What rock is most likely to have gold in it?
Verdict summary
Quartz is the rock most often associated with gold: most lode gold occurs in quartz veins, especially rusty, iron-stained quartz near faults. Gold is also found in the contact zones between granite-type intrusions and older metamorphic rocks such as schist and greenstone.
Hot fluids moving through cracks deposit quartz and, sometimes, gold. When the sulphide minerals in those veins weather, they leave rust-coloured stains and cavities, which prospectors look for.
Most quartz carries no visible gold. Old workings, the regional geology map, and assays or stream-sediment chemistry tell you whether a particular vein system is mineralised.
Sources: USGS mineral deposit models; State and national geological survey bulletins.
How can you tell if a rock has gold or fool's gold? Real gold is soft and bends or flattens when pressed with a pin; fool's gold (pyrite) is hard and brittle and shatters. Gold leaves a golden-yellow streak on unglazed porcelain, while pyrite leaves a greenish-black streak. Gold stays the same colour in shade, while pyrite and mica glitter only in sunlight.
What is the difference between placer gold and lode gold? Lode gold is still in the rock, usually in quartz veins. Placer gold has weathered out of that rock and been moved by water or gravity into gravels, where it can be panned, sluiced or detected.
Where is gold most likely to be found? Gold is most likely to be found where it has been found before: in and downstream of historic gold mining districts. In streams it collects where water slows, such as inside bends, behind boulders and in bedrock cracks (placer gold). In rock it sits mostly in quartz veins along faults (lode gold).
Primary sources cited
- USGS mineral deposit models
- State and national geological survey bulletins