Open System Re-Os Isotope Behavior in Platinum-Group Minerals during Laterization?

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 Os-187/Os-188 varying from 0.11973 & PLUSMN; 0.00134 to 0.12215 & PLUSMN; 0.00005 (2 sigma uncertainty) whereas (ii) lateritic PGM are more radiogenic in terms of Os-187/Os-188 (from 0.12390 & PLUSMN; 0.00001 to 0.12645 & PLUSMN; 0.00005; 2 sigma 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.