Hong Kong-based mining investor Regent Pacific Group has formalised a $345 million bid for junior iron ore miner BC Iron.

Regent Pacific said the $3.30 offer represents a 4 per cent premium to the shares' last close at $3.17 and an 18 per cent premium to the shares' one-month volume-weighted average.

BC Iron's board unanimously recommended the offer.

"The offer from Regent Pacific is an all-time-high price for our company," said managing director Mike Young.

"BC Iron shareholders will benefit from having the opportunity to crystallize immediate value now with the certainty of cash."