THE HELLE IGNEOUS ROCK AND ASSOCIATE PORPHYRY COPPER MINERALIZATION (EASTERN BELGIUM): A SUMMARY OF THE PRESENT-DAY KNOWLEDGE
Geological Survey of Belgium, 13 Jenner str., B1000 Brussels
Abstract
ABSTRACT : This paper summarizes the mineralogical, petrological, geochronological and metallogenical data acquired at the present-day (2002) on the Helle igneous rock and the associated cupriferous mineralization. This sill-shaped intrusion surrounded by a plurihectometric aureole of spotted schists was described as tonalité in the old literature. In fact, the petrographical composition of the intrusion is variable. Diorites, monzodiorites quartz diorites, granodiorites and quartz granodiorites have been identified. Most of the rocks however correspond to quartz diorite (trondhjemite and tonalite) and to a lesser extent, to granodiorite. A geochronology study (U-Pb isotopic ratios of zircon) indicates that the magma emplacement took place between the Silurian and the lower Devonian (minimum age of emplacement : around 381 ± 16 Ma). The mineralization associated to the intrusion shows many similarities with the porphyry copper deposits. However, the small size of the intrusion and the low Cu and Mo considerably reduce its mining interest, at least in the present-day economic and technologic conditions.