HR: 0800h
AN: C11A-1067    [Abstracts]
TI: Magnetic Tracking of Gas Hydrate Deposits.
AU: * Lowe, C
EM: clowe@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 6000, 9860 West Saanich Road, Sidney, BC V8L 4B2 Canada
AU: Enkin, R J
EM: renkin@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 6000, 9860 West Saanich Road, Sidney, BC V8L 4B2 Canada
AU: Judith, B
EM: jubaker@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 6000, 9860 West Saanich Road, Sidney, BC V8L 4B2 Canada
AU: Dallimore, S R
EM: sdallimore@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 6000, 9860 West Saanich Road, Sidney, BC V8L 4B2 Canada
AB: Analysis of recovered core from the Mallik gas hydrate field in the Mackenzie Delta, Northwest Territories, Canada demonstrates that the magnetic properties of hydrate-bearing strata differ significantly from those strata lacking gas hydrate. The recovered core, which extends from just above (885 m) to just below (1152 m) observed gas hydrate occurrences (891-1107 m), comprises a series of six stratigraphic units that are either sand or silt dominated. Gas hydrate is preferentially concentrated in the higher porosity, sand-dominated units. Although the sediment source region for the Mackenzie Delta is sufficiently large that silts and sands have similar primary mineralogy, their magnetic properties are distinct. Magnetite, apparent in silt units with porosities too low to accommodate significant gas hydrate deposits, is reduced to iron sulphide in the gas hydrate-bearing sand horizons. The degree of the observed magnetic reduction increases with increasing gas hydrate concentration. Furthermore, silts retain their primary magnetism, whereas sands are remagnetized. Two independent investigations of marine gas hydrate occurrences (Blake Ridge, offshore eastern USA and Cascadia, offshore western Canada) demonstrate similar magnetic reduction within known gas hydrate fields, and an even larger depletion of magnetic minerals in vent zones where methane is actively fluxing to surface. Collectively, the findings from these three regions indicate that porosity and structure are fundamental controls on methane pathways. Investigations are presently underway to determine the precise triggers and chemical pathways of the observed magnetic reductions. However, findings to date indicate that magnetic studies of host sediments in gas hydrate systems provide a powerful lithologic correlation tool, a window into the processes associated with gas hydrate formation, and form the basis of quantitative analysis of magnetic surveys over gas hydrate deposits.
DE: 0915 Downhole methods
DE: 0925 Magnetic and electrical methods (5109)
DE: 1051 Sedimentary geochemistry
DE: 1519 Magnetic mineralogy and petrology
DE: 1714 Geomagnetism and paleomagnetism
SC: Cryosphere [C]
MN: Fall Meeting 2005