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Forrest, Kimball, 1983

Geologic and isotopic studies of the Lik deposit and the surrounding mineral district, De Long Mountains, western Brooks Range, Alaska

Bibliographic Reference

Forrest, Kimball, 1983, Geologic and isotopic studies of the Lik deposit and the surrounding mineral district, De Long Mountains, western Brooks Range, Alaska: University of Minnesota, Minneapolis, Ph.D. dissertation, 161 p., illust., maps.


The Lik deposit is located in the De Long Mountains of northwest Alaska, 20 km northwest of the Red Dog deposit; together the deposits form the De Long Mountains mineral district. It is a sediment-hosted submarine exhalative Zn-Pb-Ag deposit within black shales and cherts of the Mississippian Kuna Formation. The regional structural geology is dominated by thrusting formed during the Cretaceous. Results from field mapping and diamond drilling have been interpreted to indicate that the mineral deposits formed in an intracratonic rift basin, although volcanics are absent, implying that rifting stopped prior to reaching an active spreading stage. Proven reserves of the Lik deposit are 25 million tons grading 8.8% Zn, 3.0% Pb and 34 g/ton Ag. These are in a zone 2,000 m long and 500 m wide; however, mineralization continues along strike to the north and south. Drill sections through the deposit show that the mineralized horizon varies from tabular to complexly folded, and the site of sulfide deposition is interpreted to lie in a graben. Textural studies have indicated a long sinuous zone of complex and brecciated textures in the center of the deposit trending parallel to strike. This is inferred to be an ore fluid vent or line of vents. Sulfur isotopic values of sulfide minerals range from near 0‰ to 19‰, and show a distinct pattern of progressive enrichment in 34S away from the central axial zone, supporting the vent hypothesis. Oxygen isotope values from quartz and chert, contemporaneous with mineralization, range from 22.1‰ in the central zone to 25.9‰ along the flanks, and their distribution is interpreted to be the result of progressive cooling away from the vent zone. Both sulfur and oxygen isotopic patterns suggest that the Lik deposit formed by the mixing of an exhalative fluid which contained metals and H2S, with seawater containing bacterially derived H2S, and the resultant cooling caused metal sulfide deposition. In addition to Lik and Red Dog, other smaller deposits have been discovered in the district and it is proposed that all deposits are located within one of three sub-parallel third-order basins.

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