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Otago, Clutha River |
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South Island, New Zealand |
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Au
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Super Porphyry Cu and Au
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The Otago region of the South Island, New Zealand has produced 260 tonnes of gold over the 130 years to 1995, from a range of operations up to and including large scale dredging.
The Central Otago region is drained by a single catchment, the Clutha River system, whose active and Recent stream gravels host major placer deposits of gold.
In tributaries, such as the Manuherikia and Shotover Rivers, eluvial placers are developed over schists containing sparse gold bearing veins. These schists are overlain by variably auriferous Miocene fluvial sediments with up to 300 micron detrital gold. The Miocene sediments were eroded during Quaternary warping and uplift of the schists.
Gold in the Miocene sediments has been chemically mobilised on the degraded unconformity to form nuggets up to 2 cm across. This unconformity has been eroded to produce alluvial fans with coarse alluvial gold, which have been in turn uplifted and eroded to form younger fans.
Subsequent groundwater activity resulted in further nugget rims and an increase in grain size.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1995.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Craw D, Youngson J H, Koons P O 1999 - Gold dispersal and placer formation in an active oblique collisional mountain belt, Southern Alps, New Zealand: in Econ. Geol. v94 pp 605-614
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Pitcairn I K, Teagle D A H, Craw D, Olivo G R, Kerrich R and Brewer T S, 2006 - Sources of Metals and Fluids in Orogenic Gold Deposits: Insights from the Otago and Alpine Schists, New Zealand : in Econ. Geol. v101 pp 1525-1546
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Scanlan, E.J., Scott, J.M., Wilson, V.J., Stirling, C.H., Reid, M.R. and Le Roux, P.J., 2018 - In Situ 87Sr/86Sr of Scheelite and Calcite Reveals Proximal and Distal Fluid-Rock Interaction During Orogenic W-Au Mineralization, Otago Schist, New Zealand : in Econ. Geol. v.113, pp. 1571-1586.
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Sibson R H and Scott J 1998 - Stress/fault controls on the containment and release of overpressured fluids: Examples from gold-quartz vein systems in Juneau, Alaska; Victoria, Australia and Otago, New Zealand: in Ore Geology Reviews v13 pp 293-306
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Youngson J H, Craw D 1999 - Variation in placer style, Gold morphology, and Gold particle behavior down gravel bed-load rivers: an example from the Shotover/Arrow-Kawarau-Clutha River system, Otago, New Zealand: in Econ. Geol. v94 pp 615-634
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Youngson J H, Craw D 1995 - Evolution of placer gold deposits during regional uplift, central Otago, New Zealand: in Econ. Geol. v90 pp 731-745
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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