| Abstract:The granitoids in Nanling region, such as migmatites, migmatic granites, contaminated granites and crustal remelted granites, which were probably related to the mineralizations of rare earth, rare metals and W, Sn, Mo, Bi, often constitute along the Caledonian uplifts huge composite bodies bearing characteristics of multiple stages and multiple facies. The rare metal-rich pegmatites related to the migmatization of the Caledonian epoch are distributed along outer border of the migmatic zone, while the rare earth, rare metal and nonferrous metal deposits, which had connection with the Middle and Late Yenshanian crustal remelted granites, are often seen spread along the periphery of the composite granitic bodies in the Caledonian uplifts or along the faulted zone on the margin of the uplifts. It has also been observed that Be-, W-, Sn-, Mo-, Bi-bearing quartz veins often rapidly thin out and disappear in the Nb-, Ta-rich and W-, Mo-bearing granitic dikes or directly change into Nb-, Ta-rich granitic dikes at depth, that the Nb-,Ta-rich granites successively grade into Nb-, Ta-poor granites or W-bearing granites, rare earth-bearing granites and barren granites, and that rare elements-rich pegmatites directly change into Nb-, Ta-rich granites in the strike or dip direction. The granitic rocks and their related ore deposits display regularity in their variation of rock-forming elements, ore-forming elements and mineral assemblages, having evident volutional characteristics of heredity and development. Besides, according to some geochemical data, the lower Paleozoic strata in this region are rich in rare earth and rare metals (see Table 2), while some Upper Paleozoic strata have relatively high abundances of W, Sn, Bi, Pb, Zn. These strata, therefore, presumably constituted the source material of mineralization in the processes of migmatization, granitization and differentiation of the crustal remelted granitic magma. The foregoing discussion indicates evidently that the granitic magmas which gave rise to mineralizations of rare earths, rare metals, W, Sn, Mo, Bi, and other elements in Nanling region were the products of migmatization, granitization of older sediments and rocks, which produced relatively large batholiths through repeated replacements at various stages of crustal evolution. These batholiths eventually formed granitoid masses as a result of repeated and consistent remelting, differentiation and intrusion. Different minerogenetic elements were concentrated at different petrogenetic stages and formed accordingly various kinds of mineral deposits genetically related to each other, thus constituting in time and space the petrogenetic- minerogenetic evolutional sequences as shown in Table 6. These deposits generally evolved from the centers of migmatization and granitization radially outward, which finds expression in an apparent zoning: from early to late periods or spatially in upward or outward succession, the ore-forming elements appear in sequence of ∑Ce→∑Y, Nb or Y, Be→Nb (Ta, Hf, W) →W (Mo, Bi, Be, Nb, Ta) →Sn (Nb, Ta, sulfiaes). The various types of deposits derived from the same magmatic source occupied vertically relatively fixed spatial positions respectively and graded into each other, denoting a regular and orderly zoning of mineral deposits and making up a completed and intergrated minerogenetic model as shown in Fig. 2. |
