ALTERATION AND ENRICHMENT IN CALCITE-QUARTZ-MAN- 

 GANESE GOLD DEPOSITS IN THE PHILIPPINE ISLANDS 



By F. T. Eddingfield 

 (From the Division of Mines, Bureau of Science, Manila, P. I.) 



The agency of manganese in the production of secondary al- 

 teration has been discussed by W. H. Emmons. 1 He states : 2 



Since there are no data which show the effect of highly carbonated 

 waters on these reactions, I have so far as possible eliminated examples 

 of gold deposits in limestone, and the discussion is confined mainly to de- 

 posits in noncalcareous rock. 



From this statement and particularly from the discussion 

 which follows, it appears that the case, where the ore deposit 

 itself contains calcite, had not been separately considered. It 

 is my belief that the majority of cases of manganiferous gold 

 deposits which do not conform to the theories of secondary en- 

 richment advanced by Emmons are calcite-bearing veins. An 

 examination of the descriptions of the ore deposits in the last, 

 section of the article mentioned above will show that the major- 

 ity of deposits which do not show impoverishment in the upper 

 level nor enrichment near ground-water level, are calcite-bear- 

 ing. These cases will be cited later. 



Many ore deposits of the Philippine Islands are made up 

 of quartz and manganese with large amounts of calcite. Veins 

 of this character are so numerous that they may be said to rep- 

 resent an important type of Philippine deposits. Attempts have 

 been made to apply Emmons' hypothesis to these ores; but in- 

 vestigations in the laboratory and in the field seem to indicate 

 that the reactions which take place in this class of deposits are of 

 such a character as to produce entirely different results. 



These ores contain practically no copper. While I believe 

 that, if the copper content is relatively small compared with 



1 Bull. Am. Inst. Min. Eng. for 1910 (1910), No. 47, 767. 

 'Loc. cit., 772. 



125 



