Lead Deposits in the Upper Cambrian of Central Texas

The lead and zinc deposits in the Upper Cambrian rocks of central Texas are reviewed in the light of new detailed information. Included are analytical data for all deposits, detailed stratigraphic sections of the Cambrian rocks, and maps at a scale of 4 inches to the mile. Igneous rocks of Carboniferous or younger age in the area are recognized for the first time. It is concluded that a magmatic hydrothermal origin of the lead is more probable than a leaching-meteoric origin through ground water moving laterally then upward along buried knobs. The solution history of the carbonate rocks of the Llano uplift is reviewed in connection with the possibility of a ground-water origin; and new data are presented, the most important of which are the recognition for the first time of extensive solution of Precambrian marble during the Paleozoic, the finding of MarbleFalls limestone deposited in a sink at the level of the Hickory sandstone, and the recognition that the dips about the granite knobs are caused predominantly by intrastratal solution of Cap Mountain limestone.