南岭早侏罗世锡（铁）成矿作用的背景与过程-以广东大顶大型矿床为例

Much attention has been paid to the Mesozoic tungsten mineralization in the Nanling area. Previous studies have shown that the early Jurassic period has been regarded as none magma and mineralization, which may be attributed to the special geological setting. However, recent studies have found that there develops a deposit in early Jurassic in Guangdong province, and its metallogenic background and process are far from clear. This application intends to choose Dading tin(iron) deposit as the research object, to carry out the petrology, mineralogy, system elements and isotope geochemistry and fluid geochemistry research. Try to find out the ore magma source properties, fluid properties, origin and evolution, aggregation process analysis of tin and iron, and restore the Nanling region early Jurassic tectonic magmatic evolution and tin metallogenic response. Finally, the study will further improve the understanding of the Mesozoic metallogenic process and metallogenic regularity in the Nanling region, and the tectonic evolution of Southern China area, then provide a theoretical basis for the early Jurassic tin polymetallic deposit in Nanling region at the same time.

南岭地区中生代大规模的钨锡成矿作用倍受关注。研究表明，区内钨锡多金属成矿主要集中在晚三叠世、中晚侏罗世及中⸺晚白垩世，被总结为著名的成矿三段论。早侏罗世一直被认为是特提斯构造域向太平洋构造域转换的调整期，亦是岩浆与成矿作用的沉寂期。然而，最近的研究发现，南岭地区存在早侏罗世锡多金属矿床（广东大顶锡(铁)矿床），但其成矿背景与过程还远未昭示。本申请拟对大顶大型锡（铁）矿为解剖对象，以含矿岩浆的形成、演化与成矿作用为主线，系统开展岩石学、矿床学、元素及同位素地球化学和流体地球化学的研究，试图查明含矿岩浆的源区特征、岩浆性质及演化过程、成矿流体来源及演化，解析锡、铁的聚集成矿的背景与过程。该项目的开展，将进一步丰富南岭中生代构造演化与钨锡多金属成矿作用关系研究，亦为南岭地区早侏罗世锡多金属矿勘查部署提供科学依据。

大顶Fe-Sn矿床相关的黑云母花岗岩岩体的锆石U-Pb年龄为(189.0±1.5Ma)，辉钼矿的Re-Os年龄为（185.9±4.9）Ma，确定其是南岭少见的早侏罗世成岩成矿事件。地球化学数据揭示，石背岩体的w(SiO2)、w(Nb)、w(Zr+Nb+Ce+Y)较高，且高Ga/Al值，低Y/Nb值，具A1型花岗岩特征。锆石εHf(t)范围较宽，介于-2.4~3.4之间，且与δ18O呈明显的负相关性，全岩Sr-Nd 同位素（εNd(t)=-3.3~-3.7, ISr=0.7063~0.7085）, 说明岩浆源区为古老地壳并含具有OIB特征性质幔源物质，岩浆经历了结晶分异作用，估算约40%~60%的亏损的原始地幔物质是铁的主要来源。硫化物中流体包裹体的3He/4He=4.32~20.91Ra（均值12.81Ra），40Ar/36Ar 比值介于317~2118.2之间，平均为709.86，表明铁锡成矿流体主要来自地壳，且混有地幔物质, 计算的地幔的He比例为5.38%~27.59%(平均为16.74%)。硫化物原位的δ34S 值变化范围较小，介于-3.48‰~6.46‰，均值为1.75‰，揭示其成矿物质来自岩浆。除了锡的氧化物外（锡石），磁铁矿及一些夕卡岩矿物（石榴子石、斧石）含锡元素的类质同相，此外，矿床发育锡的硅酸盐矿物（马来亚石）。通过与华南中-晚侏罗世和晚白垩世的与W-Sn 成矿岩体的对比研究，认为南岭大顶早侏罗世铁锡成矿作用与相关的黑云母花岗岩形成于印支造山后的后造山垮塌有关的伸展环境。