Leadville mining district

The Leadville mining district, located in the Colorado Mineral Belt, was the most productive silver-mining district in the US state of Colorado. It is located immediately east of the town of Leadville. Oro City, an early Colorado gold placer mining town located about a mile east of Leadville in California Gulch, was the site of one the single richest placer gold strikes in Colorado, with estimated gold production of 120,000 to 150,000 troy ounces (4 to 5 metric tons), worth $2.5 to $3 million at the then-price of $20.67 per troy ounce.

Cumulative production through 1963 was 240 million troy ounces of silver, 3 million troy ounces of gold, 987 million tonnes of lead, 712 million tonnes of zinc, and 48 million tonnes of copper. The district also produced byproduct bismuth, and iron-manganese ore.

Gold was discovered in the area in late 1859, during the Pike's Peak Gold Rush. However the initial discovery, where California Gulch empties into the Arkansas River, was not rich enough to cause excitement. On April 26, 1860, Abe Lee made a rich discovery of placer gold in California Gulch, about a mile east of Leadville, and Oro City was founded at the new diggings. By July 1860 the gold rush was on; the town and surrounding area grew to a population of 10,000 and an estimated $2 million in gold was taken out of California Gulch and nearby Iowa Gulch by the end of the first summer. But within a few years the richest part of the placers had been exhausted and the population of Oro City dwindled to only several hundred. Many claims were consolidated, and worked by ground sluicing. A ditch was dug in 1877 to provide water for hydraulic mining, but the hydraulic mining was reported to be unsuccessful.

In 1874, gold miners at Oro City had an assay done on the heavy, black sand that had been impedeing their placer gold recovery and found that it was the lead mineral cerussite, that carried a high content of silver. Prospectors traced the cerussite to its source, and by 1876 had discovered several lode silver-lead deposits, setting off the Colorado Silver Boom. Unlike the gold which was in placer deposits, the silver was in veins in bedrock and hard rock mining was needed for recovery of the ore.

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