Minerals containing elements of economic value are generally present in all igneous rocks, but the elements may not be concentrated enough to make mining economical.
Only in relatively rare circumstances are they in sufficient abundance so that mining is profitable.
If the minerals are scattered throughout a host rock, but in sufficient amounts to mine profitably, we call the deposit a disseminated deposit.
Disseminated deposits produce most of the world’s diamonds, copper, and molybdenum and also large percentages of the available tin, silver, and mercury.
Often, disseminated ores consist of minerals scattered randomly in a host rock.
Sometimes geological processes concentrate ore minerals in vein deposits consisting of veins that are centimeters to meters thick.
If ore is distributed in many small veins, geologists call the deposit a lode deposit. Vein deposits account for most of the world’s gold and silver mines, and also some copper and lead-zinc mines.
In still other kinds of igneous deposits, ore minerals become concentrated in layer