Andrew Menzies

Abstract:

The capabilities of �XRF to analyze large rock samples without any significant sample preparation has opened up new areas of research and application in the field of applied mineralogy. In this case study, we present the results of the analysis of a range of specimens from Au-epithermal deposits in Chile and New Zealand using the Bruker M4 TornadoAMICS �XRF located at Universidad Catolica del Norte, Antofagasta, Chile. The results demonstrate the ability to detect and identify the presence of Au- or Ag- bearing mineralogy whilst maintaining spatial and textural relationship information. The specimens analyzed have a gold grade of between 20 and 100 ppm with known gold and silver mineralogy dominated by native gold, electrum and acanthite with the presence of lessor concentrations of other Ag-sulfosalts. Specimens range in size from 10 to 20 cm in maximum dimension. For each specimen, a rapid (30 - 60 minutes) coarse scan at 100 to 200 �m was used to identify areas of interest which were then subsequently analysed at a higher resolution (5 to 20 �m) for longer count times per pixel (20 to 100 ms). The results were clearly able to distinguish gold and/or silver rich areas within the various specimens and highlighted the diverse range of spatial and textural conditions under which such mineralogy is formed within the vein. For example, the Au- and Ag- bearing mineralogy was commonly associated with the presence of sulphide (chalcopyrite, sphalerite, and galena) rich zones, however, in contrast there are examples where the such mineralogy occurs in areas with no sulphide mineralisation. Continued detailed analyses will provide mineralogical and elemental information which can be interpreted within a real spatial context and thus providing additional information for understanding geological processes of formation and modelling, as well as metallurgical classifications for mineral processing.