As Li Du had said before, mining was difficult. Even if they had an idea of where the gems were, if they hadn't had the little bug to help, they could only mine blindly. With the little bug's help, Li Du could determine the direction of the vein and create a map of the exact location of the gem. From there, making an excavation plan was relatively simple.
However, Li Du could not have found this gem vein without Hans' help. In this case, Hans had done a great deal of good work. Li Du gave him a ten percent share, simply because Hans had found the vein. Li Du felt that ten percent was enough, because Hans only provided information on the vein's location. He was not going to contribute anything else, and he didn't have to take any risk.