Relation of fluid inclusion geochemistry to wallrock alteration and lithogeochemical zonation at the Hollinger-Mclntyre gold deposit, Timmins, Ontario, Canada

CIM Bulletin, Vol. 78, No. 876, 1985

TED J. SMITH, St. Joe American Corporation Deadwood, South Dakota, U.S.A. and STEPHEN E. KESLER Department of Geological Sciences, University of Michigan Ann Arbor, Michigan, U.S.A

Zonation patterns are well developed in the mafic meta-volcanic rocks that host epigenetic quartz-carbonate-gold vein mineralization at the Hollinger-Mclntyre deposit. Carbonate alteration assemblages are strongly zoned about mineralization. Proceeding inward from background greenschist fades rocks to alteration envelopes enclosing individual veins, the following assemblages are observed: Assemblage I—quartz-albite-chlorite-epidote-actinolite-(calcite) Assemblage II—quartz-albite-chlorite-calcite-epidote Assemblage HI—quartz-ankerite-sericite-(chlorite-calcite) Assemblage IV—quartz-albite-ankerite-sericite Lithogeochemical zoning is equally well developed as variations in whole-rock abundances of As, Au, Ba, Rb, andSb. As and Ba form the most useful zonation patterns, outlining individual ore zones as well as broader trends of mineralization. Gas chromatographic analyses of fluid inclusions in the quartz-carbonate veins indicate that the mineralizing fluid was an H2O-CO2 mixture. Locally, CH4-rich fluid inclusions are associated with graphitic and/or carbonaceous wallrocks. Fluid inclusions in ore-bearing veins have higher CO2 contents than those in non-ore veins. Extensive sampling and analyses of veins from the area surrounding the deposit reveals a well developed zonation of CO2 contents about the main zone of mineralization. Low CO2 levels (1-2 mole%) in veins are peripheral to the deposit and increase to over 12 mole% in mineralized zones. The observed zoning of the carbonate alteration assemblages is a result of the addition ofCO2 to the wallrock, which is consistent with the zoning of CO2 in the fluid inclusions. The zoning patterns delineated in this study are useful in exploration both on a deposit scale and on the scale of individual ore zones.

Keywords: Mineral exploration, Fluid inclusion, Geochemistry, Wallrock alteration, Gold mineralization, Zoning patterns, Trace elements, Economic geology