What is it about?
The nickel sulphide and platinum-group element deposits of the East African Nickel Belt contain abundant disseminated chromite grains that crystallized during the magmatism that formed the nickel and platinum mineralization. Here, I show that the chromite grains from different types of deposit have distinctive compositions that are inherited from the magmatic mineralizing processes. In particular, the abnormally low ratio of ferric (Fe3+) to ferrous (Fe2+) iron in the chromite indicates the important role of graphitic sediment assimilation that resulted in nickel sulphide mineralization.
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Why is it important?
Chromite is a resistate mineral, able to survive many alteration and weathering processes, unlike the sulphide minerals that contain high-grade nickel deposits. Therefore, it can potentially be used as an indicator for the presence and type of nickel deposits in a mineralized belt. However, the effect of the various magmatic and later alteration processes on the chromite composition needs to be fully understood, and this article aims to add to this understanding.
Perspectives
The use of chromite as an exploration indicator should be important when prospecting in deeply-weathered tropical terrains, as it can be one of the few means to directly test the presence of nickel-hosting ultramafic rocks in the ground. Sampling of streams and soils for resistate chromite should be used as a complement to more expensive but often inconclusive geophysical survey methods.
Dr David M Evans
Natural History Museum, London
Read the Original
This page is a summary of: Chromite compositions in nickel sulphide mineralized intrusions of the Kabanga-Musongati-Kapalagulu Alignment, East Africa: petrologic and exploration significance, Ore Geology Reviews, March 2017, Elsevier,
DOI: 10.1016/j.oregeorev.2017.03.012.
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