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 AvocarnResources Limited) into a 1.3 Mt/a operation in the space of four years from discovery to fi rst goldrnpour (2008). The current in situ Resource for Trident is estimated to be 5 900 000 t @ 5.0 g/t forrn940 000 ounces at a cut-off of 1 g/t or 2 g/t depending on ore style. Production to date (Alacerrnand previous owners) is in excess of 500 000 ounces. The deposit lies towards the southern endrnof the Norseman-Wiluna Greenstone Belt in the Archaean Yilgarn Craton, where it is centred onrnthe historical Higginsville Mining Centre, midway between the world class gold centres of St Ivesrn(+15 Moz) and Norseman (+6.5 Moz).rnTrident is hosted primarily within a thick, weakly differentiated gabbro with subordinate mafi crnand ultramafi c lithologies and comprises a series of north-northeast trending, shallowly northrnplunging ore zones. The deposit comprises two main mineralisation styles; large wallrock-hostedrnore-zones comprising sigmoidal quartz tensional vein arrays and associated metasomatic wall rockrnalteration (Eastern Zone, Western Zone and Apollo) hosted exclusively within the gabbro; andrnthin, lode-style, nuggety laminated quartz veins (Athena and Artemis) that formed primarily atrnsheared lithological contacts between the various mafi c and ultramafi c lithologies.rnThe initial interpretation of the Trident Deposit was based on steeply-dipping structuresrncontrolling the zones of mineralisation, with much of the targeting and drill-testing aimed atrnthis style of orebody. Subsequent exposure of the orebodies has identifi ed a series of shalloweastrndipping mineralised systems (interpreted to be large reverse shears) that at their intersectionrnwith the steep-dipping structures cause signifi cant gold enrichment. It is postulated that bothrnorientations are primary fl uid pathways with the intersection between the two resulting in zonesrnwith signifi cantly high concentrations of gold mineralisation (in excess of 300 000 ounces).rnThis new understanding on ore controls at Trident has identifi ed that the thin lode-style shearhostedrnlaminated veins are continuous for over 1700 m along strike as they step en echelon downplunge.rnIn addition, a repetition and periodicity to the intersection between these steep dippingrnlode-style systems and the shallow-dipping mineralised zones (estimated to be 700 - 900 m downplunge)rnhas been identifi ed which has considerably increased the down-plunge potential of thernTrident Deposit.