Accelerated precipitation of Mn-rich rocks in the early Paleoproterozoic ocean is considered to reflect the irreversible rise of oxygen in the atmosphere during the Great Oxidation Event (GOE), 2.501–2.220 billion years ago. But the precipitation conditions, pathways, mechanisms, and linkages to ocean redox, broadly remain unresolved. The Lagoa do Riacho Mn deposit in Borborema Province, northeastern Brazil, Ceará state, consists mainly of manganese-rich and manganese-poor silicates deposited during the GOE epoch. Negative Ce anomalies in the manganese-poor silicates point to the scavenging of Ce³⁺ onto Mn-oxyhydroxide reactive surfaces in the oxygenated surface waters. In contrast, samples with positive Ce anomalies, predominantly associated with the manganese-rich silicates, indicate a reductive dissolution of Mn-oxyhydroxides across a redoxcline, enriching the anoxic bottom water with Ce and Mn²⁺. A paleoredox reconstruction based on couple Mn, Mo, and U systematics supports the existence of the proposed Mn-oxide redox shuttle that enriched the anoxic sediment pile with Mn precipitated from the oxygenated shallow surface waters. This study uncovers a unique pathway in Paleoproterozoic Mn mineralization involving the transfer of Mn oxides from an oxygenated upper ocean reservoir to a predominantly deep anoxic silicate reservoir that was subsequently metamorphosed. The proposed Mn oxide sink switch mechanism is different from the commonly reported reductive transfer of Mn to a diagenetic carbonate sink during the Paleoproterozoic.

早古元古代海洋中富锰岩石的加速沉淀被认为反映了25.01-22.2亿年前大氧化事件（GOE）期间大气中氧气的不可逆上升。但降水条件、途径、机制以及与海洋氧化还原的联系，大体上仍未得到解决。Lagoa do Riacho Mn 矿床位于巴西东北部塞阿拉州 Borborema 省，主要由 GOE 时期沉积的富锰和贫锰硅酸盐组成。贫锰硅酸盐中的负 Ce 异常表明 Ce ³⁺的清除到含氧地表水中的 Mn-羟基氧化物反应表面上。相反，具有 Ce 正异常的样品，主要与富锰硅酸盐有关，表明 Mn-羟基氧化物在氧化还原线中的还原溶解，使缺氧底水富含 Ce 和 Mn ²⁺. 基于 Mn、Mo 和 U 系统学的古氧化还原重建支持提出的 Mn 氧化物氧化还原梭的存在，该梭使缺氧沉积物堆富含从含氧浅表层水中沉淀的 Mn。这项研究揭示了古元古代锰矿化的独特途径，涉及锰氧化物从含氧的上层海洋储层转移到主要是深部缺氧硅酸盐储层，随后发生变质。所提出的锰氧化物汇转换机制不同于通常报道的在古元古代期间锰向成岩碳酸盐汇的还原转移。