BIF成因研究进展

BIF在全球广泛分布，BIF型铁矿是铁的重要来源。根据产出的构造背景将其分为阿尔戈玛型（Algoma-type）和苏必利尔湖型（Lake Superior-type）。BIF主要产出于前寒武纪的古老克拉通和/或年轻地体，形成时代集中在3.0～2.0 Ga，峰期为2.5 Ga左右。前人对BIF型铁矿的成因研究着重于BIF的物质来源和Fe²⁺ 氧化沉淀机制两个方面，但都尚未达成共识。物质来源的观点主要有大陆风化剥蚀、海底热液、海底热液和海水的混合物、热液淋滤洋壳、既有大陆物质来源又有热液来源，沉淀机制主要有生物沉淀和非生物沉淀两种认识，前者是指Fe²⁺ 利用微生物（如蓝藻）光合作用产生的O₂氧化成Fe³⁺，或Fe²⁺ 直接被微生物代谢氧化，后者主要包括热液与海水混合、密度流作用、相分离、紫外线引起Fe²⁺ 氧化沉淀等。

Research progress on the genesis of BIF

Globally widespread banded iron formations are the most significant source of iron around the world. Based on the tectonic environment, BIFs are divided into two types, i.e., Algoma-type BIF and Lake Superior-type BIF. BIFs occur predominantly in Precambrian cratons and terrains. According to the geologic record, most BIFs share a similar age between 3.0 Ga and 2.0 Ga, the peak period of which is ca. 2.5 Ga. A significant proportion of previous work on the genesis of BIF focused on the source and deposition mechanism of ferrous iron. There is, however, no unanimous consensus yet on these issues. In terms of the source, different opinions include continental weathering, hydrothermal fluid, mixture of hydrothermal fluid and seawater, and hydrothermal leaching of the oceanic crust. With regard to the deposition of ferrous iron, two primary mechanisms have been proposed, biotic and abiotic. The former implicates that ferrous iron was oxidized to ferric iron through the oxygen generated by microorganisms' oxygenic photosynthesis such as cyanobacteria, or was directly oxidized by them, whereas the latter indicates that ferrous iron was deposited through the mixing of hydrothermal fluid and seawater, density current, phase separation, and flux of ultraviolet photons.