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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, Petrology, metallogeny and U-Pb geochronology of the Paleoproterozoic mafic-ultramafic Hamutenha intrusion, Angolan Shield(Elsevier BV, 2022-10-12)The Hamutenha intrusion (Huíla province, SW Angola) is a 3-km-long elongated magmatic body defined by a set of two intrusive units. The northern unit is formed by alternating bands of dunites and olivine gabbros, while the southern unit is composed of amphibole diorites. The Hamutenha body is hosted by the Paleoproterozoic Epupa Complex in the Angolan Shield, SW margin of the Congo Craton. A mineralogical, petrological and geochemical study of the Hamutenha intrusion has been performed. The constrained compositional features of the parental melt suggest interaction of tholeiitic magmas with a significant enrichment in Fe and Ti. Although disseminated Fe–Ni–Cu-(Co) secondary sulphides are observed, both the crustal contamination parameters and generally low bulk-rock metals contents indicate that these elements were most likely previously extracted from the parental melt. U–Pb zircon dating of amphibole diorite samples from the southern unit yields a date of 1844 ± 14 Ma. These data suggest that the emplacement of these rocks was previous to the KC emplacement and it was probably related to the Paleoproterozoic Epupa Complex magmatism. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Turonian-Coniacian Definition of the Caribbean Plate: Tectonic and Metamorphic Record in the Median Belt, Dominican Republic(Taylor & Francis, 2023-01-08)Uplift and unroofing of Jurassic-Cretaceous, mantle and crust, arc- and plume-related rock units in the Median Belt of the Dominican Republic exposed basement rocks with a protracted record of tectono-thermal events delineating the evolution of the northern edge of the Caribbean plate. In this article we focus on crustal rock units in the north-eastern half of the Median Belt. First 40Ar/39Ar dating of metamorphic ferri-winchite (86.4 ± 2.5 Ma; crystallization date) and albite (82.3 ± 5.8 and 79.8 ± 1.6 Ma; cooling dates) in metabasites of boninitic photolith from the Aptian-Albian Maimón Formation in the Ozama shear zone points to a tectono-metamorphic event in the Upper Cretaceous. Beltwide, this event caused syn-metamorphic N- to NNE-directed, simple-shear dominated, mylonitic and phyllonitic deformation of the Maimón Formation at peak metamorphic conditions of 8.2 kbar and 380°C. Such conditions are consistent with subduction of a coherent portion of forearc (represented by the Maimón Formation) to depths of ~25-29 km. The tectono-metamorphic event dated here overlaps with the inception of Turonian-Coniacian SW-dipping subduction and metamorphic sole formation in a back-arc position recorded in the Moa-Baracoa ophiolite complex in neighboring Eastern Cuba. Contemporaneity between the subduction inception of forearc and back-arc portions of the Caribbean arc and the main pulse of plume activity recorded in the Caribbean Large Igneous Province (CLIP) suggests that plume activity promoted general plate instability leading to a regional-scale plate reorganization. This mantle-plume-induced plate margin reorganization was coeval with the inception of the NE-dipping subduction of the Farallón plate beneath Central America leading to the definition of the Caribbean Plate by double-verging subduction zones along its northern and southwestern margins.