"It’s looking very much the WINS deposit it is.Hard to recover the Zircon through the HRTs."... I'm not really sure what you're talking about tbh... Coburn looks more like a LOSS than a WINS deposit, and though HRT helped recover some of my wife's good humour, don't know what it's got to do with zircon recovery lol.
Your point I guess is that the winnowed, dunal style sands with lighter zircon grains are more difficult to recover through via electrostatic high tension rollers than the remarkably high recoveries predicted in the perfect world of the laboratory, +/- a error level of confidence (of which STA management chose to plug in the very best figures from that confidence interval)? The evolution of zircon recoveries can be summarised in these two tables. Before Luke the magician turned up, zircon recoveries through MSP to final product was ~70%, his final DFS assumed a heroic 99.8% (incl minor contribution from trash).
As to why STA might be struggling with zircon recovery atm, I can only speculate as a geologist. One issue may be that Coburn looks like a bimodal deposit, there being 2 styles of mineral sands present (bottom, low, sheet of beach/dune strands) and the thicker, typical dunal style of sands with prominent ridge generally running down the east side of the deposit (where they are mining now).
I speculate that the lower sheet beach-dune sands deposited over the flat clay basement was probably a higher energy system (water and wind). Basically, this means larger, heavier mineral grains possibly deposited in the lower-dune than transported and winnowed over longer distances into, up and over the thick Upper-Dune unit. The Coburn zircon product grain size is D125, meaning the 'average' grain size is 125 micron. If there is a bi-modal size variation between the Lower and Upper dunal sands, then the d125 is misleading, because at times the mine will be situated in the Upper unit only, not a perfect average of the two mined at the same time. Maybe the Upper unit zircon is D100 and the Lower unit is D150...
As I've pointed out in recent posts, the new mine plan has the DMU's sitting in the thick eastern Upper Dune Unit, in an area that seems devoid of any high grade Lower Dune strands. Not just is the current pit sitting on predominantly/only the low-grade Upper Dune Unit, it is sitting on the 'back-dune' part of the Upper Dune. The action of winnowing and blowing the lighter sand grains up the fore-dune (front) and over the back also works for zircon. On average, the smaller, lighter zircon grains are more likley to be separated and transported over the back of the dune, while the heavier zircon grains are more likely to resist wind transport and thus concentrate the larger, heavier zircon grains in the fore-dune.
The possible implication of the new mine plan to only mine the thick, no overburden east Upper Unit back-dune, instead of east-west avg across deposit, is that only smaller, lighter zircon is being sent to the MSP and the MSP is struggling to recover a Premium zircon product at any sort of decent recoveries... let alone the DFS's heroic, almost unbelievable perfect recoveries
The evolution in my understanding of the Coburn having invested over recent time seems proportional to the evolution of production reality replacing Luke's fantastic DFS assumptions over time...
GLTA Mushies
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