Platinum-group elements and gold geochemistry and mineralogy in the Ray-Iz ophiolitic chromitites, Polar Urals

摘要

In this work we report new data on the platinum-group elements (PGE) and gold distribution in chromitite from the Ray-Iz ophiolite (Polar Urals), along with the new discovery of native gold included in chromite crystals. The negative slope of the chondrite normalized PGE-Au patterns reflects the predominance of Ru-Os-Tr phases in the platinum-group minerals (PGM) assemblage as typical of ophiolitic chromitites. Despite of the low Au contents several grains of native gold have been found. This discrepancy may be due to the random distribution of the gold grains in the investigated samples. The unusual occurrence of the native gold as inclusion in fresh chromite implies that it was trapped at high temperature. This type of gold occurrence is uncommon for ophiolitic chromitites, in which gold minerals are occasionally found associated with altered silicates matrix, or in secondary magnetite coating the chromite crystals.