Duane had several strokes over past years. He believed he was under some spiritual attacks. As odd as that sounds, there seems to be some very odd effects on those searching for answers on the ranch.
Last year, Duane's son Chad, who was on the show with him making daredevil searches for the treasure, ended up in jail for ignoring arrests and then was accused of killing his cellmate. Chad is presently under psychiatric supervision.
It may seem like the skinwalker theme runs through all this, but there were also vibes of aliens and cursed land. In fact, in two amazing episodes of Gaia's "Cosmic Disclosure," (S1E9 and E10) Duane opened up about the other side of the ranch - the alien/UFO aspect.
Under Duane's insistence, the show is continuing, being led by Josh Feldman and his father (treasure hunters) and some beloved helps like Eric Drummond and James Keenan. It is on Wednesdays on Discovery Channel.
RIP Duane. Life well-lived and well-loved. You live in the "real" world now - the one with no pain and all the answers to all your questions.