The Pebble deposit formed about 90 million years ago when older sedimentary and igneous rocks were intruded by a granitic magma laden with hot fluids carrying dissolved copper, gold, molybdenum and silver as well as quantities of rhenium and palladium. As the fluids cooled, concentrations of sulfide minerals hosting the copper, gold, molybdenum and silver metals precipitated in thin quartz veins and as small grains disseminated throughout the granitic and adjacent sedimentary and igneous rocks. This type of deposit is referred to as a porphyry copper deposit with associated gold, molybdenum and silver.
Since acquiring Pebble in 2001, Northern Dynasty has expanded known mineral resources by more than 1,000%, while discovering significant new areas of high-grade mineralization. With more than 1,000,000 feet of drilling in 1,200 holes, a significant proportion of known mineralization at Pebble is in the measured or indicated category.
In total, the current Pebble resource estimate includes 6.44 billion tonnes in the measured and indicated categories containing 57 billion lb copper, 70 million oz gold, 3.4 billion lb molybdenum and 344 million oz silver; and 4.46 billion tonnes in the inferred category, containing 24.5 billion lb copper, 37 million oz gold, 2.2 billion lb molybdenum and 170 million oz silver(1)
. Quantities of palladium and rhenium also occur in the deposit. The Pebble deposit possesses the volumes, grades, and metallurgical characteristics to potentially support a modern, long-life mine.
(1) 2014 Pebble mineral resource estimate