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Location: 144 km NE from Ceduna, South Australia, Australia
Level 4, 12 Gilles StreetAdelaideSouth Australia, Australia5000
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The Tunkillia Project extends over a large portion of the Central Gawler Craton of South Australia which is bound to the east by the Gawler Range Volcanic Province. The central portion of the Gawler Craton consists of a variety of geological units and is structurally complex. Archaean metamorphic rocks and greenstone-belt units are distributed along WSW–ENE trends. During the Palaeoproterozoic, granitoids including the Tunkillia Suite were emplaced possibly with associated deformation. During these deformation episodes, major shear zones developed, including the east-trending Yerda and Oolabinnia Shear Zones and north-trending Yarlbrinda Shear Zone. The Yarlbrinda Shear Zone and Yerda Shear Zone are up to several kilometres wide with ductile shearing and deformation probably occurring before ~1600 Ma and before Mesoproterozoic anorogenic magmatism. During the Mesoproterozoic, widespread anorogenic magmatism across the central portion of the craton resulted the Gawler Range Volcanics, Hiltaba Suite granite (1595-1575 Ma) and emplacement of minor gabbroic plugs. Development of Cu-Au +/- U mineralisation at Olympic Dam and Prominent Hill and gold dominant mineralisation at Tunkillia and Tarcoola occurred during this period. Typical lithologies encountered across the Tunkillia project (including Area 51) from west to east include variably sheared chlorite-biotite-rich augen gneiss (Tunkillia Augen Gneiss) grading into a highly chloritised and mylonitised phyllonitic shear. The phyllonitic shear zone grades into a weakly gneissic unit to the east which is variably altered by sericite to form the central alteration zone. This unit has a sheared contact with the footwall granite. The host rocks have been intruded by at least two later episodes of dyke emplacement. The mafic dyke appears to form the footwall to the main mineralisation at Area 223. Relationships between dyke emplacement and the mineralisation remain unclear. The dykes appear to cross-cut mineralisation at most of the Tunkillia project prospects and deposits and are unmineralised in fresh rock. But in the weathered zone gold occurs within the weathered dyke and also to east of this apparent ‘bounding’ lithology. The main mineralisation appears to occur within en-echelon sets of quartzsulphide tension veins predominately bounded by duplex shears, with brittle fractures extending into the hanging wall. The mineralised positions across the Tunkillia project has undergone extensive weathering which formed a leached kaolinitic profile capped by a silcrete layer. No palaeochannels are observed at Area 223 or Area 51 although they do occur elsewhere in the Tunkillia area. At 50-60 metres depth near the base of the weathering profile a zone of supergene mineralisation is developed which shows some enrichment compared with the underlying primary lodes. Gold appears to have been laterally dispersed over a distance of tens of metres within the oxide zone.DimensionsThe Area51 deposit is defined with approximately 1000 m strike and is between five and 10 metres thick on the main structure and up to hundred metres wide in the overlying oxide mineralisation. The depth of the deposit had been defined beyond 300 m below the surface. The reported resource has been reported to 150 m below the surface. Mineralisation strikes NW (UTM) and dips steeply to the SW ~80°. The shear structure and contained mineralisation are expected to propagate to depth and are open.
