Mineralium Deposita最新文献

Tungsten mineralization in the Bodó mineral district (9 Mt with an average grade of 2% WO₃) is in a sequence of metasomatized marbles and W-(Mo)-skarn lenses in the Seridó Belt, northern Borborema Province. The marble lenses have variable amounts of diopside, grossular, scapolite, phlogopite, and tremolite. The skarn lenses are mainly composed of massive grossular, diopside, vesuvianite, epidote, and quartz. A spatially related granite yielded a SHRIMP U‒Pb zircon date of 536.6 ± 3.4 Ma and a ⁴⁰Ar/³⁹Ar biotite date of 490.65 ± 0.67 Ma, whereas a nearby pegmatite yielded a ⁴⁰Ar/³⁹Ar muscovite date of 501.63 ± 0.59 Ma. Literature data for molybdenite in the skarn mineralization yielded a Re‒Os date of 510 ± 2 Ma, which is coeval with U‒Pb dates of columbite-tantalite from other regional pegmatites (515–509 Ma). Therefore, it is likely that pegmatite magmatism acted as the source of fluid and heat for the mineralization. The C–O stable isotope data for marbles and skarns are consistent with interaction of magmatic fluid and host marble at variable XCO₂ conditions. T-XCO₂ pseudosections define peak conditions of metamorphism/metasomatism at 650–600 °C over a wide range of XCO₂ (between 0.4 and 0.8), whereas the retrograde stage started at ~ 550 °C. Late garnet crystallization at low XCO₂ (< 0.2) indicates high H₂O influx, while scapolite crystallization required high XCO₂ (~ 0.8). Together with the interpretation of textural relationships, these observations indicate that skarn and marble formation occurred under open-system conditions with fluctuating XCO₂ fluid composition as a consequence of magmatic fluid infiltration.

The Wigu Hill Carbonatite, located south of Uluguru Mountain, is amongst the REE-endowed carbonatites in Tanzania. The carbonatite comprises apatite dolomite carbonatite that has been locally brecciated and intruded by small bodies of mica dolomite carbonatite. These early carbonatites are fine to medium grained, poorly enriched in REE₂O₃ (< 0.4 wt%), and show elevated Nb (> 200 ppm). The early carbonatites are crosscut by REE-bearing carbonatite dikes that host pegmatitic, well-preserved pseudomorphs after burbankite. The REE-bearing carbonatites are characterised by high REE₂O₃ (6–10 wt%), and pseudomorphs that vary in colour and mineralogy, reflecting the dissolution of primary burbankite through reaction with evolving carbothermal fluids in two major phases; (1) early altered burbankite formed yellow-colored pseudomorphs typified by an assemblage of synchysite-(Ce) with high (La/Ce)_N - (La/Nd)_N ratios, barite, Ca-strontianite, calcite, and quartz; and (2) subsequent late alterations by highly evolved fluids resulted into green and pink-colored pseudomorphs consisting of synchysite-(Ce) with low (La/Ce)_N - (La/Nd)_N ratios, barite, Ca-strontianite, fluorite, calcite, quartz, apatite, monazite, and Al-REE-phosphates. The stable C-O and Mg isotopes signatures of dolomite across Wigu Hill indicate a pristine mantle source (δ¹³C_VPDB -4.1‰ to -6.2‰; δ¹⁸O_VSMOW +6.5‰ to + 7.31‰ and δ²⁶Mg -0.44 to + 0.19‰), and are locally modified by surface processes which resulted in bastnaesite enriched zones with up to 15 wt% REE₂O₃. Textural, geochemical, and stable isotope data tracks a polygenetic evolution of Wigu Hill with the main REE mineralization phase occurring at the end of magmatic phase as a result of magmatic fractionations. Reworking by carbothermal fluids and locally by surface process has resulted in REE enrichment.

Two magmatic REE-rich occurrences, located near Jamestown, Colorado, and hosted in the Precambrian Longs Peak granite batholith, exhibit unusual textures that suggest formation by fluoride-silicate melt immiscibility. Both contain small (<2 mm diameter) globular F-, P-, and REE-rich segregations of fluorite and monazite-(Ce). In addition, the northern of the two localities preserves evidence of a second melt immiscibility event in the form of larger (up to several cm diameter) aplite-hosted globular segregations of fluorite and the REE minerals allanite-(Ce), monazite-(Ce), fluorbritholite-(Ce), törnebohmite-(Ce), and cerite-(Ce). The southern of the two localities lacks these cm-scale globular textures, but instead contains much larger aggregates of these same REE minerals, with up to >57 wt. % ΣREE₂O₃, yet no fluorite, as well as large aggregates of allanite-(Ce) and quartz, and an amphibole-bearing REE-rich rock containing allanite-(Ce), other REE minerals, quartz and minor apatite. A new Nd-Sm laser ablation age of 1.422(24) Ga on monazite-(Ce) and allanite-(Ce) from the southern locality implies the same age of formation of 1.420(25) Ga as for the northern locality, with equally similar initial ε_Nd1.42Ga values of these REE minerals. A newly discovered third locality, containing primarily allanite-(Ce), minor monazite-(Ce), and thorite, without fluorite, extends the number, spatial distribution and total volume of these mineralogically unusual magmatic REE occurrences. We suggest that the REE were concentrated in these three localities by multiple stages of fluoride-silicate melt immiscibility. For the southern locality, slower cooling of a possibly larger magma volume, or in a deeper environment, allowed greater aggregation of the immiscibly separated REE-rich phases, as well as loss of the volatile element F, resulting in a greater availability of Ca accommodated by the crystallization of amphibole and minor apatite.

The Xiaoxi’nancha porphyry Au-Cu deposit is located in Yanbian, Jilin Province, NE China. Gold-Cu mineralization is mainly associated with chlorite-sericite alteration. The ⁴⁰Ar/³⁹Ar age of pre-mineralization hydrothermal biotite in potassic alteration defines a relatively well-defined cluster at ~ 111 Ma to 114 Ma with a total fusion age of 112.0 ± 0.3 Ma. In-situ secondary-ion mass spectrometry U-Pb dating of hydrothermal titanite occurring with chalcopyrite yielded an intercept age of 109.0 ± 2.4 Ma. The similarity between the biotite and titanite formation ages suggests a mineralization age of ~ 110 Ma. Chlorite, quartz and apatite coexist in equilibrium and are closely related to mineralization. The Al-in-chlorite geothermometer indicates a formation temperature of 236–351℃ (mean 309℃), and the quartz-apatite pair yielded an average formation temperature of 306℃. The in-situ δ³⁴S compositions of sulfide have restricted and slightly positive values (pyrite 2.3 to 3.9‰, chalcopyrite 1.6 to 3.8‰ and molybdenite 2.3 to 3.7‰). The fluid δ¹⁸O values, calculated assuming quartz-fluid equilibrium, vary from 2.4 to 5.5‰ (average = 4.0‰). Therefore, the ore-forming hydrothermal fluids were of moderate-temperature with predominantly magmatic characteristics. Apatite exhibits distinct variations in structure and composition, and slight variations in oxygen isotopic composition. The areas in apatite with dark BSE textures are characterized by lower δ¹⁸O values, Cl contents and temperatures and higher F contents, consistent with the result of water–rock interaction rather than mixing with meteoric water. The water–rock interaction and its resulting cooling, can reduce the metal solubility, likely triggering mineralization at Xiaoxi’nancha.

Orthopyroxene oikocrysts and globular ores are both observed in the Shitoukengde Ni-Cu sulfide deposit within the Eastern Kunlun Orogenic Belt in China. Through the utilization of microbeam X-ray fluorescence (micro-XRF) and electron probe micro-analyzer (EPMA) mapping techniques, complemented by 3D morphology analysis using high-resolution X-ray computed tomography (HRXCT), we conducted a comprehensive investigation into the 2D and 3D textures of orthopyroxene oikocrysts and globular ores in the Shitoukengde Ni-Cu sulfide deposit. The contents of orthopyroxene oikocrysts within the lherzolite gradually increases as it approaches the contact with coarse-grained orthopyroxenite. Both the orthopyroxene oikocrysts in the lherzolite and the cumulus orthopyroxene in the coarse-grained orthopyroxenite are centimeter-sized and contain corroded chadacrysts of olivine, exhibiting similar Cr-Al sector and oscillatory zoning. It indicates that the orthopyroxene oikocrysts rapidly grew in a dynamic and fluctuating magmatic environment, rather than in a static crystal mush. We propose that the orthopyroxene oikocrysts initially grew in a boundary layer between an olivine orthocumulate and an orthopyroxene-saturated magma. The orthopyroxene oikocrysts and olivine crystals were then entrained within a flowing magma and redeposited in their current location. Globular sulfides in the coarse-grained orthopyroxenite can reach sizes of up to one centimeter and are not accompanied by silicate caps. The particle size distribution (PSD) plots of the globular sulfides exhibit concave-up PSD curves, indicating that the larger sulfide droplets are likely formed through the coalescence of sulfide microdroplets. During postcumulus processes, the downward migration and coalescence of microdroplets within the interstitial framework of orthopyroxene cumulate lead to the formation of larger sulfide blebs. The coalesced sulfide blebs were then stranded in the pore spaces of the crystal mush due to the capillary effects, resulting in the formation of centimeter-sized globular sulfides. The morphology of coalesced sulfide droplets within orthopyroxene cumulate is influenced by the relative sizes of the sulfide blebs, pore bodies, and pore throats within the interstitial framework. This study proposed a cumulus origin for the orthopyroxene oikocrysts and highlights that the coarse-grained rocks facilitate the formation of the globular ores.

Chromium-zoning patterns in pyroxene from the economically significant Ni-Cu sulfide deposits at Nova-Bollinger (Western Australia) and Kevitsa (Northern Finland) were investigated using XRF mapping, automated mineralogy, and EPMA analyses. At Nova-Bollinger, complex Cr-zoning patterns are found widely throughout the cumulus orthopyroxene and clinopyroxene within the Lower Intrusion, a small chonolith that hosts the vast extent of the sulfide mineralisation. Cumulus pyroxenes with visible sector and abrupt zonation patterns have been found up to 150 m vertically away from the massive sulfide ore. Complex zoning patterns are observed throughout the Kevitsa intrusion, in the form of strong oscillatory zoning in cumulus clinopyroxene and sector zoning in idiomorphic orthopyroxene oikocrysts. Kevitsa pyroxenes show varying degrees of hydration, leading to epitaxial replacement by amphibole. Cr zonation is visible through the early stages of this alteration, with preservation enabled by the presence of Cr-rich epitaxial amphibole; however, the remnant zoning is lost as the amphibole alteration progresses. Results suggest that Cr zonation in pyroxene may be an effective indicator of dynamic recharged conduits and therefore an indicator of favourable conditions for metal enriched magmatic sulfide ore formation. Such indicators have significant vertical extent from the ore body and can survive partial alteration, which makes them a useful tool for prospectivity assessment of drilled intrusions. Furthermore, our data show that there is potential for complexly zoned pyroxene to be used as an ex-situ prospectivity indicator in glacial till.

The Baoshan district in the southwestern Sanjiang Tethyan domain is an important part of the worldclass Southeast Asian tin (Sn) belt. However, the timing and controlling factors of Sn mineralization are poorly constrained. Here, we conducted laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of cassiterite and monazite, and cassiterite trace element analysis on the Shiganghe and Tiechang Sn deposits (Baoshan district) to unravel the temporal evolution of the regional Sn mineralization. The U–Pb dating of two cassiterite samples from Shiganghe yielded Tera-Wasserburg lower intercept ages of 75.5 ± 3.9 Ma and 75.9 ± 4.8 Ma. U-Pb dating on cassiterite and the cogenetic monazite from Tiechang yielded 32.8 ± 1.3 Ma and 32.2 ± 1.0 Ma, respectively. These ages confirm both Late Cretaceous and Oligocene Sn mineralization events in the Baoshan district. Geological characteristics, and age and geochemical data of cassiterite indicate that Shiganghe is a quartz-vein-type Sn deposit, genetically related to the Late Cretaceous granite that intruded the Ordovician Zhibenshan pluton. Tiechang resembles distal skarn Sn deposits related to the ~ 32 Ma magmatism along the Chongshan shear zone. Tin mineralization in the Tengchong-Baoshan district occurred mainly from the Late Cretaceous to Oligocene, corresponding to the Neo-Tethyan subduction and the subsequent India–Asia continental collision.

The Flatreef occurs at a depth of 700 m under the farm Turfspruit 241 KR in the Northern Limb of the Bushveld Complex. The Flatreef forms part of the Platreef of the Northern Limb, which contains magmatic rocks of the Rustenburg Layered Suite of the Bushveld Complex. The structure of the Flatreef is a flat-lying to gently westerly dipping monoclinal to open fold, 1 km wide and 6 km long. Distinctive features within the Flatreef include the development of cyclical magmatic layering with locally thickened pyroxenitic layers, and associated economically significant poly-metallic mineralisation. Geophysical evidence, exploration drill core, and recent underground exposure show that deformation had a major influence on the Flatreef mineralization. Block faulting and first generation folding affected the orientation and shape of the sedimentary host-rock sequence prior to intrusion of the Rustenburg Layered Suite. These structural and host-rock elements controlled the intrusion of the Lower Zone, and to a lesser degree, the Critical Zone correlatives of the Bushveld Complex in the Northern Limb. During intrusion reverse faults and shear zones and a second generation of folds were active, as well as local extension along layering. Syn-magmatic deformation on these structures led to laterally extensive stratal thickening across them, including the Merensky-Reef correlative that forms part of the Flatreef. This deformation was likely to have been driven by subsidence of the Bushveld complex. Many of these structures were intruded by granitic magmas during the late stages of intrusion, and they were reactivated during extension after intrusion. Thus, structures were active before, during and after the intrusion of Northern Limb, and the structural evolution determined the current geometry and mineral endowment of the Flatreef.

The regolith-hosted rare earth element (REE) deposits in South China are important sources of the world’s REE production. The alteration processes of primary REE-bearing minerals in granitic bedrock remain unclear so that the pathways of REE mobilization from primary minerals to regolith-hosted REE deposits have not yet been well established. Allanite is the principal REE repository in granitic bedrock and may have undergone alteration during deuteric fluid metasomatism and supergene weathering. Here, we document the allanite in the bedrock of the Zuokeng regolith-hosted REE deposit in South China to decode the REE mobilization during interaction of allanite with two different types of fluids. Most allanite grains have four distinct domains in the backscattered electron (BSE) images. Domain 1 is of magmatic origin and enriched in light REE (LREE), whereas Domains 2, 3 and 4 are of hydrothermal origin with different degrees of enrichment in middle to heavy REE (M-HREE). In particular, Domain 4 appears as overgrowth rims with the highest M-HREE concentrations among hydrothermal domains and likely crystallized from Cl-rich deuteric fluids exsolved from granitic magmas, evidenced by consistent U–Pb ages (ca. 159 Ma) and ε_Nd(t) values (-9.4 to -7.3) of Domains 4 and 1. The preferential removal of LREE and uptake of M-HREE from Domains 2 and 3 to Domain 4 is thus attributed to metasomatism by Cl-rich deuteric fluids. On the other hand, some allanite grains in weathered bedrock also interacted with F- and carbonate-rich groundwater and were gradually replaced by synchysite-(Ce) and calcite. Consequently, LREE were concentrated in synchysite-(Ce), whereas M-HREE may have been lost to groundwater. This study unravels that the enrichment of LREE and M-HREE in altered bedrock was initially facilitated by F-, carbonate-rich fluids and Cl-rich deuteric fluids, respectively, which are likely crucial for developing regolith-hosted LREE and M-HREE deposits in South China.

This paper provides a top-down nanoscale analysis of Cu-Ni-Fe sulfide inclusions in laurite from the Taitao ophiolite (Chile) and the Kevitsa mafic-ultramafic igneous intrusion (Finland). High-resolution transmission electron microscopy (HRTEM) reveal that Cu-Ni-Fe sulfide inclusions are euhedral to (sub)-anhedral (i.e., droplet-like) and form single, biphasic or polyphasic grains, made up of different polymorphs, polytypes and polysomes even within a single sulfide crystal. Tetragonal (I4(stackrel{-}{2})d) and cubic (F(stackrel{-}{4})3m) chalcopyrite (CuFeS₂) host frequent fringes of bornite (Cu₅FeS₄; cubic F(stackrel{-}{4})3m and/or orthorhombic Pbca) ± talnakhite (Cu₉(Fe, Ni)₈S₁₆; cubic I(stackrel{-}{4})3m) ± pyrrhotite (Fe_1 − xS; monoclinic C2/c polytype 4C and orthorhombic Cmca polytype 11C) ± pentlandite ((Ni, Fe)₉S₈; cubic Fm3m). Pentlandite hosts fringes of pyrrhotite, bornite and/or talnakhite. Laurite and Cu-Fe-Ni sulfide inclusions display coherent, semi-coherent and incoherent crystallographic orientation relationships (COR), defined by perfect edge-to-edge matching, as well as slight (2–4º) to significant (45º) lattice misfit. These COR suggest diverse mechanisms of crystal growth of Cu-Fe-Ni sulfide melt mechanically trapped by growing laurite. Meanwhile, the mutual COR within the sulfide inclusions discloses: (1) Fe-Ni-S melt solidified into MSS re-equilibrated after cooling into pyrrhotite ± pentlandite, (2) Cu-Ni-Fe-S melts crystallized into the quaternary solid solution spanning the compositional range between heazlewoodite [(Ni, Fe)_3±xS₂] (Hz_ss) and ISS [(Cu_1±x, Fe_1±y)S₂]. Additionally, nanocrystallites (50–100 nm) of Pt-S and iridarsenite (IrAsS) accompanying the sulfide inclusions spotlight the segregation of PGE-rich sulfide and arsenide melt earlier and/or contemporarily to laurite crystallization from the silicate magmas. Cobaltite (CoAsS)-gersdorffite (NiAsS) epitaxially overgrown on laurite further supports the segregation of arsenide melts at early stages of chromitite formation.