SCANNING-PROTON-MICROPROBE MAPPING OF MINOR AND TRACE-ELEMENTS ALONG MINERAL CLEAVAGES, FRACTURES AND GRAIN-BOUNDARIES - EVIDENCE FOR ELEMENT MOBILITY

The scanning proton-microprobe and proton-induced X-ray emission have been used to map and analyze the distribution of trace elements at gra in boundaries, fractures and cleavage planes in a rare-element-enriche d pegmatitic syenite from the Eden Lake syenite complex, Manitoba. In the vicinity of metamict britholite, fractures and cleavages in minera ls and grain boundaries between minerals show elevated abundances of r are earth, alkali, transition and large-ion lithophile elements. The e lements were probably released from metamict britholite and deposited from a fluid that had migrated along these surfaces after the crystall ization of the rock. Semiquantitative point analyses were done on frac tures in quartz and K-feldspar cleavages, where problems related to ma trix corrections are minimized. These features show local concentratio ns of ca. 200 ppm Mn, 4500 ppm Fe, 30 ppm Zn, 10 ppm Rb, 100 ppm Sr, 1 00 ppm Y, 200 - 700 ppm Nd, 20-50 ppm Pb, 30 ppm Th and 70 ppm U. Thes e levels are significantly higher than what is found in the surroundin g undamaged quartz and between cleavages in K-feldspar.