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Baddeleyite, Zirconolite and Calzirtite in Lateritic Rocks from Ryoke and Chichibu Terranes, Japan

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Baddeleyite, Zirconolite and Calzirtite in Lateritic Rocks from Ryoke and Chichibu Terranes, Japan 42 Journal of Mineralogical andD. NishioPetrological and T. Sciences, Minakawa Volume 99, page 42─53, 2004 Baddeleyite, zirconolite and calzirtite in lateritic rock from Ryoke and Chichibu Terranes 43 Baddeleyite, zirconolite and calzirtite in lateritic rocks from Ryoke and Chichibu Terranes, Japan * * Daisuke NISHIO and Tetsuo MINAKAWA *Institute of Biology and Earth Science, Petrology and Economic Geology, Graduate school of Science ─ And ─ Engineering, Ehime University, Bunkyo ─ cho 2 ─ 5, Matsuyama, Ehime 790 ─ 8577, Japan Baddeleyite, zirconolite and calzirtite were found in lateritic rocks from Ryoke and Chichibu Terranes in southwestern Japan. This is a new type of natural occurrence of the minerals. The lateritic rocks are associ- ated with limestone widely distributed into Ryoke metamorphic and Chichibu non ─metamorphic complexes. Baddeleyite, zirconolite and calzirtite are associated with Ti minerals such as anatase, ilmenite, perovskite and titanite. Calzirtite occurs simultaneously with perovskite. Rhabdophane─(Ce) like minerals also occurs in the lateritic rocks such as in emeries from Ko ─Oge Island. Baddeleyite and calzirtite have compositions close to the ideal compositions, ZrO2 and Ca2Zr5Ti2O16. Zirconolite, CaZrTi2O7, accommodates significant amounts of Fe, Nb, Ta, and small amounts of Al and REE. Minor amounts of ACT are also found in the mineral. The chemi- cal substitution in zirconolite is controlled by the reaction: REE3+ + 2(Al + Fe)3+ + (Nb + Ta)5+ ←→ Ca2+ + 3Ti4+. Baddeleyite is a relict of the lateritization stage, or formed by the decomposition of zircon. Zirconolite formed during the prograde stage of metamorphism by the reaction; calcite + 2anatase + baddeleyite ←→ zirconolite + ─ CO2. The formation of calzirtite in Ca metasomatic emery is independent from the deformation of zirconolite during the prograde stage of metamorphism. Introduction rane. Zirconolite from the Shinkiura mine was found in the metamorphic laterite as emery, belong to the Chichibu The sedimentary and metamorphic rocks related to Terrane. Calzirtite found in the lateritic metamorphic rock laterite occur in the Ryoke and Chichibu Terranes of from Ko─Oge Island, are part of the Ryoke Terrane. Japan (Iwao, 1978; Nishio and Minakawa, 2003). The Although zirconolite occurs in a wide range of rock major minerals in the host lateritic rock were described types and parageneses, the majority come from carbon- (e.g. Shimazaki et al., 1984; Nishio and Minakawa, 2003; atites (e.g. Williams and Gieré, 1996). Occurrences of Nishio et al., 2003), but the Zr ─bearing mineral was not. this mineral from laterite and related rocks have not yet The Zr minerals generally occur as accessory phases in been reported. Baddeleyite and calzirtite were not found the host rock. These Zr minerals usually contain REE in lateritic rocks, either. (rare earth elements including Y) and ACT (actinide In this paper we intend to report on newly discov- element). Therefore, the behavior of Zr minerals in a ered natural occurrences. We will also describe the crys- rock also controls the behavior of minor elements such tal chemistry of baddeleyite, zirconolite and calzirtite as REE and ACT. We discovered three Zr minerals, from the Ryoke and Chichibu Terranes in southwestern baddeleyite, zirconolite and calzirtite, from the Ryoke Japan. and Chichibu Terranes of Japan. Baddeleyite found in lateritic metamorphic rocks from Yuge, Ko ─ Oge and Mu- Interpretation of zirconolite and calzirtite tsuki Islands, belongs to the Ryoke Terrane. The lateritic sedimentary rocks from Kuwao, where baddeleyite was Zirconolite and calzirtite, together with their polytypes, found, belong to the Chichibu Terrane. Zirconolite found have compositions nearly equivalent to CaZrTi2O7 and ─ in the metamorphic laterite of Yuge, Myojin, Ko Oge and Ca2Zr5Ti2O16, respectively. In this study, the names of Mutsuki Islands, are from the metamorphic Ryoke Ter- zirconolite and calzirtite are used here as group names. D. Nishio, d─[email protected]─u.ac.jp Corresponding author The nomenclatures of zirconolite and calzirtite are de- T. Minakawa, [email protected]─u.ac.jp fined as follows. 42 D. Nishio and T. Minakawa Baddeleyite, zirconolite and calzirtite in lateritic rock from Ryoke and Chichibu Terranes 43 only by single ─ crystal X ─ ray diffraction, because the Zirconolite two polytypes change in a continuous manner in small domains. Calzirtite ─ 1O transforms into another polytype Zirconolite is metamict or non ─ metamict mineral with tetragonal symmetry (calzirtite ─ 1Q) after heating to with many polytypes: zirconolite ─ 2M is a two layered 700 ─ 1350°C (Callegari et al., 1997). monoclinic polytype, zirconolite ─3O is a three layered orthorhombic polytype, zirconolite─3T is a three layered Geological setting trigonal polytype of CaZrTi2O7 (Bayliss et al., 1989). Zirkelite is a cubic mineral with (Ti, Ca, Zr)O2－x, and Figure 1 shows the location and geological map of polymignite is metamict zirconolite (Bayliss et al., the region studied in this paper. The Geiyo Islands are 1989). Smith and Lumpkin (1993) and Coelho et al. located in the central area of the Seto Inland Sea. From (1997) described synthetic 4M and 6T phases related to east to west, Yuge, Myojin, Ko ─ Oge and Mutsuki Islands zirconolite, which appear to be supercells of the zircono- are included in Ehime Prefecture. Cretaceous plutonic lite ─ 2M and 3T structures, respectively. rocks are widely distributed in the Geiyo Islands, and are considered to be part of the Ryoke Terrane (Suyari Calzirtite et al., 1992). The Islands of Yuge, Myojin, Ko ─ Oge and Mutsuki are mainly composed of schistose and massive Two polytypes of calzirtite have been reported: cal- granite or granodiorite, gneiss, schistose hornfels and zirtite ─ 1Q is a tetragonal polytype, and calzirtite ─1O is plagioclase ─amphibole schists. Limestone is included an orthorhombic polytype of Ca2Zr5Ti2O16 (e.g., Rossell, in gneisses, crystalline schist or schistose hornfels (e.g. 1982; Sinclair et al., 1986; Callegari et al., 1997). The Miyahisa et al., 1980; Shimazaki et al., 1984; Matsuura, tetragonal and orthorhombic forms are distinguishable 2000; Seno and Matsuura, 2000; Nishio and Minakawa, Figure 1. Location and geological map of Yuge, Myojin, Ko─Oge and Mutsuki Islands from Ryoke Terrane and Kuwao and the Shinkiura mine from Chichibu Terrane, Japan. 44 D. Nishio and T. Minakawa Baddeleyite, zirconolite and calzirtite in lateritic rock from Ryoke and Chichibu Terranes 45 Figure 2. Backscattered electron image of baddeleyite, zirconolite and calzirtite and the rhabdophane ─(Ce) like mineral from the Ryoke Terrane and Chichibu Terrane, Japan. A: from Yuge Island, B: in Ca─added zone from Ko─Oge Island, C: from Kuwao, D: from Shinkiura mine, E: in non─metasomatic zone from Ko─Oge Island. All, allanite─(Ce); An, anatase; Ap, apatite; Bd, baddeleyite; Clz, calzirtite; Ilm, ilmenite; Mgt, magnetite; Rha, rhabdophane─(Ce) like mineral; Sc, scheelite; Zir, zirconolite. 2003; Nishio et al., 2003). Ohita Prefecture (e.g. Iwao, 1978; Suyari et al., 1992). Mesozoic and Paleozoic strata distributed in the south of Shikoku and Kyushu and are grouped in the Chi- Occurrence and paragenesis chibu Terrane (e.g. Karakida et al., 1992). The group in Shikoku and Kyushu are composed mainly of pelitic rock, Zr minerals are found in lateritic rocks included in chert and limestone (e.g. Yoshimura et al., 1962; Suyari limestone from the Ryoke and Chichibu Terranes. The et al., 1992). Limestone from Kuwao, Kochi Prefecture rocks are characterized by high Al, Fe and Ti and low Si is non ─metamorphosed, although it has suffered slight content. Localities where baddeleyite, zirconolite and alteration and skarn formation through contact with the calzirtite were found are summarized in Table 1. The oc- Ohkueyama granite intrusion from the Shinkiura mine, currences and paragenesis of baddeleyite, zirconolite and 44 D. Nishio and T. Minakawa Baddeleyite, zirconolite and calzirtite in lateritic rock from Ryoke and Chichibu Terranes 45 Figure 3. Photomicrographs of zirconolite and calzirtite from Yuge Island and Ko─Oge Island from the Ryoke Terrane, Japan. A and B from Yuge Island; C, D, E, and F from Ko─Oge Island. Bars are 30um long. A, C, and E: Plane─polarized light, B, D, and F: Crossed polars. Bd, baddeleyite; Clz, calzirtite; Pv, perovskite; Zir, zirconolite. Table 1. List of occurrences of baddeleyite, zirconolite and calzirtite in the lateritic rock from Ryoke Terrane and Chichibu Terrane, Japan +, obserbed; −, not obserbed. 46 D. Nishio and T. Minakawa Baddeleyite, zirconolite and calzirtite in lateritic rock from Ryoke and Chichibu Terranes 47 Table 2. Chemical compositions of Zr minerals from the Ryoke Terrane, Japan * total Fe as Fe2O3. Bd, baddeleyite; Clz, calzirtite; Zir, zirconolite; Zr, zircon. Zir(L) and (H) are Low and High Zir in Figure 2B, respectively. calzirtite are described as follows. on Yuge, Myojin and Mutsuki Islands. The composition of the lateritic rocks from Ko ─Oge Island is consistent Ryoke Terrane with emery (Nishio et al., 2003). Emery in the region is classified in two zones, one as a non ─metasomatic zone, Recrystallized lateritic rocks with dark color are included and another as a metasomatically Ca─added zone (Nishio in limestone from Yuge, Myojin, Ko─Oge and Mutsuki Is- et al., 2003). Calzirtite is only found in the latter. The lands. The lateritic rocks from these islands show a little constituent minerals of the lateritic rock from each island difference
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