Exploration implications of hydrothermal alteration associated with epithermal Au-Ag deposits

Abstract

This paper will present a synopsis of the results from a three year AMIRA project (P588) entitled ``Epithermal Gold-silver Deposits: Geological, Geochemical and Isotopic Vectors to Target Major Deposits'. Research was undertaken at the Ladolam, (Papua New Guinea), Gosowong, and Mt Muro (Indonesia), Cerro Vanguardia (Argentina) and Twin Hills and Bimurra (Australia) deposits. The sizes and styles of the deposits varied greatly from a low-grade to barren small vein-stockwork system at Bimurra and Twin Hills to high grade veins systems of different scales such as Gosowong, Mt Murro and Cerro Vanguardia to a large breccia-hosted low grade, disseminated system at Ladolam. At each of the deposits alteration mineralogy and zonation were determined using a combination of surface mapping, drill hole logging, petrology, SWIR (PIMA), XRD and potassium feldspar staining. Electron microprobe analyses of specific minerals, whole-rock and trace element whole rock analyses and stable isotope geochemistry were utilised to characterise the geochemical signature of the hydrothermal alteration. Results of this research have 1) substantially increase our knowledge of the mineralogical and whole-rock geochemical characteristics of hydrothermal alteration associated with low-and intermediate sulfidation epithermal deposits, 2) developed a range of vectors that point towards ore, both on district and deposit scales, which can be used when exploring in epithermal environments and 3) proposed a set of criteria for distinguishing potential ore grade systems from barren or low grade epithermal systems.