Sediment samples were collected during three Ocean Network Canada expeditions to three hydrothermal vent fields at the Endeavour segment of the Juan de Fuca Ridge. The sediments were collected at variable distances (≤ 1340 m) from the vents fields by push core and, in some cases, by suction sampling from base of a chimney structure. The geochemistry of the sediments was investigated in order to understand their formation and the mass fluxes associated with these hydrothermal systems. Qualitative and quantitative approaches have been applied to deconvolve sediments bulk compositions into mass fractions of the different components that they are made up of. Qualitative analysis identified five different end-member components (hydrothermal plume particles, hydrothermal chimney fragments, terrigenous sediment, basalt fragments and organic matter). Using Q-mode factor analysis only three main components are identified. This is due to the geochemical similarity of (i) the hydrothermal plume particles and hydrothermal chimney fragments which are grouped together in this analysis, and (ii) the terrigenous sediment and basalt which are also grouped. Mass fractions of each component were calculated by using a numerical inversion procedure. The samples collected at the base of the chimney are composed of 20-40% plume particles and 56-72% chimney fragments with little contribution from other sediment sources. With increasing distance from the vent fields the contributions of these “hydrothermal” sources to the sediments drop rapidly to <50% within 90 m of the vents and <25% within 120 m from the vents. The mass fraction and chemical composition of the plume particles component, along with the estimates of the chemical flux out of hydrothermal vents and sedimentation rates in the area, are used to make a preliminary estimation of the chemical flux into the ocean. / Graduate / 0372 / 0996 / 0547 / armaghan.attar@gmail.com

The Atlantis II Deep is a location of modern submarine hydrothermal activity along the slowly spreading Red Sea rift axis. Venting of high-temperature hydrothermal fluids, similar to those associated with black smokers, takes place in a brine pool and has led to the accumulation of 90 Mt (dry, salt free) of stratiform, metalliferous sediment. The conditions of mineralization are unique in the modern oceans, but have been widely suggested as a possible analog of some important ancient stratiform base metal ore deposits. This study shows that many of the proposed genetic models for these ancient deposits may be highly simplified and do not take into account rapid diagenetic transformations, widespread non-equilibrium processes, and many other aspects of metal deposition. Sediment cores of the Atlantis II muds were last studied more than 30 years ago. High-resolution sampling and careful re-examination of the mineralogy and geochemistry of the sediments, using modern analytical techniques has significantly improved the understanding of the different processes responsible for the formation of the finely layered metallifeous sediments. The geochemistry of the individual layers is controlled by highly variable detrital, hydrogenic and hydrothermal input. Primary depositional pathways from the brine pool are the main control on basin-wide metal distribution (e.g., increasing Cu/Zn away from the vents) including variable enrichment in trace metals via scavenging from the brine pool and from the enriched pore waters. Cu and Zn have been deposited not only as sulfides but also with poorly crystalline Si-Fe-(oxy)hydroxides. A significant proportion of the original non-sulfide Cu and Zn are diagenetically transformed into sulfides, but also carbonates and clays, in large part reflecting sulfide deficient pore waters. Negative δ34S values, previously unrecognized in the sulfide- and metal-rich units, indicate a source of bacteriogenic sulfide. Syn-diagenetic processes also appear to have been responsible for the sharp laminations in the sediments, as well as distinctive zoning of carbonate and clay minerals around the vent source. The early diagenetic transformations observed in the Atlantis II Deep may not be preserved in the ancient rock record but nevertheless have important implications for metal deposition in some of the world’s largest and richest base metal ore deposits.