HR: 1340h
AN: V23A-1234    [Abstracts]
TI: Major and Trace element Geochemistry of Hydrothermal Minerals From the Sudbury Structure: Implications for Fluid Architecture
AU: * Campos-Alvarez, N O
EM: campos3@uwindsor.ca
AF: Department of Earth and Environmental Sciences, University of Windsor, Windsor, ON N9B 3P4, Canada
AU: Samson, I M
EM: ims@uwindsor.ca
AF: Department of Earth and Environmental Sciences, University of Windsor, Windsor, ON N9B 3P4, Canada
AU: Fryer, B J
EM: bfryer@uwindsor.ca
AF: Department of Earth and Environmental Sciences, University of Windsor, Windsor, ON N9B 3P4, Canada
AU: Ames, D E
EM: dames@nrcan.gc.ca
AF: Geological Survey of Canada, 601 Booth St., Ottawa, ON K1A 0E8, Canada
AB: The Sudbury structure mainly comprises a layered intrusive body (the 2.5 km thick Sudbury Igneous Complex; SIC), and the overlying 1.4 km thick Onaping (OF) and Vermilion (VF) Formations. This sequence and the underlying basement have been affected by extensive hydrothermal fluid circulation, postulated to involve deep formational brines, sea water, and/or orthomagmatic fluids derived from the SIC. Late-stage magmatic fluids are indicated by miarolitic cavities (Kfs-Qtz-Ep-Chl-Hbl), which are common throughout the upper part of the SIC but also occur in the overlying Onaping Intrusion (OI) and towards the footwall of the SIC. Mineralogically similar veins (Ep-Qtz-Kfs-Chl) also occur in the SIC and OI, and possibly represent the migration of these orthomagmatic fluids away from their source. Hydrothermal epidote shows similar major element chemistry (e.g. Fe/Fe+Al) irrespective of epidote type or stratigraphic position. In general, epidote from the SIC displays average Fe/Fe+Al ratios from of 0.16 to 0.32. Similar values (0.19 to 0.32) are reported for epidote from the OF. Epidote from cavities are characterized by relatively flat HREE patterns, variable degrees of LREE fractionation, and moderate to strong positive Eu anomalies (Type I). However, some show a relatively flat LREE pattern, slightly enriched HREE and moderate positive Eu anomalies (Type II). A third group (Type III), show steep REE patterns with moderate to strong fractionation between HREE and LREE, and moderate positive Eu anomalies. Vein epidote is characterized by Type I patterns only. These data suggest that fluids of comparable temperature and composition precipitated epidote and related minerals in both miarolitic cavities and veins through the SIC and OF. Calcite occurs as a replacement mineral in the OF, in amygdules (Qtz-Chl-Cal-Ep-Sulph) in syn-depositional aphanitic dikes in the OF, and as bands, discordant aggregates and replacement phases (blocky calcite) in the VF, which lies above the OF. Amygdule calcite displays either relatively flat REE patterns, with minor LREE fractionation and no Eu anomalies (not observed in Ep), or the Type III patterns seen in epidote. Replacement carbonate in the OF show the Type I and II patterns characteristic of epidote. Banded and unmineralized blocky calcite displays flat, yet irregular, REE patterns, with minor negative Ce anomalies, and no Eu anomaly. Discordant and blocky calcite associated with minor sulphide mineralization displays moderate LREE fractionation and flat to slightly enriched HREE patterns, with a strong positive Y anomaly and negative Ce and Eu anomalies, suggesting seawater involvement. The REE geochemistry of VF carbonates is thus distinctly different from that of epidote and carbonate deeper in the system. Similar REE patterns observed in hydrothermal epidote and carbonates suggest that fluids of similar composition and temperature circulated through both the SIC and OF. However, the distinct character of some sulphide-related VF carbonates suggests the involvement of different fluids, or deposition under different conditions. The distinct positive Eu anomaly in epidote and carbonate is consistent with precipitation from relatively hot, reduced fluids. Variations in REE chemistry within single samples suggests that the REE systematics are complex and that fluids evolved with time. Finally, a potential fluid connection between the footwall and hanging wall of the SIC, as has been previously suggested, is potentially demonstrated by the ubiquitous Eu anomaly found across the entire Sudbury hydrothermal system.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting