SEDIMENTARY EXHALATIVE ZN-PB-AG DEPOSITS (MODEL 31a; Briskey, 1986) by Karen D. Kelley, Robert R. Seal, II, Jeanine M. Schmidt, Donald B. Hoover, and Douglas P. Klein SUMMARY OF RELEVANT GEOLOGIC,GEOENVIRONMENTAL, AND GEOPHYSICAL INFORMATION Deposit geology Lens-like bodies of stratiform sulfide minerals (lead, zinc, ± iron) as much as a few tens of meters in thickness are interbedded withfine-grained dark clastic and chemical sedimentary rocks. These deposits may have large lateral extent (hundreds of meters to kilometers). Mineralized rock varies from a single layer to numerous bodiesthat may be vertically stacked or lateral equivalents. The most common associated sulfate mineral is barite which may be peripheral to or stratigraphically above the deposit (Rammelsberg and Meggen,Germany; Tom, Yukon Territory; Lady Loretta, Australia; and Red Dog, Alaska), or it may form crudely segregated mixtures with sulfide minerals (Cirque, British Columbia). Many deposits have no associatedbarite (HYC, Australia; Sullivan, British Columbia; and Howard's Pass, Yukon Territory). Stockwork, disseminated, or vein-type ore, interpreted as feeder zones to stratiform mineralized rock, aresometimes found underlying or adjacent to stratiform ore and are sometimes accompanied by alteration of footwall rocks (fig. 1). U.S. Bureau of Mines (1993) statistics show that in 1993 the two mines inthe United States with greatest zinc output were Red Dog, Alaska and Balmat, N.Y. In 1994, the Red Dog mine produced 533,500 t of zinc concentrate with an average grade of 55.8 weight percent zinc(Mining Journal, 1995). Mines in the Balmat district produced 499,000 t in 1993. Both mines also produce lead and silver. Examples
Red Dog, Lik, and Drenchwater (Alaska); Balmat (N.Y.); Meggen andRammelsberg (Germany); Faro and other
deposits in the Anvil district, Tom, Jason, and Howard's Pass (Yukon Territory); Cirque and Sullivan (British
Columbia); Lady Loretta, McArthur River, Mount Isa,...