RARE-EARTH ELEMENT MOBILITY AT CONSTANT INTER-REE RATIOS IN THE ALTERATION ZONE AT THE PHELPS DODGE MASSIVE SULFIDE DEPOSIT, MATAGAMI, QUEBEC

Rare earth elements (REE) from La to Ho were mobile and enriched in hydrothermally altered rocks below the Archean Phelps Dodge Cu-Zn volcanogenic massive sulphide deposit in northwestern Quebec. Largest net enrichment was in the moderately altered quartz-chlorite zone where La concentration increased six-fold and LaNYbN steepened from 1.9 to 13.0; the intensely altered chloritite zone had both minor net REE enrichment and depletion. Yb and Lu were immobile throughout both zones. The mobile REE were added and subtracted in constant chondrite-normalized inter-REE proportions: 1.0 La, 0.79 Ce, 0.57 Nd, 0.49 Sm, 0.01 Eu, 0.10 Tb and 0.02 Hb. Small additions of Eu relative to generally larger additions of LREE and Tb produced enhanced negative Eu-anomalies. The REE were mobilized at the hot (> 300 C) core of the alteration system and deposited at the cooler periphery. Other sites of intense alteration and water/rock interaction display similar REE changes, indicating that selective REE enrichment at constant inter-REE ratios is a widespread phenomenon.