关键词: 平英岩体, 宝坛锡矿, 锆石U-Pb定年, Hf同位素, 新元古代, 桂北

Abstract:

Granite samples from the Pingying plutons have been analyzed for zircon U-Pb ages, Hf isotope and whole-rock geochemical
compositions to discuss the emplacement age, genetic type, source and relationship with the Baotan tin deposit. Zircon
LA-MC-ICP-MS U-Pb dating gives a weighted mean 206Pb/238U age of 834.2±5.1 Ma for the coarse-grained biotite granite in the central
phase, indicating that it was formed in the Neoproterozoic. The granite samples are strongly peraluminous with high silica and alkali
contents and enriched in Cs, Rb, U and Ta, but relatively low in Ba, Sr and Ti. Chondrite-normalized REE diagrams of the granite are

right inclined and show strongly negative Eu anomalies with Eu/Eu* values ranging from 0.05 to 0.31. Theε Hf(t ) values of zircon grains
vary from -12.6 to -1.6 with a peak of -4.8~-3.0, and the two-stage Hf model ages range from 1.83 to 2.51 Ga with a peak of 1.9~2.0
Ga. These characteristics indicate that the Pingying granite was formed by partial melting of the Paleoproterozoic basement rich in
boron, and experienced strong differentiation. This study shows that the Neoproterozoic biotite granite in the Jiuwandashan-
Yuanbaoshan area has the potential for tin mineralization and it is an important part of the evolution of multi-period granite and tin
polymetallic metallogenic series in South China as well.

Key words: pingying granite, baotan tin deposit, zircon U-Pb dating, Hf isotopic composition, Neoproterozoic, Northern Guangxi