Tar mine. Tar is a thick black semisolid substance that contains hydrocarbons of organic origin. The hydrocarbons may be oil residues that have become trapped in rocks. If large quantities of tar are present, it may be mined to obtain the oil for use as a fuel. This mine is near the Rio Hollin, part of the headwaters of the Amazon, in north-eastern Ecuador. Oil accounts for over half of the exports from Ecuador. However, much of the oil lies below rainforests, and there are concerns about damage to the environment by the oil industry.