Abstract
The diamonds from the Painin garimpo, on the Tapajós River, in Itaituba, state of Pará, were mined in alluvial gravel in geological terrains dominated by the Barreirinha, Itaituba and Monte Alegre Paleozoic formations. 30 diamonds extracted from the concentrates of this garimpo were analyzed by stereomicroscopy, optical microscopy, x-ray diffraction, scanning electron microscopy with EDS and luminescence. The average weight of these specimens is 0.42 ct and the predominant forms are dodecahedral and octahedral, in addition to others such as ballas and bort. Surface figures, microstructures, luminescence, and various inclusions are recognized. The inclusions can be classified as syngenetic (periclase, diopside, among others) and epigenetic (eg minerals of crandallite group). Green covers were also observed. This study, however, was not able to solve the problem of the genesis of the diamond in the studied region, as happens to date with most secondary diamond deposits in the Amazon region (Tapajós, Tocantins and Tepequém-Maú), except for those related to kimberlite pipes of Mato Grosso Rondônia.
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