PGE-rich chromitite

Ore deposit type: Magmatic in mafic-ultramafic rocks

Provenance: Merensky Reef, Bushveld Complex, South Africa

Description: Chromitite horizon (dark gray) with traces of sulphides and PGM, separating a pegmatoid orthopyroxenite (lower part; mostly composed of centimetric, brown orthopyroxene crystals and subordinate interstitial plagioclase) from a norite (upper part; composed of millimetric orthopyroxene crystals and plagioclase). The sample is a portion of the Merensky Reef, a less than one metre-thick layer of pegmatoid pyroxenite, bounded at the top and bottom by thin chromitite levels with rare sulphides, belonging to the Rustenburg layered suite (Bushveld Complex, South Africa). The Merensky Reef is renowned for the high PGE grades occurring around the chromitite levels. The PGE minerals are very fine-grained and are only visible under a microscope.