Fy) OREO Fe aL SL Lk ROSS RO TE hoe ER TER SRR eT

364 V. DOLMAGE.

The microscopic study of the ore showed that bornite, ar- gentite, chalcopyrite, covellite and hornsilver are present, be- sides the minerals already named.

The chalcocite is of two kinds, a pure white variety, which forms the bulk of the ore, and a bluish form, which is present in only small amounts. The white chalcocite is quite homogeneous, and when etched is seen to be formed of rounded but distinct crystals closely fitted together in small spaces in the quartz. It clearly replaces the quartz, in some places forming small veinlets and rounded shapeless masses, but it undoubtedly also fills many spaces, which were once empty cavities, the crystal outlines of the quartz being still preserved. Some of the larger areas which have diameters up to three fourths of an inch occupy cvaities of this nature. Almost all of the larger areas have peculiar cracks crossing them, which fade out towards the margins and become wider at the center. None of them were seen to cross from one area of chalcocite to another and all were of this peculiar shape. The size of the cracks varies directly with the size of the grains in which they occur, those in the largest grains can easily be seen — with a hand lens. They strongly suggest shrinkage cracks and are of constant occurrence. Some of them are filled with cal- cite or other gangue minerals, while many of them are empty.

The blue chalcocite is confined to the epidote areas and is fre- quently traversed by wide open cracks along which it is altered to covellite. In the epidote band on the vein wall there is much blue chalcocite in the form of rounded irregular grains not con- nected with any veins, and which are all cracked and altered to covellite. They seem to be residual grains which have been altered by the solutions which deposited the epidote. Simliar chalcocite was found in the calcite, but some of it appeared to re- place it along small veinlets.

Bornite was observed in only one specimen, and here in micro- scopic amounts, but is said to have been rather plentiful since the time of the examination, in the small branch vein to the east and some 30 feet above the tunnel. The bornite, which was found in one of the specimens at hand, did not show its relation