Halogen geochemistry of footwall breccia and associated units of the main mass of the Sudbury Igneous Complex, Ontario

Abstract

The potential for the halogen elements (F, Cl, Br, I) to be used as geochemical indicators for contact-style Ni-Cu-PGE mineralization along the lower contact of the Sudbury Igneous Complex (SIC) has been investigated. Specifically, halogen anomalies present within and around footwall breccia "plumes" as well as surrounding lithologies have been examined to determine how bulk and soluble halogens are related to mineralization. Two environments (one barren of mineralization, and the other hosting significant sulphide ore deposits) containing these structures were compared. There are no significant differences in bulk major and trace element geochemistry of rocks between these environments; however there were differences in halogen geochemistry. Two dominant fluid sources were recognized as having contributed to the water-soluble halogen budget of the samples: a high Cl[superscript -]/Br[superscript -] fluid phase of probably magmatic origin, originating from the SIC, and a low Cl[superscript -]/Br[superscript -] fluid phase derived from fluid release during dehydration of hydrous minerals in footwall rocks or from infiltration of saline groundwaters.