576 



EXPLORATION GEOPHYSICS 



As shown in Figure 357 this deposit consists of a narrow outcrop of 

 silicified sandstone which varies in width from 25 to 150 feet. The outcrop 

 extends for a distance of about IV^ mile in a broad arc. The thickness of 

 the rock varies from IV^ to over 20 feet, as shown by the outcrop and core 

 drilHng. 



Fig. 357. — Location map, Fremont Butte quartzite deposit 

 (Courtesy of United States Department of the Interior, Bureau ol 

 Reclamation.) 



As in the case of similar deposits in western and central Kansas and 

 adjacent parts of Nebraska, the origin of this silicified sandstone deposit 

 is uncertain. t There is evidence, however, that the outcrops are remnants 

 of silicified portions of old braided stream channels. The sinuous course 

 of the main outcrop and of numerous lesser outcrops in the general area 

 supports this theory. The fact that the sandstone bodies as outlined by 

 drilling and resistivity studies appear to be lenticular in cross-section, with 



t J. C. Frye and A. Swineford, "Silicified Rock in the Ogallala Formation," State Geol. Sur. 

 Kans., Bull. 64, part 2, July, 1946 (Lawrence, Kans.). 



