The BRGM and the textbook prospecting example of Neves Corvo in Portugal
Two complex drilling operations, in 1973 and 1977, were needed to identify these structurally complex ore masses lying at a considerable depth. Thanks to the geologists' competences and perseverance, the Neves Corvo mine opened in 1984.
This copper, zinc and tin mine located in the well-known southern Iberian pyrite belt at Neves Corvo in Portugal holds Europe's largest sulphide ore mass, which is also one of the world's largest. The total metal content in the deposit amounts to some 250 000 t of tin, 3 540 000 t of zinc, 3 460 000 t of copper and 800 000 t of lead. An initial work phase drawing on the results of previous geophysical explorations would produce the first model of the deposit, and drilling for core samples began in 1973.
Competence and perseverance of the geologists
The second sampling operation, in 1977, would drill through the mass of sulphide ore. While the deposit was discovered by gravimetric prospecting, the campaign's successful outcome was essentially due to the competence and perseverance of the geologists in combining different exploration techniques. Because of the depth of the ore masses and their structural complexity, the other geophysical methods applied were not effective. The ore is extracted from stratiform sulphide deposits enclosing a dense network of small seams, or stockwork. The Zn-Pb-Cu ore lies in single or multiple layers running through volcanic sedimentary terrain midway between the Devonian and the Carboniferous.
From the 1977 core samples, five mineralised deposits were identified at depths of 300 m to 700 m. Potential sulphide ores in the five recognised deposits amounted to more than 250 Mt of run-of-mine ore including 200 Mt across the Neves Corvo, Graça and Zambujal sites.