Just read over the post, don't know how that shock emoji...

Just read over the post, don't know how that shock emoji inserted into op-cost? Too many topics jumping all over the place to be easily understood, I'll try again to be more concise from memory of the webcast.

Bruce said the oversize is highly random over drill holes, between drill holes and as seen in the pit. However, with dozer push mining down long slopes over deep sections OS does seem to even out into a more constant average. In answer to one question, he said the DMU performed better when long slopes are pushed than when trying to more selectively mine even though more OS may be present in the long slope. Basically, long slope dozer push is likely best mining method.

Aircore drill bits are ~70mm diameter, pushing down air under high pressure while spinning to break up sand and carry it to the surface cyclone for collection. It's common for weakly indurated sands to break back down into <1mm grains from drilling action, thus reporting to the sand fraction and assay sample, not as OS. Ripping indurated sand with a dozer tine might not liberate weakly indurated sand below 1mm so aggregates of >2mm sand grains are screened off as OS by the DMU. In this situation, more OS and less sand is found in the mine than was reported in the drilling assays... KMS are currently drilling with larger diameter, more gentle sonic drilling to try and better map the induration for future mine planning.

OS that assayed as liberated sand particles from, including HM, is actually indurated in the pit and lost to recovery as OS. Maybe a lot of sand is reporting to blocky chunks of indurated material, which explain stories posted of dozers spending long periods running back and forth over indurated material trying to break it up into liberated sand particles that the DMU can process and send to the wet plant and eventually for recovery to product.

With variations of induration as the mining slope advances the problem of OS ore losses will vary I'm sure. Another problem is that indurated material is harder wearing on the equipment and for various reasons slows down the volume of ore the DMU can process without higher ore losses, breakdowns or blockages. Bruce was fairly emphatic that after ~6 months the OS was reporting higher than expected, and unless the situation changed in different areas of the deposit looked like it might be a permanent issue to deal with. Hopefully much of the TB deposit did not under-report OS and they just got unlucky in the starter pits?

Currently, when operating at it's best, higher OS is limiting the DMU to sending ~75% of the expected undersize sand fraction of the ore reserve through to the WCP than expected. That's a 25% HM per tonne of ore from mine plan... all things being equal. There may be some tweaks to the DMU or more DMU capacity to make up for this and get the WCP operating at 100% of it's design feed rate, but that still means mining 30% more ore for the expected HM product (all things being equal).

All things do not appear equal though. Fortuitously, so far there is more Ilm-Zir in the volume of sands going to the wet plant than expected based on assay grades, which means more tonnes of product than expected in the 75% of undersize ore being processed. My maths says 13% more HM than predicted by assays and/or recovery through the WCP is required to turn around a 25% ore loss (ie 75% expected sand in ore) into only a 15% VHM product tonnes loss (ie 85% of expected product from DFS). 15% less product per month, if the OS under call exists through the deposit, is not great but it's a lot better than 25%.

It will take some time, and actual mining in areas covered by new sonic drilling before a more definitive call can be made on what the real losses to OS are at TB LOM. Likewise, it will take some time to see what equipment and/or mining improvements may reduce HM losses if higher than planned OS is the reality. It will also take time to access why more ilm-zir is being recovered to more product than expected, and if that is deposit wide or only a sporadic thing?

Bruce seemed confident they would get the mining rate up to nameplate, eventually to ~2.9Mt/mth as planned for the DMU. He wasn't very confident that the 25% loss of wet plant material per tonne of ore would improve to 100% of design or even close. It seems they have enough experience now to say there is and will continue to be some additional OS and wet plant sand/HM losses moving forward. Hopefully, the OS is more in low-HM seams and more HM continues reporting to product than expected per tonne of ore...

GLTAH