By MARK THIESSEN Associated Press ANCHORAGE, ALASKA (AP) — The U.S. Army Corps of Engineers says a proposed gold and copper mine at the headwaters of the world’s largest sockeye salmon fishery in Alaska would cause “unavoidable adverse impacts.” The corps is asking the backers of Pebble Mine to come up with a mitigation plan within 90 days for nearly 3,000 acres of land and nearly 200 miles of streams it says could be affected if the controversial mine moves forward. The mine backers say the letter was expected, and they have had crews out mapping mitigation sites for weeks. They say the news not is related to recent tweets by mine opponents, including a son of President Trump.