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I-M Project History

A Legendary Mine

The Idaho-Maryland was once California’s greatest gold mine by annual production and the largest employer in Nevada County. The mine was closed in World War II so that its human resources could be used to assist in America’s victory. The mine opened for a short period after the war but was again called to sacrifice due the Bretton Woods Agreement, designed to stabilize the post war world economy and rebuild Europe. The fixed the price of gold at $35 per oz made the mining of American gold unprofitable. After nearly a century of operation and an immense contribution to the economy, through the production of 2.4 million oz of gold, the mine was closed in 1956.1

History picture 1
Eureka-Idaho-Maryland Vein (Idaho #1 Vein) An outcrop of massive white quartz was discovered in 1851 on the Eureka claim and commercial mining commenced in 1863. The vein passed into the Idaho and then the Maryland claims and each owners successfully continued mining until 1901.
From 1865-1892 the Eureka or Idaho Mine was the leading gold-producer in the United States. A total of 935,000 oz of gold at an average mill head grade of 1.12 oz per ton (38.6 gpt) was produced from the continuous Idaho #1 vein during this era.
History picture 2
Consolidation & Reopening The mine was inactive from 1902 – 1919 due to decreasing grades and lack of capital. Mining Engineer Errol Macboyle consolidated the mining claims in the area and attracted Harry Whitney Payne’s Metals Exploration Company, to finance the reopening of the mine. A major capital investment was made to dewater and refurbish the mine in 1919 and conduct underground exploration. Metals Exploration Company decided to cease exploration in 1925 not realizing they were in close proximity to a major extension of the orebody.
History picture 3
Idaho #3 Vein Discovery Errol Macboyle was able to option the mine in 1925 before it was flooded and continued exploration using tribute (lease) miners. In 1927 a major discovery was made after extending an old exploration tunnel. This discovery, the Idaho #3 vein, ultimately produced 686,000 oz of gold at an average mill head grade of 0.60 oz per ton gold (20.4 gpt) . The income from this mining allowed the rapid expansion of the mine.
History picture 4
Idaho-Maryland Reins By 1938 the Idaho-Maryland Mine was the second largest gold mine in the entire USA by annual production, exceeded only by the mighty Homestake Mine. In 1940 and 1941 the mine production averaged 920 tons per day with a mill head grade of 0.38 oz per ton (12.9 gpt) and 121,000 oz of gold production per year.
History picture 5
War Time Closure In 1942 all US gold mines were ordered to close so that their human resources could be used for base metal mining to help win the war.
A new headframe and hoist was constructed, just before closure, in order to accommodate the planned 2x increase in production and a depth of 5,000 feet. (Mining at that time was at 1,600 feet depth)
The iconic concrete silo which remains onsite today was part of this expansion plan.
History picture 6
Fixed Price of Gold The mine opened for a short period after the war but was again called to sacrifice due the Bretton Woods Agreement, designed to stabilize the post war world economy and rebuild Europe. The fixed the price of gold at $35 per oz and high cost inflation made the mining of American gold unprofitable. After nearly a century of operation and an immense contribution to the economy, through the production of 2.4 million oz of gold, the mine was closed in 1956.

Download Historic Newspaper Articles

HISTORIC GOLD PRODUCTION1

Total Production

References

1) AMEC Foster Wheeler Americas Limited. Technical Report on the Idaho-Maryland Project. June 2017.

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