A global-scale exploration risk analysis technique to determine the best mineral belts for exploration

Abstract

The Global Zinc Project was developed by Pasminco Australia Ltd to provide a world view of zinc mineralisation and a methodology to prioritise geological provinces for exploration and the discovery of potentially economic ore deposits. The project grew in response to increasing risk from falling global discovery rates, maturing of exploration terranes in traditional areas, and the uncertainties of quantifying the risks for mineral investment in newly emergent countries. Components of the project involved the digital integration of a global mineral occurrences database, delineation of zinc provinces, ore deposit models, reverse economic studies, plate tectonic reconstructions and country risk analysis. The data were analysed in two separate modules. The Prospectivity Rating Module provides a quantitative comparison between the observed geology of a province and the mappable features of ore deposit models. It ranks the prospectivity of a province for the potential occurrence of one or more orebodies of a particular type. The Combined Rating Module incorporates the prospectivity rating with other risk factors, geological, commercial and sovereign to provide an overall rating for the mineral province. Four major questions encompass the range of risk elements: (i) is there an undiscovered and potentially economic orebody in the province; (ii) can it be found by available exploration technology; (iii) will the company get access to the ground to find it; and (iv) what is the sovereign risk? This paper focuses on methodology, with some example outputs. The methodology has the advantage of being able to compare data from many different countries, mineral provinces and deposit styles on a level playing field. It provides a template for rigorous data collection and assessment, allows for the identification of missing data, and key risk issues in each mineral province. It also provides a basis for presenting the exploration decision making process to non-technical stakeholders. An additional outcome of the Global Zinc Project was the confirmation that four classes of zinc deposits have a superior ability to yield high grade and potentially economic orebodies. These are the Broken Hill type, shale-hosted deposits, Irish-type carbonate hosted deposits and intrusion-related mantos.