Mineralium Deposita最新文献

Precambrian iron oxide copper-gold (IOCG) systems have commonly experienced multiple mineralising and tectonothermal events and identifying their timing and geodynamic framework is challenging. World-class IOCG deposits in the Olympic Cu-Au Province, South Australia, are dominated by hematite and formed in the upper crust, while the magnetite-dominated Cu deposits hosted in granulite facies rocks are considered to represent the deeper expression of giant IOCG system. However, the application of novel in-situ Lu-Hf apatite geochronology reveals the magnetite-hosted Cu mineralisation is significantly younger and unrelated to the well-known ~ 1590 Ma Gawler Craton IOCG systems. Apatite Lu-Hf ages from the granulite that predates Cu mineralisation give ages of 1490 Ma. Infiltration of Cu-bearing fluids resulted in recrystallisation of apatite, LREE mobilisation and formation of secondary monazite. Lu-Hf ages for syn-mineralisation apatite give 1460 Ma, consistent with c. 1460 Ma U-Pb ages from secondary monazite. In contrast to the apatite in situ Lu-Hf ages, all apatite types produce a single U-Pb age of c. 1460 Ma, demonstrating the ability of Lu-Hf to preserve a more complete history of apatite formation than U-Pb in high- to medium-temperature rock systems. The timing of mineralisation coincides with the onset of Nuna fragmentation, representing a previously unrecognised driver for mineral system formation in southern Australia that installed Cu in crust previously dehydrated during a long history of granulite-grade tectonic events. The recognition of this Cu system in rocks generally considered unprospective shows that continental breakup can rejuvenate metallic systems in otherwise unprospective crust.

Stratiform sediment-hosted Cu deposits are significant global sources of Cu and other important metals. The Polish Kupferschiefer produces Ag, Au, Pb, Ni, Se, and Re as by-products, whereas Co is one the of most important metals in the stratiform sediment-hosted Cu-Co deposits of the Central African Copperbelt and the Namibian Dolostone Ore Formation deposit. This study combines new and published laser ablation inductively coupled plasma mass spectrometry sulfide trace element data from these stratiform sediment-hosted copper districts. All the investigated districts exhibit sulfides occurring as disseminations and within later veins. Chalcopyrite, sphalerite, and pyrite trace element contents vary significantly between the metallogenic districts as well as between different ore stages. Random Forest discriminates the stratiform sediment-hosted Cu(-Co) districts based on trace element geochemistry. High Ag and Tl in chalcopyrite is attributed to the Polish Kupferschiefer, Ga and Ge to the Katanga Copperbelt, and Zn and In to the Dolostone Ore Formation deposit. Sphalerite from the Polish Kupferschiefer and the Dolostone Ore Formation deposit can be distinguished on the basis of the Fe and Cd contents. Cobalt and As are significantly elevated in pyrite from the Katanga Copperbelt and Mn in pyrite from the Dolostone Ore Formation deposit. The trace element contents also show that the stratiform sediment-hosted Cu(-Co) deposit sulfide data cluster separately from other deposit types. The variation in sulfide trace element contents between the three investigated stratiform sediment-hosted Cu(-Co) districts suggests that sulfide chemistry is related to the geology of the host basin and the nature of the underlying basement, which includes preexisting ore occurrences.

In the Voisey’s Bay complex, sulfide-matrix breccias developed through the percolation of dense sulfide melt, leading to the displacement of the silicate melt within partially molten silicate-matrix breccias. In these sulfide matrix-breccias, hydrous silicate rims are commonly present at the interface between the sulfide matrix and the silicate framework. Multiple lines of evidence support a magmatic origin of these hornblende-biotite rims, which was largely coeval with the emplacement of the sulfide melt in the magmatic breccias. The formation of the hornblende-biotite rims required the addition of alkalis and water that could not have entirely been sourced from either the sulfide melt or the silicate framework. Through the integration of compositional maps with major and trace element analyses of the main accessory minerals, we propose that the critical components required for the development of the hydrous silicate rims in sulfide-matrix breccias originated from an immiscible Fe-Ti-P melt. Distinct textural and compositional features of apatite, hercynite, ilmenite and magnetite support the presence of small amounts of Fe-Ti-P melt in the sulfide melt. This Fe-Ti-P melt likely formed through melt immiscibility in the early stages of the development of the Voisey’s Bay complex, and was transported in the magma conduits together with the sulfide melt.

The contributions of early potassic and later phyllic alteration stages to Cu endowment of the giant Dexing porphyry Cu–Mo–Au system in South China are determined using changes in the Cu isotope composition of hypogene chalcopyrite from three vein stages. The δ⁶⁵Cu values of chalcopyrite (δ⁶⁵Cu_cpy values) from the potassic (stage 1: -0.05‰ to 0.21‰) to the phyllic alteration stages (stage 2: -0.03‰ to 0.24‰) are relatively invariable, but chalcopyrite in the propylitic alteration stage (stage 3) has notably lower isotopic values (-0.35‰ to 0.02‰). The sharp decrease in δ⁶⁵Cu_cpy values in the latest vein stage is likely a result of precipitation of significant amounts of isotopically heavy chalcopyrite in the phyllic alteration environment. The overall isotopic evolution can be simulated, using a Rayleigh fractionation model, with the majority of Cu having precipitated during the phyllic alteration stage. By comparing our data with published Cu isotope results from other porphyry deposits, we demonstrate that the systematics of δ⁶⁵Cu_cpy values during different hydrothermal alteration stages could convincingly trace the relative timing and mechanism(s) of Cu precipitation in porphyry Cu systems. Spatial mapping of Cu isotopes at Dexing suggest that sharp decreases of δ⁶⁵Cu_cpy values in hypogene zones may be used to delineate the boundary of high-grade ore zones.

Cerros Taguas is one of the high-sulfidation epithermal Au-Ag deposits (131.35 Mt @ 0.29 g/t Au, 8.8 g/t Ag, 0.11% Cu) of the Taguas project, located in the northern sector of the El Indio belt (~ 29°S), Central Andes, Argentina. Zircon LA-ICP-MS U-Pb dating of a rhyolitic tuff that hosts Au-Ag mineralization constrain the timing of volcanism to the middle Miocene (12.14 ± 0.14 to 11.85 ± 0.26 Ma). Above 3800 m.a.s.l., the rocks display advanced argillic alteration, characterized by alunite + pyrophyllite + dickite ± diaspore ± topaz. Hypogene alunite associated with epithermal Au-Ag mineralization yielded a ⁴⁰Ar/³⁹Ar plateau date of 9.5 ± 0.4 Ma. Below 3800 m.a.s.l., the presence of sericitic alteration (muscovite + illite + quartz) and a molybdenum halo associated with molybdenite-bearing B-type and pyrite ± quartz D-type veins suggests a transition from epithermal to porphyry-style mineralization. Molybdenite in quartz-dominated B-type veins and molybdenite ± quartz veins cross-cutting the rhyolitic tuff yielded ID-NTIMS Re-Os dates of 10.60 ± 0.06 and 10.48 ± 0.05 Ma. A nominally older molybdenite ID-NTIMS Re-Os date (11.10 ± 0.11 Ma) was obtained for the hydrothermal cement of a breccia. The timing of molybdenum mineralization at Cerros Taguas was broadly coeval with the emplacement of inter-mineralization porphyritic stocks and slightly older than molybdenite mineralization in the nearby Valeriano and El Encierro porphyry deposits. The occurrence of a porphyry-style mineralization at Cerros Taguas reflects the prospectivity for porphyry deposits beneath Miocene-age volcanic rocks and advanced argillic alteration zones in the northern sector of the El Indio belt.

MVT-related elements show a specific enrichment pattern in a geothermal scale.

Comparison with fluid parameters suggests pressure reduction and CO₂ degassing as basis for mineral formation and element enrichment.

Exchange processes at the contact surface mineral-fluid and changes in the redox potential allow for element-specific concentration changes.

Methane oxidation and sulfate reduction cause major chemical changes.

Isotope data track the observed chemical variations.

The Paleo-Tethys tectonic zone has been recognized as a world-class rare-metal (Li-Rb-Be-Nb-Ta) pegmatite belt. Previous studies indicate that the rare-metal pegmatite mineralization is related to the Late Triassic–Early Jurassic granitoids. However, it remains debated which granites, among the various coeval I-, A- and S-type granitoids in the tectonic belt, are responsible for the rare-metal pegmatite mineralization. We address these questions through a systematic geochemical study of the Bailongshan granite complex, which is composed of both biotite granites and two-mica granites and is related to the largest Li deposit in this zone. The similarities in Sr–Nd–Hf–O isotopic compositions between the two-mica granites (I_Sr=0.7176 to 0.7183, εNd(t)= − 10.7 to − 10.1, εHf(t)= − 14.12 to − 4.58, δ¹⁸O = 10.11 to 13.46‰) and rare-metal pegmatites (I_Sr=0.7181 to 0.7189, εNd(t)= − 11.72 to − 10.68, εHf(t)= − 12.15 to − 5.37, δ¹⁸O = 10.37 to 12.37‰), both showing affinity with sedimentary source, provide convincing evidence that the rare-metal pegmatites were derived from the two-mica granites. The differences in these parameters between the two-mica granites and the biotite granites (I_Sr=0.7083 to 0.7086, εNd(t)= − 5.9 to − 5.7, εHf(t)= − 6.64 to − 1.50, δ¹⁸O = 7.27 to 9.36‰, characteristic of I-type granites) indicate that they were derived from different sources. Trace element modeling indicates that the pegmatites were produced via extremely high fractional crystallization (> 90%) of the two-mica granites, which is also supported by the difference in δ⁷Li values between the two-mica granites (-0.6 to 0.5‰) and pegmatites (2.04 to 4.94‰). Comparison of the geochemical data between the two-mica granites and metasedimentary rocks in the area suggests that the rare metals in the mineralizing magmas were most likely derived from the partial melting of metapelites of the Triassic Bayanharshan Group. The relatively high temperatures (771 to 830 °C) estimated from the Ti-in-zircon thermometer for the two-mica granites favor extraction of rare metals from both biotite and muscovite in the source rocks during the partial melting. The results of this study, together with published data of Late Triassic to Early Jurassic granitoids in the Paleo-Tethys tectonic zone, indicate that the rare-metal pegmatite mineralization is related to S-type granites, but not all S-type granites are fertile. The combination of rare-metal-rich source rocks (metapelites), high temperatures due to an external heat source favoring the release of rare metals from the source rocks, and high degrees of fractional crystallization facilitating further enrichment of rare-metals in the pegmatite magmas, is critical for the rare-metal mineralization.

Li–Cs–Ta (LCT)-type granitic pegmatites commonly occur adjacent to granitic bodies. For many pegmatite fields, it is not obvious whether the pegmatitic melt originated from an evolved granitic magma or from low-degree partial melting of metasedimentary rocks. The Ke’eryin granitic pegmatites in the Songpan–Ganze orogenic belt, China, which hosts large Li₂O reserves around large-volume granitic intrusions, including biotite granite (BG), two-mica granite (TG), and muscovite granite (MG), present an excellent location to investigate the petrogenesis of granitic pegmatites and associated Li mineralization. Our results suggest that these granites were generated from a common magma source and emplaced in pulses, coupled with fractional crystallization. These granites and associated pegmatites show discordant trends in the bulk-rock Zr/Hf and Nb/Ta ratios and apatite Y/Ho and Sr/Y ratios, which reflect an evolution from granitic magma to flux-rich pegmatite melts. Pegmatitic melts might have derived from TG magma during evolution from BG to TG and MG magma. Initial ⁸⁷Sr/⁸⁶Sr ratios of BG apatite (0.7161–0.7188) and low bulk-rock Fe₂O₃/FeO ratios (0.04–0.22) imply that the Xikang Group at depth might have undergone high-degree partial melting to produce the original granitic magma. This melting of metasedimentary rocks, resulting in a large-volume magma with low flux and rare-metal contents, was followed by protracted fractionation during multiple pulses of magma emplacement. This process resulted in the formation of flux- and rare metal-rich pegmatite melts from granitic magma. This mechanism may be applicable to many LCT-type pegmatites associated with large granitic complexes worldwide.

The amethyst and agate geodes from the Los Catalanes Gemmological District in Uruguay represent one of the main deposits of its kind worldwide. The geometry of the deposit is horizontal, with an irregular distribution of amethyst geodes within the upper level of the basalt lava flows and shows strong variations in their abundance, as well as quality, geometry, and shape. Reliable exploration guides are scarce, and the limited knowledge of the geological parameters controlling its occurrence makes exploration unpredictable, leading to inaccurate reserve estimation. Based on cutting-edge methods including nucleation-assisted microthermometry of one-phase fluid inclusions and determination of triple oxygen isotope in silicates and carbonates, as well as analysis of geode-hosted water and groundwater, we estimate the crystallisation temperatures in the range between 15 and 60 °C. These low temperatures point to amethyst crystallisation after the emplacement of the complete basalt pile. The mineralising fluid shows isotopic signatures consistent with meteoric water and very low salinities from pure water up to rarely over 3 wt% NaCl-eq., likely sourced from the groundwater hosted in the aquifers in the basaltic sequence and underlying units. Based on the insights provided by the new data, we propose the combination of open- and closed-system crystallisation inside pre-existing cavities due to the episodic infiltration of meteoric water in a rather stable geological context.