Where I live you will never find the kind of quantities that you would in the California Motherlode, only glacial placers, and not much chance of hitting anything big. Unless the property owner is willing to pitch in half of the work there's no way I would offer half. I bring 100% of the tools, equipment, and experience to the table, the property owner contributes only the place to exercise them, and gold in the ground is worth zero until it is recovered. If initial sampling indicated that I might make more than just gas money I would be inclined to offer him a case of beer, and perhaps some help around the place in exchange for access, but that would be about it. In a different location with the prospect of actually pulling enough out of the ground to make a living I would offer a contract granting the owner up to 10%, but again, unless he plans to do more than hold his hand out I wouldn't offer more.