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Item type:Publication, Low-temperature hydrothermal Pt mineralization in uvarovite-bearing ophiolitic chromitites from the Dominican Republic(Springer Science+Business Media, 2021-10-15)Platinum-group elements (PGEs) occur in ophiolitic chromitite in the Dominican Republic as platinum-group minerals (PGMs) in spatial association with hydrothermal uvarovite and chromian clinochlore. Bulk-rock total PGE content in a single analyzed chromitite sample is of 6.54 g/t. Three main PGM types are distinguished: euhedral magmatic laurite completely encased in chromite, subhedral to euhedral Ru-Os-Fe-(Ir) compounds partially encased in chromite, and anhedral Pt-Fe–Ni-rich grains exclusively embedded in uvarovite or chromian clinochlore. The Ru-Os-Fe-(Ir) compounds are interpreted as magmatic Ru-Os sulfides that experienced desulfurization during hydrothermal alteration of the chromitites, whereas the Pt-Fe–Ni-rich grains are hydrothermal in origin. We propose a model in which the Pt-Fe–Ni-rich PGMs formed via the accumulation of nanoparticles directly precipitated from the hydrothermal fluids. An estimation of the temperature of crystallization of uvarovite and chromian clinochlore suggests hydrothermal alteration of the chromitite within the thermal range of 150–350 °C. Thermodynamic modeling shows that, within this range of temperature, Pt could be mobilized as aqueous bisulfide complexes (HS−) by S-poor, highly reducing hydrothermal fluids originated during serpentinization of the host chromitite rock. The crystallization of Ni sulfides in the chromitite would drop the S concentration of the fluid, causing the precipitation of Pt as native element. Ultimately, this process contributes to constrain the conditions for the genesis of hydrothermal PGE mineralizations in ophiolitic chromitites. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Ultramafic-hosted volcanogenic massive sulfide deposits from Cuban ophiolites(Elsevier Ltd, 2022-11-01)Ultramafic-hosted volcanogenic massive sulfide deposits (UM-VMS) located in the Havana-Matanzas ophiolite (Cuba) are the only known example of this type of mineralization in the Caribbean realm. UM-VMS from Havana-Matanzas are enriched in Cu, Ni, Co, Au, and Ag. The mineralization consists of massive sulfide bodies mostly composed of pyrrhotite and hosted by serpentinized upper mantle peridotites. Chemical composition of unaltered cores in Cr-spinel grains found within the massive sulfide mineralization and in the peridotite host indicates formation in the fore-arc region of the Greater Antilles volcanic arc. A first stage of serpentinization probably took place prior to the sulfide mineralization event. The UM-VMS mineralization formed by the near-complete replacement of the silicate assemblage of partially serpentinized peridotites underneath the seafloor. The sequence of sulfide mineralization has been divided into two stages. The first stage is characterized by a very reduced hydrothermal mineral assemblage consisting of pyrrhotite, Co–Ni–Fe diarsenides, chalcopyrite, Co-rich pentlandite, and electrum. In the second stage, pyrite and Co–Ni–Fe sulfarsenides partially replaced pyrrhotite and diarsenides, respectively, under a more oxidizing regime during the advanced stages of ongoing serpentinization. The proposed conceptual genetic model presented here can be useful for future exploration targeting this type of deposit in the Caribbean region and elsewhere. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Germanium- and Gallium-Rich Sphalerite in Mississippi Valley–Type Deposits: The San Vicente District and the Shalipayco Deposit, Peru(Springer Science and Business Media Deutschland GmbH, 2023-06-01)Sphalerite in Mississippi Valley–type (MVT) deposits hosts significant resources of both germanium and gallium. Here, we provide a survey on the distribution of Ge, Ga, and other minor and trace elements in sphalerite from MVT deposits in the Eastern Cordillera and sub-Andean regions of Peru, including the San Vicente deposit and the nearby Chilpes and Huacrash prospects, and the Shalipayco deposit. We present also a micro- and nano-scale textural characterization of Ge-rich sphalerite. In situ laser ablation-inductively coupled plasma-mass spectrometry analyses yielded Ge contents (inter-quartile range [IQR] = 164–36 ppm for the San Vicente district and IQR = 425–101 ppm for the Shalipayco deposit) that overlap with the range reported for sphalerite from other MVT deposits elsewhere. The highest Ge contents (IQR = 1207–375 ppm, up to 1861 ppm) were found in Fe-poor orange sphalerite deposited during a volumetrically minor second mineralization step in the San Vicente deposit located mainly in steep veins that crosscut the main first-step mineralization dominated by darker sphalerite. Reddish-brown sphalerite from Chilpes (IQR = 445–22 ppm, up to 1745 ppm) and brownish orange sphalerite from Huacrash (IQR = 650–34 ppm, up to 855 ppm) also yielded remarkably high Ge values. In Shalipayco, the highest Ge contents were analyzed in late Fe-poor yellow sphalerite (IQR = 375–267 ppm, up to 1119 ppm). The highest Ga contents were determined in reddish-brown sphalerite from the Chilpes prospect (IQR = 1156–0.26 ppm, up to 3943 ppm), although Ga contents are, in general, much lower than those of Ge in most analyzed sphalerite (IQR = 27–0.22 ppm in the San Vicente district and IQR = 2.8–0.081 ppm in the Shalipayco deposit). These figures place some of the analyzed sphalerite types among the Ge- and Ga-richest samples ever reported. Linkage of textural and compositional data points to light-colored, chiefly orange and yellow sphalerite generations crystallizing at lower temperatures and relatively late in the paragenetic sequences as those with the highest Ge contents. In contrast, the paragenetic control on Ga enrichment is unclear. Focused ion beam and high-resolution transmission electron microscopy (FIB-HRTEM) investigation combined with trace element content correlations reveal selective partitioning of Ge and Ga into sphalerite as structurally bound elements and their incorporation via substitution mostly coupled to monovalent cations triggering polytypism.