Is the Mount Isa copper deposit the product of forced brine convection in the footwall of a major reverse fault
Is the Mount Isa copper deposit the product of forced brine convection in the footwall of a major reverse fault
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DOI：
10.1130/g20108.2
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发表时间：
2004-04
期刊：
影响因子：
5.8
通讯作者：
S. Matthäi;C. Heinrich;T. Driesner
中科院分区：
文献类型：
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作者：
S. Matthäi;C. Heinrich;T. Driesner
地球化学和质量平衡约束以及稳定同位素数据表明，伊萨山（澳大利亚）的铜矿床是由来自上覆伊萨山群变沉积岩的还原富硫流体与来自下伏变玄武岩进入角砾状接触带的富铜氧化流体混合形成的。我们进行了数值模拟，以测试沉积物是否可能是由伊萨山断层带上渐进位移驱动的强制流体对流形成的，变质等级的偏移量为 200 8C。结果表明，每年 1 毫米的抬升会导致区域流体流动组织成稳定的、渗透率控制的循环系统。通过氧化变玄武岩的远场平流叠加在断层下方变沉积岩中的小规模对流上。随着大规模对流的势头增强，角砾岩逐渐冷却，这与矿物学和流体包裹体的演化相一致。对于实际的抬升率，测得的矿体中二氧化硅富集度（$190 Mt SiO2）在 1 m.y 内即可实现。还原流体和氧化流体按照高品位铜铁硫化物沉淀所需的比例混合，并借助两种流体流入最具渗透性和最强烈对流矿体区域的比率的快速振荡。
Geochemical and mass-balance constraints in conjunction with stable isotope data in- dicate that the copper deposit of Mount Isa (Australia) formed by mixing of a reduced sulfur-rich fluid from overlying Mount Isa Group metasedimentary rocks with a copper- rich oxidized fluid entering a brecciated contact zone from underlying metabasalts. We have performed numerical simulations to test whether the deposit may have formed by forced fluid convection driven by progressive displacement on the Mount Isa fault zone, indicated by an ;200 8C offset in metamorphic grade. Results indicate that uplift of $1 mm/yr induces regional fluid flow organizing into a stable, permeability-controlled cir- culation system. Far-field advection through the oxidized metabasalts is superimposed on smaller-scale convection in the metasedimentary rocks beneath the fault. As convection on the large scale gains momentum, the breccia progressively cools, consistent with min- eralogic and fluid-inclusion evolution. For realistic uplift rates, the measured silica en- richment in the orebody ($190 Mt SiO2) is achieved in ;1 m.y. Reduced and oxidized fluids mix at the proportions required for high-grade copper-iron sulfide precipitation, aided by rapid oscillations in the influx ratio of the two fluids into the most permeable and vigorously convecting orebody region.