Actively forming kuroko-style massive sulfide mineralisation and hydrothermal alteration at Iheya North, Okinawa Trough

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doi: 10.1180/minmag.2013.077.5.25
Author(s): Yeats, C. J.; Hollis, S. P.
Author Affiliation(s): Primary:
CSIRO, Earth Science and Resource Engineering, Kensington, West. Aust., Australia
Volume Title: Goldschmidt abstracts 2013
Source: Mineralogical Magazine, 77(5), p.2556; Goldschmidt 2013, Florence, Italy, Aug. 25-30, 2013. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Note: In English
Summary: IODP Expedition 331 drilled five sites at the Iheya North hydrothermal field within the Okinawa Trough backarc basin. At Iheya North, hydrothermal alteration and sulfide mineralisation is hosted in a geologically complex mixed sequence of coarse pumiceous volcaniclastic and fine hemipelagic sediments, overlying dacitic to rhyolitic volcanic substrate. At Site C0016, coring adjacent to the foot of an actively venting sulfide mound intersected massive sphalerite-(pyrite-chalcopyrite)-rich sulfides that strongly resemble the black ore of the Miocene-age Kuroko deposits of Japan - the first time that such material has been recovered from an active seafloor hydrothermal system. The sulfide mineralisation shows clear microtextural evidence of formation via a combination of surface detrital and subsurface chemical processes, with at least some sphalerite precipitating into void space in the rock. Altered volcanic rocks beneath the massive sulfide exhibit quartz-muscovite/illite and quartz-Mg-chlorite alteration, reminiscent of the proximal footwall alteration typically associated with ancient volcanic-hosted massive sulfide mineralisation. At the nearby Site C0013, a likely location of recent high-temperature discharge, intense hydrothermal alteration obliterates primary mineralogy and texture. Near surface alteration is dominated by kaolinite and muscovite with locally abundant native sulfur, suggesting acidic fluids; grading to Mg-chlorite dominated assemblages at depths of >5m below sea floor. Late coarse-grained anhydrite veining overprints the earlier alteration and is interpreted to have precipitated from downwelling seawater that penetrated the sediments when hydrothermal activity at the site waned. Sulfide-bearing samples from Site C0016 and Site C0013 have been sectioned and mapped using scanning electron microscope (SEM) and proton induced X-ray emission (PIXE) techniques for major and trace element composition. Sphalerite from C0016 contains very little iron, which is consistent with the low overall iron budget of the hydrothermal system. PIXE analyses are currently underway and trace elemental distributions revealed by this technique will be presented.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 27 Economic Geology, Metals; Emission spectra; Expedition 331; Hydrothermal alteration; IODP Site C0016; Iheya North hydrothermal field; Integrated Ocean Drilling Program; Kuroko-type deposits; Major elements; Massive deposits; Massive sulfide deposits; Metasomatism; Mineral composition; Mineral deposits, genesis; Mineralization; North Pacific; Northwest Pacific; Okinawa Trough; PIXE spectra; Pacific Ocean; Precipitation; SEM data; Spectra; Textures; Trace elements; West Pacific; X-ray spectra
Coordinates: N274727 N274727 E1265348 E1265348
Record ID: 2014065214
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland