The origin of breccia-hosted uranium deposits in carbonaceous metasediments of the Iberian Peninsula: U-Pb geochronology and stable isotope studies of the Fe deposit, Salamanca Province, Spain

Journal Article · Sun May 01 04:00:00 EDT 1994 · Economic Geology (plus the Bulletin of the Society of Economic Geologists); (United States)

DOI:https://doi.org/10.2113/gsecongeo.89.3.584· OSTI ID:7058111

Both, R A ^[1]; Arribas, A ^[2]; Saint-Andre, B de ^[3]

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1. Univ. of Adelaide, South Australia (Australia). Dept. of Geology and Geophysics
2. Univ. Politecnica de Madrid (Spain). Dept. de Ingenieria Geologica
3. U.S.T.L., Montpellier (France). Lab. de Geochimie Isotopique

The Upper Proterozoic-Lower Cambrian schist-graywacke complex of the Iberian peninsula hosts several important uranium deposits, which are characterized by their occurrence in fracture and breccia zones and by the mineral association pitchblende + coffinite + carbonates + adularia + Fe sulfides. The Fe mine, in Salamanca province, is not only the largest known deposit of this type but also the most important uranium deposit in Spain, with current reserves in excess of 16,000 metric tons of U[sub 3]O[sub 8]. Primary mineralization occurs as narrow veins occupying fractures and in cavities as finely laminated sediments showing a variety of geopetal textures. Three stages of primary mineralization, separated by episodes of fracturing and brecciation, are recognized. Chlorite compositions and fluid inclusion data show that wall-rock alteration and ore deposition took place over a temperature range of approximately 280[degree] to less than 60 C, probably to subsurficial temperatures in the final stage of mineralization. The combined geologic evidence suggests deposition of the ore from a hydrothermal system that formed in response to the effects of Alpine tectonics on the Variscan basement. Meteoric water descended via steeply dipping faults, and as well as undergoing extensive isotope exchange with, also leached uranium and other components from, the metasediments of the schist-graywacke complex, particularly carbonaceous slates. The fluid was probably expelled toward the surface through the fracture and breccia system by seismic pumping. The episodic nature of the mineralization may have been controlled by fault movements that initiated brecciation and release of fluid pressure, leading to ore deposition in fractures and cavities.

• OSTI ID: 7058111
• Journal Information: Economic Geology (plus the Bulletin of the Society of Economic Geologists); (United States), Journal Name: Economic Geology (plus the Bulletin of the Society of Economic Geologists); (United States) Vol. 89:3; ISSN 0361-0128; ISSN ECGLAL
• Country of Publication: United States
• Language: English

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