Reflectance spectroscopy applied to mapping the hydrothermal alteration at the Mamão gold deposit, Andorinhas Greenstone Belt, Carajás Mineral Province, Northern Brazil

Abstract

The Mamão gold deposit is located in the eastern portion of the Amazonian Craton, Northern Brazil, and hosted in Archean metamafic rocks of the Andorinhas greenstone belt. Troy Resources Ltd. mined the deposit between 2008 and 2015, producing about 350 koz via underground operation. The deposit exhibits structural and mineralogical characteristics that allow its classification as an orogenic gold deposit. Reflectance spectroscopy is a non-destructive, fast, and low-cost technique that was applied in drill cores at the Mamão deposit to map and refine stages of hydrothermal alteration. The hydrothermal alteration is marked by a distal or chlorite zone; an intermediate or carbonate zone; a proximal or potassic zone, and a gold-rich quartz vein-hosted orebody. The reflectance spectroscopy has confirmed the diversified mineralogical compositions (tourmaline, amphibole, mica, epidote, carbonate, and chlorite) observed along the hydrothermal zones, having been confirmed by a petrographic study. The study has also demonstrated that chlorite abundance decreases from the edge to the center of the altered profile, proving a fast and reliable result to the mapping of the hydrothermal halos in Archean greenstone belts, which is an important tool for the vectoring of gold mineralization, acting as an excellent mineral prospecting tool.

KEYWORDS:
Archean gold deposit; reflectance spectroscopy; mineral mapping; hydrothermal alteration; Amazonian craton