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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, REE Ultra-Rich Karst Bauxite Deposits in the Pedernales Peninsula, Dominican Republic: Mineralogy of REE Phosphates and Carbonates(Elsevier B.V., 2023-06-01)Karst bauxites have recently received renewed attention for their potential as non-conventional REE sources. Karst bauxites from the Pedernales Peninsula in the Dominican Republic stand among the world's richest in REE. Bauxite ore from two deposits from this bauxite district, Aceitillar and El Turco, have been selected for this study due to their outstanding REE contents and contrasting mineralogy. REE (La to Lu) contents in Aceitillar, range from 0.07 to 0.16 wt%, and Y from 0.01 to 0.13 wt%, whereas El Turco contains between 0.28 and 1.40 wt% REE, and 0.33 to 1.48 wt% Y. The characterisation of REE mineralisation was performed through powder and monocrystal XRD, SEM-EDS, and EMP analyses. REE phosphates and carbonates reveal textural features that suggest significant REE mobilisation and re-deposition within the bauxite profile. The identified REE minerals can be classified into: i) primary monazite(-Ce) and minor monazite(-La); ii) secondary Y- and Nd-dominant phosphates; and iii) secondary Gd- and Nd-carbonates of the (hydroxyl)bastnäsite group. While monazites are ubiquitous in the two studied deposits, secondary phosphates are predominant in El Turco while secondary carbonates are exclusive of Aceitillar. This contrasting mineralogy is explained by the total concentration of carbonate and/or phosphate in the karst bauxite groundwater solutions. REE phosphates are the most stable phases at [CO32−]total/[PO43−]total ≤ 2; whereas REE carbonates are stable at near neutral pH when the total aqueous carbonate concentration is two orders of magnitude higher than that of phosphate. Results of this investigation contribute to a better understanding of the formation REE minerals in the supergene environment and can be applied in REE separation methods. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Rare Earth Element and Yttrium (REY) Hyper-Enriched Karst Bauxites of the Mercedes-Aceitillar Mining District, Sierra de Bahoruco, SW Dominican Republic(Society of Economic Geologists, Inc, 2026-02-23)Rare earth elements, including yttrium (REYs), are the most sought-after among the so-called critical or strategic elements for the low-carbon energy industry. In the past decade, karst bauxite deposits have been targeted as potential nonconventional sources of these elements. The karst bauxite deposits from the Mercedes-Aceitillar mining district, classified as Fe-rich bauxites and bauxites sensu stricto, contain anomalously high REY contents oscillating between 514 and 28,787 ppm (median of 1,489 ppm), making them the most REY-enriched karst bauxites globally. Most of the samples studied are enriched in light rare earth elements (La-Nd; up to 7,449 ppm) and Y (up to 14,830 ppm). However, the most REY-enriched bauxites yield particularly high middle rare earth element (Sm-Gd; up to 4,579 ppm) and heavy rare earth element (Tb-Lu; up to 6,163 ppm) contents. In addition, the studied bauxites contain significant amounts of other critical metals, such as Sc and Ga (median of 62 and 39 ppm, respectively). The mineralogy consists predominantly of Al oxyhydroxides (mostly gibbsite), with variable amounts of Fe oxyhydroxides and kaolinite. The REY mineralogy in samples with high REY contents (>3,000 ppm) consists mainly of REY-bearing phosphates (e.g., monazite, xenotime, rhabdophane, churchite) and/or carbonates (bastnäsite group). In samples with moderate REY contents (<3,000 ppm), the main REY-bearing minerals are Al oxyhydroxides, onto which the REYs are most likely adsorbed. These findings indicate that the potential extraction of REYs and other critical metals, such as Sc and Ga, in the studied bauxites from the Mercedes-Aceitillar mining district could add, on average, an ~20% surplus to the revenue obtained from Al2O3 exploitation. The unprecedented REY contents discovered in these karst bauxites from the Dominican Republic present a unique opportunity to unravel critical metal concentration mechanisms in supergene environments and to develop new geochemical models for nonconventional REY deposits.2