Lower Ledge

Prospect, Probably inactive

Alternative names

Haley and Rogers

Commodities and mineralogy

Main commodities Au
Other commodities As; Pb
Ore minerals arsenopyrite; galena; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale PA
Quadrangle map, 1:63,360-scale D-4
Latitude 56.97631
Longitude -135.1105
Nearby scientific data Find additional scientific data near this location
Location and accuracy The location of the Lower Ledge prospect is somewhat uncertain but it is probably at an elevation of about 430 feet along the creek that drains from Pinta Lake to the head of Silver Bay. The prospect is about 0.6 mile north-northeast of the center of section 32, T. 56 S., R. 65 E. The surface and underground workings are shown by Bittenbender and others (1999, figs. 22-24).

Geologic setting

Geologic description

This deposit is one of many of similar deposits (PA002 to PA018) scattered over an area of about 6 square miles at the head of Silver Bay (Bittenbender and others, 1999). The deposits are gold-quartz veins with sparse sulfides, usually only pyrite and arsenopyrite. Samples that have been analyzed with modern methods usually show anomalous arsenic even if arsenopyrite is not identified in the rocks, and several parts per million mercury. The veins are often parallel to the bedding of the host rock which is graywacke and argillite of the Sitka Graywacke of Cretaceous age (Loney and others, 1975). Many of the so-called veins in the early literature are actually fault zones with lenses of quartz or concentrations of quartz stringers along the fault zone. Prospecting began in the area in 1871. The Stewart Mine (PA012) was located in 1872 and it was the first lode-gold mine in Alaska. The Silver Bay area has been prospected intermittently to the present but the veins are relatively small and most are low grade. The area has produced relatively little gold, many of the properties have not been active since before 1900, and there has been no production since the early 1940s.
The early history and exact location of this prospect are obscure although it was mentioned in several early reports (Becker, 1897; Knopf, 1912). Bittenbender and others (1999, figs. 22-24) located a 63-foot adit and a flooded shaft that are probably the Lower Ledge prospect. The adit is along a 1.5-foot-thick fault zone that cuts graywacke and contains quartz stringers up to 1/2 inch thick. The shear zone strikes S 70 W and dips steeply south to vertical. Samples taken in the adit contained no precious metal values. Samples of quartz from a dump near the shaft had very low precious metal values but contained minor pyrite and arsenopyrite, and rare galena. One sample of quartz float in the creek near the shaft contained 2,350 parts per billion gold.
Geologic map unit (-135.112263546237, 56.9759437093089)
Mineral deposit model Low-sulfide, gold-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Cretaceous or younger based on the age of the host rock.

Production and reserves

Workings or exploration The prospect was explored by a 63-foot adit and a now-flooded shaft of uncertain age.
Indication of production Undetermined
Reserve estimates None.
Production notes No record of production; probably none.

Additional comments

MAS number: 0021160016.

References