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U-Th-Pb isotope chronology of sulfide ores and rocks in the early Proterozoic metavolcanic belt of northern Wisconsin.

Economic Geology

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Abstract

Lead from galena of massive sulphide deposits in the metavolcanic belt of northern Wisconsin was probably derived from 3700 m.y. old source material 1800-1900 m.y. ago. Approximately 3500 m.y. old rocks occur within 100-300 km to the north and west. The U-Th-Pb systems of the metavolcanic and granitic rocks in the belt were reset about 1600 m.y. ago during retrogressive metamorphism. The ages from lead isotope data are in accord with Rb/Sr whole-rock, Rb/Sr and K/Ar mineral, and U-Th-Pb zircon dating. A concordia plot of whole-rock lead data shows that many of the rocks lost lead 200-400 m.y. ago during uplift and erosion. Meta-volcanic rocks near Crandon, Wisconsin, had lead isotope compositions 20 m.y. ago that match those in the Pb-Zn ores in Palaeozoic rocks of the upper Mississippi valley. Possibly the volcanic rocks were a source of lead for the Pb-Zn ores. Similar ores might therefore occur between the northern Wisconsin metavolcanic belt and the upper Mississippi valley.-G.J.N.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
U-Th-Pb isotope chronology of sulfide ores and rocks in the early Proterozoic metavolcanic belt of northern Wisconsin.
Series title:
Economic Geology
Volume
79
Issue:
2
Year Published:
1984
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
338
Last page:
353
Number of Pages:
16