Mineralogy and petrology of the Sokoman Iron Formation near Ardua Lake, Quebec

Abstract

The Proterozoic Sokoman Iron Formation near Ardua Lake, Quebec at the western edge of the Labrador Trough has undergone considerable diagenetic changes but probable only very low-grade metamorphic conditions. Locally, intense folding and thrust faulting are present. Comparisons have been made with the well-established stratigraphy of the relatively undeformed Sokoman Iron Formation in the Howells River area, 65 km along strike to the south of Ardua Lake.Representative assemblages for some of the members are as follows: quartz–chamosite–siderite–ankerite–K–spar–graphite±biotite±stilpnomelane (Ruth shale); chert–magnetite–siderite–talc±ankerite±stilpnomelane (Lower Iron Formation); chert–hematite–magnetite–talc–dolomite±riebeckite (Lower Red Cherty –Pink Grey Cherty); and chert–dolomite–magnetite–stilpnomelane±albite±hematite (Lean Chert). Although the assemblages may be strongly recrystallized, many of the original, sedimentary textural features and mineralogy have been preserved. Chert (and recrystallized quartz), hematite, magnetite, carbonates (calcite, manganoan siderite and manganoan dolomite) and possibly stilpnomelane are considered to be the recrystallization products of sedimentary precursors. Albite, chlorite and riebeckite are considered to be authigenic or diagenetic in origin; only biotite and members of the talc–minnesotaite series are considered to be reaction products of late diagenesis and subsequent very low-grade metamorphism.