近日，东华理工大学Chen Xilian等人揭示了西藏冈底斯带Dongga英云闪长岩的岩石成因、氧化态和挥发分含量，及其对斑岩铜矿化的意义。2024年1月8日，国际知名学术期刊《地球化学学报》发表了这一成果。

研究人员提供了冈底斯带中部Dongga英云闪长岩的锆石U-Pb定年及微量元素、磷灰石主量及微量元素的数据，结合已发表的全岩地球化学和同位素资料，揭示了该岩体的岩石成因、氧化态、挥发性含量及铜矿化潜力。Dongga英云闪长岩的锆石U-Pb年龄为179.4±0.9 Ma。表现出较高的全岩V/Sc值(8.76-14.6)，相对较低的磷灰石Ce_N/Ce_N^*比值(1.04-1.28)，较高的锆石(Eu/Eu^*)_N(平均为0.44)，较高的Ce⁴⁺/Ce³⁺值(206-1896)以及较高的?FMQ值(1.3-3.7)，这些数据表明其岩浆氧逸度较高。

Dongga英云闪长岩具有角闪石斑晶，相对较高的全岩Sr/Y比值(20.3-58.9)和较低的锆石Ti温度较低(502-740℃)，反映出岩浆含水量较高。根据磷灰石SO₃含量估算的岩浆硫含量(0.002-0.024 wt%)表明，岩浆硫含量富集。

结合前人研究和收集到的Sr-Nd-Hf同位素资料，研究人员认为Dongga英云闪长岩来源于与新特提斯洋板块俯冲有关的较年轻的下地壳。与Xietongmen含矿斑岩比较，Dongga英云闪长岩在岩浆来源、构造背景、岩浆氧化还原状态、挥发性组分等方面均表现出显著的相似性，表明Dongga英云闪长岩具有较高的斑岩型铜成矿潜力，对今后的成矿找矿勘查具有重要指导意义。

据悉，西藏冈底斯带经历了侏罗纪俯冲作用和新生代大陆碰撞作用，是全球著名的岩浆岩和斑岩铜矿带。该带内发现了许多侏罗纪侵入体。除了大型Xietongmen矿床中的石英闪长斑岩外，该带其他侏罗纪侵入体的铜成矿潜力尚不清楚。

附：英文原文

Title: Petrogenesis, oxidation state and volatile content of Dongga tonalite in the Gangdese belt, Xizang: Implication for porphyry Cu mineralization

Author: Zhang, Liqiang, Chen, Xilian, Zou, Shaohao, Xu, Deru, Wang, Xuena, Wang, Hua

Issue&Volume: 2024-01-08

Abstract: The Gangdese belt in Xizang has experienced both Jurassic subduction and Cenozoic continental collision processes, making it a globally renowned region for magmatic rocks and porphyry copper deposits. Numerous Jurassic intrusions have been identified in the belt. Apart from the quartz diorite porphyry in the large Xietongmen deposit, the Cu mineralization potential of other Jurassic intrusions in this belt remains unclear. This study presents zircon U–Pb dating and trace elements, apatite major and trace elements as well as published whole-rock geochemical and isotopic data of the Dongga tonalite in the central part of the Gangdese belt, aiming to reveal the petrogenesis, oxidation state, volatile content, and Cu mineralization potential of this intrusion. The Dongga tonalite has a zircon U–Pb age of 179.4±0.9 Ma. It exhibits high whole-rock V/Sc values (8.76–14.6), relatively low apatite Ce_N/Ce_N^* ratios (1.04–1.28), elevated zircon (Eu/Eu^*)_N values (an average of 0.44), high Ce⁴⁺/Ce³⁺ values (205–1896), and high ?FMQ values (1.3–3.7), collectively suggesting a high magmatic oxygen fugacity. The Dongga tonalite features amphibole phenocrysts, relatively high whole-rock Sr/Y ratios (20.3–58.9), and lower zircon Ti temperatures (502–740 °C), reflecting a high magmatic water content. Estimation of magmatic sulfur content (0.002–0.024 wt%) based on apatite SO₃ contents indicates an enriched magma sulfur content. Combined with previous studies and the collected Sr–Nd–Hf isotopes, the Dongga tonalite is derived from juvenile lower crust related with subduction of the NeoTethys oceanic slab. When compared with Xietongmen ore-bearing porphyries, the Dongga tonalite exhibits remarkable similarities with the Xietongmen ore-bearing porphyries in terms of magma source, tectonic background, magmatic redox state, and volatile components, which indicates that the Dongga tonalite has a high porphyry Cu mineralization potential, and therefore, provides important guidance for the future mineralization exploration.

DOI: 10.1007/s11631-023-00664-0

Source: https://link.springer.com/article/10.1007/s11631-023-00664-0