Mount Schwatka

Occurrence, Inactive

Alternative names

East Fork Flat Creek

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Zn
Other commodities Mo; Pb
Ore minerals smithsonite; unknown zinc mineral(s)

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale D-1
Latitude 65.9172
Longitude -147.061
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents closely-spaced multiple mineral occurrences and anomalies at the headwater divide between the upper East Fork of Flat Creek and an unnamed east tributary of Jefferson Creek located about 6 miles northeast of Mt. Schwatka. The site is at elevations of 2,000 to 3,000 feet and involves all of Sections 26 and 35, T. 13 N., R. 3 E., of the Fairbanks Meridian. The location is accurate within 0.5 mile and denotes the center point of these two sections.

Geologic setting

Geologic description

The Mount Schwatka area is a fault-bounded block about 35 to 40 miles east-west and composed of marine sedimentary and volcanic rocks (Chapman and others, 1971). Like the Crazy Mountains to the east, it is one of several fragmented geologic blocks termed klippen-like features (Payne, 1959) comprised of North American plate geology that are tectonically emplaced along the Tintina Fault (Payne, 1959). The Tintina Fault is a major feature of northwest North America and in central Alaska it has resulted in conspicuous fault-lineated valleys and elongate but discontinuous hills and ridges composed of sedimentary rock that abut the Yukon River basin. It is generally believed these rocks are correlative to the Selwyn Basin in the Yukon Territory (Tempelman-Kluit, 1977). This implies that there has been as much as 280 miles of right lateral displacement along the Tintina Fault.
In the Mt. Schwatka area a Cambrian black shale unit is overlain by Ordovician-Silurian volcanic rocks including the Fossil Creek Volcanics (Blodgett and others, 1987). In the local area of this occurrence the shale unit also includes intermediate tuffaceous limestone, andesite, and locally pyroclastics, gray shale, and chert (Barker, 1980). Stratigraphically overlying the volcanic rocks is the Tolovana Limestone (Chapman and others, 1971), which prominently caps some of the higher terrain.
Similar to the Selwyn Basin, the Mt. Schwatka area features a number of lead-zinc occurrences, some with minor copper, and mostly localized in early- to mid-Paleozoic marine sediments and volcanics including intermediate tuffaceous. Most mineral occurrences are hosted in, or near, fault zones and breccia.
Sulfides of copper, lead, zinc and their associated oxides occur in quartz veins that cut outcropping sequences of calcarenite (?), tuffaceous limestone, and commonly iron-stained argillite rocks within a complex structural setting (Barker, 1980). A few subcrops of dense iron-rich tuff, chert and shale were noted. This host sequence is bounded on the north and east by the Tolovana Limestone, which caps the higher ridges. At a few locations specks of galena were noted in the limestone near contacts with underlying argillaceous rocks.
Geologic map unit (, )
Mineral deposit model Zinc replacement body? (Cox and Singer, 1986; model 19a).
Mineral deposit model number 19a?
Alteration of deposit Most original mineralization has been destroyed by oxidation and gossan development. Smithsonite is generally a carbonate-altered sphalerite (Barker, 1980).

Production and reserves

Workings or exploration
Sulfides of copper, lead, zinc and their associated oxides occur in quartz veins that cut outcropping sequences of calcarenite (?), tuffaceous limestone, and commonly iron-stained argillite rocks within a complex structural setting (Barker, 1980). A few subcrops of dense iron-rich tuff, chert and shale were noted. This host sequence is bounded on the north and east by the Tolovana Limestone, which caps the higher ridges. At a few locations specks of galena were noted in the limestone near contacts with underlying argillaceous rocks.
On a west-facing ridge slope a boulder train of smithsonite occurs; samples contained 30 to 46.5 percent zinc, up to 0.175 percent lead, and 0.18 percent copper. Near the head of this slope an argillite sample was anomalous with lead, zinc, and also reported 6 ppm silver and 195 ppm molybdenum. The source was not found exposed. Isolated patches and pods of sulfides with malachite staining occur in the host sequence. Peripheral to the area, about 7 of 15 widely spaced soil samples and 9 of 10 stream sediment samples contained anomalous values of one or several of these metals.
The evaluation of this site was one visit with no follow-up.
Indication of production None

Additional comments

This site is on land now included in the Yukon Flats National Wildlife Refuge, which excludes mineral exploration activities.

References

Reporters J.C. Barker
Last report date 3/15/2016