COMPOSITION OP ORES. 547 



Iron and manganese might be more properly considered gangue mate- 

 rials. They are mainly in the form of hydrated sesquioxide and protoxide, 

 respectively. A little protoxide of the former and jjeroxide of the latter ore 

 was found. The foi'mer may be combined as basic sulphate, which, as will 

 be seen later, sometimes forms considerable bodies. The latter is probably 

 anhydrous, as pyrolusite is frequently distinguishable in actual crystals and 

 sometimes forms considerable ore masses. Although no actual pyrite was 

 observed in the Leadville deposits, there is little doubt that iron existed in 

 this form in the original deposits. With regard to the original form of 

 manganese there is more uncertainty, as- the sulphides of this metal are 

 relatively rare. It sometimes occurs as carbonate, in association with sul- 

 phides of other metals, losing its carbonic acid when they are oxidized. 

 It is so common an associate of iron in oxidized ores and so seldom noticed 

 in unaltered sulphides that it might be thought to have been in part brought 

 in as oxide during secondary alteration. It is possible that some of the 

 iron in the ores may be combined with silica as silicate and with arsenic as 

 ai'seniate. These were not absolutely proved to exist, as it was not con- 

 sidered of sufficient importance to give the time necessary for the tests. 



Zinc occurs in the above ores in very small proportion, and probably 

 in the form of silicate (calamine), since this is the only mineral of zinc that 

 has been observed in the Leadville deposits. It is rarely visible, and gen- 

 erally forms fine, needle-like, silky white crystals, lining drusy cavities and 

 cracks or joints in the vein material and limestone. There is little doubt 

 that it originally occurred as zinc blende, and, from analogy with the Ten- 

 Mile deposits, it may be presumed that it formed a much larger proportion 

 of the deposit in its original form than it does now. The much greater 

 solubility of its sulphate than that of the other metals would account for 

 its more thorough I'emoval by surface waters. 



Of other metals cobalt is the only one not already mentioned that 

 is detected by the above analysis. In addition to this, copper, bismuth, 

 molybdenum, and vanadium have been locally observed in mineral combi- 

 nation, and Mr. Guyard claims to have detected nickel, tin, indium, sele- 

 nium, tellurium, and cadmium in the furnace products. 



