Coupled substitutions in goldfieldite-tetrahedrite
minerals from the Iriki mine, JapanMASAAKISHIMIZU

University Museum, University of Tokyo, Tokyo 113, JapanAND
CHRISJ.

STANLEY

British Museum (Natural History), London SW7 5BD, U.K.
Abstract

Chemical compositions of goldfieldite-tetrahedrite series minerals from the Iriki mine in Japan arereported for the frst time. The compositional variations of coexisting goldfieldite [atomic proportion
Te > (Sb + As + Bi)], tellurian tetrahedrite [Sb > (Te + As + Bi)], and Te-free tetrahedrite from thislocality are considered alongside data from the literature. These show that the substitution of (Sb,As) 3+ for Te 4+ in natural goldfieldite-tetrahedrite series minerals occurs by the following two99.
+2+3++3+;4+mechanisms: 0) tetrahedrlte, Culo(Cu,Fe,Zn)2 (Sb,As)4 $13 and goldfieldlte, Culz(Sb,As)e Te e $13form a continuous solid-solution according to the coupled substitution of Cu+Te ;4+ for(Cu,Fe,Zn)Z+(Sb,As)3+, and (ii) goldfieldite, Cu~-2(Sb,As)3§and the ideal end-member,Cu[oTe~+Si3 might also form a continuous solid-solution by the coupled substitution ofD(vacancy)Te ;4+ for Cu+(Sb,As) 3+. According to this work, the general formulae of tellurian
9+2+3+tetrahedrlte
and goldfieldlte
are, therefore, respectwely,
Cul0+x(Cu,Fe,Zn)z_x(Sb,As)4xTex4 + $13,
9+4+3+-"with x = 0 to 2 and Cu12_yTe2+y(Sb,As)2_sS~3, wath y = 0 to 2.
K EYw ORDS : goldfieldite-tetrahedrite series, coupled substitutions, Iriki mine, Japan.

Introduction

THE tetrahedrite structural formula can be represented in ~geeneral as: (Cu,Ag)~G[Cu4(Fe, Zn,Cd,Hg)21~6 (Sb,As,Bi,Te)~4sM-(S,Se)xt3,in
which TRG refers to trigonal, TET tetrahedral,and SM semi-metal sites, as mentioned, forexample, by Sack and Loucks (1985). Goldfieldite was first reported by Ransome (1909)
from Goldfield, Nevada, U.S.A., and Thompson(1946) confirmed that this mineral has the tetrahedrite structure on the basis of X-ray powder
diffractometry. Although many studies of thechemical composition of tetrahedrite and tellurJan tetrahedrite have been made (e.g. Charlat andLdvy, 1974; Ixer and Stanley, 1980; Pattrick andHall, 1983; Johnson et al., 1986), those ofgoldfieldite are few (e.g. from Goldfield in Ldvy,
1967, and Kato and Sakurai, 1970; from Butte,Montana, U.S.A. in Springer, 1969, Criddle andStanley, 1986; from Kawazu, Japan in Kato andSakurai, 1970; from Sardinia in Frenzel et al.,
1975; from U.S.S.R. in Tsepin et al., 1977;

Novgorodova et al., 1978; Kovalenker et al.,
1979, 1987; Loginov etal., 1983; Spiridonov etal.,
1984; Sakharova et al., 1984; lgumnova, 1986).
Moreover, many of these data deviate fromstoichiometry and the charges do not balance,probably because of uncertainty in electron
microprobe analyses, impurity, Cu vacancy, andoxidation.
Kase (1986) reports ten chemical compositionsof tellurian tennantite from Japanese Besshi-type
deposits, and Knittel (1989) shows one analysis ofarsenian goldfieldite and three of tellurian tennantite from the Marian gold deposit in Philippines. These data illustrate the coupled substitution (Cu,Fe,Zn)2+(As,Sb) 3+ ~ Cu+Te 4+, as
experimentally shown by Kalbskopf (1974).
This paper reports chemical compositions ofgoldfieldite-tetrahedrite series minerals from theIriki mine, Kagoshima Prefecture, Japan, anddiscusses the substitution mechanism of (Sb,As)for Te in natural goldfieldite-tetrahedrite series
minerals9

Mineralogical Magazine, December 1991, Vol. 55, pp. 515-519,~ Copyright the Mineralogical Society

516

M. SHIMIZU AND C. J. STANLEY
Table

Occurrence of goldfieldite--tetrahedrite

I

Chemicaltetrahedrite

The Iriki mine is located in a post-Miocene
epithermal A u - A g mining area in the southernpart of Kyushu, Japan. The deposits of the Iriki
mine were worked for A u - A g - C u in 1917, butlater worked for kaolin and closed in the 1950s.
The mineralisation was composed of auriferous
pyrite-quartz veins and argentiferous pipe-likebodies (Uetani et al., 1966). Kinoshita and Kim(1938) gave a brief description of the geology andore deposits of the mine; the deposits lie within abrecciated rhyolite dike which cuts hornblendepyroxene andesite. The latter is overlain mainly
by Miocene tuff and mudstone, and all these arecovered by Recent volcanic ash and pumice
deposits. The rhyolites are strongly silicified andsurrounded by kaolinised areas.
Goldfieldite and tetrahedrite occur in twoforms in the argentiferous pipe-like bodies. Massive goldfieldite contains tiny inclusions of nativetellurium (up to 1.0 wt.% Se), hessite (up to 0.8wt.% Se), and hemusite of about 10 ~tm across,and rims strongly silicified rhyolite breccias in thecenter of the pipe-like bodies. This goldfieldite issurrounded by concentric bands of (i) goldfieldite-native-tellurium-hessite-hemusite, (ii)tetrahedrite, (iii) tetrahedrite--famatinite, (iv)
tetrahedrite-famatinite-chalcopyrite, and (v)chalcopyrite-pyrite-marcasite-sphaleritegalena, from the centre to the rim, and all these
coexist with quartz. The goldfieldite-bearing band
can be further subdivided into four goldfielditedominant zones ranging from 3 mm to 5 mm inwidth. Goldfieldite does not contain inclusions
near its boundary with tetrahedrite. Here, goldfieldite occurs as euhedral grains of about 100 ~tm
in size.
Another, though rare, occurrence of goldfieldite is as networks coexisting with hemusite,
pyrite, marcasite, chalcopyrite, sphalerite, and an
unknown mineral in the strongly silicified rhyolite
breccias.
Chemical composition
Because goldfieldite often includes minutetellurium phases such as native tellurium andhessite, the polished sections were carefully
examined under the microscope at high magnification both in air and oil. The compositions werecross-checked by electron-microprobes of Cambridge Instruments Microscan IX at the British
Museum (Natural History) and JEOL 733II at theGeological Institute, Faculty of Science, University of Tokyo, using the conditions as mentionedin Harris et al. (1984) and Shimizu et al. (1988).
Te-L~ counts were corrected for partial overlap
by Sb-L~ in the minerals.

fromcomposition
theIrikiof T e - f r e emine,Japan.

12

345

Cu
AgFeZnMn
Cd
SbAs
SnBiSSe
total

46.00
0.07
0.30
0.29

44.35
0.10
0.99
0.10

45.90
0,08
0,44
0.31

46.10
0.13
0,28
0,01

43.13
0.08
2.46
0.16

1.00

0,40
0,02
23.82
3.54
0,22

Atomicproportions

Cu
AgFe
Zn
Mn
Cd
SbAs
SnBiSSe
mol.%
tetr
tenn

11.925
0.010
0,089
0.072
0,168
0.002
3.227
0,748
0.031

0,56
0.01
23.85
3.400.23
24.59
0.46
99.76

23.83
3,47
0.17
24.71
0.72
99,44
based

24.48
0.71
99.92
on

29

0.41

1.04

22.65
4.40
0,46
25.52
0.24
100.20

22.43
5.61
0,ii
25.23
0.53
100.78atoms,

11,901
0.012
0.130
0,077
0.120
0.003
3,221
0,779
0.031

12,6320.096

11.509
0,015
0.292
0,025
0.300
3.227
0.763
0.013
12,7060.150

11.951
0.011
0.710
0.039
0.305
2,972
1,202

12.5770.148

11.786
0.019
0.081
0,003
0,122
3.022
0.954
0.036
12,929
0.049

80.6
18.7

80.6
19.1

79.9
19.3

75.3
23,8

71.1
28.7

0.008
12.694
0.108

Representative chemical compositions of Tefree tetrahedrite from the Iriki mine are shown in
Table 1. The tetrahedrite end-member moleculein the mineral ranges from 62.4 to 89.6 mol.%(no. of analysis, n = 8), and the number of copper
atoms ranges from 10.95 to 11.85, based on a unit
formula of 29 atoms. The empirical formulae on
the basis of total atoms = 29 (Table 1) are all closeto CuI2(Sb,As)4SI3.
Representative chemical compositions of tellurian tetrahedrite and goldfieldite are shown in
Table 2. The number of copper atoms in tellurian
tetrahedrite is also greater than ten, ranging from10.75 to 11.96 (n = 10), and in goldfieldite is from10.75 to 12.01 (n = 19). The tellurium content of
the latter is up to 18.5 wt.% corresponding to
59.9% of the goldfieldite end-member molecule(no. 8 in Table 2).
The empirical formulae of tellurian tetrahedrite are close to Cu12(Sb,As,Te)4S13 (nos. 1 to
3 in Table 2), and those of goldfieldite are close toCu12(Te,As,Sb)4S13, with Te < 2 (nos. 4 to 6 inTable 2) and Cu12_x(Te,Sb,As)4S13, with Te = 2
to 2.74, x ~< 0.67 (nos. 7 to 11 in Table 2). Notethat Z(Cu + Ag + Fe + Zn + Mn) atoms is lessthan twelve in the case of Te > 2.

Substitution of (Sb,As) for Te in natural
goldfieldite-tetrahedrite series minerals
The relationship between the proportion of Teand (Sb + As + Bi) in goldfieldite-tetrahedrite

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M. S H I M I Z U A N D C. J. S T A N L E Y

518

C\X~J11o~./Te + Sb + As + Bi :/+265Te 4+~0132(Sb + A s + B i ) 3§
FIG. 1. Relationship between Te and (Sb + As + Bi) ingoldfieldite-tetrahedrite from the Iriki and Kawazu
mines, Japan. Numbers on the figure correspond to thenumbers of the analyses in Table 2.

from the Iriki and Kawazu mines, Japan, verifies
the substitution of (Sb + As + Bi) by Te (Fig. 1),
through which the charge balance is not attained.
Fig. 2 reveals Z(Cu + Ag + Fe + Zn + Mn)
atoms is less than twelve in the case of Te > 2.
Kalbskopf (1974), on the basis of an X-ray
study of synthetic goldfieldite-tetrahedrite,
pointed out that the substitution of Sb by Te
is coupled with a decrease in Cu TRG until
theend-member
goldfieldite
formula1110OO098o

7o2

Te5~

TET~

TRG~o

U6 %U6_xle4313 , with x = 2, is reached.
N o v g o r o d o v a et al. (1978), Johnson (1982), Kase(1986), and Knittel (1989) confirmed the coupled
substitution of (Cu,Fe,Zn)2+(As,Sb) 3+ forC u + T e 4+ in natural tellurian tennantite, and ourdata confirm this and also extend it to include
tellurian tetrahedrite. Also this paper first confirms the coupled substitution of Cu+(As,Sb) 3+for V3(vacancy)Te 4+ in natural goldfieldite with
Te = 2 to 2.74, based on Z(Te + Sb + As + Bi) =4. Chemical analyses of Springer (1969), Tsepinet al. (1977), N o v g o r o d o v a et aL (1978), Kovalenker et al. (1979, 1987), and Knittel (1989)
indicate the occurrence of the Cu vacancy as
discussed by Kalbskopf (1974) and Johnson(1982), and some of these authors mention thatthe extra charge caused by substituting Te 4+ for
Sb 3+ may be compensated by the Cu vacancy.
H o w e v e r , their data show the Cu vacancy tooccur whether or not the number of Te atoms isgreater than two, based on Z(Te + Sb + As + Bi)= 4, and, m o r e o v e r , do not permit the chargebalance to be maintained.
As shown in nos. 7 to 11 in Table 2, the generalformulae of natural goldfieldite with Te > 2 fromthe Iriki and Kawazu mines, Japan are represented by Cu12_x(Te,Sb,As)4S13, with x ~< 0.67.
The tabulated data also demonstrate the two-step
substitution of (Sb,As) for Te in the goldfieldite.
.
.
.
.
+
tetrahednte series, i.e. 0) tetrahednte, Cum(Cu,2+3++Fe,Zn)2 (Sb,As)4 S13 and goldfieldlte, Cu123+4+,(Sb,As)2 Te2 S13 form a continuous sohd-solution according to the coupled substitution of(Cu,Fe,Zn)2+(Sb,As)3+ ~ Cu+Te 4§ as reported
by N o v g o r o d o v a et al. (1978), Johnson (1982),and Kase (1986), and (ii) goldfieldite, Cuaz(Sb,As)23+Te4+S13 and the ideal end-member,Cu~0Te4~S13, only known as a synthetic phase,
also form a continuous solid-solution series by thesubstitutionofCu+(Sb,As) 3+~-~[3(vacancy)Tea+
The general formulae of tellurian tetrahedriteand goldfieldite are respectively therefore,+2+344+
C U l o + ~ ( F e , Z n ) 2 _ ~ ( S b , A s ) 4 _ x T e x $13, with x =+4+3+
with0 t o 2 and Cu12 yTe2_ y(Sb,As)2_yS13,y=0
to 2.

Acknowledgements
0li,512.0"

189Eu + Ag + Fe + Zn+ Mn
Fie. 2. Relationship between Te and (Cu + Ag + Fe +Zn + Mn) in goldfieldite-tetrahedrite from the Iriki andKawazu mines, Japan. Numbers on the figure correspond to the numbers of the analyses in Table 2.

We are grateful to Dr. A. Kato for permitting us toanalyse the Kawazu specimens, to Drs. A. J. Criddle,M. Gunnesch and P. Henderson for their criticalreading of the manuscript and Dr. C. T. Williams for hishelp with the electron microprobe analyses. One of us,M.S., thanks the Fujiwara Foundation offNaturalHistory for financial support and the Ministry ofEducation, Science and Culture of Japan for an
Overseas Research Fellowship.

GOLDFIELDITE-TETRAHEDRITE

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