Sorry PM, I didn't clarify what the table was with sufficient...

Sorry PM, I didn't clarify what the table was with sufficient care. The table is the results of crushing the material to 75um and then putting it through bottle roll leach tests so there is regular movement of the material. It doesn't show that the heap leach works well. It shows that there can be excellent recovery rates (97%) from laterite material if the processing method for that laterite (and other) material is to grind it down to 75um and then leach it for 48 hours. Recovery rates well into the 90%'s are to be expected from the test work underway with only one sample failing to get to 90% and that sample was incidentally at cut-off grades (0.37%) so it may never have even left site in a real-world scenario. Other elements of the test work in the report show that you get nearly identical results with much shorter leach periods. For ore other than laterite a leach period of 8-12 hours will usually generate a result that doesn't change much after that.

The industry standard gold fire assay process works for chunks of gold because within many gold mines there is a significant amount of the ore that is present in the form of coarse gold that can be liberated by gravity methods. Little nuggets of gold can however result in nuggets being unevenly distributed and more/bigger nuggets in one spot than another. Due to the weight of drill core being only in the kilogram's, the "nugget" to do this can be tiny - smaller than 1mm. Even within the same depth of the drill core you might get different results. In this case two bits of the drill core have gone different pathway's. One got an assay result to know the results of that drilling exercise. The assay test destroys that bit of material. Later on some/all of the remaining drill core is used in the met test work. If it were to contain a nugget of gold (or the assay test work contained a nugget of gold that wasn't in the later sample) you would get a different result within the calculated head grade. You should however get a similar result to the calculated head grade if assay work were done on that separate sample but only in some types of tests can you use it both way's.

The lab-based column leach tests had recovery rates of 34 to 81 percent depending on day and material in optimal lab conditions with presumably near optimal application of the NaCN (Sodium Cyanide) to the leach and no real-world hinderances like rain. I'm not sure of the industry standard expected drop in recovery rates from test work to real world application but I'd expect it to be significant. Gold with this sort of lab column leach results may have near or sub 50% gold recovery rates in a real world application. The leach test would perhaps leave over half the gold behind which is why TG6 is evaluating sending the post Diemen leach test ore to the mill for re-processing.


If on-site leach tests were successful, then there is no further trucking/toll milling because you have taken the ore, obtained what gold you can from it and the remaining material including any gold still contained is waste. If there is enough residual gold after the onsite heap leach to warrant toll milling of the material, the heap leach is arguably a failure and not worth doing (on that subset of material). You might as well have put the material that went into the heap leach onto a truck at the outset and avoid the costs of maintaining the heap leach in operation. You would also save the cost of the Sodium cyanide in the heap leach and materials to neutralise the cyanide after the leach and recovering the gold from the leach liquids.