The ReCYN plant at Martabe is presently under development and due for commissioning in October this year. It is understood the project risk is reduced for Martabe as they have an existing Detox plant using SMBS/Peroxide, which can be reverted to at any time.
Mt. Morgan Gold/Copper Project, Queensland, Australia.
Mt. Morgan was the largest gold and copper producer in Australia at the turn of the last century and funded the BP company. The legacy are the usual holes in the ground containing very low pH waters which are also contaminated with copper and other metals. These waters require continuous detoxification before river discharge, at a significant ongoing cost to the Queensland Government. In 2018 Carbine Resources Pty Ltd proposed a re-treatment program for the tailings that would solve the environmental problem and be economically positive. The project failed to be sufficiently commercially attractive to attract funding, partly due to excessive Royalty obligations. The final version of the flowsheet did incorporate the ReCYN process, but the rest of the flowsheet was not optimised to take full advantage of the ReCYN Plant. Consequently, the capital and operating costs were high and when combined with the excess Royalty and project purchase cost, the project was not bankable. GreenGold has re-assessed the process flowsheet and proposed a simplified version, making better use of the ReCYN process. The capital and operating costs are substantially lower, and a different Royalty arrangement has made the project look much more attractive. Several fundamental flowsheet changes are made possible by the ReCYN process, including the placing of flotation after CIL. Cyanide soluble copper has been a significant impediment in developing this project for many years. Since the last commercial scale process plant ceased operations in the district in 1971, several companies have looked at developing the project. ACH Resources Pty. Ltd. (ACH) acquired the mining leases in 2016 and have carried out a programme of infill drilling and test work to support a development case. A significant amount of attention has been focussed on the cyanide soluble copper problem as it follows much of the gold. A flotation plant was included in the initial proposed flowsheet with the CIL treatment of the float tailings and sale of the concentrate for gold and copper credits. Typically, the gold and copper are not efficiently recovered by flotation where CNsolCu is present in the ore, and substantial CNsolCu reports to the float tail, affecting cyanide consumption and detox cost. The copper concentrate grade is also not always at a saleable level. The copper is not of a high enough grade to provide any substantial revenue benefit and therefore becomes a nuisance component. The copper represents less than 10% of the revenue under the flotation scenario and even less of the net value but consumes a large portion of the time and effort. ACH is now considering a revised flowsheet that excludes the flotation step. The ore is simply cyanide leached for gold and copper dissolution, gold adsorbed onto carbon and the tailings treated through the ReCYN process for cyanide and copper recovery. The high copper levels produced in the leach are kept off the carbon by using high Free cyanide levels. This is made possible because of the cyanide recovery process and ensures maximum gold and copper dissolution. The ReCYN plant tailings can be treated through a flotation plant if it is economically justified. Following the leach, where a substantial quantity of copper is removed, flotation may not be economically feasible. Gold recovery in the leach is very high (+95%), and there is little gold value in the concentrate. The revised flowsheet has a much-reduced capital and operating cost and focusses on the gold, where the majority of the value is. The above is not an exhaustive review of the flowsheet changes but demonstrates the basic improvement allowed by the ReCYN Process. The project is presently at the DFS stage. Ravensthorpe Gold Copper Project, Western Australia.
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