Salt Chuck is a historic mining site at the head of Kasaan Bay, on the east coast of Prince of Wales Island, about 39 miles (63 km) northwest of Ketchikan and 4.5 miles (7.2 km) southwest of Thorne Bay, Alaska. The lagoon sits within a Paleozoic mafic-ultramafic intrusion, roughly 429 million years old, made up of clinopyroxenite and layered gabbro that cuts through older metavolcanic and sedimentary rock of the Descon Formation. Copper-sulfide minerals such as bornite and chalcopyrite, concentrated near the pyroxenite-gabbro contact, formed the ore body later mined at Salt Chuck. The U.S. Coast and Geodetic Survey published the local name in 1943. “Chuck” is a Chinook Jargon word for water; applied here it denotes a salt lagoon that fills at high tide, sometimes with a bore, and empties, or partly empties, at low tide, sometimes through a reverse bore or a waterfall. A powerful or dangerous chuck is known as a “skookum chuck,” from the Chinook Jargon word for strong.

The Salt Chuck Mine, a gold, silver, copper and palladium mine and mill, was established in 1905 and operated, most intensively from 1915, until 1941, processing more than 326,000 tons of ore rich in copper sulfides. At least 25 mill structures remain on site. Milling crushed and floated the sulfide ore, and operators discharged the resulting tailings, along with petroleum products and PCB-laden electrical equipment directly onto the tidelands, a standard practice at that time. An estimated 100,000 cubic yards (76,000 cu m) of tailings lie mostly in the intertidal zone south of the mill, on state-owned tidelands. Those tailings hold sulfide minerals that can oxidize into acidic, metal-laden drainage when exposed to air and fresh water, but because most of the deposit sits below the tideline, seawater’s natural alkalinity buffers much of that acidity. Government sampling has found the chief risk is not low pH but elevated, bioavailable copper leaching into marine sediment, which is toxic to invertebrates in the adjacent mudflats.

At the state of Alaska’s request, the Environmental Protection Agency (or EPA) added Salt Chuck Mine to the Superfund National Priorities List in March 2010. Contaminants documented at the site include PCBs, copper, lead, mercury, selenium, vanadium, nickel, arsenic, petroleum and polycyclic aromatic hydrocarbons. The US Forest Service removed debris and contaminated soil from the uplands in 2011, and from 2011 to 2013 the EPA sampled soil, sediment, water and marine life. Its remedial-investigation report, finalized in 2018, found no unacceptable risk to human health. Cleanup is not yet complete: since 2021 the EPA has tested biochar, a charcoal-like material that binds heavy metals, to reduce copper’s toxicity to marine life in the tidal sediments. Read more here and here. Explore more of Salt Chuck Mine and Kasaan Bay here: