ZEOLITIZATION PROCESSES IN BASIC LAVAS OF THE BAUCARIT FORMATION, NORTHWESTERN MEXICO

Basalts and basaltic andesites in terbedded with sandstones in the mol assic Baucarit Formation of northwestern Mexico show contrasting zeoli te and clay assemblages in amygdales and in veins cross-cutting the fl ows. In amygdales, heulandite-clinoptilolite, chabazite, offretite/eri onite and phillipsite are associated with a di-smectite clay. in veins , mesolite, analcime and stilbite are associated with minor clay, quar tz and calcite. The low temperature nature of the zeolites and clays s uggests that the infiltrating fluid had a temperature below 100 degree s C and probably ca. 60 degrees C, The absence of a pervasive alterati on and a lack of correspondence between clay and host-rock chemistry s uggest that this fluid was probably of a meteoric and fresh water char acter, which subsequently evolved into a more alkaline nature followin g interaction with glassy material in the interbedded mollassic sedime nts.