NODULAR-BEARING SCHISTS NEAR PEARL, 

 COLORADO.' 



The central area of the Pearl district consists of schistose 

 rocks which are cut by numerous dikes of coarse pegmatite, 

 varying from two to forty feet in width, and having a general 

 northwesterly and southeasterly strike. Numerous copper pros- 

 pects are being developed upon these, and in several instances 

 bodies of copper ore have been discovered. Associated also are 

 veins of quartz, which are of great interest because of the fine 

 crystals of spinel, of the variety ceylonite, which they contain. 

 Octahedra of from 5 to 25""" in diameter are found in large 

 quantity. That which makes them especially interesting is the 

 fact that all the crystals contain quartz inclusions in the greatest 

 abundance, often to such an extent as considerably to lower 

 their specific gravity. The spinel occurs in portions of the 

 dikes which are almost wholly quartz. The included quartz 

 appears to be identical with that surrounding the spinel. It 

 would seem, therefore, that part of the quartz had crystallized 

 out before the formation of the spinel, and the remainder fol- 

 lowed the crystallization of the spinel. In other words, we have 

 two generations of quartz crystals, the first generation being 

 partly included in the spinel. 



To the southwest of this lies another area of schistose rocks 

 which are cut by dark basic dikes. These dikes are mineralized, 

 and upon them prospects are also being opened up. They are 

 an example of what the average miner firmly believes to be 

 always the case — increase of value in depth. At the surface 

 they show little sign of mineralization, but upon sinking chalco- 

 pyrite appears in considerable quantity, and seems to have been 

 original with the dike matter, as the dike is perfectly fresh and 

 shows no sign of mineralizing action. If the chalcopyrite was 



' The recently opened mining town of Pearl is situated in Larimer county, Colo., 

 about two miles south of the state line between Colorado and Wyoming, and at an 

 elevation ot about 8,400 feet (barometric). 



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