The function of organic matter is a key point to understand the mineralization of ore-forming fluids. Organic matter and ore-forming fluids are both derived from basins and have the same conduits during their migration. Thus, organic matter migrates together with ore-forming fluids. The most effective way to understand its function is to see its changes during the migration and concentration of fluids. The original fluid and organic matter are from the source rock in the basin. The fluid salinity from the source rock is rather low, which means that there is a small amount of material concentrated from the source rock. This suggests that the function of the organic matter be rather small during the first migration of the oil. During the secondary migration of the fluid, the salinity is increasing, and the temperature is dropping down. The organic matter helps the concentration and transport of the ore-forming material by complexation, reduction, adsorption and supplying the fluid with acidic environment. The destruction of reservoirs can create great changes of physical and chemical properties of the fluid and is an important factor to cause the deposition of ore-forming material.