114 



like valleys, — of which the Similkameen valley is a typical 

 example — are the result of stream erosion following that 

 uplift. These valleys have, however, since been modified 

 by glaciation to their present U-shape. Glaciation has 

 also, to some extent, been responsible for smoothing out 

 the irregularities of the surface and reducing the summit 

 levels of the region. 



Nickel Plate Mine. 



The Nickel Plate mine is situated on the eastern slope 

 of Nickel Plate mountain at an elevation of about 5,700 

 feet (1,737 rn-) above sea level. The ore deposits in it 

 are of contact metamorphic origin and occur at the contact 

 of dykes and sheets of gabbro in limestones which have 

 been altered by the gabbro. They are irregular in outHne 

 and have usually a well-defined boundary only on the side 

 of the gabbro. 



The gangue of the ore bodies contains minerals formed 

 by the alteration of limestone, including garnet, epidote, 

 diopside, amphibole, quartz, calcite, and axinite. 



The principal ore mineral is arsenopyrite, with v/hich 

 occur chalcopyrite, pyrrhotite, zinc blende, pyrite, native 

 gold, and sometimes tetradymite. These minerals are 

 distributed through the gangue in crystallized individuals, 

 or fill minute fractures in it. The valuable content of the 

 ore is gold alone, which in that now being mined, averages 

 about $11.00 to the ton. 



These deposits afford an excellent illustration of contact 

 metamorphism induced by the intrusion of igneous 

 bodies into calcareous rocks, and show the resulting altera- 

 tion of the original carbonates to silicates. They illustrate 

 also the formation of ore bodies by the transfer of ore 

 material from the igneous rock to the sedimentary, under 

 such conditions of temperature and pressure, that the 

 constituents introduced, and those originally present and 

 recrystallized, are intergrown together as a result of 

 contemporaneous crystallization. 



In the association of gold with arsenopyrite in deposits 

 of this origin the Nickel Plate ore deposits are unique and 

 have no known counterpart on the continent. In the 

 classification of ore deposits, they are therefore placed in a 

 division by themselves, and are called the "Arsenopyrite 

 type" of contact metamorphic deposits. 



