South Africa's Gold Fields Ltd. and Silver Standard Resources Inc. have made three joint, unsolicited bids for Kirkland Lake Gold and recently sweetened their offer to about $1.4 billion, three sources familiar with the process said. The latest bid has also been rebuffed, said the sources, who requested anonymity as the issue is confidential. The names of the bidders have not been previously disclosed.

Kirkland Lake confirmed the rumours Friday afternoon..

The latest offer for Kirkland Lake represented a premium of more than 50 percent of its value on Thursday. Its shares, which were trading at $7.42 just ahead of the news, jumped as much as 8 per cent to hit $8.17 before being halted on the Toronto Stock Exchange.

If Gold Fields and Silver Standard succeed in their bid, it would scupper Kirkland Lake's planned acquisition of miner Newmarket Gold for about C$1 billion in stock.

Newmarket could not immediately be reached for comment. Gold Fields and Silver Standard both said they did not comment on market speculation.

In an Oct. 28 shareholders circular filing to discuss that merger, Kirkland Lake said it received two bids without naming the bidders.

Shareholders have a Nov. 23 deadline to vote on Kirkland Lake's bid to buy Newmarket.

Kirkland Lake is a midsized producer operating four gold mines and two mills in a bullion-rich belt of northeastern Ontario.

With its high-grade production and reserves located in a safe, mining-friendly jurisdiction, Kirkland Lake's appeal is bolstered by a scarcity of growth opportunities in the gold sector. It also has more than $200 million of cash and equivalents on hand.

Gold Fields and Vancouver-based Silver Standard's second bid for Kirkland, submitted in late October, valued the company at roughly $1.3 billion, two of the sources said. Kirkland's market capitalization as of Thursday was about $922 million.

Kirkland Lake said in the Oct. 28 circular that both the bids, comprised of cash and stock, were not financially superior to the proposed combination with Newmarket.

The sources said it is possible new bidders may enter the fray, noting companies such as Yamana Gold Inc. and Hecla Mining Co. have assets in the area where Kirkland Lake operates.

Investor advisory firms ISS and Glass Lewis have recommended to shareholders of Kirkland Lake and Newmarket that they vote for the deal.

"There's not a lot of synergy between the two companies, but I think there's a bigger picture that maybe some people are missing," said Joe Foster, fund manager at Van Eck, the biggest shareholder of Kirkland Lake and second-biggest at Newmarket.

"What they're doing is creating a niche company: a high-grade underground miner, and that takes a certain skill set."

Luxor, Newmarket's third-biggest shareholder, said it also supports the deal with Kirkland.

Kirkland Lake ran a strategic review in 2014 that did not result in partnerships or acquisitions.