Lead isotope patterns in Proterozoic stratiform mineralization in the Bushmanland Group, Namaqua Province, South Africa

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doi: 10.2113/gsecongeo.92.2.248
Authors:Reid, D. L.; Welke, H. J.; Smith, C. B.; Moore, J. M.
Author Affiliations:Primary:
University of Cape Town, Department of Geochemistry, Rondebosch, South Africa
University of the Witwatersrand, South Africa
Volume Title:Economic Geology and the Bulletin of the Society of Economic Geologists
Source:Economic Geology and the Bulletin of the Society of Economic Geologists, 92(2), p.248-258. Publisher: Economic Geology Publishing Company, Lancaster, PA, United States. ISSN: 0361-0128
Publication Date:1997
Note:In English. 37 refs.; illus., incl. sect., 4 tables, sketch maps
Summary:Galena in giant Proterozoic sediment-hosted Pb-Zn sulfide deposits in the Bushmanland Group of South Africa has a very uniform Pb isotope composition, with 206Pb/204Pb = 16.74-16.82, 207Pb/204Pb = 15.54-15.62, and 208Pb/204Pb = 36.63-36.71 (all 2σ ranges). Four separate orebodies (Broken Hill, Black Mountain, Big Syncline, and Gamsberg) show very little departure from these mean data, suggesting that they were all formed from a common mineralizing fluid. Compared to other giant Proterozoic deposits, whose Pb isotope signatures generally plot very close to model crustal growth curves, the Bushmanland ores have very radiogenic compositions. Model ages are significantly younger than the age of mineralization, which is constrained by an Sm-Nd isochron age of 1649±95 Ma obtained on metabasaltic amphibolites in a stratigraphically overlying formation. The extreme upper crustal signature could have been derived from a source bed lower in the Bushmanland stratigraphy, characterized by abundant acid volcaniclastic material, that was a product of crustal reworking of basement rocks to the Bushmandland basin, 1700 to 1600 Ma.
Subjects:Absolute age; Amphibolites; Copper ores; Dates; Galena; Isochrons; Isotope ratios; Isotopes; Lead; Lead-zinc deposits; Lithostratigraphy; Mesoproterozoic; Metal ores; Metals; Metamorphic rocks; Mineral deposits, genesis; Mineralization; Models; Ore-forming fluids; Patterns; Pb-206/Pb-204; Pb-207/Pb-204; Pb-208/Pb-204; Precambrian; Proterozoic; Radioactive isotopes; Silver ores; Sm/Nd; Stable isotopes; Stratiform deposits; Sulfides; Upper Precambrian; Africa; Cape Province region; Namaqualand; South Africa; Southern Africa; Broken Hill Deposit; Bushmanland Group; Cape Province South Africa
Abstract Numbers:98M/494
Record ID:1997059827
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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