The approximate location of the Jumbo prospect is in Section 36 on the southeast flank of Banded Mountain just above Through Glacier at an elevation of about 3400 feet (Elliott and Koch, 1981, p. 10, loc. 21). The location is probably accurate to within about a quarter of a mile.

The country rocks in the area of this prospect are metamorphosed pelitic strata of the Jurassic or older Mesozoic Hazelton Group, which are underlain and locally intruded by the Triassic Texas Creek Granodiorite; and the Eocene Hyder Quartz Monzonite, which intrudes the Hazelton and Texas Creek rocks (Berg and others, 1977, p. 15-17; Koch, 1996).

The deposit (Buddington, 1929, p. 101) consists of quartz fissure veins up to about 2 feet thick that cut metagraywacke, argillite, and banded hornfels and contain pyrite, galena, molybdenite, and traces of chalcopyrite and sphalerite. A field investigation in 1972 by the U.S. Bureau of Mines did not locate the Jumbo prospect or find the Jumbo adit reportedly driven sometime after Buddington's work (1929). Samples of quartz veins, breccia zones, and iron-stained, locally sulfide-bearing country rocks collected in 1972 in the general area of the Jumbo prospect (Berg and others, 1977, p. 101-110) contained up to 200 ppm Ag, 6 percent Pb, 8 percent Zn, and more than 2000 ppm Mo, but the average values of these metals was much lower. The veins also contain minor Cu, Zn, and Au.

An adit is said to have been driven sometime after 1929.

The Jumbo prospect on Banded Mountain (Buddington, 1929, p. 101) was originally staked in 1925 with 2 claims, restaked as a 6-claim group in 1933, 1935, and 1941, and covered in 1969 by the Marmot group of 51 claims (Berg and others, 1977, p. 40-41, 100-114). This record covers the area described as 'Marmot, lower basin (Jumbo area)' in Berg and others (1977, p. 101-106).