Características geológicas e origem dos conglomerados diamantíferos das regiões de Diamantina (Mesoproterozóico) e de Romaria (Cretáceo Superior), Minas Gerais

Abstract

Diamond-bearing conglomerates occur in the Sopa Brumadinho Formation of the Middle Proterozoic Espinhaço Supergroup and have been mined in the area of Diamantina, central Minas Gerais, since 1725. On the other hand, similar deposits occur at the base of the Upper Cretaceous Uberaba Formation in the area of Romaria in western Minas Gerais and have been mined since the end of the last century. Although these occurrences differ in age by almost 1.5 Ga, they display several geological characteristics that point to their deposition in fans developed in tectonically active áreas. In addition, their diamond content is low, ranging from 0.01 up to 0.07 ct/m³. Apparently the most remarkable difference between them is the absence of kimberlitic indicator minerais such as Cr-pyrope garnet and Mg-ilmenite among the heavies in the Diamantina District.