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Largentiere |
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France |
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Pb Zn Ag
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Super Porphyry Cu and Au
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The Largentiere sandstone hosted Pb-Zn-Ag deposit is located at Ardeche in southern France, some 50 km north of Nimes, within a fault bounded block of Triassic and Jurassic sediments on the south-eastern margin of the Massif Central and on the northern limit of the Bassin du Sud-Est.
The deposit was mined from 1964 to 1981 with a pre-mining reserve of 10 Mt @ 3.8% Pb, 0.5% Zn, 80 g/t Ag. This reserve comprises a larger disseminated 2 to 3% Pb mass within 4 preferential beds, encompassing smaller tonnages of 5 to 6% Pb vein ore.
The host sequence include the transgressive Triassic Basal and Roubreau Sandstones which were deposited unconformably on complexly deformed Hercynian crystalline rocks and Permin siliciclastics. The chief host, the Roubreau Sandstone, which contains, pebbles, gravels and sands, was deposited in a periodically flooded distal braided river system close to an evaporitic, peritidal environment, within a series of fault bounded depressions. Galena, sphalerite and barite, whether disseminated or in veins, are spatially associated with normal faulting, with the richest ore being near NNE faults and their intersection with NNW trending cross faults.
The Roubreau Sandstone is an arkose, with 50 to 80% quartz and <50% feldspar. The intergranular spaces are largely filled with authigenic material, including galena, sphalerite and barite, while the chief cement is quartz. The authigenic quartz cement sometimes contains flecks of galena, sphalerite and barite. Mineralisation is developed over an area of some 4.5 x 6.5 km.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1997.
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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Guoxiang Chi, Rheaume P, Schrijver K 1997 - The Largentiere Sandstone Pb-Zn-Ag deposit, Ardeche, France: fluid inclusion and geologic eveidence for an epigenetic origin: in Econ. Geol. v92 pp 108-113
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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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