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Golden Cross |
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North Island, New Zealand |
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Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Golden Cross low sulphidation, adularia-argillic epithermal quartz vein gold-silver deposit is located 9 km to the north-west of the township of Waihi on the Coromandel Peninsula, North Island, New Zealand, some 100 km south-east of the city of Auckland.
The deposit is situated near the southern end of the 200 km long, north-south trending Hauraki Goldfield which is defined by a series of more than 50 epithermal gold-silver deposits that are associated with the subaerial Miocene to early Quaternary Coromandel volcanic zone. This zone is part of a late Cenozoic continental margin volcanic arc related to the boundary between the convergent Australian and Pacific plates.
A regional NNW trending structural high of Jurassic lithic-volcanic greywacke is overlain by Miocene to Pliocene andesites with lesser dacites and rhyolites of the Coromandel volcanic zone, which young to the south where they merge with the currently active Taupo volcanic zone. Some porphyry style mineralisation is associated with dykes and sills of dioritic porphyry cutting the basement and lower volcanics, while epithermal Au-Ag mineralisation is mainly associated with a sequence of andesitic and dacitic to rhyolitic lavas, tuffs and sedimentary derivatives emplaced during the Miocene to Pliocene.
The Golden Cross mineralisation is hosted by andesitic lavas, breccias and tuffs; epiclastic sedimentary rocks; dacitic lavas and breccias and pyroclastic flow units of the Coromandel Group. These lithologies have been grouped into the 7.9 Ma Waipupu Formation (andesitic lava flows, locally intercalated with volcanic breccias and lithic crystal tuffs), 7.2 Ma Waiharakeke Dacite (dacitic lava flows and tuff breccias intercalated with minor lithic crystal tuffs), and the post-ore 6.7 to 6.6 Ma Whakamoehau Andesite (unaltered andesitic to dacitic lava flows).
The Golden Cross veining is hosted by hydrothermally altered andesites and dacites that form a layered stratigraphic sequence that includes well bedded units that are tilted at ~50° to the SE. These host units were eroded by a surface with moderate relief prior to the emplacement of the unaltered Whakamoehau Andesite. Adularia alteration has been dated at 6.9 Ma.
Five epithermal vein systems have been identified at Golden Cross, namely the Empire South Vein, Tramway, Golden Cross 1 Reef, Empire Zone and Taranaki-Hippo vein. The Golden Cross mine was exploited in two areas, an open pit based on the stockwork veins and underground extraction of the Empire vein system, which collectively represent the Empire Zone.
In the Empire Zone, the underground ore occurred in crustiform- and colloform-banded quartz veins in which the gold and siver was present as electrum, acanthite, polybasite, pyrargyrite and minor accompanying base metal sulphides. Within the central vein-rich core of the deposit, earlier quartz with lesser adularia is variably overprinted by illite which occurs at depth and close to the veins, and grades outwards and upwards into illite-smectite at shallow levels. Calcite is also widely dispersed throughout the alteration zone, while pyrite is virtually ubiquitous. The shallow stockwork ore of the open pit comprised massive to weakly banded veins.
The underground vein system was mined over a strike length of 500 m where it comprised the steeply dipping, up to 12 m wide Empire hangingwall vein, with subsidiary, shallowly dipping, <1 to 4 m thick and up to 60 m long, footwall veins. The stockwork zone was composed of 1 to 20 cm thick, closely spaced veins that dipped both to the east and west.
The principal structures are the 10 to 20 m wide, north-south striking, dip-slip Western Boundary Fault (represented by a zone) which defines the western limit of stockwork mineralisation and parallels the Taranaki-Hippo vein system to the north, and the NNE trending Empire Fault that controls the Empire Zone, the Golden Cross 1 Reef and the Empire South Vein. The Empire Fault is steeply west dipping with an apparent reverse displacement of from a few tens to 300 m. The stockwork zone is immediately to the west of the Empire zone veins, wedged between the two faults which converge to the south.
Between 1991 and when the mine closed in 1998, 5.1361 Mt of ore was mined for 20.59 t Au and approximately 65 t Ag (Au:Ag ratio of 1:3.1) representing recovered grades of 4 g/t Au, 12.6 g/t Ag. The combined historic production has been estimated at approximately 23.5 t Au and 73.1 t Ag.
The most recent source geological information used to prepare this decription was dated: 2007.
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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Begbie M J, Sporli K B and Mauk J L, 2007 - Structural Evolution of the Golden Cross Epithermal Au-Ag Deposit, New Zealand: in Econ. Geol. v102 pp 873-892
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Christie A B, Simpson M P, Brathwaite R L, Mauk J L and Simmons S F, 2007 - Epithermal Au-Ag and Related Deposits of the Hauraki Goldfield, Coromandel Volcanic Zone, New Zealand: in Econ. Geol. v102 pp 787-816
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De Ronde C E, Blattner P 1988 - Hydrothermal alteration, stable isotopes, and fluid inclusions of the Golden Cross epithermal Gold-Silver deposit, Waihi, New Zealand: in Econ. Geol. v83 pp 895-917
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Mauk J L and Simpson M P, 2007 - Geochemistry and Stable Isotope Composition of Altered Rocks at Golden Cross Epithermal Au-Ag Deposit, New Zealand: in Econ. Geol. v102 pp 841-871
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Mauk J L, Hall C M, Chesley J T and Barra F, 2011 - Punctuated Evolution of a Large Epithermal Province: The Hauraki Goldfield, New Zealand : in Econ. Geol. v.106 pp. 921-943
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Simmons S F, Aregart G, Simpson M P, Mauk J L 2000 - Origin of massive Calcite veins in the Golden Cross low-Sulfidation, epithermal Au-Ag deposit, New Zealand: in Econ. Geol. v95 pp 99-112
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Simpson M P, Mauk J L and Simmons S F, 2001 - Hydrothermal alteration and hydrologic evolution of the Golden Cross epithermal Au-Ag deposit, New Zealand: in Econ. Geol. v96 pp 773-796
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White, N.C., Leake, M.J., McCaughey, S.N. andd Parris, B.W., 1995 - Epithermal gold deposits of the southwest Pacific: in J. of Geochemical Exploration v.54, pp. 87-136.
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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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