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In situ Rb-Sr geochronology records multiple fluid pulses in Neoproterozoic sequences from the Lubambe-Mingomba Cu deposits in the Zambian Copperbelt
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DOI：10.1016/j.precamres.2026.108059.png)
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Abstract
En 中文
Beta-decay chronometers such as Rb-Sr are useful in constraining geological histories in Proterozoic basins. However, solution-based beta-decay Rb-Sr dating has limited applicability to resolve complex alteration history in Proterozoic basins affected by multiple thermal and fluid-flow events. This study applies tandem laser ablation ICP-MS/MS Rb-Sr dating to K-rich minerals to constrain depositional and alteration history of Neoproterozoic metasedimentary rocks in the Central African Copperbelt. Multiple generations of K-feldspar, muscovite, biotite-phlogopite and illite from the Lubambe-Mingomba Cu deposit yield both detrital (similar to 1700-920 Ma) and post-depositional ages (767-466 Ma) tied to successive alteration episodes. Altered K-feldspars show trace element redistribution and Rb-Sr resetting relative to detrital grains with broad depletion in Ba, Pb and Na and enrichment in Fe, Ti, Co and REEs. Cathodoluminescence emission broadly correlates with alteration intensity and style, suggesting its potential use as a proxy for feldspar alteration. The oldest alteration age (767 +/- 95 Ma) records early diagenetic processes involving seawater-derived fluids, indicated by initial Sr-87/Sr-86 ratios similar to values for Tonian seawater and overlaps published Re-Os ages (820-770 Ma) for early Cu mineralization. Late Tonian ages (similar to 713 Ma) from altered detrital K-feldspars likely mark rift-driven thermal and fluid flow processes coeval with the break-up of Rodinia supercontinent. Ediacaran ages (636-600 Ma) likely record Congo-Kalahari convergence and brine migration associated with halokinesis. Early Cambrian (similar to 530 Ma) ages and late Cambrian-Ordovician ages (480-459 Ma) record peak Lufilian to post-Lufilian fluid flow. Phlogopite and fine-grained illite yield comparable Cambro-Ordovician ages (528-466 Ma), indicating widespread resetting during the Pan-African event in the Central African Copperbelt. These results show that in situ analysis coupled with detailed petrography can reveal progressive Rb-Sr re-equilibration in K-bearing minerals tied to tectono-hydrothermal episodes. This approach is useful for refining the chronostratigraphic framework for fluid flow in altered Proterozoic basins worldwide.
Keywords:
In situ Rb-Sr dating
Sediment-hosted Cu deposits
Central African Copperbelt
K -feldspar
Illite
Fluid-flow Alteration
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