摘要
The Madi rare metal granite is a complex massif,which contains a variety of rare metals,such as Nb,Ta,Li,and Be.In this paper,the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry(MC-ICP-MS).The precise crystalline age of the granite was obtained from monazite U-Pb dating,and the source of the granite was determined using Li-Nd isotopes.The Madi rare metal granite is a high-K(calc-alkaline),peraluminous,S-type granite.The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma,which is Early Jurassic.The granite is characterized by a relatively wide range ofδ7 Li values(+2.99‰to+5.83‰)and high lithium concentrations(181 ppm to 1022 ppm).The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation.An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation.The lithium isotopic composition of the granite significantly differs from that of the wall rock,but it is very similar to that of a primitive mantle peridotite xenolith(meanδ7 Li value+3.5‰).The plot of Li concentration versusδ7 Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas.Based on the above-described evidence,the granite was mainly derived from the crust,but it was contaminated by a deep granitic magma.
The Madi rare metal granite is a complex massif, which contains a variety of rare metals, such as Nb, Ta, Li, and Be. In this paper, the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry(MC-ICP-MS). The precise crystalline age of the granite was obtained from monazite U-Pb dating, and the source of the granite was determined using Li-Nd isotopes. The Madi rare metal granite is a high-K(calc-alkaline),peraluminous, S-type granite. The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma, which is Early Jurassic. The granite is characterized by a relatively wide range of δ7 Li values(+2.99‰ to +5.83‰) and high lithium concentrations(181 ppm to 1022 ppm). The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation. An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation. The lithium isotopic composition of the granite significantly differs from that of the wall rock, but it is very similar to that of a primitive mantle peridotite xenolith(mean δ7 Li value +3.5‰). The plot of Li concentration versus δ7 Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas. Based on the above-described evidence, the granite was mainly derived from the crust, but it was contaminated by a deep granitic magma.
基金
the project of“Comprehensive integration and service of mineral geology and its metallogenic regularity in China”from China Geological Survey(Grant No.DD20160346)
