A unique $50 Panama Pacific pattern is up for grabs at Bonhams.

It's expected to sell for around $160,000-180,000 in a December 13 coins and banknotes auction in New York.

This Panama Pacific test strike is one of a kind

The lot was minted on an oversized copper planchet as a trial for the popular issue, which was released for the 1915 Panama-Pacific International Exposition in San Francisco.

The glittering event was held to commemorate the opening of the Panama Canal, one of the greatest engineering feats of the 20th century.

The auction house comments: "Extremely sharp definition is evident over both surfaces and the exceptional surfaces of this copper-red Gem radiate vibrant mint luster throughout.

"A single mentionable carbon spot at 3 o'clock on the obverse is the only mark of note."

An 1839 Gobrecht $1 "name removed" coin carries an identical estimate of $160,000-180,000.

The issue (named after its engraver Christian Gobrecht) was minted from 1836-1839 and was the first silver dollar struck since 1806.

This 1839 specimen is one of a number of restrikes that were actually produced around 20 years later.

The chief treasurer commissioned them for friends and fellow collectors, but the practice was halted when mint employees began making restrikes of other rare coins to sell.

Bonhams comments: "The 1839 Gobrecht dollar is a rarity in any grade, however, this exceptional Gem is also tied as the finest certified by PCGS."