Abstract The sensitivity of ion-concentration distribution models to three key model assumptions, the pore-size distribution of clay media, the ‘distance of closest approach’ of ions to the clay surface, and the accessibility of sub-nanometer-wide clay mineral interlayer spaces to anions, was explored by solving the Poisson-Boltzmann equation for swelling and nonswelling clay materials. The calculations show that all three model assumptions impact significantly on values predicted for the anion-accessible porosity. As a consequence, macroscopic measurements of anion exclusion in clay media cannot be used to test any of the three model assumptions independently of the other two. Information gained at the nanoscale, a detailed characterization of pore-size distribution in particular, is necessary to develop accurate predictive models of the anion accessible porosity of clay media.

Abstract Alaska is commonly regarded as one of the frontiers of North America for the discovery of metalliferous mineral deposits. A recurring theme in the history of the state has been “rushes” or “stampedes” to sites of newly discovered deposits. Since about 1965, mining companies have undertaken much exploration for lode and placer mineral deposits. During the same period, because of the considerable interest in federal lands in Alaska and the establishment of new national parks, wildlife refuges, and native corporations, extensive studies of mineral deposits and of the mineral resource potential of Alaska have been conducted by the U.S. Geological Survey, the U.S. Bureau of Mines, and the Alaska Division of Geological and Geophysical Surveys. These studies have resulted in abundant new information on Alaskan mineral deposits. In the same period, substantial new geologic mapping has also been completed with the help of new logistical and technical tools. One result of the geologic mapping and associated geologic studies is the recognition of numerous faultbounded assemblages of rocks designated as tectonostratigraphic (lithotectonic) terranes. This concept indicates that most of Alaska consists of a collage of such terranes (Silberling and others, this volume, Plate 3). The purpose of this report is to summarize the local geology, geologic setting, and metallogenesis of the major metalliferous lode deposits and placer districts of Alaska. The term “major mineral deposit” is defined as a mine, mineral deposit with known reserve, prospect, or occurrence that the authors judged significant for any given geographic region. This report is