MT. MORGAN TAILINGS PROJECT Mt. Morgan in Queensland is the home of one of the longest and most important mining ventures in Australian history. The project played a part in changing world history through the enormous wealth it provided the shareholders. Unfortunately, the understanding of its environmental impact was not relevant for most of its 120-year life. A company called Heritage Minerals has taken on the task of developing the project to process the tailings and contribute to the environmental rehabilitation of the site. The site is dominated by 100Mt of acid-forming rock waste dumps and pyrite rich tailings dams surrounding a 10Mm 3 lake of acidic, metal-contaminated water. The Mt. Morgan project fluctuated between being an open cut and underground mine and from producing gold to copper and then back to gold. Process methods have covered many options, including novel chlorine leaching processes and various pyro-metallurgical circuits. Mt. Morgan is a history well worth reading for both technical and social significance. Over the last thirty years, five companies have attempted to make a feasible project from treating the remaining tailings dumps. Marginal economics caused by low metal prices, high acid levels in both the pit water and tailings, high cyanide soluble copper levels and ownership changes have contributed to companies giving up on the prospect. High soluble copper levels, up to 500g/t, and high lime consumptions of up to 40kg/t have presented challenges for the operating cost. The ReCYN III circuit is able to change the operating cost economics by recycling free and complexed cyanide and producing a high-grade copper concentrate. Gold recovery is included as part of the ReCYN III circuit. Fortunately, the stars are more aligned for Heritage Minerals with a robust gold price and access to new technology. The project owner is presently completing a Feasibility Study for a 2Mtpa tailings treatment project, that includes a ReCYN III circuit. CROSSING THE CHASM (5) The above title is taken from a book that describes the tortuous path for acceptance of new technology, not least of all in the mining industry. New technology acceptance is the challenge being faced with the ReCYN process. The ReCYN technology has the potential to replace carbon and become the third significant technology in gold recovery from cyanide circuits, a disruptive move. The economic argument is compelling, which gives the advantage to accelerate acceptance. ReCYN allows the continuing use of cyanide as a proven lixiviant, overcoming concerns of introducing new technology to replace cyanide. The benefit of improved environmental outcomes is a further incentive (6) . Often the ReCYN plant can be an add-on to an existing circuit, thereby reducing the risk of introducing new technology to ongoing gold production. ReCYN Technology is presently being evaluated for over thirty projects worldwide, including by many of the world's leading gold producers. The degree of evaluation depends on many factors often related to the corporate culture of the mining company. The Martabe Gold Project in Indonesia is the third and most significant ReCYN project for GreenGold, but many more ReCYN projects will need to be brought on-line to gain broader industry acceptance and Cross the Chasm. ACKNOWLEDGMENTS The author would like to acknowledge the consultants and mining companies referenced in the Paper for permission to use their information. The views of the author do not necessarily represent those of the referenced Companies.
REFERENCES 1. Stephen La Brooy, Fixing the Cyanide Issue – Alleviation or Replacement. ALTA 2017
ALTA 2020 Gold-PM Proceedings
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