Blacksand Beach

Occurrence, Undetermined

Commodities and mineralogy

Main commodities Au; Fe; Ti
Other commodities PGE; Zr
Ore minerals ilmenite; magnetite; native gold; pge; rutile; zircon
Gangue minerals garnet

Geographic location

Quadrangle map, 1:250,000-scale YA
Quadrangle map, 1:63,360-scale B-4
Latitude 59.38
Longitude -139.43
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Blacksand beach placer is about 10 miles long extending northwesterly between the Ahrnklin and Dangerous Rivers. The coordinate location is the approximate mid-point of the beach, which extends northwesterly into the Yakutat B-5 quadrangle. The deposit coincides with a named geographic feature (Blacksand Spit); it is location 7 of Cobb (1972). It is southeast of the Situk beach placer (YA007).

Geologic setting

Geologic description

The Blacksand deposit is on a modern spit that extends along the coast line for about 10 miles. It was derived by high-energy reworking of underlying unconsolidated sediments of Holocene age (Foley and others, 1995; Reimnitz and Plafker, 1976) and from the density stratification of the alluvium constantly brought down by the Ahrnklin and Dangerous Rivers, which head in the Fairweather Range.
Black and garnet sand lenses 0.1 to 0.2 feet thick contain interlocked magnetite-ilmenite or garnet and, more rarely, gold. Cobb (1979, p. 19) cites a reliable report of a PGE (platinum) from the mouth of the Situk River.
Geologic map unit (-139.43169343652, 59.379714283638)
Mineral deposit model Beach placer: single-cycle deposits of high-energy systems.
Age of mineralization Holocene

Production and reserves

Workings or exploration The beach has been mined on a small scale for many years. It was sampled by Thomas and Berryhill (1962), MacKevett and Plafker (1970; sample no. 67Apr76C), Reimnitz and Plafker (1976, samples 39, 40, and 41), and by Foley and others (1995, samples 276, 277 and 278). Thirteen beach locations were sampled by Thomas and Berryhill; their sample number 26 (table 12) contained 0.00012 ounce/cubic yard gold, 11.7 pounds/ cubic yard titanium, and 25.8 pounds/cubic yard iron. Six of the thirteen samples contained 10 pounds or more of titanium/cubic yard. The maximum amount of titanium reported by Thomas and Berryhill was 47.4 pounds/cubic yard; maximum iron was about 150 pounds/cubic yard. Reimnitz and Plafker (1976) reported from 0.010 to 0.050 ppm gold in their samples. Gold was determined by atomic absorption, hence it may not correlate with the amount that could be recovered by placer mining and processing. Gold was not found by Foley and others (1995) in their head splits, but was reported in two of three spiral concentrates of the samples. Spiral concentrates also contained as much as 3.1 percent titanium and 1665 ppm zirconium.
Indication of production Yes; small

Additional comments

The beach is in the Tongass National Forest.

References