546 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



nial or arsenical sulphides in which it commonly occurs in nature. As 

 regards the probability of its having existed in the latter combinations, it 

 is significant that in the Adelaide ore, which contains scarcely any silver, 

 only a trace of arsenic and no antimony are found; whereas both are pres- 

 ent and in appreciable quantities in the richer ores, 2 and 4. It will be 

 seen later that these substances are generally detected in the vein materials, 

 and are found in considerable quantities in the smelting products, antimony 

 being in relatively larger proportions than arsenic. It will also be seen that 

 all the vein materials and the country rocks adjoining the ore bodies contain 

 a small but persistent percentage of silver. 



Lead occurs mainly as carbonate, sometimes as sulphate, and quite 

 often in the form of chloro-phosphate. In the Little Chief ore a little 

 sulphate still exists, but no appreciable amount of pyromorphite. In the 

 Adelaide ore, on the other hand, only a trace of sulphate is found, but a 

 notable proportion of pyromorphite, while in the Waterloo ore this mineral 

 amounts to 32.07 per cent, as against 61.78 per cent, of cerussite. Analysis 

 4 shows no pyromorphite, but the evidence of many tests of ores and vein 

 materials besides those given above and the composition of smelting prod- 

 ucts, all show that this mineral is very common and widespread throughout 

 the region. The amount of carbonic acid given in Analysis 4 is notably 

 insufficient for the lime, magnesia, and oxide of lead. If it is assumed 

 that the sulphur is all combined with the latter, the mixture contains only" 

 one part of anglesite to three parts of cerussite. Even this is, however, 

 opposed to the evidence of observation, for anglesite can but rarely be seen 

 in the ores, whereas cerussite is most common. 



That the lead originally occurred in the form of galena is shown by 

 the frequent occurrence of the unaltered mineral in the center of masses of 

 carbonate. A chemical test of one of these galena nodules showed that 

 between it and the carbonate was an extremely thin crust, made up mostly 

 of sulphate. It is, therefore, probable that in the alteration it passed first 

 into sulphate and then into carbonate, although the intermediate product is 

 not always distinguishable. 



In the Iron mine a considerable amount of native sulphur, associated 

 with cerussite, was found as an alteration product of galena. 



