A first report of variscite tairona artifacts (a.d. 1100-1600) from the Sierra Nevada de Santa Marta, Colombia, and its implications for precolumbian exchange networks in the region

Archaeoznetric analyses (Raman Spectroscopy Analysis, X-Ray Diffraction, and Electron Microprobe Analysis) of greenstone beads of the precolumbian Tairona culture (A.D. 1100-1600) of the Sierra Nevada de Santa Marta, Colombia, have revealed that they are made of variscite-group minerals. These beads were curated at the Museo del Oro, Bogota, and the Archaeology Laboratory of the Universidad del Norte, Barranquilla. Variscite minerals of the variscite-strengite series are rare in nature, and therefore provenance data of source material are useful for the development of intercultural influence models. The abundance of this rare material in prehistoric Colombian collections strongly indicates not only that this material had important symbolic and prestige value for ancient Tairona societies (Nahuange and Tairona periods) but also that these societies participated in ancient trade routes, including, at least, the Andes of present-day Colombia and Venezuela, and the southern Caribbean coast

Mineralogy and geochemistry of Fe-Ti oxide ores from the Don Dieguito massif type anorthosite suite, Sierra Nevada de Santa Marta, Colombia

Fe-Ti oxide ores are commonly associated with Proterozoic massif-type anorthosite bodies emplaced during the Grenville orogeny (~1.2-1.0 Ga). Some of these anorthositic bodies occur in the northernmost part of the Santa Marta Massif, Colombia. They locally contain crosscutting Fe-Ti(-V) ore bodies between the El Hierro creek and the Don Dieguito river. We have distinguished two types of Fe-Ti(-V) ores: i) oxide-apatite norite (fine grained ilmenite and magnetite disseminated in an assemblage of apatite, amphibole, chlorite, rutile and sericitized plagioclase) and ii) banded nelsonite (coarser grained ilmenite, magnetite and apatite distributed in bands, with minor baddeleyite, srilankite and högbomite)

Fluid flow in the subduction channel: Tremolite veins and associated blackwalls in antigoritite (Villa Clara serpentinite mélange, Cuba)

Exotic blocks of massive antigorite-serpentinite (antigoritite) document a deep-seated subduction channel in the Villa Clara serpentinite-matrix mélange, central Cuba. The petrological and geochemical characteristics of antigoritite allow distinguishing two types of rock: i) antigoritite and ii) dolomite-bearing antigoritite. Both types are intimately related in field exposures and represent deep peridotite infiltrated by H2O-CO2 fluid mixtures that triggered antigoritization and local carbonation. Fluid infiltration continued after antigoritization forming a vein network as a potential response to hydrofracturing that precipitated tremolitite in the veins and triggered fluid-antigoritite reaction forming blackwalls. The mineralogical and chemical zoning in the blackwalls (Atg + Chl + Tr adjacent to antigoritite and Chl + Tr adjacent to the tremolitite vein) attest for multi-step metasomatic processes during fluid-rock interaction characterized by advection of infiltrating fluid towards the blackwall and, possibly, by diffusion out of the blackwall towards the fluid-filled vein. Tentative thermodynamic modeling of the blackwall domain Atg + Chl + Tr points vein network formation at 400–500 °C and 5–10 kbar during exhumation in the subduction channel, suggesting the infiltration of deep-seated pressurized fluid that triggered hydrofracturing. The chemical compositions of antigoritites, veins and blackwalls indicate a LILE- and LREE-enriched fluid evolved from the subducting plate, while Srsingle bondNd isotope systematics are compatible with an external fluid composed of a mixture of fluids evolved from sediments and, probably to a lesser extent, altered oceanic crust.This research was funded by projects MICINN PID2019-105625RB-C21 (co-funded by Fondo Europeo de Desarrollo Regional, FEDER), Junta de Andalucía P20_00550, Catalonian project SGR 2014-1661 and the University of Granada. LD acknowledges PhD grant BES-2013-063205 of the Spanish Ministry of Economy and Competitiveness and scholarship of Fundació Universitària Agustí Pedro i Pons. Funding for open access charge: Universidad de Granada / CBUA

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

Petrographic and Geochemical Characteristics of the Djabatoure Massif Metamagmatites from Pan-African Orogen in Togo, West Africa

The Dahomeyide orogen in Togo and adjoining parts of SE-Ghana and Benin records the suture of West Africa Craton (WAC) into NW Gondwana. The suture zone corresponds to a narrow and lithologically diverse area with HP granulites complexes. In Togo, the Djabatoure massif, located in the central part of Togo, belongs to the suture zone. The aim of this paper is to present the petrographic and geochemical characteristics of the Djabatoure massif in order to understand its implication in the geodynamic evolution of the Dahomeyide belt in Togo. The methodology implemented is based on a synthesis of previous works, a petrographic study of twenty thin sections and a geochemical study through discrimination diagrams of fifteen samples. The result shows that the Djabatoure massif is composed of granulites, pyroxenites, amphibolites, talcschists and gneisses. These rocks were equilibrated under granulite facies conditions and subsequently partially retrogressed to amphibolite facies. They display tholeiitic affinity, enriched LREE and negative anomalies in Nb, Zr and Ti indicating subduction zone magma. These features are consistent with protoliths of tholeiites, N-MORB and volcanic arc basalts affinities. The Djabatoure massif rocks were set up in oceanic environment and are thought to have been derivated from a metasomatized mantle

Petrographic and Geochemical Characteristics of the Djabatoure Massif Metamagmatites from Pan-African Orogen in Togo, West Africa

The Dahomeyide orogen in Togo and adjoining parts of SE-Ghana and Benin records the suture of West Africa Craton (WAC) into NW Gondwana. The suture zone corresponds to a narrow and lithologically diverse area with HP granulites complexes. In Togo, the Djabatoure massif, located in the central part of Togo, belongs to the suture zone. The aim of this paper is to present the petrographic and geochemical characteristics of the Djabatoure massif in order to understand its implication in the geodynamic evolution of the Dahomeyide belt in Togo. The methodology implemented is based on a synthesis of previous works, a petrographic study of twenty thin sections and a geochemical study through discrimination diagrams of fifteen samples. The result shows that the Djabatoure massif is composed of granulites, pyroxenites, amphibolites, talcschists and gneisses. These rocks were equilibrated under granulite facies conditions and subsequently partially retrogressed to amphibolite facies. They display tholeiitic affinity, enriched LREE and negative anomalies in Nb, Zr and Ti indicating subduction zone magma. These features are consistent with protoliths of tholeiites, N-MORB and volcanic arc basalts affinities. The Djabatoure massif rocks were set up in oceanic environment and are thought to have been derivated from a metasomatized mantle

Petrographic and Geochemical Characteristics of the Djabatoure Massif Metamagmatites from the Pan-African Orogen in Central Togo, West Africa

The Dahomeyide orogen, in Togo and adjoining parts of southeast Ghana and Benin, represents the suture of West Africa Craton (WAC) into northwest Gondwana. The suture zone corresponds to a narrow and lithologically diverse area with high pressure granulite complexes. The Djabatoure massif, located in the central part of Togo, belongs to the suture zone. The aim of this paper is to present the petrographic and geochemical characteristics of the Djabatoure massif in order to better understand the geodynamic evolution of the Dahomeyide belt in Togo. The methodology implemented is based on a synthesis of previous works, a petrographic study of 20 thin sections, and a geochemical study through discrimination diagrams of 15 rock samples. Results show that the Djabatoure massif is composed of granulites, pyroxenites, amphibolites, talcschists and gneisses. These rocks were equilibrated under granulite facies conditions and subsequently partially retrogressed to the amphibolite facies. The Djabatoure massif rocks also display tholeiitic affinity, enriched LREE, and negative anomalies in Nb, Zr and Ti; all these characteristics indicate subduction zone magmtism. These features are consistent with protoliths of tholeiites, N-MORB, and volcanic arc basalts affinities. The Djabatoure massif rocks were emplaced in an oceanic environment and likely originated  from a metasomatized mantle

An Alternative Scenario on the Origin of Ultra-High Pressure (UHP) and Super-Reduced (SuR) Minerals in Ophiolitic Chromitites: A Case Study from the Mercedita Deposit (Eastern Cuba)

The origin of the assemblage of ultra-high pressure (UHP), super-reduced (SuR) and several crustally derived phases in ophiolitic chromitites is still hotly debated. In this paper, we report, for the first time, this assemblage of phases in ophiolitic chromitites of the Caribbean. We studied the Mercedita chromitite deposit in the eastern Cuban ophiolitic complexes. The mineral phases were characterized using microRaman spectroscopy, energy-dispersive spectroscopy with a scanning electron microscope (SEM-EDS), X-ray microdiffraction and electron microprobe analyses. Mineral concentrates were prepared using hydroseparation techniques. We have identified oriented clinopyroxene lamellae in chromite, oriented rutile lamellae in chromite, moissanite hosted in the altered matrix of the chromitite, graphite-like amorphous carbon, corundum and SiO2 hosted in healed fractures in chromite grains, and native Cu and Fe-Mn alloy recovered in heavy-mineral concentrates obtained by hydroseparation. This assemblage may correspond to UHP-SuR conditions, implying recycling of chromitite in the mantle or formation of the chromite grains at deep mantle depths, followed by emplacement at a shallow level in the mantle. However, the chromitite bodies contain gabbro sills oriented parallel to the elongation of the chromitite lenses, and these show no evidence of HP/UHP metamorphism. Therefore, the identified "exotic" phases may not be indicative of UHP. They formed independently as oriented clinopyroxene lamellae in chromite during cooling (clinopyroxene and rutile), in super-reduced microenvironments during the serpentinization processes, and by transference of subducted crustal material to the mantle wedge via cold plume

HP-LT rocks exhumed during intra-oceanic subduction: the example of the Escambray massif (Cuba).

High-Presssure metabasites embedded in a serpentinite or metasedimentary matrix from the Sancti Spiritus dome (Escambray massif, Central Cuba) have been studied in order to better understand the origine and the evolution of the Northern Carribean boundary plate during the Cretaceous, in a global subduction context. Geochemical analyses (major, trace elements and isotopes) of the high pressure rocks show that they could be partially derived from the Cretaceous calc-alkaline arc described in Central Cuba, these were probably incorporated in the subduction zone by tectonic erosion. The High-Pressure rocks record a prograde path from the epidote bearing amphibolite facies to the barroisite bearing eclogite facies (P = 19 ± 2 Kbar, T = 590 ± 90 °C). These metabasites show evidence of retrogression starting from the glaucophane bearing eclogite facies to the lawsonite bearing blueschist facies. Therefore, these HP/LT rocks are characterized by a counter-clockwise cooling P/T path, which can be explained by the exhumation of HP rocks while the subduction was still active. Concordant geochronological data (Rb/Sr and Ar/Ar) suggest that the main exhumation of HP/LT rocks from the Sancti Spiritus dome occurred 70 Ma ago by top to SW thrusting. The retrogressed trajectory of these rocks, means that the northeast subduction of the Farallon plate continued after 70Ma. The final exhumation can be correlated with the beginning of the collision between the Bahamas platform and the Cretaceous island arc that induced a change of the subduction kinematic

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