The Tarcoola Goldfield region is located in the central Gawler Craton, and forms the northern portion of the Central Gawler Gold Province. Gold deposits underlying the Tarcoola Ridge and adjacent areas have been exploited by in excess of 50...
The Tarcoola Goldfield region is located in the central Gawler Craton, and forms the northern portion of the Central Gawler Gold Province. Gold deposits underlying the Tarcoola Ridge and adjacent areas have been exploited by in excess of 50 historic surface and underground mines and by many small-scale workings that were opened up since the first discovery of alluvial gold at Tarcoola in 1893. But in more recent times company-led gold exploration and mining activity in the Tarcoola region has only been intermittent, with WPG Resources Ltd recommencing operations at the Perseverance open cut mine in late 2016. This report presents the results of Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA–ICP–MS) geochronological analyses done on 7 samples of sedimentary, igneous and mineralised/altered lithologies from the Tarcoola Goldfield region. These samples were collected with several purposes in mind; to examine the sources of sediments in the Tarcoola Formation, to determine the ages of previously unconstrained igneous rocks, and to constrain the ages of signatures of past deformation events seen in regionally significant shear zones and within mineralised structures in the Tarcoola Gold Camp. Dating of two detrital zircon samples collected from northern and south-western exposures of Tarcoola Formation sediments produced a spectrum of ages as interpreted from their geochronology data probability density diagrams, with a large age peak in the late Palaeoproterozoic, a smaller cluster at the late Archaean to early-Palaeoproterozoic (c. 2600–2400 Ma) and small peaks at the early-Mesoarchaean and early- to mid-Palaeoproterozoic. A comparison was made of the detrital zircon ages obtained from the Tarcoola Formation with ages previously determined for the nearby c. 1715 ± 9 Ma Labyrinth Formation (Fanning et al. 2007), the unconformably underlying Eba Formation, and a quartzite from the No. 17 Bore prospect to the north (Reid et al. 2009), which thereby revealed some common trends: • These lithologies have age peaks that are commonly observed from c. 2.8–2.5 Ga and at c. 3.1 Ga, similar to the Tarcoola Formation. This supports a mutual source of sediments for these formations. • The quartzite at No. 17 Bore shares many detrital age data similarities with the Eba Formation, suggesting that it was possibly deposited at a similar time. • Comparison of detrital zircon age data from the Tarcoola Formation with those of the more distant Corunna Conglomerate showed more consistent similarities across the whole age spectrum. Dating of two samples from a large (30 km east-west by ~24 km north-south), irregular pluton of Hiltaba Suite granite to the north of Tarcoola produced the first age constraints on this pluton. The Cooladding Granite sample taken from the south of the pluton was emplaced at 1582 ± 9 Ma, whereas the ‘Konkaby West’ Granite sample from the north of the pluton, was emplaced at 1573 ± 9 Ma. Bounding the northern margin of the pluton are the northeast-trending Bulgunnia Shear Zone, and the northwest-trending Lake Labyrinth Fault, which consequently must be younger than the 1573 ± 9 Ma ‘Konkaby West’ Granite. The Pinding Granite dated sample was emplaced at 1591 ± 12 Ma, making it part of the Hiltaba Suite. This confirms that the Pinding Granite was incorrectly assigned to the Paxton Suite on the basis of geochemical similarities by Budd (2006), and validates the aeromagnetic data interpretation that this granitic body truncates the Tarcoola Formation. These preliminary data potentially suggest that the Hiltaba Suite felsic intrusives in the Tarcoola region may represent a single continuously evolving magmatic system from c. 1590–1575 Ma, implying that the Malbooma and Jenners supersuites are the two endmembers of that system. To investigate this in more detail, more precise geochronology is required from more of the Hiltaba granite plutons in the Tarcoola region. The current dataset is too small to be able to identify meaningful trends between granite fractionation, evolution and age, particularly with the anomalous Ambrosia Granite, which does not follow the proposed trend. The timing of mineralisation at the Tarcoola Goldfield, dated at 1564 ± 15 Ma, is recorded by monazite which was sampled from the north-northeast striking ‘Granite Shear’ at the Perseverance open cut mine.
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