The Guichon Creek batholith, located in south-central British Columbia, is host to numerous porphyry copper deposits that are considered as being closely related to the pluton. Variations in major and trace element distribution are consistent with a model of crystallization-fractionation of a K-poor calc-alkaline magma of intermediate composition. Relatively low Rb and Rb/Sr values, and high K/Rb ratios are consistent with Sr isotopic ratios that suggest a subcrustal source region for the generation of the magma, probably by partial melting of subducted oceanic crust at relatively shallow depths.Cu, like other femic elements, (Zn, Mn, V, Ni, Co, Ti) generally decreases with increasing fractionation, which reflects normal differentiation trends. The apparent lack of positive correlation between Cu contents of rocks and ore potential of intrusive units may be explicable if mineralization is regarded as an independent by-product of magma generation, rather than the result of differentiation processes. Close relationships between trace metal values and degree of fractionation emphasize the need for assigning different background values to each intrusive unit, during geochemical exploration.