Major element distributions in meta-rhyodacitic flows and fragmental rocks surrounding the Louvem volcanogenic copper deposit show a broad linear anomaly parallel to the local strike. At least 420 m long and up to 210 m wide, this altered area contains rocks that have high Fe+2, S, and low Na2O, CaO, and CO2 values. Included in the central portion of this large anomaly is a 100 m by 50 m highly altered area that contains rocks with high H2O and MgO values and crudely outlines the ore deposit.Element-ratio maps and a map showing percentage peraluminous character all display easily recognizable anomalies that mark the zone of altered rocks enclosing the ore deposit. Of the element ratios investigated at Louvem, Al2O3/Na2O appears to offer the most practical tool for mineral exploration.The chemical zoning of the altered fragmental layer that includes the copper ore is symmetrical about the long axis of the stratigraphically concordant orebody, but in a longitudinal direction this symmetry is absent. Instead, the alteration changes progressively from dominantly chloritic at the western end to pyritic at the eastern end of the study area. This alteration pattern seems to suggest that ore deposition was effected by hydrothermal solutions moving along the layer of now-altered fragmental rocks. By analogy with the chloritic alteration pipes underlying pyritic volcanogenic deposits, it seems probable that the direction of fluid flow was from west to east.