FORMATION OF SCHEELITE-BEARING AND SCHEELITE-BARREN SKARNS AT LOST CREEK, PIONEER MOUNTAINS, MONTANA

By looking for the differences in the origin of mineralized and barren skarns and comparing their field appearance, petrology, and major element chemistry, a petrogenetic theory was developed that may have some possible economic application. The deposits of the Brown's Lake-Lost Creek area of southwestern Montana were chosen for such a study because they appear to be typical scheelite-bearing skarns. Other previously examined characteristics which bear on the development of this theory are the association of tungsten ore at Bishop with dark-colored rock in preference to adjacent lighter colored skarn and the occurrence of the ore in monominerallic or biminerallic portions of the skarn.