The Lac Des Iles Palladium Deposit, Ontario, Canada. Part II. Halogen variations in apatite

Abstract

Analysis of apatite from the Mine Block Intrusion (MBI) of the Lac des Iles Igneous Complex shows two pronounced trends in the halogens. Apatite from relatively fresh norite and melanorites from the Pd-sulfide zone contain up to 57 mol% chlorapatite endmember with significant hydroxyapatite component. In contrast, in altered rock (amphibolite and greenschist assemblages) the chlorapatite component is typically less than 10 mol% with wide variation in the F- and OH-endmember components. The latter trend is attributed to Cl loss to degassing and alteration, whereas the former is attributed to Cl enrichment in the ore-bearing rocks. It is suggested that the relatively H2O-rich and intermediate Cl content of the early igneous fluids degassed from the deeper levels of the MBI can explain the high Pd/Pt and Pd/Ir ratios of the deposit. A model is presented in which disseminated Pd-rich sulfides are initially introduced by a high-temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock. This high-temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions.