Mineralium Deposita最新文献

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.

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.