Geologic description
The Lakeside Mine was first described by Chapin in 1918 and little work has been done on it since. The rocks in the vicinity consist of locally pegmatitic, Ordovician gabbro and hornblendite and Silurian or Ordovician basaltic volcanic rocks (Gehrels, 1991). The gabbro has been dated at 440 Ma and 449 Ma (Eberlein and others, 1983).
According to Chapin (1918), two shear zones contain chalcopyrite. One shear zone is about 5 feet wide, strikes N20W and dips NE; the other is about two feet wide, vertical, and strikes N20W. In 1916, the workings consisted of a 41-foot shaft and a 41-foot crosscut that interested both shear zones. Roehm (1941) indicated that the deposit had been developed by a 100-foot shaft with 50-foot drifts at the 50-foot level and at the bottom of the shaft. He also indicated that there had been copper production in 1917 and 1918. Maas and others (1991, p. 47) indicate that the chalcopyrite occurs in irregular pods, disseminations, and seams in two fault zones that strike N 35 W; the faults are near a gabbro-basalt contact. Their best samples contained 1.57 percent copper, 0.28 percent nickel, and 892 parts per million cobalt; all of the samples contained less than 5 parts per billion platinum-group metals. (Wilcox (1937 [PE 121-2]) mentioned the potential for Pt-group metals at this site.) |
