Prediction and mitigation of environmental issues at gold mines in southern New Zealand: Successes and lessons

Speaker:  Professor Dave Craw, Emeritus Professor, University of Otago, New Zealand

Abstract:  Accurate prediction of environmental issues from pre-emptive rock studies is the aim. Successes are heart-warming, but the lessons (best not to call them failures) can be most instructive, and this webinar will cover both. Southern NZ has 150 year history of gold mining, both placer and hard-rock. The biggest issue for placer mining has always been downstream suspended sediments. This issue is affected by geology and is partly predictable and manageable, but subtle features can lead to large negative effects. Revegetation after mining raises some philosophical questions: is the target a uniform restored landscape or enhanced biodiversity? Hard-rock gold mining involves predictable arsenic issues that can be controlled. However, antimony has some negative and positive surprises. Acid-base accounting is useful and accurate, but associated elevated sulphate discharges are an emerging issue that requires attention. The main conclusion is that we need to understand the whole rock mass before mining commences. This point is already well known in theory, but some of the small things that we gloss over in practice, can have significant negative consequences.

Bio:  Dave Craw is a lecturer and researcher in economic geology and environmental geology for 35 years at University of Otago,  New Zealand. His principal research topics relate to orogenic and placer gold: exploration, mining, processing and downstream environmental issues. Dave has worked closely with active mine projects to enable prediction of key environmental parameters.