Apodaca, L.E., 1993, Genesis of lode gold deposits of the Rock Creek area, Nome mining district, Seward Peninsula, Alaska: University of Colorado, Boulder, Ph.D. dissertation, 222 p., illust., maps.
The Nome mining district is located in northwest Alaska in the southwestern part of the Seward Peninsula. Lode gold deposits of the Rock Creek area, Nome mining district are located approximately 16 km north of Nome, Alaska and are hosted by greenschist-facies Paleozoic(?) metasedimentary rocks of the Nome Group. Gold-bearing veins, which occur predominantly in tensional fractures, are composed of quartz, carbonate (dolomite to ankerite), chlorite, feldspar (albite), gold, and minor sulfides (arsenopyrite, pyrite, galena, sphalerite, stibnite, chalcopyrite, and some jamesonite). The wall rock alteration is generally weak, and consists of silicification, carbonatization and sulfidation adjacent to the mineralized veins. The study of fluid inclusions by microthermometry and mass spectrometry, along with stable isotope studies, has aided in constraining fluid sources and conditions of ore deposition. Fluids from the mineralized veins consist of H2O-CO2 , N2CH4H2S, have low salinity (75 wt.% NaCl) and are comprised of both water-dominated and gas-dominated inclusions. Mineralized veins formed at minimum temperatures of 184-272oC and minimum pressures are inferred to be 1-1.5 kbar corresponding to depths of at least 2.8-3.9 km. Isotopic compositions of the ore fluids for [delta] 18O ranged from 6.1 to 9.0 per mil, and [delta] D ranging from $93 to $145 per mil. The oxygen isotopic data are consistent with metamorphic water but the hydrogen isotopic data for the Rock Creek area are probably not sufficient to define the source of the mineralizing fluid. The fluids that formed the gold-bearing quartz veins were emplaced post-kinematically, as indicated by the observation that undeformed veins crosscut the metamorphic foliation of their host rocks. Relative age relationships between the Rock Creek area, the tectonic history of the Seward Peninsula, and age constraints on mineralization from other gold-bearing deposits of the Seward Peninsula indicate that gold-bearing veins were emplaced during the Cretaceous. Ore solutions were derived from devolatilization reactions. The fluids migrated upward into tensional fractures during uplift of the peninsula, resulting in gold deposition by changes in the redox state, precipitation of sulfides, and possibly H2O-CO2 immiscibility.
Theses and Dissertations
