Abstract:

This document reports the spatial distribution of Cu- versus Zn-rich lenses in the Flin Flon, Callinan and 777 volcanogenic massive sulphide deposits of the Paleoproterozoic Flin Flon Belt, Manitoba. Their relative distribution can be used to locate hydrothermal vent sites in VMS deposits that contain multiple sulphide lenses or deposits. Using historical and modern assay datasets, a 3D Gocad model characterizing the spatial relationships between Cu and Zn concentrations was constructed. The model shows that the Cu-rich zones decrease in size from the base to the top of the Flin Flon and 777 deposits, which is consistent with upward and outward zone-refining of the sulphide lenses. The Cu-rich zones are typically elongate parallel to the topology of the sulphide lenses, which are shaped as flattened ellipsoids that plunge parallel to a pronounced regional stretching lineation. A second, less distinct trend is oriented oblique to the stretching lineation, in both the Flin Flon and 777 deposits. The Flin Flon and 777 deposits have at least three and two distinct Cu-rich zones, respectively, suggesting the presence of separate hight-T hydrothermal vents. The Callinan deposit does not contain a Cu-rich zone, but is slightly more Cu-rich towards its south end. The deposit shows an overall decrease in Cu/Zn ratios from south to north as well as a localized decrease northerly around the interpreted vent. The Callinan ore lenses are interpreted as a clastic sulphide deposit fringing the Zn-rich shell of the 777 deposit possibly derived by mass wasting of sulphide mounds and mass flow transport of sulphide clasts during periods of tectonic instability. A lateral Zn variation is also present and suggests input of additional metals from one or more separate vents located north of the Callinan deposit.