A new technical report released by backers of the Pebble mine project includes a revised mineral resource estimate that concludes the deposit has the world’s single most significant source of rhenium, one of the rarest elements in Earth’s crust.
Rhenium, a silvery white element with a metallic luster, has good wear resistance and can withstand corrosion. About 80 percent of the world’s rhenium is used in the production of aviation engines and for high-temperature coating on rockets and missiles. It is also used for spacecraft instruments and high-temperature components such as thermal shielding, arc discharge and electrical contractors.
Rhenium is not found free in nature, but occurs in minute amounts in the mineral molybdenum, which has been identified along with copper and gold as a significant deposit in the proposed Pebble mine site. It has a high-density point exceeded only by platinum, iridium and osmium and its melting point is exceeded only by tungsten and carbon.
Very little is known, however, about the toxicity of rhenium and its compounds because they are used in very small amounts. Only a few compounds of rhenium have been tested for their acute toxicity. There are also issues related to chemical used to extract them from other metals.
The United States imports large amounts of rhenium from foreign producers and federal officials have been eager to map and conduct geophysical surveys to identify potential sources of rhenium and other critical minerals. The effort began after President Trump in 2017 directed the Interior Department to establish a list of critical minerals and develop recommendations to streamline permitting and increase the domestic production of these critical minerals.
The U.S. Geological Survey recently announced federal funds totaling $1.13 million for such surveys in Alaska, but has delayed the actual work until next summer because of the novel coronavirus pandemic.
