The nature & origin of the Tarcoola Goldfield, and implications for the central Gawler gold province, South Australia  

Authors / CoAuthors

Budd, A.R.

Abstract

The Tarcoola Goldfield in central South Australia is hosted by the Palaeoproterozoic Paxton Granite and Tarcoola Formation sediments. Both of these units are intruded by narrow dykes of the Lady Jane Diorite. Crosscutting relationships and Ar-Ar dating of sericite and hornblende demonstrate that veining, alteration and mineralization occurred synchronously with intrusion of the diorite dykes at ~1580 Ma. The Lady Jane Diorite is considered to be part of the Gawler Range?Hiltaba Volcano-Plutonic event. Mineralization at the Perseverance deposit in the Tarcoola Goldfield is hosted by both granite and the lower parts of the Tarcoola Formation. Alteration intensity and mineralization are related to fracture density, suggesting the structural regime was an important control on ore location and deposition. However, at the Tarcoola Blocks mine, mineralization is hosted entirely in the Tarcoola Formation, and very high gold grades are recorded in carbonaceous horizons, suggesting chemical processes in ore deposition. Primary fluid inclusions from mineralized quartz veins are dominated by two types, a two-phase aqueous type and a three-phase H2O-CO2(l)-CO2(v)?CH4 type. Both inclusion types have salinities of <10 wt% eq. NaCl, with evidence of other salts being present. Both types have Th between ~380?C and 150?C. At the Perseverance deposit, both inclusion types occur together in single quartz grains as primary inclusions, and are interpreted to have formed from a single evolving fluid, indicating immiscibility. Pb isotopes of galena from gold-bearing mineralization are in equilibrium with K-feldspar and whole-rock samples of the Paxton Granite. This is consistent with a local source for Pb and possibly other ore components, but not all potential reservoirs were able to be tested. Variably altered and gold mineralized samples that had Paxton Granite precursors show a loss of Nd and a trend from ?Nd(1580 Ma) values of about -6.2 in slightly altered samples towards more positive ?Nd values of about -3.3 in high grade gold samples. Of the local lithologies, the Lady Jane Diorite has ?Nd(1580 Ma) values of about +0.15 and is the most probable source of the more primitive Nd isotopic components in mineralized samples. Whether the Lady Jane Diorite is a cause of mineralization at Tarcoola, or both it and the mineralization are symptoms of the same tectonothermal event at ~1580 Ma can not be resolved with the available data. The demonstrated age relationship between the diorites and mineralisation at Tarcoola, the Nd data at Tarcoola, and the presence of similar dioritic dykes in all of the known gold prospects in the Central Gawler Gold Province are strongly suggestive that such dyking was an essential ingredient in gold mineralization throughout this province.

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nonGeographicDataset

eCat Id

61730

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Keywords

• External PublicationScientific Journal Paper

( Theme )

• economic geology

( Theme )

• alteration

( Theme )

• geochemistry

( Theme )

• metallogenesis

( Theme )

• mineral deposits

• AU-SA

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2005-01-01T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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geoscientificInformation

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[-33.0, -30.0, 133.0, 137.0]

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