Overview

Spain:

  Salamanca I
  Salamanca II
  Caceres I
  Caceres II
  Caceres III
  Caceres VI
  Guadalajara I

Australia:

  Miriam Bouchers

This area is situated in the southern part of the province, 20-30 km southeast of the provincial capital. It forms an extensive peneplain that is limited by the Sierras de Caceres to the northwest and the Sierras de Montanchez to the southeast (Figure 1). The area includes the western part of the Central Extremadura Batholith that intrudes the slates and meta-greywackes of the late
Precambrian Schist-Greywacke Complex as a series of plutons that include the Montanchez-Albala Complex in the west.

The presence of torbernite was first noted by Hernandez-Pacheco in 1945, when examining phosphate veins in the Albala granite. The JEN resumed exploration for uranium in this area in the mid-1950’s and located numerous occurrences in the granite and occasionally on the contact with the country rock. The principal occurrence, Los Ratones, was mined between 1959 and 1975.

Application was made for a ‘Permiso de Investigacion’ totaling 84 km², which includes most of the more important uranium occurrences and the eastern contact zone of the Albala granite.

Geology

The Albala pluton extends for some 25 km and is up to 16 km wide. It has an oval shape, elongated in a NNW-SSE direction. It is essentially a late Hercynian two-mica granite that is considered to be concentrically-zoned. A series of different granitic facies have been recognised:

1) muscovitic, fine to medium-grain two-mica granite
2) biotitic, fine to medium-grain two-mica granite
3) biotitic, coarse-grain granite with very little muscovite.

The first two facies are the more evolved, and are regarded as fertile for uranium as they include disseminated uraninite as an accessory mineral, as well as having elevated uranium background values.

There are an important set of late Hercynian fractures that have a NNE-SSW direction.

Uranium Occurrences

Much of the uranium mineralisation located in the Albala granite is controlled by late Hercynian vertical to near-vertical faults that trend NNE-SSW. It generally consists of pitchblende, coffinite, other black oxides, as well as various iron sulphides (pyrite, marcasite and melnicovite) and vein gangue minerals of quartz, jasper and apatite.

The numerous uranium occurrences include, Los Ratones, La Carretona, La Perdiz, La Dehesilla, La Dehesa del Medico, El Peñascal and Casa del Gallo.

Los Ratones was exploited as a small granite-hosted, vein-type, underground mine by the JEN between 1959 and 1975. It was mined to a depth of 160m, and worked along strike for 375m. A total of 125,000 tonnes of ore were extracted grading 0.227% U₃O₈.

The principal uranium mineral is massive pitchblende associated with iron sulphides in quartz veins. There was also spherulitic pitchblende and various forms of secondary black oxides. Other uranium minerals present include phophouranilite, autunite, saaleite and torbenite.

La Carretona was a small underground vein mine that was exploited by JEN between 1959 and 1964 (CISA 1991). It consists of a series of mineralised quartz veinlets and breccias that occur in a subvertical NNE-SSW trending zone, some 0.8 to 2.3 metres wide.

Minor trial mining was carried out at Las Perdizes (1955-1960), La Dehesilla (1955-1967), El Penascal (1965/6), La Dehesa del Medico (1966/7) as well as Casa del Gallo (CISA 1991).

Casa del Gallo is a mineralised, near-vertical, NNE-SSW trending quartz-apatite vein.

Berkeley Resources Ltd.
Level 9, BGC Centre, 28 The Esplanade Perth,
Western Australia 6000