Germanium-Bearing Colusite from the Yanahara Mine, Japan, and Its Significance to Ore Genesis

RESOURCE GEOLOGY, 44(1), 33•`38, 1994

Germanium-bearing Colusite from the Yanahara Mine, Japan, and Its Significance to Ore Genesis

Katsuo KASE*, Masahiro YAMAMOTO* and Chiharu MITSUNO*

Abstract: Colusite, Cu26V2(As,Ge)6S32, containing up to 4.3 wt.% Ge occurs with pyrite, chalcopyrite and bomite in sphalerite-barite-rich ores of the volcanogenic massive sulfide orebody at Hinotani L-1, the Yanahara mine. Electron microprobe analysis reveals that As and V are pentavalent and Ge is tetravalent in the mineral the same as in germanite and renierite, suggesting that the Ge-bearing colusite was precipitated under high fs2 and foe conditions. These Ge-bearing minerals sometimes occur in the Kuroko deposits related with felsic volcanism, associated with pyrite, chalcopyrite and bomite as at Hinotani, while practically no Ge-bearing minerals occur in the Besshi-type deposits related with mafic volcanism. It is concluded that the ore solutions responsible for the Hinotani L-1 orebody and possibly for whole orebodies at Yanahara are related with felsic volcanism.

ore mineralogy is similar to that of the typical 1. Introduction Besshi-type deposits. The deposit is thus ambigu- There are two major types of volcanogenic mas- ous in the classification, and sometimes called sive sulfide deposits in Japan: Kuroko deposits and Besshi-type deposits. The Kuroko deposits are genetically related with Miocene dacitic-rhy- olitic volcanism, and characterized by high Zn, Pb and Ag contents and an abundance of sulfate minerals. The Besshi-type cupriferous iron sulfide deposits, equivalent to Kieslager, occur in the se- quence consisting of basalts and sediments, or their metamorphic equivalents, and are very low in the Pb content and poor in sulfate minerals. The volcanogenic massive pyritic deposit of the Yanahara mine, located about 40 km northeast of Okayama, Southwest Japan, is hosted by felsic pyroclastic rocks, up to 30 m thick, in the Paleo- zoic black slate. The large Main orebody is ac- companied by several smaller orebodies at Yanahara (Fig. 1). The mine has produced more than 37 million tons of pyrite ores with an average grade of 44% Fe, 47% S, 0.2% Cu, 0.3% Zn and 0.02% Pb (MITI, 1980). Although felsic volcanic rocks are closely associated with the deposit at Yanahara, it is very low in the Pb content, and the

Received on June 12, 1993, accepted on September 4, 1993. Fig. 1 Map showing the distribution of massive pyritic * Department of Earth Sciences , Faculty of Science, Okayama orebodies of the Yanahara mine and of Cretaceous in- University, Tsushima-Naka 3-1-1, Okayama 700, Japan trusive and effusive rocks. Y, Ok and Os in the inserted Keywords: Ge-bearing colusite, Yanahara mine, Germanite, map indicate the locations of the Yanahara mine, Renierite, Kuroko deposit, Besshi-type deposit, Felsic volca- Okayama and Osaka, respectively (partly modified nism. from the Yanahara mine).

33 34 K. KASE, M. YAMAMOTO and C. MITSUNO RESOURCE GEOLOGY: the Yanahara-type Kieslager (MITSUNO, 1963; MITI, 1980). Germanium-bearing colusite is present in a small amount in the Hinotani L-1 orebody of the Yanahara mine. Germanium-bearing sulfide minerals such as germanite, colusite and renierite have been found in small amounts at many Cu-Zn-Pb deposits of various types throughout the world (e.g., BERNSTEIN, 1986), including the classical examples at Tsumeb, Namibia and Fig. 2 Cross section through the Hinotani and Hinotani L-1 orebodies (modified from Kipushi, Zaire. The knowl- the Yanahara mine). edge on the meaning in ore genesis of Ge-bearing minerals is, however, in- rounding slates to cordierite-biotite or biotite complete. We describe in this paper the mode of hornfels, and pyrite to pyrrhotite and/or magnetite occurrence and chemistry of the Ge-bearing in the marginal parts of the orebodies. colusite at Yanahara, and discuss its significance Most of the orebodies at Yanahara occur in the to ore genesis. felsic pyroclastic rocks of a definite stratigraphic horizon underlain by diabasic complex, and are 2. Geology and Ore Deposit dominantly composed of pyrite with small in the Yanahara Mine amounts of chalcopyrite and sphalerite. The Rocks exposed in the Yanahara mining area are Hinotani L-1 orebody in which the Ge-bearing composed of weakly metamorphosed Paleozoic colusite occurs, situated about 100 m beneath the formations called the Maizuru Group. The group Hinotani orebody to the east of the Main orebody, is divided into the lowermost, lower, middle and is conformably underlain by felsic pyroclastic upper formations. The middle formation, in which rocks and overlain by diabasic complex (Fig. 2). the orebodies at Yanahara are embedded, is 700 m Geologic data are insufficient to determine thick, and mainly consists of black slate, with whether the L-1 orebody occupies the identical some intercalations of felsic pyroclastic rock in ore horizon with the other orebodies or not, be- the lower horizons, and with sandstone and lime- cause an extent of gallery is very limited in the L- stone containing fossil coral of Middle Permian in 1 orebody. The L-1 orebody is very Zn-rich, and the upper horizons (MITSUNO, 1988). composed of sphalerite, barite, pyrite, chalcopy- A weakly metamorphosed sheeted complex rite, bornite, tennantite and galena in the order of consisting of diabase, quartz diorite and grano- decreasing amount, being markedly different in diorite is conformably present in the strata of the mineralogy from most orebodies at Yanahara. In Maizuru Group. A lack of contact aureole leads to the marginal parts of the orebody, pyrrhotite ap- an idea that the complex might have intruded with pears by the thermal effects of granitoid intrusion. consolidated state. An alternative is that the com- 3. Ge-bearing Colusite in the Hinotani plex is a fault-bounded, dismembered ophiolite L-1 Orebody derived from the oceanic crust and upper mantle (ISHIWATARI, 1985). At late Cretaceous time, The Ge-bearing colusite occurs sporadically in granitoid masses intruded into the Maizuru sphalerite and chalcopyrite, and rarely in pyrite Group, and thermally metamorphosed the sur- with a granular form, smaller than 0.1 mm across 44(1) Germanium-hearing colusite from the Yanahara mine 35

Table I Chemical compositions* and number of atoms based on 66 total atoms per unit formula of Ge-bearing colusite in the Hinotani L-1 orebody of the Yanahara mine.

* Results of electron microprobe analyses . Listed in the order of increasing Ge contents.

Fig. 3 Photomicrographs of Ge-bearing colusite (col) from the Hinotani L-1 orebody. Open nicol. Reflected light. Field width is 0.6 mm. A. Colusite associated with pyrite (py), chalcopyrite (cp) and bornite (bn) assemblage. The dark domains are mostly barite. sp: sphalerite, gn: galena, and tn: tennantite. B. Colusite in sphalerite. Abbreviations and dark domains as in A.

(Fig. 3). The association with pyrite, chalcopyrite and bornite assemblage and barite is characteristic

(Fig. 3-A). The Ge-bearing colusite is isotropic, pale brown yellow, and less brownish compared with the associated bornite under reflected light.

The powder diffraction data of the Ge-bearing Fig. 4 Relationships between number of As (NAs: solid colusite were obtained by using an X-ray micro- circles) and As+Sb+V (NA,+sb+V:open circles) to num- diffractometer on the polished surface because of ber of Ge (NGe) in Ge-bearing colusite, based on formulae calculated on the basis of 66 total atoms per for- its small grain size. Three strong reflections were mula unit. The equations are obtained by the least detected at 3.05, 1.87 and 1.60•ð, which can be in- squares regression. dexed as (222), (044) and (226), respectively, based on a cubic unit cell with a 10.6•ð

(MURDOCH, 1953). SWEATMANand LONG (1969). Chemical compo- The chemical compositions of the Ge-bearing sitions of the Ge-bearing colusite are listed in colusite and related minerals were determined on Table 1, with number of atoms calculated on the a JEOL electron microprobe analyzer operating at basis of 66 total atoms per formula unit according 25 kV and 0.02 µA specimen currents measured to ORLANDIet al. (1981). The formulae obtained on Cu metal. The correction procedure was that of from the number of atoms are very analogous to 36 K. KASE, M. YAMAMOTO and C. MITSUNO RESOURCE GEOLOGY:

Table 2 Chemical composition* of sulfide-sulfate frac- (p43n) and chemical formulae with 66 atoms per tion of sphalerite-barite-rich ore with Ge-bearing formula unit (ORLANDIet al.,1981; TETTENHORST colusite. and CORBATO, 1984; SPIRIDONOV, 1987). It is likely that Cu in colusite is monovalent. The valence states of other constituent elements can be assessed based on the balance of electrostatic charges maintained in colusite. The Ge-bearing colusite at Hinotani L-1 is simple in composition to assess the charges of constituent elements, and *Ba and S: gravimetry as BaSO 4, Fe: titration using po- the balance of charges is most reasonably main- tassium dichromate, other elements: inductively coupled tained by pentavalent As, Sb and V, tetravalent plasma-atomic emission spectroscopy. Ge, trivalent Fe, and divalent Zn. The present data, however, show no correlations between con- the ideal one proposed by ORLANDI et al. (1981): stituent elements except for the negative linear Cu26V2(As,Sn)6S32 with substitution of Ge for Sri . correlation between Ge and As. Therefore, the The Fe, Zn and Sb contents are very low, and Cu substitution relationship is not understood to and V contents are uniform for the L-1 colusite . maintain the balance of charges in the mineral. The Ge content shows a good negative linear cor- The valence states of As and Sb are different relation with As and As + Sb + V (Fig . 4), which from their valence states in tetrahedrite-tennantite implies the substitution of Ge for As. The mineral in which these elements are trivalent, suggesting with this compositional range may belong to a that the Ge-bearing colusite was precipitated un- member of colusite (PSCHENICHNYI et al., 1974). der higher foe conditions. In fact, the foe of pyrite, The associated sphalerite is close to ZnS in com- bornite and chalcopyrite assemblage is higher position with less than 0.4 mol% FeS, less than 0.1 than that of bornite-free chalcopyrite and pyrite mol% US and MnS. The associated tennantite is assemblage at a given T and total dissolved sulfur. Zn-rich with a mean composition of 8 analyses: The latter assemblage with or without tetra- Cu 10 .1(Zn1.96Fe0.04)ƒ°2.00(AS3.17Sb0 .73)ƒ°3.90S 13.0' b hedrite-tennantite is ubiquitous in the Ge-bearing ased on 29 total atoms per formula unit. colusite-free ores. One of the sphalerite- and barite-rich ores con- The Ge-bearing sulfosalt minerals hitherto taining Ge-bearing colusite in a small amount was described in the volcanogenic massive sulfide chemically analyzed for its sulfide-sulfate frac- deposits of Japan are mostly from Kuroko depos- tion, with a result of 40 ppm Ge (Table 2). Micro- its. They include germanite from Kamikita scopic observation indicates that ores with such a (TAKEUCHIet'al., 1956), germanite, renierite and Ge content are widespread in the L-1 orebody. Sn-, Ge-bearing colusite from Shakanai Sulfur isotope ratios of sphalerite, pyrite and bar- (URASHIMAet al., 1968; MIYAZAKI et al., 1978; ite from the same ore specimen as the analyzed MATSUKUMAand YUI, 1979), and renierite from one are available in YAMAMOTO et al. (1984), the Furutobe (HAYASHI et al., 1985). In the Besshi- ratios being 1.9, 1.2 and 15.1•ñ, respectively. The type deposits related with mafic volcanism, only isotope ratio of barite sulfur is close to the inferred colusite with a very small amount of Ge occurs ratio of the Permian seawater sulfate sulfur very rarely at Ikadazu, central Shikoku (KASE and (YAMAMOTO et al,, 1984), indicating the L-1 ore- YAMAMOTO, 1988). These Ge-bearing minerals body to be submarine volcanic-sedimentary type . are all associated with pyrite, chalcopyrite and

4. Discussion bornite the same as at Hinotani L-1. The association with minerals being stable under high fs2 con- NAKAI et al. (1976) studied the valence state of ditions, mainly with pyrite, chalcopyrite and Cu by X-ray photoelectron spectroscopy in 21 sul- bornite, seems to be common to the Ge-bearing fide and sulfosalt minerals including germanite, sulfide minerals hitherto described in the world (e. and found that all Cu are monovalent. Colusite g., BERNSTEIN, 1986). The balance of the electro- and germanite have analogous crystal structures static charges of these Ge-bearing minerals is 44(1) Germanium-bearing colusite from the Yanahara mine 37

most reasonably maintained by pentavalent As, HASHIGUCHI, kindly supported our field works.

Sb and V, tetravalent Ge and trivalent Fe as shown Prof. T. NUREKI of Okayama University gave us by BERNSTEIN (1986) for renierite from Ruby his unpublished data on the granitoids in the stud-

Creek, Alaska, though it is sometimes difficult to ied area. Thanks are also due to the anonymous assess the charges because of their complicated referee who kindly reviewed the manuscript and chemical compositions. Therefore, it is concluded suggested improvements. Ore samples of the L-1 that not only high fo2 conditions but also high fs2 orebody were collected by Mr. M. NISHII during conditions are needed for the precipitation of Ge- the study of his bachelor's thesis. This work was bearing minerals including Ge-bearing colusite. supported in part by Grants-in-Aid for Scientific

It is believed that the bulk of Ge is dispersed in Research Nos. 01540659 and 02302032 from the the outer Earth's crust, in substitution for Si4+ in Ministry of Education, Science and Culture of Ja- the tetrahedral framework of silicate minerals pan. (FRONDEL and ITO, 1957). According to HOERMANN(1970), the abundance of Ge is a little References larger in felsic igneous rocks than in mafic ones. BERNSTEIN, L. R. (1986) : Renierite, Cu10ZnGe2Fe4S16- Germanium appears to concentrate in some de- Cu11GeAsFe4S16: a coupled solid solution series. Amer. gree in late differentiates (MASON and MOORE, Mineral., 71, 210•`221. 1982). Thus, it is likely that ore solutions with af- FRONDEL, C. and ITO, J. (1957): Geochemistry of germanium finity to felsic volcanic rocks are generally more in the oxidized zone of the Tsumeb mine, south-west Af- rica. Amer. Mineral., 42, 743-753. enriched in Ge than those with affinity to mafic HAYASHI, K., KIKUTANI, T. and SUGAKI, A. (1985): As-bearing volcanic rocks. The Ge contents in ore solutions renierite from the Furutobe mine, Akita prefecture, Japan. may be reflected in the sulfide ores derived from Jour. Min. Petr. Econ. Geol., 80, 451•`458 (in Japanese them. In fact, the Ge contents of 122 ores from the with English abstract).

Besshi-type deposits in Japan are all below the HOERMANN, P. K. (1972): Germanium: In Handbook of Geo- value of the detection limit (5ppm). On the other chemistry (K. H. WEDEPOHL, ed.), New York, Springer- hand, in one third of total 139 analyses of Kuroko Verlag. ores the Ge contents are over 10ppm up to HORIKOSHI, E. (1958): Occurrences of barite and anhydrite in 120ppm (MITI, 1992). In the Besshi-type depos- some cupriferous iron sulfide deposits. Mining Geol., 8, its, barite and anhydrite may occur in the sulfide 328•`334 (in Japanese with English abstract). ores (HORIKOSHI, 1958; KASE and YAMAMOTO, ISHIWATARI, A. (1985): Granulite-facies metacumulates of the Yakuno ophiolite, Japan: Evidence for unusually thick 1988). Fe-oxide layers with a small amount of oceanic crust. J. Petrology, 26, Part 1, 1•`30. manganese, now metamorphosed to hematite and/ KASE, K. and YAMAMOTO, M. (1988): Minerals and geochemi- or hematite-magnetite assemblages, are com- cal characteristics of ores from the Besshi-type deposits in monly associated with sulfide ores. It is likely that the Sambagawa Belt, Japan. Mining Geol., 38, 203•`214. the fo2 conditions were high enough, locally at MASON, B. and MOORE, C. B. (1982): Principles of Geochem- least, for the.precipitation of Ge-bearing minerals istry, Fourth edition. New York, John Wiley, 344p. in the Besshi-type deposits, but the occurrence is MATSUKUMA, T. and Yul, S. (1979): Occurrence and paragen- practically none. It may imply that the ore solu- esis of bornite-rich kuroko ores containing Ge. Sn-bearing tions responsible for the Besshi-type deposits are mineral from the No. 11 ore deposits of the Shakanai very low in the Ge content. Above discussions in- mine, Akita Prefecture, Japan. Resear. Inst. Undergr. Re- dicate that the sulfide orebody at Hinotani L-1, sources, Mining Coll., Akita Univ., No. 45, 91•`104 (in Japanese with English abstract). and possibly the whole orebodies at Yanahara are MITI (Ministry of International Trade and Industry) (1980): genetically related with the closely associated Report on regional survey in the Tsuyama region during felsic volcanic rocks. the fiscal year 1979. 132p. (in Japanese). Acknowledgments: The X-ray microdiffrac- MITI (1992): Report on assessment of the mineral resources of tometer was used at the Institute for Study of the rare metals. 112p. (in Japanese). Earth's Interior, Okayama University, by courtesy MITSUNO, C. (1963): Zur Kenntnis des Oberpalaeozoikums in of Prof. E. ITOH. The geologists of the Yanahara Oestlichen Chugoku, Sudwest Japan. Geol. Rept. Hiro- mine, especially Mr. T. NAKANO and Mr. H. shima Univ. Ser. C, 12, 419•`443. 38 K. KASE, M. YAMAMOTO and C. MITSUNO RESOURCE GEOLOGY.

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柵原鉱山におけるGeを含むコルース鉱の産出とその鉱床成因論的意義

加瀬克雄・山本雅弘・光野千春

要旨:閃亜鉛鉱重晶石に富む柵原鉱山火の谷L-1鉱体物はフェルシックな火山活動と成因的関連を有する黒鉱にはGeを最大4.3wt%含むコルース鉱が黄鉄鉱黄銅鉱鉱床では,黄鉄鉱黄銅鉱,斑銅鉱と共生して時々産出す斑銅鉱に伴って産出する.コルース鉱のEPMAによる分析る.マフィックな火山活動と成因的関連を有する別子型結果は,AsおよびVは+5価,Geは+4価で含まれ,この鉱鉱床の鉱体の一部には,高いfO2環境で生成されたと考え物は高いfS2,fO2の環境で沈殿したことを示唆する.Geをられる部分もあるが,Geを含む鉱物をほとんど産しない, 含む硫化鉱物であるゲルマン鉱とレニエル鉱の既存の化柵原火の谷L-1鉱体のコルース鉱はフェルシックな火山学組成データと鉱物共生は,両鉱物ともコルース鉱と類活動に関係して生成された熱水溶液から沈殿したものと. 似した環境で沈殿することを示す,これらのGeを含む鉱結論される.