MANGANESE IN GOLD DEPOSITS 39 



fore will probably prove extensive, or represents the result of 

 concentration under more deeply seated conditions after the 

 manner indicated above. This discrimination may be easy in 

 the sulphide zone, where the fractures with rich manganiferous 

 ore are clearly shown; but in the oxidized zone one must rely 

 upon the shape and distribution of the richer portions. If they 

 are related to cracks in the mass of the oxidized ore, the inference 

 is warranted, in the absence of other evidence, that they are 

 residual secondary ore, and, being genetically related to the present 

 topographic surface, are limited. 



Native gold is, as already stated, the only gold mineral which 

 is deposited by cold solutions. But native gold is deposited by 

 primary processes also, and is by far the most abundant gold 

 mineral so deposited. Consequently, in distinguishing between 

 primary gold and gold deposited by cold solutions, one must rely 

 upon associated minerals. When secondary chalcocite or certain 

 secondary silver minerals are deposited, the attendant reactions 

 precipitate gold. Consequently, the richer bunches of gold ore in 

 the oxidized zone, residual from secondary ore formed under the 

 deeper-seated conditions, may carry also considerably more copper 

 and silver than the primary ore. But copper, and (unless cerargy- 

 rite is formed) silver also, are more readily leached than gold, 

 even when manganese is present. Hence, the evidence of this 

 character may have been destroyed. 



With respect to other minerals associated with the secondary 

 gold ore, we are not warranted, in the present state of our knowl- 

 edge, in drawing definite conclusions. From the nature of the 

 reactions, I think it may be possible to show that manganite, 

 Mn 2 3 • H 2 0, is, under conditions of incomplete oxidation, more 

 often associated with the rich gold in such relations than pyrolusite, 

 MnO,; for, as already observed, the lower oxide is more likely 

 to be precipitated than the higher, when secondary gold is depos- 

 ited under deep-seated conditions. But under oxidizing influences 

 the manganese oxides change their character so readily that this 

 criterion, if it has any value, is probably not applicable to ores 

 in the upper part of the oxidized zone, where they have been 

 exposed to more highly oxygenated waters for a longer time. I 



