Student: Edward Saunders, School of Earth and Geographical Sciences, UWA

Supervisors: Cam McCuaig, UWA

Klaus Gessner, UWA

Title: Pressure-temperature-composition constraints from geochemistry on the Tropicana gold deposit, Western Australia.

Background:

Tropicana is a recently discovered gold deposit positioned in the Northern Foreland of the Mesoproterozoic Albany-Fraser Orogen in Western Australia. It is the first gold deposit to be found in this region, and has the potential to form part of an entire new gold province. From initial work done on the deposit it appears that there are several events overprinting the original rock. This includes prograde metamorphism (to granulite facies), retrograde metamorphism and hydrothermal alteration. Little work has been done on the deposit to date, owing to its recent discovery and its remote nature. The work to date indicates that it is an intrusion related gold deposit that has been metamorphosed to granulite facies. Gold is present in disseminated pyrite (veins are not present), and there also appears to be a relationship between grain-size and mineralisation (the gold is preferentially hosted in a fine-grained feldspar gneiss).

Aim:

The project is specifically aiming to understand the structural history and alteration paragenesis of the Tropicana gold deposit, and their relationship with mineralisation. A key question to be resolved is whether the mineralisation is of Archaean or Proterozoic age.

Methodology of the project:

The objective is to establish pressure-temperature-composition conditions for the formation of the gold deposit. Data from 12 existing diamond holes and from an ongoing diamond drilling program will be used for petrological and structural analysis, using optical microscope and electron beam microprobe techniques. Features being examined will include overprinting relationships of minerals, cross-cutting relationships and timing of mineral growth relative to gold mineralisation. Chemistry of relevant mineral assemblages will be used to establish the pressure-temperature-composition conditions of the ore fluid.

Significance:

Tropicana is located in an important collision belt in Western Australia. Very little work has previously been done on the metallogeny in the Albany-Fraser Orogen, and prior to Tropicana no gold mineralisation had previously been discovered in the belt. The current work is being done to reach a better understanding on the genesis of the deposit. Determining whether the deposit is a metamorphosed Archaean deposit or a retrograde Proterozoic deposit will have a major impact on exploration strategies in this orogen.

Timeline:

The project is part of my Honours year at UWA. UWA requires that I complete 6 short courses during March-April. The ones that I have chosen are igneous petrology, SEM analysis, a special course related to my project, hydrothermal alteration analysis, structural geology and ore body visualisation. I am also required to complete a literature review on the Albany-Fraser Orogen related by late April. Field work will be carried out during May. Subsequent to this I will work on petrology and SEM analysis. I will start writing my thesis in early August for completion in October. The due date of the thesis is 30 October.