Unnamed Occurrence (ARDF - NM039; near Tigaraha Mountain), Nome Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrence (ARDF - NM039; near Tigaraha Mountain)	- not defined -
Nome Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: Several pegmatites crop out on a sharp ridge southwest of Tigaraha Mountain at elevations of about 2,800 to 3,000 feet. The pegmatite occurrences are localities 76, 77, and 78 of Hummel (1975). The location given is the approximate center of the pegmatite cluster on the ridge.
Geology: These pegmatites are south of the Thompson Creek orthogneiss, and their age is uncertain. Granite pegmatites are abundant in the Kigluaik Mountains, and others may be present near these occurrences. The pegmatites are noticeably radioactive; radioactivity measured on the ground with a scintillometer is as much as 500 counts per second or 3 to 5 times common background (Hawley and Associates, 1978, Section IV). Tourmaline and garnet are common accessory minerals, and the more radioactive pegmatites commonly contain smoky quartz. Beryl occurs in some of the pegmatite, including a body described by Moffit (1913, p. 25) about 1 mile west of the mouth of North Star Creek (NM046). Some granite pegmatites are within the Thompson Creek orthogneiss or appear to be spatially associated with it, particularly on its south or hanging wall side (Hummel, 1962 [MF 248]; Till, 1980). The Thompson Creek orthogneiss has been dated as latest Proterozoic (555 Ma, Amato and Wright, 1998), and some pegmatites may also be this age. However, metasedimentary rocks of the Kigluaik Mountains underwent granulite facies metamorphism and partial melting in the mid-Cretaceous, and some pegmatites are crosscutting to local structure and are mid-Cretaceous in age (Throckmorton and Hummel, 1979; Till, 1983; Miller and Hudson, 1991; Hudson, 1994; Till and Dumoulin, 1994; Amato and others, 1994; Amato and Wright, 1997, 1998). The host rocks to these pegmatites are amphibolite facies metasedimentary rocks that are derived from Precambrian or early Paleozoic protoliths (Sainsbury, 1972; Bunker and others, 1979; Till and Dumoulin, 1994). They are thought to have undergone regional high-pressure metamorphism along with many other rocks of Seward Peninsula in the Late Jurassic or Early Cretaceous (Sainsbury, Coleman, and Kachadoorian, 1970; Forbes and others, 1984; Thurston, 1985; Patrick, 1988; Patrick and Evans, 1989; Armstrong and others, 1986; Hannula and McWilliams, 1995). Higher temperature metamorphism overprinted these rocks in conjunction with regional extension, crustal melting, and magmatism in the mid-Cretaceous (Throckmorton and Hummel, 1979; Till, 1983; Evans and Patrick, 1987; Leiberman, 1988; Patrick and Leiberman, 1988; Miller and Hudson, 1991; Miller and others, 1992; Dumitru and others, 1995; Hannula and others, 1995; Hudson and Arth, 1983; Hudson, 1994; Amato and others, 1994; Amato and Wright, 1997, 1998). Uplift of the higher temperature metamorphic rocks took place in the mid- to Late Cretaceous and in the Eocene (Calvert, 1992; Dumitru and others, 1995).
Workings: Reconnaissance uranium exploration including airborne radiometrics, stream sediment surveys, and ground traverses have been completed in the Kigluaik Mountains.
Age: Late Proterozoic or mid-Cretaceous; either the age of the Late Proterozoic Thompson Creek orthogneiss or mid-Cretaceous amphibolite facies metamorphism.

Commodities (Major) - Be, Th, U
Development Status: None
Deposit Model: Simple granite pegmatite with rudimentary zoning.

Other Databases

Link to USGS - Alaska:	NM039

Other Regions, Features and Areas containing this locality

References