Paramedics performed emergency surgery on a 66-year-old man at the scene, but he suffered a cardiac arrest and was pronounced dead.
His brother, who is in his 70s, also suffered chest injuries.
He was airlifted to Frenchay Hospital near Bristol, where he remains (Tuesday).
More top news
Although the crime total has dropped by almost a third, high value farm equipment is still top of the thieves lists.
Teams used three tonnes of explovises to blast through the rock and uncover previously unseen chambers.
Today starts on a cloudier note with some patchy drizzle in places.