J. Japan. Assoc. Min. Petr. Econ. Geol. 74, 235-244, 1979.

THULITE AND ASSOCIATED MINERALS FROM THE

NAKADORI ISLAND, GOTO, NAGASAKI PREFECTURE

HISASHI TAKESHITA

Moji High School, Fukuoka Prefecture

and

YUKIO MATSUMOTO

Geological Institute, Faculty of Liberal Arts, Nagasaki University

The association of thulite-scolectei-prehnite in felsic volcanic pyroclastics of the Neogene Tertiary developed at the Nakadori Island, Goto, is reproted here as a peculiar case of the Green-Tuff alteration. The thulite is mangan-clinozoisite, (Ca2 .039Mg0.034Mn0.058)2.131 (Fe0.172Al2.828)3.000(Al0.023Si2.913)2.936(OH)O12. Thulite in porphyrite dikes which intrude into the pyroclastics, however, ranges from mangan-clinozoisite ((Na0 .005Ca1.939Mg0.097Mn0.044)2.082 (Fe0.049Al2.936)2.984Si2.972(OH)O12 to withermite ((Na0.006Ca2.033Mg0.019Mn0.038)2.095(Fe0.546Al2.389) 2.930Si3.000(OH)O12-(Ca1.999Mg0.002Mn0.034)2.036(Fe0.696Al2.302)2.998Si2.893(OH)O12). Scolecite associated with thulite has the chemical composition of (K0 .001Na0.012Ca0.989Mg0.004)1.006Al1.933 Si3.049O10•E3H2O. Prehnite associated with thulite and scolecite has the composition of (Na0 .001 Ca1.988Mg0 .001Fe0.006Mn0.002)1.998Al1.015(Al1.036Si2.964)4.000(OH)2O10.

porphyrites and other mafic abyssal masses. INTRODUCTION AND OCCURRENCE The felsic to intermediate pyroclastics, Thulite comprises pink zoisite as well as partially welded in their lower part, belong pink clinozoisitie. In the present study the to the Goto Volcanic Complex (Ueda, 1961), clinozoisite, light pinkish color in appearance, and are correlated to the Arikawa Forma is easily recognized under microscope by tion (Tsukahara et al., 1975) underlaid with high relief, rather low birefringence, pinkish the Goto Formation (Ueda, 1961), composed weak pleochroisms and optically positive of sandstone and mudstone. Of these, character. It becomes withermite toward volcanic pyroclastic rocks are regionally the small cores which show relatively high altered. They carry montmorillonitic clay birefringence and optically negative minerals, sericite, chlorite, and epidote in character. cases. The sedimentary basin filled with The locality is situated at the Narao large volumes of these pyroclastics has been Port, south of the Nakadori Island of Goto. recognized as a part of the Green-Tuff Region The thulite-bearing rocks are exposed in Southwest Japan (Matsumoto, 1973; within a quite restricted area, while the 1977). greenish epidote-bearing ones rather widely The leucccratic thulite-bearing rocks occur in pyroclastic formations, where they appear to grade into light greenish epidote- are intruded by many dikes and sheets of bearing rocks within a sh ??t distance (Fig.

(Manuscript received February 21, 1979) 236 Hisashi Takeshita and Yukio Matsumoto Thulite and associated minerals from the Nakadori Island, Goto, Nagasaki Prefecture 237

1). A dike rock which is not so leucocratic 74073007A) or porphyritic texture. Phe as compared with the thulite-bearing tuff nocrysts are plagioclase, An34-30, dusty breccia of dacitic composition also has kali-feldspar, and variable amounts of thulite in its silicified and pyritized part. primary quartz. Primary mafic minerals In such a part the dike rock has lost its are not observed. Epidote frequently original chilled texture (Fig. 2-1) by intense replaces plagioclase and often constructs a alteration. The chilled margin can clearly beautiful radial aggregate. Zeolite is rarely be seen (Fig. 2-2) against the boundary with found in cavities. Its features (2V(-)= epidote-bearing tuff breccia. Epidote does 41-42•‹) are as same as those of scolecite of not always develop throughout the whole the sample No. N-51. As a subordinate pyroclastic formations, but is sporadically component augite-andesite (No. 74073008) found where abyssal or hypabyssal masses is found as debris in the pyroclastics. Zonal have intruded. structure is well-developed in the pheno crysts of plagioclase, ranging from An71

to An54, and hour-glass structure is often DESCRIPTION OF ROCKS observed in the augite phenocrysts. The

As far as surveyed by the present groundmass minerals are lath-shaped plagio- authors, the Green-Tuff of the Nakadori clase, anhedral alkali feldspar, considerable Island are chiefly composed of felsic or amounts of augite and magnetite. Xeno- pumiceous tuff, siliceous shale, quartzose crystic quartz is surrounded by coronas of sandstone, and their mixed pyroclastic clinopyroxene rods or shows corroded form. assemblage. Replacement by montmoril A dusty plagioclase is also considered as a lonitic clay minerals is distinct in the Green- xenocryst which is rimmed by clear plagio- Tuff. Locally epidote is associated with clase. Chlorite, light green in color and secondary quartz in the altered pyroclastics very low in birefringence, forms pseudomorph of rhyolitic to dacitic composition. Their after olivine, associated with augite, magne component debris show eutaxitic (No. tite, and epidote replacing plagioclase.

Fig. 1 Distribution of various rocks of the Green-Tuff, developed near the environs of the Narao Port, southern part of the Nakadori Island. Legend: 1. Porphyrite dike, characterized by epidote. 2. Porphyrite dike, characterized by thulite, withermite, scolecite, wairakite and rarely

prehnite. 3. Dacite tuff and tuff breccia, containing montmorillonitic clay minerals. 4. Dacitic tuff breccia, characterized by epidote and chlorite. 5. Dacite tuff breccia, characterized by thulite, scolecite and wairakite. 6. Shale of the Goto Formation.

7. Dip and strike of the boundary between dike and country rocks. 8. Dip and strike of stratum. No. 74073001•@ Well-stratified dacite tuft, greenish in appearance

No. 74073007•@ A. Eutaxitic dacite debris B. Dacite debris No. 74073008•@ Mafic andes ite debris No. 74073009•@ Augite-hypersthene-hornblende-porphyrite No. 74072902•@ Dacite tuff breccia No. 74072903•@ Ditto, collected from a brecciated part close to the dike. No. 74073002•@ Thulite-bearing part of the dike No. 74073005•@ Porphyrite, characterized by greenish epidote. 238 Hisashi Takeshita and Yukio Matsumoto

Fig. 2. 1. Dike II, intruding into dacitic pyroclastic bed (left), shows rather melanocratic appearance on its bulk core, whereas its margin appears to have been grown dull in color (a portion where a hammer is placed). 2. Elongation of the Dike II, showing rather melanocratic chilled margin against light gray dacitic pyroclastic bed (top). 3. Pyrite (Py) enclosing thulite (Th). Scolecite (Sc) is seen in the matrix of the tuff. Crosse nicols. 4. Scolecite showing radial aggregate and rimmed by deep yellowish brown antigorite (A). 5. Thulite-prehnite assemblage. In the light portion, scolecite is present. Prehnite (Pr) encloses fine grains of thulite. Thulite and associated minerals from the Nakadori Island, Goto, Nagasaki Prefecture 239

Dike rocks are intermediate in composition. Table 1 Acute sides of Kohler's angle, An mol.% and ordering degree (o.d.) of porphyritc A thulite-bearing rock (e.g. Dike II in Fig. 1) plagioclase in propyritized thulite-bear becomes a thulite-free and epidote-bearing ing porphyrite, No. N-51, collected from rock on the elongation of the same dike. Narao

Another thulite-bearing dike (e.g. Dike I) has thulite-free core. Texture of these dike rocks is porphyritic and pilotaxitic, characterized by anhedral quartz and alkali-feldspar. Porphyritic plagioclase is rather fresh and is calcic as high as the An

content from 64 to 90%. Original mafic

minerals have been replaced by chlorite and

epidote. The marginal part of Dike I (No.

74072904) carries small amounts of thulite

Its porphyritic plagioclase is very dusty and

calcic (Ann in the core and An,, on average). important metamorphic mineral, whereas

It is intruded by many strings of opal and prehnite is rare in the pyroclastics. Prehnite

sodic plagioclase. The terminal part of associated with thulite is shown in Fig. 2-5.

Dike II is more or less brecciated to produce The only phenocryst preserved well is

pockets filled by quartz, calcite, thulite, plagioclase, though it is considerably scolecite, and pyrite in cubic or pyritehedral altered by intrusion of strings of opal and

form. Sometimes thulite and scolecite are sodic plagioclase. Measurements on acute

apparently enclosed in pyrite (Fig. 2-3). sides of Kohler's angle reveal that there may

The thulite-bearing volcanic pyroclastic be two types of plagioclase (Table 1); one is

rock (Nos. 74072902, 03) contains essential the ordered type, where the An mol.%

fragments of dacite, pumice, and accidental ranges from 75 to 84, and another is the

fragments of quartzose sandstone and tuff disordered type with the composition,

aceous mudstone. Porphyritic crystals An68-74.

are clear oligoclase to andesine (nx(min.)= OPTICS AND CHEMICAL COMPOSITIONS 1.542 nz(max)=1.557, An27-42), quartz OF THULITE AND ASSOCIATED MIN angular to subangular in form, and very ERALS dusty alkali-feldspar. Thulite, almost color-

less to light pinkish, is sporadically found, Refractive indices were measured by

and shows high relief against the felsic the immersion method, using immersion oil whose indices have been measured by groundmass or matrix of scolecite. The scolecite occurs as feather-like radial ag microrefractometer. The error of the in dices may reach •}0.002. The electron- gregates (Fig. 2-4). Its optic axial angle varies from 30•‹ to 53•‹ in negative sign. probe analysis has been carried out by Dr.

Wairakite is rarely recognized by much M. Hayashi of Research Institute of Science

larger optic axial angles than the largest and Industry, Kyushu University. In

limit of those measured on the scolecite. every case the H2O content was regarded as

A sample, No. N-51, collected from a the difference between 100% and the total obtained. large boulder of a dike, has prehnite as an 240 Hisashi Takeshita and Yukio Matsumoto

Thulite From the refractive indices the presence of Analyses Nos. 1 and 2 in Table 2 the crystals with the composition inter represent a chnozoisite whose composition is mediate between Nos. 2 and 3 should be close to the end member, Ca2Al3Si3(OH)O12, expected. Really the thulite should be of the clinoziosite-epidote series. The regarded not only as clinozositie but as composition, No. 1 (sample No. 74072903), withermite from the analyses, Nos. 3 and 4.

gives fairly good accordance with that Prehnite presumed from the optical data. In another Analysis No. 1 in Table 3 indicates that sample (No. N-51) in which zonal structure is well preserved, the scanning with prehnite associated with thulite is a variety very poor in iron. It shows nearly the electron-probe was made on the core (No. 4) lowest value of the refractive indices among through the intermediate zone (No. 3) to various prehnites and it shows rather high the rim (No. 2). It is interesting that the birefringence. contents of mangan, aluminium, and magnesium increase from the core to the Scolecite rim, while the iron content behaves Analysis No. 2 in Table 3 indicates the reversely. There may be no good accord zeolite to be scolecite, being low in contents ance in the relationship between the indices of iron and alkalis as compared with and the composition in the latter sample. Table 3 Electron-probe microanalyses of prehnite (1) and scolecite (2) from Table 2 Electron-probe analyses and optics Narao, Goto, compared with of thulite from Narao, the Naka some scolecites from other loca dori Island, Goto, Nagasaki Pre lities fecture Thulite and associated minerals from the Nakadori Island, Goto, Nagasaki Prefecture 241

Table 4 X-ray powder data of thulite from Table 5 X-ray powder data of prehnite from Narao, compared with clinozoisite Narao, compared with that from Ashcroft. from Sasaguri (a) (Seki 1959) and withermite from Yamanaka Mine (b) (Yoshimura and Momoi 1963)

Table 6 X-ray powder data of scolecite from Narao, compared with scolecites from other two localisties

Table 4 Continued

B: broad hkl: Attar Seki (1959) and Yoshi ??ra et al.(1963). * Attar Harada et al.(1968) andMizota et al.(1976). 242 Hisashi Takeshita and Yukio Matsumoto

Fig. 3 X-ray diffraction pattern of zeolites (top), extracted from the matrix of the thulite-bearing porphyrite, No. N-51. The pattern (bottom) is of pure sample of scolecite occurred as a druse mineral as shown in Fig. 2-4.

scolecites from other localities. It is rather be illustrated by the presence of withermite close to the scolecites from Kuroiwa, Niigata zonned with clinozoisite. Prefecture (Mizota et al., 1976) and from Prehnite Makinokawa, Ehime Prefecture (Kuwano, The sample has shown slightly pinkish 1977). color in appearance. The X-ray data fairly well but not exactly accord with X-RAY POWDER DIFFRACTION DATA those of the prehnite from Aschroft, British Purified powder samples for X-ray Columbia (Nuffield, 1943) (Table 5). analyses have been prepared by separation Scolecite through heavy liquids with specific gravities The pure sample was obtained from a from 2.3 to 3.3. crystalline aggregate (Fig. 2-4) similar to Thulite the sample supplied for the electron-probe The X-ray powder diffraction data analysis. Its X-ray data agree well with (Table 4) fairly agree with those of clinozo those of scolecites from several localities isite from Sasaguri, Fukuoka Prefecture (Table 6). The X-ray data of the fraction (Seki. 1959) and partially with withermite of the sample No. N-51 floated up in the from the Yamanaka Mine, Hyogo Prefecture medium of 2.3 density indicate that the (Yoshimura et al., 1963). This fact may scolecite in the matrix of the rock is Thulite and associatedn mierals from the Nakadori Island, Goto , Nagasaki Prefecture 243 accompanied with considerable amounts of is concluded that the epidote has been wairakite, small amounts of thomsonite and replaced by thulite, associating scolecite, heulandite (Fig. 3). wairakite, and other secondary minerals, under hydrothermal conditions retrogres- CONCLUSION sively proceeded. From the Goth Islands, a part of the Green-Tuff Region, the authors have found ACKNOWLEDGEMENT thulite zonned with withermite, associated with scolecite, wairakite, prehnite and other The authors wish to express their thanks to Professor Kenzo Yagi of the secondary minerals, resulted from the Green- University of Hokusei-Gakuen, Hokkaido, Tuff alteration. The present study is sum-sum for critical reading of the manuscript. They marized as followsfollows: :

The Green-Tuff is essentially composed are also indebted to Dr. Masao Hayashi of Kyushu University for performing the of volcanic pyroclastics of dacitic composi-composi tion. As a result of alteration clay minerals electron-probe and the X-ray analyses, and

are widely brought about in these rocks. to Dr. Kenji Togari, Hokkaido University,

Greenish epidote and chlorite are found in who carried out the X-ray analysis of

and around the porphyrite intrusives. It is scolecite. The present study has been clear that the intrusion has given some finanically supported by a grant in Aid for effects on metamorphism of these volcanic Scientific Research from the Ministry of Education in 1974. pyroclastic sediments as well as on auto-auto metamorphism of the dike rocks themselves.

Thulite occurs within a restricted area, where REFERENCES epidote becomes pinkish in color and calcium Harada, K., M. Hara, and K. Nakao (1968), zeolites such as scolecite and wairakite are Mineralogicalnotes on mesolite and scolecite frequently associated. The country rocks, from Japan. Min. Jour. Japan, 5, 309-320. Hayashi, M. (1973), Hydrothermal alteration in both dacite pyroclastics and porphyrite the Otake geothermal area, Kyushu. Jour. dikes, are discolored by silicification and Japan. GeothermalEnergy Association, 10, No. 3 (Ser. No. 38), 9-45. probably by dissolution of ferriferrous com-com Koizumi,M. and R. Roy (1960),Zeolite studies, 1. ponents. Synthesisand stability of the calciumzeolities. Hayashi (1973) has regarded the tem-tem Jour. Geol.,68, 41. Kuwano, N. (1977),Scolecite from Makinokawa, perature for producing epidote-chlorite- Ehime Prefecture. Chigaku-Kenkyu,77, Nos. sericite assemblage by action of hydrothermal 7-9, 261-270 (in Japaese). solution as a higher temperature than 230°C230•Ž Matsumoto, Y. (1973), Green tuff activities in northern and central Kyushu, Japan. Me- under the total pressure above 250 atm, or -Geol.Soc. Japan, No. 9, 183-193(in Japanese 150 to 250°C250•Ž below 250 atm, whereas the with English abstract). conditions to form wairakite become favor-favor (1977), Volcanic activities of the Green- tuff and the Island-arc movementin Kyushu. able at a temperature of 100 to 200°C 200•Ž below Monographof theAssociation for the Geological 150 atm. After Koizumi and Roy (1960) Collaborationin Japan (Chidanken-Sempo), a synthesised scolecite breaks down to give No. 20, 257-264 (in Japanese with English abstract). anorthite+wairakite+HZOanorthite+wairakite+H2O at a higher Mizota, T., K. Suda, Y. Takeshita,and K. Yatagai temperature than that of the scolecite being (1976), Zeolite minerals from the Kuroiwa stable. From the above consideration, it is concluded intrusive rock,that Kakizaki, the epidote Niigata has Prefecture, been replacedby thulite, associating scolecite,and wairakite, other secondary minerals, hydrothermal underconditions retrogres-sively proceeded.ACKNOWLEDGEMENTTheauthors wish to expresstheir thanksto Professor Kenzo Yagi of the Universityof Hokusei-Gakuen, Hokkaido,criticalreadingof for the manuscript.Theyalso are indebtedto Dr.Masao Hayashi of Kyushu University for performingthe electron-probeand the X-rayanalyses, and toDr. KenjiTogari, Hokkaido University, carried whoout the X-ray analysisof scolecite.The presentstudy has beensupported finanicallyby a grantin Aid for ScientificResearchfrom the Ministryof Educationin 1974.REFERENCESHarada, K., M. Hara,and K. Nakao (1968), noteson Mineralogical mesoliteand scolecite Japan. Min.fromJour. Japan, 5, 309-320.Hayashi,M. (1973),Hydrothermal alteration in the Otake geothermal area,Kyushu. Jour.Geothermal Japan.Energy Association, 10, 3No. (Ser.No. 38), 9-45.Koizumi, M.and R. Roy (1960), Zeolitestudies, and stability I. ofSynthesis the calcium zeolities. Geol.,68, Jour. 41.Kuwano,N. (1977),Scolecite from Geol.Makinokawa,Prefecture. Chigaku-Kenkyu, Soc.77,Japan, Nos.Ehime No.261-2709, 7-9, 183-193(in (in Japaese).Matsumoto, JapaneseY. English (1973), abstract).•\(1977),withGreenVolcanic activitiestuff of activitiesthe Green-tuffin andnorthern and the central Island-arc Kyushu,movement inJapan. Mem.Kyushu. of the MonographAssociation for the Geological in Collaboration Japan (Chidanken-Sempo),20, 257-264(in Japanese No.with EnglishT.,K. Suda,abstract).Mizota,Y. Takeshita, andK. Yatagai Zeolite (1976),minerals from the Kuroiwarock,Kakizaki, intrusiveNiigataPrefecture, 244 Hisashi Takeshita and Yukio Matsumoto

Japan. Sci. Repts. Niigata Univ., Geol. Min. the Nakad6ri Island, Goth, Nagasaki Ser., No. 4, 275-284 (in Japanese with English Prefecture. Paper presented on the 82th Meeting abstract). of Geol. Soc. Japan. Nuffield, E. W. (1943), Prehnite from Aschroft, Ueda, Y. (1961), A study of the Goto Group. Sci. British Columbia. Univ. Tront Stud., Geol. Repts. Kyushu Univ., Geol. Ser., 5, 51-61 (in Ser., No. 48, p. 49. Japanese with English abstract). Seki, Y. (1959), Relation between chemical com Yoshimura, T. and H. Momoi (1963), Withermite position and lattice constants of epidote. Am. from the Yamanaka Mine, Hyogo Prefecture, Min., 44, 720-730. Japan. Sci. Repts Kyushu Univ., Geol. Ser., 6, Tsukahara, S. and Y. Matsumoto (1975), Notes No. 3, 201-206 (in Japanese with English on some findings from the Neogene Tertiary of abstract).

長崎県五島中通島の桃簾石とその随伴鉱物

竹 下 寿 ・松本 径 夫

五 島列 島 は 日本列 島 の グ リー ン タフ地 域 の最 西 端 を なす 。 そ の 中 で 変 質 の 著 しい 部 分 は,ヒ ン岩 ・ハン レ イ 岩 等 火 成岩 に よ って 貫入 され た 珪 長 質 火 山砕 屑 岩 に み られ るご と く,緑 簾石 に よ っ て特 徴 づ け られ て い て,そ の 分 布 範 囲 は モ ン モ リ ロナ イ トに よっ て 特 徴 づ け られ た砕 屑 岩 に 比 し狭 い 。 桃 簾 石 は斜 ユ ウ レ ン石 ～ ウ ィ ザ マイ トで,緑 簾 石 の発 連 す る中 の狭 い 範 囲 に の み あ らわ れ,中 通 島 で は南 部 の奈 良尾 新港 と旧 港 間 の海 崖 に お い て の み 見 出 され る 。 筆 者 らは,緑 簾 石 化 を あ た え た貫 入 岩 が 被 貫 入 岩 と と もに珪 化 作 用 と黄鉄 鉱 化 作 用 を こ うむ っ て い る こ と,桃 簾石 が ス コ レス 沸 石 ・ワイ ラケ 沸 石,ま れ に ブ ドウ石 を伴 っ て い る こ とに注 目し た 。