Rb-Sr direct dating of pyrite from the Pipela VMS Zn-Cu prospect,Rajasthan, NW India |
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| Authors: | Vadlamani Ravikant P R Golani |
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| Institution: | (1) Dept. Geology, University of Rajasthan, 302004 Jaipur, India |
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| Abstract: | In unaltered volcanogenic massive sulfide (VMS) ore deposits, variable Rb/Sr ratios in the ore mineral permits application
of the Rb-Sr isotopic method to directly date the time of ore formation. In contrast, post-crystallization deformation and
metamorphism would open the system to metamorphic fluids that would alter elemental ratios. To test whether the Rb-Sr isotopic
systematics in the ore minerals had preserved the formation time in the ∼800 Ma metamorphosed VMS ores within the ∼1 Ga Ambaji-Sendra
arc terrain, Rajasthan, NW India, common sulfides, pyrite and sphalerite from the Pipela Cu-Zn prospect, were analyzed for
their geochemistry and Rb-Sr isotopic systematics. Trace and rare earth elements in these minerals are resident probably at
crystal defects, whereas all inclusions (including those from metamorphic fluids) were removed by a simple crush leach method.
Results of direct dating by the Rb-Sr method to the hydrothermal pyrite yielded an isochron age of 1025±76 Ma with an initial
Sr ratio of 0.7051±0.0006, similar to previously determined zircon U-Pb age of 987 Ma from associated rhyolites. This suggests
the applicability of the crush leach method to date formation time of metamorphosed pyrite ores. |
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