MANGANESE IN GOLD DEPOSITS 41 



remove the valueless elements more rapidly than gold, is fully 

 treated by T. A. Rickard in his paper on the "Bonanzas in Gold 

 Veins." 1 Undoubtedly this is an important process in lodes which 

 do not contain manganese, or in manganiferous lodes in areas 

 where the waters do not contain appreciable chloride. In the oxi- 

 dized zone it is sometimes difficult to distinguish the ore which 

 has been enriched by this process from ore which has been enriched 

 lower down by the solution and precipitation of gold, and which, 

 as a result of erosion, is now nearer the surface. It cannot be 

 denied that fine gold migrates downward in suspension; but in 

 all probability this process does not operate to an important 

 extent in the deeper part of the oxidized zone. If the enrichment 

 in gold is due simply to the removal of other constituents, it is 

 important to consider the volume- and mass-relations before and 

 after enrichment, and to compare them with the present values. 

 In some cases, it can be shown that the enriched ore occupies in 

 the lode about the same space as was occupied before oxidation. 

 Let it be supposed that a pyritic gold ore has been altered to a 

 limonite gold ore, and that gold has neither been removed nor 

 added. Limonite (sp. gr. from 3.6 to 4), if it is pseudomorphic 

 after pyrite (sp. gr. from 4.95 to 5.10) and if not more cellular, 

 weighs about 75 per cent as much as the pyrite. In those speci- 

 mens which I have broken, cellular spaces occupy in general about 

 10 per cent of the volume of the pseudomorph. With no gold 

 added, the ore should not be more than twice as rich as the primary 

 ore, even if a large factor is introduced to allow for Si0 2 removed 

 and for such cellular spaces. 



Rich bunches of ore are much more common in the oxidized 

 zone than in the primary sulphides of such lodes. They are 

 present in some lodes which carry little or no manganese in the 

 gangue, and which below the water level show no deposition of 

 gold by descending solutions. Some of them are doubtless residual 

 pockets of rich ore which were richer than the main ore body when 

 deposited as sulphides, but others are doubtless ores to which gold 

 has been added in the process of oxidation near the water-table 

 by the solution and precipitation of gold in the presence of the 

 1 Trans., XXXI, 198-220 (1901). 



