Characteristics of Pb-As-Sb sulfide in dead chimney collected from the ANA Site, west offshore of the Kume-jima Island, middle Okinawa Trough, Japan
Abstract
The ANA Site newly discovered hydrothermal field by geophysical survey during the cruise GK12 by R/V Kaiyo Maru No. 7 in 2012 (AIST press release, 2012), is located at the caldera bottom of the Daisan Kume Knoll with the water depth of 1050 mbsl in the west offshore of the Kume-jima Island, middle Okinawa Trough, Japan. The Daisan Kume Knoll consists mainly of rhyolite and dacite with active hydrothermal venting (Harigane, 2015). We performed the cruise KR15-16 by R/V Kairei with ROV Kaiko Mk-IV in 2015 to collect hydrothermal fluid and rock samples from the ANA Site. We obtained the samples of active chimney, dead chimney and sedimentary rock during the dives KK#667 and KK#673. Torimoto et al. (2017) reported brief petrological and mineralogical descriptions of these three types of chimney, with some occurrences of Pb-As-Sb sulfide minerals confirmed by EPMA analyses from the dead chimney sample (Torimoto et al, 2018). In this study, we report petrological and geochemical characteristics of Pb-As-Sb sulfide minerals and discuss the formation process of this dead chimney.
EPMA, XRF mapping, Laser Raman spectroscopy and microthermometric measurements were applied. Analyzed dead chimney samples consists of sphalerite, galena, barite and Pb-As-Sb sulfide minerals. The dead chimney exhibits three textures under the microscope; dendritic texture, colloform texture and radiating cluster. Pb-As-Sb sulfide minerals is closely associated with galena and often show a colloform texture. Pb-As-Sb sulfide minerals are generally white to greenish white in color with weak pleochroism and strong anisotropy. Chemical composition of Pb-As-Sb sulfide minerals show various ranges and some of them are identical to jordanite (Pb14(As,Sb)6S23), geocrosite (Pb14(Sb,As)6S23) and arsenomarcobaldiite (Pb12(As3.2Sb2.8)Σ6S21). In the ANA Site, As- and Sb-sulfide minerals are frequency hosted in the active chimney sample. This Pb-As-Sb-rich dead chimney might be produced at the middle stage of transition from active chimney to Zn-Pb-rich dead chimney.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V43F0174T
- Keywords:
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- 0930 Oceanic structures;
- EXPLORATION GEOPHYSICSDE: 1034 Hydrothermal systems;
- GEOCHEMISTRYDE: 3616 Hydrothermal systems;
- MINERALOGY AND PETROLOGYDE: 8424 Hydrothermal systems;
- VOLCANOLOGY