HR: 0800h
AN: V21D-0750    [Abstracts]
TI: Distribution and Sources of Trace Metals in Volcaniclastic Sediments of the SuSu Knolls Hydrothermal Field, Eastern Manus Basin, Papua New Guinea
AU: * Hrischeva, E H
EM: hrischeva@geology.utoronto.ca
AF: Department of Geology, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1, Canada
AU: Scott, S D
EM: scottsd@geology.utoronto.ca
AF: Department of Geology, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1, Canada
AB: Thirty-one sediment cores from the Suzette sulfide mound (renamed Solwara 1 by Nautilus Minerals Inc) in the SuSu Knolls hydrothermal field, eastern Manus back-arc basin, were studied in order to outline anomalies in metal concentrations within the mound and to explain the sources of the anomalies. The sediment cores were collected during expeditions of Nautilus Minerals Inc in 2006 and 2007. The work complements our previous study of metalliferous sediments of the SuSu Knolls and aims to provide guidelines for exploration for seafloor massive sulfide deposits in both modern and ancient back-arc environments. In contrast to mid-ocean ridges, the sedimentation in back-arc basins is more complex and involves deposition of large amount of volcaniclastic material that may mask the hydrothermal signal. The SuSu Knolls are covered by an apron of laminated dark gray volcanic sandy silts and silty sands composed of various amounts of volcanic rock fragments, volcanic glass, Ca plagioclase, pyroxene, cristobalite, Si-rich amorphous material, alunite, pyrite, barite and magnetite. In many cases the gray volcaniclastic sediments exhibit patches and layers having a black or greenish-brown color that contain fecal pellets. On the western slope of Suzette (Solwara 1), dark gray volcaniclastic sediments overlie greenish, greenish-brown and greenish-black volcaniclastic sediments containing up to 10 wt % clay-size component that comprises alteration products of volcanic glass such as smectite, chlorite and X-ray amorphous material. In most cases black and greenish-brown colored sediments contain fecal pellets at different stages of preservation. The distributions of Au (19 ppb to 2 ppm), Cu (159 ppm to 1 wt %), Zn (35 ppm to 1333 ppm), Pb (7 ppm to 977 ppm) and Ba (0.05 wt % to 2.8 wt %) outline patchy anomalies throughout the sediments of the mound. The study showed that some volcaniclastic sediments as deep as 25 cm below seafloor that are proximal to chimneys and chimney fragments do not exhibit clear metal anomalies. Local strong anomalies in metal concentrations caused by dispersal of chimney sulfides in the volcaniclastic sediments were found on the rim of the mound. More widespread anomalies were detected down to 80 cm depth in greenish-brown and greenish- black volcaniclastic sediments from the western slope of the mound. Metal anomalies in these sediments may be a result of dispersal of fine-grained particles of secondary minerals, such as atacamite and Fe-oxyhydroxides, derived from oxidation of sulfide chimneys. Another possible source of the metals is hydrothermal particles that were deposited in the sediments within fecal pellets. With the exception of local anomalies in surface sediments around active chimneys, the current particulate plume emanating from black smokers does not leave a clear signal in the sediments covering the mound.
DE: 3001 Back-arc basin processes
DE: 4832 Hydrothermal systems (0450, 1034, 3017, 3616, 8135, 8424)
DE: 4875 Trace elements (0489)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting