Inside the Thunderwork Ridge Mine, there are a bunch of nodes that spawn around the room; in about 7 minutes of running in a circuit, i gathered the 10 gold samples (and around 22 pyrite samples--grey, sell-to-shop items). this seemed reasonable. minimal mob interference.
Note: the pyrite seems to only stack in sets of 20, so have some room in your inventory or sell-to-shop as needed.