SRD41-01

Room:106

Time:May 25 09:00-09:25

Chemical analysis of individual fluid inclusion by SXRF: application to hydrothermal ore
deposits
HAYASHI, Ken-ichiro1∗
1

Faculty of Life and Environmental Sciences, University of Tsukuba

Information on chemical composition of ore-forming fluid is significant when discuss the origin and evolution of ore-forming
fluid, dissolution and transportation mechanisms of heavy metals and precipitation mechanisms of ore minerals. Salinity of fluidinclusion has been extensively reported, however data of heavy metals is scarce. Chemical compositions of individual fluidinclusion are measured recently with a development of micro-analytical techniques. Examples of SXRF analysis of individual
fluid inclusion are described.
Chemical compositions of ore-forming fluid responsible for vein-type W deposit at the Takatori mine was measured. Four mineralization stages are distinguished at the deposit, such as early wolframite-fluorite-topaz-muscovite-lepidolite, middle sulfidefluorite, late carbonate-cassiterite and final carbonate-clay mineral stages. Quartz is accompanied in all these stages. Pseudosecondary fluid inclusions hosted in quartz are selected for chemical analyses. Temporal relation of these inclusions is determinedfrom cross-cut nature of trails that accompany fluid inclusions. SXRF analyses suggest compositions of ore-forming fluid asfollows. Metal concentrations in early stage fluid are very high as 1400-3700 ppm W, 4100-6200 ppm Fe, 1000-1800 ppm Mn,
1500-3000 ppm Cu and 1800-2900 ppm Zn. Middle to late stage fluids contains 300-600 ppm Fe, 100-300 ppm Mn, 50-100 ppm
Cu and 50-100 ppm Zn with less than detection limit of W. Concentrations of ore-forming metals in fluid decreased remarkably
with mineralization.
Vapor-liquid partitioning coefficients for Cu and Zn in aqueous fluid were determined under boiling conditions at 500-650℃ and 35-100 MPa in sulfur-bearing and sulfur-free systems. A synthetic fluid inclusion technique was used to sample theexperimental system coexisting vapor-rich and liquid-rich fluid inclusions, with the Cu and Zn concentrations in individual fluidinclusions then analyzed by SXRF. The vapor-liquid distribution constant of Cu (KD = mCu(vapor) /mCu(liquid) ) is found to bestrongly dependent on the sulfur content in the experimental solutions. In sulfur-bearing systems, Cu preferentially partitions
into the vapor phase, whereas Zn preferentially fractionates into the hypersaline liquid. The KD values for Cu and Zn obtainedin this study correspond well with those obtained from natural fluid inclusions in hydrothermal ore deposits. The results suggestthat differential volatility of metals is an important factor affecting the enrichment of certain metals in different hydrothermal ore
deposits.

Keywords: fluid inclusion, SXRF, chemical analysis, ore-forming fluid

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SRD41-02

Room:106

Time:May 25 09:25-09:40

Characteristics of Magmatic Hydrothermal System at Southeastern Martabe High Sulfidation Epithermal Deposit, Indonesia
SAING, Stephanie1∗ ; TAKAHASHI, Ryohei1 ; IMAI, Akira1
1

Graduate School of Engineering and Resource Science Akita University

The Martabe Au-Ag deposit, North Sumatra Province, Indonesia is a high sulfidation epithermal deposit, which is hosted by
Neogene sandstone, siltstone, volcanic breccia, and andesite to basaltic andesite of Angkola Formation. The deposit has six
ore bodies that occur as silicified massive ore (enargite-luzonite-pyrite-tetrahedrite), quartz veins (tetrahedrite-galena-sphaleritechalcopyrite), banded sulfide veins (pyrite-tetrahedrite-sphalerite-galena) and cavity filling. All ore bodies were controlled by
N-S and NW-SE trending structures. The Barani and Horas ore bodies are located in the southeast of the Purnama ore body. Fluid
inclusion microthermometry and alunite-pyrite pairs sulfur isotopic geothermometry show slightly different forming temperature
among the ore bodies. Formation temperature of the Purnama ore body ranges from 215 to 260o C and salinity from 5 to 8 wt%
NaCl equivalent. Formation temperature of the Barani ore body ranges from 200 to 240o C and salinity from 0 to 2.5 wt% NaClequivalent and those of the Horas ore body ranges from 240 to 260o C and from 2 to 3 wt% NaCl equivalent, respectively. The
general sequences of mineralization at Martabe are divided into the early stage as main high sulfidation mineralization stage andthe late stage of oxidation and brecciation, which were followed by weathering. Sulfides (enargite-luzonite-pyrite-tetrahedrite)that were associated to gold and silver are abundant at the Purnama ore body. The Barani and Horas ore bodies are less silicified
and sulfide abundance is less than the Purnama ore body. The salinity and sulfur isotopic values indicate a mixing trend among
different fluids. Salinity of fluid inclusion decrease from higher salinity (› 5 wt% NaCl equivalent) in the Purnama ore bodyto lower salinity (‹ 3 wt% NaCl equivalent) in the Barani ore body which is directly located in southeast of the Purnama ore
body. The sulfur isotope ratio values of sulfide and sulfate in Purnama range from -4.2 to +5.5 ‰ and from +1.2 to +26.7 ‰, and those in the Barani range from -4.3 to +26.4 ‰ and from +3.9 to +18.5 ‰, respectively. The Horas ore body shows low
salinity but higher formation temperature compared to Barani which possibly indicate different mixing condition unrelated with
Purnama and Barani ore bodies. The sulfur isotope ratio values of sulfide and sulfate in the Horas ore body range from -11.8 to+3.5 ‰ and from +1.37 to +25.7 ‰. At the Purnama and Barani ore bodies, alteration assemblages consist of quartz-kaolinitedickite - alunite - illite - pyrophillite and ore mineral assemblages are mostly composed of enargite-luzonite-pyrite-tetrahedrite.
In contrast, mineralization style at the Horas ore body including the alteration assemblages (quartz - alunite - illite - dickite muscovite) and ore forming temperature is different from the Purnama and Barani ore bodies.
Keywords: epithermal high sulfidation, sulfur isotope, fluid inclusion microthermometry

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SRD41-03

Room:106

Time:May 25 09:40-10:00

Lithium isotope index as powerful research tool for earth resource
NISHIO, Yoshiro1∗
1

JAMSTEC

Lithium (Li) is one of important natural resources, because Li is used for secondary battery of electric and/or hybrid vehicles.
The lightest alkali element, Li, is one of fluid-mobile elements. The leaching of Li from sediments into fluids is dramaticallyelevated together with increasing temperature, and the fact that subsequent re-uptake of the leached Li from the fluid by sediments(which occurs as the fluid cools) takes a considerable time. Li is relatively unaffected by surface water contamination because
the Li contents of deep-rooted fluid samples are much greater than the surface water content. The two stable isotopes of Li are6
Li and 7 Li, and their relative abundances are about 7.5% and 92.5%, respectively. Furthermore, the difference in the 7 Li/6 Li
ratio between fluid and solid phases varies with the reaction temperature. As a result, the Li isotope ratio is a potentially usefulgeothermometer because the Li cation is monovalent and hence not redox sensitive, and it is not a nutrient, so it does notparticipate in biologically mediated reactions.
In this presentation, I’ll talk about fundamental feature of Li isotope tool at first, and after then I show the potential of Li
isotope tool for earth resource science.

Keywords: lithium isotope, deep crustal fluid, geochemical thermometer, fluid inclusion

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SRD41-04

Room:106

Time:May 25 10:00-10:15

Li isotopic composition of submarine vent fluids from arc and back-arc hydrothermal systems in the western Pacific
ARAOKA, Daisuke1∗ ; NISHIO, Yoshiro2 ; GAMO, Toshitaka3 ; YAMAOKA, Kyoko4 ; KAWAHATA, Hodaka3
1

GSJ, AIST, 2 JAMSTEC, 3 AORI, The Univ. of Tokyo, 4 GSJ, AIST

Submarine hydrothermal systems significant contribute to heat and elemental fluxes to the ocean. Vent fluid geochemistry in
mid-ocean-ridge (MOR) hydrothermal systems were well-studied, while studies on vent fluid geochemistry in arc and back-arc
systems with various geological characteristics were insufficient, especially in terms of lithium. To reveal control factors onlithium in arc and back-arc hydrothermal systems and lithium isotopic behavior in water-rock interaction at high temperature,
we determined Li contents and its isotopic compositions of 11 vent fluids collected from 5 submarine arc/back-arc hydrothermal
systems in the western Pacific.
Based on mass balance calculation, Li in vent fluids are dominated by seawater-rock (seawater-sediment) interaction in
sediment-starved (sediment-hosted) hydrothermal systems in arc and back-arc basins at equilibrium. Li contents in vent fluids is also influenced by phase-separated processes, by temperature-related portioning of rock Li into fluid phase, and by hostrocks and sediments. In contrast, Li isotopic composition in vent fluids is affected by host rocks and sediments, but not by phaseseparated processes. These results demonstrate that lithium is a useful tracer for investigating geological processes occurredunderground such as a phase separation process and water-rock/water-sediment interaction at high temperature.
Keywords: submarine hydrothermal system, lithium isotope ratio, vent fluid, arc, back-arc basin

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SRD41-05

Room:106

Time:May 25 10:15-10:30

Salinity of pore waters in sedimentary basins under geothermal gradients
YOSHIMURA, Shumpei1∗1Dept. Earth Environ. Sci., Yamagata Univ.

The pore waters in sedimentary basins are crucial in the control of diagenesis, sediment-hosted ore formation, and generationand transport of hydrocarbons. The chemical and hydrological properties of the pore waters are therefore of importance in theunderstanding of these geological phenomena. An increasing number of studies reported that the pore waters often have higher
salinity than seawater, and the salinity generally increases with the increase of the depth (e.g., Kharaka and Hanor, 2003). Suchsalinity distribution has been often attributed to infiltration of brines from underlying halite beds. However, the downward salinity increase is observed also in basins that are lacking halite beds (e.g., Xie et al., 2003). Therefore, more general mechanisms
may exist for the formation of the salinity distribution.
In this study, I demonstrate on the basis of thermodynamics that the chemical equilibrium of the saline water in a sediment column under gravity and the pressure and geothermal gradients results in the downward salinity increase. The chemical potential ofsolute is the function of pressure, temperature, concentration, and gravity potential. The pressure term increases with increasing
the depth, whereas the temperature term and the gravity potential decrease. The sum of these terms generally decreases with theincrease of the depth. In the final equilibrium state, the chemical potential should be constant along the column. Therefore, we
consider that the concentration term increases to keep the chemical potential constant, leading to the downward salinity increase.
Assuming that the pore water is the NaCl-H2O mixture, I calculated the concentration of NaCl in the solution using the modelof Pitzer et al. (1984) and Rogers and Pitzer (1982). The calculations showed that the salinity increased from 32 to 208 g/L in
the 2000 m-thick sediment column under the geothermal gradient of 0.05 K/m. Such a salinity increase is in the same order tothose observed in many sedimentary basins. In an isothermal case, the salinity increased only weakly, and it reached 36 g/L. This
result is consistent with the conclusion of Mangelsdorf et al. (1970) that gravity alone does not explain the observed enrichmentof salinity. If we set the salinity at the top of the column at 1 g/L, it increased to 24 g/L under the identical condition. Therefore,
the high-salinity waters are generated in fresh to brackish environments.
This study showed that the simple chemical equilibrium along the sediment column resulted in the downward salinity increase.
The method proposed here may be applicable to studies of fluids in other geological systems, such as in mantle, crustal rocks,
hydrothermal environments, and magmatic systems.
Keywords: pore waters, salinity, sedimentary basins

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SRD41-06

Room:106

Time:May 25 10:30-10:45

Distribution of rare earth elements between deep granitic groundwater and fracture fillingcarbonate
MUNEMOTO, Takashi1∗ ; OHMORI, Kazuaki1 ; IWATSUKI, Teruki1
1

Japan Atomic Energy Agency

The chemical properties of rare earth elements (REEs) and yttrium (YREE) have been widely studied as geochemical tracer
in aqueous environments. The YREE abundances in groundwater are mainly regulated by mineral-water interaction. The YREE
variability in natural groundwater system is very complex and dependent upon geologies, water flow-path, mixing and chemical
condition of groundwater. We investigated distribution of rare earth elements (YREE) between deep granitic groundwater withdiverse geochemical character and fracture filling calcite in order to understand YREE behavior in natural groundwater systems.
In Tono area, central Japan, the chemical types of groundwater varied with depth; Na-HCO3 type of groundwater in sedimentary rock, Na-Cl type in upper part of base rock granite and Ca-Cl type in deeper granite. The Na-Cl type groundwater
was collected using boreholes from 200, 300 and 400 m, the Ca-Cl type from 650 and 1150 m below ground surface. The
concentrations of YREE were measured by ICP-MS. The fracture filling calcite was obtained from drill core of boreholes similar
to the groundwater sampling. The collected samples were dissolved into 1M NH4 -acetate buffer solution (pH = 4.8) and theconcentrations of YREE in the leached solutions were measured by ICP-MS. Furthermore, in order to assess the precipitation
condition, we measured isotopic composition of O and C for calcite.
Chondrite-normalized YREE patterns of Na-Cl type groundwater exhibited enrichment in heavy REEs relative to light REE,
which was well explained by the predominance of YREE carbonate aqueous complex in the groundwater. On the other hand,
YREE patterns of Ca-Cl type groundwater were enriched in middle REEs (MREEs). In addition, Y/Ho of the Ca-Cl typegroundwater was significantly lower than that of chondrite. MREE-enrichment in natural water occurs from dissolution of
MREE-enriched Fe-oxyhydroxide [1], and lower Y/Ho than chondrite is common in distribution patterns of Fe-oxyhydroxide[2]. The concentration of Fe in the groundwater increased with depth and the Eh measurement of the groundwater showedstrongly reducing condition. Consequently, YREE in the Ca-Cl type groundwater can be explained by dissolution of MREE-rich
Fe-oxyhydroxide with sub-chondritic Y/Ho.
Oxygen isotopic composition of fracture filling calcite varied regardless of depth. The correlation between precipitation temperature and depth was not observed. On the other hand, carbon isotopic composition became heavier with depth. This result
indicates the fracture filling calcite precipitated from mixture of seawater and freshwater. For YREE patterns of fracture filling
calcite collected from 200˜400 m depth exhibited negative Eu anomaly, while the samples from 670˜1294 m along borehole
showed positive Eu anomaly when the YREE contents were normalized by granite. For the fracture filling calcite from 200˜400
m depth were precipitated from groundwater with YREE eluted from granite, because the negative Eu anomaly has been observedin mother rock granite [3]. Therefore, the positive Eu anomaly in calcite indicates that the groundwater precipitated calcite wasenriched in Eu.
[1] Johannesson and Zhou, 1999, Geochim. Cosmochim. Acta 63, 153-165.
[2] Bau, 1999, Geochim. Cosmochim. Acta 63, 67-77.
[3] Takahashi et al., 2002, Chem. Geol. 184, 311-335.

Keywords: rare earth elements, granite, groundwater

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SRD41-07

Room:106

Time:May 25 11:00-11:15

Fractionation between LREE and HREE in hydrothermal fluids associated with felsicmagmatism
SANEMATSU, Kenzo1∗ ; HOSHINO, Mihoko1
1

Geological Survey of Japan, AISTAs crustal abundances of heavy rare earth elements (HREE) are generally smaller than those of light rare earth elements(LREE), HREE are more expensive than LREE in the market. HREE-rich deposits (e.g., Longnan in China, Nechalacho in
Canada) are associated with hydrothermally-altered felsic igneous rocks such as granite and syenite. This study aims to discuss
what caused the fractionation between LREE and HREE in such igneous rocks.
Alkaline rocks, formed by magma with a low degree of partial melting, are significantly enriched in LREE and are weakly
enriched in HREE because LREE are more incompatible than HREE in magma because of their larger ionic radii. Igneous rocks,
which can be HREE-rich deposits, are probably formed by either process of alkaline magmatism enriched in certain elements
and fractional crystallization. The former is represented by intercontinental alkaline rocks such as the Nechalacho deposit andis rich in REE, HFSE (high field strength elements), fluorine and carbonate. Previous experimental studies found that solubilityof zircon is high when magma is rich in alkali elements and/or fluorine and this causes the residual melt to contain more HREE
and Zr. On the other hand, calc-alkaline granite can be a source rock of HREE-rich deposits, as represented by the Longnan
deposit. The intensive magmatic differentiation and fractionation of LREE-bearing minerals may cause the residual melt to beenriched in HREE relative to LREE. For REE ore formation, however, such deposits require further processes including thedeuteric alteration, dissolution of REE-bearing minerals and adsorption of REE during weathering.
Fractionation between LREE and HREE by complexing with various ligands is likely to occur in hydrothermal fluids produced
from felsic igneous rocks. Different previous works have suggested that REE3+ ions are complexed with carbonate, bicarbonate,fluorine, chlorine and sulfate ions. A recent study indicates that REE-fluoride complexes do not have a significant role intransportation or fractionation of REE because of their lower stability than REE-chloride and sulfate complexes above 150 ℃(Migdisov et al., 2009). However, it appears that footprint of saline fluids or sulfate minerals are not very common compared toabundant carbonatite and fluorite in REE deposits.
The HREE-rich igneous rocks are commonly accompanied by alkali alteration and fluoritization in many ore deposits andprospects, however alkali igneous rocks containing high alkali or fluorine contents are not necessarily rich in HREE. REEfluoride complexes are not significant in hydrothermal fluids, however there are insufficient data to determine an importance ofchlorine or sulfate ions in complexing with REE. Fractionation between LREE and HREE in REE deposits still remains unclear
and further studies are expected to elucidate which is the more significant process for the REE fractionation, magmatism orhydrothermal alteration.
Reference
Migdisov, A.A., Williams-Jones, A.E. and Wagner, T. (2009) Geochimica et Cosmochimica Acta, 73, 7087-7109.
Keywords: HREE, LREE, hydrothermal fluids, fractionation, ore deposits, felsic igneous rocks

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SRD41-08

Room:106

Time:May 25 11:15-11:30

Petrogenesis of granitoids in northern Palawan (Philippines) and its implications on rareearth element mineralization
PADRONES, Jenielyn1∗ ; IMAI, Akira2 ; TAKAHASHI, Ryohei2 ; GABO, Jillian aira3 ; TANI, Kenichiro4
1

Graduate School of Engineering and Resource Sciences, Akita University, Japan, 2 Faculty of International Resource Sciences,
Akita University, Japan, 3 Department of Earth Resources Engineering, Kyushu University, Japan, 4 Department of Geology andPaleontology, National Museum of Nature and Science, Japan
Global attention brought about by the increasing demand of rare earth elements (REE) has paved the way for various exploration efforts worldwide. Areas with promising REE deposits were revisited. In the Philippines, explorations are now on-goingwith studies focused on several granitic intrusions. Some of these granitic bodies are distributed in northern Palawan, which is arifted fragment of the southeastern Eurasian margin during the opening of the South China Sea basin in the Oligocene.
The granitic bodies were investigated for possible concentration of REE during magmatic differentiation. The Kapoas granitoids include granites and granodiorites that are metaluminous, high-K calc-alkaline, and belong to the I-type and ilmenite-series.
The granitoids are mostly biotite-rich and contain xenoliths of schists and diorite, quartz xenocrysts, and mafic enclaves. Two
separate intrusive bodies are observed: the Mt. Kapoas which is 13.2 Ma in age; and the Bay Peak granite which is dated 14.1 Ma.
However, both intrusives have similar geochemical signature, which show LREE enrichment. These granitic rocks were more
evolved or highly differentiated I-type, probably generated in the middle to lower continental crust . The REE-bearing minerals
are allanite and monazite. The weathered crust also show LREE enrichment. Weathered crust profile shows Ce-anomaly in the
B-horizon portion where kaolinite, muscovite and illite act as absorptive materials.
This study also confirmed the presence of the Cretaceous Daroctan granitoids aside from the well-studied Middle Miocene
Kapoas granitoids. The Daroctan granitoids include granodiorites and granites which belong to ilmenite-series. The granodiorites contain xenoliths of metasedimentary rocks, quartz xenocrysts and mafic enclaves. It is also sporadically distributed in thenorthern part of the island but these different intrusive bodies have almost similar ages. The REE-bearing minerals are monazite.
Enrichment of LREE in the weathered crust is relatively higher than that of the Kapoas.
Allanite and monazites in the study areas are enriched in Ce, La, Nd, and Sm with associated radioactive element Th. Heavy
minerals concentrated in the beach in Erawan and Ombo, which is part of the Kapoas granitoids, contain up to >10,000 ppm of
La, Ce, and Sm.

Keywords: Palawan Continental Block, Kapoas granitoids, rare earth element mineralization, monazite, allanite

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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 ℃) hot
spring 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, Tatsuo2
1

Department 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 be
expected. 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 of
specific 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-grained
sulfide ore) is characterized by dendritic texture which suggests precipitation under the quenching condition. Type II (sulfide
dominant 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 of
granitoids.
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, Akira2
1

Graduate 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, Yasushi1
1

Faculty 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 by
Carboniferous 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 to
200µm. 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. 1,000
ppm 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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