Abstract

The growing economic importance of non-sulphide Zn and Pb deposits, and the relative subtlety of their surface expression, has led us to study the potential application of spectral reflectance of non-sulphide minerals as an exploration tool. A unique database of spectral reflectance properties for over 200 non-sulphide Pb and Zn mineral specimens was compiled and minerals from several groups were found to have potential exploration application. Well-developed absorption features in the visible- to near-infrared to short-wave infrared region characterize the Pb and Zn arsenates, carbonates, phosphates and sulphates, whereas the oxides have poor spectral responses in this wavelength region and the silicate signatures are highly variable. In particular, tarbuttite (Zn phosphate) was found to have a distinct spectral reflectance signature. Tarbuttite is an important economic constituent in the Skorpion Zn deposit in Namibia, and its spectral characteristics could be applied either to regional exploration programmes or as a complement to down-hole spectrometric nuclear logging for grade and quality control. These first encouraging results point to the need for spectral reflectance studies of similar secondary minerals in order to further develop this exploration tool and enhance our understanding of supergene mineralization genesis.

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