The United States relies solely on foreign manganese for its industrial needs where it is primarily used as an additive to steel to increase strength and workability. Development of domestic manganese resources are needed to alleviate this dependence on foreign sources. Cretaceous-aged manganese nodules from the Pierre Shale Formation near Oacoma, South Dakota are one potential domestic resource. However, better characterization of their elemental compositions is necessary to assess the processes controlling their formation and their suitability as an economically viable source of manganese. In this study, the inter- and intra- variability in chemical composition and physical characteristics of nodules were evaluated using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS), and petrographic microscopy. Petrographic and scanning electron microscopy identified variation in the characteristics of matrix minerals, evidence redox zonation, and microfossils including radiolarian. Elemental analysis via ICP-MS measured an average manganese concentration of 17% within the samples, however variability in manganese and other elemental compositions were observed both between and within individual nodules. The highest concentrations of manganese were observed in phases that present as darker colored material in hand sample suggesting these phases should be targeted in efforts to utilize these nodules as a manganese resource. Overall, this work provides insight into the processes that control the formation and geochemical characteristics of manganese nodules from the Pierre Shale Formation across various size scales.

Geochemical characterization of manganese nodules from the Pierre Shale in Western South Dakota

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