Open-File Report 2014–1115
This report presents isotopic age data from mineralized granitic plutons in an area of the Alaska Range located approximately 200 kilometers to the west-northwest of Anchorage in southwestern Alaska. Uranium-lead isotopic data and trace element concentrations of zircons were determined for 12 samples encompassing eight plutonic bodies ranging in age from approximately 76 to 57.4 millions of years ago (Ma). Additionally, a rhenium-osmium age of molybdenite from the Miss Molly molybdenum occurrence is reported (approx. 59 Ma). All of the granitic plutons in this study host gold-, copper-, and (or) molybdenum-rich prospects. These new ages modify previous interpretations regarding the age of magmatic activity and mineralization within the study area. The new ages show that the majority of the gold-quartz vein-hosting plutons examined in this study formed in the Late Cretaceous. Further work is necessary to establish the ages of ore-mineral deposition in these deposits.
First posted July 23, 2014
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Taylor, R.D., Graham, G.E., Anderson, E.D., and Selby, David, 2014, Timing of ore-related magmatism in the western Alaska Range, southwestern Alaska: U.S. Geological Survey Open-File Report 2014–1115, 25 p., https://dx.doi.org/10.3133/ofr20141115.
ISSN 2331-1258 (online)
Whole Rock Sample Descriptions
Appendix. Photographs of Sample Sites