ECONOMIC GEOLOGY OF THE BAGUIO DISTRICT. 439 



„ ... . ' Parts in a 



Constituent. million. 



Silica (SiOJ 40.9 



Sulphuric acid radicle SO4 348.6 



Bicarbonic acid radicle HCO, 21.3 



Carbonic acid radicle Nil. 



Phosphoric acid radicle Trace. 



Chlorine 588.0 



Iron and aluminum Trace. 



Manganese Nil. 



Calcium 134.0 



Magnesium Trace. 



Potassium Trace. 



Sodium (Na) 388.2 



Free CO^ 2.2 



ORIGIN OF THE ORE VEINS AND DEPOSITS. 



Any discussion of the origin of the ore deposits in this region may seem to 

 many to consist largely of theory and speculation. However, we believe it can be 

 shown that many facts are known about them and that a broad discussion of 

 these facts will reveal some very practical conclusions. As no mine in the 

 district has gone below water level, the reason for the frequent use of the word 

 "probable" will be understood. Given certain conditions and knowing the results 

 arising from those conditions in other parts of the world, we can in some 

 measure understand the past and conjecture as to the future. 



The following facts seem fairly well to be established in regard to the ore 

 deposits of this district: 



( 1 ) They are intimately related to igneous intrusion. 



(2) Gold is found in quartz fissure-veins, in andesitic intrusives. 



(3) It is found in ealcite veins, in andesitic intrusives, and in diorite. 



(4) The metal is encountered in contact zones between sediments and andesitic 

 intrusives, and between andesites and diorites. 



(5) Gold was deposited from ascending waters. 



(6) it was precipitated by ferrous sulphate and in one locality probably by 

 compounds of tellurium. 



(7) The gold veins in many cases carry oxides of manganese. 



(8) The gold content is as a rule less than 30 per cent free milling. 



(9) There has been considerable secondary enrichment. 



(10) The ore deposits are found in a region of great precipitation and steep 

 slopes. 



(11) The zone of oxidation is shallow. 



The principal veins in the district follow fractures in the igneous 

 intrusions and contacts with igneous intrusives, and the metallic con- 

 tents in the writer's opinion were derived originally from minute and 

 widely disseminated particles throughout the igneous rocks. Under- 

 ground water was the age»t in this work. This water was very silicious 

 and probably hot. 



This period of ore deposition was not very long ago, as is attested by 

 the presence of very recent deposits which cany appreciable gold values, 

 originating from springs and which are found now on the surface in 

 this region. A large deposit of silicious sinter has been cut through on 



