Stillwater Mining has unveiled plans for a new commemorative palladium coin designed to mark the exploits of explorers Meriwether Lewis and William Clark.

Stillwater chief Frank McAllister revealed that the firm had commissioned a 'Lewis and Clark coin', which depicts the two men on one side and a bison as an emblem of Montana on the other.

Lewis and Clark embarked upon a voyage of discovery in 1805, heading west of the Missouri to the Northwest Passage, a water route linking the Atlantic and Pacific Oceans.

Under arduous conditions the men charted large swathes of the nascent United States, following a request from President Thomas Jefferson who wanted the men to begin exploring the newly purchased Louisiana Territory.

Mr McAllister said that whilst seeking to find a suitable promotion for Stillwater and its primary offering - palladium - he came across an account of the journey made by Lewis and Clark in Stephen Ambrose's "Undaunted Courage".

In particular the Stillwater chief was impressed by the Corps of Discovery's travels through Montana: "They spent more time in Montana than any other state."

"Furthermore, Clark probably went right across our property (the Columbus smelter) when he travelled along the river," he told the Billings Gazette.

Coincidentally, at the same time - 1803 - palladium was discovered as a metal for the first time.

Mr McAllister then took the project to Northwest Territorial Mint who helped fashion the coin, which comes in a range of sizes and in a special presentation pack.