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My impression was the hammer mills were crushing too fine and...

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TMtrader26

372 Posts.

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31/12/19

18:10

Post #: 42180499
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Originally posted by OldeFella: ↑

I have often wondered what level of metallurgical understanding there has been in the design and operation of this operation. There is a critical need to know the particle size range over which the gold occurs; without this knowledge, how do you know that you have installed the correct processing plant? A piece of plant that is designed to recover coarse gold will not be efficient at recovering fine gold.

I've not seen a flowsheet of the mill but judging from the photos that I've seen, and from all the excitement about the hammer mills, I have the impression that there has been an almost exclusive emphasis on coarse gold. If there has been little or no thought about fine gold then this is conceivably why a lot of the gold has been disappearing. I commented months ago that I agreed with Adrian Byass when he proposed investigating the tailings. Assuming that the sampling and assaying is accurate, if you have a known grade of feed into the mill and a known weight of gold produced from the mill and there's a significant discrepancy between those numbers then, disregarding conspiracy theories, the place to look for what's missing is the tailings pile. Maybe Adrian recognized that the plant was not designed to recover fine gold and reasonably deduced that fine gold would be somewhere in the tailings dump.

"You are saying that somehow some of the tailings are many multiples of grade are higher than ANYTHING that has ever been recovered from the mill.
So its gone through the mill, the low grade gold has been extracted (gravity plant), and stragely the waste has somehow got all the nuggets of gold? They didn't fall out during processing somehow? Perhaps it was "litegold"."

Tailings are notoriously difficult to sample accurately. I have no knowledge of the geography of the tailings area but stratification of material is a common problem. Stop / start operations add to the difficulty. For a whole range of reasons, yes, it is quite conceivable that some areas of the tailings are many multiples of grade higher than what was fed into the mill. When measured across the entire tailings pile then no, of course it's impossible for the grade to be higher than the overall mill feed grade, but it's entirely feasible for some areas to be of higher grade.

No, the waste has not somehow got all the nuggets of gold, it's conceivably got all the fine gold that got washed through the mill. The mill looks to be eminently capable of recovering all the nuggets and the coarse material. I know it was said tongue-in-cheek but I think you may well be spot-on - the tailings area is now home to the "litegold". Not light in the sense that this gold somehow has a lower SG than the coarse gold or the nuggets, but light in the sense that it has a lower mass than the coarse gold. There are techniques for separating high mass gold from the gangue and completely different techniques for separating low mass gold from the gangue. Does Cascavel have both?

The occurrence of high grade areas within the tailings is somewhat analogous to the occurrences of heavy mineral sands on our east and west coasts. The original host rock would have had extremely low concentrations of each of the component minerals but once the material was washed down to the coast (equivalent to the tailings pipeline from the mill) the wave action concentrated the mineral to produce high grade areas (as can happen on a tails dump). Most of our beaches (most of the tailings dump) have negligible heavy mineral, but under the right conditions there are areas of relatively high grade concentrate.

No conspiracy theories, no suggestions of malpractice - just basic metallurgy.

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My impression was the hammer mills were crushing too fine and shouldn't have been used. Any off the experts care to comment.

OGX Price at posting: 0.3¢ Sentiment: Hold Disclosure: Held
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