18 research outputs found
Nanoscale Structure of Zoned Laurites from the Ojén Ultramafic Massif, Southern Spain
We report the first results of a combined focused ion beam and high-resolution transmission
electron microscopy (FIB/HRTEM) investigation of zoned laurite (RuS2)-erlichmanite (OS2) in
mantle-hosted chromitites. These platinum-group minerals form isolated inclusions (<50 um across)
within larger crystals of unaltered chromite form the Ojén ultramafic massif (southern Spain).
High-magnification electron microscopy (HMEM), high angle-annular dark field (HAADF) and
precession electron diffraction (PED) data revealed that microscale normal zoning in laurite consisting
of Os-poor core and Os-rich rims observed by conventional micro-analytical techniques like field
emission scanning electron microscope and electron microprobe analysis (FE-SEM and EPMA) exist
at the nanoscale approach in single laurite crystals. At the nanoscale, Os poor cores consist of
relatively homogenous pure laurite (RuS2) lacking defects in the crystal lattice, whereas the Os-richer
rim consists of homogenous laurite matrix hosting fringes (10–20 nm thickness) of almost pure
erlichmanite (OsS2). Core-to-rim microscale zoning in laurite reflects a nonequilibrium during
laurite crystal growth, which hampered the intra-crystalline diffusion of Os. The origin of zoning
in laurite is related to the formation of the chromitites in the Earth’s upper mantle but fast cooling
of the chromite-laurite magmatic system associated to fast exhumation of the rocks would prevent
the effective dissolution of Os in the laurite even at high temperatures (~1200 ÂşC), allowing the
formation/preservation of nanoscale domains of erlichmanite in laurite. Our observation highlights
for the first time the importance of nanoscale studies for a better understanding of the genesis of
platinum-group minerals in magmatic ore-forming systems.This research was supported by Spanish projects: RTI2018-099157-A-I00 and CGL2015-65824-P granted
by the “Ministerio de Ciencia, InnovaciĂłn y Universidades” and Ministerio de EconomĂa y Competitividad”
(MINECO) respectively. Additional funding was provided by the RamĂłn y Cajal Fellowship RYC-2015-17596
granted by the Spanish MINECO to JMGJ. A. Jiménez-Franco is supported with a postdoctoral grant (CVU 350809)
from the National Council on Science and Technology (CONACYT) of Mexico
Desarrollos metodolĂłgicos para el estudio de nanominerales y nanopartĂculas de elementos de alto valor tecnolĂłgico en yacimientos minerales
Hasta hace aproximadamente una dĂ©cada, las nanopartĂculas y nanominerales eran unos autĂ©nticos desconocidos en el ámbito de los yacimientos minerales. Sin embargo, el progresivo desarrollo de tĂ©cnicas analĂticas más potentes ha permitido caracterizar partĂculas cada vez de menor tamaño, lo cual ha llevado aparejado una verdadera explosiĂłn de la nanociencia y sus posibles aplicaciones directas en los procesos tecnolĂłgicos o nanotecnologĂa
Ni-phyllosilicates (garnierites) from the Falcondo Ni-laterite deposit (Dominican Republic): Mineralogy, nanotextures, and formation mechanisms by HRTEM and AEM
Ni-bearing magnesium phyllosilicates (garnierites) are significant Ni ores in Ni-laterites worldwide. The present paper reports a detailed TEM investigation of garnierites from the Falcondo Ni-laterite deposit (Dominican Republic). Different types of garnierites have been recognized, usually consisting of mixtures between serpentine and talc-like phases that display a wide range of textures at the nanometer scale. In particular, chrysotile tubes, polygonal serpentine, and lizardite lamellae are intergrown with less crystalline, talc-like lamellae. Samples consisting uniquely of talc-like and of sepiolite-falcondoite were also observed, occurring as distinctive thin lamellae and long ribbon-shaped fibers, respectively. HRTEM imaging indicates that serpentine is replaced by the talc-like phase, whereas TEM-AEM data show preferential concentration of Ni in the talc-like phase. We suggest, therefore, that the crystallization of Ni-bearing phyllosilicates is associated with an increase in the silica activity of the system, promoting the replacement of the Ni-poor serpentine by the Ni-enriched talc-like phase. These results have interesting implications in material science, as garnierites are natural analogs of Ni-bearing phyllosilicate-supported synthetic catalysts. Finally, SAED and HRTEM suggest that the Ni-bearing talc-like phase corresponds to a variety of talc with extra water, showing larger d001 than talc (i.e., 9.2–9.7 Å), described as “kerolite”-“pimelite” in clay mineral literature
Desarrollos metodolĂłgicos para el estudio de nanominerales y nanopartĂculas de elementos de alto valor tecnolĂłgico en yacimientos minerales
XXXVIII ReuniĂłn CientĂfica de la Sociedad Española de MineralogĂa, Ronda, Málaga 25-28 junio de 2019
Nanoscale structure of hightemperature Ru-Os sulphides
Goldschmidt2019, Barcelona (Spain), 18-23 august, 201
Influence of Heat Treatment on the Physical Transformation of Flint Used by Neolithic Societies in the Western Mediterranean
International audienceThe Neolithic period Chassey culture in southern France from 4200 to 3500 Cal. BC developed a specialized lithic technology for flint bladelets that used a heating process as an essential part of the production. Experimental archaeology demonstrated that the heating should take place at low temperature somewhere around 250°C. To identify and quantify the physical transformations of flint at low temperature, laboratory and synchrotron experiences have been carried out on a set of heated Barremo-Bedoulian flint samples. According to our measurements, this flint consists of a nanocrystalline matrix of quartz and moganite. Evolution of mesoporous structure was observed during heat treatment. The flint transformed between 200-300°C, resulting in a reduction in the size and volume of porosity. The densification of flint is linked to changes on the nanocrystalline grain boundaries, and it is thought to have a direct impact on the improved mechanical properties from the Chassey culture lithic productions
A shallow origin for diamonds in ophiolitic chromitites
Recent findings of diamonds in ophiolitic peridotites and chromitites challenge our traditional
notion of Earth mantle dynamics. Models attempting to explain these findings involve
incorporation of diamonds into chromite near the mantle transition zone. However, the
occurrence of metastable diamonds in this context has not been considered. Here, we report
for the first time in situ microdiamonds in chromite from ophiolitic chromitite pods hosted
in the Tehuitzingo serpentinite (southern Mexico). Here, diamonds occur as fracture-filling
inclusions along with quartz, clinochlore, serpentine, and amorphous carbon, thus indicating
a secondary origin during the shallow hydration of chromitite. Chromite chemical variations
across the diamond-bearing healed fractures indicate formation during the retrograde evolution
of chromitite at temperatures between 670 °C and 515 °C. During this stage, diamond
precipitated metastably at low pressure from reduced C-O-H fluids that infiltrated from the
host peridotite at the onset of serpentinization processes. Diamond was preserved as a result
of fracture healing at the same temperature interval in which the chromite alteration began.
These mechanisms of diamond formation challenge the idea that the occurrence of diamond
in ophiolitic rocks constitutes an unequivocal indicator of ultrahigh-pressure conditions
A shallow origin for diamonds in ophiolitic chromitites: REPLY
Department of Mineralogy, Petrology and Applied Geology, University of Barcelona, Martà i Franquès s/n, 08028 Barcelona, Spain 2 Department of Mineralogy and Petrology, Faculty of Sciences, University of Granada, Avenida Fuentenueva s/n, 18002 Granada, Spain 3 Andalusian Earth Science Institute (IACT), Spanish Research Council (CSIC)–University of Granada, Avenida de las Palmeras, 4, 18100 Armilla, Granada, Spain 4 Institute of Geology, National Autonomous University of Mexico, Ciudad Universitaria, 04510 Coyoacán, CDMX, Méxic