Fluid-Rock Interaction Around Mafic to Intermediate Intrusions: Evidence from Trace Element and Isotopic Geochemistry of Minerals.

摘要

Collectively, this research deals with the nature of hydrothermal systems around mafic to intermediate intrusions, with implications for understanding the Sudbury structure hydrothermal system and the genesis of the Ferguson Lake Ni-Cu-Co-PGE mineralization.;The 87Sr/86Sr and REE composition of syngentic Vermilion Formation calcite suggest precipitation from Proterozoic seawater (∼0.7030). More radiogenic Vermilion Formation-related syngenetic and epigenetic calcite, with high Y/Dy ratios, precipitated from modified seawater. Onaping Formation-hosted replacement and amygdule calcite also involved mixing between seawater and basement-derived fluids. A fluid connection between the footwall and hanging wall of the SIC was established.;Water-rock interaction in the Ferguson Lake Ni-Cu-Co-PGE deposit (Nunavut) is manifested as widespread, post-metamorphic epidote-chlorite-calcite veins and replacement zones that contain sulfides and platinum group minerals (PGM) (mostly Pd-bismuthtellurides). The PGM that occur in magmatic massive and interstitial sulfides, are Bi-rich, and are interpreted to have formed through exsolution at 600°C. The PGM that occur in late-stage hydrothermal sulfide/silicate veins and their epidote-chlorite halos tend to be more Te-rich than the magmatic, Bi-rich PGM. The chemistry and textural setting of the PGM support a model that links the magmatic and hydrothermal end-members of the sulfide-PGM mineralization. Accordingly, primary magmatic sulfide-PGM mineralization was modified by post-metamorphic water-rock interaction.;New isotopic and chemical data on hydrothermal mineral from the Sudbury structure (Ontario) provide insights into the overall hydrothermal architecture of the structure. Early, blocky miarolitic epidote from the Sudbury Igneous Complex (SIC) has a narrow range of 87Sr/86Sr ratios (0.7071 to 0.7074), similar to the SIC (∼0.7064 to 0.7073), and is consistent with precipitation from orthomagmatic fluids derived from the SIC. The 87Sr/86Sr ratios of later, SIC-hosted miarolitic replacement and vein epidote, and of Onaping Formation-hosted replacement and amygdule epidote, are distinctly higher (up to 0.7148), and are interpreted to represent basement-derived fluids. Differences in the Eu/Eu* and SigmaREE between the blocky epidote and late epidote, indicate mixing between these two end-members, and that orthomagmatic fluids possibly circulated in the Onaping Formation. The usefulness of the REE systematics of epidote as a proxy for fluid chemistry is illustrated.