Brazilian Quartz Deposits with Special Emphasis on Gemstone Quartz and its Color Treatment

Abstract

The exploration of Brazilian quartz deposits started in the beginning of the twentieth Century, with intensification of production during the Second World War. Four geological environments are the sources for the different types of quartz in Brazil: (1) Neoproterozoic granitic pegmatites—gemstones and minor industrial quartz (2) Neoproterozoic hydrothermal veins—industrial quartz and minor gemstones, (3) Mesozoic basaltic sheets with amethyst and agate—gemstones and (4) Cenozoic secondary deposits—industrial sands. Industrial quartz occurs in Brazil as lascas and sands and the most important sources are the sedimentary deposits of Botucatu and Piramboia Formations and the hydrothermal veins of the Espinhaço Range. The production is mainly used in the metallurgical industry, in the process of production of ferrosilicon alloys and in the glass industry. Between 1996 and 2005, official data suggest a total production of 1,143,497 tons of lascas and up to 40 Mt of industrial sands. The measured resources of about 2,400 Mt, indicate a potential for growth in the industrial quartz market. The main production is located in the states of São Paulo, Santa Catarina and Minas Gerais. Transparent single crystals and lascas of quartz from pegmatites, hydrothermal veins and geodes in basalts are the most common gemological material in Brazil. Part of this production is used for color treatment via irradiation and heating, to produce more attractive gemstones, sometimes with colors that will not be found in nature such as the green-gold type.