地球化學(xué)、鋯石U-Pb年代學(xué)和Hf同位素制約
(1. 中南大學(xué) 有色金屬成礦預(yù)測教育部重點實驗室，長沙 410083；
2. 中南大學(xué) 地球科學(xué)與信息物理學(xué)院，長沙 410083)
摘 要: 寶山礦床位于坪寶礦帶的北端，產(chǎn)出與花崗閃長斑巖有關(guān)的銅鉬鉛鋅銀多金屬礦床。對采自坑道內(nèi)的新鮮巖脈進行巖石成分分析及鋯石U-Pb和Hf同位素測試。鋯石U-Pb定年結(jié)果顯示：基質(zhì)為細粒結(jié)構(gòu)的斑巖成巖年齡為(180.5±2.0) Ma，基質(zhì)為隱晶質(zhì)的斑巖成巖年齡為(165.3±3.3) Ma，表明該區(qū)在燕山早期有多次(階段)巖漿侵入活動，依據(jù)鋯石Hf同位素組成計算的平均地殼模式年齡為1 709~1 951 Ma，在εHf(t)—t圖解中，鋯石點投在2.5 Ga平均地殼演化線附近，表明巖石源區(qū)為古老地殼。結(jié)合巖石地球化學(xué)特征，認(rèn)為該區(qū)的花崗閃長巖是在燕山早期擠壓背景下由中下元古界基底地層發(fā)生增厚熔融形成的。本區(qū)成礦時代對應(yīng)于成巖時代，時限為160~180 Ma，其間巖漿的多階段侵入帶來充足的成礦物質(zhì)，最終在地殼淺部層次形成多金屬礦床。
關(guān)鍵字: 花崗閃長斑巖；銅鉛鋅多金屬礦床；地球化學(xué)；鋯石U-Pb定年；Hf同位素示蹤；寶山
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education,
Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China）
Abstract:Baoshan Cu-Mo-Pb-Zn-Ag deposit is located in the north of famous Huangshaping—Baoshan metallogenetic belt, whose formation is related closely with shallow-seated granodiorite-porphyry. Fresh samples were collected from mining tunnel, the whole rock chemical composition tests were carried out, meanwhile zircon grains were collected from granodiorite samples, and their U-Pb and Hf isotope composites were analyzed by La-ICPMS. The results of U-Pb dating display that one sample with fine-grain texture in the matrix has an age of (180.5±2.0) Ma, the other sample with cryptocrystalline texture in matrix has an age of (165.3±3.3) Ma, which implies that there is multi-stage magmatic intrusive activity in this area. According to Hf isotope compositions, the average crust model age is calculated to be 1 709−1 951 Ma, in the figure of εHf(t)—t, the points of zircon grains lie in the area neighbored to the evolution curve of 2.5 Ga average crust, suggesting that the origin of zircons comes from ancient crust. Combined with characteristics of petrogeochemistry, the granodiorites are interpreted to form in the background of crustal thickness increasing due to the regional tectonic compression. Many former studies show that the regional basement of this area is middle-lower proterozoic group, they melted to form magma which intruded to shallow position of crust to be granodiorite-porphyry along available fractures. According to former studies, the metallogenic time corresponds to the ages of two-stage magmatic rocks, the metallogenic time extends from 180 to 160 Ma, multi-stage magma activity provides abundant ore-forming material to form Baoshan multimetal ore deposit.
Key words: granodiorite-porphyry; Cu-Pb-Zn multi-metal deposit; geochemistry; zircon U-Pb dating; Hf isotope tracing; Baoshan
