Geochemistry of Lake Michigan manganese nodules

Manganese nodules, similar in composition to other freshwater and shallow marine nodules, occur on the sediment surface of green bay and northern lake Michigan. Samples have been analyzed for their iron, manganese, calcium, magnesium, sodium, potassium, inorganic carbon, organic carbon, and total nitrogen content. The nodules average 20% iron and 6% manganese. the trace metal content (copper, zinc, cobalt, and nickel) of the samples is considerably lower than that of marine material. Interstitial water is one of the major contributors of manganese and iron for the growth of nodules in lake Michigan. Cores of green bay sediment show an inverse relationship between sedimentary and interstitial manganese with the sedimentary manganese increasing to a maximum at or near the sediment-water interface. Sedimentary iron remains fairly constant throughout the length of these cores while interstitial iron decreases slightly toward the sediment-water interface. in addition, lake water may be more than a passive contributor of iron and manganese. There are indications that as much as one-half of the manganese found in lake water is particulate. The source of this material is believed to be the iron deposits of the Canadian shield that have been subsequently leached of manganese and iron.