Northern Star Resources formally rejected an initial takeover proposal from South Africa’s Gold Fields, saying the bid materially undervalued the company and was highly opportunistic. The latest report valued Northern Star’s equity at about US$27.2 billion. Northern Star is also facing mounting pressure from activist investor Elliott Investment Management for sweeping changes. Earlier details valued the shares-and-cash proposal at A$38.7 billion, a 22% premium to Northern Star’s Sept. 11 closing price, while Northern Star shares rose more than 9% intraday on Monday after the rejection. The board unanimously rejected the bid.