l||-,'i|ff,?;^|t,;*^,V°fOLpG,CAL SURVEY 3 3051 00005 8770 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/chemicalcomposit20baxt , 20 ILLINOIS STATE GEOLOGICAL SURVEY John C. Frye, Chief Urbana, Illinois November, 1964 NDUSTRIAL MINERALS NOTES •No.2o DEC i CHEMICAL COMPOSITION OF SOME DEEP LIMESTONES AND DOLOMITES IN LIVINGSTON COUNTY, ILLINOIS James W. Baxter ILLINOIS STAIt GEOLOGICAL SURVEt LitiRARY ABSTRACT Chemical analyses of dolomite and limestone from a diamond drill core taken near Forrest, Illinois, provide information that pre- viously was unavailable for areas in which these formations are over- lain by several hundred feet of other sediments and hence not subjected to weathering. The limestone and dolomite formations sampled in the drill core crop out and are quarried farther north. In general, the composition of the formations, which occur above 1300 feet in the core, is similar to that of the outcropping rocks farther north except that the strata of the Galena Group in the well are principally limestone or dolomitic limestone whereas in north- western Illinois they are mostly dolomite. The analyses show that the reef- type dolomite of Niagaran age is as high in purity in the subsur- face as it is in the outcrop areas. Niagaran age dolomite is quarried extensively at Chicago, Joliet, Kankakee, and other places in northeastern Illinois, and the dolomite and limestone of the Galena and Platteville Groups are worked at many places in northwestern Illinois. The chemical composition of these formations is rea- sonably well known where they crop out, but no data have been available as to their composition where they are overlain by several hundred feet of other rock and hence are protected from the effects of weathering and surface water. This has been a matter of interested speculation for some years. The core of hole 2 drilled with a diamond drill by the Pennsylva- nia Drilling Company near Forrest, Illinois, in the SW^ NW^ NW% section 1, T. 26 N., R. 7 E., recently became available for analysis. Approximately 3 inches were taken from each foot for permanent storage. Fifteen samples, representing the various thicknesses and depths specified in table 1, were taken for chemical analysis by crushing and splitting the remaining three- fourths of the core. The samples therefore represent a virtually continuous section of rock. Those parts of the core that were not analyzed were either missing or were composed of very impure rock. The uppermost materials encountered in the boring were clay and sand, which are glacial deposits and have a total thickness of 220 feet. Below them, 177 feet of rocks of Pennsylvanian age were chiefly sandstone, shale, and clay with some coals and thin limestones. The shallowest thick carbonate rock was the Racine Dolomite. This formation and the underlying Waukesha and Joliet Dolomites are of Niagaran age. The Racine Dolomite was found at a depth of 397 feet and extended to 613 feet, giving it a thickness of 216 feet. Four samples were taken; some of the core was not analyzed for reasons previously stated. Table 2 shows that the samples vary considerably in composition. The high silica content of sample A is due to the presence of chert and that of sample D to silt, clay, and chert. Sample B, 24 feet thick, is quite pure dolomite and is of the reef type. There is also some reef-type dolomite in sample C. The pu- rity of these samples is as high as that of the reefs in the Chicago outcrop area. Sample E, representing the Waukesha Dolomite, is relatively high in silica and alumina, reflecting the presence of clay and silt. The Waukesha is 36 feet thick in the core. Three samples, F, G, and H, represent the Joliet Dolomite, which is 168 feet thick. None of the samples has a high carbonate content. The silica and alumina present come from clay and silt. The Joliet is not greatly different from some of the outcropping Joliet in northeastern Illi- nois, Samples J, K, L, and M are limestone of comparatively high pu- rity from the Galena Group. Samples J and K contain 4 percent or less mag- nesium carbonate, but sample L contains about 10 percent and M about 7 per- cent magnesium carbonate. The fact that these strata are limestone is a departure from their usual character for they occur as dolomite in north- western Illinois. (Text continued on page 5.) (0 •o * 00 0) •o B c 0) •pI •H c 4J to •V* 4J h w tt M <0 00 u V a u (0 CO J2 CO 9) U 60 >> a Ss o 0) C i-H 1-1 •o u a « iH CO \u c CO o •H 4-1 X! CO u a. CM CO CO (0 « CO >» « o. »#k (0 CO A • M (J CO >. 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