Ann: Operations and Guidance Update, page-49

(For you @prhb. The Reply feature isn't working (again).)

"Mincor's announcement does not say that BHP will not accept off specification product - it says that BHP will not allow the offtake contract to be altered."

Yes, but that's only part of it. The announcement also goes on to say:

"Mincor will continue to deliver on-specification ore to BHP and is conducting work to improve orebody knowledge to enable optimisation of its forward mine plan to consistently deliver on-specification product. Mincor will stockpile any ore that BHP indicates will not be accepted due to product specification requirements, allowing for blending with other Mincor ore sources at a subsequent date." (Emphasis added.)

For me, that's an implicit acknowledgement by MCR that BHP is now taking a much harder line with respect to off-spec product, giving rise to the disclosure around stockpiling an undisclosed amount of off-spec ore moving forward.
In fairness, does that equate to a strict absolute rejection of any and all off-spec ore, or only the stuff that is materially outside spec? Dunno, but it's clear the MCR Board knew this development was of material enough importance to disseminate it to the market within 24 hours of receiving the notification from BHP.

The absence of any more granular information is concerning and will stoke fears of potentially greater problems that have not yet been volunteered. There's likely to be more news flow, but there's an open question on whether it will contain much in the way of required meat.

The independent expert's report that the Board will eventually release, once commissioned and completed, should make for interesting reading. It will hopefully contain a much better picture of what's going on. That said, there's no getting around the unfortunate fact that today's announcement will most certainly have a bearing on the near-term valuation outcomes in that report and the Board's subsequent recommendation.