The Salamon gold deposit (Leon, Spain)

Located 55 km NE of the provincial capital Leon, Salamon deposit, discovere d in 1985, is located on the southern slope of the Cantabrian Mountains, in the north of the Iberian Peninsula. The deposit is located on the Leon fau lt, which is a late-Variscan, E-W trending, deep structure extending for mo re than 100 km. The Leon fault has a complex history, and many mines and oc currences are located near it. The deposit is also close to small stocks an d dykes of igneous rocks with intermediate to basic composition to which th e mineralisation is related. The mineralisation is hosted mainly by the lim estones and bituminous shales of the Lena Group (Namurian-Westphalian). The re is also some mineralisation in other stratigraphic units of the Upper Ca rboniferous, such as the Marana Group or the Stephanian B sediments. Apart from local and regional exploration, a detailed mineralogical and met allogenic research has been carried out. The epithermal mineralisation of S alamon was developed in two phases: an early dominant and extensive stage, with very fine crystalline gold-bearing sulphides, mainly pyrite, arsenic-b earing pyrite and arsenopyrite, in a matrix of quartz-chalcedony (jasperoid ) and dolomite, and a later stage, of a larger crystal size, which occurs r eplacing the early stage or in pockets and veins, with greater mineralogica l variety. Last of all there is a stage of supergene mineralisation, a prod uct of the oxidant action of meteoric waters over the previous minerals. Th e hydrothermal alterations of the host rocks related to the orebodies are f undamentally decarbonatisation-dolomitisation, silicification and argilliti sation. The early stages of mineralisation were produced in a temperature o f 148-241 degreesC, while that in the later stages occurred at 86-123 degre esC. The early stage has been dated as 269 +/- 5 Ma, and this agrees with t he ages of the other deposits of the district, which lay between 292 and 26 3 Ma, and the igneous rocks of the Pena Prieta stock (277 +/- 1 Ma), all wh ich are of Permian age. The results of the studies carried out until now lead to the conclusion tha t Salamon is a Carlin-type gold deposit. (C) 2000 Elsevier Science B.V. All rights reserved.