You start to answer the question well. While it's obvious that resources exhaust over time, that's an easy answer; and the sort of thing that a smart ass analyst with little knowledge of coal geology would say..
Ive yet to delve deeply into this, mainly because the numbers presented are broad macro numbers and its difficult to get a precise answer that isn't full of opinion. Yet, I can give those opinions with the caveat that it's impossible to rate the magnitude of their influence.
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JORC Code for coal is pretty loose, sorta because it needs to be. There's a new JORC code in the pipeline, and thankfully there's talk of it including reconciliation for the first time as a requirement. This would help close the loop and hold many people accountable. This ultimately is what I'd call the biggest cause of these discrepancies being reported here at Yancoal.
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The level of skill in coal geology is severely lacking. With diversity, equity and inclusion, there has been a horrid promotion of individuals based on the colour of skin, gender, gender perception, body mass index, eye colour, hair colour. Yes, this is literally happening and has been for several decades now. I'm personally very aware that this was occurring at Rio Tinto Coal during the 2000s and still occurs across most other Tier 1s today. Most prominent at BHP. With the highly cyclical nature of the industry, this has led to a situation whereby those who are not short, fat, black, female, indigenous, transgender, etc, are removed from industry and the remaining individuals get "promoted" based on these immutable characteristics instead of merit. Again, from personal experiences, I keep coming across these over promoted individuals who are in senior positions of superintendent or principal or manager positions and they literally can't read maps, differentiate basic structures like faults/folds, and sone of them can't tell the difference between coal and mudstone after twenty years of working on a coal mine. How can we assess this failure of diversity? We can only opine about the end results, and see it in JORC notices/reports like the one we're discussing here.
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Then there are the industry practices, or lack of practice. There's sone very good people, but, their number is shrinking. Again, due to the promotion of people based on skin colour (or even perceived race (blue eye blond aboriginals?)) instead of promoting merit... because the industry does not assess based on merit, poor practices are rewarded and copied everywhere. The blind leading the blind. Reconciliation in tge JORC Code may help fix this, but, it's dependent on how hard it's pushed. Again, I know personally and professionally that when a thorough and dedicated reconciliation is done, it exposes poor practice. Provided that it's done frankly and openly.
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So yes. Back to the original point, asking the question of why has it dropped so much is incredibly important. While it gave me a chuckle to see "because we dig stuff up the numbers go down", that really was the sort of answer we'd get from a diversity hire. Perhaps all analysts should be asking how well the model reconciled against the previous 12 months of production at a minimum. In my experience, three months is as granular as it can get for the big numbers, but, at the mine level, there should be ample and open evidence of reconciliation at the block level, not strip or pit or bench, but block level. Demand full and open reconciliation. Details similar to a full JORC code report. The industry has just about lost most of the experienced players, they're getting to be 70+ years old. The new blue hair beached whale brigade at BMA should not be allowed to call themselves geologists or JORC code competent.
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Demand full, open and detailed reconciliation reports. A single table and two sentences is not enough.
(20min delay)