ALBERT

Description: Shebandowan Lakes, Ontario, are the site of at least 49 shallow (2-12 m) ferromanganese concretion deposits, widely distributed throughout the 48 km of the watercourse. X-ray diffraction and Mossbauer methods have revealed the presence of goethite in some of the concretions. Chemical analyses of the acid soluble portions of 72 samples gave an average composition of 43.1% Fe and 5.65% Mn with a low content of trace elements. The Shebandowan concretions are among the richest in iron of lake concretions reported, possibly because only the acid soluble portion was analysed. Their low content of trace elements suggests rapid growth rates and a relatively young age. A positive correlation was found between Mn and K, Ca, Mg, Cu, Ni, and Co and the relationship between the last three and Mn was deemed significant. Zn was independent of association with either Mn and Fe, probably due to the presence locally of zinc sulphide deposits. Analyses of lake bottom and influent waters suggested that frequent resampling of the sites would be required throughout the year to permit meaningful interpretation of the effect of water composition of concretions. Analyses of sediment cores from 20 concretion sites indicated an upward increase in Fe and Mn and in the Mn/Fe ratio, consistent with the model of upward migration of the elements, where Mn is more mobile than Fe. This study concludes that a considerable proportion of the elements have been supplied to the Shebandowan concretions via the diagenetic process; generally a minor fraction of the elements has been abstracted directly from the superjacent water.

Description: On June 10th, 1966 Mr. R.A. Ryder made, the first of his several discoveries of ferromanganese concretion occurrences in Shebandowan Lakes. On learning of these discoveries, Prof. D. S. Cronan decided to investigate the geochemistry of the deposits. Accordingly, field surveys were conducted over a nine day period in July 1970 with the assistance of the writer and scuba diver, Mr. R. R. Hygaard of Thunder Bay. A total of 50 concretion deposits, including Ryder's original discoveries, were located, described and sampled. Sampling at the concretion sites included taking bottom water and sediment core specimens as well as concretions. Additional sampling was made of waters influent into the lakes, the effluent and lake, bottom water at barren locations. Subsequently, seventy two concretion samples were analyzed by atomic absorption for Fe, Mn, K, Mg, Ca, Cu, Zn, Ni and Co at the University of Ottawa geochemistry lab. Several concretion samples were subjected to Mössbauer spectroscopy, electron spin resonance and X-ray diffraction experiments. The AA analysis of 47 water samples, and 20 sediment core samples, the former for Fe and Mn and the latter for Fe, Mn, Cu, Ni and Co was contracted commercially as was colorimetric determination of As in 10 concretion samples. Other work included logging of the sediment cores and examination of concretions through binocular microscope. This work presents field, and lab observations along with the analytical results and seeks to draw from them inferences regarding, the geochemical environment and origin of the Shebandowan Fe-Mn concretionary deposits. In early chapters basic data, general and detailed, as available on the area, has been compiled, both to aid thé current study and any future studies of the concretions and their environment. These are followed by chapters on field data and the overall interpretation.