A long-lived hydrothermal system in Bushveld granites at the Zaaiplaats tin mine; lead isotope evidence

Rb-Sr and Nd-Sm isotopes in fluorite related to the granites of the Bushveld Complex

“…Previous literature envisages isotopic and trace element disturbances as due to mineralisation and hydrothermal fluid circulation driven by high levels of heat generation for up to hundreds of million years after intrusion (Walraven et al, 1985;McNaughton et al, 1993). However, Cathles et al (1997) indicate that magmatohydrothermal fluid flow tends to be short-lived, typically lasting for about 1 Ma.…”

An isotopic study on the volcanics of the Rooiberg Group: age implications and a potential exploration tool

“…Model dates calculated from the Rb-Sr data by Walraven et al (1990b) indicate dates of final closure predominantly in the range 1.3 1.7 Ga (summarised in Fig. 4), several hundred million years prior to the 1.0 Ga closure times for the U-Pb system deduced by McNaughton et al (1993). "Re-setting" of the Rb-Sr dates in certain Rooiberg volcanics and the Zaaiplaats granites has been attributed to selective loss of radiogenic 87Sr.…”

“…Sr and Pb isotopic systems have been used to demonstrate that the LGS granites in the Zaaiplaats area were subjected to protracted periods of fluid circulation at temperatures in excess of about 300 ~ (Walraven et al, 1990;McNaughton et al, 1993). McNaughton et al, 1993) demonstrated that the U-Pb isotopic system in the Zaaiplaats granites was last disturbed as recently as ca.…”

“…McNaughton et al, 1993) demonstrated that the U-Pb isotopic system in the Zaaiplaats granites was last disturbed as recently as ca. 1000 Ma, i.e.…”

“…Low ages in the LGS rocks have been variously ascribed to post-crystallisation metasomatism by heated groundwaters producing selective loss of radiogenic 878r (Walraven et al, 1985) or the maintenance of long-lived hydrothermal systems in the granites because of elevated K, U and Th concentrations (McNaughton et al, 1993). These post-solidification modifications are thought to have had an important influence in the mineralisation of the LGS granites (e.g.…”