Application of portable X-ray fluorescence for exploration of carbonate-hosted sulfide mineralisation, Otavi Mountain Land, Namibia

Abstract

Otavi Mountain Land province forms part of the Damara Orogenic Belt within the Neoproterozoic carbonate platform, which is well-known for its sedimentary-hosted, polymetallic mineralized zones, including the Cu-Pb(-Ag) Kombat deposit. The mineralisation at Kombat is of massive, disseminated, veinlet-controlled and brecciated mineralisation styles it comprises mainly of bornite, chalcopyrite, galena, covellite and chalcocite associated with quartz and calcite as gangue minerals. Mineralized zones are distinctly enriched in chalcophile elements, including Pb, Cu, As and Ag. For the analysis of such rocks, laboratory-based analytical methods, including inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectroscopy (AAS), are well established, in contrast to on-site geochemical analytical methods. This study shows the applicability and limitations of portable X-ray fluorescence (pXRF) in the geochemical exploration of sulfide (Ag, Cu, Fe, Mn, Pb, Zn) ores in carbonate matrix. By using additional ICP-MS/AAS data and certified reference materials, the applicability of such portable tools can be assessed for Kombat-type ores, resulting in pXRF data of excellent or very good precision for elements like Cu, Fe, Mn, Pb and Zn (RSD ≤10%), while other elements (Ag, Sr) show poor precision. The trace element concentrations obtained by pXRF are comparable to ICP-MS results yielding a good correlation (R² ≥0.85) and acceptable accuracy and precision. Portable XRF is identified as a low-cost tool that can be used successfully in the geochemical exploration for a list of elements in carbonate-hosted sulfide ores.