Mineralium Deposita最新文献

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.

Currently, 60% of the world’s copper production comes from porphyry copper deposits, often significantly enriched by surface weathering. This paper uses new global datasets and previous work to review the critical processes required for porphyry copper formation and supergene enrichment. Porphyry copper formation requires a subducting arc to create a source magma which traverses a thickened crust subject to high exhumation rates during formation, ranging from 100’s to 1,000’s m/m.y. High exhumation rates potentially trigger magma decompression, causing fluid release, opening fluid pathways along faults and lineaments and/or facilitating telescoping, whereby early porphyry-style mineralization is overprinted and enriched by high-sulfidation mineralization at shallower crustal levels. Later supergene enrichment of the deposit requires precipitation rates > 120 mm/yr and exhumation rates ranging from 10’s to 100’s m/m.y. This allows copper sulfide sources to be continually refreshed for weathering but restricts the amount of erosion. Using the Central Andes, one of the world’s most critical porphyry copper provinces, the understanding gained from analyzing these global databases can explain the temporal and spatial pattern of known deposits. These constraints were used to inform mappable target criteria and data required for mineral exploration at a range of different scales, from orogen (> 100,000 km²), to terrane (100,000–1,000 km²) to arc (1,000–100 km²). The results can be used to help illustrate and inform global exploration strategies for supergene-enriched porphyry copper deposits.

Platinum-group element (PGE) mineralization associated with the Sudbury Igneous Complex (SIC), Canada, generally occurs within brecciated footwall rocks. At the Crean Hill and Vermilion deposits, variations in the ore mineralogy, textures, and whole rock geochemical signatures suggest that PGE deposition involved three stages. During the magmatic stage, sulfide melts were segregated at the base of the SIC and infiltrated the footwall rocks to form sulfide(-PGE) breccia and disseminated PGE mineralization (Crean Hill), and sulfide-PGE veins (Vermilion). Sulfide fractionation is suggested by the disappearance of Ru-bearing michenerite, a decrease in Ru, Rh and Ir tenors, and an increase in Pt, Pd and Au tenors and Cu/Ni away from the SIC contact. The syn-tectonic remobilization stage occurred between ~ 480–550 °C, as suggested by the composition of shear-hosted gersdorffite. At Crean Hill, Pd and Au were decoupled from Pt and remobilized via fluids into the footwall rocks, resulting in Pd and Au enrichment as disseminated michenerite and argentian gold along shear zones. At Vermilion, higher fluid-rock ratios and metamorphic semi-metal melts caused extensive remobilization of Pt, Pd and Au, and deposition of complex telluride, antimonide and arsenide grains within shear zones. A late metasomatic stage at < 300 °C (gersdorffite composition) is observed at Vermilion only, where it caused epidote-albite-quartz-calcite alteration of the SIC rocks and deposition of low-temperature sulfides and precious metals in veins crosscutting shear zones. Together, these findings demonstrate how PGE mineralization should be examined relative to its host rock geology and evolution to resolve the distribution of precious metals in modified Ni-Cu-PGE deposits.

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.