I recently read a Feasibility Study where the exact words in the Executive Summary were that “the metallurgy is simple and straight forward”. Sounds very reassuring to the casual reader? The question I asked if this is the case then why is the project now in trouble? The Financier said exactly “just the question we need answered”

The financier asked me to undertake Due Diligence and find out what has gone wrong as they are owed a large sum of money and things are not looking good with regards to meeting the loan repayment schedule. I subsequently went to site and found the Geologists said it was not until we removed the overburden that we realised we got the Geology wrong. The structure of the orebody is complex and we didnt put enough holes into it to pick up the metallurgical variability. spatially they had the resource right. Once we started mining the ore we knew we had a different beast to deal with. They had a JORC reserve but the metallurgy failed in sufficient drill holes.

The metallurgy Manager said the original metallurgical holes were biassed and not representative of the orebody. What the plant had to process was very different to the original metallurgy samples. The flowsheet was based on flawed samples and the plant they had was not well suited to the ore characteristics. Another issue was that the weathering was assumed to be a flat profile whereas the reality was flat in some parts and very deep where the structures were faulted. This proved very difficult for processing where in a bulk mining situation the oxide, transition and fresh ores behaved very differently.

The news became even worse with there now being seven ore types and five of them could not be mixed together. Individually they processed with their own acceptable characteristics but when you mix them together the outcomes are not optimum.The project was struggling and the plant operators could not cope with the ore changes. “It was a case of not knowing what they dont know”. The metallurgical work that had been undertaken was first class but it was missing variability sampling which would have shown up the issues. This was not done because of budget and time constraints.Apparently more diamond holes had been requested but this was reduced to meet budget and time constraints.

The metallurgy can be simple but watch out when you are up against highly disseminated complex polymetallic or double refractory ores. These ores can destroy companies if they are not aware of what they are up against. managing the geological, mining and metallurgical risks are core to project success.

Metallurgy is a specialist discipline and the sophisticated technical tools and alternate process routes means you need personnel skilled in the art. Just like you dont get a Plumber to do your tax return you need the best advice possible when developing projects.

Author: WASMA

The history of the Western Australian School of Mines Alumni (WASMA) reflects the ups and downs of the Western Australian School of Mines (WASM) and the role it has played in supporting graduates in a range of activities and events. It also describes the important role that graduates have played in ensuring WASM remains in Kalgoorlie. Learn more.