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Stockpiles Sampling, Modeling and Reconciling (7 replies)

Alan Carter
8 months ago
Alan Carter 8 months ago

I've read some comments in other debates on stockpile sampling, modelling and reconciling but here is my question:

How do you manage very large, old, buried stockpiles (up to millions of tons, dumped years to decades ago, buried a couple meters down) for which you have some historical production records and sufficient confidence that most of the ore grades are above the current cut off grade?

Do you consider is worth to drill the stock? What has been your experience?
How can you build a reliable stockpile model for grades and tons?
Has anybody built one? If yes, have you done stockpile to plant reconciliation?

8 months ago
Standartenfurer 8 months ago

Many questions to be answered, e.g.:

How well were stockpile records kept?
Do any people remain who were part of stockpiling along the way?
What are recovery & throughput expectations?
What fraction of processing feed? Does it make sense to blend or treat separately?
Are alternative processing conditions necessary?
Have found surprises in old stockpiles, e.g., waste products co-dumped, waste and ore, etc.

Alan Carter
8 months ago
Alan Carter 8 months ago

Thanks for your comment and let's say:

The production records were kept appropriately, but are not sufficient for all the stocks.
There are a couple of guys remaining from the stockpiling period.
Throughput and recovery should behave quite similar to current conditions.
More than a half of the feed it's supposed to come from the old stocks.
Alternative processing conditions are not an option.

8 months ago
Standartenfurer 8 months ago

Can you comment on flowsheet and details of ore being processed?
So this ore is not susceptible to weathering / oxidation?
How variable was orebody?
Can you advise why particular ore was stockpiled - low grade, refractory, etc.?
Can only comment more with some details!

Marshal Meru
8 months ago
Marshal Meru 8 months ago

What you need to do also depends on what sort of reporting requirements your company is subject to. If there are no reporting requirements then it comes down to the risk profile of the company/board.

Alan Carter
8 months ago
Alan Carter 8 months ago

I can give some more information:

The ore being processed is a nickel laterite.
In my knowledge, weathering should not affect it in such short periods of time.
The orebody is highly variable vertically as well as horizontally.

8 months ago
Hauptsturm 8 months ago

A difficult and risky problem! Given that you are dealing with nickel laterites I'm assuming you are dealing with mostly clay materials that will have been mixed and irregularly layered (perhaps dumped in pushed?) in the stockpile building process, which means any spatial continuity is likely nonexistent. As such, the best you can hope for is to sample a volume using some close spaced (perhaps 10x10m grid) drill sampling (or perhaps pitting) and then take the average grade of the samples as being the best estimate of the lot. I would not attempt to drill too deeply - perhaps test a layer no thicker than 6 m in the first pass to define a batch that could reconcile with cross-belt sampling. Note however, if there are lot of cobbles and boulders in the stockpiles then this BIG problem a will likely make any drill sampling approach a total waste of time and money.

Sugar Watkins
8 months ago
Sugar Watkins 8 months ago

I would agree with you but I would ask a couple of other questions. Do you have a pre-stockpile topography? - Paper is fine - you will have to digitize it. Then you can survey it as it stands now and have a volume. As suggested you could drill it - I would suggest you consider sonic drilling as it deals better with unconsolidated material. You may be able to probe some holes with a nuclear density tool - depends on how the holes hold up but that may give moisture and density and so tons which would be very helpful. Or bulk sample density might work. Grade estimation is, as he points out difficult in stockpiles. If you have sampling you will want to not only look at the results but the variability so you get an idea of what to expect. Bulk samples or process test batches (even better) are a good idea to look at recovery. Sit down with the people who were there and the top map (if you have one) and ask them to describe how the dump grew over time.

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