Mineral Chemistry of Schulenbergite and Its Zn-Dominant Analogue from the Hirao Mine, Osaka, Japan

JournalMineral ofchemistry Mineralogical of schulenbergite and Petrological and its Sciences,Zn−dominant Volume analogue 102, frompage the233 Hirao─ 239, mine2007 233 Mineral chemistry of schulenbergite and its Zn-dominant analogue from the Hirao mine, Osaka, Japan * * ** *** Masayuki OHNISHI , Isao KUSACHI , Shoichi KOBAYASHI and Junji YAMAKAWA *Department of Earth Sciences, Faculty of Education, Okayama University, 3－1－1 Tsushima－naka, Okayama 700－8530, Japan **Department of Applied Science, Faculty of Science, Okayama University of Science, 1－1 Ridai－cho, Okayama 700－0005, Japan ***Department of Earth Sciences, Graduate School of Natural Science and Technology, Okayama University, 3－1－1 Tsushima－naka, Okayama 700－8530, Japan Schulenbergite and its Zn－dominant analogue occur in the Hirao mine, Osaka Prefecture, Japan. The minerals were found as crusts on the same gallery wall and in cracks of altered shale. The minerals occur as aggregates of hexagonal platy crystals up to 0.5 mm across and 0.05 mm thick. The schulenbergite is greenish blue to blue－green in color, and the Cu/(Cu + Zn) molar ratio varies from 0.67 to 0.42. The Zn－dominant analogue of schulenbergite is pale blue in color, and the Cu/(Cu + Zn) molar ratio varies from 0.30 to 0.21. The average unit cell parameters of schulenbergite and its Zn－dominant analogue calculated from the X－ray powder diffraction data were: a = 8.256 (2) and c = 7.207 (3) Å, and a = 8.292 (2) and c = 7.271 (4) Å, respectively. It is likely that schulenbergite and its Zn－dominant analogue from the Hirao mine were formed as secondary minerals from Cu and Zn ion－bearing solution that were derived from chalcopyrite and sphalerite in the host rock. Keywords: Schulenbergite, Zn－dominant analogue, Hirao mine, Osaka, Japan INTRODUCTION Japan, the occurrence of schulenbergite has been reported at the Mikawa mine, Niigata Prefecture (Kojiro et al., Schulenbergite, (Cu,Zn)7(SO4,CO3)2(OH)10·3H2O, was first 1999) and the Hirao mine, Osaka Prefecture (Ohnishi et described by Hodenberg et al. (1984) from dumps of the al., 2001). These samples were identified using X－ray Glücksrad mine and five other localities in Germany. It powder diffraction and by qualitative analysis using an occurs as light green－blue tabular crystals, with an aver- electron microprobe. age diameter of 150 μm and a thickness of about 2 μm, in During a mineralogical survey of the Hirao mine in association with serpierite, linarite, brochantite, cerussite, Japan, schulenbergite (Sample 1) and its Zn－dominant smithsonite, posnjakite, and namuwite. Mumme et al. analogue (Sample 2), showing a wide variation in compo- (1994) reported on the crystal structure of Cu－rich schul- sition, were discovered. This paper discusses the mode of enbergite from the Cap Garonne mine in France. Schulen- occurrence and the mineral chemistry of schulenbergite bergite has also been documented from the Smallcleugh and its Zn－dominant analogue from the Hirao mine. mine (Livingstone et al., 1990), the Penrhiw mine (Mason and Green, 1995), the Waterbank mine (Rust, 1995), and OCCURRENCE the Frongoch mine (Green et al., 1996) in the UK. Moreover, Livingstone et al. (1992) reported on the chem- The Hirao mine (Lat. 34°50′N, Long. 135°28′E) was ical composition, X－ray powder diffraction data, and the developed in shale that includes lenses of sandstone and physical properties of the Zn－dominant analogue of chert belonging to the Minoo complex of the Tamba ter- schulenbergite from the Bastenberg mine in Germany. In rene of Jurassic age at Minoo (Minoh) City, which is located about 17 km north of Osaka City (Matsuura et al., doi:10.2465/jmps.061130 1995). The host rock consists of chlorite, which was M. Ohnishi, [email protected] Corresponding author altered during a hydrothermal alteration process. The ore I. Kusachi, [email protected]－u.ac.jp S. Kobayashi, [email protected] and gangue minerals found in the gallery have been sum- J. Yamakawa, [email protected]－u.ac.jp marized by Ohnishi et al. (2001, 2002, 2004). Sphalerite 234 M. Ohnishi, I. Kusachi, S. Kobayashi and J. Yamakawa Mineral chemistry of schulenbergite and its Zn−dominant analogue from the Hirao mine 235 Figure 1. Photograph of the schulenbergite from the Hirao mine. is the predominant mineral, and this is disseminated in the altered shale among the minerals occurring at the mine. The general appearance of schulenbergite and its Zn－dominant analogue is very similar. The minerals were found as crusts on the same gallery wall and in cracks of altered shale. The minerals occur as aggregates of hexagonal platy crystals, up to 0.5 mm across and 0.05 mm thick (Fig. 1). The schulenbergite is greenish blue to blue－ green and its Zn－dominant analogue is pale blue in color. The associated minerals of the schulenbergite were: smithsonite, ramsbeckite, anatase, and limonite, and the associated minerals of the Zn－dominant analogue of schulenbergite were: hydrozincite, brianyoungite, and limonite. Figure 2. SE images of schulenbergite (a), and Zn－dominant ana- Secondary electron (SE) images of the schulenbergite and logue (b), from the Hirao mine. Abbreviations: Sch, schulen- －－ its Zn－dominant analogue are shown in Figure 2. From bergite; Zn sch, Zn dominant analogue of schulenbergite; Zc, zinc carbonate mineral. the mode of occurrence, it is likely that the schulenbergite and its Zn－dominant analogue at the Hirao mine were formed as secondary minerals in Cu and Zn ion－bearing Mumme et al. (1994) in Table 1. solution that were derived from chalcopyrite and sphaler- The infrared absorption (IR) spectrum of schulenber- ite in the host rock. gite from the Hirao mine was measured using a Perkin− Elmer System 2000 FT−IR spectrometer located at Oka- PHYSICAL AND OPTICAL PROPERTIES yama University of Science, using the KBr pellet method in the region 4000 to 450 cm－1 (Fig. 3). The strong ab- Schulenbergite from the Hirao mine is translucent with a sorption band at 3394 cm－1 was attributed to the O－H pearly luster. Optically, the mineral was uniaxial negative stretching vibration, and the weak absorption at 1637 cm－1 with refractive indices of ω = 1.661 (2) and ε = 1.643 (2). was attributed to the H－O－H bending vibration. The －1 The mineral has a perfect {0001} cleavage. The density, absorption bands at 1104 and 1015 cm were due to the ν 3 －1 measured using a heavy liquid method, was 3.18 (1) and ν 1 SO4 stretching vibrations, and the band at 605 cm 3 3 g/cm , and the calculated density was 3.39 g/cm (Z = 1). was due to the ν 4 SO4 bending vibration. Weak bands at The Vickers microhardness was 48.8 (30.4－76.2) kg/mm2 1509 and 1321 cm－1 were due to the vibrations associated (10 g load), and the Mohs hardness was 1 to 2. No fluo- with the carbonate group. Several absorption bands at rescence was observed under irradiation using short－ or 881, 792, and 513 cm－1 in the low frequency region may － long wave ultraviolet light. The mineral was easily dis- be attributed to (Cu,Zn)O6 octahedra. solved in dilute HCl and HNO3 showing effervescence. The mineralogical properties of the Zn－dominant These properties are compared to those observed by analogue of schulenbergite could not be determined Hodenberg et al. (1984), Livingstone et al. (1992), and because of the close association of the mineral with fine 234 M. Ohnishi, I. Kusachi, S. Kobayashi and J. Yamakawa Mineral chemistry of schulenbergite and its Zn−dominant analogue from the Hirao mine 235 Table 1. Physical and optical properties of schulenbergite (1－3) and its Zn－dominant analogue (4) 1, Hirao mine, Osaka, Japan (Present work); 2, Glücksrad mine, Germany (Hodenberg et al., 1984); 3, Cap Garonne mine, France (Mumme et al., 1994); 4, Bastenberg mine, Germany (Livingstone et al., 1992). Figure 3. IR spectrum of schulenbergite from the Hirao mine. particles of zinc carbonate impurities. Figure 4. TG and DTA curves of schulenbergite from the Hirao mine. THERMAL ANALYSIS and its Zn－dominant analogue were obtained using a Thermogravimetry (TG) and differential thermal analysis Rigaku RINT－2500V diffractometer located at Kurashiki (DTA) of schulenbergite were carried out using a Rigaku University of Science and the Arts, using graphite－mono- － TG 8120 thermal analyzer located at Okayama University, chromatized CuKα1 radiation generated at 40 kV and 240 in air from room temperature to 1000 °C at a heating rate mA. The XRD data are given in Table 2, and are com- of 10 °C/min (Fig. 4). The strong endothermic peak at pared with the data reported by Hodenberg et al. (1984) 322 °C was due to the loss of water molecules in the cop- and Livingstone et al. (1992). The unit cell parameters per and zinc octahedral layers (Mumme et al., 1994). The refined using the least squares method from the XRD data exothermic peak at 535 °C was probably due to a struc- of schulenbergite and its Zn－dominant analogue were: a tural transformation of dehydrated copper and/or zinc sul- = 8.256 (2) and c = 7.207 (3) Å, and a = 8.292 (2) and c = fate. The endothermic peak at 823 °C was due to the 7.271 (4) Å, respectively. The lengths of the a－ and c－ decomposition of the sulfate groups. On heating the min- axes of the Zn－dominant analogue of schulenbergite were eral at 1000 °C, tenorite (CuO) and zincite (ZnO), appear- slightly longer than those of schulenbergite itself. ed as crystalline phases. CHEMISTRY X-RAY CRYSTALLOGRAPHY Electron microprobe analysis of schulenbergite and its X－ray powder diffraction (XRD) data for schulenbergite Zn－dominant analogue revealed the presence of Cu, Zn 236 M.

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