Iron mobility in shallow hydrothermal systems: insights from hematite-quartz veins and breccias from Arkaroola

Abstract

A series of hydrothermal hematite and quartz veins are found within the Adelaidean cover sequence at Petalinka Waterfall and Mt Oliphant as well as within the Mt Painter Inlier in the Radium Ridge Breccia and Mt Gee Sinter. Past studies have described a genetic relationship between the Radium Ridge Breccia and Mt Gee Sinter formations. Mineral geochemistry and U-Pb monazite and hematite dating have supported this claim as well as expanded the hydrothermal history of the local area. Monazite formation at ca 360 Ma across the two locations suggests early generations of hematite at Mt Gee predate this age, with a resetting of hematite occurring around ca 300 Ma. The Mt Gee Sinter has been seen to crosscut Cretaceous tillite, giving a maximum age of this generation of hydrothermal activity of ca 220 Ma. Hematite mineral geochemistry also genetically links the hematite and quartz veins found at Petalinka Waterfall and Mt Oliphant. These veins also see multiple generations of vein formation, initiating with the Delamarian Orogeny, evident from monazite dating from Petalinka Waterfall at ca 493 Ma coupled with textural evidence from Mt Oliphant. Second generation veining has been dated using U-Pb dating of hematite, giving an age of ca 350 Ma. This suggests the geothermal conditions at ca 360-350 Ma were regional with Petalinka Waterfall hematite dates correlating with Mt Painter Inlier monazite dates. Oxygen isotope analysis of quartz and hematite suggest metamorphic sourced hydrothermal fluid at temperatures of 450oC at the Mt Painter Inlier and Petalinka Waterfall and 600oC at Mt Oliphant. This hydrothermal fluid was likely very saline, similar to the hydrothermal veins discussed by Bakker and Elburg (2006).