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Candelaria |
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Nevada, USA |
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Ag Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Candelaria mine is located in Mineral County, south-central Nevada, USA, 40 km from the California border
The oldest rocks in the area are the Ordovician cherts, argillites and dolomite of the Palmetto Formation. These are unconformably overlain by the Diablo Grit, a Permian sandstone, and by the siltstones and mudstone of the lower Triassic Candelaria Formation. The lower Carboniferous to Triassic Pickhandle Gulch Complex is in contact with the Candelaria Formation along the Pickhandle Thrust. It comprises serpentinite, mafic volcanics and structurally interleaved sediments. Cretaceous intrusives, ranging from diorite to granite form a dyke-sill complex within the Candelaria Formation, following contacts and thrusts. These are known as the Mine Sequence intrusives. A thick sequence of Tertiary to Quaternary volcanics overlie the district (Moller, 1987).
The Pickhandle Thrust is a local sole plate of the Permo-Triassic Sonoma Orogeny Golconda Thrust. It has developed a broad shear zone parallel to bedding in the lower part of the Candelaria Formation, known as the Candelaria Shear. A series of ENE trending normal faults has offset all stratigraphic units and thrusts (Moller, 1987).
Alteration and mineralisation throughout the district show an association with areas of thrust related structural preparation and with Mine Sequence Cretaceous intrusives. Alteration in Candelaria sediments and dykes is a district scale sericite±pyrite, quartz, carbonate which is best developed in the 1 to 30 m thick lower Candelaria Shear. Mafic and ultramafic rocks of the Pickhandle Complex have a pre-mineral silica-carbonate replacement zone up to 80 m thick above the thrust. Irregularly developed silicification also occurs within this structural horizon (Moller, 1987).
Approximately 65% of the open pit reserves are hosted by the basal member of the Candelaria Formation within the lower Candelaria Shear. Where un-oxidised, the ore is hosted by carbonaceous, variably calcareous silty mudstone and contains abundant veinlets of quartz with disseminated pyrite, sphalerite and galena. High grade veins parallel to the shear fabric consist of pyrite-sphalerite-galena-chalcopyrite-jamesonite in a quartz-carbonate gangue. Oxidised sediment hosted ores contain abundant Fe and Mn oxides which contain the bulk leachable silver. Cerargyrite and argentite are present but not in economic quantities (Moller, 1987).
About 25% of the ore is hosted by serpentine and mafic volcanic rocks of the Pickhandle Gulch Complex within the thrust zone. The same suite of sulphide and oxide minerals occur in the quartz-dolomite gangue. The remainder of the ore is hosted by the Mine Sequence intrusives and by strongly sheared basement rocks of the Ordovician Palmetto Formation (Moller, 1987).
During the Cretaceous to mid-Tertiary deep supergene weathering caused the breakdown of sulphides and the migration of Ag downwards to the base of the oxidised zone. This is evidenced by an increase in the both silver grade and leachability with depth to coincident maxima between 100 and 180 m. Significant carbon and sulphide occur below this depth (Moller, 1987).
Reserves in 1983 were 4.5 Mt @ 0.21 g/t Au, 137 g/t Ag = 1 t Au (Bagby & Berger, 1985).
The pre-mining resource amounted to more than 3900 t (130 Moz) of Ag (Thompson, et al., 1995).
For detail contact the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1995.
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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Moeller S A, 1988 - Geology and mineralization of the Candelaria District, Mineral 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 135-158
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Moeller S A, Nerco Minerals Co. 1987 - Geology and mineralization in the Candelaria district, Mineral 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 240-242
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Thomson B, Aftalion M, McIntyre R M, Rice C 1995 - Geochronology and tectonic setting of silicic dike swarms and related Silver mineralization at Candelaria, western Nevada: in Econ. Geol. v 90 pp 2182-2196
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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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