M.H. Delevaux
R. E. Zartman
M. R. Brock
A. V. Heyl
1966
<p><span>Analyses of lead isotopes in </span>galena<span> in carbonate rock ore deposits collected from several mineralized </span>districts<span> in the Central and Eastern Interior of the United States support previous studies in establishing that the </span>galena<span> is anomalously radiogenic ("J"type")- This </span>study<span>, using care-fully selected samples to test some géologie relationships, shows region-wide and distrietwide systematic variations in isotope ratios. The genetic implications of thèse variations are discussed. Two mechanisms of origin are considered to explain thèse variations in </span>isotopic<span> ratios. One involves mixing of leads from multiple sources, the other calls for variable lead-isotope ratios originating from a single source. Several source materials for the lead ores have been suggested; whether a single source has predominated, or two or more main sources have predominated is still unresolved. Slopes from Pb206/Pb204 versus Pb207/Pb204 plot are compatible with a contribution of lead by the 1300 ± 300 m.y. basement rocks that underlie the deposits. The spatial relationships of alkaline igneous rocks to several of the minerai </span>districts<span> in the </span>Mississippi<span> </span>Valley<span> région suggest a possible mag-matic source for the lead. </span>Isotopic<span> analyses of </span>galenas<span> closely associated with several of the intrusive rocks are similar in </span>isotopic<span> composition to adjacent ore leads, but genetic implications are ambiguous. </span>Galena<span> oc-curring in shales in the </span>Mississippi<span> </span>Valley<span> région outside mineralized </span>districts<span> contains ordinary lead. Théories that call upon such shales to be the major source of the lead in the depoaits of the </span>Mississippi<span> </span>Valley<span> type must explain this distinct différence in </span>isotopic<span> compositions. </span>Galena<span> collected from </span>districts<span> within the </span>Appalachian<span> Ridge and </span>Valley<span> Province contains notably less radiogenic lead than that from the </span>Mississippi<span> </span>Valley<span> minerai </span>districts<span>, and the lead is of the ordinary type.</span></p>
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10.2113/gsecongeo.61.5.933
en
Society of Economic Geologists
Isotopic study of galenas from the upper Mississippi Valley, the Illinois-Kentucky, and some Appalachian Valley mineral districts
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