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CARYOPILITE AND GREENALITE FROM THE DEPOSITS

IN SHIKOKU, SOUTHWEST JAPAN

MAsAHARu NAKAGmafi'', MAsAro FuKuoKAb, KENTA4o KAKEHi", Go KAKiucHia, YuuKi TAMAKJa and TAKAAKi TANIGucHI"

al 1iculty ofSbience, Kbchi Uhiversiol Kbchi 780-8520, J4pan tFkeculty ofintegratedArts and SZriences, H}roshima Uhiversipt Higashi-Hiroshima 739-8521, Jopan

(Received November 1, 2014. Accepted Nevember 20,2014)

ABSTRACT

Caryopilite, Mn2'-rich serpentine group , is a major constituent of the manganese ores in the North Chichibu belt in the Shikoku region, SW Japan, The Nomh Chichibu belt is thc Jurassic accretionary complex

containing abundant chert beds of Permian-1[tiassic age and has been subjected to low-grade metamorphism of the prehnite-pumpellyite to pumpellyite-actinolite facies. Caryopilite close to Mn end-member in compo- sition and having IMpolytype commonly occur in the chert-hosted manganese deposits. Greenalite, the Fe2' analogue of caryopilite, has 1T polytype and rarely occurs in some chert-hosted deposits. Fe-rich caryopilite having intermediate composition between caryopilite and greenalite and having IMpolytype occurs in an iron-manganese deposit and a manganese deposit associated with basalt. Manganoan chlorites also eccur in

these deposits,

Key words: Caryopilite, Greenalite, Manganese deposit, Accretionary complex, Shikoku

INTRODUCTION GEOLOGY AND DEPOSIT

Caryopilite is an Al-poor and Mn2"-rich serpentine group The locations of the manganese and iron-manganese ore de- mineral, and greenalite is its Fe2' analogue. They are now posits are shown together with the geotectonic subdivision of known to have modulated structures containing islands of Shikoku in Fig. 1 . The Shikoku Island is composed of several tetrahedral rings (Guggenheim and Eggleton, 1988, 1998). accretionary belts which display various grades of regional Caryopilite occurs as a major constituent of manganese ores metarnorphism, The Sanbagawa metamerphic belt, on the

in Japan and was described as bementite in older literature,south ofMTL, is a high-P/T type regional metamorphic belt, It Greenalite is rare and is known to oecur in seme banded iron is composed ofbasic, quartz, pelitic and psarnmitic schists of formatiens, In the Shikoku region of SW Japan, a manganoan the greenschistfblueschist to eclegite facies. The southernmost greenalite was found in the manganese ore from the Matsuo part of the Sanbagawa belt was once called the Mikabu belt, mine, Kochi Prefecture, and was named tosalite for lbsa, the The Nomh Chichibu belt comprises the Early-Middle Jurassic old distriet name of Koehi (Ybshimura, 1967), accretienary complexes and has been subjected to low-grade In the Shikoku region, several accretionary belts are distrib-metamorphism of the prehnite-pumpellyite to pumpellyite- uted and characterized by different grades of regional meta- actinolite facies. The South Chichibu belt comprises the morphism. Bedded manganese ore deposits occur in many Middle Jurassic to Early Cretaceous accretionary complexes.

localities within the accretionary belts, Caryopilite is a major These complexes ofNonh and South Chichibu belts are com-

constituent of the manganese ores. ln this paper, we report the posed of tenigenous clastic rocks containing older oceanic paragenesis and ehemical characteristics of caryopilite and blocks of chert, limestone and greenstone. The southemmost greenalite in the manganese ores, together with some genetic regien of the Shikoku is occupied by the Cretaceous North considerations. Shimanto and Tertiary South Shimanto belts which comprise

the clastics-dominated accretionary complexes. [[he manganese and iron-manganese deposits are disuib- uted in the Sanbagawa, Mikabu, North Chichibu and South

. Chichibu belts. The deposits are abundant especially in the Corresponding author: Masaharu Nakagawa, Faculty ofScience, Kochi University, Kochi 780-8520, Japan. e-mail: [email protected] Chichibu belts which contain abundant chert beds. Some

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80 M. NakagaM,a et at,

FIG, 1, Distribution ofmanganese and iron-manganese deposits shown within the generalized geological framewerk of Shikoku, SW Japan (modi- fied from Nakagawa et al,, 2009, 2012). e: rnanganese deposit, -: iren-manganese deposit. 1-1O: the mine number mentioned in Table 1. MTL: Median Tectonic Line. BTL: Butsuzo Tlectonic Line. Ryoke: Ryoke metamorphic belt. Sanbagawa: Sanbagawa metamorphic belt. Mk/ Mikabu greenstone, N. Chichibu: North Chichibu belt, Kr: Kuresegawa belt. S, Chichibu: South Chichibu belt. N. Shimanto: Nerth Shjmanto belt, S. Shimanto: South Shirnanto belt, The geological subdivisjon is based en Suyari et al. (1991), Matsuoka ct al. (1998) and GSJ (201O).

manganiferous iron deposits of small scale occur in the North old mines in the Shikoku region (Fig. 1). The geolgy and his- Shimanto belt. tory ofthe rnines are reviewed in the comprehensive treatises In the Shikoku region, the manganese deposits can be clas- by Ybshimura (1952, 1969) and Miyahisa and Sawamura sified into two types based on the geological setting, mineral- (1973). We have re-examined the ore deposits based on our ogy and genetic characteristics (Nakagawa et al., 2009, 2011; new field and laboratory investigations. The wall rock charac-

Nakagawa, 2012), The manganese deposits occur mostly teristics and available fossil age data fbr the ore deposits are

in bedded chert or its rnetamorphosed equivalent. In these summarized in Table 1. In the Chiehibu belts, the microfossil

deposits classified as Type I, the ores consist mainly of rho- ages of the chert are Permian to Triassic around the deposits,

dochrosite, caryopilite, and . These chert- whereas the ages of the clastic matrix of olistostrome are

hosted manganese ores are considered to have been manga- Jurassic.

nese nodulefcrust-bearing siliceous sediments on deep-sea The ore samples were examined by X-ray powder diffi/ac- floor and have been converted to manganese ores by low- tion (XRD) method to characterize the constituent grade metamorphism through subduction-accretion process. ofthe samples, employing a Rigaku MultiFlex diffractometer The mineral assemblages ofthe ores refleet the rnetarnorphic housed at the Kochi University. The representative ore sam- grade ofthe accretionary complexes. Some manganese depos- ples were polished well with diamond paste and analyzed its were metamorphosed at the deeper levels. using an electron probe microanalyzer (EPMA) housed at the Iron-manganese deposits and some manganese deposits,Hiroshima Uniyersity. To obtain quantitative estimates on classified as Type II, are associated with greenstone and red mineral chemistry, EPMA analyses were performed with a chert. The mineralogy and texture of these ores are differentJEOL JXA-8200 Superprobe at an aecelerating voltage of 15 from those of the chert-hosted manganese ores. Geoehemi- kV; a bearn current of 10 nA and a beam diameter of3 pm. cal similarities of these ores to those of modern submarine The quantitative calculation of all elements was done by ZAF hydrothermal deposits were noted by Kato et al. (2005) and correctlon, Fojinaga et al. (2006). These deposits occur directly over basalt and are considered to have been the hydrothermal RESUIJIrSANDDISCUSSION precipitates assoeiated with the mid-oceanic ridge or oceanic islandvolcanism. Ml'neralogy ofmanganese ores The mineral constituents of the ore samples have been ANALYTICALPROCEDURE examined by XRD and EPMA analyses. The results are summarized in Table 2. Back-scattered electron images of the For the present study of caryopilites, manganese and iron- representative samples are shown in Fig, 2. manganese ore samples were collected frorn the representative Manganese deposit ofthe Minamiyama mine (No. 1, Fig, 1)

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Cti,),qpiliteandGreenalitefivmShikoku 81

TABLE 1,Wall roek eharacteristics and fossil age data efmanganese and iren-manganese deposits in Shikoku.

No. Mine Tbrrane TYpe Wall rock Ageofchert 12345678910Minamiyama MikabuNorthChichibuIIIIIIIIIIIIQuartzschist FukuharaDesuNiroMatsuoAnanai-Fukinaro ChertChertChertGreenstone,Early-MiddleTriassic NomhChichibu Permian

Nonh Chichibu

Nonh Chichibu chert

Nonh Chichibu Greenstone, red chert Middle Permian

Arianai-Honomori NorthChichibu Greenstone, red chert PerrnianEarlyPerrnian

Kunimiyarna NorthChiehibu (FeMn) Greenstone, red chert Tbkoroyama Nomh Chichibu II ChertChert Ttiassic

Hitogawa South Chichibu

The mine numbers are the same as those in Fig. 1. The age data for chert are based on the biostratigraphic studies by Suyari et al. (1982, 1983), Momoi et al. (1992), Fojinaga and Kato (2005), and others.

TABLE 2.Mineral constiments of manganese and iron-manganese ore sarnples examined by EPMA, AnalysisNo. Mine Constituentminerals

1,21 Minamiyama Rhedonite,pyroxmangite,,rhodochresite,caryopilite,

manganoan chlorite, quartz, ganophyllite, le17, FukuharaFukuharaDesuNiroNiroNiroMatsuoAnanai-FukinaroQuartz,caryopilite,rhodonite,barianbannisterite

182,3415, Quartz, greenalite, stilpnemelane Quartz, caryopilite, rhodochresite, rhedonite Quartz,caryopilite,rhodonite,ganophyllite 1622, Quartz, greemalite, rhodoehrosite 2311,125,6 Quartz, , manganoan chlerite, barite Iron-richcaryopilite,rhodochrosite,magrietite

Caryopilite, barian ganophyllite, manganoan , quartz, barite, calcianrhodochrosite,barianonhoclase

24, 2513, Ananai-Honomori Piementite-(Sr),manganaxinite,manganoanchlorite,manganoancalcite,barite

14, 2678,9 Kunimiyama Iron-richcaryopilite,magrietite,manganeancalcite,pennantite

Tbkoroyama Quartz, caryopilite, braunite, calcian rhodochrosite, barite Hitogawa Quartz,caryopilite,rhodochrosite

The analysis numbers are the same as those in fables 3 and 4.

occurs in quartz schist in the Mikabu belt, The highly meta- barite (Fig. 2h). The manganese ore from the Matsuo mine (No. morphosed ore shows several layers consisting mainly of 5, Fig. 1) consists of iron-rich caryopilite, rhodochrosite and rhodonite, efpyroxmangite and spessartine, and ofrhodochro- magnetite (Fig, 2f), The caryopilite appears to have replaced site and caryopilite (Fig. 2a). Manganoan chlorite also occurs the magnetite crystals. Numereus veinlets of rhodochrosite locally in accessory amounts. In the North Chichibu and South cut the caryopilite granules and the residual magnetite, Iron- Chichibu belts, many manganese deposits occur in bedded manganese ore of the Kunimiyama mine (No. 8, Fig. 1) con- chert (Type I). Tlie manganese ores embedded within chert in sists mainly of iron-rich caryopilite and magnetite (Fig. 2g). the Fuknhara, Dosu, Niro, Tbkoroyama and Hitogawa mines Manganoan calcite and manganese-rich chlorite occur locally (Nos, 2, 3, 4, 9, 10, Fig. 1) consist mainly of caryopilite, rho- in accessery ameunts in the aggregates ofcaryopilite, Some of dochrosite, rhodonite, braunite and quartz (1[bble 2, Fig. 2b). the magnetite might have altered to the caryopilite, Greenalite-quartz ore (Fig, 2c) is found in the Fukuhara and Niro mines. Rhodochrosite-manganoan chlorite-quartz ore ( Zii:yopilite andgreenalite (Fig. 2d) occurs in the Niro mine. Modulated 2:1 layer silicate The representative X-ray powder difiiaction patterns of the minerals such as ganophyllite, baimisterite and stilpnomelane manganese ores are given in Fig. 3. Caryopilite shows XRD occur in these deposits, pattern of the IM structural type (Fig. 3a), Greenalite shows Iron-manganese deposits and some manganese deposits XRD pattern of the 1 T structure (Fig. 3c). XRD pattern ofFe- occur between greenstone and red chert (Type II). The man- rich caryopilite from the Matsuo mine (Fig. 3b) is similar to ganese ore associated with greenstone in the Ananai-Fukinarothat of the caryopilite (Fig. 3a), whereas d(OOI) and d(O02) mine (No, 6, Fig. 1) contains caryopilite, barian ganophyllite,values of the Fe-rich caryopilite are the same as those of the manganoan calcite, barite and barian omhoclase (Fig, 2e). The greenalite (Fig. 3c), ore of the Ananai-Honomori mine CNo, 7, Fig. 1) consists of Based on X-ray powder diffi:action and electron diffiraction strontiopiemontite, manganaxinite, manganoan chlorite and data, it has been known that caryopilite is mostly composed

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82 M. Nakagawa et aL

FIG.2. Back-scattered electron images ef manganese and iron-manganese ores frorn the Shikeku regien. a: pyroxmangite, spcssartinc, caryopilite and rhedochrosite ef the Minamiyama rnine. b: caryopiljtc, rhodochrosite, rhodonite and quartz ofthe Dosu mine. c: greenalite a]d quartz of the Fukuhara rnine. d: rhodochrositc, manganoan chloritc and quartz efthcNiro mine, e: caryopitite, barian ganophyllite and manganoan calcite of the Ananai-Fukinaro mine. fi Fe-rich caryopilite, rhodochrosite and magnetite of the Matsuo mine, g: Fe-rich earyopilite, Mn-ricb chlorite and magnetite of the Kunimjyama mine. h: piernontjte-(Sr}, manganaxjnite and manganoan ehlorite ef t]ic Ananaj-Honomerj minc. a, b, c and d occur within chert, e, L g and h occur between greenstone and chert. C: caryopilite. R/ rhodochresite. S/ spessartine. Px/ pyroxmangite. Rd: rhodonite, G: greena]ite. Q: quartz, Ch: ch]orite. Ca/ calcite. Ga/ ganophy]lite. M; magnetite, P: piementite-(Sr), Mn: manganaxinite,

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Ctxo,opilite and Greenalitej7vm Shikoku 83

Q Q stmcture, These small (Fe+Mn+Mg+Al)fSi ratios of caryo- pilites and greenalites are in accord with their defeetive layer ootc7,2T stmctures as pointed out by Newman and Brown (1987). The Q ratios of the caryopilite samples are smaller than those of the a Q sarnples, smaller ratios of car>fopilites may oo2c3.64 greenalite The be interpreted by the need to adjust for the larger misfit between ,9. c Q 2.52,9,, QQ Mn2'-rich octahedral sheet and the siliceous tetrahedral sheet ]o as also pointed out by Newman and Brown (l987). The triangular diagrarri 4) shows the relative R (Fig. abundance of divalent cations, Fe2', Mn2' and Mg2', in the

caryopilite-greenalite samples. The compositions are very close to the Fe-)vin edge, The caryopilite sample (analysis b 1) from the Mikabu belt has appreciable Mg content, Many caryopilite samples (analyses 2-9) have compositions near to Mn end-member. Fe-rich caryopilites from the Matsuo and Kunimiyama mines (analyscs 11-14) have intermediate com- positions between caryopilite and greenalite, Q1f Q The name tosalite was preposed by Ybshimura (1967) for an interrnediate member of the caryopilite-greenalite series QQ from the Matsuo mine, The material is a manganoan greena- ootG7,21 litejudged from the wet chemical analysis, Guggenheim et al. QQQ c (1982) analyzed four tosalites from the same rock sample by electron microprobe. The average formula derived from O02G3.60 G2,6tG2.eo the analyses is (Neq.oisC%.omKo.oo4)(Fe3.gisMnononMgo.624Alo.s26) and is as No. 19 in Fig. 4. The !.21L (Si3.sgeAle.iio)Oio(OH)splotted sample is described to be the mixture of IMand 1Tpolytypes. The manganoan greenalite has larger Al and smaller Si con- s2e(cu)10152e253e354e4S tents than the Matsuo materials of the present study (analyses 11, 12), although one (analysis 12) has a little 1arger Al FiG. 3. X-ray powder diffraction patterns of the manganese ores. a: content and 1arger sum ef octahedral cations and may contain caryopilite-quartz ore of the Hitogawa mine. b: Fe-rich caryopilite- Al in beth tetrahedral and octahedral We consider rhodochrosite ore of the Matsuo mine. e: greenalite-quartz ore of positions. the Fukuhara mine. Q: quartz. R: rhodochrosite. C: caryopilite (IM). that both the manganoan greenalite and the Fe-rich caryopilite G: greenalite (1T). eccur in the Matsuo deposit, The manganese and iron-manganese deposits in the Chichibu belts CNos. 2-1O, Fig. 1) sheuld have been metamor- of IMpolytype, and greenalite is dominantly composed of phosed at almost same conditions, although the type I and II IT polytype (Ybshimura et al., 1958; Steadman and Ybuell, deposits differ from each ether in their origins. The chemical 1958; Bayliss, 1981; Guggenheim et al,, 1982). Some samples differences observed for the caryopilites from the Shikoku are fbund in the mixture ofboth the polytypes, In the present region might have arisen from the differences of their origins, studM most ofthe caryopilite samples from the Shikoku region

showed XRD patterns of 1Mpolytype. The greenalite samples Mlrnganoan chlorite from the Fukahara and Niro mines showed XRD patterns The EPMA data on chlorites are given in [[hble 4, Substan- of 1T polytype, although very weak diffiraction peaks of IM tial amounts of Mn is contained in the clinochlore-chamosite polytype are recognized in their XRD patterns (Fig, 3c). chlorites frem the manganese and iron-manganese deposits. In The electron microprobe analyses for caryopilites and particular, the chlorites from the Type II deposits (analyses 24, greenalites are given in [lable 3. The structural forrnulae were 25, 26) are more }vfri-rich. The chlorite from the Kunimiyama calculated on the basis ofa tota1 anionic charge of28 (Oio(OH)smine (analysis 26) is a pennantite because Mn is the dominant forrnula unit) of the ideal serpentine structure. Caryopilites divalent cation. and greenalites have Mn2" and Fe2' as the dominant octahedral cations, respectively, They contain little A13', All the micro- SUMMARY AND CONCLUSIONS probe analyses show a considerable excess of Si (4.11-4,41 atoms) and a deficiency of total octahedral cations relative to Caryopilite occurs commonly with rhodochrosite and the ideal serpentine composition, These are consistent with rhodonite in the chert-hosted manganese deposits in the North their modulated layer structures as pointed out by Guggen- Chichibu belt which comprises the Early-Middle Jurassic heim et al. (1982), accretionary complexes containing abundant chert beds of In the Chichibu belt, the ratio (Fe+Mn+Mg+Al)/Si lies Pemian-Triassic age and has been subjected to low-grade between 1.163 and 1.244 for the caryopilite samples (analysesmetamorphism of the prehnite-pumpellyite to pumpellyite- 2-10), and between 1,236 and 1,257 for the greenalite sam- actinolite facies, Greenalite rarely occurs in some chert-hosted ples (analyses 15-18), compared to 1.5 for the ideal serpentine deposits, Manganoan chlorite also occurs in some deposits.

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TABLE 3, Electron microprebe analyses ofcaryopilite and greenalite from the Shikoku region,

l 2 3 4 5 6 7 8 9

Si02TiO,Al,03FeO'MnOMgOCaONa20K,O37.74 36.71 36.47 36,31 36.63 38,06 37.82 38,6S 38.14 o.el e.oo o.oo O.13 e.o3 O.05 o.eo o.eo O.Ol O.95 e.28 O.l5 1,09 O.69 O,74 O.Sl O.42 O,22 3.5642.S9 O,5850,51 1.7149.44 3,0947,80 1.8148,46 2,0247,32 O.1349.51 O.5247.74 O.5448,17

5.16 O,88 O05 O.48 1.48 1,54 O.90 2.52 221 o.ro O.04 O.IO O,05 O.ll O,05 O.06 O.04 O,05 O.04 o,oo O.03 o,oo O,02 o,oe O.Ol o.oo O,Ol O.Ol o.oo o.oo O.02 o,os O.03 o.oo o.oo o.oo

Total 90.1689,OO88.6588,96892789,8188.9389.8889,35

Nltmbers ofcations on the basis ofOJoCOIDs siTiAlFei'Mn2'MgZect.**RISi***CaNaK4258O.OOIO.126O.3364.070O.8685.4011.268O.O12o.eogo.eol4,335o.oooO.040O,057S,052O.1565.3051.224e.ooso.oooo.ooo4.336o.oooO.021O.1704.978O.1335.3021223O.O13O.O06o.ooo4,286O.OllO,152O,3054.78eO.085S,3331,242O,O07o,oooO,O034293O.O02O.09SO.1784,811e2585.3441.244O.O13O.O04e.oo74,381O.O04o,loeO.1954.613O,2645,1761.181O,O06o,ooeO,O054.412e.oeoe.o7oO.O124.893O.IS75.1321.163O.O07O.O02o.oeo4.410o,oooO.056o,oso4.613O.4295,1481.167O.O04o.oooo.oeo4,402O.OOIO.029O.0524,710O,3815.1731,175O,O07O.O02o.ooo

IO 11 12 13 14 15 16 17 l8

SiOiTi02Al,O,FeO*MnOMgOCaONaiOK,O37.40 36,64 34.51 36.44 35,97 36,79 3623 35.86 36,28 o.oo O.03 O.04 O.04 o,oo o.oo O.Ol o.oo O.02 O.6415,9134.04 O.6222.8226.68 1.612S.1524.05 1,OO22.8527,9S Lll26,6924.78 O.]542.16 O.1242.96 O.3046.91 O,2247.30

9.46 8.81 5.76 5.51 1,41 225 2.76 O,76 O.99 1.36 1.05 O.41 O,33 O.13 O.04 O.03 O,11 O,13 O.03 O.02 O.03 O.08 o.oo O.02 O.03 o,oo O.02 o.oo O.04 O.06 o,oo O.Ol O.Ol o.oo O,Ol o,oo O.Ol o.oo O.03 o.oo

Tota1 89.5489.0988.1889,1589.6989,9689.2489.3589,73

IVitmbers ofcations on the basis ofOio(OH)s siTiAlFe2'Mn!'MgEect.**RISi***CaNaK4.352o.oeoO.0871.5483.355O.2445.2341203O.O16o.oooO.O024,292O.O03O.0852.2352.647O.3925,3621249O,O05O.O04O.O024.112O.O03O.2262.5062.427O,4905.6521.374O.O04O,O06o.ooo4297O.O03O.13822542.791O.1335.3191237O.O14o.oooO.O024.237o.oooO.1542.6292.473O.1745.4301282O.O16o.eoso.ooo4.32ro,oooO.0204.142O.941O,2385,3411.236O.O04o.oooO.O024.309o.eooO.O174.274O.887O.1875.3651245e.oo3o.oego.ooo4.289o.eooO.0424.692O.584O.0735.3911,257O.O04O,O13o.oos4.313O,O02O.0304,703O.554O,0585.3471.239e.ollo.oooe.ooe

" total Fe as FeO. ** sum of ions in octahedral pesition. "*(Fe2'+Mn2'+Mg!"+A13')fSi.

1: caryopilite from the Minamiyama mine. 2, 3: caryopilite from the Dosu mine. 4: caryopilite frem the Nire mine. 5, 6: caryepilite from the Ananai-Fulcinaro mine. 7: caryopilite from the Tbkeroyarna mine. 8, 9/ carye- pilite from the Hitogawa mine. 10: ferroan caryopilite from the Fukuhara rnine. 11, 12: Fe-rich caryopilite from the Matsuo mine. 13, 14: Fe-rich caryopilite from the Kunirtiiyama mine, l5, l6: greenalite from the Niro rnine, 17, 18: greenalite from the Fukuhara mine,

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thryopititeandGreenaliteYiomShikoku 85

Mg Fe-rich caryopilite haying intermediate composition Mg between caryopilite and greenalite occurs in the magnetite- bearing ores from an iron-manganese deposit and a manga-

nese deposit which occur drectly over basalt, The Fe-rich caryopilite has IM polytype. Mn-rich chlorite lpennantite) also Fe occurs in the iron-manganese deposit.

ACKNOWLEDGEMENTS

We thank Mr. YL Shibata of the Natural Science Center for Fe 432Mn Basic Research and Development of Hiroshima University for hiskind help EPMA FiG, 4. Relative proponions ofFe2', Mn2' ancl Mg2' for caryopilite and with analyses. We thank two anenymous greenalite. e: caryopilite. -: greenalite. 1-18: the analysis number referees whose comments were usefu1 in reyising this papez mentioned in fable 3. 19: manganoan greenalite from the Matsuo mine (Guggenheim et al., 1982). REFERI]NCES

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