# Chemical Signatures of Ge in Magnetic of Wugang BIF, China
## 1 Introduction  
The reconstruction of the early earth conditions is essential for understanding the links between ocean chemistry and the evolution of the biosphere and atmosphere [1]. Banded iron formations (BIFs) are Precambrian sedimentary successions defined as laminated chemical sediments containing >15% Fe, with alternating layers of Fe-rich minerals, and chert of various scales [2]. It is well known that anoxic and ferruginous marine conditions occurred in the Archean and Paleoproterozoic eras, and BIFs precipitated until soluble iron was exhausted, causing their cessation [3]. These are the primary products of marine iron oxyhydroxides formed via diagenetic bacterial iron reduction [4]. Therefore, BIFs can be used as essential geological proxies for understanding the tectonic evolution processes, compositions of the early hydrosphere and atmosphere, and biological activities caused by their formation at specific geological times and conditions to understand early earth conditions [5, 6]. Previous studies on the reconstruction of early earth conditions have included thermodynamic calculations of phase equilibria to understand the Archean subseafloor basalt-hosted hydrothermal system [7], redox processes in ferruginous anoxic oceanic conditions [1], evidence for ferruginous conditions from geochronological data with mineralogy, sedimentary features, and REE (rare earth element) systematics from a suite of Fe-rich chemical sedimentary rocks [3, 8], experiments on the simulation of Precambrian ocean chemistry from marine photoferrotrophs, and marine Fe(III)-reducing bacteria [9]. Recently, numerous studies have focused on the trace element composition of magnetite in BIFs because it can be used as a direct or indirect provenance fingerprint of thegenetic conditions and mineralization styles of ore deposits [10; 11; 12; 13; 14; 15]. Magnetite is a representative ore mineral found in BIFs, with a hydrothermal origin and an inverse AB\({}_{2}\)O\({}_{4}\) spinel structure [14; 16]. Nb\({}^{5+}\), Ta\({}^{5+}\), Mo\({}^{4+}\), W\({}^{4+}\), Ti\({}^{4+}\), Si\({}^{4+}\), Ge\({}^{4+}\), Sn\({}^{4+}\), V\({}^{3+}\), V\({}^{4+}\), Cr\({}^{3+}\), Al\({}^{3+}\), As\({}^{3+}\), Ga\({}^{3+}\), Mn\({}^{2+}\), Zn\({}^{2+}\), Ni\({}^{2+}\), Co\({}^{2+}\), Cu\({}^{2+}\), Mg\({}^{2+}\), and Ca\({}^{2+}\) can enter the structure of the magnetite [14]. Specifically, divalent cations such as Mg\({}^{2+}\), Fe\({}^{2+}\), Ni\({}^{2+}\), Mn\({}^{2+}\), Co\({}^{2+}\), and Zn\({}^{2+}\) are present at site A, and trivalent cations such as Al\({}^{3+}\), Fe\({}^{3+}\), Cr\({}^{3+}\), V\({}^{3+}\), Mn\({}^{3+}\), and Ga\({}^{3+}\) are present at site B. In addition, Ti\({}^{4+}\) can enter site B by substituting for a divalent cation [17; 18]. Magnetite can crystallize in igneous, metamorphic, and sedimentary environments over a wide range of pressures and temperatures [14]. Hydrothermal ore deposits usually contain up to 10 ppm of trace elements, such as Ti, Si, V, Al, Ca, Mg, and Na [19]. Among the trace elements in magnetite, the distribution and chemical behavior of Ge (belonging to subgroup VIa of the periodic table) are closely related to ore-forming fluids, such as hydrothermal fluids, which contribute to the precipitation of magnetite. Ge exists in two oxidation states, Ge\({}^{2+}\) and Ge\({}^{4+}\). Ge\({}^{4+}\) is more common and stable than Ge\({}^{2+}\), and most Ge\({}^{2+}\) are unstable under atmospheric conditions [20]. Ge\({}^{4+}\) in silicate minerals can easily substitute Si\({}^{4+}\) because they have similar geochemical signatures [21]. Ge exhibits different chemical behaviors in various geological environments because it possesses siderophilic, lithophilic, chalcophilic, and organophilic behaviors [21]. Ge is present in minor quantities in silicate minerals and is widely distributed in oxides, hydroxides, hydroxysulfates, and sulfides [20]. As Ge is not confined to specific conditions, it can occur as a minor and trace element in various types of ore deposits [21; 22].