Sediment Source of Bayan Obo Marginal Rift and Genesis of Ore-Bearing Dolomite of the Giant REE Deposit
Detrital zircon ages of Jianshan Formation H4 quartz sandstone of Bayan Obo Group record two major tectonic-magmatic events in the northern margin of the North Chian Craton (NCC). One Group of age concentrates in the Late Archean—Early Paleoproterozoic (2379~2596 Ma), and the other in the medium Paleoproterozoic (1761 —1946 Ma). The results are consistent with the zircon ages of basement rocks in the Bayan Obo region. The 207Pb-206Pb isochron age (1649±45 Ma) of the sedimentary carbonate rocks of the Bayan Obo Group may represent its deposition times. The Pb isotope compositions of ore-bearing dolomite marble are quite different from those of the sedimentary carbonate rocks of the Bayan Obo Group. In the Pb isotope composition and tectonic diagram, the ore-bearing dolomite marbles are concentrated near the mantle evolution line and close to depleted mantle end member [(206 Pb/204 Pb)j = 15. 04 ~ 16. 49, (207pb/204pb)i = 15.17~15.28, (208pb/204Pb), = 31. 20 — 36.40 ], but the sedimentary carbonate rocks are distributed near the orogenic evolution line and close to the pelagic sediment end member [(206Pb/204Pb)i = 17. 28~19. 35, (207Pb/204Pb)i = 15. 47~15. 69, (208Pb/204Pb)i = 36. 62~37.12 ].
detrital zircons ore-bearing dolomite marblePb isotopeU-Pb isotopic ageBayan Obo Group
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