Short Wavelength Infrared Spectral Characterization of the Mineralogy of Gokona and Nyabigena Andesite-Hosted Gold Deposits in North Mara, Tanzania

Abstract

The mineralogy of Gokona and Nyabigena gold deposits in Tanzania have been studied using Short Wavelength Infrared (SWIR) Spectrometry technique with an aim to fingerprint hydrothermal system responsible for the formation of the deposits and establish pertinent mineralogical signatures for gold deposition. Gokona and Nyabigena deposits are hosted in porphyritic andesite to basaltic andesite that contains plagioclase phenocrysts, pyroxene, hornblende and Fe-Ti oxides as primary minerals. Other minerals are actinolite, chlorite, epidote, albite and hematite, which indicate metamorphism of the rock under greenschist facies conditions. Hydrothermal alteration of the rock produced chlorite, sericite, carbonates (ankerite, siderite and calcite), pyrite and quartz, which is consistent with formation of the minerals in mid‑crustal levels (< 5 km). Depth of absorption features of SWIR spectra for chlorite and sericite from borehole samples revealed intense formation of the minerals in the deposits. Sericite is proximal to ore zones, less crystalline and mainly muscovitic to phengitic in composition, whereas chlorite occurs distal to the ore zones, and is mainly intermediate (Fe-Mg) to Fe-rich in composition. These phyllosilicates indicate both pH and temperature control during hydrothermal alteration and provide signatures that can be targeted in exploration to extend mine lifespan.

Keywords:    Hydrothermal alteration; Short Wavelength Infrared Spectrometry; Gold exploration; Musoma-Mara Greenstone Belt; North Mara mines