Canadian pgm firm Stillwater Mining has begun producing palladium bullion designed to commemorate the exploits of the Lewis and Clark expedition.

Stillwater chief Frank McAllister announced plans to mark the Lewis and Clark adventure earlier this year, after reading about the famous explorers who took a route through the firm's Montana region.

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.

Northwest Territorial Mint is minting and selling the palladium bullion, which is fashioned from .9995 pure palladium, with refining from Johnson Matthey.

The bullion is the only American produced palladium bullion available and is issued in the form of bars and rounds of one ounce and rounds of fractional ounces.

Each round features the Montana Buffalo in a classic design on one side and details of the assay certification on the other.

The 200-year anniversary of the Lewis and Clark journey also coincides with the discovery of palladium by William Hyde Wollaston, a noteworthy British chemist.

In 1804 he named the metal after a newly discovered asteroid called Pallas, which was derived from the Greek Goddess of wisdom.