336 



DEPARTMENT OF TiHE INTERIOR 



2 GEORGE V, A. 191)2 



The presence of sulphur interferes with the determination of the relative 

 proportions of the iron oxides in this rock. The analysis clearly corroborates 

 the microscopic evidence that we here have a common type of dunite. 



PORPHYRITIC HAHZBURGITE (PlORITE?). 



At the Dewdney trail south of the head-waters of Santa Rosa creek, the 

 older andesitic traps of the Rossland volcanic group enclose a mass coloured 

 on the map as harzburgite. It is a massive, deep green rock, bearing on 

 its surface abundant cleavage-faces of idiomorphic enstatite, which is embedded 

 in a compact base of olivine and its derivative, serpentine. Many outcrops 

 are characterized by spheroidal weathering, and the rock has assumed a strong 

 brown colour. Here and there it is sheared and thus locally converted into 

 nearly pure serpentine. 



The enstatite phenocrysts measure 1 cm. or more in length by 1 to 2 mm. 

 in diameter. Besides olivine the only other constituents are chromite and 

 magnetite; the latter may be entirely secondary from the altered olivine. The 

 enstatite is generally fresh but has yielded some secondary talcose material. 

 The olivine occurs in unusually small grains, which vary from 0.02 mm. to 

 0-6 mm. in greatest diameter, with an average diameter of probably not more 

 than 0-1 mm. This fine texture of the olivine ground-mass suggests that the 

 mass did not crystallize under a heavy cover. In the field the mass was taken 

 for a thick flow and it is quite possible that it does represent the lava corres- 

 ponding to a peridotite. A second visit to the locality might solve this inter- 

 esting problem of relations; meanwhile the rock may be called a harzburgite. 

 and is described among the intrusives. 



Mr. Connor has analyzed the fresh specimen (No. 392) collected, with 

 result as follows : — 



Analysis of porphyrinic harzburcjite (effusive?). 



M'ol. 



Si0 2 42-99 -716 



Ti0 2 tr 



Al 2 O s Ml -Oil 



Fe.A 1-87 -012 



Feb. 5-91 -082 



MnO -05 



MgO 43-14 1-079 



CaO -10 -002 



SrO none 



BaO none 



Na-0 -29 -005 



K 2 -13 -001 



H 2 at 110°C -51 



H 2 above 110°C 4-00 -222 



P 2 5 -04 



NiO -15 



100-29 



Sp. gr 3-075 



