江南造山带基底变质沉积岩中锂元素分布和富集机制及对锂成矿的制约  

Distribution and enrichment mechanism of lithium in meta-sedimentary rocks in the Jiangnan orogen and implications for lithium mineralization

作　　者：苟树林 于津海[1] 蔡元峰[1] 蒋威 毛志奇 GOU Shulin;YU Jinhai;CAI Yuanfeng;JIANG Wei;MAO Zhiqi(School of Earth Sciences and Engineering,Nanjing University,Nanjing,Jiangsu 210046,China)

机构地区：[1]南京大学地球科学与工程学院,江苏南京210046

出　　处：《地质学报》2023年第11期3696-3714,共19页Acta Geologica Sinica

基　　金：国家自然科学基金重点项目(编号91962221)资助的成果。

摘　　要：内容提要:江南造山带是我国重要的稀有金属成矿带,已发现多处与锂相关的花岗伟晶岩型稀有金属矿床。锂等稀有金属元素在源区基底岩石中的富集是花岗伟晶岩型锂稀有金属矿床成矿的物质基础,但是江南造山带基底岩石中锂的分布及其富集机制仍不清楚。本文详细调查研究了江南造山带东段新元古代冷家溪群、双桥山群、溪口岩群和板溪群变质沉积岩和星子杂岩。这些基底变质岩的岩石类型包括变质砂岩、泥质板岩、千枚岩和云母片岩以及少量片麻岩。地球化学分析结果显示,冷家溪群、双桥山群和溪口岩群变质沉积岩具有相似的成分,变质砂岩和云母片岩-片麻岩整体上比泥质板岩和千枚岩具有较高的SiO_(2)含量,较低的TiO_(2)、Al_(2)O_(3)、K_(2)O、MgO和TFe_(2)O_(3)含量。泥质板岩和千枚岩含有更高的稀有金属元素含量,其中锂含量达到61.8×10^(-6),而变质砂岩的锂丰度为44.9×10^(-6)。板溪群具有最低的稀有金属元素含量(Li=30.8×10^(-6))。冷家溪群、双桥山群和溪口岩群浅变质沉积岩中的锂含量与化学风化指数(CIA)和MgO、TFe_(2)O_(3)含量具有较好的正相关性,而且与岩石中的黏土矿物含量,尤其是绿泥石含量,具有很好的正相关性。因此,沉积岩中锂的富集明显地受化学风化作用控制,即锂的富集机制是黏土矿物的吸附作用,尤其是蒙脱石和绿泥石。在中高级变质岩中,绝大多数的Li赋存于黑云母、白云母和十字石中。通过对冷家溪群变质沉积岩的部分熔融模拟显示,在部分熔融过程中,云母类矿物的分解和熔融是熔体中锂含量升高的直接原因;云母完全熔融消失,熔体中的锂浓度达到高峰;继续熔融将稀释熔体中的锂含量。影响熔体中锂浓度的主要因素是源岩中锂含量和部分熔融程度,而部分熔融程度取决于源岩成分、水含量和温压条件。压力增加有利于熔体对The Jiangnan orogen is one of the important metallogenic belts of rare metals in China.Several granite-pegmatite type lithium rare metal deposits have been found in this belt.The enrichment of lithium and other rare metal elements in the basement rocks is the material basis for the mineralization of the granite-pegmatite type lithium rare metal deposit.However,the distribution and enrichment mechanism of lithium in the basement rocks of the Jiangnan orogen are still unclear.In this paper,the Neoproterozoic Lengjiaxi Group,the Shuangqiaoshan Group,the Xikou Group and the Banxi Group meta-sedimentary rocks and the Xingzi complex in the eastern section of Jiangnan orogen are investigated in detail.These basement rocks include metasandstone,argillite,phyllite,mica schist and less gneiss.Analytical results show that meta-sedimentary rocks of the Lengjiaxi,Shuangqiaoshan and Xikou groups have similar compositions,and metasandstones,mica schists and gneisses have higher SiO_(2) and lower TiO_(2),Al_(2)O_(3),K_(2)O,MgO and TFe_(2)O_(3) than argillites and phyllites.The argillites and phyllites generally contain higher rare metal element contents,with mean lithium content up to 61.8×10^(-6),whereas the metasandstones have lower lithium abundances with a mean of 44.9×10^(-6).The Banxi Group has lower rare metal element content(Li=30.8×10^(-6)).Lithium content of meta-sedimentary rocks of the Lengjiaxi,Shuangqiaoshan and Xikou groups exhibit a good positive correlation with the chemical index of alteration(CIA),MgO,TFe_(2)O_(3),and with the clay minerals in the rocks,especially chlorite.Therefore,lithium concentrations of sedimentary rocks are obviously controlled by chemical weathering,that is,the mechanism of lithium enrichment is the adsorption of clay minerals,especially montmorillonite and chlorite.The majority of lithium concentrates are in biotite,muscovite and staurolite in middle-and high-grade metamorphic rocks.The modeling of partial melting of the meta-sedimentary rocks of the Lengjiaxi Group shows that the d

关 键 词：江南造山带 变质沉积岩 锂的分布和富集机制 部分熔融模拟 

分 类 号：P618.71[天文地球—矿床学] P588.3[天文地球—地质学]