Geochemical approaches in the discrimination of synvolcanica intrusions as a guide for volcanogenic base metal exploration: an example from the abitibi belt, Canada

摘要

Synvolcanic plutons are fundamental in the formation of volcanogenic massive sulphide deposits (VMS). Since the plutons are much larger than the actual deposits, they make a valuable guide in the location and identification of large areas for potential VMS deposits. However, in orogenic belts with a long history of magmatism, identification of target plutons is challenging. Using the Achaean Abitibi greenstone belt as an example, it is shown that synvolcanic intrusions may be identified using relatively inexpensive major element geochemistry. Two methods were developed and validated with known synvolcanic and syntectonic intrusions. The first method involves the chemical comparison of samples from the intrusion and from its surrounding volcanites. Using Al_2O_3 v. TiO_2 diagrams, it is demonstrated that synvolcanic intrusions follow the same trend as their volcanic counterpart, whereas syntectonic intrusions define a restricted discordant compositional field. The second approach uses Pearce element ratio (PER) analysis to quantify the alteration recorded by the plutons. This work has led to the identification of nine new synvolcanic plutons that constitute the first priority targets for VMS exploration.