Flat Creek Prospect, Fairbanks Mining District, Fairbanks North Star Borough, Alaska, USAi

Regional Level Types
Flat Creek Prospect	Prospect
Fairbanks Mining District	Mining District
Fairbanks North Star Borough	Borough
Alaska	State
USA	Country

Location: The location is on Flat Creek, between First Pup and Second Pup. The Flat Creek prospect is located just south of mile 51 of the Steese Highway, on the lower 3.5 miles of the Flat Creek drainage.
Geology: The following geologic description is taken from Freeman, 1986: The presence of two quartz cobbles containing visible gold as well as the occurrence of jamesonite indicate that a nearby lode source for gold has contributed to the placer gold on Flat Creek. The general geologic fabric in the vicinity of the Flat Creek prospect is dominated by highly deformed northeast-trending low- to medium-grade pelitic and volcanic metamorphic rocks. Foster and others (1983) mapped a large northeast-trending thrust fault in the area which trends across the south flank of Twin Buttes, through the headwaters of Dexter Creek and crosses Flat Creek near the confluence with Second Pup. Lithologies to the north of the thrust consist of medium- to coarse-grained muscovite-garnet-quartz plagioclase schist with local lenses(?) of chlorite-rich schist. This rock unit contains marker lenses composed of up to 70 percent white to pale yellow muscovite and up to 20 percent fine to medium-grained garnet. The unit is cut by numerous small dark green to green and pink mafic to ecologitic dikes and sills containing amphibole, chlorite, garnet, plagioclase and carbonate. The base of this thrust unit is highly sheared where it is in contact with the more resistant quartzites which underlie the thrust. Lithologies south of and overthrust by the Flat Creek thrust are composed of pelitic, psammitic and volcanic protoliths which trend N45E and dip variably northwest and southeast off the flanks of a regional-scale northeast-trending antiform whose axial plane follows the uplands between Twin Buttes and Mt. Ryan. The dominant lithology in this terrane is gray to gray-green quartzite and quartz mica schist composed of a medium-grained aggregate of quartz and lesser amounts of muscovite and feldspar (Foster and others, 1983). Mylonitic fabrics have been identified in this rock unit, probably as detachment or sympathetic thrust faults along bedding planes on the flanks of the antiform. Original lithologic compositions often are obliterated by post-metamorphic silicification and shearing attendant with mylonitization. This rock unit exhibits metamorphic assemblages which range from the chlorite zone of the greenschist facies to the staurolite and kyanite zones of the amphibolite facies. Zircons from arenitic units of this lithologic package have yielded U/Pb ages ranging from 1558 to 1797 mybp and a single Pb/Pb date of 2086 Ma (Foster and others, 1983), indicating a possible Proterozoic parentage for the zircons. However, the age of the sedimentary units in which the zircons were deposited probably is somewhat younger, perhaps as young as Devonian (J. Dillon, oral commun., 1986). Quartzite and quartz mica schist is mapped as the principal bedrock lithologies in the upper Dexter Creek and First Pup basins, all of Second Pup basin, and the whole of the Flat Creek valley above its confluence with Second Pup. Subordinate to psammitic lithologies, but perhaps more important with respect to metallogeny, are the interbedded pelitic and volcanic units which are mapped in the upland areas south of the Flat Creek prospect. Chlorite-magnetite greenschist of mafic volcanic origin is the most widespread volcanic lithology in the area. This rock unit contains abundant magnetite in a fine-grained chloritic host rock which is interbedded with quartzite, shale and minor marble lenses. It is probable that many of the rock units mapped as quartzite and quartz-mica schist are in fact metarhyolitic exhalite and aquagene tuff units which comprise a major portion of the section. There are no published accounts of mining activity; however, inspection of infrared imagery of the Flat Creek area indicates extensive surface disturbance in Flat Creek between Dexter Creek and Second Pup Creek, two major left-limit tributaries of lower Flat Creek. The morphological descriptions of valley alluvium and colluvium given by the prospect owner, Dick Byrd, along with the common occurrence of free mercury and amalgam in prospect samples suggests that Flat Creek proper was mined, probably by hand methods (Freeman, 1986, p. 2).
Workings: There are no published accounts of mining activity; however, inspection of infrared imagery of the Flat Creek area indicates extensive surface disturbance in Flat Creek between Dexter Creek and Second Pup Creek, two major left-limit tributaries of lower Flat Creek. The morphological descriptions of valley alluvium and colluvium given by the prospect owner, Dick Byrd, along with the common occurrence of free mercury and amalgam in prospect samples suggests that Flat Creek proper was mined, probably by hand methods (Freeman, 1986, p. 2).
Production: No published accounts of production, but see 'Workings/exploration' field.

Commodities (Major) - Au
Development Status: Undetermined
Deposit Model: Placer gold deposit (Cox and Singer, 1986; model 39a)

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Link to USGS - Alaska:	CI019

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References