西藏洛巴堆矽卡岩型铁多金属矿床石榴子石和锆石U-Pb测年及地质意义

石榴子石是矽卡岩型矿床中最常见的蚀变矿物之一,因此,对石榴子石进行年代学研究能够准确限定矽卡岩型矿床的成矿时代.青藏高原冈底斯成矿带中部发育众多矽卡岩型多金属矿床,由于缺乏精确的成矿年代学数据,制约着对这些矿床成因和动力学背景的深入认识.因此,文章以该成矿带具有代表性的洛巴堆矽卡岩型铁多金属矿床为研究对象,通过对赋矿矽...

Garnet/zircon U-Pb dating and geological significance of Luobadui skarn iron polymetallic deposit in Tibet

Garnet is one of the most common alteration minerals in the skarn deposit, and hence garnet geochronology can accurately define the ore-forming age of the skarn deposit. Many skarn-type polymetallic deposits are developed in the central part of the Gangdese metallogenic belt, Tibet. However, the lack of accurate mineralization chronologic data severely restricts deep understanding of the genesis and geodynamic setting of these deposits. Therefore, in this paper, the authors chose the representative Luobadui skarn iron polymetallic deposit in this metallogenic belt as the research object to conduct investigation. Through LA-ICP-MS U-Pb dating of garnet in ore-bearing skarn and granodiorite, the authors expect that U-Pb dating could accurately define the mineralization age of the deposit. Backscattering and electron microprobe analysis shows that the garnet in the Luobadui skarn deposit has generally developed zoning structure, and the end member composition is dominated by grossular-andradite, which has the U values from 0.4×10^-6 to 28.1×10^-6. The garnet LA-ICP-MS U-Pb dating data show that the age of garnet formation is (62.7±2.3)Ma(n=94). Meanwhile, the zircon U-Pb age of the granodiorite in close contact with skarn is (62.6±0.8)Ma (n=30), which is consistent with the formation age of the garnet. This result indicates that the Luobadui deposit was formed in the Paleocene and had a close genetic relationship with synchronous granodiorite. Combined with the 65~50 Ma India-Eurasia collision event, the dating results show that the Luobadui skarn iron polymetallic deposit was formed in the India-Eurasia initial collision setting. In addition, this study shows that the garnet U-Pb dating system is less affected by the erosion and uplift of the Tibet Plateau compared with the result of Ar-Ar dating method. The garnet U-Pb dating can accurately define mineralization age of the skarn-type deposit and has an extensive application prospect.