April 1st luncheon registration may now be completed online.  Please register online by Friday, March 28th.

Advance luncheon registration cost is $21 for non-members and $16 for members. Students may attend free of charge.  Same-day luncheon registration cost is $25.

The Apirl 1st Luncheon will be sponsored by Bay West

The Apirl 1st Luncheon will be co-hosted by the Association for Women Geoscientists

Presentation Title

The Pebble Copper Porphyry Deposit, SW Alaska

by Marcella Hartman, PG

Presentation Abstract

Copper porphyry deposits are the number one source of copper, supplying roughly 60% of the world’s supply. These deposits have formed at convergent plate boundaries throughout Earth’s history, but due to strong erosion rates, most are known to be Cenozoic or Mesozoic in age. Copper porphyries are generally large (>100 Mt), intrusive, epigenetic, conical to cylindrical shaped deposits of low to moderate grade (0.3-2.0%) derived from crystallizing magma reservoirs with associated hydrothermal alteration (USGS, 2010).

The Pebble deposit is a Cretaceous copper porphyry system located in southwest Alaska. It contains the fifth largest copper resource and largest gold resource of any known porphyry system (Goldfarb, 2012). This 10.8 billion ton deposit hosts 81 billion pounds of copper, 107 million ounces of gold, and 5.5 billion pounds of molybdenum, divided between the contiguous West Zone (discovered in 1989) and East Zone (discovered in 2005). Pebble has been analyzed through several geophysical methods, soil sampling, geologic mapping, and logging of over 1 million feet of core. The geology consists of the Kahiltna Flysch country rock, which was intruded by granodiorite and diorite sills, alkalic intrusions, and a granodiorite stock. Associated hydrothermal alteration introduced disseminated and stockwork mineralization, which occurs mainly as chalcopyrite, bornite and molybdenite. After mineral emplacement, the Pebble deposit was covered by Tertiary volcanics, which later eroded, allowing Pebble to be discovered and assessed as economically feasible for extraction.

Speaker Biography

Marcella graduated with a B.S. degree in geology from the University of Minnesota. Her experience has been split between civil engineering and exploration projects. She has worked on two major exploration projects: the Nokomis Cu-Ni-PGE deposit in northern Minnesota and the Pebble Cu-Au-Mo deposit in Southwestern Alaska. She also spent three years working for CNA Consulting Engineers, a Minneapolis-based firm specializing in underground construction and excavation. Marcella is currently a sales representative for the air and dioxin laboratories at Pace Analytical.