(1. 中南大學(xué) 地球科學(xué)與信息物理學(xué)院 有色金屬成礦預(yù)測教育部重點實驗室，長沙 410083；
2. 中國科學(xué)院 地球化學(xué)研究所 礦床地球化學(xué)國家重點實驗室，貴陽 550002；
3. 湖南省有色地質(zhì)勘查局二總隊，湘潭 411102)
摘 要: 包金山金礦床是近年在湘中地區(qū)探獲的以金為主的多金屬礦床，其成礦與印支晚期巖漿活動關(guān)系密切。利用高精度SIMS鋯石U-Pb定年方法得到礦區(qū)兩條花崗閃長斑巖年齡分別為(225.1±1.5) Ma和(223.3±1.4) Ma，在誤差范圍內(nèi)一致，屬印支晚期大規(guī)模巖漿活動的產(chǎn)物；礦區(qū)兩條花崗閃長斑巖的176Hf/177Hf值均集中分布在0.2825附近，對應(yīng)的εHf(t)值介于-5.9~3之間，平均為-3.98，兩階段模式年齡TDM2為0.96~1.45 Ga，平均為1.35 Ga；δ18O值為0.824%~0.973%；Hf-O同位素研究表明花崗閃長斑巖主要為中元古代下地殼巖石重熔形成，且有部分幔源物質(zhì)參與成巖作用；與紫云山花崗巖體對比分析，表明兩者為同源巖漿演化的產(chǎn)物，且間接指示包金山金礦成礦時間為227~223 Ma；花崗閃長斑巖形成于多板塊匯聚的動力學(xué)背景，為印支地塊向北擠壓和太平洋板塊向西俯沖共同作用的結(jié)果。
關(guān)鍵字: SIMS 鋯石U-Pb年齡；Hf-O同位素示蹤；花崗閃長斑巖；包金山礦床；湘中
（1. Key Laboratory of Non-ferrous Metals Metallogenic Prediction, Ministry of Education, School of Geosciences and Info-physics, Central South University, Changsha 410083, China;
2. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences，Guiyang 550002, China;
3. The Second Corps of Nonferrous Geological Prospecting Bureau in Hunan Province, Geological Exploration Institute, Xiangtan 411102, China）
Abstract:Baojinshan gold deposit is Au-dominated polymetallic deposit discovered recently in central Hunan, its mineralization is considered to be closely related to the magmatic activities in late Indosinian. High accuracy SIMS zircon U-Pb age determination was used in this study to obtain the ages of two granodiorite-porphyry dykes at (225.1±1.5) Ma and (223.3±1.4) Ma, indicating that this deposit was the product of extensive magma activity in late Indosinian. The 176Hf/177Hf values of two granodiorite-porphyry dykes intensively distributed around 0.2825, with the corresponding εHf(t) ranged from -5.9 to 3, averaging -3.98. The TDM2 model age was estimated from 0.96 GPa to 1.45 Ga, averaging 1.35 Ga; the δ18O value of granodiorite-porphyry ranged from 0.824% to 0.973%. Hf-O isotope analysis shows that the granodiorite-porphyry is mainly formed by the rock remelting of Mesoproterozoic lower crust, and mantle-sourced materials are considered to participate the diagenesis. Contrastive analysis on the granodiorite-porphyry in Baojinshan with Ziyunshan granite suggests that both of them are the products of comagmatic evolution, which indirectly indicates that the metallogenetic time of Baojinshan gold deposit ranges in 227-223 Ma. The granodiorite-porphyry is formed under the multi-plates convergent dynamics background, and affected by the northward squeeze of Indochina Block and westward subduction of Pacific Plate.
Key words: SIMS U-Pb zircon dating; Hf-O isotopes tracing; granodiorite-porphyry; Baojinshan gold deposit; central Hunan Province
