Since NWE provided a Top 20 for NWEOB as at 26th Nov (and MIN wasn't in the Top 20 with the no.20 holding 7m options), there has been minimal trading in options - only 54m NWEOB traded up to yesterday, so relatively not much.
In any event, MIN would not need to disclose holding options to the ASX, only if/when they exercised the options to heads.