PL RNR REE a as COPGER SLL ZER VEINS-OF TELKWA DISTRICT. 369 important to shake the theory that the primary ore of this claim also came from solutions emanating from the granitic stock. According to this theory, it matters not whether the chalco- cite be considered as primary, or as secondary after bornite, and that the hematite followed the bornite-gangue contacts instead of the chalcocite-gangue contacts, but for reasons that will be given in a later paragraph the chalcocite is believed to be primary. Primary Chalcocite—One of the most disputed points in the current literature on economic geology, and at the same time a most critical point, is the question whether or not chalcocite is ever a primary mineral. It is conceded by all that it is a most common secondary product, and while a few believe that it may, in rare cases, be primary yet there are many who maintain that no case of the primary origin has yet been proven. It 1s, there- fore, with some timidity that I claim for this chalcocite a primary origin, though the evidence seems to point strongly in that direc- Ol tne inportance Ol “the Matter rests on the question, whether the mineral can be taken as a positive criterion for prov- ing the ore in which it is found to have been enriched by descend- ing meteoric waters. Some of the strongest evidence against the enrichment theory for this ore comes from the relations observed in the Excelsior claim. The microscopic structures show fairly certainly that some of the bornite of the graphic structures is of later date than some of the chalcocite. Areas of chalcocite surrounded by nar- row persistent rims of bornite which send sharp wedge-shaped spikes into the chalcocite cannot be explained in any other way, and such were seen in several cases. The bornite rims are often connected with the bornite of the graphic structure, as for ex- ample, in Plate XXIII., d. This being the case, then, if the chal- cocite is secondary, the bornite must also be considered secondary. But there is no evidence to substantiate this, the bornite is often closely associated with the chalcopyrite, but there is no sign of veining or replacement along the gangue contacts, or indeed any structural evidence of secondary replacement. On the contrary their smooth, rounded contacts, and mutual intergrowths indi- cate a contemporaneous and a primary origin for both. The BERGE Bee unin, Y