ZIRCONOLITE (versus ZIRKELITE) IN LUNAR ROCKS, D. A. Wark*, A. F. Reid**, J. F. Lovering* and A. El Goresy***. *School of Geology, Univ. of Melbourne, Parkville, Victoria, Australia 3052; **Div. Mineral Chemistry, CSIRO, P.O. Box 124, Port Mel- bourne, Victoria, Australia 3207; ***Max-Planck-Institut fur Kernphysik, Postfach 1248, 69 Heidelberg 1, West Germany.

In a detailed study of the uranium-enriched phases present in the late-stage mesostasis regions of lunar basalts; Lovering and Wark [I] observed that the mineral character is tically showing the greatest uranium enrichment was a phase designated by them as "Phase B". On the basis of a preliminary microprobe analysis they further suggested that "Phase B" was possibly related to the min- eral zirconolite (CaZrTi 0 ) described by Borodin et-- al. [2] from amphibolized pyroxenites20? the Afrikanda massif of the Kola Penin- sula in the U.S.S.R. Other workers subsequently studied similar phases and referred to them in various ways (e.g. Phase B [3], Phase Y [4]) while Busche et al. [S] concluded that their analyti- cal data for the phase con5rsmore closely to the zirkelite formula (gener ii zd A~+B+05) than to the zirconolite formula (generalized A? B$ 07) . f he confusion of zirconlite versus zirkelite terminology in the lunar literature is paralleled by the confusion in the literature concerned with the terrestrial occur- rences of both minerals. However, new studies by Reid --et al. [6], based on the synthesis of zirconolite-structure phases (Table 1), have demonstrated that both synthetic and natural terrestrial phases have similar monoclinic structures (Table 2) and composi- tions (Table 3) which conform to the generalized formula

2+ 4+ 4+ (MI) (MII) (MIII)Z O7 in which: MI '+ = ca2+ and ~e", with minor 2+ 2+ Mg ,Mn ,co2+, etc. 4+ = zr4+, with minor U '+,~h~+,pb2+ I 4+ = Ti4+, with minor ~b~+,~a~+,~l~+,~r~+,etc. M~~~ The substantial amounts of y3+, REE~' present are distributed equally between and M 4+ sites gyd, as the temperature formation is increased, d&!tional Zr can go into the M 49f sites along with the Ti49 . Synthetic zirconolites formedla& 1300°C have Ti/Zr=2.75 while those formed at 1500°C have Ti/Zr=1.31 suggesting that Ti/Zr ratios in natural zirconolites could prove to be a sensitive geothermometer. If the terrestrial phases from the Russian occurrences vari- ously called zirconolite or zirkelite are structurally identical, as several authors have usggested [7] [8], t en these new studies confirm a zirconolite-type structure $1.e. A 9+~4~07) rather than a zirkelite-type structure (i.e. A~~B~05) for these phases.

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Consequently, zirconolite is the preferred name for this mineral species and zirkelite should no longer be used. New, detailed microprobe analyses of Phase B grains from lunar rocks are reported (Tables 4A and B). The analyses by Wark were carried out using synthetic zirconolites as standards for Ti, Zr, Ca, Fe, Y, Nb, etc. while in all analyses special attention was paid to unravelling the problems of complex line interferences for the REE's. These data illustrate the extremely complex chem- istry of Phase B (-30 elements with concentrations >0.1%) and con- firm a zirconolite-type structural formula for Phase B. The Ti/Zr ratio in lunar zirconolites ranges from 1.07 to 1.52 and indicates a temperature of formation of 1400-1450°C. A re-exami- nation of previously reported analyses for the similar lunar minerals designated Phase B [3], Phase Y [4] and "zirkelites" [5] [9] indicates that all can be reasonably calculated as zirconolites. An x-ray study of a 20 um zirconolite grain from mare basalt 10047,68 is currently in progress.

REFERENCES [I] Lovering, J. F. and Wark, D. A. "Uranium-enriched phases in Apollo 11 and Apollo 12 basaltic rocks," Proc, Second Lunar Science Conf., Geochim. et Cosmochim. Acta Suppl. 2, vol. 1, 151-158, 1971. [2] Borodin, L. S., Nazarenko, I. I. and Rikhter, T. L. "On a new mineral zirconolite - a complex oxide of the AB307 type," (in Russian), Doklady Akad. Nauk SSSR, 110, 845- , 1956. [3] Haines, E. L., Albee, A. L., ~hodos,A. A. and Wasserburg, G. J. "Uranium-bearing minerals of rock 12013." Earth Planet. Science Letters, -12, 745-154, 1971. [4] Peckett, A,, Phillips, R. and Brown, G. M. "New zirconium- rich minerals from Apollo 14 and 15 lunar rocks," Nature, -236, 215-217, 1972. [5] Busche, F. D., Prinz, M., Keil, K. and Kurat, G. "Lunar zirkelite: A uranium-bearing phase," Earth Planet. Science Letters, 16, 313-321, 1972. [6] Reid, A. F., Wark, D. A. and Lovering, J. F. "Characterisa- tion of zirconolite (versus zirkelite)" - in preparation. [7] Borodin, L. S., Bykova, A. B., Kapitonova, T. A. and Pyatenko, Yu. A. "New data on zirconolite and its niobian variety," (in Russian), Doklady Akad. Nauk SSSR, 134, 1188-1191, 1960. [8] Pudovkina, Z. V. and Pyatenko, Yu. A. "On zirconolite and its crystallographic characteristics" (in Russian), Tr. Mineral. Mez. Akad. Nauk SSSR, 17, 124-133, 1966. [9] Haggerty , S.E. "The mineral chemistry of some decomposition and reaction assemblages associated with Cr-Zr, Ca-Zr and Fe-Mg-Zr titanates," in The Apollo 15 Lunar Sample, Ed. J. W. Chamberlain and C. Watkins (Houston: Lunar Science Institute), 1972.

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Wark, D. A. et al.

Tebll 4A: Amlyres of tirconolltcs in 1uri.r rocks

Tnbl. 2 : Man~clinlclattlcs p.r..atdll (9.005 A1 of ~ymthstl~ ~ir~on~lltelmd terrostrl.1 zlr~~n~litefrom Aldan, U.S.S.R.

Synth.tlc Zlrconolllel ZC1 12.411 7.270 11.460 100.51. 2C2 12..473 7.218 11.103 100.66. ZCS 11.421 7.111 11.214 100.43. ZCI 12.492 7.248 11.891 100.71.

Terreltrl.1 Z

"A" 110. Arbarmltkh m.sslf. Aldm, U.S.S.R. (Aftor mn.ml for 10 hour. st IOO'C In v.cuw rltb n1ct.l s.ttor)

7.bl. 3 : *nalyres of rcrrelrri.1 :rrconolitcl Ira AlJa and Lola Prn~nsul. rczlons of U.S.S.R.

From -re basalt 100Ib.?O. Ma1Y.t. D. A. 1.11. F~ODurc ba1.11 1004-. IIA: loOI:.l3. Analyst. A. El Go1011. 110: 1001'.:5. A;alr,t. D. A. nark. 11C: 10017.~S. *nalr,t. U. A. lark Fro. rrcrystall~rcdbrrccl. 1I305.:7. hall1t. D. Fro. marc hara:t lI065.95. A~alrrt.A. El Gores,. From mare b.s.11 i5538;4. *nrly,z.~o. A. W.?k.

Table 41: Structural formulac of :lr~onolit.s 1n (unrr rorL, bared on ~~ll~'l~lll14r~UlllJ~tO~

*F~"IF~~'ratio taken from Iorodxn G 82. (1960) Hrcon~lif~A: Arbarastkh m~ssif. Aldm. U.S.S.R. 2lrconolltr 1: Afrikand. .sss~f. 101. PC.1.IUl.. U.S

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