【摘要】 西藏甲玛矿床南坑矿段新取得重大找矿突破。铜、铅、锌均已超过大型规模,但其矿化结构、蚀变特征与主矿体有明显差异,成岩成矿作用时限尚不明确。勘查成果表明,南坑矿段矿体以矽卡岩型为主,呈不规则"厚板状"产于推滑覆构造体系中。矿石类型以块状铜铅锌矿石为主,具有厚度大、品位富等特征。本文以南坑矿段的典型矿化蚀变特征研究为基础,利用LA-ICP-MS锆石U-Pb测年和Hf同位素分析,获得含矿斑岩²⁰⁶Pb/²³⁸U加权平均年龄为14. 8Ma,与主矿体岩浆活动时限（17. 0～13. 9Ma）一致,说明二者属于同一岩浆作用的产物。同时,Hf同位素分析结果显示,南坑矿段含矿斑岩的¹⁷⁶Hf/¹⁷⁷Hf比值较高,为0. 282803～0. 282902,ε_Hf（t）值均为正值,主要集中在1. 4～4. 9,平均值为3. 6,表明其岩浆源区可能存在幔源组分的加入,是碰撞后伸展背景下新生下地壳部分熔融的产物。此外,南坑矿段明显受滑覆构造控制,区域推覆构造形成的红塔复背斜轴部高位岩块失稳向北滑覆,形成铜山滑覆体,岩浆热液沿滑覆构造交代角岩和大理岩形成厚大的富铜铅锌矿体。因此,岩浆活动时限和矿床地质特征,均揭示甲玛矿区南坑矿段与主矿段属于中新世同一岩浆作用的产物,但南坑矿段的成岩成矿作用受滑覆构造控制更为明显。更多还原

【Abstract】 Recently,a prospecting breakthrough in the exporation of the south pit ore-body in Jiama copper-polymetallic deposit has been achieved. As for the quantity of its mineral resources,copper,lead and zinc in this ore-body all reach large-size reserves.However,its mineralization and alteration obviously different from the main orebody of the Jiama deposit. The chronology of petrogensis and metallogeny of this orebody is still unclear. The exploration achievements shown that the south pit ore-body is predominantly in skarn mineralization,and it occured as a thick irregular plate in the thrust-gliding nappe tectonic system. The ore types are mainly composed of massive copper,lead and zinc ores,which characterized by high grade,large thickness. On the basis of detailed study on alteration and mineralization characteristics of the south pit ore-body,U-Pb dating of LA-ICP-MS zircon and Hf isotope analysis were carried out to investigate the ore-bearing porphyry. The results show that the weighted average ²⁰⁶Pb/²³⁸U age of 30 zircons is 14. 8 Ma,consistent with the mineralization magmatism time limit in the main orebody area（ 17. 0 ～ 13. 9 Ma）,suggesting that they were derived from the same magma chamber. Meanwhile,Hf isotope analysis data show that ore-bearing porphyry zircon Hf isotope ¹⁷⁶Hf/¹⁷⁷Hf ratios are relatively high（ 0. 282803 ～ 0. 282902）,with a positive ε_Hf（ t） value range of 1. 44 to 4. 92,indicating that their material sources have some mantle source composition and are generated by partial melting of the newborn lower crust during the post-collisional crustal extension period. In addition,the distribution of the south pit ore-body is controlled by a thrust-gliding nappe tectonic system,namely,the Tongshan gliding nappe structure,which developed as a result of northward slippage of the unstable high anticline block. This system was formed by thrust deformations,and during its formation,thick and large copper-rich ore-bodies developed due to the metasomatism of hornfels and marble in decollement structures by magmatic hydrothermal fluids. In conclusion,the south pit orebody and the main ore-body were derived from the same Miocene magmatism according to the age of magmatism and geological features,but the petrogensis and metallogeny of the south pit ore-body was obviously controlled by a gliding nappe tectonic system.更多还原