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| Ore zones in black |
As usual, the prospectors in the Leadville area were seeking gold, and the exploitation of lead was a later development.
The ore is related to igneous intrusions that forced their way into the limestone, forming sills, which are igneous bodies that are parallel, or concordant, with bedding planes in sedimentary rocks. The molten material came in along the weak zones that bedding planes created. The lead was most likely deposited by hot waters associated with the magmas. The water dissolved parts of the limestone, and the ore minerals, such as galena, lead sulfide, were deposited in the fissures and cavities that had been dissolved. The magmas are of Tertiary age, so the ores were deposited around 300 million years after the limestone formed during the Mississippian.
Zinc and silver are often associated with lead deposits, and the total cumulative production at Leadville, Colorado, includes more than 240 million ounces of silver, making Leadville more famous for silver than for lead. The district also produced more than 700 million tons of zinc, and almost a billion tons of lead.
The Leadville Limestone in Utah was eroded and dissolved by a period of karst formation, and the resulting porosity makes the Leadville a target for oil and gas exploration in Utah.
—Richard I. Gibson
Leadville history
Cross section from Argall, in Ries (1925). Public domain.
Very interesting post for me. I once did surveys for the rare Leadville milkvetch in that high limestone country. It's called Astragalus molybdenus so I suspect there are molybdenum mines there too. I guess it was (appropriately) called A. plumbeus originally, but that name was used earlier for another milkvetch, so the Leadville one was rechristened molybdenus. It's a place I want to go back to now that I'm much more into "plants and rocks"
ReplyDeleteVery cool - thanks for the comment. Leadville is just a few miles down the road from Climax, at Fremont Pass - and Climax is among the largest molybdenum deposits in the world. I don't know that moly was an important byproduct at Leadville, but it might have been.
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