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Cryptic alkaline magmatism in the oceanic Caribbean arc (Camagüey area, Cuba)
(Elsevier, 2020-12-01)
Mid and Late Cretaceous arc-related basaltic rocks in the Camagüey area, East Central Cuba, record an intriguing seemingly random enrichment in alkalis that suggests alkaline affinity, representing an oddity in the Greater Antilles. In this study, the petrology and geochemistry of volcanic rocks from the Camujiro, Piragua and La Mulata Formations have been investigated. The rocks bear a diverse mineral assemblage including feldspars (plagioclase and potassium feldspar), clinopyroxene, phlogopite and amphibole with both equilibrium and disequilibrium textures. Clinopyroxene porphyritic crystals show conspicuous oscillatory and convolute zoning and reveal events of mafic recharge and crystallization in equilibrium with alkaline and calc-alkaline basaltic magmas and their mixtures. Composition of fluorophlogopite xenocrystals is consistent with crystallization from mafic alkaline liquids. Unlike whole-rock major element composition, immobile trace element abundances suggest a systematic calc-alkaline affinity. Chondrite-normalized rare-earth element (REE) patterns are similar to those of calc-alkaline and high-K (and [sbnd]Th) calc-alkaline rocks from the Caribbean Antilles. Geochemical modelling indicates that the parental basic magmas formed by a 5–10% hydrous partial melting of spinel-facies depleted mantle fluxed by fluids evolved from subducted oceanic crust and pelagic sediments, as well as fractional crystallization. Random enrichment in alkalis in studied samples is attributed to the entrainment during ascent of material derived from mafic alkaline melts injected in the upper mantle or the root of the island-arc. Our new data establish a mature stage in the evolution of the Caribbean island-arc by Cenomanian times capable of sourcing alkaline melts and the existence of a thickened island arc crust that favored fractional crystallization and magma chamber recharge processes unlike in previous stages of the island-arc construction.
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Trace element geochemistry of sphalerite and chalcopyrite in arc-hosted VMS deposits
(Elsevier, 2021-08-26)
Trace element compositions of sphalerite and chalcopyrite have been investigated for four arc-hosted Cretaceous VMS deposits (María Teresa, Perubar, and Palma in Peru, and Cerro de Maimón in the Dominican Republic) using laser ablation inductively-coupled plasma mass spectrometry. In sphalerite, Fe, Mn, Cd, Hg, Ag, Sb, Se, In, Ge, and Ga are lattice-bound, whereas Sn, Tl, Bi, and Pb occur at least partly as mineral microinclusions. Significant variations in the contents of minor and trace elements are observed in sphalerite grains from individual deposits. A strong negative correlation between Fe (Inter-Quartile Range [IQR] 44,009–18,168 ppm) and Zn indicates a dominant Fe2+ ↔ Zn2+ simple isovalent substitution. Regarding potential high-tech by-products, the contents of In (IQR 42–1.6 ppm, up to 415 ppm) and Ga (IQR 31–5.9 ppm, up to 96 ppm) in the studied sphalerite are normally much higher than those of Ge (IQR 0.85–0.16 ppm, up to 9.3 ppm). Correlation trends suggest Cu+ + In3+ ↔ 2Zn2+, Cu+ + Ga3+ ↔ 2Zn2+, and more complex substitution mechanisms of Zn involving combinations of monovalent (Cu+, Ag+), divalent (Ge2+?), trivalent (In3+, Ga3+, [Sn3+?]), and quadrivalent (Ge4+, Sn4+) cations. As for chalcopyrite, Zn, Ag, Sn, Cd, Se, In, Ga, and Ge are interpreted to be lattice-bound, whereas Mo, Au, Tl, Sb, Pb, and Bi probably occur as microinclusions. Relative to sphalerite, chalcopyrite is depleted in In (IQR 28–8.4 ppm, up to 49 ppm) and Ga (IQR 8.3–2.9 ppm, up to 24 ppm) and enriched in Ge (IQR 5.9–0.70 ppm, up to 80 ppm). Of the other trace elements, Zn (IQR 426–190 ppm) is the most highly concentrated in the studied chalcopyrite, followed by Ag (IQR 136–23 ppm), Se (IQR 64–22 ppm), Sn (IQR 53–1.3 ppm), and Cd (IQR 12–6.0 ppm). General positive correlation trends between Zn, Cd, In, Ge, and Ga in chalcopyrite suggest varied coupled substitution mechanisms of Fe and Cu with fluctuating valences due to covalent bonding. Trace-element distribution patterns in sphalerite and chalcopyrite were studied for the zone-refined Sofía-D massive sulfide body in the María Teresa deposit, which comprises a lower lower portion of dominant pyrite sheathed upward by zones of chalcopyrite (Cu zone), sphalerite (Zn zone) and galena + sphalerite ± fahlore ± barite (Pb – Zn – Ag zone). Bottom to top of the sulfide body, sphalerite records progressive depletion in In, Cu, Mn, and Se, and enrichment in Ge. This distribution pattern agrees with increasing crystallization temperatures and/or volatile magmatic influx towards the lower portion of the massive mineralization. Distribution of trace elements in chalcopyrite is rather uneven except for a sustained enrichment in Se towards the basal portion of the sulfide body. The fact that such trends are preserved in spite of extensive recrystallization during thermal metamorphism in parts of the Sofía-D massive sulfide mineralization suggests i) a closed metamorphic system and ii) that element interdiffusion was prominently local. Accordingly, we propose that sphalerite lattice-bound trace elements distribution patterns described in this article can help determine the polarity of massive sulfide bodies in VMS districts in metamorphosed and tectonized terranes.
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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.
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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.
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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.
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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.
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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.
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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.
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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 (&gt;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 (&lt;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.
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Mineralogy, geochemistry and origin of karst bauxite deposits from the Reserva Fiscal Ávila, SW Dominican Republic: Mineralogy and geochemistry of the RFA karst bauxites
(Universitat de Barcelona, 2025-05-07)
The energy transition, which aims to reduce carbon emissions and to slow down climate change, demands an ever-increasing supply of the so-called “critical metals”. Rare-earth Elements and Yttrium (REY) are among the most critical metals, as they are indispensable in most technologies associated with the generation and storage of renewable energy. In recent years there has been a growing interest in the potential of karst bauxites as nonconventional sources of REY and other critical metals such as Sc and Ga. The Sierra de Bahoruco (SW Dominican Republic) contains the most REY-enriched karst bauxites globally. In view of the high potential for hosting important REY contents, the Dominican Republic government has declared the Reserva Fiscal Ávila (RFA), a state-owned area within the Sierra de Bahoruco for assessment and exploration of its REY resources. In this study, we present the first data on the mineralogy and composition of bauxitic rocks from the RFA. The bauxitic deposits comprise clayey bauxites and Fe-rich bauxites that are composed predominantly of Al-oxyhydroxides (gibbsite, boehmite and nordstrandite), kaolinite and Fe-oxyhydroxides. The bauxites are enriched in REY, with a median value of 1,310ppm and up to 2,542ppm, with a consistent enrichment in Light REE (LREE) and Y compared to Middle REE (MREE) and Heavy REE (HREE). The positive correlation between the contents of REY and Th, and negative correlation with K, makes gamma-ray spectrometry an appropriate tool for the exploration. In addition, bauxitic rocks from the RFA contain significant Sc (up to 105ppm) and Ga (up to 54ppm) contents, and their extraction could potentially represent a substantial economic surplus to the revenue generated solely from the aluminum production.
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