374 V. DOLMAGE.

numerous small veins in the pyrite. These veins become so large and numerous in some of the pyrite as to leave only small skel- etons of the original grains. Associated with the chalcopyrite, and intergrown with it in a manner strikingly similar to the graphic structure, is a large amount of zinc blende. It replaces the gangue and pyrite, and appears in every way to have been de- posited with the chalcopyrite. The common rule for the sequence of ihese two minerals is for the blende to slightly precede the chalcopyrite, but no evidence could be found to prove that rule: in this ore.

The bornite-chalcopyrite ore of the central part of the vein is by far the richest, specimens collected by W. F. Robertson assayed 63 per cent. copper, 81 oz. silver, and 0.04 oz. gold per ton. The transition from the chalcopyrite-pyrite ore to the bor- nite ore cannot be traced owing to the lack of outcrops, but in the main shaft it was noted that there was more chalcopyrite at the ends than in the center of the shaft. ‘The structures seen under the microscope showed mutual contacts between the chal- copyrite and bornite in most of the cases but towards the south of the tunnel there was some chalcopyrite which forms narrow rims around the bornite with many spikes pointing into it, and giving it a distinctly later appearance. This ore contains also a large amount of silver-bearing tetrahedrite which was seen as rounded or elongated masses with smooth even contacts in the bornite and chalcopyrite, but with a preference for the chalco- pyrite, or the contacts of the bornite and chalcopyrite. It was never seen in veins and is undoubtedly primary, having come in with the copper sulphides or in places slightly later than them. Magnetite grains become common in the eastern part of the main trench. They contain small veinlets of hematite which never go beyond the edges of the magnetite, and many of them are sprinkled over with numerous specks of chalcopyrite which - grade down in size to submicroscopic. A few of these grains were composed of bornite, and some of the larger ones were slightly altered to covellite. Tetrahedrite was also found. No hematite outside of the magnetite grains was seen in this ore ex- cepting a very few scattered blades and rounded grains in the