How could you separate wood chips and pieces of granite rock?

Burn the wood chips. Alternatively, shake them around for a little while, the granite is heavier and would settle to the bottom, so you could remove the wood from the top, this isn't 100% effective, but it's more effective than setting it on fire. This can be accomplished by shoveling the mixture into water (a wheelbarrow, a buck, some other large container). The chips float and can be skimmed off. The granite sinks and can be shoveled out later.