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Mule Canyon |
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Nevada, USA |
| Main commodities:
Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Mule Canyon low-sulphidation, epithermal Au-Ag deposits are located in northern Lander County, Nevada, USA, 20 km southeast of Battle Mountain.
They lie at the north end of the Shoshone Range, near the western side of the NNW trending middle Miocene Northern Nevada rift and were formed during the regionally extensive tholeiitic bimodal basalt-rhyolite magmatic episode that was associated with extensional faulting related to the development of the rift.
The basement rocks to the host volcanics in the northern Shoshone Range comprise Ordovician, Silurian and Devonian deep water marine siliciclastic sediments of the Roberts Mountains allochthon that were thrust eastwards over equivalent continental margin sediments during the Middle Palaeozoic Antler Orogeny. These are overlain by a regionally extensive early Oligocene rhyolite ash-flow tuff (the Caetano Tuff) and are unconformably followed by several hundred metres of middle Tertiary continental sediments, mainly shallow lacustrine, composed of coarse debris flows, conglomerate, sandstone, siltstone, mudstone and minor limestone, which were in turn overlain by the Miocene volcanics of the Northern Nevada rift.
Mineralisation is hosted by a 16.4 and 15.8 Ma basalt-andesite eruptive centre, comprising a 400 m thick package of around 15 flow units, formed during an early mafic phase of the bimodal volcanism. Hydrothermal alteration and the Au-Ag ores developed at near 15.6 Ma and were tightly controlled by NNW to north striking high-angle fault and breccia zones formed during rifting, emplacement of mafic dikes and eruption of mafic lavas.
Two types of ore are recognised at Mule Canyon, namely:
1). Early replacement represented by disseminated and vesicle-filling pyrite, marcasite, and arsenopyrite in argillically altered or weakly silicified rocks. Gold is present as auriferous arsenopyrite and arsenian pyrite overgrowths coating earlier formed pyrite and marcasite.
2). Late open-space filling as narrow stockwork quartz-adularia veins, banded and crustiform opaline and chalcedonic silica-adularia veins, silica-adularia cemented breccias, and sparse carbonate-pyrite and/or marcasite veins. Gold and silver are present in electrum and Ag sulphide and selenide minerals, with minor to major amounts of pyrite, marcasite, and arsenopyrite and local stibnite.
Individual ore zones are around 200 to 300 m in strike length and 25 to 60 m wide and extend for 100 to 200 m down dip at steep angles of over 60°. Ore was present to the surface at 4 of the 6 deposits of the district.
Hydrothermal alteration is zoned progressively outward from the identified fluid conduits from silica-adularia to adularia-smectite to smectite (intermediate argillic) and finally smectite-carbonate (propylitic) on the outer margins with field relations indicating that the silica-adularia phase is superimposed on the argillic and propylitic alteration. All of these alteration assemblages contain abundant pyrite and/or marcasite ± arsenopyrite, but have little or no steam-heated acid-sulphate alteration.
Age dating shows that hydrothermal alteration and gold deposition occurred about 0.2 million years after the last mafic lava eruptions and that mineralisation was emplaced between the cessation of mafic lava eruption and the onset of the more silicic magmas derived from sources several kilometres away.
Mule Canyon is similar to most other low-sulfidation Au-Ag deposits associated with Miocene tholeiitic bimodal basalt-rhyolite magmatism in the Great Basin such as Sleeper, Midas and Buckhorn. They differ however in that they have a high iron sulphide content, lack appreciable silicification and only have narrow discontinuous quartz veins.
Mule Canyon comprised six small deposits that together contained: 8.2 Mt @ 3.81 g/t Au for 31 tonnes of gold.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2003.
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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John D A, Hofstra A H, Fleck R J, Brummer J E, Saderholm E C 2003 - Geologic setting and genesis of the Mule Canyon low-Sulfidation epithermal Gold-Silver deposit, north-central Nevada: in Econ. Geol. v98 pp 425-463
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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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