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Environmental Behavior of Mineral Deposits

Bald Mountain copper-zinc-gold-silver deposit, northern Maine - USGS has been conducting research to characterize the natural chemical signatures associated with this type of deposit, and to determine what conditions and processes affect the long-term mobility of heavy metals in the weathering environment. Both aspects of this study are providing necessary information to refine models for the formation and weathering of this type of mineral deposit in the eastern United States, and thus aid mineral exploration and mineral-resource and environmental assessments.

The Bald Mountain volcanic-associated massive sulfide deposit offers unparalleled opportunities to study natural geochemical backgrounds because it was discovered in an area that has not experienced historic metallic mining. The deposit is hosted by a moderately dipping sequence of Paleozoic submarine volcanic rocks, basalt with lesser rhyolite, and subcrops beneath 0 to 15 m of glacial till. The mineralization consists of: (1) a hypogene massive sulfide zone (pyrite and pyrrhotite with lesser chalcopyrite, sphalerite, and arsenopyrite); (2) a supergene sulfide zone (pyrite, chalcocite, covellite, and enargite); and (3) a gold-bearing gossan zone (goethite, quartz, and trace remnant sulfide minerals). Ground waters in and around the deposit show elevated concentrations of dissolved iron, base metals (copper, zinc, nickel, cobalt, cadmium, and lead), arsenic, and sulfate compared to regional surface waters and ground water upgradient from the deposit. Subsurface weathering of the Bald Mountain deposit appears to significantly and naturally elevate the concentration of dissolved constituents in ground waters relative to regional surface waters.

	Clayton Lake (visible in map below) with Bald Mountain in the background. The Bald Mountain deposit is situated in the remote and undeveloped North Maine Woods.
	Map of the Bald Mountain area.
	Artesian well, Bald Mountain. Although the area has never experienced mining activity, the ground waters in and around the Bald Mountain deposit naturally have elevated concentrations of iron, arsenic, and other "heavy" metals.
	Geochemical studies include ground and surface water sampling within and adjacent to the buried Bald Mountain deposit to characterize natural variations around a massive sulfide deposit.

Products

Seal, R.R., II, Foley, N.K., Haffner, D.P., and Meier, A., 1998,

Environmental geochemistry of surface and ground waters around the Bald Mountain massive sulfide deposit, northern Maine: natural backgrounds from a mineralized, but unmined area [abs.]: Geological Society of America, Abstracts with Programs, v. 30, p. A128.

Collaborators

Collaborators for this field area include the Black Hawk Mining Company.