In 1879, prospectors searching for another Leadville were led to the Aspen area by geological maps that showed outcrops of Leadville Limestone. They found silver ore on Aspen Mountain, but ore production was small until the Denver and Rio Grande Railroad reached the town in 1887 and provided economic shipment of ore to smelters. Ore occurs in the Mississippian Leadville Limestone and the lower part of the overlying Pennsylvanian Belden Formation. Ore minerals include galena, sphalerite, and native silver. Early production was almost all silver, but after 1900, lead and zinc became economically important. Major mining operations continued until 1952. Total production was 101 million troy ounces of silver, 294 tons[vague] of lead, and 11,000 tons[vague] of zinc.