Chat (mining)

Chat is a local term in the Tri-State Mining District for gravel-like waste created by ore crushing in lead-zinc mining operations there in the late 1800s and mid-1900s. Chat is mainly composed of chert, dolomite, and sulfide minerals, but is contaminated with lead, zinc, cadmium, and other metals.

The contamination of chat piles varies, lessening each time the pile is re-milled. Most of the heavy metals are present in fine particles in the chat, rather than the gravel-sized stones which are what it is mostly sold for. These fine particles can be blown by wind (20% of fine particles were subject to wind transport in one Oklahoma town studied). Once airborne, they can be inhaled by humans (6% were of appropriate size in that town) or deposited into soil or water.

As of 2006, about 100 million tons of chat were present in the Oklahoma, Kansas, and Missouri tri-state mining region.

A 2020 study of showed that Picher, a town surrounded by chat piles but not currently engaging in industrial activities, had 2-5x the benchmark level of lead contamination (here Tulsa, Oklahoma). The chat piles contributed at least 10% of the inbound lead contamination per year (mass flux) to a lake 18 km away, and likely much more to Picher itself.