The accumulation of Ni in serpentines and garnierites from the Falcondo Ni-laterite deposit (Dominican Republic) elucidated by means of μXAS

Ni-bearing serpentines and garnierites (Ni-bearing Mg-phyllosilicates) are the main Ni ores in the Falcondo Ni-laterite deposit (Dominican Republic). In the present paper a set of garnierite samples and the associated Ni-bearing serpentines with characteristic mineral compositions and textures, from the saprolite horizon, were studied by EMPA, μXRF and μXAS. The ultimate goal is to elucidate, for the first time, the Fe speciation and the Ni local environment of saprolite ores from Ni-laterites of the Dominican Republic. The chemical composition of the minerals has been obtained by means of EMPA and the Ni, Fe and Cr elemental maps obtained by μXRF allowed distinguishing the saprolite fragments containing Ni-bearing serpentines and Fe oxyhydroxides from the garnierite veins. The Fe K-edge μXANES demonstrated that Fe in the Ni-poor primary serpentine is mostly in the Fe2+ form, whereas in the Ni-bearing serpentine constituting the bulk of the saprolite and in the Fe-bearing garnierite Type I Fe was in the form of Fe3+. In parallel, the local environment of Ni determined by means of Ni K-edge μEXAFS confirmed that in Ni-poor primary serpentines Ni formed a homogeneous Ni-Mg solid solution, in garnierites formed Ni-Ni clusters, and in Ni-bearing secondary serpentines Ni was found in Ni-Mg and Ni-Ni mixed sites. This paper explains the accumulation of Ni, the speciation of Fe in garnierites with various mineral compositions and in Ni-bearing serpentines from the saprolite horizon in Ni-laterite deposits

Estudi geològic i mineralògic de mines de l'època Neolítica a la Serra de les Ferreres (Mines de Gavà)

Aquest estudi s'ha efectuat en dues fases, seguint el desenvolupament de les obres que van donar lloc a les intervencions arqueològiques. El primer estudi va ser efectuat per Carme Cirera, sota la direcció de Joan Carles Melgarejo, i va tenir lloc durant els treballs d'excavació de la mina número 83. El segon estudi va ser efectuat posteriorment pel mateix Joan Carles Melgarejo i per Joaquín Proenza, i va tenir lloc durant els treballs d'excavació de les mines números 84 i següents

Uvarovite in podiform chromitite; the Moa-Baracoa ophiolitic massif, Cuba

The chromitite pods of the Moa-Baracoa massif, in the eastern ophiolitic belt of Cuba, contain pre-existing gabbro sills. This association is affected by two processes of hydrothermal alteration. The chromitites and the hosting dunites and harzburgites are affected first by regional serpentinization; a second alteration, represented by chloritization accompanied with formation of ferrian chromite, is mainly located in the pods and their immediate vicinity. The altered chromitite pods and enclosed gabbro sills iue cross cut by millimeter-wide veins. The vein filling consists of a sequence of clinochlore, uvarovite, chromian clinochlore, rutile, titanite and calcite. Uvarovite also occurs in the vicinity of veins Uvarovite is concentrically zoned, covering compositions in the uvarovite-grossular solid solution series between Uva17 and Uvae:; the andradite component is very low. These compositions suggest a complete miscibility along the grossular-uvarovite join at relatively low temperature. On the basis of the mineral sequence and mineral chemistry (major and trace elements), the uvarovite crystals, as well as the vein assemblage, formed by a low-temperature leaching, Ca probably from the gabbro sills, and Cr and Al from the chromite dunng the formation of ferrian chromite Cr and A1 would have been mobile only at the scale of a pod during this process

The metallogenic evolution of the Greater Antilles

The Greater Antilles host some of the world’s most important deposits of bauxite and lateritic nickel as well as significant resources of gold and silver, copper, zinc, manganese, cobalt and chromium. Beginning in Jurassic time, sedimentary exhalative base metal deposits accumulated in marine sedimentary rift basins as North and South America drifted apart. With the onset of intraoceanic subduction during the Early Cretaceous, a primitive (tholeiitic) island arc formed above a southwesterly-dipping subduction zone. Podiform chromite deposits formed in the mantle portion of the supra-subduction zone, directly above subducted Proto-Caribbean oceanic lithosphere. Within the nascent island arc, bimodal-mafic volcanogenic massive sulfide deposits formed in a fore-arc setting; mafic volcanogenic massive sulfide deposits formed later in mature back-arc basins. The Pueblo Viejo gold district, with five million ounces in production and twenty million ounces in mineable reserves, formed at 108-112Ma, in an apical rift or back-arc setting. By Late Cretaceous time, calc-alkaline volcanism was well established along the entire length of the Greater Antilles. Volcanogenic massive sulfide deposits including shallow submarine deposits characteristic of the primitive island arc gave way to porphyry copper and epithermal precious metal deposits typical of the mature island arc. Oblique collision of the Greater Antilles with North America began in the Late Cretaceous in Cuba and migrated eastward. Orogenic gold and tungsten deposits that formed during the collision event are preserved in ophiolites and in metamorphic core complexes. Since the Eocene, regional tectonism has been dominated by strike-slip motion as the North American continent moved westward relative to the Caribbean Plate. Large nickel-cobalt laterite deposits were formed when serpentinites were exposed to weathering and erosion during the mid-Tertiary. Bauxite deposits were derived from the weathering of volcanic ash within a carbonate platform of Eocene to Miocene ag

New mineralogical data on platinum-group minerals from the Río Santiago alluvial placer, Esmeraldasprovince, Ecuador

Mineralogical studies on platinum-group minerals found in placer deposits from the Río Santiago (Ecuador) are scarce. In this investigation, one sample collected from the Río Santiago alluvial placer was studied via a multi-disciplinary approach, including optical microscopy, scanning electron microscopy, electron microprobe, and Raman spectroscopy. Whole-rock geochemistry data of the sample confirms elevated Au and platinum-group elements contents and the chondrite-normalized pattern reveals pronounced positive Ir and Pt nomalies. Free grains of platinum-group minerals were separated via hydroseparation techniques and identified as: i) Pt-Fe alloy (Pt3Fe), ii) tulameenite (Pt2FeCu) and iii) hongshiite (PtCu). The most abundant platinum-group mineral is Pt-Fe alloy (85%) that occasionally hosts cuprorhodsite (CuRh2S4) inclusions. Although the primary source remains unknown, the geochemical and mineralogical data suggests that the source of platinum-group minerals in the Río Santiago alluvial placer is a mafic-ultramafic Ural-Alaska type complex. Possible primary sources are the mafic and ultramafic rocks found in the mafic basement of the coastal region and the Western Cordillera (Piñón, San Juan and Pallatanga units), which derive from the Late Cretaceous Caribbean Colombia Oceanic Plateau (CCOP)

Ore mineralogy of bimodal-mafic VMS deposits hosted in Early Cretaceous Greater Antilles island-arc tholeiite series

VMS deposits in the Greater Antilles are described throughout the Dominican Republic and Cuba, genetically linked to two main episodes of the island-arc tectonic and magmatic evolution: 1) bimodal mafic type deposits, formed during the earliest stages of island-arc volcanism and 2) mafic (Cyprus) type, formed in mature back-arc basins (Nelson et al., 2011). Bimodal-mafic VMS deposits are in the main hosted in tholeiitic volcanic rocks of Early Cretaceous age of the Maimón and Amina Formations in Cordillera Central of the Dominican Republic and in Los Pasos Formation and Purial Complex in central and eastern Cuba respectively. Mild though decided trend toward Sb enrichment in tennantite from stratiform ores in the San Fernando and Antonio deposits with respect to Cerro de Maimón parallel lower values of Se and As and higher contents in the more incompatibles Sb, Te and Bi in galena. These nuances in ore geochemistry support a slightly more primitive setting of formation of VMS mineralization in the Maimón Formation denoted by the lithogeochemistry of the hosting volcanic units.Postprint (published version

Reactive transport modelling: the formation of Ni-laterite profiles (Punta Gorda, Moa Bay, Cuba).

Ni-laterites represent one of the main Ni sources worldwide, with about 40% of the annual production (Gleeson et al.,2003). The Punta Gorda Ni laterite deposit is part of a larger province of nickel laterites in northeast Cuba (Moa Bay district) (Lavaut, 1998) developed from serpentinized peridotites