北武夷地区梨子坑盆地与Pb-Zn成矿关系密切的晚中生代火山-侵入杂岩成因及其动力学背景研究

The northern Wuyi area is represented by a series of Mesozoic volcanic basins and several Pb-Zn-(Ag) deposits closely related to Late Mesozoic magmatism. Extensive studies have been carried out on Tianhuashan basin, and obvious prospecting achievements have been made on Lengshuikeng Ag-Pb-Zn deposit hosted within the basin in these area. However, there are very few studies on volcanic-intrusive complexes and related deposits at other basins that have similar ore-forming geological conditions, which hampers the prospecting breakthrough and understanding of geodynamic setting in this area. In order to better understand the possible link between magmatism and formation of Pb-Zn-(Ag) mineralization，this project chooses Lizikeng volcanic basin from the northern Wuyi area as the subject investigated. Petrography, mineral chemistry, lithogeochemistry and isotopic geochemistry, as well as zircon U-Pb dating and Hf-O isotopic analysis, will be carried out on the volcanic-intrusive complex and quenched mafic enclaves together with several mafic dikes developed within it. By comparing with previous data obtained in Tianhuashan basin, we aim to better constrain the age and magmatic evolution of the volcanic-intrusive complex at Lizikeng basin, unravel its petrogenetic link to the formation of Pb-Zn mineralization, and discuss the Late Mesozoic geodynamic setting in the northern Wuyi area.

北武夷地区分布着一系列火山盆地和众多与晚中生代岩浆活动密切相关的Pb-Zn-(Ag)多金属矿床。前人对该地区天华山盆地及其中的冷水坑Ag-Pb-Zn矿床开展了较详细的研究并取得了重要的找矿进展，而对成矿地质条件十分类似的其他盆地中火山-侵入杂岩及相关矿床的研究则较为薄弱，这一现状制约了对整个北武夷地区成岩成矿动力学背景的认识及该区的找矿突破。本项目拟选择北武夷地区研究比较薄弱的梨子坑盆地为研究对象，对与Pb-Zn矿化关系密切的火山-侵入杂岩以及其中所发育的暗色微粒包体和基性岩脉开展岩相学、矿物化学、全岩岩石地球化学和同位素地球化学，以及锆石的原位微区U-Pb定年、Hf-O同位素组成的综合研究。通过与天华山盆地己有工作的对比，本项目旨在约束梨子坑盆地火山-侵入杂岩的形成时限和岩浆演化过程，并探讨其与Pb-Zn成矿作用的可能联系，进而对北武夷地区晚中生代成岩成矿的地球动力学背景进行探讨。

北武夷地区是华南重要的多金属成矿带，在该带内分布有众多Pb-Zn-(Ag)矿床。这些矿床与晚侏罗世的岩浆活动具有密切的成因联系。笔者对梨子坑盆地中的早白垩世花岗质岩石进行了矿物学和地球化学特征的研究，识别出了三种类型的岩石：石英二长岩，花岗斑岩和二长花岗岩。他们均形成于133-129 Ma，对应着该区早白垩世的火山-侵入活动。全岩地球化学数据表明这三种花岗质岩石均是I型花岗岩。石英二长岩和花岗斑岩具有一致的低全岩εNd(t)值，变化范围在-10.36 到-9.64，锆石εHf(t)值变化范围在-14.15到-8.20，表明其起源于元古代镁铁质-中性下地壳源区，没有显著地幔物质的贡献。二长花岗岩也有负的但是稍高的εNd(t)和εHf(t)值，变化范围分别是-7.61到-7.06和-9.32到-7.00，表明其也起源于元古代难熔源区，加上少量地幔物质。本次研究表明二长花岗岩是含Nb和W的花岗岩，具有高度演化的特征。他们具有高的Nb和W含量，包含很多典型稀有金属矿物，比如含W金红石，Nb金红石，铌铁矿族矿物。本次早白垩世含W和含Nb花岗岩的发现表明北武夷地区还存在稀有金属矿化的潜力，为在华南地区寻找稀有金属矿床开辟了新思路。