There isn't any signs nor anything to indicate that Kennecott wants people to keep away. There are a few other trails going south out of Butterfield Canyon, all are used by hikers often. Kennecott security is often in the area but they don't seem to care at all. They do post signs about a mile north, where you can overlook the mine up on West Mountain.
It's difficult in Utah to find the actual owners of private land, the disclosure laws are some of the toughest in the country. But whoever owns the land south of Butterfield Pass, it seems they are open to the same attitude as the owners of Lowe Peak. There is a misconception that Lowe Peak is on BLM land. The access is but the majority of the mountain itself is not. Anyone who has climbed Lowe has trespassed, luckily the owners don't mind recreational use. Same for the Butterfield Peaks/Kelsey Peak area.