Proposed Title 1: - Queen's University

CHAPTER 4
FLUID EVOLUTION AND GENESIS OF URANIUM
MINERALIZATION IN THE SOUTH ALLIGATOR VALLEY AREA,
NORTHERN TERRITORIES, AUSTRALIA
Abstract
Uranium deposits in the South Alligator Valley Mineral Field, Northern Territories,
Australia, are hosted in deformed and metamorphosed volcanoclastic rocks and calcareous
and carbonaceous sedimentary units of the Koolpin Formation, at the unconformity with
overlying El Sherana Basin sandstones. The ore is confined to greenschist facies host rocks
that are cut by the El Sherana-Palette fault, a northwest-striking, southwest dipping and
dextral strike-slip fault system. Petrographic studies on polished thin sections combined
with electron microprobe analysis, stable isotope geochemistry, and geochronology of
uranium-bearing minerals at the El Sherana and Coronation Hill deposits have identified a
multistage fluid history, involving hydrothermal alteration and uranium mineralization.
The pre-ore stage mineralogy consists of sericite, quartz, chlorite, and calcite
alteration at temperatures at ca. 300°C, interpreted to result from regional greenschist
metamorphism of the basement rocks during the ca. 1860-1840 Ma Nimbuwah event and
prior to deposition of the ca. 1840-1830 Ma El Sherana Basin. The basement pre-ore
alteration is followed by diagenesis of the El Sherana Basin sediments by oxidizing low
latitude basinal brines that produced a kaolinite+quartz+hematite assemblage. The ore stage
of uranium, gold, and galena formed at ca. 1820 Ma from evolved basinal brines that
originated from the El Sherana Basin and descended downward into basement rocks along
132