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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 is Proterozoic-aged shear hosted gold system located in the central Gawler Craton region of South Australia. The deposit lies within the regional-scale Yarlbrinda shear zone which represents the boundary between several major crustal domains. The deposit has dimensions of approximately 1 km along a north north-westerly strike, with primary zones of mineralisation having a steep west south-westerly dipping orientation. Higher grade zones of mineralisation are primarily hosted within multiple zones of quartz veins, within a broader zone of lower grade gold mineralisation. A significant zone of flat lying gold mineralisation occurs at the base of weathering above fresh rock. No historical mining or prospecting has taken place at the deposit.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.Area 51The primary lithologies at Area 51 are the Tunkillia Granite, after a 1690-1670 Ma granite intrusion, and the Tunkillia Augen Gneiss. The deposit is totally enclosed with the Yarlbrinda Shear zone and all lithologies have undergone some level of deformation and alteration, with the extreme end member forming a finely laminated phyllonite grading to a coarser shear foliation designated as mylonite. The large-scale control on mineralisation is strain partitioning within the broader shear zone, associated with sericite alteration and quartz-calcite ± base metal veins either parallel to or at a low angle to the strain partitioning. The broad bulk of the gold mineralisation is hosted in the NNW trending subvertical shear partition zone, with additional mineralisation in secondary quartz and stockwork vein halos associated with two south-west dipping brittle faults in the footwall and a flat lying supergene horizon where the sub-vertical mineralisation intersects the weathering profile. A poorly mineralised NNW striking fault, the Central A51 Fault, is a late brittle fault generally corresponding to the hanging wall of the deposit and is considered a hard boundary to the mineralisation.The 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
