404 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Section B, drawn approximately through the line of the Argentine 

 tunnel and at right angle to the line of strike, gives the best representation 

 of the geological structure, the lines having been determined by careful 

 measurement. Section C, on the other hand, is rather a theoretical repre- 

 sentation of what may probably be found on this line, reasoning from what 

 is observed on either side of it, there being no underground explorations on 

 its plane. 



ore deposits. Deposition of ore in this region has been extremely irreg- 

 ular, as might have been expected from the complicated nature of the 

 different intrusive bodies which have traversed the sedimentary formations. 

 The main body of rich ore thus far discovered has been, as already men- 

 tioned, at the contact of White Porphyry and Parting Quartzite. This is 

 found mainly in the Camp Bird and Pine claims, coming actually to the 

 surface as an outcrop. It is not improbable that this and the small bodies 

 found in the Adelaide mine are the replacement of isolated portions of the 

 Blue Limestone, detached from the main body by the intruding porphyry. 

 There is evidence also of considerable replacement action all along the 

 contact of the White Porphyry with the Blue Limestone, both on the basset 

 edges and on the upper surface of the latter. 



In the Adelaide mine, as shown by the developments of the Ward 

 and Adelaide shafts, the ore occurrence is extremely irregular. Lenticular 

 bodies or pockets of sand carbonate are found between the White and 

 Gray Porphyry and at the contact of the latter with the Parting Quartzite. 

 Moreover, at the bottom of the Ward shaft a considerable body of vein 

 material is said to have been opened in the lower Gray Porphyry, from 

 which some silicates of copper were obtained. At the time of visit these 

 workings were abandoned and could not be examined. The ore in general 

 is carbonate of lead, with the usual gangue of iron oxide, but here rather 

 silicious, as might be expected from the country rock. The masses of sand 

 carbonate found in the Adelaide mine are remarkably pure, and have the 

 appearance at a little distance of a white quartz sand. They contain, how- 

 ever, but little silver. A complete analysis of a specimen of one of these 

 may be found in Appendix B, Table VIII. It contains about 95 percent, of 

 carbonate of lead, with a slight admixture of pyromorphite or chloro-phos- 

 phate of lead. 



