Philipsburgite from the Yamato Mine, Yamaguchi Prefecture, Japan
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Journal of MineralogicalPhilipsburgite and Petrological from Sciences, the Yamato Volume mine 106, page 153─ 157, 2011 153 LETTER Philipsburgite from the Yamato mine, Yamaguchi Prefecture, Japan Yohei SHIROSE and Seiichiro UEHARA Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan Philipsburgite, (Cu,Zn)5Zn(AsO4,PO4)2(OH)6·H2O, an As analogue of kipushite, was discovered in the Yamato mine, Yamaguchi Prefecture, Japan. Philipsburgite occurs in the form of spherical aggregates, 0.5 mm in diame- ter, with bright green in color. It is associated with malachite and cornwallite in cavities of the oxidized rocks, which consist of quartz and goethite. Spherical philipsburgite consists of platy crystals, 100 μm in length and 1 μm in thickness, with sharp termination. The empirical formula is (Cu4.91,Zn0.09)Σ5.00Zn1.00[(AsO4)1.63(PO4)0.37] Σ2.00(OH)6·1.60H2O on the basis of O = 11 in the anhydrous part per formula unit and the water content was measured by thermogravimetric analysis. The composition is closest to the As end member thus far reported. The unit cell parameters from the X-ray diffraction data are a = 12.359(8), b = 9.247(7), c = 10.734(5) Å, β = 97.22(5)° and V = 1216.9(9) Å3. Keywords: Philipsburgite, Yamato mine, Arsenate, XRD, Chemical composition INTRODUCTION small massive limestone intruded by Cretaceous granite. The ore was divided into two types, primary massive sul- Philipsburgite, (Cu,Zn)5Zn(AsO4,PO4)2(OH)6·H2O, is a ra- fide deposits including chalcopyrite, pyrrhotite, arsenopy- re arsenate-phosphate mineral that crystallizes in space rite, sphalerite and etc., and secondary oxidized zones in- group P21/c, Z = 4. It is an As analogue of kipushite. The cluding malachite, chrysocolla, etc. (Ueno and Doi, 1956). mineral was first described by Peacor et al. (1985) from Recently, Ohnishi et al. (2007) reported preisingerite, - the Black Pine mine, near Philipsburg, Montana, USA. Bi3O(OH)(AsO4)2, joseite A, bismuth, bismutite, cupro- Subsequently, the mineral was reported from Neublach, tungstite, ferritungstite, russellite, jarosite, clinoclase and Black Forest, Germany (Walenta et al., 1985), the Potts cornwallite from the oxidized zone. Gill mine, Caldbeck, Cumbria (Braithwaite and Ryback, Philipsburgite occurs in the form of spherical aggre- 1988), the Gold Hill mine, Tooele County, Utah (Kokinos gates, 0.5 mm in diameter. It is semi-opaque, bright green, and Wise, 1993) and so on. However, descriptive mineral- with a dull luster on the growth surface, and pale green ogy of philipsburgite with both chemistry and X-ray dif- and pearly luster on the fracture surface (Fig. 1). Scanning fraction data has been published by just two reports (Pea- electron microscopy (SEM) reveals that the spherical cor et al., 1985; Walenta et al., 1985). This study deals philipsburgite is made up of radiating aggregates of tabu- with the occurrence and mineralogical properties of phil- lar or prismatic crystals (Fig. 2). The single crystals, 100 ipsburgite found at the Yamato mine, Yamaguchi Prefec- μm in length and 1 μm in thickness, have a large face ture. This is the first discovery of philipsburgite in Japan. (100) as the dominant form and are elongate along b axis with sharp terminated edges. It is directly associated with OCCURRENCE AND PHYSICAL PROPERTIES spherical malachite and the botryoidal clusters of dark green cornwallite in the cavities of the oxidized rock, The old Yamato copper mine is located at Shimo, Ofuku, which consists of drusy quartz and minor goethite (Fig. 1). Mine City, Yamaguchi Prefecture, Japan (Lat. 34°13´N, At the site where the philipsburgite was collected, chryso- Long. 131°11´E). The ore body is a skarn deposit made colla, vesuvianite, pseudomalachite, REE rich zalesiite, up of the latest Paleozoic chert and slate with lens or clinoclase and brochantite also occur in the oxidized rocks doi:10.2465/jmps.101021e consisting of quartz and goethite. Y. Shirose, [email protected] Corresponding author S. Uehara, [email protected] 154 Y. Shirose and S. Uehara Figure 1. Photograph of a cavity including philipsburgite from the Yamato mine. Spherical blight green philipsburgite on dark green cornwal- lite. Scale bar is 1 mm. CHEMICAL COMPOSITION Chemical analyses of philipsburgite were carried out us- ing a JEOL JSM-5800LV SEM equipped with an Oxford ISIS energy dispersive X-ray spectrometry. Quantitative analyses were performed at an accelerating voltage of 20 kV, beam current of 0.5 nA, and beam scan area of 4 × 4 μm. The standards used were pure Cu (for CuKα), sphal- erite (for ZnKα), arsenic (for AsKα) and LaP5O14 (for PKα). The ZAF method was used for data correction. The water content was measured by thermogravimetric analy- sis (TGA) for 0.480 mg samples using an SII SSC/5200. The weight loss was recorded in the range 25-600 °C at a heating rate of 10 °C/min. The averaged chemical compo- sition of philipsburgite from the Yamato mine and previ- Figure 2. Secondary electron image of philipsburgite from the ous value are presented in Table 1. The empirical formula, Yamato mine. Scale bar is 20 μm. which is calculated on the basis of O = 11 per formula unit in the anhydrous part, is (Cu4.91,Zn0.09)Σ5.00Zn1.00 Philipsburgite from the Yamato mine 155 Table 1. Chemical composition of philipsburgite and kipushite 10.734(5) Å, β = 97.22(5)° and V = 1216.9(9) Å3. DISCUSSION Philipsburgite and kipushite are isostructural, and can be represented by the general structural formula (M1)2(M2)3(M3)(XO4)2(OH)6·H2O; where M1 = Cu (dis- torted octahedral sites), M2 = Cu or Zn (regular octahe- dral sites), M3 = Zn (a tetrahedral site) and X = As or P (tetrahedral sites) (Piret et al., 1985; Peacor et al., 1985). The present philipsburgite, Cu2.00(Cu2.91Zn0.09)Zn1.00As1.63 P0.37, has the highest As/(As + P) value and the composi- tion closest to end member philipsburgite thus far report- ed (Table 1). Unit cell parameters of philipsburgite from the Ya- * Number of analyzed spots. mato mine are larger than those of the Black Pine mine; ** The water content was measured by TGA. the result of the higher As content (Peacor et al. 1985; 1. Yamato mine, Yamaguchi Prefecture, Japan (this study). Piret et al. 1985; Walenta et al. 1985) (Fig. 3). Extrapolat- 2. Cu5Zn(AsO4)2(OH)6·H2O. 3. Philipsburgite, Black Pine mine, Montana (Peacor et al., ing from these data to the unit cell parameters of a phil- 1985). ipsburgite end member, the unit cell volume of philipsbur- 4. Philipsburgite, Potts Gill mine, Cumbria (Braithwaite and Ry- gite is about 3.2% larger than kipushite. The cornwallite- back, 1988). pseudomalachite solid solution is similar to the kipushite- 5. Philipsburgite, Neubulach, Black Forest, Germany (Walenta philipsburgite series, with increase in unit cell parameters et al., 1985). 6. Kipushite, Kipushi, southern Shaba, Zaire (Piret et al., 1985). with increasing As. Arlt and Armbruster (1999) reported that the average As-O bond length (1.674 Å) in cornwal- lite is about 0.14 Å longer than corresponding P-O bond [(AsO4)1.63(PO4)0.37]Σ2.00(OH)6·1.60H2O, in good agree- length (1.538 Å) in pseudomalachite, which enlarges the ment with previously published philipsburgite chemis- unit cell volume of cornwallite by about 5% compared tries. with pseudomalachite. The volume change is the similar to that found in the the philipsburgite-kipushite series. CRYSTALLOGRAPHY The arsenates found in association with philipsburgi- te from the Yamato mine are cornwallite, clinoclase and X-ray diffraction (XRD) data were collected on crystal zalesiite. These minerals have a close chemical composi- fragments using a Rigaku RINT RAPIDII curved imaging tion to each other as shown in the copper(II)-arsenate ter- plate microdiffractometer utilizing monochromatized nary diagram (Fig. 4). The paragenetic sequence of those CuKα radiation generated at 40 kV and 30 mA. The frag- minerals is first cornwallite, next clinoclase, philipsburgite ments were randomized using a Gandolfi-like motion or zalesiite. A stability field diagram for the copper(II)-ar- about two axes (oscillation on ω and rotation on φ). The senate minerals was reported by Magalhães et al. (1988) XRD data are listed in Table 2 together with those of the and Williams (2005), which shows dependence on copper original description of philipsburgite (Peacor et al., 1985). ion activity and pH of the aqueous solution. Olivenite, These data are incorporated in PDF card #38-384. Peacor which does not occur with philipsburgite at the Yamato et al. (1985) indexed the XRD data from d = 12.2 Å to mine, crystallizes in lower copper ion activity and pH 2.497 Å. Those peaks that were not addressed by Peacor than cornwallite and clinoclase. Magalhães et al. (1988) et al. were indexed by the International Center for Dif- reported that the stability field of cornwallite is very nar- fraction Data (ICDD) and are included on the PDF card. row, explaining the rarity of cornwallite in nature. At the Several weak diffraction peaks are found in the Yamato Yamato mine, cornwallite was commonly found at the specimen, which are not listed in the original powder area where philipsburgite occurred, and philipsburgite is data. These peaks are indexed by comparison of the inten- much rarer than cornwallite there. It is assumed that phil- sity calculation using the atomic parameter of kipushite ipsburgite has the narrow stability field similar to that of (Piret et al., 1985) as a substitute for philipsburgite, which cornwallite, or the amount of zinc in aqueous solution is had not been made crystal structure analysis.