Metals liberated from clay and carbonate minerals as they are changed from clays and low-pressure disordered carbonate forms enters the remaining pore fluid which by this time has become concentrated into what is known as a deep formation brine. The solution of metal, salts and water produced by diagenesis is produced at temperatures between 150 - 350°C. Hydrothermal fluid compositions are estimated to have a salinity of up to 35% NaCl with metal concentrations of 5-15 ppm Zn, Cu, Pb and up to 100ppm Ba and Fe. High metal concentrations are able to be carried in solution because of the high salinity. Generally these formational brines also carry considerable sulfur.