576 CENTRAL MINERAL REGION OF TEXAS. 



this metal may eventually be obtained in Sufficient amount to give it some im- 

 portance as an adjunct in the output of both copper and lead ores, should 

 those hereafter be profitably worked. In the Baby head district the ores are 

 of excellent quality, being largely of the class popularly known as "gray cop- 

 per," some of which is here very rich in silver. But the sparse dissemination 

 of the mineral in the quartz in most cases gives uncertain hopes of profit in 

 the mining, although it can not be said that any very comprehensive tests of 

 the ore bodies have heretofore been made. 



The copper ores of both the Baby head and Pecan Creek districts, perhaps 

 also those of Mason County, sometimes yield silver in notable and paying pro- 

 portions. Probably this occurs as tetrahedrite, freibergite, or some similar 

 mineral of the "gray copper" class, but it is usually so completely mingled 

 with malachite, azurite, bornite, chalcopyrite, etc., that it is impossible to de- 

 termine its separate mineral composition. This mode of occurrence is the 

 most promising in the region from the developments already made, for there 

 is evidence in such copper deposits as are now considered that richer and 

 more abundant supplies exist at greater depths. There has been no observa- 

 tion of any proportional agreement in the silver contents of the copper-bear- 

 ing veins. That is to say, increase in percentage of one metal does not imply 

 either increase or decrease of the other. At the same time it is true, as a very 

 general statement, that the silver ores are usually associated with copper ores 

 in these districts. Just why some of the rich copper-carrying minerals are 

 almost barren of silver in some localities, while others of the same character 

 in different situations are occasionally highly argentiferous, is an unsettled 

 question as to details. But the structural features as observed in the field 

 make it evident that the trend of the Burnetian rocks has had much to do 

 with these results. Other later trends have modified the structure in other 

 parts of the copper field, but in the limited area in which the silver ores have 

 been discovered the Burnetian expression is most apparent. This district 

 comprises a narrow tract extending from the valley of the Little Llano Creek 

 in the course north 75° west, via the head of Yoakum Hollow, the "Mexican 

 Diggings" on Babyhead Creek, and the principal former workings on Pecan 

 Creek, to near the head of Magill Creek, all in Llano County. Eastward and 

 westward from the ends of this belt the later rocks cover the Burnetian strata 

 more deeply than is consistent with the economical working of any possible 

 buried deposits of the kind, and the complications induced by subsequent dis- 

 turbances have added so much uncertainty that no hope can be held out for 

 deep shaft prospecting in those areas. There is, however, a continuation of 

 the same trend in exposures north of the Baldwin Canyon, on Cold Creek, 

 and westward nearly to Field Creek, as well as in the country intervening 

 between Magill Creek and Cold Creek. These last named outcrops are south 



