Hostname: page-component-78c5997874-s2hrs Total loading time: 0 Render date: 2024-11-13T09:27:33.608Z Has data issue: false hasContentIssue false
  • English
  • Français

Oxygen, carbon and strontium isotope study of the carbonatitic dolomite host of the Bayan Obo Fe-Nb-REE deposit, Inner Mongolia, N China

Published online by Cambridge University Press:  05 July 2018

M. J. Le Bas ,
B. Spiro  and
Yang Xueming
M. J. Le Bas
Affiliation:
Geology Department, Leicester University, LE1 7RH, UK
B. Spiro
Affiliation:
Isotope Geosciences Laboratory, NERC, Keyworth, Nottingham, NG12 5GG, UK
Yang Xueming
Affiliation:
Geology Department, Leicester University, LE1 7RH, UK
Get access Rights & Permissions [Opens in a new window]

Abstract

The large Fe-Nb-REE deposit at Bayan Obo is hosted by a dolomite marble within the thrust complex of marbles, quartzites and slates that belongs to the Bayan Obo Formation of mid-Proterozoic age. The dolomite is either a dolomitized sedimentary limestone subsequently mineralized and tectonically thrust and folded, or a dolomite (or dolomitized) carbonatite intrusion with late-stage recrystallization and mineralization that has been subsequently tectonically deformed.

O and C isotope data indicate that the sedimentary limestones and dolomites of the Bayan Obo Formation, which occur in the thrust stack together with quartzites and slates, have values of δO c. +20 per mil (SMOW) and δC c. zero. In contrast, the coarser grained facies of the large (0.5 × 10 km) dolomite marble which hosts the REE ore body has δO per mil values between +8 and +12 and δC values between −5 and −3, whereas the finer-grained recrystallized and REE-mineralized dolomite marble which occurs close to the ore bodies has δO between +12 to +16 and δC between −4 and zero. 87Sr/86Sr data confirm this distinction: >0.710 for the sedimentary rocks and <0.704 for the coarse- and fine-grained dolomite marbles.

These data are taken to indicate that the large and coarse-grained dolomite was an igneous carbonatite (as borne out by its fenitic contact rocks and trace element geochemistry), and that the finer grained dolomite recrystallized under the influence of mineralizing solutions which entrained groundwater. The stratiform features in the coarse-grained dolomite that are evident in the field are interpreted as tectonic layering.

Keywords

carbonatitedolomitelimestonemarbleBayan Obooxygen isotopescarbon isotopesstrontium isotopes
Type
Intraplate Alkaline Magmatism
Information
Mineralogical Magazine , Volume 61 , Issue 407 , August 1997 , pp. 531 - 541
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1997

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

*

present address: Geology Department, Southampton University, SO14 3ZH, UK

**

present address: Department of Earth & Space Sciences, China University of Science and Technology, Hefei, Anhui 230026, China

References

Academia Sinica. (1988) The geochemistry of Bayan Obo ore deposit. Science Press, Beijing, Institute of Geochemistry, 1—554.Google Scholar
Bai, Ge and Zhongxin, Y. (1985) Carbonatites and related mineral resources. Bull. Inst. Mineral Deposits, Chinese Academy of Geological Sciences, Beijing, 13, 1—195.Google Scholar
Baldock, J. W. (1973) Potassic fenitisation, trachytes and agglomerates at the Bukusu carbonatite com-plex, Uganda. Overseas Geology & Mineral Resources, 42, 1-24.Google Scholar
Chao, E. C. T., Back, J. M. and Minkin, J. A. (1992) Host-rock controlled epigenetic, hydrothermal meta-somatic origin of the Bayan Obo REE-Fe-Nb ore deposit, Inner Mongolia, P.R.C. Appl. Geochem., 7, 443-58.CrossRefGoogle Scholar
Chao, E. C. T., Tatsumoto, M., Minkin, J. A., Back, J. M., McKee, E. H. and Yingchen, R. (1993) Multiple lines of evidence for establishing the mineral paragenetic sequence of the Bayan Obo rare earth deposit of Inner Mongolia, China. In Proceedings 8th IAGOD Quadrennial Symposium (Maurice, Y.T., ed). Stuttgart, Schweizerbart, 55–73.Google Scholar
Clarke, L. B., Le Bas, M. J. and Spiro, B. (1994) Rare earth, trace element and stable isotope fractionation of carbonatites at Kruidfontein, Transvaal, S. Africa. Proceedings of the 5th Kimberlite Conference, V 1. Kimberlite, related rocks and mantle xenoliths. Companhia de Pesquisa de Recursos Minerais, Brasilia, 236–251.Google Scholar
Deines, P. (1989) Stable isotope variations in carbonatites. In Carbonatites: Genesis and Evolution (Bell, K., ed). Unwin Hyman, 301-59.Google Scholar
Drew, L. J. and Meng, Q. (1990) Geological map of the Bayan Obo area, Inner Mongolia. U.S.G.S. 1:50 000 Misc. Investigation Map 1-2057.Google Scholar
Drew, L. J., Meng, Q. and Sun, W. (1990) The Bayan Obo iron-rare-earth-niobium deposits, Inner Mongolia, China. Lithos, 26, 43-65.CrossRefGoogle Scholar
Hall, S. M. and Veizer, J. (1996) Geochemistry of Precambrian carbonates: VII. Belt supergroup, Montana and Idaho, U.S.A. Geochim. Cosmochim. Acta, 60, 667-77.CrossRefGoogle Scholar
Knudsen, C. and Buchardt, B. (1991) Carbon and oxygen isotope composition of carbonates from the Qaquarssuk Carbonatite Complex, southern West Greenland. Chem. Geol., 12, 263—74.Google Scholar
Le Bas, M. J., Keller, J., Kejie, T., Wall, F., Williams, C. T. and Peishan, Z. (1992) Carbonatite dykes at Bayan Obo, Inner Mongolia, China. Mineral. Petrol., 46, 195-228.CrossRefGoogle Scholar
Liu, T. (1986) A discussion on the genesis of dolomite in Bayan Obo, Inner Mongolia — with emphasis on the composition of oxygen and carbon isotopes. Geol. Rev., 32, 150-9.Google Scholar
McCrea, J. M. (1950) On the isotopic chemistry of carbonates and a palaeotemperature scale. J. Phys. Chem., 18, 849-57.CrossRefGoogle Scholar
McDonough, W. F. and Sun, S.-s. (1995) The composition of the Earth. Chem. Geol., 120, 223-53.CrossRefGoogle Scholar
Nielsen, T. F. D. and Buchardt, B. (1985) Sr-C-O isotopes in nephelinitic rocks and carbonatites, Gardiner complex, Tertiary of East Greenland. Chem. Geol., 53, 207-17.CrossRefGoogle Scholar
Reid, D. L. and Cooper, A. F. (1992) Oxygen and carbon isotope patterns in the Dicker Willem carbonatite complex, southern Namibia. Chem. Geol., 94, 293-305.CrossRefGoogle Scholar
Robinson, G. W. and Chamberlain, S.C. (1984) Famous mineral localities: the Sterling mine, Antwerp, New York. Mineral. Rec., 15, 199-216.Google Scholar
Sutherland, D. S. (1965) Nomenclature of potassic-feldspathic rocks associated with carbonatites. Geol. Soc. Amer., Bull., 76, 1409-12.CrossRefGoogle Scholar
Tu, G.-Z., Zhao, Z. and Qiu, Y. (1985) Evolution of Precambrian REE mineralization. Precamb. Research, 27, 131-51.CrossRefGoogle Scholar
Veizer, J. (1990) Trace elements and isotopes in sedimentary carbonates. In Carbonates (Reeder, R.J., ed.). MSA Reviews in Mineralogy, V. 11, 265-99.Google Scholar
Wang, J., Tatsumoto, M., Li, X., W. R., P. and Chao, E. C. T. (1994) A precise 232Th-2∼ chronology of fine-grained monazite: age of the Bayan Obo REE-Fe-Nb ore deposit, China. Geochim. Cosmochim. Acta, 58, 3155-69.CrossRefGoogle Scholar
Woolley, A. R. (1969) Some aspects of fenitization with particular reference to Chilwa Island and Kangankunde, Malawi. Bulletin of the British Museum (Natural History), Mineralogy, 2, 189—219.Google Scholar
Woolley, A. R. and Kempe, D. R. C. (1989) Carbonatites: nomenclature, average chemical com-position, and element distribution. In Carbonatites: Genesis and Evolution (Bell, K., ed.). Unwin Hyman, 1–14.Google Scholar
Yuan, Z., Bai, G. and Wu, C. (1992) Geological features and genesis of the Bayan Obo REE ore deposit, Inner Mongolia, China. Appl. Geochem., 7, 429-42.Google Scholar