Gordon, Georgina1, Dmitrijeva, Marija2, Berthiaume, Jonathon2
1Geological Survey of South Australia, Adelaide, Australia.2Fortescue Metals Group Ltd., Keswick, Australia.
The Vulcan iron-oxide copper gold (IOCG) deposit in South Australia lies 30 km northeast of the world class Olympic Dam deposit. Three drill holes (VUD009, VUD015, VUD017), were chosen to examine the prospect scale alteration of white micas, across differing geophysical domains of the Vulcan IOCG prospect. A variety of breccias host mineralisation, including massive hematite and hematite-sericite-chlorite. The breccias are hosted within altered quartz-feldspar rock varying granitic to gneissic in texture. Dating of the host rock (VUD007) using zircon U-Pb geochronology showed that hematite-sericite-chlorite altered and brecciated granite was dated to 1.743+-Ma.
A spectral index for the AlOH – 2200nm white mica wavelength was plotted for the three drill cores (VUD009, VUD015, VUD017) showing excellent correlation with the aluminium assay values and iron oxide content. Sericite present in less altered, barren rocks was found to have longer wavelengths (2214-2218 nm), and transgressed to shorter wavelengths (2208-2212nm) – approaching iron enriched intervals. High aluminium content corresponded to longer wavelength sericite, opposite to iron content and differing from sericite wavelengths in the Olympic Dam deposit. A direct correlation between elevated copper and white micas was not observed.
Georgina began her spectral career at the Australian Mineral Foundation working on SWIR spectroscopy of the Data Metallogenica ore deposit sample collection. With the advent of the HyLogger instrumentation she began with the Geological Survey of South Australia 2001 and continues to work with spectral interpretation of mineral systems.