Fluid Inclusion Evidence for Ore-Forming Solutions: Phoenixville, Audubon and New Galena Mine Districts, PA

The Audubon, Phoenixville and New Galena Pb-Zn-Cu vein deposits of southeastern Pennsylvania have been investigated by microthermometric analysis of fluid inclusions in sphelerite, dolomite and quartz. The results obtained from primary and pseudosecondary inclusions in spherelite indicate that the ore was deposited by a sodium rich brine of moderate salinity (11-14 equivalent wt. % NaCl) at temperatures probably near 200 degrees C. The Na-rich character of the fluid suggests that dissolved constituents in the fluids were derived from Na-rich sedimentary rocks of the Newark basin. Local fluid-wallrock interaction may have produced slightly higher salinity fluids (15-16 equivalent Wt. % NaCl) present at New Galena. The data obtained in this study suggest that igneous activity did not necessarily cause the development of the ore fluid as mineralogical evidence indicates that temperature throughout the basin reached 200 degrees (C). Deposition of the ore occurred where connate, metal rich brines migrating through faults and fractures encountered temperature and chemical conditions, developed through wall rock interaction with the ore solution, which favored sulfide precipitation