26 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254. 



and usually near one or both walls where the fissuring is best devel- 

 oped. The occurrence of rich ore bodies in basic dikes in the Port- 

 land (Anna Lee), Moose, Elkton, Conundrum, Pinto, and other mines 

 has tended to exaggerate the importance of these dikes in general, 

 and some have even supposed a genetic relation to exist between 

 them and the mineralization of the district. a Such an hypothesis, 

 however, loses sight of the vast amount of profitless work that has 

 been expended in the district in driving on the usually unproduc- 

 tive basaltic dikes, and the very small proportion of the known ore 

 bodies that can be shown to have any connection whatever with these 

 intrusions. That the basaltic dikes are not always readily mineralized 

 even when accompanied by fissuring is shown in the interesting case 

 of the Strong mine, where the ore occurs as mineralized granite on 

 each side of the dike, while the latter is barren. 



DEPTH OF OXIDIZED ZONE. 



At a few points, as in the Abe Lincoln and El Paso mines, tellurides 

 are found almost at the surface. It is much more common, however, 

 to find an upper zone, from 200 to 400 feet deep, in which free gold 

 prevails and which gradually changes to the zone of pure telluride 

 ores. As may be expected from the varying surface form and condi- 

 tions of drainage, there is great range in the depth attained by oxida- 

 tion. Partial oxidation extends in many mines to a depth of over 

 1,000 feet, especially along the often more or less open fissures. In 

 the Wild Horse mine the zone of complete oxidation reaches a depth 

 of 1,100 feet and then suddenly ends. In the Isabella mine partial 

 oxidation attained at least 1,200 feet, and the same applies to the Gold 

 Coin mine in Victor, although telluride ores prevail at that depth as 

 well as in many levels above. The question is chiefly one of depth of 

 ground water and of facilities for circulation of oxygen. Further 

 data bearing upon this problem may be found on page 31. 



RELATIONS OF ORE BODIES TO DEPTH. 



It is well known that the payable ores in auriferous lodes are rarely 

 equally distributed in the lode, but form tabular bodies of more or less 

 regular outline. The projections of these ore bodies on the plane of 

 the lode often appear as elongated areas with greater vertical than 

 horizontal extent. The ore bodies or shoots of Cripple Creek show 

 great similarity to those of other gold-bearing veins; their limit in 

 depth is usually as well defined as their extent in a horizontal direction. 



Of sixty pay shoots of Cripple Creek mines plotted together for 



aStevens, E. A., Basaltic zones as guides to ore deposits in the Cripple Creek district: Trans. Am. 

 Inst. Min. Eng., vol. 33, 1903, p. 686. 



