Vintage Story mod for locating ore
To craft, you need a couple pieces of the ore that you want to locate as well as two charcoal, in the following configuration:
CC
OO
After you've crafted your knocker, start knocking on some stone with it! Just hold right click on any stone until it spits out some numbers at you. The intensity level isn't calibrated to the type of ore yet, so just try to triangulate the position of the ore by finding out which direction makes the number go higher. The number goes higher not just by proximity, but also density of the ore cluster.