Pressure, temperature, and timing of mineralization of the sedimentary rock-hosted orogenic gold deposit at Klipwal, southeastern Kaapvaal Craton, South Africa
| العنوان: | Pressure, temperature, and timing of mineralization of the sedimentary rock-hosted orogenic gold deposit at Klipwal, southeastern Kaapvaal Craton, South Africa |
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| المؤلفون: | Spencer Johnson, David Selby, Sakthi Saravanan Chinnasamy, R. Uken, Juergen Reinhardt |
| المصدر: | Mineralium deposita, 2015, Vol.50(6), pp.739-766 [Peer Reviewed Journal] |
| بيانات النشر: | Springer Science and Business Media LLC, 2015. |
| سنة النشر: | 2015 |
| مصطلحات موضوعية: | Arsenopyrite, Mineralization (geology), South Africa, Kaapvaal Craton, Geochemistry, Metamorphism, Orogenic gold deposits, engineering.material, Geophysics, Geochemistry and Petrology, visual_art, Breccia, visual_art.visual_art_medium, engineering, Economic Geology, Fluid inclusions, Pyrite, Shear zone, Klipwal, Vein (geology), Geology |
| الوصف: | Gold mineralization in the Klipwal Shear Zone (KSZ) at the Klipwal Gold Mine is confined to laminated quartz-carbonate lodes, stringers, and associated alteration in sandstone and siltstone of the Delfkom Formation in the upper Mozaan Group of the Mesoarchaean Pongola Supergroup. The moderately dipping brittle-ductile KSZ strikes N-S with an oblique-reverse, sinistral sense of shear. The deformational events that are recognized include an early compressional phase that produced anastomosing shears defined by shear fabrics with numerous shear-parallel laminated quartz-carbonate fault-fill veins and, in places, extensional quartz vein stockworks, and a late brittle reactivation phase that produced fault breccias, displacing earlier extensional veins. Three closely spaced economic reefs (lodes) are developed: the main R-reef constitutes the KSZ, while the J- and H-reefs represent footwall splays. Alteration comprises chlorite, muscovite, epidote, feldspar, and carbonates along with pyrite, arsenopyrite, and chalcopyrite +/- pyrrhotite. An inner alteration zone is dominated by laminated quartz-carbonate veins with alternating quartz-carbonate-rich and muscovite-chlorite-rich laminae, whereas the proximal zone is characterized by alteration halos of K-feldspar, albite, epidote, chlorite, and muscovite along with carbonates and associated quartz veins. Chlorite thermometry from the inner and proximal zones yielded temperatures of 267 to 312 A degrees C. Arsenopyrite compositions provide temperatures in the same range, 255 to 318 A degrees C. Fluid inclusion microthermometry and Raman spectrometry of quartz veins in the mineralized reefs reveal the presence of metamorphogenic aqueous-gaseous fluid with an average salinity of 6.5 wt% NaCl equiv. Fluid compositions and estimated pressure-temperature (P-T) range (1.1 to 2.5 kbar at 255 to 318 A degrees C) are typical of orogenic gold deposits. Devolatilization during the regional facies metamorphism of the Pongola Supergroup is considered the likely fluid-forming event with fluid flow focused into a "compressional jog" of the KSZ. Shear-induced pressure fluctuations generated a phase separation of the initial aqueous-gaseous fluid, producing a gaseous and low-salinity aqueous fluid. This, together with fluid-rock interaction, and a decrease in fO(2) lead to sulfide and gold precipitation at Klipwal. Re-Os data from six sulfide samples constrain the age of sulfide precipitation and, by inference, gold mineralization, to 2563 A +/- 84 Ma, with an initial Os-187/Os-188 = 0.29 A +/- 0.08 (MSWD = 0.38). This age is distinctly younger than the post-Pongola granites (2863-2721 Ma), ruling out the association of granite emplacement with mineralization. This would suggest that mineralization is linked to the regional D-3 folding event which reactivated the KSZ after emplacement of the post-Pongola granites and that final brittle, post-mineralization reactivation is related to Karoo age faulting. Low initial Os values suggest that ore fluid interacted with mafic rocks, leaching non-radiogenic Os, the likely source being the deeper seated Nsuze Group volcanics and/or the greenstone belts that underlie the Pongola Supergroup. |
| وصف الملف: | application/pdf |
| تدمد: | 1432-1866 0026-4598 |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_dedup___::76f0631a05683056e2ee5ca5c6f2b9ea https://doi.org/10.1007/s00126-014-0573-9 |
| حقوق: | OPEN |
| رقم الأكسشن: | edsair.doi.dedup.....76f0631a05683056e2ee5ca5c6f2b9ea |
| قاعدة البيانات: | OpenAIRE |
Find this article in full text from Springer Verlag. | تدمد: | 14321866 00264598 |
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