赣南淘锡坝矿床岩浆岩年代学、地球化学特征及其与成矿关系

Geochronology and geochemical characteristics of magmatic rocks and their relationship with mineralization in Taoxiba deposit,southern Jiangxi Province

淘锡坝大型锡矿位于华南武夷山成矿带与南岭成矿带的交接部位,其矿床类型、成因、成岩成矿关系十分复杂,且一直缺乏有效的约束。文章围绕着矿床内发育的岩浆岩开展了系统的岩石学、锆石U-Pb年代学和岩石地球化学研究。淘锡坝矿床岩浆岩具有多阶段多岩相演化特征,从早到晚分别为:凝灰岩→中-粗粒似斑状花岗岩→细粒花岗岩→花岗斑岩。LA-ICP-MS锆石U-Pb年代学研究显示,淘锡坝锡矿具有140~148.4 Ma(中酸性火山岩)和122.3~138 Ma(花岗岩类)2个主成岩期。淘锡坝花岗岩具有高硅、富钾、贫钙的特点,属A型花岗岩,凝灰岩具有高硅、富钙的特点。尽管二者均相对富集不相容元素Rb、Th、U、Nb,亏损Ba、Sr等高场强元素,但其具有不同来源和演化进程,前者主来源于古老地壳物质,并且有明显的幔源物质的加入,经历了斜长石的分离结晶,后者主要来源于古老地壳物质的部分熔融,经历了钾长石的分离结晶。此外,淘锡坝花岗岩成岩年龄与成矿年龄一致,而凝灰岩年龄则显著早于成矿年龄(114~138.2 Ma),并且花岗岩相对于凝灰岩具有更高的演化程度和更低的氧逸度条件,更加有利于锡的富集。因此,淘锡坝矿床锡矿化应与花岗岩关系更为密切,成矿母岩为中-粗粒似斑状花岗岩与细粒花岗岩,形成于燕山晚期华南大规模陆壳伸展的背景之下。

The Taoxiba large tin deposit is located at the junction of Wuyishan Metallogenic Belt and Nanling Metallogenic Belt in South China.Its deposit type,genesis,magmatism and relationship between magmatism and mineralization are very complex,and has been lack of effective constraints.This article conducts systematic petrology,zircon U-Pb chronology,and rock geochemistry research on magmatic rocks developed in the ore deposit.The magmatic rocks in the Taoxiba deposit exhibit multi-stage and multi-phases evolution characteristics,ranging from early to late:tuff→medium to coarse-grained porphyritic granite→fine-grained granite→granite porphyry.LA-ICP-MS zircon U-Pb dating studies show that it has two main magmatic periods:140~148.4 Ma(intermediate-acid volcanic rocks)and 122.3~138 Ma(granitoid).The Taoxiba granite has the characteristics of high silicon,rich potassium and poor calcium,belongs to A-type granite,and the tuff has the characteristics of being rich in silicon and calcium.Although they both are relatively enriched in incompatible elements such as Rb,Th,U,Nb,and depleted in Ba,Sr,etc.,they have different sources and evolutionary processes.The former mainly comes from old crustal materials,with a significant addition of mantle derived materials,and has undergone the fractional crystallization of potassium feldspar.The latter mainly comes from partial melting of old crustal materials,and has undergone the fractional crystallization of plagioclase.In addition,the forming age of the Taoxiba granite is consistent with the mineralization age,while the tuff age is significantly older than the mineralization age,and the granite has a higher degree of evolution and lower oxygen fugacity conditions compared to tuff,which is more conducive to the enrichment of tin.The mineralization of the Taoxiba tin deposit is more closely related to granite,and the metallogenic parent rock is medium to coarse-grained porphyritic granite and finegrained granite,formed in the context of large-scale continental extension in southern China during the late Yanshanian period.