A Geochemical and Spatial Characterization of the Champagne Hot Springs Shallow Hydrothermal Vent Field, Dominica, Lesser Antilles

Studies of seafloor hydrothermal activity and its associated geochemical and mineralogical effects have primarily focused on deep sea systems. These processes are not limited to deep sea locations. Numerous shallow hydrothermal systems have been identified along the submerged flanks of volcanic islands such as Vulcano Island, Italy and Ambitle Island, Papua New Guinea. This study investigates the Champagne Hot Springs shallow marine hydrothermal system, located along the submerged flank of the Plat Pays volcanic system on the southwest section of the island of Dominica, Lesser Antilles. The main objective is determine the source of the hydrothermal fluids and gases and their related effect on sediment and precipitate chemistry. A detailed map of the vent field will also be generated to accurately present vent locations and distribution. Geochemical and mineralogical analyses of vent waters, pore waters, gases, sediments and precipitates were determined by High Pressure Liquid Chromatography (HPLC), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Neutron Activation Analysis (NAA), Scanning Electron Microscopy (SEM), Electron Dispersive X-Ray Analysis (EDX), Powder X-Ray Diffraction (XRD), Gas Chromatography and Mass Spectrometry. These analyses have revealed the following: (1) The vent waters and pore waters are mixtures of seawater and meteoric derived hydrothermal fluids in varying proportions. The relative input of each component is both temperature and flow rate dependent. (2) The simultaneous increase in pH and Eh caused by mixing between Fe2+ rich vent fluids and seawater forms precipitates and sediment coatings of hydrous ferric oxides. The elevated concentrations of As and Sb in the precipitates and sediments relative to average Caribbean seafloor sediments is a function of adsorption to the surface of the hydrous ferric oxide, (3) Pore waters in the immediate vicinity of sediment covered vents carry Fe2+ rich fluid to the sediment/seawater interface, where rapid oxidation of soluble Fe2+ to insoluble Fe3+ leads to precipitation of hydrous ferric oxide coatings on sediment grains and subsequent formation of hydrothermally altered sand patches, (4) The gas samples are typical arc-type gases and have both meteoric and magmatic signatures