74 



otherwise favourable, are deeply buried beneath heavy 

 accumulations of drift. 



The principal ore bodies, now being developed, occur 

 in limestone, close to or adjoining the granite. Numerous 

 discoveries have also been made in the granite, often at 

 considerable distances from the limestones. The limited 

 amount of work done on these has so far, however, not 

 disclosed ore bodies of commercial value. The constituent 

 minerals and general character of the ore bodies in the two 

 formations, are very similar. Copper minerals seldom 

 occur in the andesites, but are not altogether unknown 

 there. 



The principal economic minerals of the district are 

 bornite and chalcopyrite. Tetrahedrite, chalcocite, mala- 

 chite, azurite, cuprite, malaconite, chrysocolla, and native 

 copper also occur. The oxides are conspicuous in all the 

 workings, but except at the Pueblo, are seldom important 

 as ores. The iron sulphides are not abundant and nowhere 

 form large masses. The iron oxides, magnetite and 

 hematite, on the other hand are widely distributed, and 

 both occur in large masses. Other metallic minerals of 

 less frequent occurrence are arsenopyrite, stibnite, galena, 

 sphalerite, and molybdenite. Gold and silver occur in 

 all the ores, the values ranging from traces up to several 

 dollars per ton. Gold is ocasionally found native. The 

 principal non-metallic minerals accompanying the ores 

 are andradite, augite, tremolite, actinolite, epidote, calcite, 

 clinochlore, serpentine, and quartz. Of these, andradite, 

 augite, calcite and tremolite are the most abundant. 

 Quartz is sparingly distributed and seldom occurs in 

 quantity. 



The ore bodies fall into two classes: — those in which 

 the copper minerals are associated with magnetite and 

 hematite; and those in which the various silicates, prin- 

 cipally garnet, augite, and tremolite are the chief gangue 

 minerals. 



The magnetite ore bodies are numerous, and occur 

 enclosed completely in altered limestone, along the lime- 

 granite contact, and in a few instances in areas of altered 

 granite. The largest bodies, so far discovered, are: the 

 Best Chance, 360 feet (109 m.) in length; the Arctic Chief, 

 230 feet (70 m.) ; and the Little Chief, 100 feet (30 m.) 

 The magnetite masses are always sprinkled, more or less 

 plentifully throughout, with grains and small masses of 

 bornite and chalcopyrite. The copper percentage varies 



