CSA Global Principal Consultant-Geology, Rob Mackie is looking forward to meeting you when he presents his co-authored paper, “A new simplified multivariate approach to defining geochemical exploration targets from regional stream sediment data” at Exploration 2017 between 21-25 October in Toronto, Canada.
The theme of this decennial conference is “Integrating the Geosciences – the Challenge of Discovery” – a topic that looks towards future mineral exploration challenges and the next wave of discoveries as commodities markets rebound to fulfil their medium and long term potential. In this environment, looking back helps us to look forward and we invite you to join us for a unique learning exchange and interaction with the top professionals in their fields – working together for an integrated future of discovery.
The interpretation of stream sediment data for mineral exploration is complicated by the influence of bedrock lithology, the effects of scavenging by secondary Fe and Mn hydroxides, clays and organic matter, and by dilution dependent on the size of the catchment area draining through the sample site. A number of ways have been proposed in the literature to correct for the effects of background variations in lithology, but most are driven by a knowledge of the bedrock geology that may not always be available in reconnaissance exploration programs. We present a new approach for correcting for lithological and scavenging influences that is data-driven. Lithological controls on stream sediment geochemical data are identified by interpreting the results of principal component analysis. Values for elements strongly controlled by lithology are corrected by regression against the relevant component(s). Positive residuals represent elevated geochemical concentrations above what is defined by background bedrock geology. These positive residuals represent samples worthy of further investigation and allow regional data sets to be gridded to reveal trends in elevated metal concentrations above background. The residuals are incorporated in weighted sums models which define geochemical indices using element associations typical for a given mineral deposit type. These models are refined through validation against known mineral occurrences and then weighted by catchment area to define anomalous catchments for follow-up investigation. The selected catchments include not only those that have anomalous raw element values, but also highlight areas with more subtle raw data responses that may have been overlooked by previous exploration campaigns. Use of the approach is illustrated through selected examples of high quality geochemical analyses from British Columbia and Yukon, and the results compared to other methods, including levelling of stream sediment data based on dominant catchment lithology, an estimated background value for catchments based on proportions of different lithologies within the catchment, and the presence or absence of particular lithologies in each catchment.
ABOUT THE AUTHORS
MSc, BSc (Geology), P.Geo
Rob is a professional geologist with more than 10 years’ experience in the mineral exploration industry with a focus on Ni-Cu-PGE sulphide and gold exploration. Through his involvement in numerous reconnaissance and early-stage drilling programs, Rob has gained significant experience in a full range of technical and managerial aspects of exploration including data compilation, targeting, design and management of field campaigns, bedrock mapping, core logging, mentoring and reporting. He has a strong background in the interpretation of surficial media and rock geochemistry, and is an advocate of team-based targeting studies involving the integration of geological, geochemical, geophysical data.
BSc (Hons) Geology, MSc, PhD, Grad Diploma
Dennis has more than 30 years’ experience in applied geochemistry in a wide range of environments, in both the minerals and the petroleum industries, and as an academic and in geological surveys. For the last 10 years he has been involved as a consultant in the development of geochemical exploration programs for precious and base metals exploration in Australia, North America, South America and Africa. He is also active in the preparation of technical reports, reviews of quality control data and in the development of new sampling techniques.