Early-day Leadville sprawled among its mine dumps at an elevation of 10,200 feet. The Sawatch Range, in the background, contained many smaller mining communities, now deserted. Mt. Massive, the state’s second highest peak, forms the crest of the continental divide here. (State Historical Society of Colorado photo)
In 1875 a smelter was erected a few miles downstream from Oro to process cerussite—silver-rich lead carbonate—that occurred in the [placer] sands. For years this mineral had been considered a nuisance because, being much heavier than sand, it tended to separate out with the gold. The new town of Leadville sprang up near the smelter and shortly afterward more [lode] deposits were discovered south of the placer workings. From $63,000 in 1875, production climbed to $2,500,000 in 1878 and more than $15,000,000 in the peak year of 1882.
Geologically, the ores of this district occur as Tertiary replacements and [veins] in Ordovician, Devonian, and Mississippian limestones. The “Blue” or Leadville Limestone, of Mississippian age, contains the richest ore. Ore deposits were formed after the limestones had been faulted and cracked extensively by mountain-building movements; the ores themselves probably crystallized from molten or gaseous materials involved in related igneous intrusions. River gravels and glacial debris mask the true nature of the [lode] deposits, but studies in the mines show that the [fault] systems along which ores are deposited trend north or north-northeast.
The Leadville district is now experiencing its third mining boom as a newly recognized lead-zinc orebody is being developed. Production is expected to reach 700 tons of ore per day by 1971. Total production of gold, silver, lead, zinc, and copper in the district has reached $500,000,000.
Breckenridge
Breckenridge was also discovered in 1859, with [placer] gold the first attraction. The placers gave out in 1862 after about $3,000,000 in gold had been recovered. Earliest attempts to mine the rich silver and lead [veins] of the district were in 1869.
As at Leadville, the [sedimentary rocks] of the area were intruded by granitic masses in Tertiary time, but here the sedimentary rocks are mostly Pennsylvanian sandstones and shales. These rocks were badly faulted and broken during the intrusion, and the ores were deposited as the granitic material cooled. The [lode] deposits occur mostly in small [veins] well hidden by surface sands and gravels. Some of the veins yielded exceptionally beautiful crystallized wire and flake gold, specimens of which are on display at the Colorado School of Mines library in Golden and in the Denver Museum of Natural History.
Dredging for alluvial gold was attempted in 1898 in the Breckenridge district, but this method of extracting gold was not successful until 1905. A number of dredges operated between 1910 and 1925. These floating behemoths shovel up gold-bearing gravels from the bottom and one side of the pond on which they float, sort out the gold in giant sluiceboxes, and spew out the leftover gravels in great arc-shaped heaps that can be seen near Breckenridge and Fairplay and in a number of other valleys in Colorado. They depend for their operation on a plentiful supply of water and a shallow water table, but they can sift through quantities of gravel at relatively low cost. All told, about $7,000,000 in gold has been dredged from this district.
Fairplay
