310 IRVINC. 



It has been shown on page 293 that there are at least two 

 series of intrusions — first the rhyohte-andesite series, and second 

 the series involving the phonolites. The phonolites are the 

 later intruded rocks. The question now arises, is it to one or 

 both ot the series of intrusions that the mineralizing action is 

 attributable ? To this a positive answer cannot be gi\'en, but 

 the widespread occurrence of purplish fluorite. and the presence 

 of tellurium in the ores are so similar to the conditions at Crip- 

 ple Creek, and in the Judith Mountains, that one cannot well 

 avoid considering the phonolite here, as there, to be the chief 

 agent that has rendered ore bearing solutions chemically active. 



Dcrivafiivi of tJic Gold. — For the deri\ation of the gold four 

 possible sources can be suggested : 



A. By lateral ' i. From the leaching out of the small amount of 

 secretion. ' free gold present in the rocks of the Cambrian 



j formation. 



2. From the leaching out of small amounts in 

 I the porph)'ries. 



B. By accen-|3. From the leaching out o{ the free gold and 

 sion bv in- i sulphurets o{ the underh'ing slates and schists, 

 nitration. _j^ From the derivation of the gold from an 



, indefinite horizon below, /. <•., probably the 

 same source from which the Algonkian gold 

 was derived. 



The form of the ore shoots and their association with verti- 

 cals, will make it at once apparent that the ores are not in any 

 sense the result of lateral secretion, but that they have come 

 from depths far below their present position. 



We are then left to decide whether the solutions have de- 

 rived their burden of gold, from the older deposits in the Algon- 

 kian, or from deeper sources below. It is not improbable 

 that both of these explanations are true. Tellurium it is true, 

 has not yet been detected in the Algonkian ores, but it ma}' 

 exist in the sulphurets in depth. 



