GOLD DEPOSITS. 515 



considerable amount of gold ore is said to have been taken. The tunnel by 

 which it was opened also cut a body of carbonate ore, which at that time 

 was not considered worth extracting. 



These deposits, together with that of the Colorado Prince mine, would 

 seem at first glance to be of different character, and perhaps of different 

 origin and manner of formation, from the normal carbonate deposit of the 

 Leadville region, and more in the nature of the ordinary fissure vein. The 

 somewhat limited study which it has been possible to make of them tends to 

 show, however, that the process of ore deposition was essentially the same 

 in both cases. There is no evidence of any pre-existing cavity which was 

 filled by foreign gangue material ; but the ore currents, following in this case 

 a fracture or jointing plane, instead of a stratification plane, deposited grad- 

 ually their load of metallic sulphides by a chemical interchange with the 

 material of the rock through which they passed. Gold seems to have been 

 principally deposited in the more acidic or silicious rocks and silver in the 

 calcareous or basic ones. This preference is not confined to the Leadville 

 region, but is seen in other mining districts. Its reason, however, is not yet 

 satisfactorily explained from a chemical standpoint. 



As regards their relative age, the little evidence that can be obtained 

 seems to indicate that the carbonate deposits are older than the gold veins 

 under consideration, since the former must have been originally deposited 

 before the folding and faulting took place ; whereas, if the assumption that 

 the latter occupy fault planes be correct, it is probable that they were formed 

 subsequently to this period. 



PLACER DEPOSITS. 



It is worthy of note that California gulch has furnished almost all the 

 placer gold which made this region known long before its wealth in silver 

 was even suspected, while Iowa and Evans gulches, adjoining it on either 

 side, which are carved out of the same series of rocks and are both larger 

 and contain more detrital material, have thus far yielded little or no return 

 to the placer miner. The question naturally arises, therefore, why should 

 the smaller gulch contain, as it did, exceptionally rich gravels and its neigh- 

 bors be practically barren 1 Although placer mining had been virtually 

 abandoned before this investigation was undertaken and these deposits no 



