赣北大湖塘矿床的含铌钽与含钨花岗岩成岩成矿特征对比研究

Comparative Study of Petrogenesis and Mineralization Characteristics of Nb-Ta-bearing and W-bearing Granite in the Dahutang Deposit,Northern Jiangxi Province

大湖塘钨多金属矿床位于江西北部三县(武宁、修水、靖安)交界处,是近年来发现的一个超大型钨矿床,与燕山期含钨花岗质岩浆活动密切相关。本次研究发现该区还存在含铌钽花岗斑岩,利用全岩地球化学特征、矿物的结构和主微量元素成分、以及锆石和铌铁矿族矿物U-Pb同位素年代学,对比含铌钽花岗斑岩和含钨似斑状花岗岩成岩成矿特征,以探讨两类不同成矿花岗岩的成因及成矿联系。研究得出:!含铌钽花岗斑岩的U-Pb LA-ICP-MS锆石和铌铁矿族矿物同位素年龄分别为146±2Ma和144±5Ma,与含钨似斑状花岗岩的成岩成矿年龄(150～140Ma)接近;(2)含铌钽花岗斑岩全岩的Nb/Ta和Zr/Hf比值分别为1.7和13,云母为含锂白云母,Li_2O和F含量最高可达2.1%和3.8%,K_2O/Rb_2O比值24,而含钨似斑状花岗岩中具有相对较高的Nb/Ta(～4.8)和Zr/Hf(～30)比值,云母也以白云母为主,含有0.32%Li_2O和1.5%F,K_2O/Rb_2O比值88,表明含铌钽花岗斑岩的演化程度比含钨似斑状花岗岩更高;(3)两类花岗岩中的成矿指示性矿物有明显差异,含铌钽花岗斑岩中包括具有岩浆成因特征的铌铁矿族矿物、钨铌锰矿、锡锰钽矿、含铌钽黑钨矿、含铌钽金红石和富集稀有金属元素的含锂白云母;而含钨似斑状花岗岩中主要体现为热液期形成的黑钨矿、白钨矿、金红石和锡石。本次研究认为,含铌钽花岗斑岩的原始岩浆中富含铌钽钨等元素,高挥发组分和岩浆流体的作用有利于岩浆期稀有金属成矿作用的发生;而含钨似斑状花岗岩中钨成矿作用发生在岩浆作用的后期,与后期流体作用相关性更大,这些信息也验证了大湖塘矿床发生了多期多阶段钨锡稀有金属成矿作用。

The tungsten mineralization,located at the junction of Wuning,Xiushui and Jing＇an counties in northern Jiangxi Province,south China,is a superlarge tungsten deposit discovered recently.It is closely associated with the middle Mesozoic W-bearing granitic magmatism.This study found that the Nb-Tabearing granitic porphyry occurs in this area.The diagenetic and metallogenic characteristics of Ni-and Tabearing granite porphyry and porphyritic granite were compared using geochemical features,mineral structure,major and trace elements compositions,and U-Pb istopic chronology of zircon and Nb-and Feminerals to understand the relationship between the genesis of ore-forming granite and its relation to mineralization.The results show that（1）the zircon and columbite U-Pb isotopic age of the Nb-Ta-bearing granitic porphyry is 146±2 Ma and 144±5 Ma,respectively,closed to the age of the formation and Wmineralization of the W-bearing porphyritic granite.（2） The Nb-Ta-bearing granitic porphyry has low Nb/Ta of 1.7 and Zr/Hf of 13,in which the micas（Li-muscovite）contain the Li2O and F content up to 2.1 and 3.8%respectively and the K2O/Rb2O ratio as low as 24.The W-bearing porphyritic granite has high Nb/Ta of 4.8 and Zr/Hf of 30 and muscovite contains Li2O of 0.32% and F of 1.5% and K2O/Rb2O of88,respectively,indicating that W-bearing porphyritic granite has a higher degree of evolution than the porphyritic granite.（3） The indicator minerals of the Nb-Ta-bearing granitic porphyry include magmatic oxide minerals（columbite-group minerals,wolframoixiolite,wodginite,Nb-Ta bearing wolframite and Nb-Ta bearing rutile）and rare-metal-bearing Li-muscovite forming during the later magmatism enriched in fluids.The W-bearing porphyritic granite is mainly represented by wolframite,scheelite and secondary rutile formed during hydrothermal stage.It can be concluded that the parent magma of Nb-Ta-bearing granitic porphyry is rich in Nb,Ta and W,and high volatile components and abundant magmatic fluids benefit for Nb-Ta-W mineralization,while W mineralization occurred later than the magmatic stage of the W-bearing porphyritic granite and is related to the hydrothermal fluids.Further,the study has confirmed the multi-staged mineralization occurring in the Dahutang deposit.