Oxygen isotope sedimentology of gold- and uranium-bearing Witwatersrand and Huronian Supergroup quartz-pebble conglomerates

摘要: The relation between Au and U content provenance has been evaluated for a number of quartz-pebble conglomerates from the Archean Witwatersrand Early Proterozoic Huronian Supergroups, through analysis oxygen isotope composition siliceous detritus within these rocks. Oxygen compositions quartz, quartzite, chert pebbles, as well individual sand-sized quartz grains in matrix of conglomerates, were measured using conventional laser fluorination techniques. Significant heterogeneity delta(18)O values quartzite pebbles sands within individual samples these suggests that they have preserved delta(18)O values their source Preservation of original sand conglomerates whose matrix displays typical metamorphic texture implies limited oxygen silica mobility, recrystallization by pressure solution in presence small amounts intergranular fluids. Oxygen analyses along Main `'reef'' (conglomerate) West Rand Consolidated gold mine, Witwatersrand, indicate reflect local variations in provenance. Yet, overall distributions for quartz pebbles Au- U-bearing reef the directly overlying Monarch `'reef'' (conglomerate) same mine are identical, implying an similarity source rocks. Comparison between these two reefs other Witwatersrand including polymictic Welkom area Witwatersrand basin, moreover, was similar throughout deposition much Central Group. Differences ore content Au/U ratio Group are compatible with differences sedimentology. In contrast to Supergroup, delta(18)O different conglomerates throughout Supergroup indicate distinct in provenance. A erude positive correlation and proportion greater than or equal 11.5 per mil exists conglomerates. U-bearing Matinenda Formation Elliot Lake have very low proportion above mil. Matinenda sampled closer present outcrops of Archean greenstone terranes, Lorrain and Livingstone Creek Formations, higher pebbles with or equal also higher contents. Differences and quartz help identify sediment sources. Absence quartz sands mil, but presence such same sediment, may indicate which yields little no material in fluvial settings. pebbles and for quartz likely rocks compositionally homogeneous granites related pegmatites dominant of uranium, whereas hydrothermal lode veins of gold.