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引用本文:杨永春,余君鹏,赵得龙,李生栋,刘家军,王学银,王小强,孔维琼,王作刚. 甘肃省滴水山金矿区火山岩锆石U-Pb年龄、岩石地球化学特征及其形成的构造背景[J]. 中国地质, 2019, 46(6): 1454-1480.
YANG Yongchun,YU Junpeng,ZHAO Delong,LI Shengdong,LIU Jiajun,WANG Xueyin,WANG Xiaoqiang,KONG Weiqiong,WANG Zuogang. Zircon U-Pb dating and geochemistry of the volcanic rocks in the Dishuishan gold deposit in Gansu Province and its tectonic setting[J]. Geology in China, 2019, 46(6): 1454-1480(in Chinese with English abstract).
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甘肃省滴水山金矿区火山岩锆石U-Pb年龄、岩石地球化学特征及其形成的构造背景
杨永春1,2, 余君鹏2, 赵得龙3, 李生栋2, 刘家军1, 王学银2, 王小强2, 孔维琼2, 王作刚2
1.中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083;2.甘肃省地质矿产勘查开发局第四地质矿产勘查院, 甘肃 酒泉 735000;3.甘肃省地质矿产勘查开发局第二地质矿产勘查院, 甘肃 兰州 730020
摘要:
滴水山金矿床为北祁连造山带西段赋存于火山岩中的构造蚀变岩型金矿床。LA-ICP-MS锆石U-Pb测年结果表明,滴水山金矿区安山质晶屑凝灰岩年龄为(479.7±6.9)Ma,形成时代为早奥陶世,花岗闪长岩年龄为(426.9±6.7)Ma,时代为中志留世,含金黄铁绢英岩锆石U-Pb年龄(482.7±9.5)Ma,代表了赋矿火山岩的形成年龄,成矿时代应晚于(426.9±6.7)Ma;岩矿石地球化学特征表明,赋矿火山岩富集大离子亲石元素(LILE,如K、Rb、Th),明显亏损高场强元素(HFSE,如Nb、Ta、P、Ti),岩矿石稀土元素配分形式基本一致,呈右缓倾,轻稀土相对富集,具弱的铕负异常,形成于洋壳俯冲的岛弧环境,由俯冲板片脱水产生的流体交代地幔楔发生部分熔融而形成,在岩浆向上运移的过程中遭受了上地壳混染。花岗闪长岩SiO2=67.48%~72.68%,K2O+Na2O=7.15%~7.44%,里特曼指数δ值1.78~2.07,铝质指数A/CNK介于0.95~1.19,富集K、Rb、Th、U等大离子亲石元素和亏损Nb、P、Ti等高场强元素,稀土分配曲线呈右倾,轻稀土相对富集,具中等铕负异常,属钠质钙碱系列、弱过铝质I型花岗岩类,形成于弧-陆碰撞的火山岛弧环境,具壳幔混合成因的特点。综合区域地质资料,滴水山金矿成岩成矿构造背景为早奥陶世北祁连洋盆向阿拉善陆块之下俯冲,形成岛弧火山岩,为矿源层;中志留世,因弧-陆碰撞,形成同碰撞花岗闪长岩,晚志留世后造山作用及造山后的伸展,导致金的富集。
关键词:  锆石U-Pb测年  火山岩  地球化学  滴水山金矿  矿产勘查工程  北祁连造山带
DOI:10.12029/gc20190614
分类号:P597.3;P588.14
基金项目:国家自然科学重点基金(41730426)、中国地质调查局地质调查项目(DD20160012、121201004000172201-47)联合资助。
Zircon U-Pb dating and geochemistry of the volcanic rocks in the Dishuishan gold deposit in Gansu Province and its tectonic setting
YANG Yongchun1,2, YU Junpeng2, ZHAO Delong3, LI Shengdong2, LIU Jiajun1, WANG Xueyin2, WANG Xiaoqiang2, KONG Weiqiong2, WANG Zuogang2
1.State Key Laboratory of Geological Processes and Mineral Resources, China University of Geoscience, Beijing 100083, China;2.No.4 Geological and Mineral Exploration Party of Gansu Bureau of Geology and Mineral Resources, Jiuquan 735000, Gansu, China;3.No.2 Geological and Mineral Exploration Party of Gansu Bureau of Geology and Mineral Resources, Lanzhou 730020, Gansu, China
Abstract:
Located in the west part of North Qilian orogenic zone, the Dishuishan gold deposit is one of the altered cataclastic rock type deposits hosted in volcanic rocks. LA-ICP-MS zircon U-Pb chronology indicates that the andesitic crystal tuff was emplaced at (479.7±6.9) Ma, the granodiorite was emplaced at (426.9±6.7)Ma, and the gold bearing beresite was emplaced at (482.7±9.5)Ma, which represent the ages of ore-bearing volcanic rocks, whereas metallogenic age should be later than (426.9±6.7)Ma. The geochemical data suggest that the trace elements of volcanic rocks are rich in K, Rb, Th, and relatively depleted in Nb, Ta, P, Ti. The volcanic rocks and related mineral ores have similar chondrite-normalized REE patterns, exhibiting right-dip curve, the LREE are relatively enriched and Eu negative anomaly is weak. Combined with the trace elements and the REE characteristics, the authors infer that the volcanic rocks were formed in an island-arc setting, related to subduction of Qilian oceanic crust. The volcanic magma contaminated by the upper crust probably came from the partial melting of the mantle wedge, which had undergone metasomatism induced by the subduction fluid. The chemical composition of the granodiorite reveals SiO2 values ranging from 67.48% to 72.68%, K2O+Na2O values ranging from 7.15% to 7.44%, Rittmann index ranging from 1.78 to 2.07, and aluminous index A/CNK values ranging from 0.95% to 1.19%; the trace elements show enrichment of K, Rb, Th, U and relative depletion of Nb, P Ti. The LREE are relatively enriched and Eu negative anomaly is medium. The granodiorite belongs to Na calc-alkaline series weakly peraluminous I-type granitoid, and was formed in a volcanic island-arc setting of arc-continent collision and indicated crust and mantle source. According to regional geological data, the metallogenic tectonic background of the Dishuishan gold deposit was developed from the subduction of the North Qilian ocean basin beneath Alxa land block in Early Ordovician, which formed island-arc volcanic rock, and acted as main source bed→arc-continent collision in Middle Silurian period, which formed syncollisional granodiorite after Late Silurian period, and Qilian orogeny and intraplate extension in the post orogenic stage led to the enrichment of gold.
Key words:  zircon U-Pb dating  volcanic rocks  geochemistry  Dishuishan gold deposit  mineral exploration engineering  North Qilian orogenic belt