STRUCTURAL CONTROLS ON VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN THE PALEOPROTEROZOIC CHISEL SEQUENCE, SNOW LAKE, MANITOBA

The Chisel sequence is a 3 – 5 km thick volcanic succession that occurs within the Snow Lake arc assemblage of the Paleoproterozoic Trans-Hudson Orogen. It is host to six economic Zn-Pb-Cu-Ag-Au volcanogenic massive sulfide (VMS) deposits (the Chisel Lake, Lost Lake, Ghost Lake, Chisel North, Photo Lake, and Lalor deposits) that are now interpreted to have formed within a single time-stratigraphic ore interval. Three main deformational events associated with the Hudsonian orogeny are recognized in the Snow Lake district and have influenced the current geometry and location of the Chisel sequence VMS deposits. D₁ is characterized by tight, isoclinal F₁ folds without a preserved S₁ foliation. D₂ produced a strong S₂ foliation that is the dominant planar fabric in the volcanic rocks of the Snow Lake district. Elongate amygdules and clasts, stretched quartz aggregates, and aligned amphibole crystals define an L₂ lineation. D₃ is characterized by upright, open to closed NE-striking F₃ folds with a weak axial planar S₃foliation.

This investigation provides a new understanding of the location and structural modification of the VMS deposits in the Chisel sequence by expanding on previous deposit-scale structural studies at the Chisel, Chisel North, and Photo Lake deposits and by incorporating new findings at the Lalor deposit. The dominant structures controlling the current geometry of the VMS deposits are the D₁ and D₂ structures present on the scale of the Chisel sequence. At the Photo Lake deposit, the two base metal lenses (#1 lens and #2 lens) have been folded about an isoclinal F₁ fold and elongated along L₂. The #2 lens is overturned and the #1 lens is the folded, transposed stringer zone to the #2 lens. These findings are consistent with the geometry of the Chisel and Chisel North deposits, which are also folded by isoclinal F₁ folds and elongated along L₂. The Lalor deposit occurs in the footwall to a fault and consists of several base metal lenses that have been folded about a recumbent isoclinal fold. Both of these structures dip shallowly to the northeast and may be either D₁ or D₂ structures. These findings have major implications for future exploration in the area because they indicate that folding and potentially faulting have repeated the productive Chisel ore interval.