Abstract
The mineral cuprostibite (Cu2...Sb) is found in pneumatolytic-hydrothermal veins associated with lujavrite at three localities. Cuprostibite occurs associated with loellingite, chalcopyrite, argentite, native silver and ?antimonian silver in analcime- ussingite-rich veins at the Taseq slope locality, with loellingite, chalcocite, dyscrasite, allargentum, galena and sphalerite in analcime-rich veins at the Kangerdluarssuk loeality and with loellingite, rohaite, sphalerite, silver (1), silver (2), allargentum, digenite, chalcocite and cuprite in analcime-rich veins at the Kvanefjeld locality. Supergene alteration of cuprostibite and some of the associated ore minerals has taken place. Cuprostibite occurs in granular masses. It has uneven fracture, a poor basal cleavage, purple colour, distinct metallic lustre, distinct reflectance pleochroism and strong, yellow, deep red to black-polarization colours. The microindentation hardness is 216-249 (VHN50g). Determined and calculated density 8.36 and 8.42 g/cm3, respectively. Cuprostibite is tetragonal, α 4.0000±0.0006 Å and c 6.1000±0.0017 Å. Microprobe analyses of two samples gave the formulae Cu2.02 Sb0.98 and Cu2.10 (Sb0.86T10.04) 0.9. Dyscrasite, allargentum, galena, sphalerite and an unnamed mineral [(Sb,Cu) 2(Pb,[Fe,Ca])Si0.4 (O,OH,H2O) y , y = max. 9.6] occur in very small amounts in association with cuprostibite at Kangerdluarssuk. Alteration of dyscrasite, allargentum and associated cuprostibite has resulted in the formation of antimonian silver as host for senarmontite, cuprite and native copper. Rohaite (TlCu5SbS2) from Kvanefjeld is a new mineral and is associated with chalcocite, euprostibite, antimonian silver, cuprite, loellingite, and sphalerite. The mineral is tetragonal with a 3.801 ±0.002 Å and c 20.986±0.008 Å. A superstructure has caused a doubling of the a cell dimension. Rohaite has been partly altered to an extremely fine-grained mixture of digenite and senarmontite having the bulk chemical composition: Sb2O3 x 3.86 CU1.93S1.00 with small contents of thallium, iron and lead. Supergene alteration of digenite and chalcocite at Kvanefjeld has resulted in the formation of two varieties of blaubleibender covellite (CU1.13S and CU1.42S), covellite and connellite. Djurleite (CU1.96S) has exsolved from the digenite. Supergene alteration of euprostibite has resulted in the formation of senarmontite, Sb-malachite, cuprites and native copper. Senarmontite occurs as very fine-grained material intergrown with an unidentified copper-antimony mineral. Sb-malachite may possibly be a submicroscopic mixture of normal malachite and an unidentified Sb-rich phase. 'Cuprites' comprise normal cuprite and closely associated phases containing variable amounts of antimony, Lead and silicon. Connellite, brochantite, linarite and senarmontite are supergene. Cell dimensions and microprobe analyses for connellite and linarite are listed.
Highlights
The minerals chalcothallite and cuprostibite were described as new minerals by Semenov et al (1967) and Sørensen et al (1969) respectively
In 1968 cuprostibite was found in an analcime vein on the Kvanefjeld plateau to the north of the Taseq slope, and in 1970 relatively large quantities of this mineral were found in analcime-aegirine veins at the head of the Kangerdluarssuk fjord in the southern part of the intrusion
Several primaryand secondary ore minerals occur associated with cuprostibite
Summary
The minerals chalcothallite and cuprostibite were described as new minerals by Semenov et al (1967) and Sørensen et al (1969) respectively. These minerals were discovered in 1964 in ussingite veins on the Taseq slope in the northern part of the Ilimaussaq intrusion in South Greenland Several primaryand secondary ore minerals occur associated with cuprostibite. Those at the type locality for cuprostibite on the Taseq slope have been mentioned by Sørensen et al (1969), those at the other two localities of Kvanefjeld and Kangerdluarssuk are described here.
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