[graham] BISMUTHINITE AFTER MOLYBDENITE 191 



On Phenacite, and a Pseudomorph of Bismuthinite after 

 Molybdenite, from Northern Quebec 



Location and Mode of Occurrence of the specimens 



The specimens described below came from the Height of Land 

 Mining Company's property, on the west bank of Kewagama river, 

 in the extreme north of Preissac township, northern Quebec. The 

 locality is about fifteen miles south of the Trans-continental Railway 

 (which here, for a short distance, follows the Height of Land), and 

 fifty-two miles east of the Quebec-Ontario provincial boundary. 



The property of the Height of Land Mining Company is situated 

 on the western margin of an extensive granite (Laurentian) batholith. 

 The peripheral zone of this mass, where it crosses the Kewagama river, 

 is unusually pegmatitic in character, and the rock is traversed by a 

 great number of quartz veins; these, as well as tongues of pegmatite, 

 also appear cutting the neighbouring Keewatin schists. The quartz 

 veins are themselves undoubtedly pegmatitic, and represent the last 

 and most acid intrusions of the same magma which gave rise to the 

 granite. Molybdenite and bismuthinite occur in the pegmatitic and 

 aplitic faciès of the granite, and, more especially, in the quartz veins. 

 Both minerals are very erratic in their distribution, and bismuthinite 

 is relatively much the less common. The bismuthinite usually occurs 

 along fracture planes within the veins and filling cracks in other 

 minerals, such as pyrite, and in some places it surrounds and encloses 

 minute crystals of molybdenite. It thus appears to have been intro- 

 duced later than the latter mineral, and this view receives support 

 from the occurrence here of a pseudomorph of bismuthinite after 

 molybdenite, which is described below. 



Other minerals which have been met with in these quartz veins 

 include the following: — beryl, fairly abundant in some of the veins, 

 in greenish sub-translucent prismatic crystals, which may attain a 

 diameter of three or four inches; phenacite, only observed in specimens 

 from one vein and described below; fluorite, of a deep purple colour; 

 pyrite, chalcopyrite, and sphalerite. Some of the veins show low 

 values in gold. 



Pseudomorph of Bismuthinite after Molybdenite 



This interesting specimen was collected in 1907 by Mr. J. A. 

 Dresser, who later presented it to the McGill University Mineral 

 Collection. It is shown in Plate I, figure 1, which is reproduced from a 

 photograph, and is about natural size. 



As may be seen, the specimen consists of two apparently hexagonal 

 crystals, about equal in size, of similar shape, and attached in parallel 



