Vol. 4] Laivson. — The Robinson Mining District. 



337 



ternally deformed condition of the porphyry which while open- 

 ing np the rock to the permeation of the ground water, with its 

 mineral matter in solution, would render that permeation irreg- 

 ular and so give an irregular distribution of the values. (2) 

 The presence of a dyke of dense fine textured minette to the 

 northeastward of the present mine workings would undoubtedly 

 affect the underground circulation, although what its effect 

 upon the deposition of the ore may have been is not yet clearly 

 apparent. 



In order to get an idea of the average contents of the ore of 

 the Ruth Mine, an analysis was made at the writer's suggestion 

 by Mr. Herbert Ross of an average sample. In the development 

 of the mine samples have been taken for assay every five feet of 

 the ground traversed. As there are about 5,000 feet of drifts, 

 shafts and crosscuts in the mine, the ore of all kinds was repre- 

 sented at the time of the analysis (1904) by about 1,000 samples. 

 Of these every fifth sample was used in equal proportions and 

 thoroughly mixed. By the process of quartering this was re- 

 duced to a convenient quantity and analyzed. Owing, however, 

 to the adverse conditions under which the analysis was made, 

 the results were not satisfactory except as regards the determin- 

 ations of sulphur, 6.00 per cent., iron, 5.34 per cent., and copper. 

 2.61 per cent. These results show that on an average the ore 

 of the mine contains 10 per cent, of pyrite and 3.25 per cent, of 

 chalcocite. It is to be noted, however, that much is included in 

 the sample taken which would not be regarded as ore and mined 

 in regular mining operations, so that the average copper content 

 of the actual ore is higher than the analysis shows and is prob- 

 ably about 3 per cent. The development of the mine and its 

 carefully maintained assay chart show that there is a very ex- 

 tensive body of ore of this average value with considerable 

 ground running well above the average, and in spots reaching 8 

 and 10 per cent. There are no well defined boundaries or limits 

 to the ore body except the oxidized zone above and the dyke of 

 minette on the northeast. This dyke is probably of limited thick- 

 ness and under the general conditions of deposition of the ore 

 above set forth, it should be regarded as of the nature of an 

 interruption to the ore and not as its final limit, it being quite 



