Porphyry Au-Cu mineralization controlled by reactivation of an arc-transverse volcanosedimentary subbasin

Located in the accreted remnants of the Ordovician Macquarie Arc (Australia), Cadia East is the largest alkalic porphyry Au-Cu deposit currently known. The deposit is centered on a 2-km-long, northwest-trending volcanosedimentary subbasin, which was identified by mapping variations in the distributi...

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Bibliographic Details
Published in:Geology (Boulder) 2015-09, Vol.43 (9), p.811-814
Main Authors: Fox, Nathan, Cooke, David R, Harris, Anthony C, Collett, Dean, Eastwood, Graeme
Format: Article
Language:English
Subjects:
Australasia
Australia
Basins
Cadia East Deposit
copper ores
dikes
Economic geology
Geological time
gold ores
intrusions
Macquarie Arc
metal ores
mineral deposits, genesis
mineralization
Mineralogy
Minerals
New South Wales Australia
Ordovician
Paleozoic
porphyry copper
porphyry gold
sedimentary basins
Sedimentation & deposition
Silurian
volcanism
Volcanoes
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Summary:Located in the accreted remnants of the Ordovician Macquarie Arc (Australia), Cadia East is the largest alkalic porphyry Au-Cu deposit currently known. The deposit is centered on a 2-km-long, northwest-trending volcanosedimentary subbasin, which was identified by mapping variations in the distribution and thickness of faulted sedimentary marker horizons. The normal faults that define the subbasin predate porphyry mineralization and are oriented parallel to a major arc-transverse lineament. Porphyry Au-Cu mineralization was controlled by reactivation of the subbasin during postorogenic extension as the Macquarie Arc was accreted to the Gondwana margin in the early Silurian. Dilation of the northwest-trending subbasin faults facilitated emplacement of alkalic porphyry dikes and associated sheeted quartz-sulfide veins that define the Cadia East orebody. During the middle Silurian, north-trending fault-bound marine basins buried Cadia East, significantly enhancing preservation of the ore system. These north-trending faults were optimally oriented for reactivation during Devonian east-directed compression, leaving the mineralized Cadia East volcanosedimentary subbasin largely intact. We identify the significance of reactivated premineralization structures within an arc-transverse lineament in controlling porphyry Au-Cu mineralization in a postsubduction setting. At Cadia East, the manifestation of such premineralization structures can be observed at regional, district, and deposit scales, and highlights the influence of preexisting crustal architecture on the structural character, geometry, and preservation potential of porphyry deposits throughout the arc life cycle.
ISSN:0091-7613
1943-2682
DOI:10.1130/G36992.1