390 MR. A. J. E. ATKTN ON THE GENESIS [NOV. 1904, 



The origin of the gold in the reefs is probably the same as the 

 origin of the reefs themselves. Both were deposited in fissures 

 formed by strains during the upheaval of the schists. There is 

 evidence that some of the veins are accretions formed in gradually- 

 widening fissures, and were not deposited in one gaping chasm. 



This is especially apparent in the B.C. ledge, where thin films of 

 graphitic schist appear as partings in the vein on the hanging-wall 

 side, giving the reef a banded appearance. These may be taken 

 as part of the original wall which broke away with the early 

 accretions of silica, and became enveloped in the subsequent de- 

 positions as soon as the fissure widened again sufficiently for the 

 ascending waters to deposit a fresh crust of mineral salts. At 

 present, the parting on the hanging wall consists of a soft gangue 

 of friction al debris, among which the acid mine-water may still be 

 depositing mineral wealth. 



These reefs, deposited by waters ascending from profound depths, 

 holding in solution their minerals dissolved under conditions of great 

 heat and pressure, would have a tendency to increased richness, 

 at the depth where the gradually -lessening conditions of their 

 solubility favoured the precipitation of mineral salts. 



As most probably this rich zone is still intact, and awaits the 

 advent of deep-miniug for its discovery, another source must be 

 looked for in trying to solve the problem of the occurrence of the 

 gold in the placers. 



While all the reefs carry gold in greater or less quantities, none 

 have been found the richness of which would account for the placer- 

 gold ; yet it is a well-known fact that rich outcrops exist in most 

 quartz-veins, unless removed by weathering of the enclosing rocks. 

 This greatly-enriched zone above the water-level must be con- 

 sidered as of purely- secondary origin: a concentration, in fact, 

 from the rock-masses of the reef above. 



This concentration takes place in two ways. The first by 

 leaching of the pyrites, while the less soluble gold is left in the 

 honeycombed quartz, whereby the vein-matter is made lighter 

 while not reduced in bulk, which so becomes the richer per ton. 

 The second method is purely chemical, and is an actual enrichment 

 by precipitation. 



The key to this secondary enrichment is found in the solubility 

 of gold in solutions of ferric sulphate, as pointed out by Le Conte 

 and Wurtz. The ores of these reefs are such that, on their decom- 

 position, quantities of this substance would be formed from thepyrites 

 present. While the pyrites furnishes the solvent for the gold, it acts 

 also as a precipitant for the same ; and the two processes of solution 

 and precipitation are going on at the same time, and are taking 

 place at the present day. 



The area of the reef in which these forces come into play is 

 limited by the level of the circulating surface-waters, which remove 

 the dissolved gold and carry it down to a lower level, where, coming 

 into contact with undecomposed pyrites, it is again precipitated. 

 This process, going on continually — for although Nature works with 



