粤北大宝山斑岩钼钨矿床赋矿岩体锆石LA-ICP-MS U-Pb年龄与矿床形成动力学背景分析

LA-ICP-MS Zircon U-Pb Age and Dynamic Background of the Dabaoshan Porphyry Associated with Mo-W Mineralization in Northern Guangdong Province

粤北大宝山斑岩钼钨矿床赋矿岩体出露面积0.18km2,矿化主要以细脉状及浸染状产于斑岩及其内外接触带中。系统的薄片观察表明,该岩体岩性比较复杂,有碱长花岗斑岩、普通花岗斑岩、白云母二长花岗斑岩及白云母花岗闪长斑岩。本文分析了碱长花岗斑岩及白云母二长花岗斑岩锆石LA-ICP-MSU-Pb年龄,碱长花岗斑岩锆石年龄为166.6±2.1Ma,MSWD=1.17;白云母二长花岗斑岩锆石年龄为166.2±3.1Ma,MSWD=2.3。两个样品的锆石U-Pb年龄基本一致,表明大宝山斑岩钼钨矿床岩体形成于燕山早期。据斑岩矿床年龄、斑岩矿床在十杭带时空分布特征及华南地区中生代构造背景,提出大宝山斑岩钼钨矿床岩体的形成可能与侏罗纪太平洋洋壳向南西俯冲而引发的的十杭带深断裂构造活动复活有关。

The Mo-W bearing Dabaoshan porphyry is located in the north of Guangdong province with outcrop area of 0.18 km2. The Dabaoshan porphyry Mo-W ore is characterized by veinlet and disseminated mineralization oc- curred in the porphyry and the contact zone. Thin section observation indicates that the Dabaoshan Mo-W porphyry consists mainly of alkali feldspar granite porphyry, granite porphyry, muscovite monzonitic granite porphyry and muscovite granodiorite porphyry. Alkali feldspar granite porphyry has LA-ICP-MS U-Pb age of 166.6 -＋ 2. 1 Ma （ MSWD = 1.17） and the muscovite monzonitic granite porphyry has zircon LA-ICP-MS U-Pb age of 166.2 _＋ 3.1 Ma （ MSWD = 2.3 ）. The LA-ICP-MS U-Pb ages of alkali feldspar granite porphyry and muscovite monzonitic gran- ite porphyry are almost identical within error. Our new set of the Dabaoshan porphyry zircon LA-ICP-MS U-Pb data suggests that the Dabaoshan porphyry was emplaced during early Yanshanian. Based on the forming age of the por- phyry and the tectonic background of South China during Mesozoic, it is proposed that the Dabaoshan porphyry as- sociated with Mo-W mineralization was resulted from the tectonic resurgent of Shihang rift triggered by the south- westwards subduction of the ancient Pacific plate in Jurassic.