Abstract

Similarities in mineralization and alteration style, host rocks, fluid compositions, and alteration-related 40Ar/39Ar ages from several recently discovered gold prospects support the existence of a significant Mesoproterozoic gold province spanning an arcuate region at least 300 km in length in the central Gawler craton, South Australia. At the recently discovered prospects of Tunkillia, Nuckulla Hill, Barns, and Weednanna, as well as at the historically mined Au deposit at Tarcoola, gold occurs as disseminated and veinlet-hosted mineralization focused in brittle to brittle-ductile faults and shear zones. Host rocks are principally ~1715 to ~1680 Ma granites but also include Hutchison Group (2000-1860 Ma) and Tarcoola Formation (~1650 Ma) metasedimentary rocks. Hydrothermal alteration is characteristically zoned around gold mineralization, with intense sericite-pyrite alteration and quartz veining proximal to gold mineralization and chlorite ± epidote ± hematite alteration distal from mineralization. Alteration was either synchronous with or, in some cases, continued after deformation. Gold is associated with pyrite and minor to trace galena, sphalerite, and chalcopyrite. Iron oxides are low in abundance in mineralized zones, which correspond to demagnetized zones. Fluid inclusion analyses suggest that multiple fluids were present in some systems, but one key fluid type occurs in each of the gold prospects: a low- to moderate-salinity (up to 10 wt % NaCl equiv) fluid with homogenization temperatures mostly in the range of ~150° to 300°C and commonly containing CO2 or associated with CO2-rich inclusions. Several features of the prospects are similar to those of orogenic- and intrusion-related gold deposits, but neither the prospect-scale geology nor the regional geologic setting in the central Gawler craton is sufficiently well understood to establish a genetic model or to confidently classify the mineralizing system. Hydrothermal white micas from several of the central Gawler craton gold prospects yield reproducible 40Ar/39Ar plateau ages of between 1567 and 1583 Ma. These ages, together with U-Pb zircon ages of granitic host rocks, constrain the timing of mineralization to the interval ~1690 to 1570 Ma, although we interpret the 40Ar/39Ar results to indicate a narrower mineralizing interval at ~1580 ± 10 Ma. This age range overlaps with, and is indistinguishable from, the range of U-Pb zircon ages reported from regional Hiltaba Suite granites and Gawler Range Volcanics, although igneous rocks of this age have not been identified locally at each of the prospects.
Google map showing geographic bounding box with values North bound -29.0 East bound 138.0 West bound 133.0 South bound -34.0
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Product Type/Sub Type

dataset - External Publication - Scientific Journal Paper

Constraints

license
Creative Commons Attribution 3.0 Australia Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

2007

Product Type

dataset

Topic Category

geoscientificInformation

Keywords

External Publication
Scientific Journal Paper
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

North bound
-29.0
East bound
138.0
West bound
133.0
South bound
-34.0

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Unknown

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onLine

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distributor
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Metadata File Identifier

a05f7892-f9e0-7506-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

Metadata Date Stamp

2010-10-11

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

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pointOfContact
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
Related Links
For information on acquiring this product,
please contact the Geoscience Australia Sales Centre via:

fax:
+61 2 6249 9960; or
phone:
1800 800 173 (within Australia);
 
+61 2 6249 9966 (outside Australia).

Please note that support hours are 9 am to 5 pm weekdays