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Relief 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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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Relief Canyon gold deposit is located approximately 95 km to the SSW of the town of Winnemucca, and falls within Pershing County, in central western Nevada, USA. It is 45 km to the south of the Florida Canyon mine and 12 km south of the Rochester District deposits. All three deposits are on the western margin of the north-south trending Humboldt Range.
At Relief Canyon the late Triassic Grass Valley Formation has been thrust over the late Triassic Natchez Pass Formation. The lower plate Natchez Pass Formation is composed of 300 m of massive grey to dark grey, locally carbonaceous, dolomitic limestone which has silty and sandy sections as beds up to a metre in thickness. Traces of pyrite are found within the unit below the base of oxidation. The upper plate Grass Valley Formation comprises more than 200 m of interbedded, thinly parted argillite, hard grey to brown quartzite, siltstone and shale. A few beds are slightly calcareous and some of the shales are dolomitic. Below the zone of oxidation these beds are often slightly carbonaceous, and the siltstone, shale and argillite are frequently black and highly carbonaceous (Parratt, et al., 1987).
Two types of intrusive, both of which appear to be pre-mineralisation, are found at Relief Canyon. These include a few intersections of adamellite (quartz-monzonite) dykes up to 3 m thick, which contain no mineralisation, and dolerite (diabase) dykes which are generally propylitically altered. A significant proportion of the deposit is masked by Quaternary alluvium (Parratt, et al., 1987).
The strike of bedding in both of the main formations is to the south-west. The main structural feature at Relief Canyon is the Relief Fault, a low angle thrust which has been folded into a broad north-east trending anticline that plunges shallowly to the south-west. At Relief Canyon its strike is approximately NW-SE. A small fold perpendicular to the plunge of the anticline forms a dome over the southerly portion of the Relief Canyon gold deposit. The thrust varies from a 'knife edge' feature with no brecciation to a zone up to 75 m thick. In general it varies from 0 to 30 m in thickness. A number of north-east and north-west trending normal faults slightly offset the Relief Fault (Parratt, et al., 1987).
Gold mineralisation at Relief Canyon is found along the highly brecciated thrust contact between the two formations. Weak gold mineralisation often occurs above the thrust in the Grass Valley Formation. Most of the ore grade mineralisation however, is below the thrust in the brecciated Natchez Pass Formation, or where the two formations are mixed as a result of movement along the thrust (Parratt, et al., 1987).
Several types of gold mineralisation are recognised. A large part of the ore is present as a jasperoid breccia. The jasperoid breccia often grades downwards into grey silicified limestone and silicified limestone breccia. The silicified limestone is usually vuggy, with drusy quartz and gold values. In this zone below the main jasperoid mass, jasperoid stringers containing gold extend into the un-altered limestone. Significant amounts of ore occur as a mixed breccia composed of upper plate rock, fresh limestone, clay and jasperoid breccia. Gold also occurs in fresh limestone breccia that contains substantial amounts of clay and in fresh clay. In jasperoid breccia with clay seams, the gold is related to both the silicification and the clay. In the mixed breccias and limestone breccias the gold is associated with argillic alteration. A detailed study of grade distribution indicates that the higher grades are often associated with argillic alteration rather than silicification (Parratt, et al., 1987).
Gold mineralisation appears to be disseminated and has the typically associated trace element suite of As, Sb, Hg and F, although none show a direct correlation with Au. Typical ranges of values from samples with anomalous Au include 0.3 to 40 g/t Ag, 17 to 2600 ppm As, 1 to 430 ppm Sb, 1.8 to 18 ppm Hg and 190 ppm to 11% F. Gold has not been observed in any polished sections. Pyrite within the un-oxidised zone is present as both euhedral and subhedral crystals and as framboids. Iron oxides from these show similar pseudomorphed forms. The framboidal pyrite is arsenian (Parratt, et al., 1987).
22.5 Mt @ 0.86 g/t Au = 19 t Au (Reserve, 1988, Min J, Gold Service, May 1989).
7.25 Mt @ 1.37 g/t Au (Production +Reserves, 1983, Bagby & Berger, 1985).
The Relief Canyon mine produced 13.4 t Au at an average grade of 1.27 g/t Au between 1985 and 1989.
The most recent source geological information used to prepare this decription 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.
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Parratt R L, Wittkopp R W and Bruce W R, 1987 - Geology and mineralization at the Relief Canyon gold deposit, Pershing County, Nevada: in Johnson J L (Ed.), 1987 Bulk Mineable Precious Metal Deposits of the Western United States - Guidebook for Field Trips Geol. Soc. Nevada pp 362-367
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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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