PART IV. SUMMARY AND CONCLUSIONS AND REFERENCES
In part I, we described the characteristics and paragenesis of the giant Bayan Obo REE-Fe-Nb ore deposit:
In part II, we described and discussed evidence for Caledonian subduction, origin of the Caledonian Hejao granitic rocks 50 km south of the Bayan Obo mine region, and the probability that Caledonian subduction and regional metamorphism provided a repeated activation mechanism and heat source that helped to generate not only REE- and Fe-rich hydrothermal ore fluids of Bayan Obo, but also the A-type and S-type anorogenic Hejao granitic rocks.
In part III, we discussed the giant Bayan Obo REE-Fe-Nb ore deposit as a cornerstone example of a giant ore deposit in terms of the following parameters: (1) the Early Proterozoic and crustal sources of REE's, Fe, and Nb on the basis of (a) occurrence of large amounts of LREE-rich allanites in Early Proterozoic gneisses and pegmatites, and (b) isotopic indicators of large negative eNd values; (2) the favorable tectonic setting for mineralization during the Caledonian orogeny; (3) the probable mechanism for concentrating ore metals in the hydrothermal solutions in source reservoirs; (4) the geochemical evolution, based on the mineral paragenetic sequence; (5) the mode of transport of REE complexes from the lower sialic crust to the H8 unit of the Bayan Obo Group; (6) the ages of episodes of mineralization; (7) the Middle Proterozoic H8 marble as the favorable reservoir rocks hosting the Bayan Obo ores; and (8) the less permeable H9 pelitic biotite and albitized biotite schist as cap rocks that probably preserved the ore within the upper part of the H8 marble host rocks.
Bayan Obo and the Andean giant and super giant porphyry Cu-Mo ore deposits were both formed in subduction zone environments over long periods of time. Although the ore types differ, comparison of these deposits may help to increase our understanding of the paragenesis of giant polymetallic deposits.
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