江西岩背斑岩锡矿的成岩成矿时代及其地质意义

Rock-forming and Ore-forming Ages of the Yanbei Porphyry Tin Deposit in Jiangxi Province and Their Geological Significance

岩背锡矿地处南武夷山西坡江西会昌县境内。该矿以富含原生黄玉为特征,是本区至今发现的唯一大型独立锡矿床。笔者对矿区内含锡花岗斑岩和成矿作用早阶段形成的石英—黄玉—锡石—硫化物脉进行了Rb-Sr同位素年代学研究,获得全岩和石英矿物Rb-Sr等时线年龄分别为(128.1±3.3)Ma(2σ,MSWD=1.07,Ir=0.7163±0.0052)和(125.5±6.1)Ma(2σ,MSWD=1.5,Ir=0.7130±0.0050),表明岩背锡矿的成岩成矿作用均发生于早白垩世晚期,其成因与中生代火山期后高位侵入的花岗斑岩密切相关。

Located in western Wuyi Mountain within Huichang County of Jiangxi Province, the Yanbei tin deposit with rich original topaz is the only large-sized tin deposit so far discovered in the study area. Isotopic chronological study of the tinbearing granite-porphyry and quartz-topaz-cassiterite veins formed at the early ore-forming stage shows that the quartz-topazcassiterite veins have a quartz fluid-inclusion Rb-Sr isochron age of （ 125.5 ± 6.1） Ma（2cr, MSWD = 1.5, Ir = 0.7130 ±0.0050）, which accords with the whole-rock Rb-Sr isochron age（ （ 128.1 ± 3.3） Ma, 2or, MSWD = 1.07, Ir = 0. 7163 ± 0.0052） of the granite-porphyry. It is thus concluded that the rock-forming and ore-forming activities of the Yanbei tin deposit occurred during the early Cretaceous episode, with the mineralization closely related to the post-volcanic high-level emplaced granite-porphyry.