【作者】 周清；

【导师】 姜耀辉；

【作者基本信息】 南京大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 德兴斑岩铜矿是中国最大的斑岩型铜矿,属环太平洋斑岩型铜矿带西带的一部分。前人已对该矿床做了大量的研究,但在含矿斑岩成因及其成岩成矿构造背景等方面仍存在很大的分歧。针对德兴斑岩铜矿目前研究现状及存在问题,本论文在前人工作基础上,重点对德兴斑岩铜矿三个矿区的含矿斑岩开展了锆石U-Pb年代学、元素和Sr-Nd-Pb同位素地球化学以及锆石原位Hf同位素地球化学研究,同时还开展了辉钼矿Re-Os年代学、矿石Pb同位素地球化学和大脉型矿石中热液锆石U-Pb年代学、微量元素地球化学以及流体包裹体测温等研究工作。通过研究取得了新进展。LA-ICP-MS锆石U-Pb定年结果表明,德兴三个矿区的含矿斑岩均形成于中侏罗世早期(170-171 Ma)。含矿斑岩主要属于高钾钙碱性系列,同时具有埃达克岩特征,例如,高Sr、低Y和Yb含量,高Sr/Y和La/Y比值以及高Mg#。这些含矿斑岩的初始87Sr/86Sr比值介于0.7044-0.7047之间,εNd(T)值介于-1.4～+0.5之间,锆石原位εHf(T)值介于+2.6～+4.6之间。斑岩具有非常高的放射成因Pb同位素组成,初始206Pb/204Pb比值可达18.377,207Pb/204Pb比值可达15.614,208Pb/204Pb比值可达38.491。这些Sr-Nd-Pb-Hf同位素特征明显不同于扬子下地壳和太平洋洋中脊玄武岩,但与西太平洋海沟沉积物相一致。详细的元素和同位素地球化学数据表明,德兴含矿斑岩形成于与古太平洋板块俯冲有关的活动大陆边缘环境。俯冲大洋板片(主要为上覆沉积物)部分熔融形成的熔体,在其上升过程中与岩石圈地幔相互作用,最终形成了高钾钙碱性的埃达克质斑岩岩浆。辉钼矿Re-Os定年结果表明,德兴斑岩铜矿主成矿作用与岩浆侵入作用几乎同时发生(～171Ma)。德兴斑岩铜矿中辉钼矿含有非常高的Re和187Os含量,完全不同于陆壳改造(南岭成矿带)或拆沉加厚下地壳部分熔融(东秦岭-大别成矿带)所形成的辉钼矿的Re-Os同位素组成特征,而与俯冲板片起源的含矿斑岩相关的辉铝矿(太平洋东岸Cordillera和Andes成矿带)极为相似。可见,德兴斑岩铜矿更可能形成于活动大陆边缘环境,与前文通过含矿斑岩成因研究得出的结论相一致。矿石中黄铁矿的Pb同位素组成与含矿斑岩相一致,而明显不同于与围岩双桥山群地层有成因联系的矿石Pb同位素组成。Os-Pb同位素组成特征表明成矿物质主要来自含矿斑岩岩浆,是板片起源的埃达克质岩浆通过与岩石圈地幔相互作用从岩石圈地幔中萃取出来的。大脉型含矿石英脉中锆石SHRIMP U-Pb年代学、微量元素地球化学以及流体包裹体研究结果表明,德兴斑岩铜矿存在早白垩世晚期(～104.3 Ma)成矿作用事件,该期成矿热液显示中低温低盐度特征,形成矿区大脉型矿石。有关该期成矿事件机制及经济价值还有待今后进一步研究。更多还原

【Abstract】 The Dexing porphyry copper deposits (Tongchang, Fujiawu and Zhushahong), comprising the circum-Pacific porphyry copper ore belt, is the largest porphyry copper deposit in China. Although considerable studies have been done for the deposits, there are some controversies on the petrogenesis of the ore-bearing porphyries and geological setting. This paper presents new LA-ICP-MS zircon U-Pb and molybdenite Re-Os dating, whole-rock elemental, Sr-Nd-Pb isotopic and in-situ zircon Hf isotopic geochemistry for the three ore-bearing porphyries, Pb isotopic geochemistry for pyrites, SHRIMP U-Pb dating and trace elemental geochemistry, as well as fluid-inclusion measurements for the ore-bearing quartz veins or their hydrothermal zircons, in order to better constrain their petrogenesis and metallogeny.LA-ICP-MS zircon U-Pb dating shows that the Dexing ore-bearing porphyries were emplaced in the early Middle Jurassic (～171 Ma). The porphyries are mainly high-K calc-alkaline and show some adakitic affinities, i.e. characterized by high Sr and low Y and Yb contents, with high Sr/Y and La/Yb ratios, and by high Mg#, higher than pure crustal melts. These porphyries have initial 87Sr/86Sr ratios of 0.7044-0.7047,εNd(T) values of-1.4 to+0.5 andεHf(T) (in-situ zircon) values of +2.6 to+4.6. They show unusually radiogenic Pb isotopic compositions with initial 206Pb/204Pb up to 18.377,207Pb/204Pb up to 15.614 and 208Pb/204Pb up to 38.491.These Sr-Nd-Pb-Hf isotopic signals are distinctly different either from the Pacific MORB or from the Yangtze lower crust, but similar to the subducting sediments in the West Pacific trenches. Detailed elemental and isotopic data suggest that the Dexing porphyries were emplaced in a continental arc setting coupled with the westward subduction of the Paleo-Pacific plate. Partial melting of the subducted slab (mainly overlying sediments), with subsequent melts interacting with the lithospheric mantle wedge, formed the high-K calc-alkaline porphyry magmas.The molybdenite Re-Os dating indicates that the associated Cu-Mo mineralization was nearly contemporaneous (～171 Ma) with the porphyry emplacement. The molybdenites from the Dexing porphyry copper deposits show high rhenium and 187Os contents, which is obviously different from those related to crust re-melting (Nanling Metallogenic Belt) or partial melting by the delamination thickened crust (east Qinling-Dabie Metallogenic Belt), but compatible with those related to partial melting by the subducted slab (Andes and Cordillera Metallogenic Belts). Thus, the Dexing porphyry copper deposits should be emplaced in an active continental arc setting, which is consistent with the studies above on the ore-bearing porphyries. Pb isotopic compositions in Pyrites from Tongchang and Fujiawu are uniform and distinctly different from those derived from Shuangqiaoshan Strata meta-sedimentary rocks, but similar to those of the ore-bearing granodiorite porphyries. Detail Pb-Os isotopic evidences suggest the sources of Cu-Au-Mo metals were related to the intrusion magmas, other than the wall-rocks. They should be mainly extracted from the lithospheric mantle, after the oceanic crust-derived adakitic magmas interacting with the lithospheric mantle wedge.SHRIMP zircon U-Pb dating, trace elemental geochemistry and fluid-inclusion measurements for the ore-bearing quartz veins indicate that a subordinate Cu mineralization related to the hydrothermal event occurred at the late stage of Lower Jurassic (～104.3 Ma). The ore-forming fluids show epithermal and low salinity affinities, which is distinctly different from the magmatic fluids. We uncertain whether this metallogenic event has contributed some economic ore-bodies to the Dexing porphyry copper deposit. Thus, a further study should be done in the future.更多还原