Denton - Rawhide

Nevada, USA

Main commodities: Au Ag
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The Denton - Rawhide gold-silver deposit is located in northern Mineral County, south-western Nevada, USA. It is approximately 45 km to the north-west of the Paradise Peak mine and 75 km NNE of Borealis.

The Rawhide ore deposit is associated with the Miocene Rawhide volcanic centre which covers an area of 6.5 x 12 km and is composed of mafic, intermediate and silicic intrusions, flows and pyroclastics, with minor associated volcano-sedimentary rocks. The lowermost exposed unit of the volcanic centre consists of a variable sequence of ash tuffs, crystal lithic lapilli tuffs and volcaniclastic sedimentary rocks that exceed 245 m in thickness. This unit is referred to as the 'lithic tuff', and in the area of the Rawhide deposit is overlain by andesitic flows, the principal host to bulk mineable ore. The andesite flows are overlain in turn by a distinctive sequence of stratified tuffaceous sedimentary rocks and intercalated volcanic breccia which appears to be restricted to the immediate vicinity of Rawhide. Finely stratified, siliceous, grey to black, pyritic siltstones within this sequence are interpreted to have formed during sub-aqueous hydrothermal venting into a lacustrine environment. Coarse grained volcanic breccia interlayers increase in frequency and thickness up-section. Prior to lithification, these sediments were variably tilted and deformed during the emplacement of a biotite rhyolite intrusive complex and related breccias (Black, et al., 1990).

Several pod-like ore zones occur within a north-west striking area of 2440 x 400 m. Individual ore zones have irregular geometries, but are typically elongated in the same direction. Mineralised veins strike at north to north-east, transverse to the overall trend. Bulk mineable ore occurs preferentially in intensely fractured andesite along the hangingwall of the rhyolite intrusion, and is characterised by abundant, closely spaced, sheeted to stockwork quartz-adularia veins. Ore is found in zones of primary permeability in porous lithic tuffs and volcaniclastic sedimentary rocks. It is finely disseminated and accompanied by pervasive silicification and adularia development, with only minor, or no associated veining. Ore zones are characterised by the hydrothermal assemblage quartz-adularia-illite-pyrite. Adularia associated with mineralisation yields a K-Ar age of 15.7±0.6 Ma. Argillic alteration predominates on the margins of the deposit. Late kaolinite-alunite-opal veins are considered to have resulted from supergene oxidation. The deposit is extensively oxidised to a depth of up to 215 m (Black, et al., 1990).

Gold occurs as electrum in both oxide and sulphide ore. Silver is present primarily as embolite and lesser cerargyrite in oxide ore and as silver selenides, sulphides and sulpho-salts in sulphide ore. The pyrite content in sulphide ore is typically 1 to 5% by volume. The Au:Ag ratio averages 10:1 in both the oxide and sulphide zones and generally increases with distance from ore. Minor Ag enrichment is present locally along the sulphide-oxide boundary (Black, et al., 1990). Production in 1993 was 3.2 t Au (AME, 1995).

Published production and reserve figures include:

    29 Mt @ 1.2 g/t Au, 11 g/t Ag = 35 t Au (Mineable Reserve, 1989, Black et al., 1990).
    30 Mt @ 0.45 g/t Au, 7 g/t Ag = 13 t Au (Leach Reserve, 1989, Black et al., 1990).
    44 Mt @ 0.9 g/t Au (Proven + Probable Reserve, 1994, AME, 1995).
    31.9 Mt @ 0.705 g/t Au, 11.68 g/t Ag (Denton-Rawhide reserves, Dec. 1999, Kinross, 2000).

Mining ceased in 2002 and leaching has continued to at least 2005 when 1 t of Au was produced (Rio Tinto Ann. Rep., 2006).

The most recent source geological information used to prepare this summary was dated: 2006.    
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.

  References & Additional Information
   Selected References:
John, D.A., du Bray, E.A., Henry, C.D. and Vikre, P.G.,  2015 - Cenozoic Magmatism and Epithermal Gold-Silver Deposits of the Southern Ancestral Cascade Arc, Western Nevada and Eastern California: in   New Concepts and Discoveries, Geological Society of Nevada, 2015 Symposium, Reno/Sparks, Nevada, May 14 to 24, 2015,   Symposium Proceedings, pp. 611-645.

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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