大氧化事件前条带状铁建造（BIF）巨量成矿的关键控制因素：以鱼洞子BIF为例

条带状铁建造（Banded Iron Formation; BIF）是全球最重要的铁矿资源，于大氧化事件（Great Oxidation Event; GOE）前（约2.60–2.45 Ga）达到了成矿规模的峰值。成矿物质来源和二价铁氧化机制是BIF成矿的关键控制因素。然而，陆源Fe对GOE前BIF巨量成矿的贡献缺乏定量评估；GOE前BIF形成时海水的氧化还原状态仍需进一步限定。前期工作显示，扬子西北缘鱼洞子杂岩中磁铁石英岩原岩为2.48–2.45 Ga BIF，形成于GOE（约2.45–2.30 Ga）前夕。本项目拟以鱼洞子BIF为研究对象，将全岩主微量元素和Fe-Nd同位素相结合，定量评估陆源Fe和海底高温热液Fe的成矿贡献，准确限定BIF形成时海水的氧化还原状态。项目研究成果将为GOE前BIF巨量成矿的关键控制因素提供新的制约，也为丰富BIF成矿理论和找矿实践提供新的科学依据。

Banded iron formation (BIF) is the most important iron resource in the world. The most economically valuable BIF was deposited between ca. 2.60 and 2.45 Ga, before the onset of the Great Oxidation Event (GOE) (ca. 2.45–2.30 Ga). Two key factors control BIF deposition: sources and the oxidation mechanism of ferrous iron. However, the contribution of terrigenous-derived Fe to the pre-GOE BIF (ca. 2.6–2.45 Ga) lacks a quantitative assessment; the redox conditions of the pre-GOE seawater from which BIF deposited need to be further constrained. Preliminary work shows that the protolith of magnetite quartzite from the Yudongzi complex in the northwestern Yangtze landmass is BIF (referred to as the Yudongzi BIF). The depositional age of the Yudongzi BIF is constrained to ca. 2.48–2.45 Ga, coincident with the onset of the GOE. For this project, we will present bulk-rock major and trace elements, as well as Fe-Nd isotopic compositions of the Yudongzi BIF, to quantitatively evaluate the contribution of terrigenous-derived and submarine hydrothermal Fe and further constrain redox conditions of the pre-GOE seawater from which the BIF deposited. This study will provide new constraints on the key factors controlling the deposition of giant BIF before the GOE, and a new theoretical basis for BIF metallogenic system and exploration.