Companies developing the large Pebble deposit in Southcentral Alaska published new, higher resource estimates for the project Feb . 1. Pebble is near Iliamna southwest of Anchorage. The deposit contains substantial amounts of copper, gold and molybdenum.

Despite the greater resources, Pebble still faces substantial economic challenges, particularly in developing an affordable source of energy, said Mike Heatwole, a spokesman for the Pebble Partnership, the company formed by owners Anglo American and Northern Dynasty Minerals to develop the project.

New drilling in 2008 and 2009 has boosted estimates in the higher-confidence "measured and indicated" category by 17 percent, according to the Pebble Partnership announcement.

Within this category, the estimated reserves of contained copper increased 12 percent, the gold estimate increased 14 percent and molybdenum increased 16 percent, the company said.

Measured and indicated is a category of resource defined by tightly spaced drill holes in which geologists have a high degree of confidence.

At a 0.3 percent cutoff grade for ore mining, the Pebble deposit is now estimated to contain 5.9 billion tonnes of ore at an average grade of 0.78 percent "copper equivalent," where the metal value is expressed in a way that combines values of all three minerals.

Based on this, Pebble is now estimated to containing 55 billion pounds of copper, 67 million ounces of gold and 3.3 billion pounds of molybdenum in the measured indicated category, the company said.

An additional 4.84 billion tons of ore at an average grade of 0.53 percent copper equivalent is estimated in the "inferred" resource category, where resources are indicated by more widely spaced drill holes.

The inferred resource is estimated to contain an additional 25.6 billion pounds of copper, 40.4 million ounces of gold and 3.3 billion pounds of molybdenum.

Pebble spokesman Mike Heatwole said the company is still working on a pre-feasibility study to develop the project. More exploration drilling is planned in 2010, but details of the program are still being worked out, he said.

Environmental work for the year is now gearing up, but drilling won't begin until May, Heatwole said.

The company will not file for its state and federal permits this year, as was planned, but will focus on completing an environmental studies baseline document and a conceptual mine plan. Both of these are needed before permits can be filed, he said.

Power requirements for the mine won't be known with precision until a mine plan is developed. Estimates have been made that 200 megawatts to 300 megawatts of electricity would be needed but the volume of ore milled each day, which is still being worked out, would partly determine the power requirements.

Whether the mine is an underground project, even partly, also would affect power demand because underground mining requires more electricity than a surface mine, Heatwole said.

Pebble's project plan to date has assumed that power would be supplied from the existing power grid on the Kenai Peninsula via a submarine cable crossing lower Cook Inlet and a land transmission line to reach the inland mine site.

Other alternatives are being considered, however, including a small-scale liquefied natural gas regasification plant built at a new port on west Cook Inlet with either gas or electricity shipped to the mine.

Tim Bradner can be reached at

tim.bradner@alaskajournal.com.