Ophiolitic chromites

Walker R. J., Prichard H. M., Ishiwatari A., and Pimentel M. (2002) The osmium isotopic composition of convecting upper mantle deduced from ophiolite chromites. Geochim. Cosmochim. Acta 66, 329—345. 

The range of values measured on mantle peridotites overlaps with other estimates for the composition of the convecting upper mantle such as PUM and ophiolitic chromites. Nevertheless, the mean yQs value of ca. —2.0 differs from the estimate based on ophiolitic chromitites by 3.0 yQs units and from PUM by about 4.0 yQs units (Fig. 3.32). This result does not sit easily with a simple chondritic model for the upper mantle. 

We analyzed chromites from 1) podiform chromitite deposits from the mantle section of the Thetford Mines Ophiolite (TMO), southern Quebec Appalachians (Canada) 2) stratiform chromitite seams found within the Stillwater Complex, Montana (USA). In addition, we also analyzed chromite in lavas from different tectonic settings in order to 1) verify whether the IPGE solubility in chromite could be related to geological setting and... 

Palladium, platinum, rhodium, ruthenium and iridium in chromite-rich rocks form the Semail ophiolite, Oman. Canadian Mineralogist, 20, 537-548. 

Cassard D. (1980) Structure et origine des gisements de chromite du Massif du Sud (ophiolite de Nouvelle Caledo-nie). University of Nantes. 

The mineral chromite tends to have high Os and low Re concentrations and is resistant to chemical change after crystallization. It is therefore a robust phase and because of its low Re-content does not require a large age correction in ancient samples. Massive chromitites are commonly found in ophiolites and so... 

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