gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1998.62A.1.54 Using Noble Gas Isotope and Abundance Information to Place Constraints on Basinal Fluid Origin, Relative Timing, Transport Mode and Mass Balance: He-N₂ Rich Gases in the Mid-Continental USA Ballentine C. J. Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109-1063, USA Lollar B. S. Dept. Geology, The University of Toronto, Ontario M5S 3B1, Canada 1998 62A 1 102 103 Copyright © 1998, The Mineralogical Society 1998