粤东莲花山断裂带韧性剪切的温压条件及其对钨锡铜多金属成矿作用的约束

Temperature and pressure conditions of dynamic metamorphism with its constraints on polymetallic mineralization of tungsten,tin and copper in Lianhuashan fault zone in eastern Guangdong Province

广东莲花山断裂带西南段分布有棉洋-双华(Ⅰ)、北山嶂-九龙嶂(Ⅱ)、五指嶂-锅子嶂(Ⅲ)、梅陇-鲘门-观音山(Ⅳ)4条韧性剪切带,呈巨型构造透镜体沿北东向展布。已有研究表明韧性剪切带与本区钨、锡、铜多金属成矿作用关系密切,控制着矿床的空间分布,是重要含矿、控矿构造。按照变质程度和矿物组成,区内韧性剪切带由核部至边部可以划分为石英透镜体→石榴子石(堇青石)糜棱岩→糜棱片岩→片岩→原岩等;通过对其中的石榴子石、黑云母等典型矿物进行电子探针分析(EPMA),并利用石榴石-黑云母地质温压计估算了4条韧性剪切带形成的温压条件,它们分别为484~526℃/4.92~7.72kbar、458~469℃/2.17~2.67kbar、536~551℃/1.28~1.67kbar、512~516℃/4.38~4.87kbar,与区内变质岩野外地质变形、变质特征相吻合,且火山岩为主的地区变质压力明显高于花岗岩为主的地区。研究显示,变质条件对区内变质分带和多金属成矿作用有明显的控制,棉洋-双华和梅陇-鲘门-观音山韧性剪切带的压力条件相对较高,金属成矿以钨、锡多金属成矿为主;而北山嶂-九龙嶂和五指嶂-锅子嶂韧性剪切带的压力相对较低,金属成矿则以铜、铅、锌成矿为主。

The southwestern part of Lianhuashan fault zone distribute four dynamic metamorphic zones,Mian yang-Shuanghua(Ⅰ),Bei Shanzhang-Jiulongzhang(ⅡI),Wuzhizhang-Guozizhang(Ⅲ)and Meilong-Houmen-Guan yinshan(Ⅳ),with characteristic lens along the northeast fault.It has been shown that they are the important ore-bearing and ore-controlling structure in this region.According to the degree of metamorphism and mineral composition,the dynamic metamorphic zone can be divided into quartz lens,garnet(cordierite)mylonite,mylonite,schist,protolite and so on.Based on the result of the EPMA of typical minerals such as garnet and mica,through the garnet-biotite geothermometer,we estimate the temperature and pressure conditions of metamorphism in four dynamic metamorphic belts respectively,484~526℃/4.92~7.72 kbar,458~469℃/2.17~2.67 kbar,536~551℃/1.28~1.67 kbar,512~516℃/4.38~4.87 kbar,which are highly consistent with the field geological deformation and metamorphism characteristics of dynamic metamorphic rocks,and the pressures in volcanic-dominated areas are higher than that in granite-dominated areas.Studies have also shown that metamorphic conditions have obvious control over metamorphic zones and polymetallic mineralization,tungsten and tin polymetallic mineralization are mainly inⅠ,Ⅳbelts with higher pressure conditions,while copper,lead,zinc and silver inⅡ,Ⅲbelts with lower pressure conditions.