Ultramafic-hosted volcanogenic massive sulfide deposits from Cuban ophiolites

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.Spanish Government PI0975CAP Investigacion PUCP-2022 Program PID 2019- 105625RB-C21MCIN/AEI PRE 2020-092140 2022-A- 004

A track record of Au–Ag nanomelt generation during fluid‑mineral interactions

This research was financially supported by Grant PID 2019-105625RB-C21 funded by MCIN/AEI/10.13039/501100011033, by Grant 2021 SGR 00239 funded by Gestió d’Ajuts Universitaris i de Recerca de Catalunya. Additional funding was provided by a “Ayudas predoctorales 2020” number PRE 2020-092140 PhD grant to DD-C by the Spanish Ministry of Science and Innovation and the Proyecto de Excelencia de la Junta de Andalucía (Spain), PROYECTEXCEL_00705 to JMGJ. Laura Casado (Instituto de Nanociencia de Aragón (INA)—University of Zaragoza) and María del Mar Abad (CIC, University of Granada) are acknowledged for her assistance with FIB and HRTEM respectivelyThe online version contains supplementary material available at https:// doi. org/ 10. 1038/ s41598- 023- 35066-yRecent studies have reported the significant role of Au-bearing nanoparticles in the formation of hydrothermal gold deposits. Despite the ever-increasing understanding of the genesis and stability of Au-bearing nanoparticles, it is still unknown how they behave when exposed to hydrothermal fluids. Here, we study the nanostructural evolution of Au–Ag nanoparticles hosted within Co-rich diarsenides and sulfarsenides of a natural hydrothermal deposit. We use high-resolution transmission electron microscopy to provide a singular glimpse of the complete melting sequence of Au–Ag nanoparticles exposed to the hydrothermal fluid during coupled dissolution–precipitation reactions of their host minerals. The interaction of Au–Ag nanoparticles with hydrothermal fluids at temperatures (400–500 ºC) common to most hydrothermal gold deposits may promote melting and generation of Au–Ag nanomelts. This process has important implications in noble metal remobilization and accumulation during the formation of these deposits.MCIN/AEI/10.13039/501100011033, PID 2019-105625RB-C21Gestió d'Ajuts Universitaris i de Recerca de Catalunya 2021 SGR 00239Ministerio de Ciencia e Innovación PRE 2020-092140 PhDProyecto de Excelencia de la Junta de Andalucía PROYECTEXCEL_00705Instituto de Nanociencia de Aragón (INA)-Universidad de ZaragozaComisión de Investigaciones Científicas (CIC), Universidad de Granad

A track record of Au-Ag nanomelt generation during fuid‑mineral interactions

Recent studies have reported the signifcant role of Au-bearing nanoparticles in the formation of hydrothermal gold deposits. Despite the ever-increasing understanding of the genesis and stability of Au-bearing nanoparticles, it is still unknown how they behave when exposed to hydrothermal fuids. Here, we study the nanostructural evolution of Au–Ag nanoparticles hosted within Co-rich diarsenides and sulfarsenides of a natural hydrothermal deposit. We use high-resolution transmission electron microscopy to provide a singular glimpse of the complete melting sequence of Au–Ag nanoparticles exposed to the hydrothermal fuid during coupled dissolution–precipitation reactions of their host minerals. The interaction of Au–Ag nanoparticles with hydrothermal fuids at temperatures (400– 500 ºC) common to most hydrothermal gold deposits may promote melting and generation of Au–Ag nanomelts. This process has important implications in noble metal remobilization and accumulation during the formation of these deposits

The chromitites of the Neoproterozoic Bou Azzer ophiolite (Central Anti-Atlas, Morocco) revisited

The Neoproterozoic Bou Azzer ophiolite in the Moroccan Anti-Atlas Panafrican belt hosts numerous chromitite orebodies within the peridotite section of the oceanic mantle. The chromitites are strongly affected by serpentinization and metamorphism, although they still preserve igneous relicts amenable for petrogenetic interpretation. The major, minor and trace element composition of unaltered chromite cores reveal two compositional groups: intermediate-Cr (Cr# = 0.60 - 0.74) and high-Cr (Cr# = 0.79 - 0.84) and estimates of parental melt compositions suggest crystallization from pulses of fore-arc basalts (FAB) and boninitic melts, respectively, that infiltrated the oceanic supra-subduction zone (SSZ) mantle. A platinum group elements (PGE) mineralization dominated by Ir-Ru-Os is recognized in the chromitites, which has its mineralogical expression in abundant inclusions of Os-Ir alloys and coexisting magmatic laurite (RuS2) and their products of metamorphic alteration. Unusual mineral phases in chromite, not previously reported in this ophiolite, include super-reduced and/or nominally ultra-high pressure minerals moissanite (SiC), native Cu and silicates (oriented clinopyroxene lamellae), but "exotic" zircon and diaspore have also been identified. We interpret that clinopyroxene lamellae have a magmatic origin, whereas super-reduced phases originated during serpentinization processes and diaspore is linked to late circulation of low-silica fluids related to rodingitization. Zircon grains, on the other hand, with apatite and serpentine inclusions, could either have formed after the interaction of chromitite with mantlederived melts or could represent subducted detrital sediments later incorporated into the chromitites. We offer a comparison of the Bou Azzer chromitites with other Precambrian ophiolitic chromitites worldwide, which are rather scarce in the geological record. The studied chromitites are very similar to the Neoproterozoic chromitites reported in the Arabian-Nubian shield, which are also related to the Panafrican orogeny. Thus, we conclude that the Bou Azzer chromitites formed in a subduction-initiation geodynamic setting with two-stages of evolution, with formation of FAB-derived intermediate-Cr chromitites in the early stage and formation of boninite-derived high-Cr chromitites in the late stage

REE ultra-rich karst bauxite deposits in the Pedernales Peninsula, Dominican Republic: Mineralogy of REE phosphates and carbonates

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

Goethita, maghemita y hematites como menas de Ni y Co en lateritas de tipo óxido: lecciones aprendidas del estudio del distrito de Moa, Cuba

El Ni y el Co son metales estratégicos en la construcción de sociedades sostenibles, sus propiedades físicas y químicas los hacen imprescindibles en la denominada transición energética que permitiría alcanzar los ambiciosos objetivos de descarbonización de la economía. Los yacimientos lateríticos de Ni-Co contienen alrededor del 70 % de las reservas mundiales de Ni y representan la segunda fuente de obtención de Co a nivel mundial. En consecuencia, los mayores productores de Ni en el 2021 fueron países que albergan grandes yacimientos lateríticos de Ni-Co (Indonesia y Filipinas; https://pubs.usgs.gov/periodicals/mcs2022/mcs2022-nickel.pdf). Los enormes recursos de Ni en cortezas lateríticas desarrolladas sobre rocas ultramáficas ricas en olivino, unidos a su localización muy cerca de la superficie en comparación con los depósitos de sulfuros magmáticos de Ni, conlleva a que los yacimientos lateríticos sean la opción más atractiva para la industria del Ni

REE en las bauxitas kársticas de la Sierra de Bahoruco (República Dominicana): geoquímica y mineralogía

Los elementos de las tierras raras (REE, divididas en LREE: La- Gd y HREE: Tb-Lu+Y, a veces distinguiendo las MREE: Sm-Gd) tienen un papel muy relevante en la denominada transición del sector energético hacia fuentes renovables que permitan alcanzar el objetivo de cero emisiones netas de carbono. Esta transición depende de la disponibilidad de metales y en particular de REE (p. ej. en la fabricación aerogeneradores y vehículos eléctricos) (Goodenough et al., 2018; Charles et al., 2021). En la actualidad, las principales fuentes de REE son los yacimientos de carbonatitas y rocas alcalinas (típicamente ricos en LREE±U±Th). Sin embargo, los yacimientos secundarios como los de REE adsorbidos en arcillas, y las bauxitas kársticas, destacan por su potencial de concentrar significativamente estos elementos (Goodenough et al., 2018). En la Sierra de Bahoruco (suroeste de la República Dominicana) existen importantes afloramientos de bauxitas kársticas con contenidos muy altos en REE (Torró et al., 2017). Este trabajo tiene como objetivo estudiar la mineralogía de las fases portadoras de REE en el contexto de los perfiles de bauxitas kársticas de la Sierra de Bahoruco, a partir de muestras representativas de una veintena de depósitos

Petrología y geoquímica de la ofiolita neoproterozoica de Bou Azzer (Marruecos)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Minerales 'exóticos' en cromititas ofiolíticas. Implicaciones para la geodinámica mantélica

Los depósitos ofiolíticos de cromita constituyen un rasgo característico de la secuencia mantélica de las ofiolitas (González-Jiménez et al., 2014 y referencias en éste). Los cuerpos de cromititas se encuentran en dunitas y harzburgitas distribuyéndose a lo largo de una zona de espesor variable, entre 1 y 2 km, debajo de los niveles de gabros bandeados de la corteza inferior oceánica. El origen de cuerpos monominerálicos de cromita en el manto, especialmente el mecanismo de concentración de cromita y el ambiente tectónico de formación, continúa siendo un tema sujeto a debate (e.g., Proenza et al., 1999; González-Jiménez et al., 2014). A tal efecto, se han propuesto hipótesis basadas en: i) cristalización cotéctica de cromita+olivino y su posterior separación mecánica; ii) procesos de mezcla o contaminación de magmas; iii) asimilación de piroxenitas y gabros; iv) aumento del grado de polimerización del fundido debido a la pérdida de agua; v) cambios en la fugacidad de oxígeno. Todas estas hipótesis asumen procesos a baja presión en el manto (<20 km profundidad)

Nanomaterial accumulation in boiling brines enhances epithermal bonanzas

Abstract Epithermal bonanza-type ores, characterized by weight-percent contents of e.g., gold and silver in a few mm to cm, are generated by mixtures of magmatic-derived hydrothermal brines and external fluids (e.g., meteoric) that transport a variety of metals to the site of deposition. However, the low solubilities of precious metals in hydrothermal fluids cannot justify the high concentrations necessary to produce such type of hyper-enriched metal ore. Here we show that boiling metal-bearing brines can produce, aggregate, and accumulate metal nanomaterials, ultimately leading to focused gold + silver ± copper over-enrichments. We found direct nano-scale evidence of nanoparticulate gold- and/or silver-bearing ores formed via nonclassical growth (i.e., nanomaterial attachment) during boiling in an intermediate-sulfidation epithermal bonanza. The documented processes may explain the generation of bonanzas in metal-rich brines from a range of mineral deposit types