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Location: 34 km SE from Paraburdoo, Western Australia, Australia
16 Douro PlacePerthWestern Australia, Australia6005
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GeologyThe Ashburton Cold Project is located on the northern margin of the Ashburton Basin and within the extents of the crustal scale Nanjilgardy Fault Zone that roughly traces the contact between the Ashburton Basin to the south and the underlying Hamersley Basin strata to the north. The project tenements are situated predominantly within the Wyloo Groups' Mt McGrath Formation and Duck Creek Dolomite and the underlying Cheela Basalt and Beazley River Quartzite of the Shingle Creek Group.Three phases of deformation are recognised in the Ashburton Basin sediments associated with the 1820Ma-1770Ma Capricorn Orogeny". These include D1 forming a shallowly south dipping penetrative cleavage and tight folding with steeply south dipping fold axes, D2 forming west to northwest trending tight to isoclinal folds with a pronounced axial planar cleavage dipping sub-vertically to steeply to the southwest or northeast, and D3 which is recognised as local re-folded D2 folds that may have formed in response to late-stage sinistral movement on faults in the southwestern Ashburton Basin.West northwest striking structures including the Nanjilgardy Fault parallel the D2 fold axes or shallowly crosscut them and show dextral strike slip displacements that occurred in the latter part of the Capricorn Orogeny. Segments of the Nanjilgardy Fault show strike slip and/or oblique to normal dip slip displacements that link to form negative-flower-structure geometries, typical of divergent wrench fault zones.Two gold mineralising events have been dated in the Capricorn Orogen including a 1770Ma event co-eval with the tail end of the Capricorn Orogeny and a 1680Ma event coincident with extension during the early stages of the Marangaroon Orogeny. Both mineralising events have been identified from dating at Mt Olympus indicating the Nanjilgardy Fault has undergone repeated reactivation events over a significant period.MineralisationThe primary structural controls for mineralisation at the historically mined pits are interpreted to be second order faults within the northwest trending Nanjilgardy Fault Zone that crosscuts the western end of the Diligence Dome and in bedding sub-parallel and high angle faults in the surrounding flanks of the Dome. The Project is situated along an axis of a distinct SE plunging antiform which has its southern limb truncated by a large sub-vertical NW-SE striking fault known as the Zoe Fault.Mineralisation is hosted in siltstones, sandstones, conglomerates and dolomites of the Mt McGrath Formation and the Cheela Springs Basalt. The units dip to the south and around Mt Olympus the geology becomes complicated by folding and faulting. The base of oxidation at Mt Olympus is up to 100m below the original surface.Mineralisation is structurally controlled and associated with minor sulphidic quartz veins and with zones of intense sulphides. Coarse grained, highly fractured pyrite (typically 5 to 15% of the rock) is the dominant sulphide with minor arsenopyrite and small amounts of chalcopyrite, digenite, covellite and tetrahedrite. Gold occurs as veinlets and blebs in pyrite.Gold mineralisation occurs within broad, sulphidebearing shear zones developed along lithological contacts and competency contrasts in the sedimentary sequence. Two principal mineralised trends are recognised being a steeply south-dipping, discontinuous zone along the Zoe Fault, and a series of moderately southdipping sediment-hosted lodes north of the Zoe Fault, truncated to the northwest by basaltic units.The sediment-hosted lodes thicken and increase in grade toward the Zoe Fault, with moderately south-plunging high-grade shoots developed at the intersection of the two trends. Mineralisation extends more than 950m down plunge, to depths exceeding 500m below the natural surface.The majority of gold mineralisation is hosted within bedding-parallel zones in extensively fractured, altered and sulphidised coarse-grained sediments of the Mount McGrath Formation. These zones dip moderately (30-55°) to the southeast, with additional mineralisation in quartz veins.The rocks have undergone pervasive sulphide-silica-sericite-hematite-carbonate alteration and are highly brecciated. Mineralisation at Mt Olympus is associated with minor sulphidic quartz veins and with zones of intense sulphide enrichment. Gold occurs as fine veinlets of 5-10 microns enclosed within pyrite.At West Olympus, mineralisation is predominantly developed within thick tensional quartz veins that cross-cut bedding-parallel shears, with additional mineralisation along the sediment-basalt contact is nearly always located within the sediment, some metres away from the contact itself.
