Westphalian granite. Fifty-four new K/Ar age determinations for micas from granitic rocks, greisens, metafelsite dikes, and kaolinized granite are statistically identical. Sheeted vein mineralization, greisenization, and kaolinization were simultaneous processes which occurred in the time interval between granite crystallization at 301 + or - 12 m.y. and cooling below a mica closure temperature approximately 250 degrees C at 273.6 + or - 1.1 m.y. Kaolinization was a single-stage, hydrothermal process related to formation of the sheeted quartz-tourmaline + or - cassiterite + or - wolframite veins.--Modified journal abstract.