Zincian chromite inclusions in diamonds: Possibility of deep recycling origin

• DOI: 10.2465/jmps.101014
• Publication Date: 2011-02-18T05:20:23Z
• Authors: Shoji ARAI; Satoko ISHIMARU
• Keywords: 01 natural sciences; 12. Responsible consumption; 0105 earth and related environmental sciences

It was reported by Meyer and Boyd (1972) that zincian chromite, having 2 wt% to 3 wt% ZnO and high (>0.9) Cr# (= Cr/(Cr + Al) atomic ratio), appears as inclusions in diamonds obtained from kimberlite. Zincian chromite is characterized by a low ( 0.8); moreover, the major-element chemistry of these chromites is similar to that of the magnesiochromite inclusions in diamonds. Spinels obtained from altered rocks show a chemical range that comprises the zincian chromite inclusions found in diamonds. The origin of these inclusions possibly lies in deep recycling. They were initially formed at the Earth's surface in altered/metamorphosed peridotites; they then sank deep down into the mantle and were entrained to the surface again by kimberlite magmatism.