Archean Geology of the Northern Block of the Ishpeming Greenstone Belt, MarquetteCounty, Michigan. Chapter F

摘要

The investigation is a continuation of mapping of the Ishpeming greenstone beltby Michigan Technological University personnel begun during the summer of 1984 under the direction of Bornhorst and continued during successive summers represents approximately 24 person-months of field work. Geologic mapping has utilized a combination of compass-and-pace along traverse lines and direct plotting on topographic sheets where topographic features are distinctive. One hundred fifty-two whole-rock geochemical analyses have been made by X-ray fluorescence on an automated Phillips wave-length dispersive spectrometer at Michigan Technological University using a modification of the technique described by Rose and others (1986). One hundred seventy-three samples were analyzed for gold using fire assay and neutron activation (1 ppb detection limit), and 22 samples were analyzed for silver using inductively coupled plasma (0.5 ppm detection limit). One hundred eighty-six thin sections have been studied. Plagioclase compositions were determined by the Michel Levy technique when albite twinning was present and otherwise by the relief relative to the mounting epoxy (n=1.54). Actinolite and hornblende have been distinguished on the basis of color and ZC (Winchell and Winchell, 1951).