The Delmonico claim, on which the mine is located of the same name, lies on the western slope of Bull Cliff, just east of Deadwood. It belongs to the Stratton estate and is worked by lessees. The development consists of a shaft 600 feet deep, 300 feet of which have recently been completed, and three levels at 100-foot intervals. Development in the lower part of the mine is in progress. Drifts and crosscuts probably aggregate 2,500 to 3,000 feet.
The principal rock of the mine is latite-phonolite, but phonolite breccia is reached on level 2, 350 feet south of the shaft. Ninety feet south of the shaft on this level the basalt dike from the Deadwood No. 2 crosses the north-south drift.
Only one vein of any importance has been encountered. It has a north-south course, dips steeply to the west and lies just east of the shaft. It consists of an oxidized and shattered zone 2 to 5 feet wide in latite-phonolite. Fifty feet south of the shaft a body of oxidized ore was encountered which was shipped as broken, and contained 1.5 to 2 ounces per ton. A stope on this ore shoot is 4 to 5 feet wide, 35 feet long, and 100 feet high. The southern limit of the shoot is the basalt dike, which is also being stoped near the vein. This was the only shoot that had been found in the mine at the time of visit.