Style and genesis of base metal sulphide mineralisation of Angas prospect - Strathalbyn area, South Australia

This item is only available electronically.Angas prospect is a small stratiform Pb-Zn-Ag mineralised region located on the southeastern flank of the regionally metamorphosed Mount Lofty Ranges, approximately 50km southeast of Adelaide. The Angas prospect is hosted by Cambrian flysch-like metasediments, that reached mid-amphibolite facies during Cambrian-Ordovician orogeny. High base metal content mineralisation occurs as massive metamorphically recrystallised, coarse-grained sphalerite, galena, pyrite, and pyrrhotite. Intergranular and intergrown sulphides and gangue, suggest a syngenetic origin. Disseminated base metal sulphides are pervasive within the host-unit lithology. Geochemical analyses of silicate/spinel minerals reveal trends that make them important primary exploration targets. Increasing zinc content in staurolite provides a vector toward increasing base metal content. Manganiferous garnet defines the boundaries of a geochemical anomaly that hosts the Angas prospect orebody, indicating its importance as a primary exploration target. Gahnite (zinc-spinel) is found only to occur within a restricted region of the geochemical anomaly, and is mainly associated with areas of high base metal content. The sulphur isotopic signature suggests a dual source of sulphur derived from the mixing of modified Cambrian seawater with biogenic sulphur, producing delta34S around zero o/oo. Model Pb isotopic signature ages indicate a syngenetic origin. The sphalerite geobarometer tentatively suggests that the base metals sulphides experienced the same metamorphic pressures as silicate/spinel assemblages. Comparison of the geochemical anomaly at Angas prospect with modern seafloor hydrothermal precipitates show remarkable mineralogy similarities. Supplementing these data are the similarities that exist between Angas prospect whole-rock signatures and ancient hydrothermal systems (e.g. exhalative Broken Hill-type deposits) and unmetamorphosed exhalatives of Dee Range (Queenland). It is concluded from this study that Angas prospect mineralisation was syngenetic and occurred during a period of crustal extension in the Early Cambrian.Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 199