408 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



above the Gray Porphyry consisted of remarkably pure white sand car- 

 bonate, free from admixture of clay and showing no galena. A complete 

 analysis of a specimen taken from this horizon may be found in Appendix 

 B. Those below the Gray Porphyry, whose connection with the ore body 

 in the Argentine mine was afterwards traced, consisted of carbonate of lead, 

 with iron-stained vein material, and in some cases, where the ore extended 

 down into the quartzite, of unaltered galena. 



The Adelaide No. 2 shaft found no ore at the contact of the White and 

 Gray Porphyries. It was sunk through the lower ore body, the upper por- 

 tion of the Parting Quartzite, the White Porphyry included in it, and into 

 the lower body of Parting Quartzite. 



The Terrible No. 2 shaft was sunk through Gray Porphyry, Parting 

 Quartzite, White Porphjny, and Parting Quartzite again, into the White 

 Limestone. No ore was found at the contact, and the White Limestone 

 was not replaced, as in the Ward shaft, but was a crystalline rock with some 

 decomposed iron-stained material at its upper surface, and with layers or 

 lenticular bodies of white chalcedony throughout its mass, which are char- 

 acteristic of this horizon. 



The ore occurrence in these mines is distinguished from that of the 

 majority of mines in this district by a total absence of manganese, a small 

 amount of iron oxide, a relatively low tenor in silver, and a more frequent 

 occurrence of gold, some of the fragments which occur in the quartzite being 

 comparatively rich in this metal. The occurrence of copper ore in the 

 Gray Porphyry is also exceptional, the nearest analogy being the body in 

 the Little Johnnie and Uncle Sam, on Breece Hill, ovei looking South Evans 

 gulch. 



Double Decker. — Qn the north side of Stray Horse gulch, opposite the 

 Argentine, are the two shafts of the Double Decker mine, which have 

 obtained from the Lower Quartzite a certain amount of gold ore. At this 

 point all the overlying strata have loeen removed by erosion and the Lower 

 Quartzite forms the rock surface. Both shafts have been sunk in this forma- 

 tion, and one of them has passed through it into the underlying crystalline 

 rocks of the Archean. Neither was being worked at the time of examina- 

 tion, consequently no detailed information could be obtained, nor were any 

 data as to amount or value of ore extracted available. 



