SAPPHIRE AT MANTIQUEIRA RANGE, SOUTHERN OF RIO DE JANEIRO STATE: PROVENANCE STUDIES USING MINERALOGICAL ANALYSIS AND CHEMICAL ANALYSIS OF MINERALS

Sapphire at Mantiqueira Range, Southern of Rio de Janeiro state: provenance studies using mineralogical and mineral chemistry analyses

Abstract

Brazil has significant reserves of precious stones, especially those from the Eastern Pegmatitic and Borborema Provinces, such as paraiba tourmaline, emerald and imperial topaz. Corundum exploits (ruby and sapphire) are still reduced in the country and are located mainly in the states of Mato Grosso, Goiás, Santa Catarina and Minas Gerais. Mineral exploration campaigns carried out in drainages in the southern portion of the state of Rio de Janeiro collected 25 corundum grains, with dimensions smaller than 2 mm and between 2 and 5 mm. Analysis of mineral chemistry by Micro X-ray fluorescence allowed the study of provenance based on the Cr₂O₃/Ga₂O₃ ratios, indicating formation by a metamorphic process. SEM/EDS analysis identified solid inclusions of biotite, apatite and ilmenite. The presence of the mineral associations spinel, kyanite and cordierite in the Neoproterozoic metasediments reinforce the genetic association of the corundum with metamorphic rocks in amphibolite facies (upper grade) to granulite.