VISIBLE AND NEAR INFRARED SPECTRAL STUDY OF REDUCED GOLD SKARN MINERALOGY FROM THE NAVACHAB GOLD DEPOSIT, NAMIBIA, AFRICA

The Navachab gold deposit, an auriferous sheeted quartz vein swarm and associated skarn system (sensu lato), is located 10 km southwest of Karibib within the Southern Central Zone of the Pan-African Damara Orogen and is currently the only producing gold mine in the country. The deposit was discovered in October 1984, production began in 1989, is currently producing 2.3 t/y at 1.8-2.0 g/t Au with current ore reserves calculated at 13.6 Mt and a life expectancy until 2013.

Visible and near infrared (Vis/NIR) reflectance spectra (0.35- 2.5 mm) provide an efficient method for field and laboratory identification of minerals. This study examines field Vis/NIR spectra of over 300 samples collected from the surface and drill core at the Navachab gold mine. Multivariate analysis was used to differentiate spectral end members of calcite, chlorite, dolomite, grossular (?), muscovite, nontronite, phlogopite, prehnite(?), talc, and tremolite. Calcite, chlorite, phlogopite, and tremolite are related to mineralization and alteration observed at both outcrop and microscopic scale within and surrounding the skarn system. The minerals allow spectral differentiation of important rock types including calcite marble, dolomite marble, calc-silicate marble, mica schist, and skarn. The mineral distribution determined from spectra of surface samples and drill core can be used to develop a 3-D model of vertical and lateral mineralization and alteration occurring within and proximal to the skarn system.

In addition to field and lab-based studies, most of the minerals identified spectrally can be differentiated in the wavelength range of 2.05-2.45 mm that is used in hyperspectral remote sensing methods. These results substantiate the use of hyperspectral remote sensing methods to generate mineral classification maps and delineate future exploration targets.