SRD41-P01

Room:Convention Hall

Time:May 25 18:15-19:30

Epithermal mineralization at Takarajima of the Tokara Islands
NAGAHARA, Masato1∗ ; ISHIBASHI, Jun-ichiro2 ; OKUMURA, Ryo3 ; TAKAMIYA, Koichi3 ; YOKOSE, Hisayoshi4
1Graduated School of Science, Kyushuu University, 2 Faculty of Science, Kyushu University, 3 Kyoto University Research Reactor
Institute, 4 Graduate School of Science and Technology[Introduction] The Ryukyu volcanic arc is located southwest of Kyushu across 1200 km length. Volcanic isldans of theTokara Islands are known to belong to the Ryukyu arc, whereas several submarine volcanoes in the west part have not been wellinvestigated. Yokose et al. (2007, 2010) proposed existence of some large submarine calderas at intervals of about 100 km inthis region. Takara Shima island and Ko-Takara Shima Island located about 80 km north of Amami-Oshima, are considered as toconstitute a part of somma of the Takara Shima Caldera. In Takara Shima Island, occurrence of altered tuff breccias associatedwith obvious quartz veins including sulfide minerals had been reported (Osako, 1976; Nakano et al., 2008). A few trials of mining
operation had been attempted in the island, such as at the Takara Shima gold mine and Sagigazaki copper mine, until 1960’s. In
May 2013, we found large boulder rocks of a few meters diameter associated with numerous quartz veins, at the Tsumiishi coast
located at the east part of the island. We report mineralogy of the quartz veins and sulfide minerals within them, and discusspressure and temperature conditions of the mineralization.
[methods] We collected about 10 samples from the Tsumiishi coast and the ruin of the Takara Shima gold mine. The former
samples were split off with a hammer from the boulder. The later samples were collected from the ground where used to bea spoil bank of the gold mine. Rock forming minerals and sulfide minerals were investigated by microscopic observation, andanalysis using an electron probe micro analyzer (EPMA) and x-ray diffract meter (XRD). Chemical composition of the sulfide
minerals was determined by EPMA analysis. Abundance of trace elements in the quartz veins was examined by instrumental
neutron activation analysis (INAA). Homogenization temperature of fluid inclusions in the quartz veins was detemined using aheating stage.
[results] Variety of quartz veins were observed from vein of dozens cm width to stockwork texture with a few µm width. We
identified chlorite, pyroxene and plagioclase as rock forming minerals, among which some of pyroxene was altered to chlorite. As
ore sulfide minerals, chalcopyrite, galena, sphalerite and pyrite were identified in most of the samples. As minor sulfide/sulfate
minerals, covelline, tetrahedrite, chalcocite, greenockite and barite were identified. Electrum was found in only one sample
collected from the gold mine ruin, whereas trace amount of Au was determined by INAA in the quartz veins of the samples
collected both from the gold mine ruin and Tsumiishi coast. Pseud-acicular and mosaic (jigsaw) textures were observed in thequartz veins in some samples from the Tsumiishi coast. Homogenization temperature of fluid inclusions containing two phasesin the quartz vein was determined as above 210 ℃ for only one sample from the Tsumiishi coast.
[discussion] The characteristic textures of the quartz vein suggest boiling of hydrothermal fluid (e.g., Henley, 1985) which
may accompany precipitation of metal sulfide minerals . Existence of liquid-vapor two-phase fluid inclusions in the quartz vein
supports this idea, and enables.us to estimate mineralization depth around 200-300 m based on the homogenization temperature.
Together with this range of mineralization depth, the observed assemblage of sulfide minerals suggests intermediate sulfidation
type epithermal mineralization, which is usually observed at about a few km away from the heat source magma (e.g., Sillitoe,2010). Therefore, the epithermal mineralization at Takara Shima island could be attributed to hydrothermal activity which isdriven by a heat source magma beneath the submarine caldera (sea)floor. Present activity of high temperature (nearly 100 ℃) hotspring at the Ko-Takarashima may suggest continuity of the hydrothermal system.

Keywords: Hydrothermal mineralization, Submarine volcanic caldera, sulfide mineralization

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SRD41-P02

Room:Convention Hall

Time:May 25 18:15-19:30

Mineralogical and Geochemical Study of Hydrothermal Ores from the Hatoma Knoll Hydrothermal Field in the Okinawa Trough
TOTSUKA, Shuhei1∗ ; NAKANO, Hiroki1 ; SHIMADA, Kazuhiko1 ; ISHIBASHI, Jun-ichiro1 ; NOZAKI, Tatsuo21Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, 2 Research and Development
Center for Submarine Resources, JAMSTEC
Hydrothermal activity at the Hatoma Knoll in the ca. 1500 m water depth of southern Okinawa Trough is characterized byabundant sulfate (anhydrite and barite) mineralization associated with active venting of significantly Cl− depleted hydrothermal
fluid up to 300 oC. Since exclusive sulfate mineralization would be explained by less participation of metal species into thevapor phase during the phase separation of hydrothermal fluid, sulfide mineralization below or just above the seafloor could beexpected. In order to investigate potential for sulfide mineralization at the Hatoma Knoll, we intensively collected hydrothermal
sulfide/sulfate ores which were half buried within a sediment-covered seafloor. We report mineralogical and geochemical featuresof these brecciated mound ores and collapsed chimneys.
Our samples were collected during dive expeditions of YK07-04, NT08-13, NT11-20 and KY14-02, employing the manned
submersible SHINKAI 6500 or ROV (remotely operated vehicle) Hyper-Dolphin 3000 of JAMSTEC. Constituent mineral of thecollected samples was identified by microscopic observation and X-ray diffractometery (XRD), and chemical composition ofspecific sulfide minerals was determined by an Electron Probe Micro Analyzer (EPMA).
Based on the mineral assemblage and its texture, the hydrothermal ores can be classified into five types. Type I (fine-grainedsulfide ore) is characterized by dendritic texture which suggests precipitation under the quenching condition. Type II (sulfidedominant ore) is dominated by abundant sulfide minerals of sphalerite, galena and tetrahedrite. Among this type of ores, somespecific ores were recognized and identified as following two sub-types; (1) Type II’ (Sb-rich chimney) is characterized by abundant occurrence of Sb-contained sulfide minerals such as tetrahedrite, and (2) Type II” (coarse-grained sulfide ore) is distinctivefrom other samples by substantially larger grain size of sphalerite up to 1 cm. Type III (barite dominant As-rich chimney) is
characterized by abundant occurrence of barite with arsenic sulfide minerals (orpiment and realger).
Two interesting features were recognized with respect to the chemical composition of sulfide minerals. Sphalerite crystal in
the Type I chimneys often exhibits an anomalously high Mn content up to 11.4%. Moreover, tetrahedrite in the Type II’ sample
contains high Ag content ranging from 8.27 to 18.90 %. Ag content and Sb/(Sb+As) ratio in the tetrahedrite crystal shows apositive correlation, although some ore samples showed an unusually high Ag content. Some Ag-Sb bearing sulfide minerals
other than tetrahedrite were also identified, which supports strong correlation between Ag and Sb.
Keywords: Okinawa Trough, Hatoma Knoll, Seafloor massive sulfide ore deposit, Ag-rich tetrahedrite

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SRD41-P03

Room:Convention Hall

Time:May 25 18:15-19:30

Sulfur isotopic compositions of stibnite in antimony deposits, southern Myanmar
SANEMATSU, Kenzo1∗ ; MANAKA, Takayuki2
1

Geological Survey of Japan, AIST, 2 Neko Minerals Co., Ltd.

Antimony (Sb) deposits are generally formed by precipitation from metamorphic (diagenetic) or hydrothermal fluids and canbe accompanied by Au or W in some deposits. In southern Myanmar, many Sb deposits are distributed north and south although
the ore genesis is not studied well. In this study, we discuss sulfur isotopic compositions of stibnite (Sb2 S3 ) and Sb(-Au) mineralization of some Sb deposits.
The Sb deposits are hosted by the Carboniferous to Early Permian Mergui and Lebyin Groups consisting mainly of mudstone,sandstone and limestone, consisting of stibnite-quartz vein-type and disseminated ore bodies. It is not well understood whether
the ore bodies were formed from metamorphic fluids or fluids which are contributed from magmatic hydrothermal components.
Granitic rocks (both magnetite-series and ilmenite-series), which could be the heat source of the hydrothermal fluids, are regionally distributed in the Sb metallogenic province although volcanic rocks are rarely found. The Sb ores consist mainly of stibnite
and quartz, and occurrences of other minerals are uncommon. Stibnite occurs as euhedral elongated crystals and coexists withmassive milky quartz. Fine-grained pyrite crystals are found in stibnite and quartz under a microscope. In one of the samples,stibnite is rimed by an alteration mineral, cervantite (Sb2 O4 ).
Sulfur isotope ratios (δ 34 S) of stibnite range widely from -9.4 to +8.2 ‰. The light isotope ratios (δ 34 S <0 ‰) are interpreted
probably from sulfur of sedimentary host rocks, whereas the heavy isotope ratios (δ 34 S >0 ‰) are attributed to result fromcontributions from high-temperature or oxidized hydrothermal fluids. Magnetite-series granitoids generally show heavier sulfur
isotope ratios than ilmenite-series, however no significant relationship was found between the isotope ratios and distribution ofgranitoids.
Stibnite is accompanied by Au mineralization and Au is recovered in some of the Sb deposits. Results of fire assay show thatthese Sb ores contain 0.1 to 3 ppm Au, approximately. The Au-bearing stibnite samples show positive sulfur isotope ratios.
Keywords: antimony, stibnite, sulfur isotope, deposits, gold, Myanmar

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SRD41-P04

Room:Convention Hall

Time:May 25 18:15-19:30

REE-bearing Minerals in Granitoids at Sibolga and Panyabungan, North Sumatra, Indonesia
IWAN, Setiawan1∗ ; TAKEYUKI, Ogata2 ; TAKAHASHI, Ryohei2 ; IMAI, Akira21Graduate School of Engineering and Resource Science, Akita University, Japan, 2 Department of Earth Resource Science, Faculty of International Resource Sciences, Akita University,Granitoids in the western part of North Sumatra are being studied to elucidate the genesis of REE mineralization on the basisof mineralogical and geochemical methods. Eleven samples were analyzed by petrography, XRF, SEM and ICP-MS to identify
REE-bearing minerals and determine REE concentration.
The granitoids at Sibolga and Panyabungan are separated by 166 km distance, which formed in different settings, but both of
the two magmas share ilmenite-series and metaluminous affinity. Petrographic study revealed that granitoids in Sibolga are Atype and ilmenite-series alkali feldspar granite and quartz syenite, formed within plate setting, and that I-type and ilmenite-series
quartz syenite in Panyabungan was formed in volcanic arc setting. Allanite, apatite and titanite in the granitic rocks at Sibolga
and Panyabungan contain Y, Ce, La, Pr, Nd, and Yb.
The setting changed due to change in tectonics during Late Permian to Cretaceous, from continental rift to magmatic arc setting. The enrichment of REE in the Sibolga and Panyabungan granitoids was caused by crystallization of allanite, apatite, andtitanite.

Keywords: Sibolga, Panyabungan, Granitoids, A-type, I-type, ilmenite-series

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SRD41-P05

Room:Convention Hall

Time:May 25 18:15-19:30

Metallic mineralization and petrography of granitoids at the Phon Tiou - Boneng tin mining area, central Laos
TAKAHASHI, Ryohei1∗ ; ITO, Yoshiya2 ; CHARUSIRI, Punya3 ; IMAI, Akira1 ; VEERAVINANTANAKUL, Apivut3 ;WATANABE, Yasushi11Faculty of International Resource Sciences, Akita University, JAPAN, 2 Faculty of Engineering and Resource Science, Akita
University, JAPAN, 3 Department of Geology, Chulalongkorn University, THAILAND
Recently demand and price of tin have been increasing because of development of lead-free solder alloy as a global industry
standard. Indium tin oxide (ITO) is also known as a high technology material used for liquid crystal display and so on.
The Phon Tiou and Boneng deposits located in central Laos are medium-scale (>10,000 t Sn) residual and placer tin deposits
with total reserves of 10,100 t and 11,600t Sn, respectively. The mining target is cassiterite (SnO2 ). Besides, there are several
base metal and precious metal deposits and prospects in this area. Recently, Laotian, Thai, Chinese, Russian and North Korean
companies are mining mainly tin and processing using shaking table method, in addition to small-scale miners. There are few
studies that described metallic mineralization in this area. Objectives of this study are to elucidate petrographic and chemical
characteristics of granitoids and metallic mineralization in the Phon Tiou - Boneng tin mining area, specially revealing a sourcerock of cassiterite, based on magnetic susceptibility, radioactivity, microscopic and EDS-SEM observation, bulk chemical compositions and sulfur isotopic compositions.
The Phon Tiou - Boneng tin mining area is located in Truong Son fold belt formed by Indosinian orogeny during PermianTriassic period. Basement rock of the study area is Silurian-Devonian sandstone, mica schist and limestone. It is covered byCarboniferous and Jurassic sedimentary rocks, and Quaternary alluvial deposits. There are Triassic granitoids of the Say Phou
Ngou and Phon Tiou complexess.
Magnetic susceptibility of the Say Phou Ngou and Phon Tiou granitoids complexes ranges from 0.02×10−3 to 1.5×10−3 SIand from 0.02×10−3 to 0.15×10−3 SI, respectively, indicating characteristics of almost ilmenite-series. The radio activity ofgranitoids ranges from 0.19 to 0.34µS and there is no distinct difference between the two complexes. Both the granitoids arecomposed mainly of quartz, K-feldspar, plagioclase, biotite of 300-700µm across and +/- zircon as primary minerals, showing
equigranular texture. On the basis of the modal compositions, the Say Phou Ngou and Phon Tiou granitoid complexes are classified petrographically as syenogranite-monzogranite, and syenogranite, respectively. The granitoids of Say Phou Ngou complex(162-242 ppm Zr) contain relatively large amount of zircon included in biotite compared to those of the Phon Tiou complex(64-74 ppm Zr). The Phon Tiou complex (6-9 ppm Sn) is slightly enriched in tin compared to the Say Phou Ngou complex (2-3ppm Sn).
Grain size of cassiterite contained in alluvial deposits and the concentrate after the table shaking separation ranges from 50 to200µm. The SnO2 concentrate is ca. 60 wt% and the concentrate contains magnetite, goethite, zircon (ca. 1,500 ppm Zr) andwolframite (ca. 450 ppm W). A sample of cassiterite-bearing alluvial deposits collected from a mining site contains ca. 1,000ppm Sn and ca. 500 ppm Zr. The Sn content of a hard rock collected from the outcrop beside the mine is up to ca. 1,500 ppm, andwe concluded that it is the source rock of cassiterite. The rock is composed mainly of equigranular quartz of 150-200µm acrossand their interstice is filled by goethite and cassiterite, implying that it is a hydrothermally altered and/or leached granitoid.
δ 34 SCDT of sulfides from sulfide veins in an outcrop and ores in a stockpile are negative suggesting that the sulfur was derived
from biogenic sulfide of sedimentary rocks and/or from ilmenite-series granitoid magma into which biogenic sulfide of sedimentary rocks was incorporated.
Keywords: Laos, Phon Tiou - Boneng, residual and placer tin deposits, cassiterite, granitoids

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