The Development of Paleokarst and Other Solution Features in the Mississippian Leadville Dolomite, Central Colorado
John F. Hall, JR., 1990. "The Development of Paleokarst and Other Solution Features in the Mississippian Leadville Dolomite, Central Colorado", Carbonate-Hosted Sulfide Deposits of the Central Colorado Mineral Belt, David W. Beaty, Gary P. Landis, Tommy B. Thompson
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The Mississippian Leadville Dolomite in central Colorado hosts a large number of paleokarst and other solution features ranging in age from the Mississippian to the present. In many cases, these features provided pathways of high permeability for subsequent fluid movement. Four main episodes of dissolution have been identified.
In the early Osagean, prior to deposition of the Castle Butte Member, subaerial exposure and minor karstification of the Red Cliff Member of the Leadville Dolomite formed breccias at the surface and karst solution features in the shallow subsurface.
In the Late Mississippian, following the retreat of the sea from central Colorado, extensive karst features developed on and within the Leadville Dolomite.
Following burial of the Leadville Dolomite in the Pennsylvanian, hydrothermal solution features of various ages were created. Pennsylvanian age, migrating basinal brines and/or convecting hydrothermal fluids associated with igneous intrusive activity in the Laramide and/or mid-Tertiary may have caused the dissolution.
Finally, in the late Tertiary or early Quaternary, karstifieation was initiated as erosion exposed the Leadville Dolomite to meteoric water.
Figures & Tables
Carbonate-Hosted Sulfide Deposits of the Central Colorado Mineral Belt
The carbonate-hosted ore deposits at Leadville, Gil-man, Red Cliff, Aspen, Alma, Tincup, Kokomo, and Mount Sherman have enjoyed a long and storied production history. These orebodies, as well as dozens of smaller deposits, are all located in the central Colorado mineral belt and together constitute an important metallogenic province (Figs. 1 and 2).
Recorded metal production of the major districts in this province to date has consisted of 1,630,000 metric tons of zinc, 1,500,000 metric tons of lead, 145,000 metric tons of copper, 15,600,000 kg of silver, and 110,000 kg of gold (Table 1). For several reasons these figures represent only a portion of the metal concentrated by nature in these deposits:
1. Early production records are probably incomplete.
2. Inefficient methods were used to process much of the ore mined during the 1800s, particnlarly for zinc and copper.
3. The ores in the principal mining districts were partially removed by erosion prior to mining.
4. Significant reserves remain in the Leadville district.
In comparison to other mining districts around the world, the carbonate-hosted sulfide deposits of the central Colorado mineral belt have produced relatively low tonnages of high-grade ore (Table 2). The largest of the districts is Leadville, which to date has produced aboul 24,000,000 metric tons of polymetallic ore. By contrast, the Aspen district has produced only an estimated 4,000,000 metric tons of ore (Table 2), but that ore averaged about 1,000 g/metric ton silver. Although all of the deposits in this metallogenic province are polymetallic, the economic significance of the various metals is not equal. The ores at Gilman, Aspen, and Leadville were valuable primarily for their contained Zn-Cu-Ag, Ag-Pb, and Ag-Au-Pb-Zn, respectively (Table 2).
The first discovery of gold in Colorado was made in July 1858, in a stream draining the eastern Rocky Mountains. This led to the “Pike's Peak” gold rush of 1859, during which an estimated 50,000 people moved into the area (Blair, 1980). These so-called “Fifty-Niners” established most of the mining districts in the northeast portion of the Colorado mineral belt during the summer of 1859. By late 1859 the prospectors had penetrated the Continental Divide, and in April 1860, the placer gold deposits at Leadville were discovered.
A rush to Leadville ensued, and as a result of heavy mining pressure, the Leadville placers were essentially depleted by 1868. The much larger and more valuable carbonate replacement ores at Leadville,