Typomorphism of Chrome-Spinellide From Chaya Nickel-Bearing Pluton

Chrome-spinellide have been studied from ultramafites of Chaya gabbronorite-peridotite-dunite pluton (North Pre-Baikalia). The composition of chrome-spinellide corresponds to chrome picotite with high content of Al2O3 up to 40 wt.%. In rocks chrome-spinellide occupy two structural positions: inclusions in olivine and interstices differing in morphology and composition. Interstitial chrome-spinellide contain numerous silicate inclusions filled with Opx, Hb, PI, Bt and ilmenite laminar segregations which are the product of disintegration of solid solution. Evolution of chrome-spinellid composition from early differentiates to late ones owes to Fe, Cr → Al + Mg isomorphism, interstitial spinels are, however, more rich in Cr as compared with inclusions in olivine. The conclusion on two generations of chrome-spinellide has been made on the basis of study of silicate inclusions. Comparison of the composition of chrome-spinellide from the Chaya massif with those of possible structural equivalents shows them to differ greatly from laminated intrusions and to be close to ultramafites of ophiolite associations.