The active sulfide chimney ore sampled from the flank of the active Tiger chimney in the Yonaguni Knoll IV hydrothermal system, South Okinawa Trough, consists of anhydrite, pyrite, shalerite, galena, chalcopyrite and bismuthinite. Electron microprobe analyses indicated that the chalcopyrite and bismuthinite contain up to 2.4 wt. % Sn and 1.7 wt. % Pt, respectively. The high Sn-bearing chalcopyrite and Pt-bearing bismuthinite are the first occurrence of such minerals on the submarine hydrothermal systems so far reported. The results confirm that the Sn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn 4+ Fe 2+ for Fe 3+ Fe 3+ while Pt enters the bismuthinite structure as a solid solution during rapid growth. The homogenization temperature of the fluid inclusions in anhydrite (220-310℃) and metasured end-member temperature of the vent fluids (325℃) indicate that the minerals are precipitated as metastable phases at temperature around 300℃. The Sn-bearing chalcopyrite and Pt-bearing bismuthinite expess the original composition of the minerals deposited from a hydrothermal fluid with temperatures of about 300℃

Chiba, Hiroshi

Gena, Kaul

Kase, Katsuo

Okayama University Scientific Achievement Repository

OKAYAMA UniversityEarth Science Reports,Vol. 12, No. I, 1-5, (2005)Tin-bearing chalcopyrite and platinum-bearing bismuthinite in theactive Tiger chimney, Yonaguni Knoll IV seafloor hydrothermalsystem, South Okinawa Trough, JapanKaul GENA, Hitoshi CHmA and Katsuo KASEDepartment ofEarth Sciences, Faculty ofScience, Okayama University, Okayama 700-8530, JapanThe active sulfide chimney ore sampled from the flank of the active TIger chimney in the Yonaguni Knoll Nhydrothermal system, South Okinawa Trough, consists of anhydrite, pyrite, sphalerite, galena. chalcopyrite andbismuthinite. Electron microprobe analyses indicated that the chalcopyrite and bismuthinite contain up to 2.4wt. % Sn and 1.7 wt. % Pt, respectively. The high Sn-bearing chalcopyrite and Pt-bearing bismuthinite are the firstoccurrence of such minerals on the submarine hydrothermal systems so far reported. The results confirm that theSn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn#Fe2+ for Fe3+Fe3+while Pt enters the bismuthinite structure as a solid solution during rapid growth. The homogenization temperatureof the fluid inclusions in anhydrite (220-31O°C) and measured end-member temperature of the vent fluids (325°C)indicate that the minerals are precipitated as metastable phases at temperature around 300°C. The Sn-bearingchalcopyrite and Pt-bearing bismuthinite express the original composition of the minerals deposited from ahydrothermal fluid with temperatures of about 300°C.Keywords: Sn-bearing chalcopyrite,Pt-bearing bismuthinite, Active sulfide Chimney, Yonaguni Knoll IV,Okinawa Trough, seafloor hydrothermal system.I. IntroductionSince 1998, a lot of seafloor hydrothermal activitiesand massive sulfide deposits were discovered in theOkinawa Trough. Among them, hydrothermal activity inthe southern most part of the Okinawa trough was fustdiscovered during Yokosuka-Shinkai 6500 cruise YK00-06 (August 2000) and called Yonaguni Knoll IVhydrothermal system (Hsu et al., 2003). The site wasrevisited during leg 2 of the Yokosuka - Shinkai 6500cruise YK04-05 (2004). Preliminary mineralogical studyindicated that sulfide chimney ores are polymetallic andconsist of sphalerite, pyrite, wurtzite, chalcopyrite, galena,tennantite tetrahedrite series, bornite, covellite,nukudamite, alabandite, stibnite, barite, anhydrite, calciteand rhodochrosite (Suzuki et al., 2005).Chalcopyrite with up to 2.4 wt. % Sn andbismuthinite with up to 1.7 wt. % Pt occur in an activesulfide chimney ores from the flank of the Tiger chimneyfield of the Yonaguni Knoll site. Chalcopyrite with highSn content and bismuthinite with high Pt content have notbeen reported preViously for the submarine hydrothermalsystems. We present here the result of mineralogicalstudies of this active sulfide chimney ore.IT. Tiger chimney in Yonaguni Knoll IV hydrothermalsystem.The Tiger chimney is located at 24°50.8TN and122°42.02'E and at a depth of 1369 m in the YonaguniKnoll IV hydrothermal system. The chimney field consistsof a broad basal mound of fallen dead chimneys fragmentsthat stand 20 m high above the adjacent valley floors ofthick sediments. The active chimneys at the summit of themound emit clear fluids with end-member temperatures ofabout 300°C while the black smokers on the flanks emitvent fluids with end-member temperatwes of 325°C. Sixsulfide chimney ores were collected from the Tigerchimney during the Yokosuka - Shinkai 6500 cruiseYK04-05. An active sulfide chimney ore collected fromthe flank of the Tiger chimney was used in this study (Fig.la). During the time of sampling, the vent fluiddischarging through the orifice of the chimney has anend-member temperature of about 325°C. Bulk chemicalanalysis of four fresh volcanic rocks from these areasindicated that the rocks are rhyolite with silica content of71-73 wt. % and total alkalis of6.6 to 7.7 wt. %.ill. Sample description and ore mineralogyFrom macroscopic observation, the ore shows strong2Kaul GENA, Hitoshi CHIBA and Katsuo KAsE#816-8-01Chimney wall4cmaTe~r-------------~~oIZone C Zone B I Zone A~b IIIIse :~: :~I II,ICIlFig. 3 Photomicrographs illustrating the textures of the mineralsin the chimney. (A) Transmitted light photomicrograph ofcoarse-grained anhydritc in Zone C, (B) Reflected lightphotomicrograph of fine grained sulfides of pyrite (py),galena (g1), chalcopyrite (cp) and sphalerite (sp) in Zone C,(C) Reflected light microphotograph of coarse grained pyritein Zone B, (D) Reflected light photomicrograph of zigzagcontact margin of Zone A and Zone B, (E) Reflected lightphotomicrograph of the fibrous bismuthinite (hi) in Zone B,and (F) Reflected light photomicrograph of bismuthinitelaths cutting the contact margins of chalcopyrite (Zone A)and pyrite (Zone B).Note: anh =anhydrite, sp =sphalerite, py =pyritegI =galena, cp =chalcopyrite, bi =bismuthiniteFig. 2 Representation of the occurrences of major minerals in thechimney's cross section.This textural relationship indicates that bismuthiniteis deposited later than pyrite and chalcopyrite. The grainsizes of bismuthinite are generally less than 40 !J.11l indiameter and 900 J.Ull in length.mineralogical variation from the interior to the exterior ofthe sulfide chimney ore. The average thickness of thechimney's wall is about 4 cm and consists of three distinctzones (Fig. Ib). Zone A (interior) consists predominantlyof chalcopyrite while Zone B and Zone C consist mainlyof coarse grained pyrite and anhydrite, respectively. Thetextural relationships between the three zones suggest anabrupt replacement of zone C by zones B and A due to thechange of physical chemical environment on transportaCross the chimney wall (Fig. la & Ib).Fig. 1 (a) Photograph of the cross-section of the chimney oreused in this study and (b) Sketch showing the mineralogicalzonation seen in the chimney, A: chalcopyrite rich zone, B:pyrite rich zone and C: anhydrite rich zone.From microscopic observations, the entire chimneyore consists of chalcopyrite, pyrite, sphalerite, galena,bismuthinite and anhydrite. Also, the chimney ore showstrong mineralogical zonation from interior to exterior(Fig. 2)Anhydrite occurs in the exterior of the chimney ascoarse grained crystals. It forms radiating sheaves ofbladed crystals up to Imm long and constitutes about 80%of all the minerals in zone C (Fig. 3A). The blackish colorof zone C is due to the inclusions of disseminated finegrained sulfide minerals of pyrite, galena and chalcopyritediseased sphalerite (Fig. 3B). Zone B consists ofpredominantly coarse grained pyrite (Fig. 3C) with minoramount of bismuthinite with fibrous habit (Fig. 3E). Thecontact margin between zones A and B is clearly definedby a zigzag (sawtooth) contact morphology (Fig. 3D).Randomly orientated bismuthinite displaying a fibroushabit (Fig. 3E) is interspersed throughout the contactmargin of zonesA and B (Fig. 3F and Fig. 4)3TIn-bearing chalcopyrite and Platinum-bearing bismuthiniteIt was recognized that bismuthinite with fibrous habitis restricted to the contact margins of zones A and B (Fig.4). Bismuthinite fibers are generally orientated parallel tothe growth direction of the chimney walls (Fig. 4).equivalent) are consistent with seawater salinity (3.2wt. % NaCl, Volker et al., 2002). However, some salinitiesof the fluid inclusion are slightly higher than seawatersalinity.Table 1. Chemical composition of Sn-bearing chalcopYrite4.34 2.79 2.17 7.02 7.70 6.04 8.68 3.5812345678Number of atoms per formula unit, based on 8 total atoms.60.0848.110.020.0052.75100.961 2 3 4 5Cu 0.14 0.07 0.00 0.07 0.02Fe 47.87 48.05 48.02 47.49 46.63Sn 0.00 0.00 0.00 0.00 0.00Bi 0.12 0.33 0.50 0.62 1.56S 53.27 53.17 53.22 53.46 53.42Total 101.40 101.61 101.73 101.64 101.64Table 3. Chemical composition of pyriteNumber of atoms per formula unit, based on 5 total atoms.Cu 0.05 0.04 0.06 0.06 0.05 0.06Fe 0.03 0.04 0.03 0.04 0.02 0.04Bi 1.89 1.88 1.90 1.88 1.83 1.86Pt 0.03 0.04 0.04 0.04 0.04 0.04S 2.99 3.00 2.97 2.98 3.05 3.00Cu 2.01 2.02 2.03 201 2.01 2.02 2.05 2.03Fe 2.00 1.99 1.98 1.94 1.96 1.94 1.87 1.97Sn 0.04 0.02 0.02 0.06 0.07 0.05 0.07 0.03Bi 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00S 3.96 3.96 3.97 3.99 3.96 3.99 4.01 3.97Slannile (wt.%)Table 2. Chemical composition of Pt.bearing bismuthinite1 2 3 4 5 6Cu 0.69 0.45 0.80 0.73 0.70 0.76Fe 0.32 0.45 0.38 0.39 0.28 0.48Bi 79.19 79.05 79.02 77.62 76.95 77.37Pt 1.30 1.69 1.54 1.60 1.57 1.66S 19.17 19.29 18.95 18.91 19.69 19.18Total 100.67 100.93 100.69 99.25 99.19 99.45Cu 34.61 34.95 35.01 34.42 34.41 34.80 35.13 35.11Fe 30.26 30.23 29.95 29.24 29.56 29.46 28.12 29.95Sn 1.20 0.77 0.60 1.94 2.13 1.67 2.40 0.99Bi 0.19 0.19 0.11 0.04 0.06 0.15 0.00 0.00S 34.46 34.58 34.49 34.53 34.29 34.71 34.63 34.59Total 100.72 100.72 100.16 100.18 100.46 100.79 100.28 100.64•'1'\~,,>,~i::~! '~~..~.?'~ ~...::,,~. -The chemical composition of chalcopyrite, pyrite andbismuthinite were obtained by electron probemicroanalyser (EPMA), using JEOL-JXA-733 superprobe of Okayama University, while the X-ray mappingand back-scattering images of chalcopyrite, pyrite andbismuthinite were obtained by using the automatedJEOL-JXA-8600 super probe of Yamagata University. Theanalytical conditions of EPMA at Okayama University areacceleration voltage of 20kY, a beam current of 20nA andstandards of CuFeS2, Bi, Sn and Pt. The analytical resuItsare processed using ZAF correction factor. In addition, theanalytical conditions of EPMA at Yamagata University areacceleration voltage of 15 kV, a beam current of 20 oA,ZAF correction factor and standards of ZnS, CuFe~, Sn,Bi, MoO, Sb2S3, Au and Ag. The analytical data ofYamagata University were processed by the on-linecomputer using sulfide ZAF in the XM-86 PAC programformulated by JEOL.IV. Result of electron probe microanalysesFig. 4. Back scattering image of chalcopyrite (cp). pyrite (py)and bismuthinite (hi) along the contact margin of zone A andZone B. Bismuthinite crystals with fibrous habit are randomlydisseminated within the pyrite and chalcopyrite grains.Electron probe microanalyses indicated that thechalcopyrite, pyrite and bismuthinite contain minoramount of trace elements. The results of chalcopyrite,bismuthinite and pyrite analyzed under these conditionsare listed on Tables 1, 2 and 3, respectively.Fluid inclusion measurement was done for thirty three(33) two phase (liquid + vapor) fluid inclusions hosted bythe anhydrite. The homogenization temperatures rangefrom 220° to 310°C, which are slightly lower than theend-member temperature of the vent fluid (325°C). Thesalinities of the fluid inclusions (2.9 to 4.3 wt. % NaCINumber of atoms per formula unil, based on 3 lotal atoms.Cu 0.00 0.00 0.00 0.00 0.00 0.00Fe 1.02 1.02 1.02 1.01 1.00 1.03Sn 0.00 0.00 0.00 0.00 0.00 0.00Bi 0.00 0.00 0.00 0.00 0.Q1 0.00S 1.98 1.97 1.97 1.98 1.99 1.97V. DiscussionSn-bearing chalcopyrite: The chaIcopyrite occurs ascoarse grained crystal with minor pores and bismuthinitewith fibrous habit (Fig. 4). The results of the X-ray4Kaul GENA, Hitoshi CHmA and Katsuo KAsE0.080.060.022.3CA) 10 eu+ Fer12.1B 0..lil @ ~ @ 8~ 0"'" *' *'+a T ++'"::lU1.9+0:04SnalomFig. 6 The number of Cu and of Fe versus the number of Sn informula unit.1966). However, the solubility of stannite is greater in thehigh temperature isometric chalcopyrite (>550°C, Moh,1975). From this study, the maximum Sn contentdetermined by EPMA is about 2.40 wt.% Sn whichcorresponds to about 8.68 wt. % starmite (Table 1). Theend-member temperature of vent fluid (325°C) and fluidinclusion data (220-310°C) indicate that the chalcopyritewith the high Sn content observed in this studyprecipitated as a metastable phase. The Sn contentrecognized in this study is exceptionally high. Theheterogeneous distribution of Sn in cbalcopyrite asobserved from the color mapping may indicate thedirection of rapid crystal growth (Kase, 1987).Pt-bearing bismuthinite: The bismuthinite displays afibrous babit in pyrite and chalcopyrite grains (Fig. 3F andFig. 4). Microprobe analysis of bismutbinite sbows acomposition of 1.3 to 1.7 wt. % platinum (Table 2). Traceconstituent associated with this mineral is copper (lessthan 0.9 wt.%) and iron (less than 1.1 wt.%). This is thefirst reported case of Pt-bearing bismuthinite occurrenceon the seafloor hydrothermal systems. The platinumcontent in the bismuthinite is much higher than theplatinum content of hydrothermally precipitated basemetal sulfides from the submarine hydrothermal system «lwt. %, Hekinian et al., 1980, Koide et al., 1991).Bismuthian sulfide minerals have never beenreported on the seafloor hydrothermal systems apart fromminor native bismuth occurrence in sulfide ores from theEscanada Trough, southern Gorda Ridge (Zierenberg et al.,1993). The mode of platinum and copper occurrence inbismuthinite is difficult to deduce from the current data.The presence of both platinum and copper within thebismuthinite may indicate coupled substitution of Pt2+Cu+for Bi3+in the bismuthinite structure. However, there is nopositive correlation between Pt2+ and Cu+ to indicate suchsubstitution. Therefore, the bismuthinite with high Ptcontent observed in this study probably precipitated as ametastable phase at temperature of 300°e. Chalcopyriteand bismuthinite with such unusual composition have notFig. 5 The X-ray maps showing the distribution of Sn inchalcopyrite and pyrite along the contact margins of zones Aand Zone B.Previous studies (Moh, 1975) showed that only 3wt. % stannite is soluble in low temperature tetragonalchalcopyrite, which is stable at temperatures below 550°Cin the ternary system of Cu-Fe-S (Yund and Kullerd,mapping of the chalcopyrite and pyrite along the contactmargins of Zone A and B clearly indicate the presence ofsignificant tin in chalcopyrite (Fig. 5A and 5B).Microprobe analysis of chalcopyrite shows a compositionof 0.5 to 2.4 % Sn (Table 1). As the tin content increases,the iron content shows a corresponding decrease (Fig. 6).Trace constituent associated with chalcopyrite is bismuth(less than 0.3 wt. %).The valence state of copper in chalcopyrite andstannite is monovalent (Nakai et al., 1976) while iron inchalcopyrite and tin in stannite are trivalent andtetravalent, respectively (Greenwood and Whifield, 1968).In stannite, iron has to be in a divalent state to maintain abalance of charges while iron is trivalent in chalcopyrite.Mixing of stannite and chalcopyrite would induce coupledsubstitution of Sn+4Fe+2 for Fe+3Fe+3• As the Sn contentincreases in the chalcopyrite of the Tiger chimney ore,there is a corresponding decrease in Fe contents whichindicates coupled substitution of Sn4+Fe2+ for Fe3+pe3+ inchalcopyrite as a solid solution towards stannite (Fig. 6).5Tin-bearing chalcopyrite and Platinum-bearing bismuthinitebeen reported in terrestrial deposits. Probably subsequentcooling after deposition and diagenesis may have changedthe original composition of the minerals throughexsolution.VI. ConclusionFrom this study, the following conclusions can bedrawn for minerals in the active sulfide chimney ore fromthe flank of the Tiger chimney field in the Yonaguni KnollIV hydrothermal system.1. Sn-bearing chalcopyrite and Pt- bearing bismuthiniteare found in an active sulfide chimney ores from theYonaguni Knoll IV hydrothermal system. This is thefirst reported case for the occurrence of such unusualminerals from the submarine hydrothermal systems.2. Sn content in the chalcopyrite is extremely high (0.51to 2.4 wt. % Sn). This indicated that the tin enters thechalcopyrite as a solid solution towards stannite bythe coupled substitution of Sn4+Fe2+ for Fe3+pe3+ inthe chalcopyrite structure at temperatures of about300°C.3. Pt content in the bismuthinite is also extremely high(1.3 to 1.7 wt. % Pt) compared to those ofhydrothermally precipitated base metal sulfides fromother submarine hydrothermal systems.4. The Sn-rich chalcopyrite and Pt-rich bismuthinite areprobably precipitated metastably in the Tiger chimneyat temperatures around 300°C.Aclmow/edgemelll: We acknowledge financialsupport from the Japanese Society for the Promotion ofScience (JSPS) for the senior author to do his postdoctoralstudies at Okayama University. We are grateful for theshipboard scientific party of Yokosuka - Shinkai 6500cruise YK04-05 (2004) research cruises for theircooperation in sampling. Gratitude is also extended to theoperation team of Shinkai 6500 and crew members of RVYokosuka for their skillful maneuver during sampling. Wewould like to also acknowledge Professor KazuoNakashima of Yamagata University for his assistance withEPMA analysis.ReferencesGreenwood, N. N. and Whifield, H. J. (1968) Mossbauereffect studies of cubanite (CuFe2S3) and related ironsulfides. J. Chem. Soc. (A), lnorg. Phys. Theor.,1697-1699.Hekinian, R., Fevrier, M., Bischoff J. L., Picot P. andShanks, W. C. (1980) Sulfide deposits from the EastPacific Rise Near 21°N. Science, 207, 1433-1444.Hsu S-c., Lin F-J., Jeng W-L., Chung Y-c., and ShawL-M. (2003) Hydrothermal signatures in the southernOkinawa Trough detected by the sequentialextraction of settling particles. Marine Chem., 84,49-66.Kase K. 1987 Tin-bearing chalcopyrite from the Izumovein, Toyoha Mine, Hokkaido, Japan. Can. Mineral.,25,9-13.Koide, M., Goldberg, E. D., Niemeyer, S., Gerlach, D.,Hodge, V., Bertine, K. and Padova, A. (1991)Osmium in marine sediments. Geochim. Cosmochin.Acta, 55,1641-1648.Moh, G H. (1975) Tin containing mineral systems. IIPhase relations and mineral assemblages in theCu-Fe-Sn-S system. Chem. Erde, 34,1-16.Nakai, I., Izawa, M., Sugitani, Y., Niwa Y. and Nagashima,K. (1976) X-ray photoelectron spectroscopic study ofcopper minerals. Mineral. J. (Japan) 8, 135-138.Suzuki, R., Chiba, H., Ishibashi, J-1. and Gena, K. (2005).Mineralogy and geochemistry of submarinehydrothermal deposits at the Dai-yon YonaguniKnoll. Society of Resource Geology, 55th AnnualConference, Abstract with Program, P26.Volker, L, David, A B. and Peter, H. (2002) ExtremeCrIBr and b37CI isotope fractionation in fluids ofmodem submarine hydrothermal systems. Mineral.Dep., 37, 765-771.Yund, R. A and Kullerd, G. (1966) Thermal stability ofassemblages in the Cu-Fe-S system. J. Petrology, 7,454-488.Zierenberg, R.A., Koski, R. A, Morton, J. L, Bouse, R.M., and Shanks, W. C. (1993) Genesis of massivesulfide deposits in a sediment-eovered spreadingcenter, Escanada trough, southern Gorda Ridge.Econ. Geol., 88, 2069-2098.

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