Northeastern (46th Annual) and North-Central (45th Annual) Joint Meeting (20–22 March 2011)

Paper No. 16
Presentation Time: 1:30 PM-5:30 PM


NGUYEN, Michael, Department of Geology, Juniata College, 1700 Moore St, Huntingdon, PA 16652, MATHUR, Ryan, Department of Geology, Juniata College, 1700 Moore Street, Huntingdon, PA 16652, MUNK, LeeAnn, Department of Geological Sciences, University of Alaska, 3101 Science Circle, Anchorage, AK 99508, LANG, James R., Hunter Dickinson Services, Inc, 1020-800 West Pender St, Vancouver, BC V6C 2V6, Canada and GREGORY, Melissa, University of British Columbia, 2020-2207 Main Mall, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC V6T 1Z4, Canada,

The Pebble Cu-Au-Mo porphyry deposit formed at about 90 Ma and is located in southwest Alaska. The total resource is 10.8 Gt which contains 80.6 Glb Cu, 5.6 Glb Mo and 107.4 Moz Au. Mineralization formed at about 90 Ma and occurs in a West Zone exposed at surface and an East Zone concealed by younger rocks. This study uses copper isotopes fractionation measured in minerals and surface waters to understand high temperature mineralization processes and current weathering processes. Sulfide minerals have measured δ65Cu values ranging from 0.78‰ to 2.28‰ (hypogene West), 0.02‰ to 1.55‰ (hypogene East), -3.49‰ to 1.88‰ (oxide West), and -5.04‰ to 1.27‰ (supergene West). The mineralization results show a relationship of the hypogene minerals to elevation whereas δ65Cu values become depleted farther from the hypogene source. Shallow groundwaters are enriched in δ65Cu above the deposit and become progressively depleted in 65Cu away from the deposit. Patterns measured in the copper isotope composition of both the minerals and surface waters demonstrate the potential use of copper isotope fractionation in exploration geology as well as to understand the copper sources to the environment.