Using portable XRF to infer adularia halos within the Waihi Au-Ag system, New Zealand

Abstract

Waihi Au-Ag mineralization is vein hosted within a relatively homogeneous andesite body. Geochemical exploration targets adularia and pathfinder (As, Sb, Hg etc.) anomalies. Adularia is formed as an alteration product of feldspars during hydrothermal alteration and occurs in anomalous concentrations near Au-Ag mineralization. This paper aims to test the potential of portable X-ray fluorescence (pXRF) to infer and map adularia and As anomalies. The pXRF was first tested on standards (CRM and ILD), it yielded accurate and precise data for most of the elements of interest (r 2 > 0.9 and APD < 10%). The second stage applied the pXRF directly on core, most elements were negatively affected, but still to a usable degree of accuracy. As was particularly effected due to its heterogeneous distribution (APD 46%). Lastly, we applied the pXRF to a suite of 300 Favona samples, their K/Al value were used as a proxy for adularia presence. XRD analysis carried out on 60 samples was used to validate adularias presence or absence. When combined with pXRF data we found a K/Al value above 0.4 generally indicated a sample contained adularia. Therefore, with further work, the pXRF could be independently used to infer adularia alteration in the Waihi setting.