PALEOMAGNETISM OF THE PINE POINT ZN-PB DEPOSITS

The Pine Point Zn-Pb deposits are Mississippi Valley-type (MVT) deposi ts in Middle Devonian dolostone of the Pine Point Formation. The media n natural remanent magnetization intensity from 509 specimens from 40 sites is 3.6 x 10(-5) A/m. This intensity is an order of magnitude low er than most MVT deposits and is close to the sensitivity of the cryog enic magnetometer, so only the stronger specimens could be analysed pa leomagnetically. Isothermal remanent magnetization testing of ores, ho st rocks, and monomineralic specimens shows that single domain to pseu dosingle domain magnetite in sphalerite is the main remanence carrier; magnetite in galena is the next most significant carrier. In contrast , barren dolostone, limestone, and calcite crystals have a much weaker remanence. Using less stringent criteria than is conventional, 17 acc eptable site mean remanence directions were determined. Remagnetizatio n circle data indicate that many of the poorly defined sites retain a reversed but nonisolated characteristic remanence. Of the 17 means, 8 form a coherent cluster, die A component, with a mean direction of D = 339-degrees, I = 78-degrees (alpha95 = 7-degrees, k = 62), giving a p ole position of 79-degrees-N, 197-degrees-E (alpha95 = 13-degrees). Th e A pole indicates with >95% confidence that the MVT ores at Pine Poin t are Late Cretaceous to Eocene in age, with a mid-Late Cretaceous to Paleocene age (84-58 Ma) being most likely. The dolostone host rocks w ere remagnetized at the same time. It is concluded that the A componen t, carried mainly by sphalerite and galena, was formed during the Lara mide orogeny (97-58 Ma) when tectonic uplift forced Zn-Pb-rich basinal brines out of the Western Canada sedimentary basin into the Presqu'il e barrier reef on the adjacent foreland shelf.