Mineralium Deposita最新文献

Sedimentary basin-hosted manganese oxides may represent an important yet underexplored source of critical metals. Here we present a stratigraphic, textural, mineralogical, and compositional characterization of Mn-oxide nodules, coatings, and veins in the Pisco onshore forearc basin, Peru. The Mn-oxide mineralization is stratabound within marine sandstone, siltstone, and tuff from the Neogene Chilcatay and Pisco formations. X-ray diffraction and electron microprobe analyses identify the Mn oxides as cryptomelane (± hollandite) and todorokite, which cement detrital grains and fossilize biological remains. Bulk chemical analyses of nodules, coatings, and veins reveal significant cobalt enrichment (mean = 0.17 ± 0.15 wt% Co; up to 0.63 wt% Co), corroborated by electron probe microanalysis of individual Mn oxide phases (mean = 0.37 ± 0.33 wt% Co; up to 2.1 wt% Co). The stratigraphic control, biomorphic replacement, mineralogy, and chemical composition collectively indicate a diagenetic origin for the Mn-oxide mineralization. The formation pathway likely involved organic matter decay or brine-hydrocarbon interactions coupled with Mn and Fe reduction, resulting in metal-enriched porewaters that circulated along structures and permeable horizons. Subsequent precipitation under oxygenated conditions occurred during late Pliocene uplift and exposure of the East Pisco Basin. This study demonstrates that diagenetic Mn oxides exposed in onshore basins represent a potential resource for manganese and critical elements such as cobalt.

The composition of quartz has historically been considered unimportant for mineral exploration, although this perspective is changing with the advancement of analytical techniques. The ability to measure trace element variations in quartz provides a unique window into the evolution of mineral deposits. Granites are currently of interest as they can host late-stage magmatic-hydrothermal mineralisation, such as Sn and other critical metals. The Nebo, Bobbejaankop, and Lease granites in the Zaaiplaats Tin Field of the Bushveld Complex represent well-exposed expressions of endogranitic Sn-mineralisation. These granites display an upward increase in their degree of hydrothermal alteration. Disseminated Sn-mineralisation is restricted to the Bobbejaankop and Lease granites and high-grade cassiterite-bearing tourmaline-quartz hydrothermal pipes that radiate upwards through these granites, terminating below the roof contact. Trace element compositions of the quartz from the Zaaiplaats Tin Field shows evidence that supports the suggested fractionation and fluid-saturation models of ore genesis. The Al/Ti and Ge/Ti ratios in quartz increase from the base to the roof and illustrate the sequential fractionation and increase in the degree of fluid-rock interaction. The trace element data display a shift from a magmatic fractionation-controlled evolution to a hydrothermally-controlled system influenced by the saturation of a late-stage magmatic-hydrothermal fluid. Thus, trace element variations in quartz can record the point of fluid-saturation and the magmatic-hydrothermal transition. Therefore, the recognition of the most evolved, fluid-saturated facies indicates lithologies with the best mineralisation potential for cassiterite. The use of trace elements in quartz extends beyond granite-hosted deposits and is potentially applicable to various mineralised systems.

The Katanga Copperbelt stands out as one of the world’s largest sediment-hosted Cu-Co provinces, contributing to over 68% of global Co and 15% of global Cu production. The age of these sedimentary Cu-Co deposits remains contentious. This paper presents the first Lu-Hf dates for apatite samples from the late diagenetic to syn-orogentic mineralization phase at Luiswishi, yielding ages of ca. 475–470 Ma. This age range is comparable with a previous Re-Os age on bornite (473 ± 4 Ma) from Kamoto and Rb–Sr and Re–Os ages for sulfides (451 ± 6.0 and 450 ± 3.4 Ma) from Kipushi but younger than the hydrothermal diagenetic mineralization (~ 800 Ma) and the mineralization event related to the Lufilian Orogeny (~ 560–500 Ma). The new Lu-Hf ages indicate a post-orogenic fluid migration at ca. 475–470 Ma in the Katanga Copperbelt, causing dissolution and reprecipitation of apatite and likely precipitation of cogenetic sulfides. The rare earth element (REE) contents of the apatite and scanning electron microprobe (SEM) images provide evidence of partial or complete remobilization of earlier high REE-rich to neo-crystalline homogeneous apatite with lower REE content.

The Nong Sua Sn deposit in Thailand is a typical vein-type deposit with three generations of tourmaline (Tur I, II and III). Tur I as disseminations (Tur Ia) or nodules (Tur Ib) in the pegmatite-aplite stock crystallized from the late-magmatic stage. Tur II coexists with quartz in a complex vein system within the stock and is of magmatic-hydrothermal origin. Tur III occurs in cassiterite-tourmaline veins within contact zones between the quartz-tourmaline vein and metasedimentary country rocks (Tur IIIa) or as smaller cassiterite-tourmaline veinlets (Tur IIIb). Both Tur I and Tur II have similar trends in chemical composition with δ¹¹B values from -15.1 ‰ to -11.5 ‰ and from -15.8 ‰ to -11.7 ‰, respectively, which can be explained by a Rayleigh isotope fractionation. The similarity suggests a common magmatic-hydrothermal system from which tourmaline crystallized. Tur III has lower Sn concentrations (22 to 143 ppm) and higher Fe³⁺/(Fe²⁺ + Fe³⁺) ratios than Tur I, Tur II, and thus crystallized under more oxidized conditions. Tur III has relatively high δ¹¹B values from -13.3 ‰ to -10.6 ‰ with corresponding δ¹¹B_fluid values from -9.1‰ to -6.4‰ for Tur III and from -14.0 ‰ to -9.0 ‰ for Tur I and Tur II. Thus, oxidizing modified meteoric water with relatively high δ¹¹B values was added to the magmatic-hydrothermal system from which the deposit formed. Precipitation of cassiterite was likely caused by the change of redox state related to fluid mixing. Our study provides new important insights about the evolution of hydrothermal fluids from the pre-ore stages to ore genesis of Sn deposits. Such an evolution of the magmatic-hydrothermal system may be a common process for Sn deposits in the Southeast Tin Province (SEAT) and elsewhere.

The southeastern Tibetan Plateau formed by the oblique indentation of India into Eurasia. The concurrent formation of major ore deposits provides an opportunity to test how structural reactivation and block rotation may have controlled mineralisation. A systematic structural analysis and low-temperature thermochronological data have been combined to establish the structural evolution and controls on emplacement of ore bodies in the Shuixie Cu–Co ore district within the southeastern Tibetan Plateau. Three deformation events (D₁ to D₃) were identified based on overprinting structural elements, with mineralization occurring during D₂. Zircon and apatite (U–Th)/He thermochronological data demonstrate that the Shuixie Cu–Co ore district was formed at approximately 28–20 Ma. The ore-controlling structures are sinistral strike-slip faults that were activated along pre-existing cleavage planes. Breccia- and vein-type ores filled the space in simple shear and transtensional zones, respectively, along the sinistral strike-slip faults. Block rotation and relatively constant stress within the oblique orogen, triggered the opening and closure of ore-controlling structures reactivated along cleavage in the Shuixie district. The genetic links between block rotation, structural reactivation, and mineralization within the oblique collisional belt could be unraveled by combining structural analysis with low-temperature thermochronology.

Porphyry copper deposits (PCDs) are the primary global source of copper, with Cenozoic PCDs in the Chilean Andes being notable for their large size and high ore grades. The Cretaceous PCDs of the Coastal Cordillera in northern Chile are comparatively smaller and predominantly sub-economic. This study investigated zircon geochemical signatures in ore‐related and barren Cretaceous intrusive rocks to assess whether magmatic fertility fingerprints differentiate between large and small PCD systems. Ore-related intrusive rocks from Early Cretaceous PCDs (116–108 Ma), including Tricolor, Dos Amigos, Cachiyuyo, and Pajonales, are characterized by high Eu/Eu* ratios (> 0.4) and relatively oxidized conditions (ΔFMQ ~ 0 to + 1). On the other hand, barren intrusive rocks emplaced during the Late Cretaceous period (98–93 Ma) display lower Eu/Eu* ratios (< 0.4) and have ΔFMQ ~ –1 to + 1. In comparison, supergiant Cenozoic PCDs of the Andean Cordillera, e.g., El Salvador, Chuquicamata, and El Teniente display high Eu/Eu* ratios (> 0.4), and are more oxidized (ΔFMQ ~ + 1 to + 3). Results from this study show that the Yb_N/Dy_N and (Eu/Eu*)/(Dy_N/Yb_N) ratios can effectively discriminate between different PCDs settings. Deposits related to magmatic differentiation with a high-water content at relatively shallow to intermediate levels (< 40 km), such as those from the Early Cretaceous, are characterized by Yb_N/Dy_N values of ~ 10–18 and (Eu/Eu*)/(Dy_N/Yb_N) ratios of ~ 6–14. In contrast, deposits where magmatic differentiation occurred at greater depth within the crust (> 40 km), like the large Cenozoic deposits in the Andes, show Yb_N/Dy_N values of ~ 3–12 and (Eu/Eu*)/(Dy_N/Yb_N) ratios of ~ 1.5–6. Furthermore, our data highlight the crucial role of geodynamic conditions, such as horizontal tectonic stress, the depth of magmatic differentiation, which may determine the size of porphyry Cu systems.

The Muluozhai rare-earth deposit in the Mianning-Dechan metallotect (China) is hosted by carbonatites genetically linked to subduction and plate collision in the eastern Tibet. The Muluozhai carbonatites comprise variable proportions of bastnäsite-(Ce), fluorite, barite and calcite, along with abundant xenoliths of nordmarkite and metabasalt wall-rocks. Muluozhai is unusual among similar deposits in plate-collision zones owing to its locally high levels of Nb, Th and U arising from the presence of U-rich pyrochlore (+ minor betafite, 19.4–29.4 wt% UO₂) and thorite (5.5–15.4 wt% UO₂) associated with zircon (up to 3.0 wt% ThO₂ and 2.0 wt% UO₂), rutile (up to 16.3 wt% Nb₂O₅ and 1.7 wt% V₂O₃) and molybdenite. The chemical variation of pyrochlore at Muluozhai records contemporaneous crystallization of zircon, thorite, fluorite and other F-rich minerals, followed by rutile, and culminates with anion-deficient Sr-rich compositions indicative of hydrothermal alteration. Pyrochlore-group phases are rare in carbonatites from plate-collision zones, and the few known examples can be distinguished from those in anorogenic occurrences, including previously and currently active Nb mines, using a combination of discrimination criteria (e.g., their U, Ti and Ta contents, Th/U, Ta/Ti and Ti/Nb ratios). Using a global database of carbonatite compositions, we suggest that these differences reflect, to some extent, the unusual geochemistry of plate-collision carbonatites and their mantle sources with respect to high-field-strength elements. However, some geochemical characteristics of these rocks (e.g., variations in Th/U and Nb/Ta ratios) may stem from “nugget effects” caused by early pyrochlore or thorite fractionation. Implications of these data for niobium exploration are discussed.

Detrital sapphire (gem corundum) in the Rock Creek deposit (Montana, USA) is identified as having originated from Eocene peraluminous rhyolitic ignimbrite, which occurs as clasts in sapphire-producing colluvium. Fine-grained corundum and other heavy minerals (allanite, various garnets, rare chromite, and others) occur in this rhyolite tuff in similar concentrations to the sapphire ore gravels, indicating derivation of the ore gravels by weathering of the tuff. Fine ash and biotite in tuff clasts show signs of subaerial alteration. The corundum-bearing tuff is predominantly composed of vitric ash particles with subordinate lithic fragments (Belt Supergroup quartzite), crystals (plagioclase, biotite, quartz), carbonised wood, and trace concentrations of various heavy minerals. A gem quality sapphire crystal (recovered by mining) hosts a secondary assemblage of plagioclase, Ti–rich/Al-poor biotite (identical to biotite phenocrysts in tuff), and vesicular rhyolitic glass filling a thin fracture through the grain, which indicates that sapphire was present in the rhyolitic magma before extrusion. The peraluminous composition of Rock Creek rhyolite, together with the presence of corundum, garnet of variable composition (some comparable to garnet in amphibolite xenoliths), and chromite suggest the assimilation of varied crustal rocks. The high alumina saturation index and rapid quenching of the rhyolite magma may promote corundum survival. Sapphire distribution at Rock Creek is expected to be controlled by Eocene paleotopography, the structure of the eruptive volcanic center(s), and the Quaternary weathering, erosion, and deposition of unconsolidated sapphire-bearing gravels.

Voluminous breccias, collectively known as the Yinmin Breccia, are widely distributed in the Kangdian metallogenic belt, Southwest China. Both sediment-hosted stratiform copper (SSC) and iron oxide-copper-gold (IOCG) deposits occur in the belt and exhibit close spatial association with these breccias. However, the origin of the Yinmin Breccia and its relationship to the two types of ore deposits remain enigmatic. Here, we integrate petrological studies with new age constraints and stable isotopic systematics to address these issues. Detailed field mapping and petrological observations allow for the classification of the conventional Yinmin Breccia into two types, namely the monomict and polymict breccias. The monomict breccia contains clasts predominantly of fragments of the Yinmin Formation and cements of quartz, carbonates, and locally sulfides, a mineral assemblage similar to the components of SSC mineralization. In contrast, the polymict breccia contains clasts of the monomict breccia, rocks of the host sequences, and dolerite intrusions, all of which are altered and cemented by IOCG-related hydrothermal mineral assemblages. Moreover, the IOCG-type alteration is observed to locally overprint and postdate the SSC mineralization and monomict breccias. A dolerite intrusion crosscutting the SSC orebody and monomict breccia yields a zircon U-Pb age of 1698 ± 29 Ma, providing a lower limit on the timing of the monomict brecciation and SSC mineralization. B-C-O-S isotopic data suggest that the monomict breccia resulted from dissolution and collapse of evaporites, whereas the polymict breccia formed due to over-pressurizing of magmatic-hydrothermal fluid during the IOCG mineralization process. We hence propose that the SSC and IOCG deposits in the Kangdian region are products of two discrete mineralization events which coincidentally occurred in the same location. This work highlights the critical linkage between hydrothermal breccias and regional mineralization.