Bl Introduction ___________________________ 1 Acknowledgments _____________________ 2 Stratigraphy __________________________ 2 Glacial sediments _____________________ 2 Volcanic rocks _______________________ 2 Hydrothermal alteration ____________________ 4 Silica minerals ________________________ 4 «-and j8-cristobalite __________________ 4 Quartz and chalcedony _______________ 5 Potassium feldspar __________________ 6 Zeolite minerals ______________________ 7 Heulandite-group minerals ____________ 7