粤东隆文矽卡岩型铁锡多金属矿床成岩成矿时代及地球化学特征

Geochronology and geochemistry of Longwen skarn-type iron-tin deposit in eastern Guangdong

中文关键词:矽卡岩  锡石U-Pb年龄  I型花岗岩  隆文铁锡矿床  粤东

keywords:skarn  cassiterite U-Pb age  I-type granite  Longwen iron-tin deposit  eastern Guangdong

中文摘要:隆文铁锡多金属矿床是东南沿海地区一处小型矽卡岩型铁锡矿床，位于粤东锡成矿带西北端，其成矿时代及成矿岩体岩浆演化过程尚不清楚。文章选择早阶段粗粒花岗岩、晚阶段细粒花岗岩及锡多金属矿石为研究对象，开展年代学与地球化学研究。结果显示，两阶段花岗岩锆石U-Pb年龄分别为（140.8±1.2）Ma、（140.7±1.4）Ma，锡石U-Pb年龄为（139.8±1.3）Ma、（140.8±1.8）Ma，成岩成矿时代为早白垩世；成矿岩体具有高硅、钙碱性及过铝质特征，呈现轻稀土元素微富集、重稀土元素平坦的配分模式，属于高分异I型花岗岩；两阶段花岗岩具有负的全岩ε^Nd(t)值和锆石ε^Hf(t)值，Nd二阶段、Hf地壳模式年龄分别为1557~1621 Ma、1341~1811 Ma。结合粗粒花岗岩内暗色微粒包体，推断隆文花岗质岩浆主要来自早中元古代地壳物质的部分熔融，有少量地幔物质加入；与早阶段粗粒花岗岩相比，晚阶段花岗岩贫TFeO、MgO和TiO₂，具有较高的Rb/Sr比值，较低的Nb/Ta和Zr/Hf比值。这表明晚阶段细粒花岗岩是早阶段粗粒花岗岩岩浆进一步分异演化的产物，是岩浆晶粥经过熔体-晶体的分离作用形成的，与锡成矿关系密切。

Abstract:The Longwen tin-iron polymetallic deposit is a small skarn-type tin-iron deposit located in the northwestern end of the eastern Guangdong tin metallogenic belt. The exact mineralization age and magmatic evolution process of ore-forming intrusion are still unclear. To shed light on this, we focused on the early-stage coarse-grained gra-nite, late-stage fine-grained granite, and skarn ore containing cassiterite for geochronological and geochemical studies. The results show that the zircon U-Pb ages of the two stages of granite are (140.8±1.2) Ma and (140.7±1.4) Ma, respectively. Similarly, the cassiterite U-Pb ages are (139.8±1.3) Ma and (140.8±1.8) Ma. These ages suggest that both the magmatic crystallization and tin polymetallic mineralization occurred during the Early Cretaceous period. The ore-forming granites exhibit characteristics of high silica, calc-alkaline, and peraluminous composition. They also show slight enrichment in light rare earth element (REE) and flat heavy REE distribution patterns, indicating that they belong to highly fractionated I-type granites. Both stages of granite exhibit negative whole-rock ε^Nd(t) values and zircon ε^Hf(t) values. The Nd two-stage and Hf crustal model ages range from 1557 to 1621 Ma and 1341 to 1811 Ma, respectively. Combined with the presence of dark microgranular enclaves in the coarse-grained granite, it is inferred that the Longwen granitic magma primarily originated from partial melting of Paleo- to Meso-Proterozoic crust with minor mantle and juvenile crust involvement. In comparison to the early-stage coarse-grained granite, the late-stage fine-grained granite is depleted in TFeO, MgO, and TiO₂, and has higher Rb/Sr ratio and lower Nb/Ta and Zr/Hf ratios. These differences suggest that the late-stage granite resulted from further differentiation of the early-stage granitic magma, through the extraction of melt from a crystal mush system. The fine-grained granite is closely related to tin mineralization in the Longwen deposit.