A fresh Look at the Stratigraphy of the Lefroy Palaeodrainage System, Eastern Goldfields, WA.

Lynham, Leah1

1James Cook University, Townsville, Australia

Buried palaeovalley sediments within the Lefroy and Cowan palaeodrainage systems and other palaeodrainage systems in the wider Eastern Yilgarn craton contain economically viable deposits of alluvial gold (Oxenburgh et al., 2017). The Lefroy Palaeodrainage System and other, parallel systems are said to have formed pre-Jurassic (Clarke, 1994), potentially from glacial scouring during the Late Palaeozoic (Eyles and de Broekert, 2001), before a depositional regime led to ~100m of buried fluvial, marginal marine and marine sediments being deposited in the buried palaeovalleys.  Little is known about the geological controls on the activation of the system, the origin of the basal placer deposits or the sedimentary controls on the channel infill. Unravelling the geological controls on the incision of the palaeovalley network and infill of the palaeochannel sediments within the Lefroy palaeodrainage System could have positive implications for future alluvial gold exploration within the area.  

Previous studies have suggested that the Lefroy and Cowan systems became separated due to uplift along the Jarrahwood axis prior to Eocene deposition (eg (Clarke, 1994, de Broekert and Sandiford, 2005), although studies disagree on how far North the Jarrahwood Axis transects the Cowan System. Building on the foundations of already completed work, new palaeocurrent data from field observations, and new stratigraphic data from the Neptune Open pit, and diamond drill cores from the area help to refine the stratigraphy of the Lefroy Palaeodrainage System, and the palaeoenvironment leading to the deposition of the Lefroy Palaeodrainage System sediments.

CLARKE, J. D. A. 1994. Evolution of the Lefroy and Cowan palaeodrainage channels, Western Australia. Australian Journal of Earth Sciences, 41, 55-68.

DE BROEKERT, P. & SANDIFORD, M. 2005. Buried Inset‐Valleys in the Eastern Yilgarn Craton, Western Australia: Geomorphology, Age, and Allogenic Control. The Journal of Geology, 113, 471-493.

EYLES, N. & DE BROEKERT, P. 2001. Glacial tunnel valleys in the Eastern Goldfields of Western Australia cut below the Late Paleozoic Pilbara ice sheet. Palaeogeography, Palaeoclimatology, Palaeoecology, 171, 29-40.

OXENBURGH, S., FALCONER, M., DOUTCH, D., EDMONDS, P., FOLEY, A. & JANE, M. 2017. Kambalda – St Ives goldfield. In: PHILIPS, N. (ed.) Monograph 32 – Australian Ore Deposits. The Australasian Institute of Mining and Metallurgy.


Biography

Leah is Researcher with the Graduate Research School at James Cook University. Her current work concentrates on reconstructing the middle-Late Eocene palaeoenvironment of the Eastern Goldfields Region, Prior to her position at JCU she worked as an exploration geologist on various projects throughout WA.

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