Arsenic as an Indicator of Black Shale Assimilation by Nickel-Bearing Mafic-Ultramafic Intrusions, Muremera-Rujungu, Burundi

What is it about?

The paper shows how the magmas carrying nickel-copper sulphide mineralization up from the mantle can be modified and chemically "tagged" by passing through certain arsenic-rich sedimentary formations, on the way to their final site of accumulation. As they reach the cool upper crust, the magmas solidify as thin sills and dykes, which can contain mineralogical and geochemical clues about the potential of the magmas to have formed valuable deposits of nickel and copper.

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Why is it important?

Arsenic and other semi-metals (antimony, bismuth) are now recognized as important components (usually in trace amounts) of magmatic Ni-Cu sulphide deposits. They are useful as tracers or markers of the origin and emplacement history of the fertile magmas that carry Ni, Cu and platinum-group elements from the mantle up into the crust. This paper reports the chalcophile element (Ni, Cu, S, As, Sb, Bi) contents of a group of basaltic sills in Burundi with the passage of the magma through As-rich black shale sediments and links the Ni-As association to high-grade Ni mineralization in the nearby Kabanga Ni deposit.

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