|
GEOHYDROLOGIC SETTING |
|
| Generalized geohydrologic section across exploration area |
| Three major geohydrologic units overlie the Precambrian basement rocks in the exploration area. The deepest unit, the St. Francois aquifer, is composed of the Lamotte Sandstone and overlying predominantly carbonate
Bonneterre Formation and contains most of the lead-zinc mineralization. The aquifer yields sufficient water for domestic and municipal use where it crops out in southeastern Missouri; however, because the top of the unit is about 1,600 ft (feet) below land surface in the vicinity of the exploration area, it is not used as a
water-supply source. Lead-zinc ore usually is concentrated within the Bonneterre Formation, and commonly is
associated with ancient reef complexes near Precambrian igneous knobs that protrude upward into the aquifer
(Leach,
1994;
Goldhaber and others, 1995; Kleeschulte,
2000). The St. Francois confining unit overlies the St. Francois aquifer. The confining unit consists of shales and carbonates of the Davis Formation and overlying Derby-Doe Run Dolomite. The approximately 300-ft thick confining unit impedes the flow of ground water between the St. Francois aquifer and the surficial Ozark aquifer. The Ozark aquifer is about 1,000 ft thick and primarily is composed of (from deepest to shallowest) the Potosi Dolomite, Eminence Dolomite, Gasconade Dolomite, Roubidoux Formation, and Jefferson City Dolomite in the vicinity of the exploration area. The Ozark aquifer is karstic and supplies large quantities of water to springs and to domestic and municipal wells throughout southern Missouri. |
Background Information
[Geohydrologic Setting] [Karst
Geology]
For more information contact:
Michael J. Kleeschulte, Hydrologist
U.S. Geological Survey
Missouri Water Science Center
1400 Independence Rd., MS 100
Rolla, MO 65401
Telephone: (573) 308-3675
Fax:(573) 308-3645
U.S. Department of the Interior, U.S. Geological Survey
Maintainer: Rita Choate, Webmaster
Updated: August 25, 2003
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