湘南荷花坪锡多金属矿区花岗质岩石Sm-Nd同位素研究

Study on Sm-Nd Isotope of Granitoids of the Hehuaping Tin-Polymetallic Deposit, South Hunan Province

荷花坪锡多金属矿床是近年来在湘南地区新发现的一个大型矿床,矿区花岗质岩石主要有印支期中粗粒似斑状黑云母花岗岩和中细粒黑云母花岗岩,以及燕山期花岗斑岩脉和强蚀变花岗斑岩脉等。其中,与成矿有关的是中粗粒似斑状黑云母花岗岩和强蚀变花岗斑岩脉。本文对区内不同花岗质岩石进行了系统的主量元素、微量元素、稀土元素和Sm-Nd同位素测试。结果表明,区内花岗质岩石富Si(SiO_2>70%)、富Al(Al_2O_3=11.06%~18.26%),K_2O+Na_2O=3.51%~8.18%,且K_2O>Na_2O,贫Ca、Mg、Fe、Ti和P,δ<3.3,A/CNK=0.93~2.85,微量元素Ba、K、Sr、P和Ti出现亏损,Rb、Ta、La、Nd、Zr和Hf出现富集,Eu/Eu*=0.06~0.34,均属钙碱性过铝质花岗岩,具S型花岗岩特点。花岗质岩石ε_(Nd)(t)=7.1~11.2,两阶段Nd模式年龄t_(2DM)=1509~1903 Ma,主要为中元古代基底部分熔融产物。花岗质岩石的ε_(Nd)(t)均高于华南地壳端元的相应值12.1,锆石ε_(Hf)(t)变化于10.14^+4.61之间,显示成岩过程中应有少量地幔物质参与,且花岗质岩石的成矿能力可能与其成岩过程中地幔物质的参与强度有关。

The Hehuaping tin-polymetallic deposit is a large-scale deposit newly discovered in Southern Hunan province It consists of four main ore bodies located in the Southeast portion of the Wangxianling granite pluton. The granitiod rocks are distinguished as two epochs： Indosinian biotite granite and Yanshanian granite porphyry dike. Tin-polymetal mineralization is related to the Indosinian middle-coarse grained biotite granite and the Yanshanian intensely altered granite porphyry dike. The granitic rocks are rich in Si （SiO2 〉 70%）, Al （Al2O3=11.06%-18.26%）, K2O＋Na2O contents varying from 3.51% to 8.18%, with K2O 〉 Na2O, A/CNK=0.93~2.85, enriched in trace elements such as Rb, Ta, La, Nd, Zr and Hf, and depleted in Ba, K and Sr, Eu/Eu＊ values of the rocks vary from 0.06 to 0.34, indicating the rocks are calc-alkaline, peraluminous S-type granite. The εNd（t） values of the granitiod rocks vary in range of-7.1 to -11.2, and two stages Nd model ages （t2DM） range from 1509 Ma to1903 Ma, showing that the granitoids were derived from remelting of the Mesoproterozoic basement rocks. Considering that the eNd（t） values of the rocks are higher than the mean value of the South China crust （-12.1）, and the rather high zircon εHf（t） values of the granitic rocks （-10.14 to ＋ 4.61）, we suggest that the mantle contribution is significant. The tin mineralization is closely related to the mantle participation.