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The deep structure of a sea-floor hydrothermal deposit
Zierenberg, R. A.; Fouquet, Y.; Miller, D. J.; Bahr, J. M.; Baker, P. A.; Bjerkgard, T.; Brunner, C. A.; Duckworth, R. C.; Gable, R.; Gieskes, J.; Goodfellow, W. D.; Groschel-Becker, H. M.; Guerin, G.; Ishibashi, J.; Iturrino, G. J.; James, R. H.; Lackschewitz, K. S.; Marquez, L. L.; Nehlig, P.; Peter, J. M.; Rigsby, C. A.; Schultheiss, P.; Shanks, W. C.; Simoneit, B. R. T.; Summit, M.; Teagle, Dah; Urbat, M.; Zuffa, G. G.
Abstract: Hydrothermal circulation at the crests of mid-ocean ridges plays an important role in transferring heat from the interior of the Earth(1-3). A consequence of this hydrothermal circulation is the formation of metallic ore bodies known as volcanic-associated massive sulphide deposits. Such deposits, preserved on land, were important sources of copper for ancient civilizations and continue to provide a significant source of base metals (for example, copper and zinc)(4-6). Here we present results from Ocean Drilling Program Leg 169, which drilled through a massive sulphide deposit on the northern Juan de Fuca spreading centre and penetrated the hydrothermal feeder zone through which the metal-rich fluids reached the sea floor. We found that the style of feeder-zone mineralization changes with depth in response to changes in the pore pressure of the hydrothermal fluids and discovered a stratified zone of high-grade copper-rich replacement mineralization below the massive sulphide deposit. This copper-rich zone represents a type of mineralization not previously observed below sea-floor deposits, and may provide new targets for land-based mineral exploration.
