Mineralogical sources for barium in cambro-ordovician aquifers of northeastern Illinois
Caithamer, Celine E.
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In local areas of northern Illinois, groundwater from the Cambro-Ordovician aquifer system contains barium (Ba++) ion in excess of the upper limit set for human consumption by the U.S. Public Health Service (1 milligram per liter). It has been suggested that the sedimentary rock units might be the source for the barium, since bulk Cambro-Ordovician rock samples contain between 25 and 1,150 ppm Ba. This study was made to identify the possible mineralogical sources of the barium. Alkali feldspar is present in large abundance in certain Cambro- Ordovician strata. Quantitative chemical analyses show that the feldspar contains BaO ranging from less than .02% within authigenic overgrowths to 3.63% within detrital cores. When the percent BaO found in the alkali feldspar is converted to Ba(ppm), the alkali feldspar Ba values are extremely close to the whole rock Ba(ppm) content found by Gilkeson and others. Conclusions are: (1) Feldspar is the most likely source for all of the Ba previously reported in chemical analyses of aquifer rocks. (2) Stability plots and microscopic pictures show feldspar is dissolving - is unstable in modern groundwater. (3) Feldspar is a likely source of the Ba++ observed in modern groundwater. (4) Hydrologic conditions may cause local variations of Ba++ in groundwater.