Coexistence of Cr- and Al-rich ophiolitic chromitites in a small area: the Sagua de Tanamo district, Eastern Cuba

摘要

Small ophiolitic chromite deposits occur within Sagua de Tanamo district (Eastern Cuba). These deposits exhibit massive, disseminated and banded textures, and enclosed in amphibole-bearing dunite and harzburgite that show mantle tectonite textures. Chromite exhibits large and continuous compositional variations from typical Al-rich (Cr# = 0.45-0.54) at Rupertina deposit, to Cr-rich (Cr# = 0.65-0.75) at Guarina deposit. These compositional variations occur between deposits separated less than 3 km. The high PGE concentrations are found in high-Cr chromitites (up to 3713 ppb of total PGE), whereas high-Al chromitites (#Cr < 0.6) systematically are poor in PGE. In general, the #Cr in chromite ore has a positive correlation with total IPGE contents. The genesis of such a continuous spectrum of chromitite can be related with a progressively changing (in time and space) hybrid melt (Mg- rich calc-alkaline melt + highly hydrated melt) at different levels in the supra-subduction oceanic mantle.