Description and geochemical composition of manganese nodules retrieved from Lake Ontario, Canada

A large deposit of ferromanganese oxide coated sands and scattered manganese nodules occurs in the northern portion of Lake Ontario. The Mn and Fe contents of the concretions are similar to those in concretions from other environments, while their Ni, Cu, and Co contents are lower than in deep-sea nodules, but higher than in most previously described lacustrine concretions. Pb and Zn are high in the coatings and exceed the concentrations found in many previously analyzed Mn deposits. Within the deposit, Mn, Ni, Co, and Zn contents are correlated, and they vary inversely with Fe. Mn, Fe, Ni, Cu, and Pb are present in the interstitial waters of the sediments underlying the deposit in higher concentrations than in the overlying lake waters, thus providing a potential source of metals for concretion formation.The origin and compositional variations in the deposit possibly can be explained in terms of the fractionation and precipitation of Fe and Mn as a result of redox variations in the lake sediments. Eh increases from south to north across the deposit in such a way that iron may be selectively oxidized and precipitated in the south and manganese, in the north. The upward diffusion of Mn, Fe, and associated elements from the underlying sediments probably provides the principal source of the metals in the south of the deposit, while metal-enriched bottom waters are probably the principal source in the north.

安大略湖北部区域产出一处大型矿床，其中赋存大量铁锰氧化物包被砂（ferromanganese oxide coated sands）与零星分布的锰结核（manganese nodules）。该类结核的锰（Mn）、铁（Fe）含量与其他环境产出的结核相近，但其镍（Ni）、铜（Cu）及钴（Co）含量低于深海结核，但高于多数已有文献记载的湖相结核（lacustrine concretions）。其包被层中的铅（Pb）与锌（Zn）含量较高，超过了此前多数已分析的锰矿床的浓度水平。在该矿床内部，锰、镍、钴与锌的含量呈正相关关系，且与铁含量呈负相关变化。矿床下伏沉积物孔隙水（interstitial waters）中的锰、铁、铜及铅浓度高于上覆湖水，这为结核形成提供了潜在的金属来源。
该矿床的成因与成分变化或可通过湖泊沉积物中氧化还原变化（redox variations）引发的铁锰分馏与沉淀机制加以解释。横跨该矿床区域，氧化还原电位（Eh）自南向北逐渐升高，使得铁可在南部区域选择性氧化并沉淀，而锰则在北部区域富集沉淀。矿床南部的金属主要来源于下伏沉积物中锰、铁及伴生元素向上的扩散作用，而北部的金属来源则主要为富金属底层水。