If it is 'cheaper' for them to buy shares on-market (e.g. they are looking to increase their offer conditions to get more onboard) then buying on market might actually be a cheaper option to increase their holdings. They can therefore hedge their bets either way by keeping the offer open for months and if the MIN share price goes down then again they can buy cheap off market.
This could go on for a long while.
The only thing that is against them in this, is the forward drilling results which would create a situation whereby they would need to increase their offer price for the remaining shareholders.
EDIT: and those who had already taken up the offer..
