Significance of muscovite and chlorite composition from the hydrothermal wolframite deposits of Panasqueira and Vale das Gatas (Portugal) and hints for ore exploration

Major- and trace-element contents of both muscovite and chlorite from the hydrothermal wolframite deposits of Panasqueira (P) and Vale das Gatas (VdG), Portugal have been determined by electronic microprobe and atomic absorption. Radiometric K/Ar ages of selected muscovites have also been determined. P muscovite distinguishes from VdG muscovite because of higher FeO ((x) over bar = 2.41 +/- 0.21% and 1.23 +/- 0.06%, respectively), F ((x) over bar = 1.14 +/- 0.20% and 0.79 +/- 0.14%, respectively), TiO2 ((x) over bar = 0.34 +/- 0.06% and < microprobe detection limit, respectively), Li ((x) over bar = 1010 +/- 30 ppm and 331 +/- 18 ppm, respectively) and Rb ((x) over bar = 1941 +/- 170 ppm and 978 +/- 62 ppm, respectively) and, conversely, lower MnO ((x) over bar = 0.04 +/- 0.01% and 0.61 +/- 0.08%, respectively) and Cu ((x) over bar = 22 +/- 11 ppm and 145 +/- 75 ppm, respectively). P and VdG chlorites are also compositionally different, as they are brunsvigites and ripidolites, respectively; in addition, the MnO/FeO ratios of VdG chlorite are much larger ((x) over bar approximate to 0.150) than those ((x) over bar approximate to 0.004) of the P mineral. As the different Fe/Mn ratios of both muscovite and chlorite correlated with the different Fe/Mn ratios of wolframite and, thus, reflect to some extent the different Fe/Mn ratios of the hydrothermal solutions in the two deposits, these ratios, along, with F, Ti, Li and Rb contents of muscovite, can be useful geochemical indicators for exploration. Paragonite-muscovite solvus thermometer gives minimum temperatures for P and VdG muscovite deposition of approximate to 360 and approximate to 250 degrees C, respectively. From the proportion of phengitic substitution in muscovite, minimum pressures have been estimated to be 0.85 and 0.95 kbar at P and VdG, respectively. Temperature calculated on the basis of Al-IV content of P and VdG chlorite are 266 +/- 23 degrees C and 275 +/- 33 degrees C, respectively. Both muscovite and chlorite temperatures are realistic. Finally, K/Ar ages of muscovite have yielded ranges of 284-295 and 295-305 Ma, respectively for the P and VdG mineralizations. These ranges are fully consistent with the Hercynian age of the granites, which the deposits are related to, and suggest that the VdG mineralization is slightly older than the P mineralization.