闽中梅仙铅锌多金属矿区花岗岩锆石U-Pb年代学、地球化学特征及其地质意义

梅仙铅锌矿位于福建省中部地区,是环太平洋中、新生代巨型构造-岩浆带中的重要成矿区之一。区内与成矿有关的侵入岩主要以花岗斑岩、黑云母花岗斑岩、钾长花岗岩和黑云母钾长花岗岩等为主。该次研究在矿床地质工作基础上,采用LA-ICP-MS锆石U-Pb法获得梅仙矿区花岗岩成岩年龄在158~155 Ma。岩石具高硅、富碱、高钾、铝饱和指数较高,以及富铁贫镁等特征,富集Cs、Rb、K、Pb等大离子亲石元素,富集Th、U、Zr、Hf等高场强元素,亏损Ba、Sr、P、Ti等元素,Ga/Al比值较低,具有明显的壳源特征,其岩石成因类型属高分异的I型花岗岩。梅仙矿区花岗岩是板内伸展造山阶段的产物,形成于古太平洋板块向欧亚大陆板块俯冲-消减后的伸展引张环境。在岩浆热液活动作用下,早期海底火山喷发沉积初始矿源层受到强烈的构造-岩浆热液叠加和改造作用,对矿质富集和矿体最终定位具有重要意义。

Geochronology,geochemistry and geological characteristics of granites from the Meixian zinc-lead polymetallic deposit in central Fujian Province

The Meixian lead-zinc deposit in central Fujian Province is one of the important metallogenic regions in the Meso-Cenozoic megatectonic-magmatic belt along the Pacific Ocean. The intrusive rocks associated with metallogenic processes in the area mainly consist of granite-porphyry, porphyritic biotite granite, K-feldspar granite, and biotite-bearing K-feldspar granite. In this study, based on geological investigation, we performed zircon U-Pb dating using LA-ICP-MS to obtained the diagenetic ages of granites from the Meixian ore deposit. The results showed that the ages ranged from 158 to 155 Ma, indicating granite production by Late Jurassic tectonic-magmatic action in the middle Yanshanian Period. The rock specimens were characterized by high silicon, alkali and potassium contents, high aluminum saturation index, iron rich and magnesium poor, enrichment of LILE and HFS, such as Cs, Rb, K, Pb, Th, U, Zr, Hf, etc., depletion of Ba, Sr, P, Ti, and low Ga/Al ratio. These characteristics are consistent with that of crust source, suggesting the highly-differential I-type granites as the rock genetic type. We further show that granites from the Meixian ore field are formed by the subduction and extension of the Paleo-Pacific Plate, and posited in the extensional orogenic stage within the plate. Magmatic hydrothermal activities played a strong role in tectonic magmatic hydrothermal superimposition and transformation for early submarine volcano-eruption and deposition, and are of great significance for mineral elemental enrichments and prediction of ore bodies.