vin, a. 2 Edding field: Calcite-quartz-manganese Gold 131 



The Eastern mine, Aroroy, Masbate, has a very wide vein 

 with large amounts of quartz, stained with iron oxide and man- 

 ganese oxide in the upper workings. In places it appears honey- 

 combed, and stained with black manganese. Very little calcite 

 is found in the upper level, but it increases with depth until 

 on the 60-meter level the vein is composed almost entirely of 

 calcite. On the 30-meter level the vein is about half calcite and 

 half quartz, and contains from 3 to 8 per cent iron pyrites. The 

 gold values are highest near the outcrop, and are found in iron- 

 and manganese-stained quartz. 



The Colorado deposit is made up of honeycombed quartz 

 stained with iron and manganese, crossed irregularly by bands 

 of hard, flinty quartz and bands of soft manganese. The band- 

 ing is very pronounced and in places is very much twisted as 

 if movement had taken place in the vein producing lines of weak- 

 ness, but generally it is parallel to the walls. The honeycombed 

 quartz has formed molds representing perfect calcite crystals 

 and cleavage, as if at one time calcite had formed the major 

 portion of the gangue. In the lowest workings some calcite has 

 been encountered. The gold values are highest near the outcrop, 

 and decrease with depth. 



In all of these examples the richest ore is at or near the surface, 

 and the values found so far appear to decrease with depth. This 

 condition would tend to indicate that no solution, or only an insig- 

 nificant amount of solution, had taken place due to the chlorine 

 reaction. All of these deposits are in regions of rugged relief 

 and heavy rainfall, so that erosion would naturally be very rapid, 

 and placer deposits would be expected in all cases. In most of 

 these veins where the values are highest, from 20 to 30 per 

 cent of the gold can be recovered by amalgamation. The char- 

 acteristics of deposits where leaching by the solution of gold 

 with free chlorine has taken place are a barren zone near the 

 surface and a zone of enrichment near the water level. Neither 

 of these features is present in the deposits cited. It is probable 

 that a slight impoverishment occurs at the outcrop, due to the 

 mechanical transportation of the fine gold along the numerous 

 cavities and passages left by the leaching of the calcite. 



ENRICHMENT IN CALCITE VEINS 



While chemical concentration has apparently not taken place, 

 it is evident that concentration of some character has occurred 

 extensively, possibly to a greater extent than in a calcite-free 

 ore deposit. This is due to the great solubility of calcite in 

 leaching waters and particularly those containing carbon dioxide. 



