Nifty's challenges lie in the mineralogy and copper distribution...

Nifty's challenges lie in the mineralogy and copper distribution within the orebody.
One particular ore type that was processed at Nifty was shales which hosted copper oxides in them. Shales are basically clays. When you apply solution to a clay it adsorbs it and prevents it from being attacked by the acid that is required to leach the copper into solution so it can be presented to the SX plant to be concentrated, purified and then electrowon into cathode. 1/3 of the oxide ore WMC and Straits were processing contained this material and in fact WMC had to stockpile this material as it couldn't process it. This ore needs to be blended with more silicious rocks (competent material) so plugging issues in the heaps don't occur.
Then once Nifty moved out of the oxide ore it went into a transitional zone- mixture of oxide and sulphides both in primary and secondary forms. Sulphuric acid alone doesn't leach sulphides and the right environment needs to be present typically a bioleach. The bugs live in the ores as you see copper leach naturally but to get the recoveries as quicky as possible there needs to be encouragement of the surrounding conditions to get the environemnt optimal for bacterial activity and this can take time and then you still look at recoveries of 60-70% at best with leach times 600 plus days. The longer the leach time, the more pad space needed to maintain production the more solution in the system the lower the grade of PLS produced even if you upgrade it the larger the SX plant needed to process the lower PLS grade. Its a vicious circle that companies get trapped in. Fortunately with Bioleaching the system is converting the sulphides present into sulphuric acid so you don't need to import as much but you still need to bring this to site in significant quanties. What people need to understand is that you can keep poring acid onto a heap but if it isn't giving up more value in copper in return there is no benefit in keeping the heap running as the acid just gets consumed by other material (gangue) and it just adds to your operating costs.
Treating the transitional material also had the challenge of native copper. This is copper metal and was basically found in two forms - sheets or crystals. When you do assaying of pulverised rocks you'll typically pick this up and it will get reported as part of the overall copper inventory but in reality in the field this material won't leach. Try pouring sulphuric acid on copper wire, it doesn't dissolve it so basically this copper remains un-leached.
Any competent rocks found at Nifty in oxide form perform well and leach economically its just there isn't enough of this material available to blend out all the other rubbish material that is present. Reprocessing the old heaps has been done a few times and is like a sugar hit. The breakout of copper inventory in the heaps as oxide and sulphide should be investigated and reported. You can bank on getting the majority of the oxide material if processed correctly circa 85 plus% but for the sulphide minerals present you'd be lucky to be getting 50% recovery from the ore that is being reprocessed as recoverable. CYM should break out the ore types and provide meaningful recoveries against each ore type as these vary depending on the mineralogy of material being processed and I doubt a universal number can be applied for all the heap leach pads at Nifty as the mineralogy of these pads varies significantly.
Will be interesting to see how the new COO explains how there is shite loads of copper still remaining to be recovered from the leach pads when in a previous life the companies he was associated with that owned the operation boasted they were able to achieve 85% recoveries admittedly this was from selected heap leach pads. Hoe this breakup is made and allocated is something that should be treated with caution, its not as easy as these guys make out... Easy option would be to pick all the ore up grind it and then leach it in tanks but the expense of grinding power and then getting the water balance right after solid liquid separation make that an unfeasible option for Nifty to consider. If people had their chance again you might have started the operation up like this which is similar to what happens at FQMs Kansanshi operation. Separate oxide and sulphide circuits operating in parallel but CAPEX costs for such processing are enormous and mining rates would have to be tripled just to keep up with plant ROM feed requirements....