Mineralium Deposita最新文献

The Augmitto-Bouzan deposit is a 12 km long segment of the Larder Lake-Cadillac Deformation Zone (LLCDz) south of Rouyn-Noranda (Québec, Canada) that is characterized by an uneven gold distribution hosted in quartz-carbonate ± tourmaline veins within Piché Group ultramafic rocks. This study compares the fluid flow conditions between the variable gold-endowed sectors to identify deposit-scale processes responsible for gold endowment. Stable isotopes indicate that quartz and tourmaline have equilibrium temperatures (228–⁠420 °C) that likely define a high vertical thermal gradient (~ 30 °C/100 m) along the LLCDz. Covariation between temperature and computed δ¹⁸O_H2O and δD_H2O is interpreted to result from mixing between a high temperature (> 420 °C), high δ¹⁸O (> 10.8‰), and low δD (< –29‰) deep-seated metamorphic fluid, and a low temperature (< 230 °C), low δ¹⁸O (< 4‰) and high δD (~ 0‰) upper crustal pore fluid. Local upwelling of auriferous deep-seated fluid, shown by interpolation of δ¹⁸O_H2O in the gold-endowed Augmitto-Cinderella and Astoria segments, was likely focused along higher permeability deformation-related pathways. Sectors of low gold endowment have lower δ¹⁸O_H2O and fluid/rock ratios, likely reflecting a larger proportion of upper crustal fluid and differences in fluid-flow behavior. Modeling of fluid flow shows that this is due to 1) weaker metamorphic fluid flux in the thinner band of Piché Group rocks and 2) more porous volcanic rocks north of the LLCDz, drawing more pore fluid into the fault. We suggest that most of the variation of gold endowment is related to variations in advection of auriferous metamorphic fluid along the segment, whereby a weaker metamorphic fluid flux or increased admixture of upper crustal fluids decrease the gold potential along the LLCDz.

Tin deposits within the Baoshan Block in western Yunnan are posited as the northern extension of the Southeast Asian Tin Belt, yet they have been relatively underexplored in terms of geochronology. This study concentrates on the Yunling tin deposit, globally recognized for its production of gemstone-quality cassiterite crystals. We applied U–Pb geochronology on cassiterite, complemented by analyses of its trace element composition and in situ oxygen isotopes in cassiterite and quartz, aiming to delineate the deposit's age and genesis. The Yunling orebodies are hosted by deformed Triassic granite, closely adjacent to the Cenozoic Nantinghe strike-slip shear zone. Three distinct hydrothermal stages have been identified: quartz-cassiterite-muscovite-tourmaline (stage I), arsenopyrite-pyrite-cassiterite-quartz (stage II), and arsenopyrite-calcite-quartz (stage III). Cassiterite grains from a quartz-cassiterite-muscovite-tourmaline vein yield a U–Pb age of 24.4 ± 1.4 Ma (2σ, n = 41, MSWD = 1.6), notably younger than the ore-hosting Triassic granite. Paired cassiterite and quartz oxygen isotopes yield δ¹⁸O_H2O values of 5.8 – 7.2 ‰, indicating a magmatic fluid source during stages I and II. The trace element compositions of the Yunling cassiterite resemble those of granite-related tin deposits, suggesting a genetic link between tin mineralization and an unexposed late Cenozoic granite intrusion. Notably, the Triassic granite of Yunling shows a lower degree of magmatic fractionation, thus presenting a limited potential for tin mineralization. The timing of mineralization is correlated with the activity of the Nantinghe fault, alongside geophysical evidence of crust-mantle decoupling and asthenosphere upwelling. Consequently, our findings imply that the Yunling tin mineralization is genetically related to hidden granites, to guide future exploration efforts in western Yunnan.

The Jinchang deposit, Ailaoshan Belt, is a hydrothermal gold-nickel deposit in which nickel mineralization formed during Triassic accretionary orogeny and gold mineralization during Miocene collisional orogeny. Although the nickel and gold orebodies largely overlap in an ophiolite melange at the contacts between ultramafic and metasedimentary sequences, nickel and gold concentrations have only a weak correlation in orebodies intersected in drill cores. The hydrothermal nickel sulfide ores are mainly concentrated at ultramafic-metasedimentary rock contacts. Broad alteration zones surround the contacts, with proximal quartz + clinochlore + magnesite in both rocks through quartz + fuchsite to distal muscovite + quartz assemblages in metasedimentary rocks. An apatite U–Pb age of 235.8 ± 1.8 Ma and a pyrite Re-Os age of 254 ± 21 Ma from the nickel mineralization indicate that it formed before the closure of the Ailaoshan Ocean. The As- and S-rich fluids during oceanic subduction leached Ni from the ultramafic rocks in the ophiolite melange forming the hydrothermal nickel sulfide ores. Orogenic gold mineralization comprises auriferous veins that host gold, Au- and Ag-rich sulfosalt. The veins cut the sulfides associated with nickel mineralization. The auriferous fluids reacted with nickel ore-stage pyrite forming porous or sieve-textures and patchy zoning in BSE images with native gold in pores. Geological and paleomagnetic evidence indicates that Miocene gold mineralization occurred in highly deformed Devonian metasedimentary rocks after the Oligocene–Miocene Ailaoshan sinistral shearing (~ 30 to 20 Ma). The auriferous fluids are most likely sourced from the metasomatized mantle lithosphere if Jinchang has a similar source to other orogenic gold deposits in the Ailaoshan Belt.

The Cathedrals Ni-Cu prospect, located at the western margin of the Eastern Goldfields of the Yilgarn Craton, is hosted within a mafic intrusion interpreted as a sill complex. U-Pb dating of apatite from the sill yielded a crystallisation age of 2336 ± 64 Ma, inferring an association of sill emplacement and Ni mineralisation related to emplacement of the c. 2400 Ma Widgiemooltha dike swarm. The sill is typically differentiated into a lower olivine orthocumulate layer overlain by a dolerite unit containing xenoliths of partially assimilated granitoids in its upper portion. The latter is interpreted to be the result of stoping and melting of the granitic hanging wall, thereby creating a gravitationally stable buoyant melt layer beneath the top contact. Ni-Cu-Fe sulfides are increasingly abundant towards the base of the sill, ranging from globular disseminated sulfides to net-textured and massive sulfides at the basal contact. The presence and orientation of sulfide globule-bubble pairs indicates a primary near-horizontal orientation. Massive sulfides commonly exhibit a loop texture with pyrrhotite grains surrounded by pentlandite and chalcopyrite. Despite the variety of sulfide textures, sulfur isotopes have a homogeneous mantle-like signature without significant mass independent fractionation. Mineral chemistries that indicate sulfide prospectivity in larger intrusions do not work as effectively in this small sill, therefore new indicators may need to be developed to explore for similar deposits. To date, there are no other known magmatic deposits of this age in Australia. Sills of this age may be more prospective than previously recognised.

The Irish Orefield is characterised by the presence of both Zn-Pb- and Cu-Ni-As-rich deposits, prospects, and orebodies in similar structural and stratigraphic positions. However, the genetic relationships between these mineralisation types are still debated. In this article, we present new mineralogical, paragenetic, and mineral-chemical observations from the Cu-Ni-As-rich ores at the classic Lisheen deposit, County Tipperary. These observations indicate the intimate association and cogenetic nature of these ores with the more abundant Zn-Pb-rich mineralisation. Specifically, both mineralisation types appear to have formed at the same time, under similar physicochemical conditions, and from the same ore fluids. In addition, both types of mineralisation contain elevated Ge contents. The cogenetic nature of the two mineralisation types, the relative absence of Cu-Ni-As-rich ores from most of the larger Irish-type Zn-Pb deposits compared to expectations derived from probable ore fluid compositions, and finally, the known geological characteristics of larger Cu-Ni-As-rich ore bodies, like Gortdrum, indicate that significant Cu-Ni-As-rich mineralisation could be present at lower stratigraphic levels across the Irish Orefield. Areas with extensive known Zn-Pb mineralisation are expected to be particularly prospective for such ores, which may occur at stratigraphic levels as deep as the Old Red Sandstone. This may have additional implications beyond Ireland, and could point to the potential for undiscovered Cu-rich ores in low-temperature carbonate-hosted Zn-Pb districts elsewhere.

The Geyer tin skarn in the Erzgebirge, Germany, comprises an early skarnoid stage (stage I, ~ 320 Ma) and a younger metasomatic stage (stage II, ~ 305 Ma), but yet, the source and distribution of Sn and the physicochemical conditions of skarn alteration were not constrained. Our results illustrate that contact metamorphic skarnoids of stage I contain only little Sn. REE patterns and elevated concentrations of HFSE indicate that garnet, titanite and vesuvianite of stage I formed under rock-buffered conditions (low fluid/rock ratios). Prograde assemblages of stage II, in contrast, contain two generations of stanniferous garnet, titanite-malayaite and vesuvianite. Oscillation between rock-buffered and fluid-buffered conditions are marked by variable concentrations of HFSE, W, In, and Sn in metasomatic garnet. Trace and REE element signatures of minerals formed under high fluid/rock ratios appear to mimic the signature of the magmatic-hydrothermal fluid which gave rise to metasomatic skarn alteration. Concomitantly with lower fluid-rock ratio, tin was remobilized from Sn-rich silicates and re-precipitated as malayaite. Ingress of meteoric water and decreasing temperatures towards the end of stage II led to the formation of cassiterite, low-Sn amphibole, chlorite, and sulfide minerals. Minor and trace element compositions of cassiterite do not show much variation, even if host rock and gangue minerals vary significantly, suggesting a predominance of a magmatic-hydrothermal fluid and high fluid/rock ratios. The mineral chemistry of major skarn-forming minerals, hence, records the change in the fluid/rock ratio, and the arrival, distribution, and remobilization of tin by magmatic fluids in polyphase tin skarn systems.

Iron-titanium-vanadium (Fe-Ti-V) oxide mineralisation is commonly associated with Proterozoic massif-type anorthosites, but the conditions required for their formation remain poorly understood. The Etoile Suite Mafic Intrusion (1149 ± 11 Ma), in the Grenville Province, Quebec (Canada), comprises a layered mafic intrusion that is coeval with nearby massif-type anorthosites. The mafic intrusion consists of troctolite and olivine gabbro cumulates, where magnetite and ilmenite are intercumulus at the base (Zone A) and top (Zone C) but cumulus (<30 modal %) in the centre (Zone B). Towards the base of Zone B, vanadium mineralisation occurs in a 1-km-thick oxide-rich wehrlite horizon, where V-rich titanomagnetite (<1.85 wt% V₂O₅) and ilmenite form semi-massive oxide layers. From the base to the top of Zone B there is an overall progressive decrease in An_pl, Fo_ol, and Mg#_cpx, and in Cr and Ni concentrations of magnetite, albeit with several reversals to more primitive compositions, including one near the base of Zone C. This indicates fractional crystallisation in an open magma chamber. The intrusion crystallised at moderate fO₂ (~FMQ 1.1 ± 0.3), resulting in the late crystallisation of V-rich magnetite from a relatively evolved magma. The parental magma was likely a high-Al basalt derived from a depleted mantle source, recording minimal crustal contamination, in contrast to coeval massif-type anorthosites that commonly contain orthopyroxene reflecting higher degrees of crustal contamination. As a result, V mineralisation in noritic anorthosites formed at higher fO₂, with early crystallisation of relatively V-poor magnetite, whereas magnetite in troctolitic-olivine gabbroic intrusions crystallised later with higher V contents, due to lower fO₂.

The unconformity-related uranium (URU) deposits in the Proterozoic Athabasca Basin are one of the most important U resources in the world. This type of U deposit can be divided into monometallic (U) and polymetallic (U-Ni-Co-As) subtypes. While it is generally agreed that the URU deposits formed from reaction between oxidizing, basinal brines carrying U and/or Ni-Co-As with reducing basement fluids or lithologies, it is debatable whether the polymetallic deposits formed from co-enrichment of U-Ni-Co-As or enrichment of U superimposed by a separate Ni-Co-As mineralization event. This study addresses this problem through mineralogical, geochemical and fluid inclusion investigation of the Midwest U-Ni-Co-As deposit. Petrographic studies indicate that the sequence of ore precipitation started with uraninite, followed by Ni-Co arsenides and sulfoarsenides and then Cu-Pb-Fe sulfides, and this sequence was repeated episodically. This observation suggests that the deposit did not form from two separate U and Ni-Co-As mineralization events, but rather multiple episodes of U-Ni-Co-As mineralization. Linear correlations between chemical ages and Si-Ca-Fe contents of the most pristine uraninite U1 suggest a maximum primary mineralization of ca. 1600 Ma, which is consistent with the inferred primary U mineralization age in the Athabasca Basin. Microthermometric and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in syn-mineralization drusy quartz indicate that the composition of the ore-forming fluids is characterized by the H₂O-NaCl-CaCl₂-KCl-MgCl₂ system and comparable to those from both monometallic and polymetallic URU deposits. The relationship between U and Ni + Co in the fluid inclusions and its comparison with other URU deposits support a model in which U and Ni-Co were co-enriched in a unified mineralization process. The development of breccia structures in the ores and the dramatic fluid pressure fluctuation revealed by fluid inclusions suggest that the deposit formed from multiple episodes of fluid flow related to repeated reactivation of basement-rooted faults.

The 18 × 4 km Davenda-Klyuchevskoe cluster in the Mogocha mineral district of the Siberian craton hosts gold, silver, molybdenum and copper in six types of mineralization. The general sulphide zoning at the Sergeevskoe and Klyuchevskoe deposits, the largest in the cluster, is similar to porphyry systems, but the orebodies form 4.5 × 1 km multiple linear sulphide-rich quartz-veinlet swarms, rather than a bulk mineralized envelope. Five types of mineralization formed at 162 − 150 Ma. They are clearly overprinted by northeast-striking epithermal Au-Ag carbonate-quartz veins. All mineralization is genetically linked to the Peak Klyuchi subvolcanic centre of Late Jurassic to Early Cretaceous age (159 − 132 Ma) which is part of the Amudzhikan intrusive complex, consisting of early complexly shaped ENE-striking granodiorite porphyry stock and dykes, intruded by magmatic to hydrothermal breccia and five generations of WNW-trending dykes of dioritic porphyry, hybrid porphyry, rhyolite, and ultimate lamprophyre. The dykes control or parallel five types of megastockwork orebodies within a dextral extensional strike-slip duplex. However, Au-Ag epithermal veins follow late-mineral northeast faults, dividing the megastockwork into several domains. The Davenda-Klyuchevskoe cluster is part of the Shilka Mo-(Au-Ag-Cu) metallogenic belt, striking within the Siberian craton just 25 km north in parallel to the Mongol-Okhotsk suture. Geochronological and petrological data suggest that the intrusive complex and its mineralization formed in relation to northward-dipping subduction prior to scissor-like suturing in this segment of the Mongol-Okhotsk Ocean in response to the northward push by the North China and Yangtze cratons towards Siberia.