Fluid inclusion data from Aznalcdllar and Los Frailes stockworks indicate that hydrothermal fluids changed continuously in temperature and salinity, both in time and space. Th values change from 140 to 380 °C and salinity from 0.4 to 12.4 NaCI eq. The highest values for both parameters ha ve being found for central stockworks and later fluids. Statistic population analysis of fluid inclusion data points to three stages of hydrothermal activity, at low (<200 °C), intermediate (200-300 °C) and high temperatures (300-400 °C). Salinity values show similar variation trend with higher values for the last hydrothermal stage