Sectiox IV., 1913. [13] • Trans. R.S.C. 



Yukonite, a New Hydrous Arsenate of Iron and Calcium, from Tagish 

 Lake, Yukon Territory, Canada; with a note on the Associated 



Symplesite. 



By J. B. Tyrrell, F.R.S.C, and R. P. D. Graham. 



Mode of Occurrence. By J. B. Tyrrell. 



The mineral here called Yukonite was found by the writer in the 

 autumn of 1906 on a mining claim on the west side of Windy Arm of 

 Tagish lake, in the southern portion of the Yukon Territory, Canada. 

 The claim was just south of the " Venus " and at the time was being 

 operated l^y Mr. T. M. Daulton. 



The country in which the mineral occurs is a part of the Coast or 

 Chilcat range of mountains, which rises in peaks and ridges to heights 

 of seven or eight thousand feet above the sea. It is crossed by many 

 transverse valleys in which often lie deep, clear, blue lakes, from the 

 sides of which the land rises in slopes which are sometimes precipitous 

 but are more often regularly and evenly graded to the summits. Many 

 of these slopes are covered with a variable thickness of broken and 

 partly decomposed rock which, in the more exposed places, support an 

 Arctic moorland vegetation, while on the sides and in the bottoms of 

 some of the deeper lateral gorges growths of coniferous timber manage 

 to subsist. 



Tagish lake, with an elevation o^ 2160 feet above the sea, occupies 

 the bottom of one of these transverse valleys and discharges its waters 

 into the upper portion of the Yukon river. 



It is an irregutarly shaped body of water, and its long southern 

 extension, which reaches down into the province of British Columbia, 

 is known as Windy Arm. From the north-west side of this arm, a 

 short distance north of the southern boundary of the Yukon territory, 

 a steep moorland slope vises to a height of several thousand feet, and on 

 this slope, but especially near its bas^e, several quaitz veins were dis- 

 covered carrying silver-bearing galena associated with pyrargyrite, 

 argentite, chalcopyrite, a^'senopyiite, and other minerals. 



The country rock in which these veins occur is a fine grained 

 greenish porphyrite of Jurassic or Cretaceous age. On account of the 

 severity of the climate, it is perpetually frozen to a considerable, 

 though unknown, depth. 



The veins strike north-west and south-east and dip at a high angle 

 into the hill away from the lake. Several of them had been opened by 



