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Geochemistry: Exploration, Environment, Analysis
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Geochemistry: Exploration, Environment, Analysis; 2007; v. 7; issue.2; p. 139-151;
DOI: 10.1144/1467-7873/07-129
© 2007 Geological Society of London

Original Article

Spectral reflectance: preliminary data on a new technique with potential for non-sulphide base metal exploration

Timothy F. McConachy1,3, Kai Yang1, Maria Boni2 & Noreen J. Evans4

1 CSIRO, Division of Exploration and Mining, 11 Julius Avenue, North Ryde, NSW 2113, Australia
2 Dipartimento di Scienze della Terra, Università di Napoli ‘Federico II', Italy
3 Current address: 14 Bannockburn Road, Pymble, NSW 2073, Australia (e-mail: TimMcConachy@bigpond.com)
4 CSIRO, Division of Exploration and Mining, 26 Dick Perry Avenue, Kensington, WA 6151, Australia

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.

Key Words: non-sulphide mineralization • spectral reflectance • weathering • oxidation