Abstract The Lisburne Group (Carboniferous-Permian) consists of a carbonate platform that extends for >1000 km across northern Alaska, and diverse margin, slope, and basin facies that contain world-class deposits of Zn and Ba, notable phosphorites, and petroleum source rocks. Lithologic, paleontologic, isotopic, geochemical, and seismic data gathered from outcrop and subsurface studies during the past 20 years allow us to delineate the distribution, composition, and age of the off-platform facies, and to better understand the physical and chemical conditions under which they formed. The southern edge of the Lisburne platform changed from a gently sloping, homoclinal ramp in the east to a tectonically complex, distally steepened margin in the west that was partly bisected by the extensional Kuna Basin (~200 by 600 km). Carbonate turbidites, black mudrocks, and radiolarian chert accumulated in this basin; turbidites were generated mainly during times of eustatic rise in the late Early and middle Late Mississippian. Interbedded black mudrocks (up to 20 wt% total organic carbon), granular and nodular phosphorite (up to 37 wt% P 2 O 5 ), and fine-grained limestone rich in radiolarians and sponge spicules formed along basin margins during the middle Late Mississippian in response to a nutrient-rich, upwelling regime. Detrital zircons from a turbidite sample in the western Kuna Basin have mainly Neoproterozoic through early Paleozoic U-Pb ages (~900-400 Ma), with subordinate populations of Mesoproterozoic and late Paleoproterozoic grains. This age distribution is similar to that found in slightly older rocks along the northern and western margins of the basin. It also resembles age distributions reported from Carboniferous and older strata elsewhere in northwestern Alaska and on Wrangel Island. Geochemical and isotopic data indicate that suboxic, denitrifying conditions prevailed in the Kuna Basin and along its margins. High V/Mo, Cr/Mo, and Re/Mo ratios (all marine fractions [MF]) and low MnO contents (<0.01 wt%) characterize Lisburne black mudrocks. Low Qmf/Vmf ratios (mostly 0.8-4.0) suggest moderately to strongly denitrifying conditions in suboxic bottom waters during siliciclastic and phosphorite sedimentation. Elevated to high Mo contents (31-135 ppm) in some samples are consistent with seasonal to intermittent sulfidic conditions in bottom waters, developed mainly along the basin margin. High d 15 N values (6-120) imply that the waters supplying nutrients to primary producers in the photic zone had a history of denitrification either in the water column or in underlying sediments. Demise of the Lisburne platform was diachronous and reflects tectonic, eustatic, and environmental drivers. Southwestern, south-central, and northwestern parts of the platform drowned during the Late Mississippian, coincident with Zn and Ba metallogenesis within the Kuna Basin and phosphogenesis along basin margins. This drowning was temporary (except in the southwest) and likely due to eutrophication associated with upwelling and sea-level rise enhanced by regional extension, which allowed suboxic, denitrifying waters to form on platform margins. Final drowning in the southcentral area occurred in the Early Pennsylvanian and also may have been linked to regional extension. In the northwest, platform sedimentation persisted into the Permian; its demise there appears to have been due to increased siliciclastic input. Climatic cooling may have produced additional stress on parts of the Lisburne platform biota during Pennsylvanian and Permian times.

Abstract T his P ortion of the field trip features visits to the worldfamous Sterling Hill and Franklin mines, in northwestern New Jersey, and their respective mining museums. Although both mines are no longer in operation, important geologic features can still be observed. At the Sterling Hill mine, we will have the opportunity to see zinc ore in place, both in an underground drift and in the Passaic open pit; at Franklin the pit is filled with water and only disseminated mineralization is still visible. The Furnace magnetite bed will also be seen adjacent to the Franklin open pit, as well as a large postore minette dike. If time permits we will visit a surface exposure of the Zero Fault in Franklin, which is an important regional structure that cuts the Sterling Hill orebody.

Abstract T he P urpose of this chapter is to review two aspects of the geochemistry of the Sterling Hill and Franklin zinc-ironmanganese deposits and the Furnace magnetite bed that underlies the Franklin deposit. These are (1) oxidation and sulfidation states determined from heterogeneous phase equilibria, and (2) stable isotopic compositions determined from analyses of carbonate, silicate, oxide, and sulfide minerals. The data place constraints on the genesis of the ores, which is the topic of the final section of the chapter. This review draws heavily from the results of my own dissertation research on Sterling Hill (Johnson, 1990; Johnson et al., 1990a) and from recent and continuing projects (Johnson et al., 1990b, Johnson, 1994, 1996, 1997; Volkert et al., 2000); it also includes the sulfur isotope results obtained by Ault (1957). For a complete review of the geology of the deposits, the reader is referred to the chapter by Metsger (2001), and to Metsger et al. (1958) and Frondel and Baum (1974). A complete catalog of the extensive literature on the deposits is given by Dunn (1995). The Sterling Hill and Franklin deposits are located in northwestern New Jersey within the Reading Prong-Hudson Highlands terrane, which is a belt of Mesoproterozoic sedimentary and igneous rocks that was regionally metamorphosed during the Grenvillian orogeny at about 1.0 Ga. Although the question has arisen as to whether the zinc and associated metals in these deposits were emplaced before or after the metamorphic event, it is now clear from structural, geochronologic, and phase equilibrium studies