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BADDELEYITE — Zro2 — from LOVASJÄRVI DIABASE, SOUTHEASTERN FINLAND

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BADDELEYITE — Zro2 — from LOVASJÄRVI DIABASE, SOUTHEASTERN FINLAND BADDELEYITE — ZrO2 — FROM LOVASJÄRVI DIABASE, SOUTHEASTERN FINLAND JAAKKO SIIVOLA SIIVOLA, JAAKKO 1977: Baddeleyite — ZrO-2 — from Lovasjärvi diabase, south-eastern Finland. Bull. Geol. Soc. Finland 49: 59—54. Baddeleyite is described from a basic intrusion from southeastern Finland. Microprobe analyses resulted in the following chemical composition besides ZrO>: HfOs 0.9—1.5, FeO 0.2, Ti02 < 0.1 and AI2O3 <0.1 percent. The mineral occurs together with zircon and quartz. Comments concerning this mineral paragenesis are pre- sented. Jaakko Siivola, Geological Survey of Finland, SF-02150 Espoo 15, Finland. Introduction nan, western Finland, (Dr. O. Kouvo and Mr. M. Vaasjoki, pers. comm., 1976). Baddeleyite, ZrO , has been described as ä This note is concerned with an occurrence an accessory mineral from very different of baddeleyite in a diabase from southeastern types of occurrences most of which are silica- Finland. Microscopic determinations and free or -poor rock types. It has been re- heavy mineral separations confirm that in corded in ultrabasic rocks (kimberlite, ilme- this case baddeleyite appears to be the nitenorite), carbonatites, alkali syenites, major Zr-bearing phase. sanidine lavas and granitic pegmatites. It has also been reported from placers, impact glasses, tektites, and especially from lunar Geological environment rocks (basalts). Recently, baddeleyite has been described also from terrestial gabbroic A differentiated basic intrusion, here call- rocks by Keil and Fricker (1974). ed the Lovasjärvi diabase, is situated be- In Finland baddeleyite has formerly been tween the large Wiborg and the smaller identified from the Sokli carbonatite (Paar- Suomenniemi rapakivi massifs in south- ma, 1970), and lately from the Porttivaara eastern Finland, (see Geological Map of Fin- albite diabase, northeastern Finland (Dr. O. land, Pre-Quaternary Rocks. Sheet 3132- Kouvo, pers. comm., 1976) and from the Savitaipale. Simonen and Tyrväinen, 1965). Jotnian diabases from Säppi and Sorkka, The trend of the diabase »dike» is N 45° Wi. southwestern Finland and from Norrgrun- Thus it coincides with the general trend of 60 Jaakko Siivola the diabase dike set described by Laitakari Mineral description (1969). The length of the intrusion is about 5 km and the width does not exeed 1 km. Baddeleyite was first detected optically in The diabase is in contact with both rapakivi a polished thin section of the Lovasjärvi granites mentioned above. Geologically it is diabase. The identification was confirmed clearly older than the rapakivi intrusions. by using the electron microprobe and X-ray This fact is verified by the eruptive breccias diffraction methods. Afterwards, the heavy and rapakivi veins in diabase which are met mineral separations made for the dating with at the both ends of the Lovas järvi proved that baddeleyite predominates over diabase »dike». The radiometric age of the zircon. diabase (1650 M.a., U-Pb age from zircon) Baddeleyite occurs as inclusions in slightly agrees with that of the rapakivi within the sericitized plagioclase (An 40—50), in frac- limits of error. The petrographic description tures between other mineral grains and in of the Lovasjärvi diabase will be given else- contact with quartz and zircon (Figs. 1—4). where in near future. Sometimes baddeleyite grains have a zircon 0,1 mm Fig. 1. Euhedral baddeleyite as an inclusion in F:'g. 3. Zircon mantled anhedral baddeleyite. Cf. slightly sericitized plagioclase. Photo E. Halme. the X-ray scanning images in Figures 5. Photo E. Halme. x i - * Fig. 2. Twinned baddeleyite between quartz and Fig. 4. Rodlike baddeleyite in plagioclase. Photo apatite. Cf. the X-ray scanning images in Figure E. Halme. 6. Photo E. Halme. Baddeleyite — ZrO> — from Lovasjärvi diabase, southeastern Finland 61 mantle as shown in Figure 3 (cf. X-ray mineral grains, resulted in the following scanning images of the same mineral grain chemical composition (besides Zr02): Hf02 in Figure 5.). The mineral commonly Shows 0.9—1.5, FeO 0.2, TiO, < 0.1 and A1203 < 0.1 a euhedral habit (Fig. 1) but, on the other weight percent. No other elements were hand, subhedral to anhedral grains are not detected. The chemistry of the Lovasjärvi rare (Figs. 2—4). Maximum length of the baddeleyite is also depicted by the X-ray euhedral baddeleyite crystals measures up to scanning pictures in Figures 5—6. Zr and Hf 0.4 mm. Prismatic baddeleyite is polysyn- are not always evenly distributed in bad- thetically twinned on the monoclinic (100) deleyite. This is depicted by the X-ray plane (Fig. 2). Untwinned grains are not scanning images in Figure 6. Baddeleyite very common. The colour of the mineral is grains, intimately intergrown with zircon, yellowish with a faint pleochroism from sometimes show small silica contents due to yellowish to pale brownish. zircon. Microprobe analyses, performed on several The crystal habit of baddeleyite is shown 62 Jaakko Siivola Fig. 6. Element distributions in baddeleyite. Zr Lai-, Hf Lai-, Fe Kai-, Si Ka-, AI Kai-, and Ca Kai- scanning images. Same grain as in Figure 2. Baddeleyite —• Zr02 — from Lovasjärvi diabase, southeastern Finland 63 Fig. 7. SEM-images (a — c) showing the tabular habit (d) of baddeleyite. X 260. in Figures 1—4, and the general morphology yite (monoclinic Zr02) is stable with zircon in Figures 7 a—d. X-ray single crystal below 1170° C. At Lovasjärvi the crystalli- determinations by Dr. M. Lehtinen and X- zation of the basic, iron rich magma commen- ray powder diffraction studies by Mr. P. ced with the formation of iron oxides and of Kallio gave the following unit cell parame- the olivine-bearing (Fo37Fa43) rock and conti- ters for baddeleyite (space group P2,/c): a0 = nued on decreasing temperature to more sili- 5.143 Ä, b0 = 5.213 Å, c0 = 5.312 Ä (± 0.01), ca-rich rocks. During this sequence the Zr- ß = 99°15', a„ : b0 : c0 = 0.986 : 1 : 1.019, with rich mineral phase appeared in the form of 3 V = 140.56 Å . baddeleyite. With increasing silica content in the melt baddeleyite crystals were at least Concluding remarks partly coated with zircon mantle. This phase The work of Butterman and Foster (1967) of crystallization is also characterized by suggests that in a silica-poor system baddele- baddelyite grains whidh are in contact with 64 Jaakko Siivola quartz. In the baddeleyite-bearing rock oli- quence baddeleyite, zircon and free quartz vine (Fo13Fa87) is still present as a minor con- is closely associated with the crystallization stituent. The final stage of the crystallization of the primary basic magma. of the Zr-rich mineral phase is the formation of zircon. It is worth while mentioning that Acknowledgements — The author is indebted to zircon crystals are transparent with beautiful, Dr. M. Lehtinen and Mr. P. Kallio for the X-ray tetragonal habit. diffraction studies, and to Mr. E. Halme for taking It may be concluded that the mineral se- the microscopic photographs. References Butterman, W. C. and Foster, W. R. (1967) Zircon Paarma, H. (1970) A new find of carbonatite in stability and the ZrOo-SiO? phase diagram. North Finland, the Sokli plug in Savukoski. Am. Min. 52: 880—885. Lithos 3: 129—133. Keil, K. and Fricker, P. E. (1974) Baddeleyite Simonen, A. and Tyrväinen, A. (1965) [Map of (ZrOa) in Gabbroic Rocks from Axel Heilberg Pre-Quaternary rocks], Sheet 3132 Savitaipale. Island, Canadian Arctic Archipelago. Am. Min. 59: 249—253. Geological Map of Finland, 1 : 100 000. Laitakari, I. (1969) On the set of olivine diabase dikes in Häme, Finland. Bull. Comm. Géol. Manuscript received, November 12, 1976. Finlande 241. .
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