GEOPHYSICS, VOL. 65, NO. 6 (NOVEMBER-DECEMBER 2000);P. 1852–1861, 10 FIGS. Seismic reflection imaging of mineral systems: Three case histories Barry J. Drummond ∗ , Bruce R. Goleby ∗ , A. J. Owen ∗ , A. N. Yeates ∗ , C. Swager ‡ , Y. Zhang ∗∗ , and J. K. Jackson § ABSTRACT Mineral deposits can be described in terms of their mineral systems, i.e., fluid source, migration pathway, and trap. Source regions are difficult to recognize in seis- mic images. Many orebodies lie on or adjacent to major fault systems, suggesting that the faults acted as fluid mi- gration pathways through the crust. Large faults often have broad internal zones of deformation fabric, which is anisotropic. This, coupled with the metasomatic ef- fects of fluids moving along faults while they are active, can make the faults seismically reflective. For exam- ple, major gold deposits in the Archaean Eastern Gold- fields province of Western Australia lie in the hanging- wall block of regional-scale faults that differ from other nearby faults by being highly reflective and penetrating to greater depths in the lower crust. Coupled thermal, mechanical, and fluid-flow modeling supports the the- ory that these faults were fluid migration pathways from the lower to the upper crust. Strong reflections are also recorded from two deeply penetrating faults in the Pro- terozoic Mt. Isa province in northeastern Australia. Both are closely related spatially to copper and copper–gold deposits. One, the Adelheid fault, is also adjacent to the large Mt. Isa silver–lead–zinc deposit. In contrast, other deeply penetrating faults that are not intrinsically reflec- tive but are mapped in the seismic section on the basis of truncating reflections have no known mineralization. Regional seismic profiles can therefore be applied in the precompetitive area selection stage of exploration. Ap- plying seismic techniques at the orebody scale can be difficult. Orebodies often have complex shapes and re- flecting surfaces that are small compared to the diame- ter of the Fresnel zone for practical seismic frequencies. However, if the structures and alteration haloes around the orebodies are targeted rather than the orebodies themselves, seismic techniques may be more successful. Strong bedding-parallel reflections were observed from the region of alteration around the Mt. Isa silver–lead– zinc orebodies using high-resolution profiling. In addi- tion, a profile in Tasmania imaged an internally nonre- flective bulge within the Que Hellyer volcanics, suggest- ing a good location to explore for a volcanic hosted mas- sive sulfide deposit. These case studies provide a pointer to how seismic techniques could be applied during min- eral exploration, especially at depths greater than those being explored with other techniques. INTRODUCTION Deep seismic reflection programs around the world are mostly directed toward understanding the tectonic evolution of the regions studied and therefore have often led only indi- rectly to an improved understanding of their mineral potential. In contrast, a seismic transect of the Mt. Isa inlier of northeast- ern Australia, sponsored by the Australian Geodynamics Co- operative Research Centre, was deliberately designed to place Manuscript received by the Editor March 22, 1999; revised manuscript received June 4, 2000. ∗ Australian Geological Survey Org., P.O. Box 378, Canberra, A.C.T. 2601, Australia. E-mail: Bruce.Goleby@agso.gov.au; Barry.Drummond@agso. gov.au. ‡Formerly Geological Survey of Western Australia, 100 Plain Street, Perth, Western Australia 6000, Australia; presently North Ltd., P.O. Box 231, Cloverdale, Western Australia 6105, Australia. ∗∗ CSIRO, Div. of Exploration and Mining, Nedlands, Western Australia 6009, Australia. §Formerly Mount Isa Mines Exploration, GPO Box 1042, Brisbane, Queensland 4001, Australia; presently Sons of Gwalia, 16 Parliament Place, West Perth, Western Australia 6005, Australia. c  2000 Society of Exploration Geophysicists. All rights reserved. major orebodies in the inlier into their regional geodynamic framework (Drummond et al., 1997). The results from the Mt. Isa transect, together with the findings of Drummond and Goleby (1993) from the Eastern Goldfields province of Western Australia, suggest that the seis- mic profiling technique could be imaging fluid migration path- ways within the crust. Higher resolution studies (e.g., Milkereit et al., 1996; Yeates et al., 1997; and Goleby et al., 1997) suggest that seismic techniques can also be successful at the orebody 1852