This report presents the results of a Geological Survey of South Australia drillhole core samples logging project addressing a selection of the cored historical exploration and stratigraphic holes that have penetrated probable Delamerian Orogeny...
This report presents the results of a Geological Survey of South Australia drillhole core samples logging project addressing a selection of the cored historical exploration and stratigraphic holes that have penetrated probable Delamerian Orogeny - age igneous and volcano-sedimentary basement to the Murray Basin in South Australia. It also includes a small number of holes from the eastern range front of the Flinders Ranges, which it was thought might be illustrative of concealed basement in the north-western Murray Basin, where few cored holes exist. The contents of this report are intended to be descriptive rather than interpretative, providing the foundation for further analytical work to be done on the drill cores, such as geochronology and geochemistry, which will be necessary to develop a stratigraphy and characterise the magmatic history of this part of the Delamerian Orogen. The holes were selected based on the information provided in lithological and stratigraphic logs available in SARIG, with the objective of including holes with a broad geographic spread which contain a diverse range of lithologies. There are, however, many cored holes that have penetrated igneous or volcano-sedimentary basement which have not been included. The 95 cored holes described herein were re-logged at the DME Tonsley Core Library during the period October 2018 to July 2020. Only the basement intervals in the holes were logged, which total over 6000 m in length. The descriptions of the cores are supported by thin section petrography, including that for 47 new thin sections collected as part of this study, plus results of the re-examination of 210 thin sections previously collected from these drillholes and stored within the GSSA thin section collection at Tonsley. Existing petrology report findings relating to the logged drillholes, contained within exploration company dataset envelopes and generated by petrography studies done as part of the Murray Basin Basement Transect Project (Farrand, 1991; Farrand & Rankin, 1991; Farrand, 1992), were incorporated into the lithological descriptions accompanying the logs. The study has been structured into five regions, (i) North-western Murray Basin margin, (ii) Truro - Cambrai, (iii) Far West, (iv) Karoonda - Coonalpyn and (v) Tintinara - Padthaway, although no geological significance is implied by these divisions. This volume contains the logs for drillholes from the North-western Murray Basin margin, Truro - Cambrai, Far West and Tintinara - Padthaway regions; the logs for drillholes from the Karoonda - Coonalpyn region will be presented in a second volume (Curtis, in prep.). A graphic lithological log is presented for each hole (except those holes with less than 1 m of core), accompanied by a description of the main lithologies, contact relationships, deformational fabrics, alteration and mineralisation. The level of detail provided in the descriptions is variable between drillholes, being largely dependent on the complexity of the rocks and the amount of petrology information available. The majority of the logs are presented at a scale of 1:100 or 1:200, but a small number are presented at a scale of 1:10 or 1:400 depending on hole length and lithological complexity. The grain size on the lithology logs is taken as the coarsest mineral phase, not the dominant grain size. A legend to the graphic logs is provided in a separate figure (Fig. 3). The cored basement depths, major lithologies, secondary mineralogy (which includes metamorphic and alteration minerals) and structural fabrics for the drillholes from each region are summarised in Tables 1–4.
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