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Florida Canyon |
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Nevada, USA |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Florida Canyon gold orebody is located some 60 km to the south-west of the town on Winnemucca in Nevada, USA.
Florida Canyon, like the Relief Canyon and Rochester deposits, lies on the western flank of the north-south trending Humboldt Range. This range is essentially a large north-south trending anticlinal structure which has been complicated by thrust and normal faults of Mesozoic and Cenozoic age (Richardson, 1987).
The ore deposit is hosted by the late Triassic Grass Valley Formation which comprises meta-pelitic, silty and sandy lithologies. These rocks are largely non-calcareous and lack interbedded carbonates. Terriginous detrital material coarser than medium grained sand is absent. Pelitic and silty rocks make up two thirds of the sequence and include slate, phyllite, argillite and micaceous siltstone. It overlies a Permo-Triassic sequence comprising i). the Permian to early Triassic Koipato Group terriginous rhyolite tuffs, followed unconformably by ii). the early to late Triassic Pride Formation calcareous and dolomitic siltstones, silty and sandy limestones and dolomites, capped by medium, thin bedded, dark and massive limestones with cherty laminated carbonates. The Pride Formation may be up to 750 m thick. This is followed in turn by iii). the massive and homogeneous limestones of the upper Triassic Natchez Pass Formation; and iv). the late Triassic Grass Valley Formation (Richardson, 1987).
In the orebody area the Grass Valley Formation has been sub-divided into four hydrothermally altered units which probably reflect original lithological differences. These include an upper silicified siltstone, a strongly oxidised hematitic siltstone, a clay altered siltstone and a lower silicified siltstone. Mineralisation occurs in structurally controlled quartz veins and micro-vein stockworks which cut the hydrothermally altered units of the Grass Valley Formation. Mineralisation does not appear to be preferentially controlled by lithology. The veining is controlled by high angle structures which trend north to north-east, with subordinate faulting and shearing trending north-west to west. These faults were largely active during the Miocene Basin and Range tectonism and are interpreted to have been the focus of hydrothermal activity (Richardson, 1987).
Gold is carried in stockwork quartz veining occurring in association with the high angle structures, although some vein quartz is barren. Native gold is present as grains from 2 to 90 µm in diameter, with most in the 5 µm range. The hypogene minerals include pyrite, marcasite, quartz and magnetite. No visible gold has been seen associated with sulphides, only with quartz. Oxidation has developed limonite and hematite from the sulphides with associated coarser gold, which may have been concentrated during oxidation from very fine gold held in the pre-oxidation sulphides (Richardson, 1987).
Production in 1994 totalled 2.82 t Au from 6.74 Mt of ore (AME, 1995).
22 Mt @ 0.82 g/t Au = 18 t Au (Reserve, 1988, Block 1, E&MJ Int Dir Min, '87/88).
19 Mt @ 0.75 g/t Au = 14 t Au (Reserve, 1988, Block 2, E&MJ Int Dir Min, '87/88).
17.8 Mt @ 0.76 g/t Au (Mineable Reserve, 1987, Richardson, 1987).
37.8 Mt @ 0.6 g/t Au (Proven+Probable Reserve, 1994, AME, 1995).
The most recent source geological information used to prepare this decription was dated: 1996.
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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Hastings J S, Burkhart T H and Richardson R E, 1988 - Geology of the Florida Canyon gold deposit, Pershing County, Nevada: in Schafer R W, Cooper J J, Vikre P G (Eds), 1988 Bulk Mineable Precious Metal Deposits of the Western United States Geol Soc of Nevada, Reno, pp 433-452
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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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