A COMPARATIVE-ANALYSIS OF ENZYME LEACH AND MOBILE METAL-ION SELECTIVEEXTRACTIONS - CASE-STUDIES FROM GLACIATED TERRAIN, NORTHERN ONTARIO

The enzyme leach and MMI (mobile metal ion) selective digestions are r apidly gaining popularity in the exploration community because of thei r successful track record in non-glaciated, arid and tropical climatic regions. Few successful case studies from high-latitude, temperate re gions have been published to date. Also lacking is a comprehensive dis cussion of the constraints and limitations of these geochemical method s and how they affect the successful interpretation of selective-leach survey results in glaciated regions. This paper evaluates each method using specific examples from four case studies undertaken in the glac iated region of northern Ontario. The case studies clearly demonstrate that both the MMI and enzyme leach selective digestions provide the e xplorationist with useful information, which, when used in conjunction with other exploration tools, can assist with the identification of p otential diamond drill targets. Notwithstanding this, the techniques d o not appear to work well as 'stand alone' methods. The importance of following strict sampling protocols and obtaining high-quality observa tional information on the sampling site and media collected cannot be overstressed. It is only by filtering out the many variables that aris e in any sampling program that a sound interpretation of the data can be made. The case studies have drawn attention to some of the apparent shortfalls of the techniques. Of these, issues such as the ability to reproduce survey results from year to year and the recognition of ano malous element associations which specifically target blind mineralisa tion are probably those which require significant follow-up work. Clea rly, additional case studies are required from the glaciated regions o f the world to assist with the optimisation of geochemical response of MMI and enzyme leach selective extractions. The mechanisms responsibl e for the formation of surface geochemical anomalies over deeply burie d mineralisation are not well understood. The observed patterns of geo chemical response in surface soils and both shallow and deep ground wa ters over concealed mineralisation should assist with the development of new dispersion models. (C) 1998 Elsevier Science B.V. All rights re served.