paragenesis, the sequence in which the minerals are formed in an ore deposit. Variations in the pressure and temperature and in the chemical constituents of a hydrothermal solution will result in the precipitation of various minerals at different times within the same ore deposit. The general sequence of deposition is gangue minerals (silicates and carbonates) first; oxide minerals next, with the sulfides and arsenides of iron, nickel, cobalt, and molybdenum contemporaneous with or closely following the oxides, and the lead and zinc sulfides following them; and last the native metals and tellurides followed by the antimony and mercury sulfides. The paragenesis at any particular location may be complicated if the ore deposit has been formed by more than one period of hydrothermal activity.