Ann: Coburn Project Commissioning of WCP Advancing Rapidly, page-96

As an overview, coming from an eng'r perspective, I have been truly astonished about the whole overburden topic, with the disparate thoughts seasoned professionals have around it. Because it is clearly extremely important for mine productivity and yield efficiency, and they need to identify the least cost way of doing it effectively, at scale. Probably, it is fine to make the following public domain points; go looking for the evidence / join the dots as you wish:

Starting with the obvious, the bulk task is to remove the (typically low volume of) topsoil to a safe place for reuse. Then to remove over-burden sufficient to get at the ore underneath and put it back into the ore's hole once finished. These are typically deep seams that go for long distances. At the very least, overburden needs to be pushed around to the void behind where mining is currently going on, and having a deep seam makes that quite the task.

There is a slight complication in that these are (usually) not layered deposits that change colour / nature when you are into 'the good stuff'. So where the ore starts and finishes is determined by drilling / geo work, then administered by survey / GPS. You can't just look at a mine and know where you are, but this aspect is only a potential efficiency robber, and manageable. But you can't mess up the overburden either and mix it in, or recovery rates plummet.

Doing the maths on costs to dozer push the volumes involved gets scary-big numbers. But one must have an executable mine plan, so this cost has to be determined for real activities that will actually work, and that goes into the macro financial models.

Moving to a blend of public domain and discoverable history:

In the early Gunson days we provided an offer for a 3,000 t/hr 90m tracked radial stacker and a pair of grass-hopper feed conveyors. Whilst they loved it, on overburden efficiency issues, they decided to pump it, figuring it was an extra bore to greatly reduce the costs to move overburden; I think topsoil was still pushed.

This "pump the overburden" thing stayed in the earlier DFS/s, as did tracked DMU's. Which I haven't bothered right now to go and find the references as this was critical to my interests and I absolutely remember posting here about an STA update that moved away from pumped overburden, with no explanation of the changed strategy or impact on costs. Which I would only have done if the docs made it plain.

I am not saying, or even suggesting, there is a smoking gun here. Just that this is a really critical area to get right, which is widely understood, and EVERY alluvial ore miner should be held to account to demonstrate they have a solid grip on these non-value adding activities, with viable processes to properly achieve the result and control costs.