Florence Bar

Mines, Inactive

Commodities and mineralogy

Main commodities Au
Ore minerals gold

Geographic location

Quadrangle map, 1:250,000-scale MZ
Quadrangle map, 1:63,360-scale D-3
Latitude 65.9456
Longitude -154.3417
Nearby scientific data Find additional scientific data near this location
Location and accuracy Gold was placer mined in the late 19th and early 20th centuries on what was then called Florence Bar, a prominent bar of sand on the west side of the Koyukuk River across from Rock Island Point. There apparently were several mines on the bar. The mines are in the SE1/4 of section 1, T. 6 N., R. 21 E., Kateel River Meridian. The location is accurate within 2,000 feet. It corresponds to location 2 of Cobb (1972).

Geologic setting

Geologic description

The Florence Bar placer mines were on a gravel bar in the Koyukuk River across the river from Rock Island Point. Most of the immediate area is covered by Quaternary flood plain, colluvium, alluvium, and terrace deposits (Patton and others, 1977). Bedrock at Rock Island Point includes Cretaceous pillow basalt and andesite flows; andesitic tuff, volcanic conglomerate and breccia; chert and fine-grained cherty tuff; and coquinoidal limestone. The rocks are widely altered to dark green hornfels. To the northeast, the andesitic volcanic rocks are in contact with Cretaceous quartz-pebble conglomerate, quartzose sandstone, andesitic and dacitic volcanic rocks, volcanic graywacke, and mudstone (Patton and Miller, 1966; Patton and others, 1977). The Indian Mountain granitic pluton, and associated latite dikes up to several hundred feet thick, intrude the Cretaceous stratified rocks about 8 miles northeast of Rock Island Point. The pluton is exposed no closer than five miles from the Koyukuk River, although several small dikes crop out on or near the river's edge (Patton and Miller, 1966).
Placer gold was known in the Koyukuk Basin in the 1890s or earlier (Schrader, 1904). It was first discovered in the sand bars of the Koyukuk River, where the river gradient is low, perhaps 5 feet per mile. The Florence Bar placer area was one of three bars (Florence, Hughes, and Tramway) mined before 1898, the Florence Bar mines produced a total of about $4,000 in gold (approximately 200 ounces of gold at $20.67 per ounce) (Maddren, 1910 [B 442]; Cobb, 1975). Early miners described the gold from Florence Bar as very fine, suggesting that it traveled a substantial distance (Smith, 1913). The source of the gold is unknown.
Geologic map unit (-154.344326500947, 65.945051848004)
Mineral deposit model Placer Au (Cox and Singer, 1986; model 39a)
Mineral deposit model number 39a
Age of mineralization Quaternary.

Production and reserves

Workings or exploration Placer gold was known in the Koyukuk Basin in the 1890s or earlier (Schrader, 1904). It was first discovered in the sand bars of the Koyukuk River. There is no record of the type of workings or their extent.
Indication of production Yes; small
Production notes About $4,000 in gold (approximately 200 ounces of gold at $20.67 per ounce) was recovered from Florence Bar before 1898 (Maddren, 1910 [B 442]; Cobb, 1975). The total gold production from the placer mines on Florence Bar is unknown.

Additional comments

This site is the Florence Bar, U.S. BLM MILS location 0020470014 (Oddenino and others, 1995; Interagency Minerals Coordinating Group, 2004).


MRDS Number A015572


Interagency Minerals Coordinating Group, 2004, Alaska Mineral Locations Database [MAS (Minerals Availability System) and MILS (Mineral Industry Location System)], http://imcg.wr.usgs.gov/dem.html (select Melozitna quadrangle).
Reporters G.E. Graham, D.J. Szumigala (Alaska Division of Geological and Geophysical Surveys)
Last report date 6/4/2004