Establishing timescales for iron oxide copper-gold (IOCG) deposit formation and the temporal relationships between ores and the magmatic rocks from which hydrothermal, metal-rich fluids are sourced is often dependent on low-precision data, particularly for deposits that formed during the Proterozoic. Unlike accessory minerals routinely used to track hydrothermal mineralization, iron oxides are dominant components of IOCG systems and are therefore pivotal to understanding deposit evolution. The presence of ubiquitous, magmatic-hydrothermal U-(Pb)-W-Sn-Mo–bearing zoned hematite resolves a range of geochronological issues concerning formation of the ~1.6 Ga Olympic Dam IOCG deposit, South Australia, at up to ~0.05% precision (²⁰⁷Pb/²⁰⁶Pb weighted mean; 2σ) using isotope dilution-thermal ionization mass spectrometry (ID-TIMS). Coupled with chemical abrasion-ID-TIMS zircon dates from host granite and volcanic rocks within and enclosing the ore-body, a confident magmatic-hydrothermal chronology is defined. The youngest zircon date from the granite intrusion hosting Olympic Dam indicates magmatism was occurring up until 1593.28 ± 0.26 Ma. The orebody was principally formed during a major mineralizing event following granite uplift and during cupola collapse, whereby the hematite with the oldest age is recorded in the outer shell of the deposit at 1591.27 ± 0.89 Ma, ~2 m.y. later than the youngest documented magmatic zircon. Hematite dates captured throughout major lithologies, different ore zones, and the ~2-km vertical extent of the deposit support ~2 m.y. of hydrothermal activity. New age constraints on the spatial-temporal evolution of the formation of Olympic Dam are considered with respect to a mantle to crustal continuum model. Cyclical tapping of magma reservoirs to maintain crystal mushes for extended time periods and incremental building of batholiths on the million-year scale prior to main mineralization pulses can explain the ~2-m.y. temporal window temporal window inferred from the data. Despite the challenge of reconciling such an extended window with contemporary models for porphyry deposits (≤1 m.y.), formation of Proterozoic ore deposits has been addressed at high-precision and supports the case that giant IOCG deposits may form over millions of years.

中文翻译：

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开启岩浆热液窗口：南澳大利亚中元古代奥林匹克大坝Cu-U-Au-Ag矿床的高精度U-Pb地球年代学

建立氧化铁铜-金（IOCG）矿床形成的时间尺度以及矿石和岩浆岩之间的时间关系（产生热液，富含金属的流体）通常取决于低精度的数据，尤其是对于元古代时期形成的矿床。与通常用于跟踪热液成矿作用的辅助矿物不同，氧化铁是IOCG系统的主要成分，因此对于理解矿床演化至关重要。普遍存在的岩浆热液含U-（Pb）-W-Sn-Mo带状赤铁矿解决了一系列与南澳大利亚〜1.6 Ga奥林匹克大坝IOCG矿床形成有关的地质年代学问题。精度（²⁰⁷ Pb / ²⁰⁶铅加权平均值；2σ）使用同位素稀释-热电离质谱（ID-TIMS）。再加上化学磨蚀-ID-TIMS锆石来自矿体内部和包围矿体的主花岗岩和火山岩，定义了一个自信的岩浆-水热年代学。奥林匹克水坝所在的花岗岩侵入体中最年轻的锆石日期表明岩浆活动一直持续到1593.28±0.26 Ma。矿体的形成主要是在花岗岩隆起后的一次重大矿化过程中以及冲天炉坍塌期间形成的，据此，最古老的赤铁矿记录在矿床的外壳中，为1591.27±0.89 Ma，比最年轻的岩浆锆石晚了约2 y。 。在主要的岩性，不同的矿石区域以及沉积物的约2 km垂直范围内捕获的赤铁矿日期支持约2 my的热液活动。考虑到地幔到地壳的连续体模型，考虑了对奥林匹克大坝形成的时空演化的新时代约束。在主要矿化脉冲之前，对岩浆储层进行周期性的挖掘以维持较长的时间段的晶体糊状岩层和百万年级基础上岩床的增量构造可以解释从数据推断的约2我的时间窗时间窗。尽管要用现代的斑岩矿床模型（≤1my）来协调这样一个扩大的窗口所面临的挑战，但元古代矿石矿床的形成已得到了高精度解决，并支持了可能形成数百万年的大型IOCG矿床的情况。在主要矿化脉冲之前，对岩浆储层进行周期性的挖掘以维持较长的时间段的晶体糊状岩层和百万年级基础上岩床的增量构造可以解释从数据推断的约2我的时间窗时间窗。尽管要用现代的斑岩矿床模型（≤1my）来协调这样一个扩大的窗口所面临的挑战，但元古代矿石矿床的形成已得到了高精度解决，并支持了可能形成数百万年的大型IOCG矿床的情况。在主要矿化脉冲之前，对岩浆储层进行周期性的挖掘以维持较长的时间段的晶体糊状岩层和百万年级基础上岩床的增量构造可以解释从数据推断的约2我的时间窗时间窗。尽管要用现代的斑岩矿床模型（≤1my）来协调这样一个扩大的窗口所面临的挑战，但元古代矿石矿床的形成已得到了高精度解决，并支持了可能形成数百万年的大型IOCG矿床的情况。