Sischu Mountain Prospects, Ruby Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Sischu Mountain Prospects	Group of Prospects
Ruby Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

The Sischu Mountain prospects are located on land selected by or conveyed to Doyon, Limited. For more information, contact Doyon, Limited.
Location: The Sischu Mountain prospects cover about 20 square miles, including Sischu Mountain and several surrounding peaks. The approximate center of the prospect area is in NE1/4SW1/4 section 30, T. 9 S., R. 27 W., of the Fairbanks Meridian. There is an airstrip at Lake Minchumina approximately 30 miles southeast of the prospects. The Sischu Mountain prospects are located on land selected by or conveyed to Doyon, Limited.
Geology: 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.
Workings: 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.
Age: Probably related to Cretaceous to Tertiary plutonism.
Alteration: On Sischu Mountain, float samples exhibit silicification and chlorite-kaolinite alteration and vein brecciation with tourmaline. An area identified by a color anomaly consists of hydrothermally brecciated sandstone fragments in a goethite matrix.
Production: There are no indications of production.

Commodities (Major) - Sn; (Minor) - As, Au, Bi, Cu, Mn, Mo, Ni, Sb, Zn, Zr
Development Status: None
Deposit Model: Plutonic-related mesothermal veining.

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Link to USGS - Alaska:	KH006

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References