VHMS favourability mapping with GIS-based integration models, Chisel Lake-Anderson Lake area

Abstract

Maps showing spatial variation of volcanic-hosted massive sulphide (VHMS) potential in the Snow Lake area have been generated by combining digital data from a variety of sources. An exploration model, based on a volcanic-hosted massive sulphide deposit model, but expanded to include regional exploration data sets, provides a conceptual framework for the extraction of predictive evidence from the raw data sources. The evidence is divided into five factors: stratigraphic evidence, evidence related to available heat, alteration evidence, geophysical evidence, and geochemical evidence. Three approaches have been applied for combining spatial evidence to predict mineral potential. (1) The weights of evidence method (data-driven) is used to characterize the spatial associations between the known deposits, and to calculate weights for each predictive map layer. (2) In the fuzzy logic method, evidence is expressed in terms of fuzzy membership functions, subjectively assigned by an expert, for each predictor map. (3) Dempster-Shafer belief theory is more flexible than fuzzy logic for representing uncertainty in the data, but is somewhat restricted in the expressiveness of the combination rules. The resulting favourability maps from each method have similar patterns that show all the known deposits in highly favourable zones and a number of prospective areas that have the right combination of factors but no known deposits. The new volcanic-hosted massive sulphide discovery at Photo Lake made during summer 1994 is in a favourable zone as predicted by these models.