Reprocessing of Geoscience Australia Tanami 2D Siesmic Data - EL 2367

Abstract

This Final report documents exploration work conducted in the Tanami by Newmont Exploration Pty Ltd (Newmont) as part of the Northern Territory Geological Survey's Geophysics and Drilling Collaborations Program. In 2005, deep crustal reflection seismic data in the Tanami Region was collected along several traverses by Geoscience Australia in collaboration with the Northern Territory Geological Survey (NTGS) and Newmont. The reprocessing of the 2D seismic data proposed to assess the broad-scale architecture and the geometry of deep-seated structures, identify potential key fluid pathways and compare characteristics of known orogenic gold mineral systems. Work conducted included the reprocessing of a subset of the 2D seismic dataset by geophysical consultant HiSies Pty Ltd (HiSies). A total of approximately 225 line km of 2D seismic data was reprocessed from two lines, 140 km of seismic line 171-05GA-T1 and 84.5 km of seismic line 171-05GAT4. The reprocessing of the seismic data was undertaken utilizing Pre-Stack Time Migration (PreSTM) sequence, as well as investigating the use of Pre-Stack Depth Migration (PreSDM) method on a subset of the data. It was observed that the PreSDM method, using a velocity model built from the PreSTM sequence, provided significant uplift in imaging over the PreSTM and legacy processing. As a result of this uplift, PreSDM was carried out on 140 km of seismic line 171-05GA-T1 and 84.5 km of seismic line 171-05GA-T4. The reprocessed seismic data mapped a number of large scale thrust faults on both seismic Line T1 and T4 and identified that known gold deposits are also underlain by major fault structures, supporting an orogenic gold mineralisation model. The seismic interpretation of fault zone areas defined eight areas of interest. The tomography data found significant lateral variation in velocities, corresponding to changes in stratigraphy including the differentiation between the Dead Bullock Formation and Mt Charles Formation and the presence of faults. Several washed out seismically attenuated geobodies correlated with known granitic intrusions and identified several others that currently do not appear on published geology maps.