Eclarite from Bleka, Svartdal, Telemark county, Norway
Alf Olav Larsen1 & Dan Topa2
1Bamseveien 5, N-3960 Stathelle, Norway (alf.olav.larsen@online.no)Zentrale Forschungslaboratorien/Mineralogisch-Petrographische Abt., Naturhistorisches Museum,Burgring 7, A-1010 Wien, Austria
2

Introduction
Eclarite, (Cu,Fe)Pb9Bi12S28, was described as a new mineral species from Bärenbad, Achsel-Alm,
Austria by Paar et al. (1983). It is regarded as a rare mineral, and apart from the type locality it hashitherto been reported in minute amounts from Felbertal, Austria (Topa 2001), from Hviezda, the Low
Tatras, Slovak Republik (Pršek et al. 2008), from Turtman Valley, Wallis, Switzerland (Ansermet2012), from Dragoons Mts., Cochise Co., Arizona, USA (Anthony et al. 1995) and Crabtree quarry,
Wake Co., North Carolina, USA (http://rruff.info). Typically, the occurrences are sulphide andsulphosalt bearing quartz veins.
In the early 1970’s one of the Bleka quartz veins which locally contained significant amounts of ore
minerals was investigated by mineral collectors. In early 2014 one of the authors (AOL) was asked toidentify a fibrous sulphosalt collected about 40 years earlier from the locality. This resulted in theidentification of eclarite and subsequently the present description of this rare mineral as the first
documentation of eclarite in Norway.

Occurrence
The gold-bearing deposit at Bleka, Svartdal in Seljord community, Telemark, was discovered in the1870’s. Mining was initiated in 1882 and continued until 1901. A second period of mining lasted
1933-1940 (Dons 1963, Åsbø 1975, Berg & Nordrum 1985). The mining was carried out along a few
main veins.
The Bleka deposit consists of quartz veins with chlorite, tourmaline and carbonates (calcite, ankerite,dolomite, siderite) as the main minerals. About 20 veins are known within the Bleka area. They varyfrom a few cm to 2.5 m, have a general NE to ENE strike and dip rather steep. The Bleka vein system
has been traced for 1100 m in the terrain and occurs in shear fractures of the Bleka metagabbro, which
is a 1-2 km wide and more than 15 km long gabbroic sill emplaced within the Proterozoic Seljord
group metasediments. The veins usually show strong zonation with quartz and chlorite close to themargins. Then follow inwards bands and zones of tourmaline (usually finely needleshaped), while thecentral part of the veins consists of carbonates. Some veins or parts of veins may, however, deviate
from this pattern. Dahlgren (2015) reported that scheelite is a common accessory mineral in the gold
bearing parts in the Bleka deposit. Ore minerals include chalcopyrite, bornite, pyrite, bismuthinite,
cosalite, clausthalite, emplectite, lillianite, galenobismuthite, gladite, krupkaite, galena, silver andsilver bearing gold (electrum) (Bugge 1935, Dons 1963, Selbekk 2010). However, no thorough studyof the ore minerals has been carried out and some of the previous sulphosalt identifications may bequestionable. In addition to eclarite, the present study confirms the occurrence of tsumoite at Bleka.

65The eclarite-bearing quartz vein occurs in the E-adit, the westernmost adit in the Bleka main mining
complex. At the entrance of the adit, where eclarite was collected, the quartz vein is 10-15 cm wide,strikes N70° and dips 70° NW (Fig. 1). Associated minerals include chalcopyrite, galena, tsumoite,gold, chlorite and ankerite. The sulphides and sulphosalts are mainly concentrated along the vein
margins.

Fig. 1. The entrance of the E-adit at Bleka. The steeply dipping eclarite bearing quartz vein is visibleon the right hand side of the adit. Photo: A.O. Larsen.

Physical properties
Eclarite from Bleka occurs as acicular crystals up to 5 mm in length, often as fan-shaped aggregates,
embedded in quartz. The crystals are heavily striated parallel the elongation. The mineral has a brighttin-white colour and metallic lustre, but tarnishes relatively quickly when exposed to humidity. Thehardness is 2.5, and calculated density (based on the unit cell dimensions and elemental composition)is 6.99 g/cm3.

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X-ray crystallography
The crystal structure of eclarite was first studied by Kupčik (1984) and later refined by Topa &Makovicky (2012). The mineral is orthorhombic, space group Pmcn. The Bleka eclarite was initiallyidentified from its characteristic PXRD pattern. Indexing and least-squares refinement were done by
the program CELREF (Laugier & Bochu 1999) using 27 diffraction lines with I/I0 > 10 within therange 20º - 60º 2θ. Quartz was used as internal standard. The unit cell dimensions found are a =4.0454(9) Å, b = 22.710(5) Å, c = 54.734(10) Å, V = 5028.5(1.8) Å3. These data are very close to
those given by Kupčik (1984) and Topa & Makovicky (2012).

Chemical composition
Quantitative chemical analyses of eclarite from Bleka were obtained with an electron microprobe. The10 point analyses reveal that the mineral has a fairly homogeneous composition and the results are
given in Table 1. The chemical formula, based on 20.85 large cations (Topa & Makovicky 2012), isCu1.46Fe0.10Ag0.13Pb7.82Bi12.64Sb0.24S27.69.

Table 1. Chemical composition(in wt.%, n.a. = number of analyses)of the Bleka eclarite

CuAgFePbBi
SbS
total

wt.%
(n.a.=10)
1.75
0.27
0.11
30.64
49.88
0.55
16.76
99.97

s.d.
0.04
0.10
0.02
0.27
0.28
0.07
0.12
0.11.

Conclusion
The present study shows that the complex Bleka deposit definitely has the potential of revealing
interesting sulphosalts. Many of the previously reported Bi-sulphosalts need further investigation
using modern analytical tools.

Acknowledgements
We are indebted to Fred Steinar Nordrum and Thore G. Pedersen for paying attention to thissulphosalt and subsequently supplied the sample for this investigation. Thanks to the proprietors of theBleka farms, Stein Schjelle and Nils Jørgen Hardang, respectively, for their positive attitude towards
field work and sampling.
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