Sischu Mountain is composed of multiple igneous phases intruding phyllite, limestone, and siltstone to the north and various volcanic rocks, including rhyolite, dacite, andesite, and basalt, to the south and east (Chapman and Yeend, 1981). The phyllite, limestone, and siltstone are of Devonian age, and the intrusive rocks are Cretaceous to Tertiary (Chapman and Yeend, 1981). Float mapping has found aplite, coarse biotite granite, porphyry granite, hornblende-biotite monzodiorite, and porphyry dikes (Bond, 1985). Regionally, the area contains a system of northeast-trending strike-slip and related conjugate faults associated with Cretaceous to Tertiary plutonic rocks and coeval or younger volcanic rocks (Clautice and others, 1993).
On Sischu Mountain, float samples exhibit silicification and chlorite-kaolinite alteration and vein brecciation with tourmaline. Disseminated pyrite and chalcopyrite occur in altered intrusive rock. Some aplite dikes contain as much as 1 percent magnetite. An area identified by a color anomaly consists of hydrothermally brecciated sandstone fragments in a goethite matrix. A rock chip of altered granite contained as much as 1,450 ppm As, 25 ppm Bi, 100 ppm Sn, and 15 ppm Mo (Bond, 1985). Clautice and others (1993) reported analyses of several samples: (1) a rhyolite dike cutting limestone contained as much as 1,200 ppm Zr, 86 ppm Cu, 542 ppm Zn, 265 ppm Ni, 136 ppm As, 35 ppm Sb, 799 ppm Mn, and 10 ppm Sn; (2) limestone near a granitic contact contained as much as 114 ppm As; (3) equigranular, biotite monzonite contained 767 ppm Zn, 47 ppm As, 23 ppm Pb, and 6 ppm Sn; (4) a rhyolite dike in limestone contained 132 ppm As, 590 ppm Mn, and 38 ppm Pb; and (5) limonitic rhyolite contained 105 ppm As and 463 ppm Mn.A regional stream sediment sampling, airborne radiometrics, and mapping program in 1975-76 and 1980 identified several anomalies. In 1984, one sample was collected. In 1985, exploration efforts consisted of mapping and collecting 12 rock chip, 7 stream sediments, and 8 pan concentrate samples (Bond, 1985). There are no indications of production.