Mineralogical characterization of the diamond of the alluvial placer from Icabaru River, Santa Elena de Uairén, Bolivar State, Venezuela

Abstract

Mineral characterization consisted on the study of 458 diamond samples representative of gem-grade and industrial grade varieties, obtained from alluvial (placer) diamond exploration located in the Icabaru and Uaiparu Rivers, Santa Elena de Uairén. Mineral analyses were predominantly focused on physical properties and average weight (0.2 and 1.0ct). Optical microscopy was used to study surface sections of diamonds andmorphological characterization which resulted in the following. In relation tocolor, distribution percentages were colorless (37%), yellow (20.5%), brown(19%), green (9,5%), black (3%), green lattice points (7.5%), and brown latticepoints (3.5%). Also, a polycrystalline variety known as carbonado, orblack diamond, was studied. Some surface shapes such as trigons, quadrilateral, block and film growth, groove and hillocks were determined through Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer technique (EDS). Morphological evolution could be established from the octahedral primitive through dissolution phenomena for (111)+(110), (111)+{hkl} facets having rhombicdodecahedron {hkl} and hexaoctahedron {110} habits. Chemical composition data were collected through Infrared Absorption Spectroscopy (FTIR), and diamond types were determined Ib with low nitrogen concentration, IaA, IaB and Ia Abdiamonds with high, average and low nitrogen concentration and IIa diamonds with no nitrogen concentration. Inclusions of olivine, ilmenite and garnet onthe crystal surface were detected by micro-Raman spectroscopy.