Uvarovite in podiform chromitite; the Moa-Baracoa ophiolitic massif, Cuba

Abstract

The chromitite pods of the Moa-Baracoa massif, in the eastern ophiolitic belt of Cuba, contain pre-existing gabbro sills. This association is affected by two processes of hydrothermal alteration. The chromitites and the hosting dunites and harzburgites are affected first by regional serpentinization; a second alteration, represented by chloritization accompanied with formation of ferrian chromite, is mainly located in the pods and their immediate vicinity. The altered chromitite pods and enclosed gabbro sills iue cross cut by millimeter-wide veins. The vein filling consists of a sequence of clinochlore, uvarovite, chromian clinochlore, rutile, titanite and calcite. Uvarovite also occurs in the vicinity of veins Uvarovite is concentrically zoned, covering compositions in the uvarovite-grossular solid solution series between Uva17 and Uvae:; the andradite component is very low. These compositions suggest a complete miscibility along the grossular-uvarovite join at relatively low temperature. On the basis of the mineral sequence and mineral chemistry (major and trace elements), the uvarovite crystals, as well as the vein assemblage, formed by a low-temperature leaching, Ca probably from the gabbro sills, and Cr and Al from the chromite dunng the formation of ferrian chromite Cr and A1 would have been mobile only at the scale of a pod during this process.