Stratiform and Strata-Bound Zn-Pb-Ag Deposits in Proterozoic Sedimentary Basins, Northern Australia
Stratiform and Strata-Bound Zn-Pb-Ag Deposits in Proterozoic Sedimentary Basins, Northern Australia
复制标题
DOI：
10.5382/av100.28
复制
发表时间：
2005
期刊：
影响因子：
5.8
通讯作者：
R. Large;S. Bull;P. McGoldrick;S. Walters;G. M. Derrick;G. Carr
中科院分区：
文献类型：
--
作者：
R. Large;S. Bull;P. McGoldrick;S. Walters;G. M. Derrick;G. Carr
澳大利亚北方元古宙沉积盆地中锌、铅、银等金属元素的丰度居世界之首。伊萨-麦克阿瑟山盆地系统有5个超大型层状沉积岩型锌铅银矿床（麦克阿瑟河、世纪、伊萨山、希尔顿和乔治费希尔）和1个超大型层控银铅锌存款矿床（坎宁顿）。主要的层状锌铅银矿床具有许多相似的地质和地球化学特征，包括：1）位置靠近区域性广泛的正断层和走滑同沉积断层，2）富含有机质的黑色页岩和粉砂岩容矿岩，3）层状、平行层理的同沉积硫化物矿物，4）黄铁矿和含铁锰碳酸盐粉砂岩分隔的堆叠矿石透镜体，5）Zn/Pb比值在远离馈电断层处呈上升趋势的横向分带，6）Zn/Pb比值在地层上呈下降趋势的垂直分带，7）在矿石周围和沿着走向的沉积岩中存在广泛的富铁锰蚀变层控晕，8）硫化物矿物的34 S值范围很广，从0到20每密耳，黄铁矿比贱金属硫化物显示出更大的分布范围，9）铅同位素比值表明铅来自盆地内来源，解释的铅模型年龄与寄主岩石的锆石U-Pb年龄相似。这些共同特征表明，层状锌铅银矿床的形成与沉积和（或）成岩作用大致同时。沉积盆地中流体流动和热输运的数值模拟表明，由沉积卤水密度变化驱动的自由对流可能是形成巨型SEDEX矿床的最重要过程。为了响应沉积凹陷阶段期间的活动构造作用，伸展断层被重新激活，使得它们穿透页岩和/或碳酸盐岩盖层到几公里的深度，并进入裂谷阶段碎屑岩储层中所含的流体。深部含金属卤水沿断层上升，并在盆地底部或附近排出。金属沉淀发生在缺氧的，富含有机物的子盆地发展相邻的同沉积馈线故障。
In terms of zinc, lead, and silver metal endowment, the Proterozoic sedimentary basins of northern Australia rank number one in the world. The Mt Isa-McArthur basin system hosts five supergiant, stratiform, sedimentary rock-hosted Zn-Pb-Ag deposits (McArthur River, Century, Mt Isa, Hilton, and George Fisher), and one supergiant stratabound Ag-Pb-Zn deposit (Cannington). The major stratiform Zn-Pb-Ag deposits exhibit many similar geological and geochemical features that include: 1) location close to regionally extensive normal and strike-slip synsedimentary faults, 2) organic-rich black shale and siltstone host rocks, 3) laminated, bedding-parallel synsedimentary sulfide minerals, 4) stacked ore lenses separated by pyritic and Fe-Mn carbonate-bearing siltstones, 5) lateral zonation exhibiting an increasing Zn/Pb ratio away from the feeder fault, 6) vertical zonation exhibiting decreasing Zn/Pb ratio up-stratigraphy, 7) an extensive stratabound halo of iron- and manganese-rich alteration in the sedimentary rocks surrounding and along strike from ore, 8) a broad range of 34S values for sulfide minerals, from about 0 to 20 per mil, with pyrite exhibiting a greater spread than base metal sulfides, and 9) lead isotope ratios that indicate derivation of lead from intrabasinal sources with interpreted lead model ages being similar to the measured zircon U-Pb ages of the host rocks. These common features demonstrate that the stratiform Zn-Pb-Ag ores formed approximately contemporaneously with sedimentation and (or) diagenesis. Numerical modelling of fluid flow and heat transport in sedimentary basins suggests that free convection, driven by density changes in sedimentary brines, may be the most important process in forming giant SEDEX deposits. In response to periods of active tectonism during the sag phase of sedimentation, extensional faults are reactivated such that they penetrate the shale and/ or carbonate cap rocks to depths of several kilometres and access fluids contained in the rift phase clastic reservoir. The deep metalliferous brines ascend the faults and discharge on, or close-to, the basin floor. Metal precipitation occurs in the anoxic, organic-rich sub-basins developing adjacent to the syn-sedimentary feeder faults.