Mineralium Deposita最新文献

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.

Cuba contains the largest number of ophiolitic chromite deposits throughout the Americas. Most of these deposits are found within the mantle section of the Eastern Cuba and Camagüey ophiolitic massifs, which contain four different chromite mining districts (Camagüey, Mayarí, Sagua de Tánamo, and Moa-Baracoa). In addition to their potential as economic resources, chromite deposits are also excellent petrogenetic indicators to interpret the nature of ancient upper mantle, processes of melt formation in the mantle, and large-scale geodynamic processes. In this sense, major and trace elements of unaltered Cr-spinel cores together with chromitite whole-rock PGE composition reveal that high-Al Camagüey and Moa-Baracoa chromite districts were formed in equilibrium with forearc basalts (FAB)-like magmas during the incipient intra-oceanic subduction of the proto-Caribbean lithosphere underneath the Caribbean lithosphere, in a subduction-initiation process. Conversely, the high-Cr Mayarí chromite district was formed in equilibrium with more hydrated melts of boninitic affinity, typical of a more advanced stage of the subduction-initiation process. Nonetheless, the shift from FAB-like to boninite-like magmatism in an intra-oceanic subduction is gradual. This progressive change is well-recorded in the Sagua de Tánamo district that contains both high-Al and high-Cr chromitites. Thus, the studied ophiolitic chromitites allow tracing the complete magmatic evolution of an intra-oceanic subduction-initiation process. Furthermore, our data exhibits that accessory Cr-spinel composition of peridotites surrounding chromitites can be used as a prospecting indicator to anticipate the composition of ophiolitic chromitite bodies. Systematically, Cr-spinel from dunites associated with high-Al chromite deposits have lower Cr# values compared to the accessory Cr-spinel from the associated harzburgites. On the contrary, Cr-spinel from dunites of high-Cr chromite deposits show higher Cr# compared to the accessory Cr-spinel from the host harzburgites.

The Late Triassic to Early Jurassic (ca. 220 to 190 Ma) Dahongliutan pegmatite belt, located in the Western Kunlun orogenic belt, NW China, is a newly discovered, large Li-Be ore district comprising > 320 individual rare-metal pegmatites. The pegmatite belt was emplaced in a post-orogenic setting in relation with a ductile shear zone related to the Dahongliutan detachment fault, which is spatially and temporally related to post-orogenic exhumation. Deformed spodumene pegmatites, mostly striking NW with dip angle of 50 ~ 80°, occur within or adjacent to the NW-striking detachment fault. We present new field observations, mineralogical, geochemical and geochronological results from the Dahongliutan pegmatite belt, which lead to the following conclusions: 1) High-medium temperature/middle-to-low pressure metamorphic rocks and granitoids were intruded by ductile-deformed spodumene-bearing pegmatites during development of the gneissic domes; 2) Spodumene pegmatites from the Aktas, Kalaka, Bailongshan and Longmenshan deposits record two age groups, a first one during the Upper Triassic at ca. 212–205 Ma, and a second one during the Lower Jurassic at ca. 195–193 Ma, as revealed by in-situ Rb–Sr dating of micas and U–Pb dating of columbite-group minerals; 3) Textural observations and geochemical analyses of coexisting quartz and spodumene further indicate that ductile deformation provided favorable conditions for enrichment of Li and Be in pegmatites. The Western Kunlun-Songpan Ganzi rare-metal pegmatite belt shows a close spatial and genetic relationship with ductile shear zones induced by detachment faulting, making it a potential proxy for exploration targeting of Li-Be-mineralized occurrences at the regional scale as well as in other metallogenic provinces worldwide.

The Ransko (ultra)mafic massif, Bohemian Massif, Czech Republic, hosts several Ni–Cu–(PGE) deposits and peculiar Zn–Cu–Ba ores. Geochronology integrated with petrography, bulk-rock, and mineral compositions together with Sr–Nd–Pb–Hf–Os–O isotopic systematics of barren and variably mineralized (ultra)mafic lithologies as well as massive ores reveal a complex evolution of the Ransko massif and its mineralizations. The Sm–Nd and U–Pb ages obtained for gabbros and cross-cutting granite porphyry, respectively, overlap with Re–Os ages of Ni–Cu–(PGE) and Zn–Cu ores and limit the formation age of (ultra)mafic rocks and metal accumulations to ~ 370–345 Ma. Compositional variations indicate derivation of parental melts of the Ransko massif from metasomatized, Variscan sub-arc mantle and underscore the importance of assimilation–fractional crystallization and crystal accumulation processes. The Ni–Cu ores were emplaced through the gravity-driven percolation of dense sulfide liquids along previously weakened structures associated with the downward crystal fractionation. The orogenic and arc-related nature of the Ransko Ni–Cu–(PGE) mineralization shares some remarkable similarities with some other Ni–Cu deposits in the European Variscan Belt highlighting the significance of these deposits emplaced in arc-related crustal domains. Yet, the variable nature of these mineralizations indicates complex processes that happen during the emplacement and evolution of the parental magmas driving their favourable metal contents.

The structurally controlled, vein-hosted copper deposit of the Frontier Mine is distinct from the vast majority of sediment-hosted, stratiform Cu(-Co) deposits of the Zambian Copperbelt. Successively emplaced vein sets document the close interplay between the progressive structural evolution of the deposit, recording northeast-southwest shortening, and associated hydrothermal fluid flow and alteration (albitization). The deposit is hosted by greenschist-facies metasedimentary rocks of the Mwashya Subgroup in the first-order hinge zone of a regional-scale, refolded, recumbent fold (F₁/F₂). Early bedding/S₁-parallel veins (Vein Set 1) formed during layer-parallel shearing and the onset of recumbent folding (F₁). This early vein generation is relatively poorly mineralized, but was associated with a near-pervasive, bedding-parallel albitization and replacement of the mainly metapelitic wall rocks. The reaction hardening process promoted brittle deformation during the subsequent upright refolding (F₂) of the rocks and the formation of a second generation of highly mineralized, saddle-reef type veins (Vein Set 2) in the hinges of particularly upright F₂ folds (F₁/F₂). The controls of Vein Set 2 by fold hinges defines the overall shoot-like geometry of the orebody, parallel to the SE-plunging folds. The subhorizontal orientation and brecciated textures of a subsequent Vein Set 3 underline the formation of veins through continued northeast-southwest shortening of the brittle wall rocks during the lock up of the refolded first-order fold. The overprinting and structural relationships between vein sets, alteration and the regional fold structures signify a syn-tectonic, long-lived, multi-phase mineralization history during the Lufilian Orogeny. 

Granite-related mineral deposits are major primary sources of the critical metals tin (Sn) and lithium (Li). The utility of accessory minerals such as zircon and apatite as pathfinders to these ore deposits has been a subject of great interest in recent years, with a number of geochemical discriminants having been developed to distinguish barren from metal-fertile and mineralised intrusions. Here, we study the potential of apatite as an indicator mineral for tin and lithium mineralisation using a compilation of published apatite trace element data as well as new data for the mineralised Cornubian batholith and barren Bhutanese leucogranites. Critical examination of common geochemical discriminants tracing magma fractionation and redox conditions (Mn, Eu/Eu*, La/Yb_N and Sr/Y) reveals large and overlapping data scatter for both barren and Sn-fertile intrusions. This calls into question the utility of these petrogenetic indicators to pinpoint tin metallogeny. Instead, prima facie metal concentrations directly related to tin mineralisation (i.e., Sn and Li) are consistently elevated in apatite from fertile and mineralised intrusions. Based on our data compilation, Li and Sn concentrations in apatite are the most robust indicators for Sn (and Li) mineralisation, and we encourage the community to include Li and Sn in their analytical routines to further test these observations and explore their implications for tin metallogeny.