Petrographic characterization of the mineralized calciumsilicate horizon in scheelite of the Bairro dos Marins, Municipality of Piquete, State of São Paulo

Abstract

In the “Bairro dos Marins” area, three types of rock associations were recognized: granitoids (Marins and Mendanha); biotite-hornblende gneiss orthoderived; and metasedimentary package that comprise biotite-muscovite gneiss, different calc-silicate rocks, quartzites and marbles. In this context, the Marins granitoid is strongly metassomatized with different sub-economic minerals occurrence, such as cassiterite, molybdenite, wolframite, fluorite, topaz and columbite-tantalite. These occurrences were correlated to greisens. The metasedimentary package has two different calc-silicate horizons: the first is intercalated in the biotite-muscovite gneiss and have variable mineralogical composition, while the second horizon is preferentially diopsidic, mineralized with scheelite and located between the biotite-muscovite gneiss and the biotite-hornblende gneiss. The scheelite mineralization presents syngeneticstratiform features related to amphibolite regional metamorphism that generates many calc-silicates rocks in a similar process of “reaction skarns”. During a retrometamorphism in the epidote-amphibolite facies, part of scheelite grains were dissolved and the tungsten was removed and dispersed.