A tailings-thickening operation is an integral part of an overall mine plan. It is therefore essential to base its design on good data. If not, it can result in wasted weeks and dollars.
A couple of years ago, a representative from a testing laboratory at an underground mine, who had examined some rock samples, called our company in to discuss problems he was having with the performance of the tailings in the paste plant. The mine had started as an open pit to extract the surface ore but was later converted to an underground operation to get at the deeper resource.
The story that emerged caused considerable embarrassment for those involved and turned on that fact that ore types differ in mines over time – common knowledge among experienced miners or geologists. To explain: Weathering causes significant changes to the characteristics of rock near the surface, creating oxidized caps.
This means that there can be significant differences between the near-surface rock, such as that which had been encountered by the open pit mine, and the deeper rock that would be removed by the underground mine.
The problem was that ore samples used in the laboratory testing had come from the near-surface open pit mine; they did not come from the depths that would be reached by the underground mine. It was the underground mine that would generate the tailings to be used in the paste plant and, eventually, for backfilling.
Because the samples used in the tests were not relevant to the rock that would be processed through the tailings plant, the whole testing program had to be scrapped and redone using tailings from the same ore type as would be encountered by the underground mine.
This problem could have been averted through consultation with experienced professionals including the mine’s operations people, the geologist, the metallurgist, or mine engineers. A mine plan arranged by year, ore type, blends and tailings generation might have pointed out the difference in current and future tailings characteristics, and suggested the proper design of the backfill plant or tailings disposal plant.
The testing of samples needs to done in a way that takes into account the operational situation because the data from those samples will be used to drive decisions.
Here are three principles to ensure that the tests and advice from the laboratory provide the basis for sound decisions on paste plant design and operation.
Many laboratory tests involving ore samples are straightforward. However, it is only through working with advisors – whether they are independent or in-house, who have experience with the operational realities of mining – that a company can gain confidence that the recommendations based on those tests will actually work out. Experience-based advice will help in designing, specifying and building a paste plant in a cost-effective way and guarantee that operations are efficient and economical.
Ask the right questions
A test is not just a test for its own sake. It is unwise to have laboratory testing of samples done in isolation from operational considerations. It is much better to make sure that the right questions get asked about the situation the mine is facing, and only then to proceed with next steps in developing a plan, which might include various types of sample testing.
Look for patterns
There are patterns to many things. Experience and observation can help point these out to avoid problems and to access available opportunities.
Mining companies and their advisers need to look for patterns in paste plant design and operation. This can include recognizing what does and does not work in the mine operation, geology and metallurgy that feed the backfill system. Through patterns and experience, lab testing can give an indication of what flow sheet options exist. This can then be followed by a screening study from which two different parameters can be tested, to see how those affect results. This leads to a final suite of testing to prove which direction is best.
This is an iterative approach that is time and money well spent – because at this point we are not tweaking $50,000 on a choice of pump, but entire flow sheets and entire large plants. The right design upfront should generate much higher payback, reduce risk and improve the environmental aspect, resulting in greater shareholder value.
Frank Palkovits, P.Eng., is president of Kovit Engineering Ltd., which provides mine backfill and tailings management, including strategic studies, consulting to detail engineering services, plant design and implementation. firstname.lastname@example.org