Mineral age dating
The epithermal characteristics of the Nankivel breccia were confirmed by petrographic analysis that identified alunite and dickite associated with silicification in strongly altered rock samples (Purvis and Pontifex 1991).In 1996 alteration mapping using a portable infrared mineral analyser delineated zones containing alunite, dickite and pyrophyllite (Gerakiteys 1996); the mineral assemblage is consistent with that found in advanced-argillic alteration systems and commonly associated with high-sulfidation epithermal As–Au–Cu mineralisation (e.g. In joint venture with Mount Isa Mines Ltd, three RC percussion holes (averaging 115 m) were drilled in September 1996 on Aberfoyle Exploration Licence 1841 on the flanks of the hills, close to the margins of blocky siliceous breccia outcrop.Also, the timing of alteration and mineralisation is usually complicated by overprinting and recrystallisation during subsequent fluid and thermal events and by the lack of dateable minerals that formed during the primary phase of mineralisation.Evidence in support of the model is significant, however, as confirmation of both the rare preservation of an ancient epithermal system and the regional prospectivity for this style of mineralisation.Drill cutting samples (2 m interval) were analysed for Au, Cu, Pb, Zn and As, but the results were not deemed significant at the time (Gerakiteys 1996).In the context of an advanced-argillic alteration system that may host high-sulfidation-style epithermal mineralisation however, these results and in particular the coherent anomalous arsenic results are now considered to be significant as an indicator to possible sites of nearby concealed mineralisation (e.g. Investigator Resources has continued to refine a model for associated Cu–Au porphyry mineralisation at depth.
Evidence of hydrothermal alteration and epithermal-style mineralisation in crystalline basement rocks along the southern margin of the Gawler Range Volcanics is now recognised as regionally extensive (e.g. At some sites this can be demonstrated to extend into the lower units of the Gawler Range Volcanics (e.g. The timing of alteration and mineralisation has been widely linked to magmatic-hydrothermal processes during the c.The significance, however, for gold exploration in a previously unrecognised hydrothermal mineralising system with possible links to extrusion of the Gawler Range Volcanics was clearly established.A subvolcanic epithermal mineralisation model was developed by Aberfoyle geologists as a focus for exploration on northern Eyre Peninsula and the southern margin of the Gawler Range Volcanics.Consequently, muscovite from samples of high-grade metamorphic rocks of Warrow Quartzite both close to and distal to the alteration system were also analysed.Muscovite has a nominal closure temperature of ~350 °C (Mc Dougall and Harrison 1999).