Abstract

A number of highly metamorphosed mafic-ultramafic complexes crop out in the core of the Hercynian orogen on northwest Iberia. Near Santiago de Compostela, disseminated Cu-Fe sulfides are being mined at Arinteiro (11 million tons, 0.67% Cu) and Bama (20 million tons, 0.5-0.6% Cu) and massive Cu-Fe sulfides at Fornas ( approximately 1 million tons, 1-2% Cu). A smaller massive sulfide at Manoca has been worked out. The complexes are Paleozoic, lie in thrust contact with Silurian melanges, and are intruded by Carboniferous granitoids. The petro-chemistry of the mafic rocks indicates that they are mid-ocean ridge basalts. The complexes are interpreted as relicts of an ophiolite. The mineralizations have the same metamorphic and structural history as their host rocks. They are found in areas of garnetiferous amphibolite in which bands of unusual mineralogy and chemistry are also prevalent. The garnetiferous amphibolites have significantly higher Mn contents than those with no garnet. The mineralizations are interpreted as volcanogenic exhalative massive sulfides and stockwork-disseminated sulfides. The bands of unusual mineralogy and chemistry, and even normal amphibolites, have high Cu values close to mineralization. These interpretations and data allow development of an exploration method involving preselection of suitable ground in which to pursue lithogeo-chemical prospecting.

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