AGE OF THE BLACK HILLS GOLD MINERALIZATION
Two galenas from the Black Hills were isotopically analyzed for lead. One galena was associated with the gold quartz veins in the Homestake Gold Mine, while the other was from a lead vein in the Spokane Mine. The ages as calculated from the lead isotope data are 1500 to 1700 million years for the Homestake galena and less than 400 million years for the Spokane galena. It is concluded that there was a period of Precambrian mineralization in the Homestake deposit which was probably contemporaneous with the pegmatites of the southern Black Hills. (D.L.C.)