Los Frailes
Other Names: Aznalcóllar
District: Aznalcollar ore field, Iberian Pyrite Belt
Commodities : Copper, Gold, Lead, Silver, Zinc
Aznalcóllar is located in the eastern extremity of the exposed Iberian Pyrite Belt, about 33 km NW of Seville in Andalucia Province, south-west Spain. The history of mining in the Aznalcóllar ore field extends over 5000 years, but modern pyrite mining commenced in 1870 with the opening of the (old) Aznalcóllar pit. The largest orebody in the district, Los Frailes, is located 4 km ENE of Aznalcóllar and is blind. It was discovered in 1988 by Boliden, who commenced open pit mining in 1997. It was, however, dogged by recovery problems and mining ceased after a few years following a damaging spill from the processing plant. The ore host, typical in the Iberian Pyrite Belt, is the late Devonian VS Volcanic-Sedimentary Group, which lies between Culm turbidites of Carboniferous age, and the underlying Devonian PQ Phyllite-Quartzite Group. Numerous thrust structures were produced by intense Variscan polyphase thin-skinned deformation, some of which dismember, repeat or juxtapose the orebodies. The ‘Rio Tinto style’ massive pyritic sulphide bodies sit in an envelope of black slate; they have distinct zoned footwall stockworks which are chloritically altered in the centre and sericite-quartz altered on the margins. Present, in addition to expected massive pyritite with low base metal content, are zones separately enriched in Zn-Pb and Cu. Pre-mining, the Los Frailes resource amounted to 70 Mt of massive sulphide @ 3.87% Zn, 2.21% Pb, 0.35% Cu and 63 ppm Ag. Together with other massive and stockwork sulphide orebodies in the Aznalcóllar field, this represents a cumulative past production and resource of some 130 Mt of ore.
(Written: May 2003)
