The gemstone deposits of Brazil: occurrences, production and economic impact

摘要

This article gathers together data on the occurrence, production and economic importance of gem deposits in Brazil, including specific information on the major deposits. Of the 100 or so different types of gemstones found in the country, the most important in terms of production and/or originality are tourmalines, topaz, opals, varieties of quartz (agate, amethyst and citrine) and emeralds. Brazil is also one of the only producers in the world of imperial topaz and Paraíba tourmaline. The country also produces diamonds, rubies and sapphires on a smaller scale. Gem production in Brazil is, for the most part, carried out by prospectors and a handful of mining companies, reducing the capacity of the government to control the production and sale of gemstones. Another factor that tends to drive the industry to operate outside the law is the high tax burden, which is as high as 53% on the sale of jewelry and 25% on uncut or polished stones. Owing to the geographical distribution of gemstone deposits and the enormous size of the country, Brazil is divided into four gem-producing areas. In the Northeast there are primarily deposits of emerald, amethyst, citrine, hyaline quartz, elbaite, aquamarine, garnet, morganite and opal. The Central region is characterized primarily by emerald and diamond deposits, whereas in the South deposits and occurrences of amethyst, citrine, agate and diamond are found. The East is characterized mainly by the presence of gemstones associated with pegmatites and hydrothermal veins, Plio-Pleistocene sedimentary placer deposits and isolated concentrations of diamonds. Gem production in Brazil mainly occurs in the states of Minas Gerais, Bahia, Rio Grande do Sul, Mato Grosso and Goiás. The State of Minas Gerais is the largest producer and exporter of gemstones in the country and is responsible for 74% of the official production, which includes imperial topaz, beryl, tourmaline, spondumene and brazilianite. The State of Bahia produces mainly emeralds, amethyst and aquamarines and is the second largest producer of uncut colored stones after the State of Grande do Sul, which is one of the most important producers in the world of two of these: namely agate and amethyst. The State of Mato Grosso produces garnet, topaz, zircon, diopside, varieties of quartz and tourmaline on a smaller scale. The State of Goiás mainly produces emeralds, along with garnet, topaz, quartz (citrine and amethyst) and tourmalines. Natural diamond production is also significant in Goiás and Mato Grosso, where diamonds have been being unearthed by prospectors since the beginning of the 20th century. At present, the best prospects for diamond production in these states are to be found in kimberlites. Of the wide diversity of gems produced, some, such as the Paraíba tourmalines and the opal from Piauí, are renowned around the world for their originality and gemological properties.