Mineral exploration under cover and the value of petrophysics - A case study from East Albany-Fraser Orogen, Western Australia.

Greenfield mineral exploration undercover presents a number of challenges. In the East Albany-Fraser Orogen, when faced with the possibility of 300-700m of cover and very little previous exploration, any available data is valuable. Collection of petrophysical data is a cost-effective method to optimise the information in the available drilling with three main benefits: Firstly, an understanding of the physical properties of the cover sequence of the Eucla Basin, the Madura and Loongana Formations and the underlying basement will aid in the geophysical modelling and development of the mapping and targeting program. Secondly, when the petrophysical data from a drill hole is effectively integrated with the mineralogy, geochemistry and observed lithology, a greater understanding of the geological controls of the petrophysical properties can be observed and the processes that are influencing them inferred. Finally, with comprehensive integration of these datasets, will significantly increase our confidence in the source, validity and interpretation of the geophysical responses. A study was undertaken utilising Geological Survey of Western Australia (GSWA) Exploration Incentive Scheme (EIS) open file drillhole data from East_Fraser Orogen. Peterophysical data were collected on the available core and new acquired drillholes and this included magnetic susceptibility, dry bulk density, apparent porosity, grain density, pwave velocity, acoustic impedance galvanic resistivity, chargeability and inducted conductivity. All drill holes reached basement, a few holes had cover that could be sampled, all holes had different levels of geochemical assaying, and petrography was available for some of the holes. The results of the integration of the petrophysical data with the mineralogy, geochemistry and observed lithology were many. They included a strong correlation between the dense observations in the core and lithological and mineralogical changes in the basement and a better understanding of the cover and the source and nature of its conductivity response.