Geophysical exploration for epithermal gold deposits at Pajingo, North Queensland, Australia

The Pajingo Epithermal System is an area of low-sulphidation epithermal veining and alteration, covering about 150 square km at the northern margin of the Drummond Basin. Tertiary and younger conductive sediments cover about 80% of the area. Gold mineralisation occurs in thin quartz veins (generally 0.5-3 m wide), and most of the ore bodies discovered to date are along the north-west trending Vera-Nancy structure. The host intermediate volcanics are magnetic, but the epithermal alteration that extends up to 50 m from the veins along the Vera-Nancy structure is magnetite destructive. Results of a high-resolution magnetic survey clearly delineate the major structures, including the Vera-Nancy structure. The quartz veins occur within broader zones of silicification, and gradient-array resistivity surveying has been successfully used to map these zones. Generally, the high resistivity zones due to silicification are coincident with the structures identified in the magnetics. Gravity and seismic surveys have aided the interpretation of regional structure. These techniques along with stratigraphic data indicate that the Vera-Nancy structure is a major north-west striking extensional fault. High resolution magnetics and resistivity continue to be the most useful geophysical tools in the ongoing exploration for additional mineralised structures within the Pajingo Epithermal System.