What is it about?
Chromite is a high-temperature mineral that occurs in small amounts in gabbroic or mafic intrusions. I have investigated the composition of chromites in a group of small mafic intrusions situated in northwest Tanzania and Burundi. The work shows that these intrusions cooled relatively slowly, in spite of their small size, allowing us to infer that these intrusions were conduits for a larger mass of magma and that the host country rock had been preheated.
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Why is it important?
During the cooling of the intrusion, chromite interacts with the surrounding more abundant minerals, developing a series of concentric compositional zones from the rim to the core of each grain. If the intrusion cools quickly, which is the case for smaller intrusions, these reaction zones are preserved and can be used to interpret the type of emplacement and the speed of cooling of the intrusion. This knowledge is important for evaluating the possibility of the intrusion to carry mineral deposits, such as nickel-copper sulfides and platinum-group elements.
Perspectives
I did this work in the frame of a larger project on chromite compositions of East African intrusions, to try to understand the peculiar "reverse" zoning that I was seeing within some grains.
Dr David M Evans
Natural History Museum, London
Read the Original
This page is a summary of: Significance of compositional zoning in cumulate chromites of the Kabanga chonoliths, Tanzania, Mineralogical Magazine, May 2018, Mineralogical Society,
DOI: 10.1180/mgm.2018.87.
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