Moly Dike; McLeod Occurrence, Kaiyuh Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Moly Dike; McLeod Occurrence	Occurrence
Kaiyuh Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

This property is on Doyon, Ltd. selected lands. For more information, contact Doyon, Ltd., in Fairbanks, Alaska.
Location: This occurrence is at the southwestern end of the Kaiyuh Mountains, 11.25 miles southeast of Blackburn, an abandoned settlement on the Yukon River. The occurrence is at an elevation of 1150 feet, approximately 250 feet northeast of hill 1170, in the SW1/4 sec. 32, T. 25 S., R. 3 W., Kateel River Meridian. It is approximately 1500 feet north of the caved trenches at the original McLeod prospect (UL003). The location is accurate within 300 feet.
Geology: This occurrence consists of molybdenite-bearing quartz veinlets in a weakly to moderately developed quartz-stockwork zone exposed in frost-riven rubble in an area of about 100 by 1000 feet. The mineralization is hosted by a suite of quartz-feldspar-porphyritic granite dikes that trend 330 degrees across hill 1170 in a swath about 400 feet wide. Individual dikes are up to 100 feet thick. Molybdenite and ferrimolybdenite are concentrated in the northernmost dike, which is highly sericitized and pervasively cut by locally molybdenite-bearing quartz veinlets that form parallel arrays and local stockworks (Bressler and others, 1979). The molybdenite occurs as discrete, platy aggregates along the margins of the quartz veinlets and as very fine grained disseminations in the quartz, imparting a distinct blue-gray color to the veinlets. Vein density ranges from 1 veinlet to more than 15 veinlets per square foot; they are mostly concentrated along the southern contact of the northernmost dike. The molybdenum content of this deposit ranges between 0.01 and 0.09% molybdenum (Bressler and others, 1979). The country rocks in the general area of this occurrence include poorly sorted, medium- to coarse-grained arkosic sandstone and subordinate siltstone, shale, and lesser intermediate to mafic volcanic rocks. The strata generally strike northwest with gentle dips to the northeast and southwest (Bressler and others, 1979). The dikes occur along the western lobe of a Cretaceous or Tertiary granitic stock composed of 20-40% bipyramidal to subhedral quartz and 10-30% feldspar phenocrysts in a matrix mostly of quartz and feldspar. Pyrite is a minor accessory (<1%), along with rare chalcopyrite; there are no mafic minerals. The outcrop area of the stock measures about 6000 by 2500 feet, and is elongate to the northeast. The exposure is centered along the boundary of sections 32 and 33, and the stock sends dike swarms into sections 4 and 28 (Bressler and others, 1979). A younger suite of biotite-quartz-feldspar porphyritic dikes exposed south of the McLeod prospect apparently does not occur at this site (Bressler and others, 1979). Also see UL003 and UL005.
Workings: Surface exploration and mapping was conducted by Bear Creek Mining Company in 1976 (Fields, 1976), and by WGM, Inc., on behalf of Doyon, Ltd., in 1979 and 1980 (Bressler and others, 1979; Lessman, 1979). Airborne and radiometric surveys were completed in 1980 (Boniwell, 1981 [DR 81-05]; Boniwell, 1981 [DR 81-08]). A 3500- by 2700-foot molybdenum soil anomaly was defined; this anomaly is open to the southwest.
Age: Late Cretaceous or Tertiary, the age of the granitic stock and its apophyses.
Alteration: The principal mineralized dike is pervasively sericitized and locally intensely silicified. The bedded rocks peripheral to the stock are thermally altered to hornfels and contain secondary pyrite and chlorite.

Commodities (Major) - Mo; (Minor) - Ag, Cu, Mn, Pb, Sn, W
Development Status: None
Deposit Model: Porphyry Mo (Cox and Singer, 1986; model 16a and 21b)

Other Databases

Link to USGS - Alaska:	UL004

Other Regions, Features and Areas containing this locality

References