Abstract
In this short communication, we present preliminary data on the Re-Os isotopic systematics of platinum-group minerals (PGM) recovered from different horizons in the Falcondo Ni-laterite in the Dominican Republic. The results show differences in the Os-isotope composition in different populations of PGM: (i) pre-lateritic PGM yield 187Os/188Os varying from 0.11973 ± 0.00134 to 0.12215 ± 0.00005 (2σ uncertainty) whereas (ii) lateritic PGM are more radiogenic in terms of 187Os/188Os (from 0.12390 ± 0.00001 to 0.12645 ± 0.00005; 2σ uncertainty). We suggest that these differences reflect the opening of the Re-Os system in individual grains of PGM during lateritic weathering. The implications of these results are twofold as they will help to (1) elucidate the small-scale mobility of noble metals in the supergene setting and therefore the possible formation of PGM at these very low temperatures, (2) better refine the Os-isotopic datasets of PGM that are currently being used for defining dynamic models of core–mantle separation, crustal generation, and fundamental plate-tectonic processes such as the opening of oceans.
Highlights
Among the applicable radiogenic isotopic systems, the 187 Re-187 Os system is arguably one of the most sensitive tools to investigate the long-term interaction between different regions of the Earth’s interior [1]
The Re-Os isotope systematics measured in situ on platinum-group minerals (PGM) from mantle-derived rocks provide robust records of these processes [2,3]
We show that two populations of PGM from the Falcondo Ni-laterite in the Dominican Republic yield distinctively different ranges of
Summary
Among the applicable radiogenic isotopic systems, the 187 Re-187 Os system is arguably one of the most sensitive tools to investigate the long-term interaction between different regions of the Earth’s interior [1]. Earlier studies, using Os-rich PGM from placers adjacent to ultramafic massifs, demonstrated a marked Os-isotopic heterogeneity that was interpreted as a proof that the convective upper mantle is isotopically heterogeneous [6,7,8,9,10] These interpretations are based on the idea that PGM were formed in the mantle and transferred to the supergene environment by mechanical processes alone without modification of their original Os isotopic compositions. PGM can form in the supergene setting [11,12,13,14,15,16] These observations raise the question of the possible open-system behavior of the Re-Os isotopic system in placer-derived PGM.
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