogranites. Critical examination of common geochemical discriminants tracing magma fractionation and redox conditions (Mn, Eu/Eu*, La/Yb_N and Sr/Y) reveals large and overlapping data scatter for both barren and Sn-fertile intrusions. This calls into question the utility of these petrogenetic indicators to pinpoint tin metallogeny. Instead, prima facie metal concentrations directly related to tin mineralisation (i.e., Sn and Li) are consistently elevated in apatite from fertile and mineralised intrusions. Based on our data compilation, Li and Sn concentrations in apatite are the most robust indicators for Sn (and Li) mineralisation, and we encourage the community to include Li and Sn in their analytical routines to further test these observations and explore their implications for tin metallogeny.

Mantle-derived mafic-ultramafic melts are the primary host for magmatic Ni-Cu-Co-PGE deposits. One common assumption about this mineral system is that Ni-fertility is a product of high-degree melting of anhydrous mantle peridotites, including a substantial contribution from olivine. However, in metasomatised mantle rocks, which partially melt at lower temperatures than anhydrous peridotites, Ni is hosted by a range of minerals, including hydrous phases such as phlogopite and amphibole in addition to olivine and orthopyroxene. The lower melting point of these hydrous phases makes Ni in phlogopite a potentially significant contributor to the Ni enrichment of mantle melts from metasomatised assemblages. We analyse a suite of phlogopite-bearing mantle rocks which display variably metasomatised assemblages using SEM mapping to quantify mineral assemblages, and laser ablation ICP-MS to determine the Ni deportment in these rocks. Phlogopite in hydrous peridotites contains 859–1126 ppm Ni equating to ~ 12% of the bulk Ni content in an assemblage containing 25% phlogopite. Mica-Amphibole-Rutile-Ilmenite-Diopside rocks contain phlogopite with 428–715 ppm Ni, which can contribute up to 50% of the bulk Ni in an assemblage of 30% phlogopite. At temperatures below the dry peridotite solidus (< 1300 °C), phlogopite can become a significant contributor of Ni to mantle melts. Thus, partial melting of metasomatised hydrous assemblages can produce Ni-fertile mafic-ultramafic magmas without substantial temperature perturbations such as those associated with mantle plumes. This opens up a range of geodynamic settings for Ni sulfide fertility, away from large igneous provinces and their plumbing systems, into settings such as orogenic belts, arcs and intraplate rifts.

Sedimentary manganese (Mn) mineralization requires a switch between anoxic and oxic water column conditions, which is commonly explained by the “bathtub ring” model and more recently interpreted by the emerging “episodic ventilation” model. To date, however, it remains unclear regarding how to distinguish between these two mechanisms, profoundly influencing Mn ore prospecting. Here, we conducted a comprehensive investigation on the Muhu Mn deposit in northwestern China. The upward lithological variations from breccia-dominated to fine-grained siliciclastic units (e.g., black shales) are typical of sequence characteristics of rifted basins. Black shales were deposited in deep waters due to continued tectonic subsidence that resulted in hydrographic restriction and bottom water euxinia, as indicated by their high ratios of Fe_HR/Fe_T and Fe_Py/Fe_HR, as well as relatively low Mo/TOC ratios. The Mn ore beds are interbedded with black shales and consist of divalent Mn minerals (e.g., rhodochrosite). They display shale-normalized positive cerium anomalies and negative inorganic carbon isotopes and Mo isotopes, suggesting that these Mn carbonate minerals originated from the diagenetic conversion of primary buried Mn oxides deposited under oxic benthic conditions. Taken together, the intimate spatial association between Mn ore beds and black shales records a dynamic temporal redox change. Such a redox shift is consistent with the “episodic ventilation” scenario, where incursions of oxygenated seawater triggered the deposition of initial Mn oxides. In contrast with the “bathtub ring” model, the ventilation scenario represents distinct spatial-temporal configurations of redox-hydrological conditions. Therefore, deciphering the detailed redox variations of Mn-hosting sedimentary successions, in conjunction with paleogeographic reconstruction, is the key to distinguishing between these two mechanisms.

Modern seafloor massive sulfide deposits distributed along mid-ocean ridges are typically classified as mid-ocean ridge basalt- and ultramafic-hosted types, based on mineralogical and geochemical characteristics that result from the different water–rock interactions between the two substrates. However, the Mirae-2 vent field (MVF-2) along Central Indian Ridge, which was newly discovered on the slope of an oceanic core complex, deviates from this common concept. Mineralogical and geochemical data indicate that the formation of chimney and mound samples was primarily controlled by changes in physicochemical fluid conditions (temperature, pH, ƒS₂, and ƒO₂) driven by varying degrees of fluid–seawater mixing. In particular, the prevalence of sulfide assemblages (pyrrhotite + isocubanite + Fe-rich sphalerite), the Cu–Au-rich mineralisation, and the enrichments of Co (average = 1109 ppm) and Sn (203 ppm) are similar to those of other ultramafic-hosted sulfide deposits, but the high amounts of barite and galena, and the enrichments of Ba (> 100,000 ppm) and Pb (up to 8.91 wt%) reflect the contribution of distinct metal sources other than ultramafic substrates. The extremely positive δ³⁴S values of pyrite (average = + 15.1 ± 1.7‰) and pyrrhotite (+ 6.37 ± 0.5‰) indicate that metals and S in the MVF-2 were likely derived from serpentinised ultramafic rocks with intense mixing of fluids with seawater, whereas the unusually radiogenic Pb isotope ratios of sphalerite (²⁰⁶Pb/²⁰⁴Pb = 18.531–18.559, ²⁰⁷Pb/²⁰⁴Pb = 15.540–15.564, and ²⁰⁸Pb/²⁰⁴Pb = 38.632–38.693) suggest that the enriched mid-ocean ridge basalts (i.e., MVF-2 basalts) near the ridge axis also had an important role in the supply of some metals (Pb and Ba) to the MVF-2 fluids. Our results indicate that the multi-stage fluid-rock reactions with basalt and subsequent ultramafic rocks produced the multi-source hydrothermal fluids, thereby resulting in the different mineralogy and geochemistry of the MVF-2 compared with other ultramafic-hosted sulfide deposits.

The Lafigué gold deposit (Western African Craton, Ivory Coast) is located in the northern part of the Toumodi-Fétékro greenstone belt, and its formation is related to the development of a NNE-SSW-striking sinistral shear zone during the regional D₂ deformation phase. Transpression is evidenced by a contractional jog expressed by E-W-trending, S-dipping thrusts. Boudinaged fault veins and horizontal extension veins infilled by a quartz-calcite-tourmaline-sulfide-gold assemblage have been developed along these thrusts. Two generations of hydrothermal tourmaline have been identified: (1) Tur_2a relates to a barren event, when (2) Tur_2b is associated with gold endowment. In situ analyses of major elements and boron isotopic ratios in tourmaline reveal that the precipitation of tourmaline and gold might result from multiple fluid discharges in damaged zones of shear zones as a consequence of fault-valve behaviour. It is expressed by a slight oscillatory zoning within the Tur_2b crystals, combined with fluctuations in the #Mg within the growth bands (#Mg from 0.56 to 0.63). The overall homogeneous crystal chemistry of Tur_2a and Tur_2b (up to 2000 µm), combined with a quite homogenous δ¹¹B between the core and the different growth bands (from -20.06 to -18.1 ‰), suggest a crystallisation from geochemically and isotopically relatively homogenous hydrothermal fluids. It suggests that no specific hydrothermal processes (such as fluid mixing, Rayleigh fractionation, changes in temperature or water/rock ratio) were sufficient enough to change the isotopic composition of tourmaline during its growth. We propose that fluid discharge and flash vaporization following the fault failure along the thrusts planes is the main mechanism allowing the crystallization of oscillatory zoned tourmaline and gold at the Lafigué orogenic gold deposit.

The Neves Corvo Cu-Zn-Pb(-Sn) deposit (Portugal) is one of the largest volcanogenic massive sulfide deposits (VMS) worldwide, hosted by Upper Devonian to Early Carboniferous rocks. Originally, it contained an early structurally controlled tin orebody (stockwork and massive cassiterite), which has now been mined out. In this study, we report the first occurrence of phosphate minerals (apatite, florencite, and xenotime) within the tin stockwork at Neves Corvo. We present a high-resolution multi-analytical study using petrographic, mineral chemistry, and whole-rock geochemical methods to understand the genesis of these phosphates and their implications for tin at the Neves Corvo deposit. Our results demonstrate that apatite forms coevally with cassiterite and has low trace element contents except for S, Sr, Y, and MREE (Middle Rare Earth Elements; 10–100 ppm) with a bell-shaped chondrite (C1) normalized REE pattern. We suggest that apatite likely formed as chlorapatite or oxyapatite that was subsequently metasomatized to fluorapatite with minor carbonate during hydrothermal alteration related to sulfide mineralization. The REE pattern of apatite, together with the presence of secondary phosphates (florencite and xenotime), indicates preferential scavenging of REE to form the latter phases due to the interaction with NaCl-rich and, to a minor extent, fluorine-rich fluids in an aluminum-saturated system. This study underscores how the analyses of primary and secondary phosphate minerals can help to track the evolution of the hydrothermal system and partially constrain the fluid composition and fluid-rock interaction processes. Therefore, the approaches outlined here are applicable to any hydrothermal ore-forming system where phosphate phases are formed.