PALEOMAGNETISM OF THE RED LAKE GREENSTONE-BELT, NORTHWESTERN ONTARIO - POSSIBLE EVIDENCE FOR THE TIMING OF GOLD MINERALIZATION

We report paleomagnetic results from (1) largely unaltered batholiths and (2) sheared and altered units in the Archean Red Lake greenstone b elt, a major gold-producing region in the Uchi subprovince of northwes tern Ontario. Group 1 includes the Hammell Lake, Killala Baird, Trout Lake and Little Vermilion Lake batholiths, which were intruded between 2730 and 2700 Ma ago (U/Pb, zircon). Group 2 includes the Howey diori te, the Dome Stock, and dikes and andesites from the Dickenson mine. T hese units, from the mineralized deformation zones (DZs) between the b atholiths, were sheared and hydrothermally altered in the same event t hat caused gold mineralization in supracrustal units. The batholiths c arry a stable reversed remanence (RLR), with D = 159-degrees, I = -74- degrees (k = 20, alpha95 = 16-degrees, N = 4 units, 14 sites). RLR has high coercivities, unblocking temperatures and remanence intensities and appears to be a primary thermal remanence dating from - 2700 Ma. T he altered units from the gold-bearing DZs carry a different remanence (RLG), with D = 180-degrees, I = - 57-degrees (k = 23, alpha95 = 3-de grees, N = 3 units, 6 sites). RLG also has relatively high coercivitie s and unblocking temperatures but its magnetization intensities are 1- 2 orders of magnitude lower than those of RLR. Opaque minerals and sil icates observed in thin section are highly altered. RLG is therefore b elieved to be a chemical or thermochemical remanence acquired almost-e qual-to 2580 Ma ago during the late stages of cooling and gold mineral ization. Seeing as RLG characterizes the shear zone rocks but is absen t from unaltered rocks outside the DZs, it could be used as a rapid pr ospecting tool in delineating areas of alteration and possible mineral ization. The paleopoles for RLR (almost-equal-to 2700 Ma) and RLG (alm ost-equal-to 2580 Ma) link with those of the Shelley Lake granite (258 0 Ma, Ar-40/Ar-39, hornblende and biotite) and the Matachewan/Hearst d ikes (2450 Ma, U/Pb, zircon and baddeleyite). The sense of motion on t he late Archean-early Proterozoic apparent polar wander path for Laure ntia, as defined by this sequence of paleopoles, is opposite to that p reviously accepted.