Probably dead bodies and hundreds of writhing snake.
If I had the climbing ropes to have a look and an offsider, I could've been tempted. It doesn't show it very well in the photo of that shaft but they've basically chiselled their way straight down through solid rock. That's why the shaft's still in such perfect condition 150 years later. They must have found a great seam of gold or really rich indicators at the surface to dig down that deep, because it would've taken them months or years to do it by hand. The other odd thing I noticed is that there didn't seem to be a corresponding sized pile of excavated material on the surface for the depth of the hole, which made me think they either set up a crushing battery nearby or used the creek downhill to wash the paying soil. The chain of mines along the reef nearby were nowhere near as deep, so maybe the success of this deep lead mine was limited. Some of these shafts in this district went down to 2400 feet. That's a hell of a depth chasing a seam.