Jumbo (near Dolomi)

Prospect, Undetermined

Alternative names


Commodities and mineralogy

Main commodities Ag; Au
Ore minerals pyrite; tetrahedrite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-1
Latitude 55.14143
Longitude -132.05197
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Jumbo prospect is probably about 0.3 mile east of Paul Lake and about 0.6 mile mile north-northeast of the center of section 6, T. 78 S, R. 89 E. The location is accurate to within 0.2 mile. This prospect is in an area with a concentration or claims and prospects, some of which cannot be precisely located or identified. The Wellfleet prospect is nearby.

Geologic setting

Geologic description

The Jumbo prospect has been described differently by Brooks (1902) and by Maas and others (1992). According to Brooks, the Jumbo prospect is a bluish quartz-breccia vein with gold and tetrahedrite that cuts graphitic phyllite. It was explored by a 40-foot shaft. Maas and others did not find the shaft in the recently logged area, but did locate a 115-foot adit in gray marble. Two veins are exposed in the adit. One is a quartz-breccia vein up to 4 feet thick that strikes N80W and dips 30N. A sample across the vein contained 2,673 parts per billion (ppb) gold. Another quartz-breccia vein is exposed for 51 feet along the adit. The vein strikes N80-90E and dips 30-35N; a 51-foot sample averaged 1,515 ppb gold.
Brooks (1902) describes the Wellfleet claim as (just?) west of the Jumbo, but Wright and Wright (1908) show it just to the south. According to Brooks, it is a 'quartz ledge' 20 to 25 feet thick in graphitic phyllite. The vein contains pyrite and samples were said to contain $2 to $4 in gold (at $20.67 per ounce). There is no record of production from either the Jumbo or the Wellfleet deposits, and no report of work on them since 1915 (Chapin, 1916).
The geology of the Dolomi area is dominated by an arcuate, generally north-trending, fault system and by a large dome centered over the eastern third of Paul Lake (Herreid, 1967). The Wales Group country rocks consist chiefly of several marble layers 200 to 1300 feet thick, interbedded with calcareous chlorite schist and marble.
Geologic map unit (-132.053640564715, 55.1410742500111)
Mineral deposit model Low-sulfide gold-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Veins are younger than the Late Proterozoic or Cambrian host rocks.

Production and reserves

Workings or exploration Brooks (1902) describes the workings as a 40-foot shaft. Maas and others (1991) could not locate the shaft but did find a 115-foot adit.
Indication of production None