Mineralogia do pegmatito Alto Serra Branca, Pedra Lavrada-Paraíba, enfatizando os fosfatos e suas paragêneses.

Abstract

The Alto Serra Branca granite pegmatite, contains several primary phosphate minerals with a large number of secondary minerals. A brief review of the regional geology, including recent changes in the subdivision of the Upper Proterozoic is followed by a discussion of several general features concerning granite pegmatites. A short description of the geology and mineralogy of Alto Serra Branca granite pegmatite is given, mphasizing two iso-structural series of primary phosphates: Triphylite-Lithiophiiite and Triplite-Zwieseiite. Phosphate minerais and the specific problems of their identification are reported, as well as analytical techniques involved and the difficulties of the correct denomination ofjhose.which form series. Analyses of the two primary phosphates are reported which show, that their composition is intermediate. Principal attention is given to detailed descriptions of a large number of different paragenesis, subdivided into two groups: those, which derived from the Triphylite-Lithiophiiite series and the others from the Triplite-Zwieseiite series. Contrary to other phosphate bearing pegmatites, Alto Serra Branca developed a large number of secondary minerals, which originate from Triplite-Zwieseiite. Among the results is the discovery of the new mineral Serrabrancaite. Two other minerals, Colquiriite and Carihintzeite, are found for the second time worldwide, with the best crystals ever observed, along with a unique paragenesis of eight different fluorites. Triplite-Zwieseiite has three different appearances, a fact, which is little understood. The primary phosphate Triplite-Zwieseiite, when cut as cabochon, shows a distinct cat's-eye effect, which represents a new gemstone. A brief discussion of the probable geochemical process which might have been responsible for the development of the secondary minerals is added.