HEAVY MINERALS IN THE SAND FRACTION OF COLLUVIO-GRAVEL OF PAININ GARIMPO (ITAITUBA, PARÁ, BRAZIL)

Abstract

The present work describes the heavy minerals identified in the sand fraction of the diamond-rich alluvium of the Painin garimpo, located on the right bank of the Tapajós River, in Itaituba, Pará. In general, secondary diamond deposits, such as those found in several regions of Brazil (Minas Gerais, Bahia, Goiás, etc.) have a very characteristic assemblage of heavy minerals, in which their minerals are known as diamond satellites. In Painin these minerals were extracted from the concentration of gravel obtained with the aid of a pan, after the extraction of pebbles, silt and clay fractions. The sand fraction was sieved in several fractions and from the fractions 0.25-0125 and 0.125-0.062 mm, the non-opaque heavy minerals were separated using bromoform as a heavy liquid. Minerals were identified by optical microscopy and x-ray diffraction. They stand out in descending order and according to the fraction sand, staurolite, tourmaline, corundum, rutile, diaspore, gold, topaz, zircon, anatase and kyanite. Of these, only corundum and diaspore are not classic heavy minerals from sedimentary rocks of the great Amazon region. These two minerals are together with the phosphates of the alunite supergroup, often found in the satellites of the secondary Painin diamond deposits, but not mentioned in those mentioned above, and likely to have an affinity with the primary nature of the diamond. Rutile, anatase and iron oxides are most frequently cited in these satellites. Probably corundum, diaspore and the alunite supergroup phosphates are characteristic for Painin.