( Stokes) An Evolving Understanding of the Controls of the Trident Gold Deposit - Higginsville, Western Australia

摘要

The Trident Gold Deposit has been successfully developed by Alacer Gold (formerly Avoca Resources Limited) into a 1.3 Mt/a operation in the space of four years from discovery to fi rst gold pour (2008). The current in situ Resource for Trident is estimated to be 5 900 000 t @ 5.0 g/t for 940 000 ounces at a cut-off of 1 g/t or 2 g/t depending on ore style. Production to date (Alacer and previous owners) is in excess of 500 000 ounces. The deposit lies towards the southern end of the Norseman-Wiluna Greenstone Belt in the Archaean Yilgarn Craton, where it is centred on the historical Higginsville Mining Centre, midway between the world class gold centres of St Ives (+15 Moz) and Norseman (+6.5 Moz).Trident is hosted primarily within a thick, weakly differentiated gabbro with subordinate mafi c and ultramafi c lithologies and comprises a series of north-northeast trending, shallowly north plunging ore zones. The deposit comprises two main mineralisation styles; large wallrock-hosted ore-zones comprising sigmoidal quartz tensional vein arrays and associated metasomatic wall rock alteration (Eastern Zone, Western Zone and Apollo) hosted exclusively within the gabbro; and thin, lode-style, nuggety laminated quartz veins (Athena and Artemis) that formed primarily at sheared lithological contacts between the various mafi c and ultramafi c lithologies. The initial interpretation of the Trident Deposit was based on steeply-dipping structures controlling the zones of mineralisation, with much of the targeting and drill-testing aimed at this style of orebody. Subsequent exposure of the orebodies has identifi ed a series of shalloweast dipping mineralised systems (interpreted to be large reverse shears) that at their intersection with the steep-dipping structures cause signifi cant gold enrichment. It is postulated that both orientations are primary fl uid pathways with the intersection between the two resulting in zones with signifi cantly high concentrations of gold mineralisation (in excess of 300 000 ounces). This new understanding on ore controls at Trident has identifi ed that the thin lode-style shearhosted laminated veins are continuous for over 1700 m along strike as they step en echelon downplunge. In addition, a repetition and periodicity to the intersection between these steep dipping lode-style systems and the shallow-dipping mineralised zones (estimated to be 700 - 900 m downplunge) has been identifi ed which has considerably increased the down-plunge potential of the Trident Deposit.