Regolith stratigraphy and gold distribution within tributary palaeochannels near Gindalbie and Kurnalpi, Kalgoorlie Region, Western Australia
thesisposted on 2023-05-26, 20:41 authored by Lynn, SF
This study investigates two sites within the Roe Palaeodrainage system in the Kalgoorlie Region of Western Australia. Both are located over southward draining tributary palaeochannels that have incised into already deeply weathered Archaean lithologies. The pre-palaeochannel regolith is only partly preserved at Gindalbie due to the site's proximity to the main trunk palaeoriver. However at Kurnalpi, there is extensive preservation of the pre-existing laterite profile beneath the palaeochannel sediments and permits an estimation of the maximum depth of palaeochannel incision: That is 25-30 metres at Kurnalpi; 40-50 metres at Gindalbie; 60-70 metres in the trunk channel. The palaeochannel sediments comprise a basal sand facies that is generally confined to the palaeoriver bed, and a conformable upper clay facies that blankets the entire palaeodrainage valley. The sediments have also been lateritized, resulting in an extensive ferruginization of the upper profile (Fe-induration, Fe-nodules and pisoliths, and mega-mottles), and at least at Gindalbie, a prominent redox front at 18-20 metres depth below which reducing conditions prevail. The sand facies has been palynologically dated by others as Middle to Late Eocene in age, thus constraining the lateritization events to pre and post-Eocene. At Kurnalpi, colluvial/alluvial incision has extensively truncated the upper profile of both the transported and in-situ regolith. This event has occurred after post-Eocene lateritization and appears to be confined to the mid and upper slopes of the catchment area. At both sites gold mineralization is extensive but is confined to the environs of the palaeochannels. At Gindalbie gold is almost exclusively distributed as discrete horizontal horizons within the palaeochannel sediments below the main redox front, with the highest grades located directly above the palaeochannel thalweg. No bedrock mineralization was encountered; and gold distribution appears to be controlled by groundwater regimes/chemistry and host lithology mineralogy. At Kurnalpi Archaean lode-style gold mineralization is spatially associated with supergene gold within both the palaeochannel sediments and the in-situ regolith. The highest gold grades from both regolith profiles are distributed about a vertical plane through the channel thalweg, with placer gold located at the base of the palaeochannel sand facies. All gold mineralization appears to be derived initially from basement lodes and distribution patterns reflect local controls such as bedrock structure, basement lithology, channel morphology and groundwater movement.
Rights statementCopyright 1994 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (M.Econ.Geol.)--University of Tasmania, 1995. Includes bibliographical references (p. 65-68)