Carbonatite dykes at bayan Obo, inner Mongolia, China
Tóm tắt
Calcite-rich dykes occur in the thrust fold belt near the Bayan Obo rare earth element (REE) deposit. They cut a thrust inlier of granitic migmatite within folded Bayan Obo Group sediments of Proterozoic age. Cathodoluminescence, X-ray fluorescence and microprobe studies show that the rock is a calcite carbonatite with Sr-Mn-bearing calcite, magnesio-riebeckite, apatite, pyrochlore, K-feldspar and biotite. One dyke was chosen for detailed analysis. Its margin is strongly REE-mineralized with much monazite developed adjacent to zoned apatite. Secondary alteration is marked by the introduction of Fe and Mn. The adjacent migmatite is fenitized to a magnesio-riebeckite-albite rock. The sedimentary dolomite of the Bayan Obo Group is composed mainly of Mn-Sr-RE-hearing ferroan dolomite and contains bands of opaque grains, apatite, monazite, fluorite and taeniolite. Many trace element and isotope similarities between the carbonatite dyke and the sedimentary dolomite are revealed, and the evidence supports the possibility that the dolomite is a dolomitized carbonatite tuff. The Bayan Obo REE mineralization also shows geochemical similarities with the mineralization seen in the carbonatites, and a possible genetic connection is presented.
Tài liệu tham khảo
Bai Ge, Yuan Zhongxin (1985) Carbonatites and related mineral resources. Bull Inst Mineral Resources, Chinese Acad Geol Sci No. 13: 1–195 (Chinese with English summary)
Bryan WB, Finger LW, Chayes F (1969) Estimating proportions in petrographic mixing equations by least squares approximations. Science 163: 926–927
Chao ECT, Minkin JA, Back JM, Okita PM, McKee EH, Tosdal RM, Tatsumoto M, Wang Junwen, Edwards CA, Ren Yingzhen, Sun Weijun (1989) The H8 dolomite host rock of the Bayan Obo Iron-Niobium-Rare-Earth-Element deposit of Inner Mongolia, China-origin, episodic mineralization, and implications. US Geol Surv Circular 1035: 8–10
—Tatsumoto M, Minkin JA, Back JM, McKee EH (1990) Multiple lines of evidence for establishing the mineral paragenetic sequence of the Bayan Obo rare earth ore deposit of Inner Mongolia, China. Proceedings of the 8th IAGOD Symposium, Ottawa, August 1990, in press
Deines P (1989) Stable isotope variations in carbonatites. In:Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 301–359
Drew LJ, Meng Qingrun (1990) Geological map of the Bayan Obo area, Inner Mongolia, China, 1:50000. US Geol Surv Misc Investigations Series, Map I-2057
——, ——Sun Weijun (1990) The Bayan Obo iron-rare-earth-niobium deposits, Inner Mongolia, China. Lithos 26: 43–65
Fleischer M, Altschuler ZS (1986) The lanthanides and yttrium in minerals of the apatite group—an analysis of the available data. N J Mineral Monatsh H. 10: 467–480
Hogarth DD (1989) Pyrochlore, apatite and amphibole: distinctive minerals in carbonatite. In:Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 105–148
Hovis GL, Delbove F, Bose MR (1991) Gibbs energies and entropies of K-Na mixing for alkali feldspars from phase equilibrium data: implications for feldspar solvi and short range order. Am Mineral 76: 913–927
Hubberton H-W, Katz-Lehnert K, Keller J (1988) Carbon and oxygen isotope investigations in carbonatites and related rocks from the Kaiserstuhl, Germany. Chem Geol 70: 257–274
Keller J (1989) Extrusive carbonatites and their significance. In:Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 70–88
Le Bas MJ (1977) Carbonatite-nephelinite volcanism. John Wiley & Sons, London New York, 347pp
— (1987) Nephelinites and carbonatites. In:Fitton JG, Upton BGJ (eds) Alkaline Igneous Rocks. Geol Soc London, Special Publ 30: 53–83
——Srivastava RK (1989) The mineralogy and geochemistry of the Mundwara carbonatite dykes, Sirohi District, Rajasthan, India. N J Mineral Abh 160: 207–227
Liu Tiegeng (1986) A discussion on the genesis of dolomite in Bayan Obo, Inner Mongolia—with emphasis on the composition of oxygen and carbon isotopes. Geol Review 32: 150–159
Lottermoser BG, England BM (1988) Compositional variation in pyrochlores from the Mt Weld carbonatite laterite, Western Australia. Mineral Petrol 38: 37–51
Marchand L, Joseph D, Touray JC, Treuil AM (1976) Criteres d'analyse geochimique des gisements de fluorine basse sur l'etude de la distribution des lanthanides—application aux gites de Maine (71-Cordesse, France). Mineralium Deposita 11: 357–379
Mariano AN (1978) The application of cathodoluminescence for carbonatite exploration and characterization. Proc First Internat Symp Carbonatites, Brazil, pp 35–57
—— (1989) Nature of economic mineralization in carbonatites and related rocks. In:Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 149–176
Möller P (1989) REE(Y), Nb and Ta enrichment in pegmatites and carbonatite-alkalic rock complexes. In:Möller P, Cerny P, Saupe F (eds) Lanthanides, tantalum and niobium. Springer, Berlin Heidelberg New York, pp 103–144
Nakai S, Masuda A, Shimizu H, Qi Lu (1989) La-Ba dating and Nd and Sr isotope studies on the Baiyun Obo Rare Earth Element ore deposits, Inner Mongolia, China. Econ Geol 84: 2296–2299
Nelson DR, Chivas AR, Chappell BW, McCulloch MT (1988) Geochemical and isotopic systematics in carbonatites and implications for the evolution of ocean-island sources. Geochim Cosmochim Acta 52: 1–17
Philpotts JA, Tatsumoto M, Hearn PP, Fan P-F (1988) On the petrography, chemistry, age and origin of the Bayan Obo rare-earth iron deposit and resulting insight on the mid-Proterozoic earth (abs). Am Geophys Union Trans 69: 517
——, ——Li Xianhua, Wang Kaiyi (1991) Some Nd and Sr isotopic systematics for the REE-enriched deposit at Bayan Obo, China. Chem Geol 90: 177–188
Veizer J (1983) Trace elements and isotopes in sedimentary carbonates. In:Reeder RJ (ed) Reviews in mineralogy, Vol. 11, Carbonates: mineralogy and chemistry. Mineral Soc America 265–299.
Wood DA, Joron JL, Treuil M, Norry MJ, Tarney J (1979) Elemental and Sr isotope variations in basic lavas from Iceland and the surrounding sea floor. Contrib Mineral Petrol 70: 319–339
Woolley AR, Kempe DRC (1989) Carbonatites: nomenclature, average chemical compositions, and element distribution. In:Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 1–14
Zhang Peishan, Tao Kejie (1986) Bayan Obo mineralogy. Science Publisher, Beijing, 208pp (Chinese with English summary).
Zhou Z, Gongyuan L, Tongyun S, Yuguan L (1980) On the geological characteristics and the genesis of the dolomitic carbonatites at Bayan Obo, Inner Mongolia. Geol Review 26: 35–42