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The Distribution of Lead Isotopes and the Origin of Kuroko Ore Deposits in the Hokuroku District, Japan

By
Udo Fehn
Udo Fehn
Department of Geological Sciences, University of Rochester, Rochester, New York 14627
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B. R. Doe
B. R. Doe
U. S, Geological Survey, National Center, Reston, Virginia 22092
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M. H. Delevaux
M. H. Delevaux
Branch of Isotope Geology, U. S. Geological Survey, Federal Center, Denver, Colorado 80225
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Published:
January 01, 1983

Abstract

The isotopic composition of lead was investigated in and around Kuroko deposits of the Hokuroku district, Japan. Although the ore leads of these deposits were found to occupy a narrow isotopic range, each ore deposit has a characteristic isotopic composition. Within a given ore deposit, black ore has a uniform isotopic composition but is significantly higher in radiogenic lead than yellow ore. The differences between ore types are, however, smaller than those between ore deposits. The volcanic host rocks are in general lower in radiogenic lead than the ores, whereas the deeper, older formations, in particular the Sasahata Formation and the Paleozoic basement, have more radiogenic lead than the ores.

On the basis of the isotopic distribution we conclude that a major part of the lead in the Kuroko deposits was derived from igneous, probably volcanic rocks with an uncertain but significant contribution coming from the underlying pre-Nishikurozawa formations. The ore fluids reached the Sasahata Formation and most likely also the Paleozoic basement. Each ore deposit within the district was formed by a local hydrothermal system. The difference in isotopic composition between the yellow and black ores reflects a shift in the proportions coming from the two major sources due to the temperature evolution of the hydrothermal system. The yellow ore seems to have a greater igneous rock lead component than does the black ore.

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Contents

Economic Geology Monograph Series

The Kuroko and Related Volcanogenic Massive Sulfide Deposits

Hiroshi Ohmoto
Hiroshi Ohmoto
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Brian J. Skinner
Brian J. Skinner
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Society of Economic Geologists
Volume
5
ISBN electronic:
9781629490007
Publication date:
January 01, 1983

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