North of 60 Mining News - The mining newspaper for Alaska and Canada's North

The future looks bright for the Pebble gold-copper-molybdenum project near Iliamna in southwestern Alaska. Northern Dynasty Minerals Ltd. President and CEO Ronald W. Thiessen said a preliminary assessment of the project indicates excellent potential for a long-life mine, having large-scale, low cost metal production.

The company said it undertook the assessment to quantify the Pebble project's cost parameters and to provide guidance for on-going engineering work to define the optimal scale of production. Preliminary forecasts and estimates in the report were developed to an order of magnitude level and are not based on systematic engineering studies, the company said in a Nov. 3 statement. The company said that at this early stage, data is incomplete and estimates were developed based on the expertise of the engineers involved. Independent engineer Derek Barratt, and Peter Beaudoin, an in-house engineer, were lead-authors of the study.

The preliminary assessment said the Pebble gold-copper-molybdenum porphyry deposit would be developed by conventional, large-scale, open pit mining methods. Four open pit stages were designed based on the block model proposed by Norwest Corp. in its February 2004 inferred mineral resource estimate of the Pebble deposit. The estimated inferred mineral resource is 2.74 billion tonnes grading 0.5 percent copper-equivalent (0.30 grams per tonne gold, 0.27 percent copper and 0.015 percent molybdenum above a cut-off grade of 0.30 percent copper-equivalent), containing 26.5 million ounces of gold and 16.5 billion pounds of copper.

Processing will produce concentrate

Processing of mill feed from the open pit will produce a flotation copper sulphide concentrate with gold and silver values as well as a separate molybdenum sulphide concentrate. Estimated metal recoveries of 88 percent for copper, 76 percent for gold and silver, and 60 percent for molybdenum were used in financial modeling.

Estimates are based on on-going test work, and are comparable to other large gold-copper porphyry mines, the company said. Copper concentrate was estimated to grade 28 percent copper, 26.6 grams per tonne gold, and 100 grams per tonne silver. Molybdenum sulphide flotation concentrate was estimated to grade 50 percent molybdenum. Copper concentrate would be transported via pipeline to a storage/dewatering/port facility at tidewater. Molybdenum sulphide concentrate would be packaged and shipped to market separately.

The preliminary assessment examined three production rate scenarios: 100,000 tonnes per day, 200,000 tonnes per day and a phased expansion from 100,000 tonnes per day to 200,000 tonnes per day in year six.

The analyses show that at the lowest production rate considered, the project would produce an annual average of 256 million pounds of copper, 365,000 ounces of gold, 8 million pounds of molybdenum, and 1.4 million ounces of silver during the first 10 years of a 62 year mine life.

At the largest scale studied, the project would produce an annual average of 470 million pounds of copper, 674,000 ounces of gold, 15 million pounds of molybdenum, and 2.5 million ounces of silver during the first 10 years of a 31 year mine life.