Geochemistry and zircon U-Pb age of ore-bearing porphyry in the Paodaoling gold deposit in Guichi, Middle-Lower Yangtze metallogenic belt
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摘要:
贵池抛刀岭金矿位于长江中下游成矿带安庆-贵池矿集区, 是该地区首次发现的独立玢岩型金矿床, 含矿岩体主要为蚀变矿化的英安玢岩。经过近两年的地质勘查, 该矿床已接近大型金矿床规模。通过对抛刀岭金矿含矿岩体锆石LA-ICPMS U-Pb测定, 其成岩年龄为146.8±2.4Ma和141.3±1.0Ma (2σ), 与长江中下游地区中生代大规模铜金成矿事件时间一致。全岩地球化学研究表明, 该岩石为过铝质, 富集大离子亲石元素(K、Rb、Pb), 亏损高场强元素(Nb、Ta、Ti) 和轻稀土富集等地球化学特征。较高的锆石Ce4+/Ce3+和EuN/EuN*显示抛刀岭含矿岩体具有较高的氧逸度特征。构造判别图解显示这套含矿岩石属火山弧花岗岩(VAG), 与长江中下游铜金矿床含矿岩体形成于同一构造背景下, 即太平洋俯冲作用引起的洋壳和地幔楔熔融形成。
Abstract:The Paodaoling gold deposit is the first discovered porphyry type gold deposit in Anqing-Guichi ore-cluster region in the Middle-Lower Yangtze metallogenic belt (LYRB). The host rocks of the Paodaoling gold deposit are trachyte andesitic porphyries. Zircon LA-ICP-MS U-Pb dating of two ore-bearing porphyries are 146.8±2.4Ma and 141.3±1.0Ma (2σ), according with the main mineralization time of LYRB. Whole rock geochemistry indicates that the ore-bearing porphyries are peraluminous, enriched in K-Rb-Pb and light REE, depleted in Nb-Ta-Ti, similar to crustal origination. These porphyries show volcanic arc granite affinities. The higher ratios of Ce4+/Ce3+ and EuN/EuN* calculated from zircon data indicate that the Paodaling intrusion has higher oxygen fugacity with potentiality for Au formation. We conjecture that the Paodaoling gold deposit was probably related to melting of mantle wedge during subduction between Paleo-Pacific plate and Izanagi plate.
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图 1
抛刀岭及周边地区地质简图(据田鹏飞等, 2012修改)
Figure 1.
Sketch map of the Paodaoling district, Anqing-Guichi region (after Tian et al., 2012)
图 3
抛刀岭金矿含矿英安玢岩镜下照片
Figure 3.
Micrograph of the Paodaoling trachyte andicitic porphyrite
图 4
抛刀岭金矿含矿岩石地球化学判别图解
Figure 4.
Discrimination diagrams of gold-bearing rocks in the Paodaoling gold deposit
图 5
抛刀岭金矿英安玢岩稀土元素配分图(a) 及微量元素蛛网图(b)(球粒陨石标准值据Sun and McDonough, 1989; 原始地幔及其他地质储库标准值据McDonough and Sun, 1995)
Figure 5.
REE chondrite normalized diagram (a) and trace elements primitive normalized diagram (b) of the Paodaoling trachyte andicitic porphyrites (normalization values after Sun and McDonough, 1989; McDonough and Sun, 1995)
图 6
抛刀岭金矿英安玢岩锆石年龄图(a, c) 及锆石稀土配分图解(b, d, 粒陨石标准化值据Sun and McDonough, 1989)
Figure 6.
Zircon U-Pb ages (a, c) and REE distribution patterns (b, d) of zircons from the porphyrites in the Paodaoling gold deposit (normalization values after Sun and McDonough, 1989)
图 7
抛刀岭含矿玢岩锆石Ce4+/Ce3+与EuN/EuN*特征
Figure 7.
Characteristics of Ce4+/Ce3+ and EuN/EuN* from zircons in the Paodaoling gold-bearing porphyrites
图 8
抛刀岭金矿英安玢岩Y-Nb (a) 和Yb-Ta图解(b)(底图据Pearce et al., 1984)
Figure 8.
Y-Nb and Yb-Ta diagram of the Paodaoling ore-bearing porphyries (after Pearce et al., 1984)
图 9
YbN-(La/Yb)N判别图解(底图据Defant and Drummond, 1990)
Figure 9.
The YbN-(La/Yb)N discrimination diagram (after Defant and Drummond, 1990)
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