During Leg 169, we recovered core from massive sulfide and the underlying sulfide feeder system of two massive sulfide deposits, the Bent Hill Massive Sulfide and the Ore Drilling Program Mound. Veins and impregnation zones of these deposits record the structural evolution of the mound and the pathways of hydrothermal fluid flow. Sulfides in the feeder system are found either as veins that typically display one episode of mineral infilling or as precipitates within the primary sedimentary pore structure. Sulfide veining is most abundant within the mud-rich units, whereas sulfide infilling of pore spaces is most common within sandy units. Sulfide veins generally crosscut the primary sedimentary structures at right angles. These observations suggest a simple model of hydrothermal fluid flow. Hydrothermal fluids are first transported from depth via focused fluid flow. Within 200 to 300 m of the surface, these fluids exit the conduit and enter sandy turbidite layers. Conductive cooling of the fluid results in the precipitation of sulfides within the sedimentary pore structure. Precipitation, in turn, inhibits additional permeable fluid flow, thereby causing fluid pressures to increase and effective pressure to decrease. This pressure regime favors the creation of subvertical fracture networks that may transport hydrothermal fluids across more impermeable mud-rich layers. Upward transport of fluids across impermeable layers may also occur through open fractures created by tectonic stresses at the ridge. Horizontal permeable flow through sandy units and focused vertical flow through mud-rich units over extended periods of time can create the underlying feeder system that may eventually result in massive sulfide.
1Marquez, L.L., and Nehlig, P., 2000. Textural analyses of vein networks and sulfide impregnation zones: implications for the structural development of the Bent Hill Massive Sulfide deposit. In Zierenberg, R.A., Fouquet, Y., Miller, D.J., and Normark, W.R. (Eds.), Proc. ODP, Sci. Results, 169 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/169_SR/chap_09/chap_09.htm>. [Cited YYYY-MM-DD]
2Department of Earth Sciences, PO Box 1002, Millersville University of Pennsylvania, Millersville PA 17551-0302, USA. email@example.com
3Bureau de Recherches Géologiques et Minières, B.P. 6009, 45060 Orleans cedex, France.
initial receipt: 3 March 1999
Date of acceptance: 25 April 2000
Date of publication: 15 August 2000