Abstract

Twenty oriented drill cores were collected from the outcrop of the Gallen massive sulfide deposit in the Rouyn-Noranda area in order to investigate remanent magnetization and anisotropy of magnetic susceptibility in the deposit. The purpose was to obtain inforrnation on the emplacement of the deposit. Electrical resistivity is high enough to allow 60-Hz alternating fields (AF) to be used for stability testing of the remanent magnetization. For thermal demagnetization, the heating chamber was first evacuated and then filled with argon. Alternating field demagnetization in a peak field of 30 mT yielded well-grouped stable directions carried by relatively high coercivity magnetite. The mean direction and pole position are: 137, +50, and 43 degrees W, 2 degrees S, dm=9 degrees , dp=6 degrees , respectively. The pole position falls on the 1,750- to 1,700-m.y. part of the apparent polar wander curve for North America, suggesting that the magnetization was acquired after the probable Archean formation of the deposit. The anisotropy of susceptibility (generally <8%) suggests preferential alignment of the long axes of the magnetite grains almost parallel to the stable remanence direction and its azimuth parallels the local structural trend. These observations suggest that the magnetic fabric is of Hudsonian age, thus implying Hudsonian deformation of this area of the Archean Superior province.

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