Heinson Graham, Didana Yohannes, Soeffky Paul, Thiel Stephan, Wise Tom
Department of Earth Sciences, University of Adelaide, Adelaide, SA, 5005, Australia.
Geological Survey of South Australia, GPO BOX 320, Adelaide, SA, 5001, Australia.
Sci Rep. 2018 Jul 13;8(1):10608. doi: 10.1038/s41598-018-29016-2.
World-class magmatic mineral systems are characterised by fluid/melt originating in the deep crust and mantle. However, processes that entrain and focus fluids from a deep-source region to a kilometre-scale deposit through the crust are unclear. A magnetotelluric (MT) and reflection seismic program across the margin of the Gawler Craton, Australia yield a distinct signature for a 1590 Ma event associated with emplacement of iron-oxide copper gold uranium (IOCG-U) deposits. Two- and three-dimensional MT modelling images a 50 km wide lower-crustal region of resistivity <10 Ωm along an accreted Proterozoic belt. The least resistive (1 Ωm) part terminates at the brittle-ductile transition at ~15 km, directly beneath a rifted sedimentary basin. Above the brittle-ductile transition, three narrow low-resistivity zones (100 Ωm) branch to the surface. The least resistive zone is remarkably aligned with the world-class IOCG-U Olympic Dam deposit and the other two with significant known IOCG-U mineral occurrences. These zones are spatially correlated with narrow regions of low seismic reflectivity in the upper crust, and the deeper lower-crust conductor is almost seismically transparent. We argue this whole-of-crust imaging encapsulates deep mineral system and maps pathways of metalliferous fluids from crust and mantle sources to emplacement at discrete locations.
世界级的岩浆矿物系统的特征是源自地壳深部和地幔的流体/熔体。然而，关于通过地壳将深部源区的流体夹带并聚焦到千米级矿床的过程尚不清楚。一项横跨澳大利亚加沃勒克拉通边缘的大地电磁（MT）和反射地震勘探项目，揭示了与铁氧化物铜金铀（IOCG-U）矿床就位相关的1590 Ma事件的独特特征。二维和三维MT建模显示，沿着一条增生的元古代带，存在一个宽50公里、电阻率<10Ωm的下地壳区域。电阻最小（约1Ωm）的部分在约15公里处的脆韧性转变处终止，正好位于一个裂谷沉积盆地之下。在脆韧性转变之上，三个狭窄的低电阻率带（约100Ωm）向地表分支。电阻最小的带与世界级的IOCG-U奥林匹克坝矿床显著对齐，另外两个与已知的重要IOCG-U矿化点对齐。这些带在空间上与上地壳中低地震反射率的狭窄区域相关，而更深的下地壳导体几乎是地震透明的。我们认为，这种全地壳成像概括了深部矿物系统，并绘制了含金属流体从地壳和地幔源到离散位置就位的路径。
