摘要
滇中老街子Pb-Ag矿床位于金沙江-哀牢山富碱斑岩成矿带内的姚安铅多金属成矿区。矿区出露正长斑岩脉、粗面斑岩脉、煌斑岩脉及白榴石斑岩脉等多种类型富碱岩脉,与Pb-Ag矿(化)体在空间上密切共生。粗面斑岩脉为矿区内最为发育的富碱岩脉之一,根据岩相学特征,可分为斑晶以钠-透长石为主的Ⅰ类和斑晶以透长石和黑云母为主的Ⅱ类。本次工作对矿区粗面斑岩脉进行了锆石LA-ICP-MSU-Pb年龄、Hf同位素及岩石地球化学分析,确定了其成岩年龄,探讨了其成因机制。结果表明,2类粗面斑岩脉锆石U-Pb年龄不具明显差别,分别为(32.32±0.2) Ma和(32.43±0.4) Ma,与区内粗面岩、正长斑岩成岩年龄以及Pb-Ag矿床成矿年龄一致。2类粗面斑岩脉均属钾玄岩系列岩石,相对富集LILE和LREE、亏损HFSE,极低的εHf(t)值(-13.55~-8.53),指示岩浆源区主要为加厚下地壳,混入了少量富集地幔组分。岩石为印-亚板块俯冲背景下,青藏高原隆升引发岩石圈拆沉作用产物,加厚下地壳和少量富集地幔部分熔融形成钾质岩浆,晚碰撞阶段的剪切-走滑作用诱发岩浆上升侵位,期间经历不同程度的岩浆演化,最终形成2类粗面斑岩脉。
The Laojiezi Pb-Ag deposit in the central Yunnan is located in the Yao’an lead polymetallic metallogenic district within the Jinshajiang-Ailaoshan alkali-rich porphyry metallogenic belt. Various types of alkali-rich dikes, such as syenite porphyry dikes, trachyte porphyry dikes, lamprophyre dikes, and leucite porphyry dikes, are exposed in the district.They are closely related to the Pb-Ag mineralized bodies in space. The trachyte porphyry dike is one of the mostly developed alkali-rich dikes in the deposit. According to the petrographic characteristics, it can be classified into two types including the Type Ⅰ whose major phenocrysts are of sodium-sanidine and Type Ⅱ whose major phenocrysts are of sanidine and biotite. The zircon LA-ICP-MS U-Pb ages and Hf isotopes and petrogeochemistry of the trachyte porphyry dikes in the deposit were investigated in this paper, in order to determine diagenetic ages and to discuss petrogenetic mechanism of the trachyte porphyry dikes. Our results suggest that the obviously similar zircon U-Pb ages of two types of trachyte porphyry dikes are 32.32±0.2 Ma and 32.43±0.4 Ma respectively, which are consistent with the diagenetic ages of the trachyte and syenite porphyry and the metallogenic age of the Pb-Ag deposit in the area. The two types of trachyte porphyry dikes belong to the shoshonite, with relatively enriched LILE and LREE, depleted HFSE, and extremely low εHf(t) values(-13.55-8.53), indicating that its magma was mainly derived from the thickened lower crust mixed with a small amount of enriched mantle components. Trachyte porphyry dikes are products of lithosphere delamination caused by the uplifting of Qinghai-Tibet Plateau under the subduction background of the India plate toward the Eurasia plate. The potassium magma was originally formed by the patial melting the thickened lower crust mixed with small amounts of enriched mantle components. Secondly, the magma was uplifted due to the shear-strike-slip fault action in the late collision stage and had experienced variable degrees of evolution during its uplifting period. Finally, the evolved magma had emplaced to the shallow level to form two types of trachyte porphyry dikes in the area.
作者
黄仲金
吴静
吴鹏
姜龙燕
杨航
HUANG Zhong-jin;WU Jing;WU Peng;JIANG Long-yan;YANG Hang(College of Land and Resources Engineering,Kunming University of Science and Technology,Kunming 650093,China;Southwest Institute of Geological Survey,Geological Survey Center for Non-ferrous Mineral Resources,Kunming 650093,China;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China)
出处
《矿物学报》
CAS
CSCD
北大核心
2022年第3期295-314,共20页
Acta Mineralogica Sinica
基金
国家自然科学基金项目(编号:41102049)
云南省“万人计划”青年拔尖人才专项(编号:YNWR-QNBJ-2018-272)
云南省矿产资源预测评价工程实验室(2010)
云南省地质过程与矿产资源创新团队(2012)。
