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
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.
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.
HISTORIC GOLD PRODUCTION1
1) AMEC Foster Wheeler Americas Limited. Technical Report on the Idaho-Maryland Project. June 2017.