Global mining giant Rio Tinto Ltd formally dangled an acquisition offer to Riversdale Mining Ltd that news reports said could reach a high of $3.78 billion.

Following its announcement of a pre-market trading halt on Tuesday, Riversdale got an official takeover offer proposal from Rio Tinto that would value the collier's market share at $16 per security, according to a news story carried by the News Ltd official site.

The bid price was still in line with Riversdale's market share price, which peaked at $16 when the mining firm announced on December 6 that a negotiation with Rio Tinto was underway for a "a possible control transaction."

That value further rose to $16.30 prior to Riversdale's announcement today that it would temporarily enter a trading halt pending the outcome of its talks with Rio Tinto.

Both entities have yet to confirm the takeover news though the likelihood of the deal's completion is not a remote one in light of Rio Tinto's ramp up efforts to push up its coal production capability to meet the growing demands of its foremost market, China.

At present, Riversdale is 24 percent co-owned by Indian firm Tata Steel and maintains a 35 percent interest in the Benga coal project located in Mozambique, which is expected to yield some 20 million tonnes per annum of coal by 2013.

The Africa-focused mining firm also operates a major coal exploration in another part of Mozambique and in South Africa, called the Zululand Anthracite project.

Once completed, Rio Tinto's acquisition of Riversdale would mark the company's first major successful merger since 2007 and would pace it in a good position to capitalise on the anticipated spikes in coal prices by next year, which is largely fuelled by China's accelerated expansion.