Study of copper mineralization in basalts of the Serra Geral Group, using X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and neutron tomography

Abstract

Michigan-type copper mineralization occurs in basalt flows of the Serra Geral Group in the Nova Prata do Iguaçu region, southwestern Paraná State, Brazil. Native copper is the main ore mineral in these mineralizations, and its supergene alteration transforms it into copper oxides, malachite and chrysocolla. As a gelatinous precipitate, chrysocolla fills amigdules and impregnates fractures in the basalt, besides covering secondary minerals and other alteration products. In this study, X-ray diffractometry and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS) were techniques used to characterize the crystallinity degree and chemical composition of chrysocolla and to identify other hydrogenated materials, in order to aid neutron 3D imaging interpretation. Chrysocolla proved to be an efficient neutron attenuator, yielding linear attenuation coefficients in the 0.8–1.3 cm^-1 range, whereas the ore body (basalt) yielded values in the 0.5–0.6 cm^-1 range. This contrast between the coefficients contributed to the good resolution of the tomographic images and films, allowing the visualization of the distribution of chrysocolla in the basalt samples and the estimation of the volumetric fraction of chrysocolla, with values in the 0.9–1.4% range, yielding 7.8 vol.% of chrysocolla for one of the sample. The integrated use of the three analytical techniques proved to be a possible tool for mineral potential assessment in the initial phases of mining exploration, especially when the substances of interest are rich in hydrogen.