"Early gold deposition in the Eastern Goldfields, Western Australia" by Dr. Sarah Jones (Gold Fields Ltd.).
Abstract
Most gold deposits in the Eastern Goldfields Superterrane (EGT) in Western Australia are described as orogenic gold deposits associated with structures that formed during horizontal east-west compression, relatively late in the tectonic history. Well known examples in the Eastern Goldfields include the New Holland-Genesis deposit at Agnew, Tarmoola-King of the Hills at Leonora, Wallaby and Granny Smith in the Laverton district, and Victory-Defiance and Revenge at the St Ives Camp.
Geochronological studies of mineralised assemblages across the EGT show gold deposition occurred over a broad period from ~2680 to 2620 Ma. This age range broadly coincides with the timing of D1-4 deformation events in the EGT and indicates that at least some gold deposition occurred during the c. 2672-2660 Ma D1 event. Structures associated with the early D1 event differ markedly from those formed during later east west horizontal compression (D2-4 events). The D1 event is variably described as extensional or compressional and is associated with an early layer-parallel S1 foliation that is axial planar to recumbent F1 folds that are consistently deformed by D2-4 compression.
Structural features of some of the larger gold deposits in the EGT show gold deposition occurred during multiple deformation events (e.g., Golden Mile, Waroonga, Sunrise Dam, and New Celebration). The orientation, kinematics and form of mineralised D1 structures differ markedly from those formed during horizontal east-west compression (D2-4 events) and therefore make it difficult to attribute orebody formation to a single prolonged phase of east-west compression. In addition, the Invincible deposit at St Ives, Kambalda, is truncated by c. 2665 Ma Merougil Formation, indicating formation early in the tectonic history. Further evidence for early gold deposition in the Eastern Goldfields is shown by the strong modification of orebodies by later deformation (sub-horizontal compression; D2-4 events). Mineralised structures are folded by these later events and excellent examples are observed at the Invincible deposit at St Ives, Waroonga and Songvang at Agnew, Gwalia and Harbour Lights at Leonora. The structural style of these deposits differs markedly from the more typical orogenic lode style gold deposits in the EGT.
Biography
Sarah Jones is currently the Chief Structural Geologist at Gold Fields Ltd. She has over 20 years of field mapping experience within Australia and overseas. Sarah has worked as a structural geologist for the last 12 years on numerous deposits and deposit styles. Prior to Goldfields, she was based in Kalgoorlie as a regional mapper with GSWA for about 5 years after completing a PhD on a VHMS deposit at CODES in 2001. She moved to Australia in 1996 to work at Darlot gold mine after completing her BSc and MSc at Otago University, New Zealand.
12 июл 2024
