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Exploration case study using indicator minerals in till at the giant Pebble porphyry Cu-Au-Mo deposit, southwest Alaska, USA

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Abstract

The Pebble deposit in southwest Alaska (Fig. 1) contains one of the largest resources of copper and gold in the world. It includes a measured and indicated resource of 5,942 million tonnes (Mt) at 0.42% Cu, 0.35 g/t Au, and 250 ppm Mo (0.30% copper equivalent, CuEQ, cut off) and contains significant concentrations of Ag, Pd, and Re (Northern Dynasty Minerals 2011). The deposit remains open at depth. The Pebble West zone was discovered in 1989 by Cominco American. In 2005, Northern Dynasty Minerals Ltd. (NDM) discovered Pebble East, and in July 2007, NDM partnered with Anglo American to form the Pebble Limited Partnership (PLP). The U.S. Geological Survey began collaborative investigations with PLP in 2007 to identify techniques that will improve mineral exploration in covered terranes. The Pebble deposit is an ideal location for such a study because the deposit is undisturbed (except for drilling), is almost entirely concealed by post-mineral volcanic rocks and glacial deposits, and because its distribution is well constrained in the subsurface by PLP’s drill-hole geology and geochemistry. An exploration method developed by Averill (2007) that utilizes porphyry copper indicator minerals (PCIMR) in glacial till samples was applied at Pebble; samples were collected up- and down-ice (of former glaciers) from the deposit. The distribution of several PCIMs identifies the deposit, which suggests that PCIMs may be useful in exploration for other concealed porphyry deposits in the region. In this study, we compare the efficacy of PCIMs relative to that of pond and stream sediments also collected in the deposit area. The Pebble deposit is located 380 km southwest of Anchorage, in the Bristol Bay region of southwest Alaska. There is no road network and access to the study area is by helicopter. The deposit is situated in a broad glacially sculpted topographic low at the head of three drainages, Talarik Creek, North Fork Koktuli River, and the South Fork Koktuli River (Fig. 1). The study area is in a zone of discontinuous permafrost and is masked by lichen-rich tundra vegetation.

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Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Exploration case study using indicator minerals in till at the giant Pebble porphyry Cu-Au-Mo deposit, southwest Alaska, USA
Year Published 2011
Language English
Publisher Vuorimiesyhdistys - Finnish Association of Mining and Metallurgical
Contributing office(s) Central Mineral and Environmental Resources Science Center
Description 8 p.
Larger Work Type Conference Paper
Larger Work Title Indicator mineral methods in mineral exploration: Workshop in the 25th International Applied Geochemistry Symposium 2011, 22-26 August 2011 Rovaniemi, Finland
First page 41
Last page 48
Conference Title 25th International Applied Geochemistry Symposium Workshop 3: Indicator mineral methods in mineral exploration
Conference Location Rovaniemi, Finland
Conference Date August 21, 2011
Country United States
State Alaska
Online Only (Y/N) N
Additional Online Files (Y/N) N