Naujakasite from the Ilímaussaq alkaline complex, South Greenland, and the Lovozero alkaline complex, Kola Peninsula, Russia: a comparison Alexander P. Khomyakov, Henning Sørensen, Ole V. Petersen and John C. Bailey Naujakasite, Na6(Fe,Mn)Al4Si8O26, long known from the Ilímaussaq alkaline complex, South Greenland, was not reported until 1999 from other occurrences of alkaline rocks in spite of the fact that the mineral is composed of common elements. In 1999, a variety of naujakasite rich in Mn was found in the Lovozero alkaline complex in the Kola Peninsula, Russia. This variety has 2+ been approved by the IMA as a new mineral, manganonaujakasite, Na6(Mn0.53Fe 0.47)Al4Si8O26. At Ilímaussaq naujakasite is a rock-forming mineral in the highly evolved rock naujakasite lujavrite in which it may make up more than 75 vol.%; at Lovozero manganonaujakasite is a very rare constituent in mineralised lovozerite–lomonosovite lujavrite. Naujakasite appears to take the place of nepheline in hyper-agpaitic nepheline syenites characterised by exceptional- ly high Na/K ratios. The nepheline syenites at Ilímaussaq have an average Na/K (atomic) ratio of 3.08, and the naujakasite lujavrites have the extreme ratio 4.56. The nepheline syenites of the Khibina and Lovozero complexes are characterised by lower Na/K ratios, 1.27 for Khibina and 1.67 for Lovozero, and thus nepheline is stable in the hyper-agpaitic rocks and naujakasite occurs only in pegmatites. A.P.K., Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements, Veresaev Street 15, Moscow 121357, Russia. E-mail: [email protected] H.S. & J.C.B., Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. O.V.P., Geological Museum, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copen- hagen K, Denmark. Keywords: agpaite, hyper-agpaite, Ilímaussaq, Lovozero, lujavrite, manganonaujakasite, nau- jakasite, nepheline syenite The Ilímaussaq alkaline complex is the type locality presented the first set of unit cell parameters. Nauja- for naujakasite, Na6(Fe,Mn)Al4Si8O26. For half a centu- kasite was first found in outcrop in 1955 (Danø & ry, the only known specimen of this mineral was a Sørensen 1959). Based on the new material a com- boulder weighing 350 gram, collected in 1897 by the plete redescription, including a redetermination of the Swedish mineralogist G. Flink at the small peninsula unit cell parameters, was given by Petersen (1967), and Naajakasik (then Naujakasik) on the south coast of the structure was worked out by Basso et al. (1975). the Tunulliarfik fjord, well within the complex (see Naujakasite is now known to be of widespread Sørensen 2001, this volume for a map of the localities occurrence in the Ilímaussaq alkaline complex in the mentioned in the text and a brief description of the rock called naujakasite lujavrite (see further below) complex). Flink’s original label tentatively identified and may constitute more than 75 vol.% of that rock. the silvery white mica-like mineral that constituted 75% Because naujakasite is composed of the common ele- of the boulder as ‘chlorite?’. Bøggild (1933) established ments Na, Fe, Mn, Al and Si, it is surprising that for this phase as a new mineral and named it after the 100 years naujakasite was a single locality mineral. In place where it was found, and Gossner & Krauss (1933) 1998, the first discovery of the mineral outside Ilímaus- Geology of Greenland Survey Bulletin 190, 95–108 (2001) © GEUS 2001 95 saq was made by one of the authors (A.P.K.) in the cal conditions show practically identical sets of lines Lovozero alkaline complex, Kola Peninsula, Russia. and relative intensities. The unit cell parameters of The present paper describes the mineralogy and naujakasite from Lovozero are almost identical to the occurrence of naujakasite in the two complexes and parameters determined by Basso et al. (1975) for Ilí- discusses the stability relations of the mineral. maussaq (Table 1); see also Khalilov et al. 1977). The chemical analyses of the Ilímaussaq naujaka- site published by Bøggild (1933), Petersen (1967) and Semenov (1969) show that it has a very high Fe/Mn Mineralogy ratio: around Fe0.90Mn0.10 in the structural formula. The The mineralogical properties of naujakasite from the Lovozero mineral, on the other hand, is dominated Ilímaussaq alkaline complex and naujakasite from the by Mn. Recalculated on the basis of 26 oxygen atoms, Lovozero alkaline complex are compared in Table 1. the empirical formula of the naujakasite from Lovoze- X-ray powder diffraction patterns of naujakasites ro has Fe0.49Mn0.53 (Table 2). The Lovozero mineral is from Ilímaussaq and Lovozero obtained under identi- thus the Mn-dominant analogue of the Ilímaussaq 96 geology of the Kvanefjeld area based on surface map- ping and the examination of 42 drill cores from drill- ing programmes in 1958 and 1969. Several varieties of lujavrites are distinguished (Fig. 1). Naujakasite-bear- ing lujavrite outcrops in the northernmost part of the Kvanefjeld plateau and at its southern edge in the upper part of the slope facing the Narsaq Elv valley. In the first-named area, there is a succession of luja- vrites which form zones running parallel to the contact against the volcanic country rocks to the north. Nauja- kasite lujavrite occurs as a zone of crumbling, brown- ish-black lujavrite which is separated from a fine-grained, fissile arfvedsonite lujavrite to the north by a mixed zone made up of alternating bands of these two rock * Recalculated to 100% assuming all iron present as FeO, types. The naujakasite lujavrite is ten or more metres and disregarding the results of the thermogravimetric wide and can be followed for over a hundred metres. It analysis. is intersected by rare veins of green medium- to coarse- † From Petersen (1967). grained lujavrite and contains xenoliths of augite syen- ‡ Analyst: G.N. Nechelyustov. Electron microbe analysis, Superprobe 733. ite, foyaite, naujaite and contact metasomatised vol- canic rocks from the roof of the complex. The nauja- Empirical formulae kasite lujavrite in the southern part of the Kvanefjeld Ilímaussaq: plateau occurs mainly as thin sheets intruding naujaite (Na5.72K0.10)Σ5.82(Fe0.74Mn0.15Ca0.05)Σ0.94(Al3.91Si8.13)Σ12.04O26 and augite syenite with sharp, but not chilled contacts. Lovozero: Na (Mn Fe Ca ) Al Si ) O 5.96 0.53 0.49 0.01 Σ1.03 3.95 8.03 Σ11.98 26 At Tupersuatsiaat and the Taseq slope in the Nar- saq Elv valley, naujakasite lujavrite forms minor intru- naujakasite, and manganonaujakasite has been ap- sions in naujaite (Engell 1973). proved as a new mineral by the Commission of New Petersen & Andersen (1975) described an occur- Minerals and Mineral Names of the International Min- rence of naujakasite located about 1 km south-east of eralogical Association (Khomyakov et al. 2000). Tupersuatsiaat. They distinguish three modes of occur- rence: (1) as an accessory mineral in arfvedsonite lu- javrite, that is naujakasite-arfvedsonite lujavrite; (2) as a naujakasite-rich contact facies of lujavrite against a The occurrence of naujakasite in the large xenolith of naujaite, containing plates of nauja- Ilímaussaq alkaline complex kasite up to 2 cm in size and constituting up to about The first outcrop of naujakasite-bearing rocks was 75 vol.% of the rock; (3) composite flakes of naujaka- found by one of the authors (H.S.) in the bay of Tu- site in recrystallised naujaite enclosed in naujakasite persuatsiaat and described by Danø & Sørensen (1959). lujavrite. The last-named type of naujakasite contains Shiny rhomb-shaped flakes of naujakasite, up to 0.2 inclusions of nepheline which are arranged in a hex- cm across, are scattered throughout a thin dyke of agonal pattern. fine-grained arfvedsonite lujavrite intersecting a len- The only observation of naujakasite in a hydrother- ticular body of naujaite. mal vein is reported by Metcalf-Johansen (1977) who Bondam & Sørensen (1958) and Buchwald & Sø- found the mineral in an albitite vein in the roof basalt rensen (1961) described an occurrence of naujakasite to the east of Kvanefjeld. The vein consists of albite, lujavrite from an altitude of 400 m in the mountains microcline, aegirine, arfvedsonite, analcime, natrolite, south of Tupersuatsiaat. Ferguson (1964) reported that apatite, chkalovite, sphalerite, hemimorphite, wille- naujakasite lujavrite is quite common on Kvanefjeld mite, monazite, neptunite and Li-mica. Rhomb-shaped where it forms minor horizons rarely wider than 50 m crystals of naujakasite occur in miarolitic cavities in and usually only 5–10 m wide. Petersen (1967) pre- the albitite. These crystals measure 2 × 3 × 0.4 mm. sented the first detailed mineralogical description of Nyegaard (1979), Makovicky et al. (1980) and naujakasite from Tupersuatsiaat and Kvanefjeld. Kunzendorf et al. (1982) report results of mineralogi- Sørensen et al. (1969, 1971, 1974) described the cal and chemical studies of naujakasite lujavrite in cores 97 1 7 19 39 mmm0 0 0 m0 Volcanic roof 10 10 10 Altered rocks of 10 volcanic roof 20 20 20 Augite syenite 20 Medium- to coarse- 30 30 30 grained lujavrite 30 40 40 40 Aegirine lujavrite 40 50 50 50 Arfvedsonite lujavrite 50 Naujakasite lujavrite 60 60 60 60 Naujaite 70 70 70 70 Analcime vein 80 80 80 80 Late dyke 90 90 90 90 100 100 100 100 110 110 110 110 N 120 120 3 km 120 130 130 130 39 140 140 N 140 300 m 19 7 150 150 1 150 160 160 160 170 Inland ice 170 180 61ºN 61ºN 180 Gardar intrusions 190 190 60ºN 60ºN 100 km 48ºW 44ºW 200 200 98 from a drilling programme in 1977 in the northern- ding to Nyegaard (1980) the adit intersects naujaka- most part of the Kvanefjeld area.