赣北莲花山钨锡矿集区中细粒白云母花岗岩成因——来自锆石U-Pb同位素和元素地球化学的约束

    Petrogenesis of fine-grained muscovite granite in the Lianhuashan tungsten tin ore cluster area of northern Jiangxi province-Constraints from zircon U-Pb isotopes and elemental geochemistry

    • 摘要: 赣北莲花山钨锡多金属矿集区位于扬子板块东南缘,是九岭-障公山钨锡铜金多金属成矿带的重要矿集区之一,分布有茅棚店、徐家尖、八字脑、棉花坞、莳山锡钨多金属矿床(点)十余处,以及潘村萤石矿、大洲高岭土矿等非金属矿产3~4处,但多为中小型矿床矿点,始终未有较大找矿突破,且对成矿期花岗岩缺乏精确的年代学及地球化学测试数据。对茅棚店锡钨矿床中细粒白云母花岗岩进行了岩相学、锆石U-Pb测年、地球化学特征研究,为区域成矿规律研究提供了直接证据。结果表明,白云母花岗岩锆石LA-ICP-MS U-Pb年龄为127.5±1.0 Ma,燕山期岩石单元由中粗粒似斑状黑云母花岗岩→中细粒似斑状黑云母花岗岩→中细粒—粗粒似斑状二云母花岗岩→中细粒白云母花岗岩→花岗斑岩组合。地球化学研究表明,该中细粒白云母花岗岩为高分异S型花岗岩,具有高硅(SiO2=75.08%~75.40%)、富碱、过铝质的特征及较高的分异指数DI,轻、重稀土元素分馏明显,呈左高右低的深"V"形,Eu表现为强烈的亏损,具有稀土元素四分组效应,Rb/Sr、Rb/Ba平均值分别为53.92和60.30,指示岩浆经历了多阶段分离结晶作用,此高分异花岗岩是区内钨锡矿床最主要的成矿地质体。

       

      Abstract: Lianhuashan tin-tungsten polymetallic ore concentration district in northern Jiangxi province is located on the southeast edge of the Yangtze plate.It is one of the important ore concentration districts of the Jiuling-Zhanggongshan tungsten-tin-copper-gold polymetallic metallogenic belt.It is determined as a class Ⅰ metallogenic prospect, with more than 10 tin-tungsten deposits(occurrences), including Maopengdian, Xujiajian, Bazinao, Mianhuawu, Shishan and so on, there are several non-metallic mining occurrences, such as Pancun fluorite deposit and Dazhou kaolin deposit, but most of them are small and medium-sized mineral deposits, and there has never been a significant breakthrough in mineral exploration.In addition, there is a lack of accurate chronological and geochemical testing data for granite during the mineralization period.The petrography, zircon U-Pb chronology and whole-rock geochemistry of the medium and fine-grained muscovite granite in Maopengdian tin-tungsten deposit are studied in this paper, which provide direct evidence for the study of regional mineralization patterns.The results show that the zircon LA-ICP-MS U-Pb age of the muscovite granite is 126.7 ± 1.2 Ma.The Yanshanian rock unit consists of medium-coarse-grained porphyritic biotite granite →medium-fine-grained porphyritic biotite granite →medium-fine-grained-coarse-grained porphyritic mica granite→medium-fine muscovite granite→ granite porphyry, which is the result of crystallization differentiation of homologous magma evolution.Geochemical studies show that the medium and fine-grained muscovite granite is a highly differentiated S-type granite, which is characterized by high silicon(SiO2=75.08%~75.40%) and rich in alkali and peraluminous and high differentiation index DI.The fractionation of light and heavy rare earth elements is obvious, showing a deep V-type with high left and low right.Eu shows a strong negative anomaly and has four grouping effect of rare earth elements.The average values of Rb/Sr and Rb/Ba are 53.92 and 60.30 respectively, indicating that the magma experienced multi-stage fractional crystallization, and the highly differentiated granite is the main metallogenic geological bodies of W-Sn deposits in the area.

       

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