FLUID INCLUSION AND STABLE ISOTOPE STUDY OF FAULT-RELATED MINERALIZATION IN TYNDRUM AREA, SCOTLAND

Gold-bearing structures in the Tyndrum area, Scotland, formed from CO2 -bearing fluids that contained 6 equiv. wt% NaCl at temperatures in th e range 290-350-degrees-C. Loss of CO2 (phase separation) from the flu ids was one cause of mineral precipitation. Oxygen and hydrogen isotop ic data suggest that the fluids were magmatic in origin but included a n additional component-probably Lower Devonian meteoric water. Sulphur isotopic ratios indicate two sources of sulphur, one magmatic in char acter and the other the country rocks. In contrast, historically explo ited base-metal veins in the area formed from highly saline (approxima tely 15 equiv. wt% NaCl), relatively low-temperature (140-200-degrees- C) fluids, which have a different stable isotopic signature from that of the gold veins. Comparison with information from other mineralizati on in the region suggests that the genesis of the Tyndrum gold veins i s related to Caledonian magmatism; the mineralizing fluids could have evolved from an underlying magma that was either granitic or appinitic .