Fantasy/adventure movie about a magic black ball?

It's a fantasy/adventure movie of the 80s-or possibly early 90s-and is something about two competing groups of people in pursuit of a black ball (the size of a bowling ball) that has some magical or mystical power to it.

Towards the end there's a confrontation between the two rival groups in a well-lit cavern or gorge, or something of the like. Someone rubs the ball the wrong way and, consequently, it precipitates an devastating earthquake, and the whole structure collapses as in the climaxes of many other movies.

I believe there was some evil character who was immobile, being rolled around in a wheelchair by a woman partner. He was dressed in black-and may have even bled black-and needed the special ball for healing. There was also a scene, midway, where someone got caught in quicksand and slowly sunk all the way through it.