SPATIAL VARIATION OF PHYSIO–CHEMICAL CONDITIONS OF THE HYDROTHERMAL FLUIDS IN FRESNILLO BASED ON FLUID INCLUSION STUDIES
Measurements from mostly primary liquid-rich inclusions at Jarillas (n=270) yields Th= 190°C to 295°C and 1 to 5 wt% NaCl eq. for calcite hosted inclusions and Th= 210°C to 260°C and 0.5 to 5 wt% NaCl eq. for quartz hosted inclusions. The minimum calculated pressures range from 5 to 70 bars with mode at 25 bars which corresponds to a paleo-depth of approximately 300 meters. For Valdecañas-East vein, west of Jarillas, we have measured primary liquid-rich inclusions hosted mainly in quartz (n=129) and have determined Th= 160°C to 310°C and 0.5 to 11 wt% NaCl eq.
Our new data from Jarillas and Valdecañas-East when compared with data from Santo Niño (Simmons 1986) shows a trend of progressive increase of average Th°C and salinity from Santo Niño Vein in the east, to Jarillas and then Valdecañas-East vein to the west. This trend in physio-chemical conditions of the hydrothermal fluids as a function of space will be used in conjunction with other geochemical tools to examine the genetic relations amongst veins and the district-wide fluid source and fluid flow.