460 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



west portions of the workings a few feet of Weber quartzite are found above 

 the ore body, sometimes in direct contact with it and again separated by a 

 slight thickness of White Porphyry; and in the extreme northwest work- 

 ings the Parting Quartzite is found beneath the ore body, between it and 

 the underlying White Porphyry, showing that here the entire thickness of 

 the original Blue Limestone horizon is represented, compressed to a thick- 

 ness of sixty to eighty feet. At the bottom of the Roberts shaft 10 feet of 

 quicksand were passed through, which probably represents the disintegrated 

 Parting Quartzite. The main west drift from the Roberts shaft on the 284- 

 foot level, which runs a little south of west, passes for the first hundred feet 

 through iron vein material containing some pay ore, then for 150 feet through 

 block (White) Porphyry, then into a second body of iron vein material, at 

 the extremity of which is some lime sand, succeeded by Parting Quartzite, 

 all dipping gently to the eastward. 1 This is evidently the continuation of 

 the ore horizon developed in Vulture No. 2, but it is noticeable that the 

 Gray Porphyry found between that shaft and Vulture No. 1 is here want- 

 ing, showing that its northern limit has been reached. The lower iron 

 body does not extend much north of this drift either, since, as shown in 

 Section A, the drift westward from Chrysolite No. 4 finds the Parting 

 Quartzite directly under the main or upper iron body. 



In this northwestern quarter of the Chrysolite ground the body of vein 

 material has averaged from sixty to eighty feet in thickness from its out- 

 crops eastward and southward. In this vein material the bodies of rich ore 

 are necessarily difficult to define, as they are simply concentrations of lead 

 and silver minerals. The whole mass contains more or less of these metals, 

 of which a certain arbitrary percentage is required to constitute pay ore. 

 The ore consists, as in other parts of the mine, mainly of carbonate of lead 

 and cWoride of silver. The discarded iron vein material, which is extracted 

 from the mine and accumulates on the dumps, constitutes a low-grade ore 

 which it will doubtless some day be found profitable to work. 



! Since the completion of field-work this drift has been pushed farther westward than indicated 

 on the map, and has passed throngh the White Limestone into the Lower Qnartzite, showing that the 

 outlines given on the map, though from somewhat meager data, are in tbe main correct and that the 

 formations basin np to the westward. This drift has also discovered a westwardly dip in the Lower 

 Qnartzite, proving further the existence of the anticline which had been assumed to exist here. 



