Abstract

The Mississippi Valley-type lead-zinc ores of the Viburnum Trend in southeast Missouri are hosted by the Upper Cambrian Bonneterre Dolostone. The ore deposits are clearly epigenetic but conventional geologic and geochemical methods have failed to give an absolute date for the time of mineralization and thus have hampered the understanding of the ore genesis. The magnetic remanences of both ore and host are very weak but measurable. The paleopoles determined from the ore samples indicate an Early Permian-Late Pennsylvanian magnetic event. The host rocks collected in the mines have been remagnetized, showing paleopole positions similar to those of the ore samples. Correlative Bonneterre Dolostone samples collected far away from mineralization have poles quite different from those of similar host rocks in the mine; they probably still retain part of the original direction acquired during their sedimentation. To explain all of the paleomagnetic results in this study best, a mechanism for resetting the paleomagnetic clock by the mineralization is proposed. According to this mechanism, the age of the magnetic event observed from the rocks in the mine would probably represent the time of the mineralization. If this premise is accepted, the mineralization in the Viburnum Trend occurred in Early Permian-Late Pennsylvanian time.The paleomagnetic methods used are regarded as being potentially applicable to many other problems of a stratigraphic and diagenetic nature. With the arrival of cryogenic magnetometers for routine usage, paleomagnetic studies of many additional deposit types will have come of age.

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