DEPÓSITOS DE QUARTZO AMETISTA EM MINAS GERAIS

Abstract

In Minas Gerais State, quartz amethyst occurs in different genetic geological environments. The present paper presents a review of the knowledge about such occurrences and deposits. Amethyst filling cavities in basalts, similar to those from southern Brazil, are restricted to Triângulo Mineiro region. Filled cavities are present at the upper portion of the central level of volcanic flows and contain, besides quartz, minerals typically formed at low temperatures such as clay minerals and calcite. Hydrothermal vein deposits are mainly related to the Espinhaço Mountain Range and vicinities to east, showing a probable Brasiliano age, and represent the largest volumes in terms of related production and researches. They show amethyst associated mostly to hyaline or milky quartz and iron oxides. In pegmatites, amethyst is not very common, although occurrences close to Teófilo Otoni are reported, besides the studied occurrence in Pancas (ES). This is situated within the context of the Eastern Brazilian Pegmatite Province, related to unzoned and little differentiated pegmatites which contain quartz, feldspar, muscovite, besides apatite, aquamarine and chrysoberyl.

Keywords: Amethyst, Mineral Deposits, Minas Gerais State