TGI 4 - Intrusion Related Mineralisation Project: a synthesis

Abstract

The Targeted Geoscience Initiative 4 (TGI 4) was a 2010-15 Government of Canada research program to conduct thematic, knowledge-driven ore systems studies aimed at assisting in the discovery of future resources through more effective targeting of buried mineral deposits. Intrusion related (e.g., porphyry) deposits are the world's most important sources for Cu, Mo, W and Sn, as well as being a major contributor of Au, Ag, and PGEs. Porphyry deposits are typically large, low- to medium-grade deposits in which mineralisation is hosted within and immediately surrounding distinctive intrusive phases within larger intrusive complexes that commonly have prolonged emplacement histories. To develop more effective exploration criteria to identify and evaluate deeply buried and/or hidden fertile intrusive mineralising systems, studies into Cu-Mo/Au and W-Mo-Sn systems are aimed at answering the following questions: i) are there distinctive proximal and distal footprints for deposit types that will allow identification of, and vectoring towards hidden economically viable deposits?; and ii) what are the triggering conditions and indicators of an hydrothermal-magmatic system of size and duration sufficient to develop a large porphyry deposit? To help answer these questions studies are being undertaken at sites associated with the Triassic-Jurassic porphyry deposits of the British Columbia interior and for the array of mineralised Devonian intrusions developed in the Canadian Appalachians. A common problem facing Cordilleran and Appalachian exploration is how to detect intrusion-related mineralization through the extensive glacial sediment cover. Consequently, research activities are focussing at identifying key geochemical and mineral indicators in till near known mineralisation and their detrital dispersal down-ice. Indicators are being developed for the detection of mineralisation, but also the alteration halos and vein systems associated with mineralization, which represent much larger exploration targets than the actual economic orebody itself. Once identified in till, these indicators can be traced to their bedrock source using reconstructed ice movement vectors. Structural relationships indicate that Sn-W-Mo mineralised intrusive systems can form due to extension associated with far removed non-orthogonal accretion. Deposits within these bodies form along fluid pathways such as the intersection of high-angle syntectonic breaks. Mineral potential can also be resolved through trace element fingerprinting. Subtle compositional changes in commonly occurring minerals (i.e., biotite) and fluid inclusions provide evidence of chemical variations related to magma fertility and vectors to mineralisation.