Petrogenesis of the highly fractionated granites and their mineralizations in Nanling Range,SouthChina

As the mostly studied region of granite in China, Nanling Range in South China is extremely attractive for its close relationship of granite with mieralizations of W, Sn, Nb, Ta, Zr, Hf, Cu, Mo, Pb, Zn, Bi, Sb, U, Li, Be, REE, etc. It was generally thought that the above mineralizations were related to the highly fractionation of granitic magma, although the fractionation mechanism was not well understood. After summarizing the various characteristics from field investigation, and combining those indoors mineralogical and geochemical observations, it was suggested that the Mesozoic Yanshanian granites displayed a long-term and even continuous separation of crystal and residual melt within a magma chamber. The coarse-grained porphyritic granite is interpreted as the early cumulate crystallized during magma evolution, whereas the fine-grained granite as the residual high-silica melt after crystal fractionation. It was proposed that the above crystal-melt separation was controlled by two factors. One is the continuous input of mafic or new set of magma from below, which mobilized the mostly crystallized mush and triggered upward movement of the intergranular and metal-rich melt. Another is the marginal pegmatite (stockscheider) cover that prevented the lost of volatiles and maintained a sufficient fractional crystallization of magma within a close chamber. All these features make the Nanling granite much different from those of the Himalayan leucogranite that was similarly fractionated, but was formed by magma movement along a large scale of ductile detachment fault. Therefore, the Nanling Range granite and Himalayan leucogranite can be classified into thermal- and structural-driven end-members, respectively, in terms of highly fractionation mechanism of granitic magma. It is expected that an overall examination and evaluation should be conducted in the future to those late stage of highly fractionated granites, in order to meet the increasing demand for critical mineral resources. Especially, by deciphering the lithological sequence, mineralogical variation and evolution, metal enrichment and magma storage of the zinnwaldite-bearing granite and related greisen, a new step could be made up for the studies of the Nanling granite and its connection to the various mineralizations.

Automated summary

Nanling Range in South China is known for its significant mineralizations of W, Sn, Nb, Ta, Zr, Hf, Cu, Mo, Pb, Zn, Bi, Sb, U, Li, Be, REE, etc. Through field investigation and indoor observations, it was found that the Yanshanian granites in Nanling Range underwent a long-term separation of crystal and residual melt. This separation was controlled by the continuous input of mafic magma and the protection of the marginal pegmatite cover. The Nanling granite and Himalayan leucogranite have different mechanisms of highly fractionated granitic magma.