Pebble Mine is the common name of an advanced mineral exploration project investigating a very large porphyry copper, gold, and molybdenum mineral deposit in the Bristol Bay region of Southwest Alaska, near Lake Iliamna and Lake Clark. The proposal to mine the ore deposit, using large-scale operations and infrastructure, is controversial. Proponents argue that the mine will create jobs, provide tax revenue to the state of Alaska, and reduce American dependence on foreign sources of raw materials. Opponents argue that the mine would adversely affect the entire Bristol Bay watershed; and that the possible consequences to fish populations, when mining effluents escape planned containments, are simply too great to risk. Much of this debate concerns the tentative plan to impound large amounts of water, waste rock, and mine tailings behind several earthen dams at the mine site.
Location, Land Status, and Mineral Rights:
The Pebble prospect is in a remote and usually uninhabited part of the Bristol Bay watershed, in Southwest Alaska. The nearest communities, about 20 miles (32 km) distant, are the villages of Nondalton, Newhalen, and Iliamna. The site is 200 miles (320 km) southwest of Anchorage, Alaska. Pebble is approximately 15 miles (24 km) north of, and upstream of, Lake Iliamna between Katmai National Park and Lake Clark National Park. The deposit area is characterized by relatively Flat land dotted by glacial ponds, interspersed with isolated mountains or ranges of hills rising one or two thousand feet above the flats. Pebble is under a broad flat valley at about 1,000 feet (300 m) above sea level dividing the drainages of: Upper Talarik Creek, and the Koktuli River.
Mining Market / Economics:
Pebble is the largest (known) undeveloped copper ore body in the World, measured by either the amount of contained metal or the amount of ore. Northern Dynasty Minerals, Ltd. estimates that Pebble contains over $300 billion worth of recoverable metals at early 2010 prices. A report released by Northern Dynasty in early 2011 predicts profits for mine owners if a large scale open-pit mine is built at Pebble, given certain assumptions about the; cost of building the mine ($4.7 billion), size of the mining operation (200,000 tons per day), years that the mine will operate, metal prices over the life of the mine, as well as particulars of the mine design plan.
Reserves and Resources:
In 1992 Pebble was estimated to contain 3 million tonnes of copper and 11 million ounces of gold in 1 billion tonnes of ore. In 2004 Northern Dynasty had outlined, through additional drilling, over 4 billion tonnes of ore, none of it in the yet undiscovered "Pebble East." Estimates in February 2008 indicated: Pebble West contains (at a copper-equivalent cut-off of 0.30%) Measured and Indicated Resources of 18.8 billion pounds of copper, 31.3 million ounces of gold, and 265 million pounds of molybdenum, contained within 3026 million tonnes of ore and Inferred Resources of 5.9 billion pounds of copper, 9.1 million ounces of gold, and 993 million pounds of molybdenum contained within 1130 million tonnes of ore.;Pebble East contains (at a copper-equivalent cut-off of 0.6%) Inferred resources of 49 billion pounds of copper, 45 million ounces of gold, and 2.8 billion pounds of molybdenum contained within 3860 million tonnes of ore.
Ore body:The Pebble deposit is hosted in porphyritic granodiorite to tonalite of Upper Cretaceous age intruded into deformed sedimentary rocks of the Jurassic to Cretaceous age Kahiltna flysch terrane. Pebble Copper is a calc-alkali porphyry copper-gold-molybdenum deposit. The ore body extends from the surface to at least 1700 meters depth. In the western part of the orebody, mineralization occurs in a complex of several small granodiorite cupolas, diorite sills, older intrusions, breccias, and sediments. The western part of the deposit is locally exposed at the surface; thin gossans are developed and oxidation reaches 100 feet (30 m) in depth. The orebody extends eastward across a fault contact, at depth. East of the fault mineralization occurs in abundant sills and in the intruded sediments. Farther east, and deeper, the sills coalesce into a deeply buried granodiorite pluton. Mineralization and ore continue into the pluton. The eastern part of the deposit was eroded when it was exposed at the surface millions of years ago. It has since been buried by a thickening-to-the-east wedge of post-mineralization-age Tertiary sedimentary and volcano-sedimentary rocks.
Regional:The Kahiltna terrane is interpreted to represent a sediment trough formed on the landward (Alaska) side of the Wrangellia volcanic arc terrane, prior to collision of Wrangellia with Alaska. The Wrangellia and Kahiltna terranes docked to Alaska in the Cretaceous Period. This part of the Kahiltna terrane is dominated by Late Triassic basalt, andesite, and sedimentary rocks overlain by Jurassic-Cretaceous andesitic turbidites. Cretaceous granitic intrusive activity was widespread in the Kahiltna terrane. Tertiary volcanic and sedimentary rocks, and Quaternary glacial deposits, developed over the older rocks.