The Lower Changjiang (Yangzi/Yangtze River) metallogenic belt, east central China: intrusion- and wall rock-hosted Cu–Fe–Au, Mo, Zn, Pb, Ag deposits
The Lower Changjiang (Yangzi/Yangtze River) metallogenic belt, east central China: intrusion- and wall rock-hosted Cu–Fe–Au, Mo, Zn, Pb, Ag deposits
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DOI：
10.1016/s0169-1368(99)00022-0
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发表时间：
1999-12
影响因子：
3.3
通讯作者：
Yuanming Pan;P. Dong
中科院分区：
文献类型：
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作者：
Yuanming Pan;P. Dong
长江下游西起湖北武汉，东至江苏镇江，拥有200多个多金属（Cu-Fe-Au、Mo、Zn、Pb、Ag）矿床，是中国最重要的成矿带之一。该成矿带位于扬子克拉通北缘，北邻大别山超高压变质带，主要由寒武系—三叠系海相碎屑沉积岩、碳酸盐岩和蒸发岩组成，覆盖前寒武纪基底，受燕山期（205 ~ 64 Ma）花岗岩体和次火山杂岩侵入。从晚元古代到三叠纪的反复构造作用导致了广泛发育的断裂和褶皱网络，涉及寒武纪-三叠纪沉积地层和前寒武纪基底。下长江成矿带燕山期花岗岩体和次火山杂岩体具有全岩δ18O值为+8‰~ +10‰，初始87sr /86Sr值为0.704 ~ 0.708，ϵNdtfrom−10 ~−17的特征，解释其成因为幼年地幔与老地壳物质混合。燕山期花岗岩类呈东向年轻化、碱度增加（由西部较老的钙碱性向东部较年轻的亚碱性），这与扬子克拉通与中朝克拉通的斜碰撞以及由早期挤压到晚期伸展或裂陷的构造演化有关。长江下成矿带多金属矿床主要集中在自西向东、鄂东、九瑞、安庆-贵池、鲁中、铜陵、宁武和宁镇7个燕山期岩浆活动特别广泛的地区。成矿的特征是在单个矿床中赋存3种不同类型的矿体：燕山期花岗岩类岩体中的矿体、燕山期岩体与晚古生代—早中生代沉积岩接触带中的夕卡岩型矿体和晚古生代—早中生代沉积岩中的层控块状硫化物矿体。主要储集层为中石炭统黄龙组、下二叠统和下中三叠统碳酸盐岩和蒸发岩。侵入岩型和矽卡岩型矿体在蚀变组合、金属含量和同位素组成等方面均表现出发育的分带性，明显是由与燕山期岩浆活动有关的热液活动形成的。晚古生代—早中生代沉积地层中的层控块状硫化物矿体长期以来被认为是浅海环境中沉积或火山-沉积喷发作用形成的。然而，近40年来的广泛研究未能提供明确的同生成矿证据。在地质关系和同位素地球化学特征的基础上，提出了这些层控块状硫化物矿体及其伴生矽卡岩矿体成因的碳酸盐岩替代矿床模型。该模式表明，燕山期岩体演化的岩浆流体与碳酸盐岩和蒸发岩围岩相互作用形成了后成成矿作用。成矿作用是形成接触带近端矽卡岩矿体和侵入带矿体的大型热液系统的一个完整而又遥远的部分。长江下成矿带的层控块状硫化物矿床与井区有许多共同的特征。
The lower valley of Changjiang, from Wuhan of the Hubei Province in the west to Zhenjiang of the Jiangsu Province in the east, contains more than 200 polymetallic (Cu–Fe–Au, Mo, Zn, Pb, Ag) deposits and is one of the most important metallogenic belts in China. This metallogenic belt, situated at the northern margin of the Yangzi craton and bordered by the Dabieshan ultrahigh pressure metamorphic belt to the north, consists mainly of Cambrian–Triassic marine clastic sedimentary rocks and carbonate and evaporite rocks, which overlay a Precambrian basement and are intruded by Yanshanian (205 to 64 Ma) granitoid intrusions and subvolcanic complexes. Repeated tectonism from Late Proterozoic to Triassic resulted in extensively developed networks of faults and folds involving the Cambrian–Triassic sedimentary strata and the Precambrian basement. The Yanshanian granitoid intrusions and subvolcanic complexes in the Lower Changjiang metallogenic belt are characterized by whole-rock δ18O of +8‰ to +10‰, initial87Sr /86Sr of 0.704 to 0.708, and ϵNdtfrom −10 to −17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials. Also, the Yanshanian granitoids exhibit eastward younging and increase in alkalinity (i.e., from older calc–alkaline in the west to younger subalkaline–alkaline in the east), which are related to oblique collision between the Yangzi and Sino-Korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes. Most polymetallic deposits in the Lower Changjiang metallogenic belt are clustered in seven districts where the Yanshanian magmatism is particularly extensive: from west to east, Edong, Jiurui, Anqing–Guichi, Luzhong, Tongling, Ningwu and Ningzhen. Mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits: orebodies in Yanshanian granitoid intrusions, skarn orebodies at the contact zones between the Yanshanian intrusions and Late Paleozoic–Early Mesozoic sedimentary rocks, and stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata. The most important host sedimentary strata are the Middle Carboniferous Huanglong Formation, Lower Permian and Lower–Middle Triassic carbonate and evaporite rocks. The intrusion-hosted and skarn orebodies exhibit well-developed zonation in alteration assemblages, metal contents, and isotopic compositions within individual deposits, and apparently formed from hydrothermal activities related to the Yanshanian magmatism. The stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano-sedimentary exhalative processes in shallow marine environments. However, extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization. On the basis of geological relationships and isotope geochemical characteristics, we propose a carbonate-hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies. This model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the Yanshanian intrusions with carbonate and evaporite wall rocks. Mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion-hosted orebodies. The stratabound massive sulfide deposits of the Lower Changjiang metallogenic belt share many features with the well …