Ore Geology Reviews最新文献

Uraninite is generally the most principal component of uranium ores and can record the significant information about uranium mineralization processes. Here, chemical compositions of uraninites from thirty-five uranium deposits of nine types (including granite-related, sandstone-hosted, volcanic-related, black shale-hosted, Na-metasomatite-hosted, peralkaline syenite-hosted, pegmatite-hosted, carbonatite-hosted, and leucocratic dyke-hosted) in China were examined, with the aim to investigate the chemical variations of uraninite from each deposit type and fingerprint uranium metallogenesis. Uraninites from the last five types contain significant abundances of ThO₂ (median = 3.81 wt%), Y₂O₃ (0.96 wt%), and ∑REE (typically ≥ 1 wt%) and low concentrations of Si, Fe, and Ca (SiO₂ + CaO+FeO typically < 1 wt%) and have middle rare earth elements (MREE)-enriched chondrite-normalized REE patterns with pronounced negative Eu anomalies, although the carbonatite-hosted type shows insignificant Eu anomaly. These characterize the affinity of intrusive-related deposits that formed at high temperatures. Uraninites from granite-related deposits generally contain negligible abundances of Th and Y, the highest CaO (up to 9.89 wt%), and highly variable ∑REE concentrations. Their chondrite-normalized REE patterns typically resemble those of the host granites, suggesting that the REE signatures were mainly controlled by the sources of REE (U). Uraniferous phases from sandstone-hosted deposits have the lowest concentrations of UO₂ (median = 66.87 wt%) and the highest SiO₂ (up to 21.63 wt%), FeO (15.72 wt%), Y₂O₃ (10.35 wt%), and P₂O₅ (9.69 wt%) and generally show LREE-enriched REE patterns, which are indicative of the predominant role of LREE-rich sources in the mineralization. In contrast, those particles characterized by flat REE patterns probably suggest the involvement of hydrothermal fluids in the mineralization. Although uraninites from black shale-hosted uranium deposits have a LREE-rich source-controlled REE pattern, they are poor in P and Y and rich in W, which can discriminate them from the sandstone-hosted type. Uraninites from volcanic-related uranium deposits have variable REE signatures, suggesting the various formation conditions from which the uraninites form. Our study indicates that uraninite chemistry can help constrain the genesis of uranium deposits and discriminate deposit types.

Understanding the petrogenesis of Miocene adakite-like igneous rocks is crucial for unraveling the formation processes of post-collision porphyry copper deposits within the Gangdese orogenic belt. This study focuses on the mineralogical, geochronological, and geochemical characteristics of the Beimulang Miocene adakite-like igneous rock series, with particular emphasis on two types of diorite porphyry (DP1 and DP2), to constrain their petrogenesis. Zircon U-Pb dating indicates that the monzogranite (MG), monzogranite porphyry (MGP), DP1, DP2 and granite porphyry (GP) were emplaced at 14.8 ± 0.1 Ma, 14.6 ± 0.1 Ma, 14.6 ± 0.1 Ma, 13.2 ± 0.1 Ma and 12.5 ± 0.1 Ma, respectively. The major element compositions of the Beimulang Miocene intrusions exhibit a differentiation trend. The Sr-Nd isotopic compositions of the MG, MGP, and DP1 align with the mixing line between the juvenile lower crust and the potassic lamprophyres. Conversely, the Sr-Nd isotopic compositions of DP2 and GP fall precisely on the Sr-Nd mixing line between DP1 and the ultrapotassic lamprophyres. Considering the reverse zoning of plagioclase in the DP1 and presence of high-Mg phlogopite in the DP2, we suggest that the Miocene magmatic series at Beimulang likely derived from the mixing of partial melts of Gangdese juvenile lower crust and mantle-derived potassic-ultrapotassic magmas. The increase in Th/Yb ratios from DP1, MG, MGP to DP2 and GP suggests that the mantle metasomatism material may have evolved from slab-derived fluids to melts derived from Indian crustal sediments. The magmatic water content and oxidation calculated from zircon trace elements, are nearly identical among the ore-causative MG and MGP, and the barren GP. However, the decrease in V/Sc ratios from the MG and MGP to GP indicates that magnetite-driven magma sulfide saturation leads to the depletion of chalcophile elements, significantly reducing the Cu mineralization potential of the GP. We suggest that the higher degree of magmatic evolution leads to the barren nature of Beimulang granite porphyry.

The temporal and genetic association between Mississippi Valley-type (MVT) Zn–Pb mineralization and hydrothermal dolomitization remains controversial. To determine the origin of hydrothermal dolomite and its genetic links with the MVT ore deposit, detailed petrographic observations and geochemical analyses were conducted on various carbonates from the giant Huize MVT Zn–Pb ore district in SW China. The following paragenetic sequence of the carbonates (from the early to late stages) was established: host limestone (ML), early diagenetic micritic dolostone (D1), late diagenetic or pre-ore fine- to medium-grained ferroan dolostone (D2) and medium- to coarse-crystalline non-ferroan dolostone (D3), pre-ore reworked D3 dolomite (D3o), ore-related void-filling dolomite cement (DC), and calcite cement (CC) related to sulfide mineralization. D2, D3, DC, and CC exhibit higher homogenization temperatures for fluid inclusion than the burial temperature, indicating a hydrothermal origin. Geochemical data indicate that D2, D3, D3o, DC, and CC display oxygen isotope depletion and radiogenic Sr isotope enrichment signatures relative to D1. Their parent fluids have more positive δ¹⁸O values and similar or lower δ²⁶Mg values relative to those of D1 and seawater. These geochemical proxies indicate that the pre-ore hydrothermal dolomites (D2 and D3) formed from modified seawater circulated in the underlying sandstone aquifers through fault-related thermal convection. DC and CC, related to Zn–Pb mineralization, were formed by the dissolution and reprecipitation of preexisting carbonates. Sphalerite shows higher temperatures and salinities compared with D2 and D3 dolostones, indicating that the ore-forming fluid, different from the hydrothermal dolomitizing fluid, originated from a deep-sourced brine. In situ U–Pb dating of D3o reveals that the pre-ore hydrothermal dolomitization occurred at 253.7 ± 8.7 Ma, and a late-stage hydrothermal imprint occurred at 203 ± 11 Ma, likely related to tectono-thermal events, including the Emeishan large igneous province and Indosinian Orogeny, respectively. These findings imply that the hydrothermal dolomitization and Zn–Pb mineralization in the Huize ore district are likely associated with the multistage basin and basement fluid flows driven by elevated geothermal gradient and tectonic compression, respectively. The void-filling DC and CC and their cathodoluminescence characteristics are useful indicators for MVT Zn–Pb ore exploration.