Regional 2D Seismic Reflection Survey at Tennant Creek Northern Territory

Abstract

Over 9 days during June 2015 HiSeis Pty Ltd acquired two-dimensional (2D) regional seismic reflection data proximal to the Tennant Creek town site and mining facilities on behalf of Emmerson Resources Limited. One 60km 2D seismic reflection line (Line 101) was acquired following the Stuart Highway 30km to the north, and 30km to the south, of the town of Tennant Creek, diverted to the east of the town site for logistical reasons. The objective of the 2D survey was to outline previously unidentified areas of prospectivity in the Tennant Creek Mineral Field by seismically imaging the upper crust along the line to improve understanding of regional geological architecture. This was achieved by acquiring 60km of 2D data with a total of 2,032 unique source points. Acquisition of this 2D dataset utilised one source, a 60,000lb Vibroseis Vehicle, as a means of producing seismic energy, delivering a linear 14 second sweep through a frequency range of 8-130Hz. The record length was 10 seconds, in an attempt to catch reflections at 10km+ in depth. Two to three identical sweeps were acquired at each individual VP (vibe position) depending on intensity of ambient noise sources (mostly traffic). All seismic vibrations were measured with a rolling spread of 600 single point geophones using the Aries II seismic acquisition system. The spacing between VPs was 30m and the spacing between geophones was 15m. Two products were produced for Line 101. These were: a) A product targeted to assist the determination of regional geological architecture down to a depth of approximately 30km. b) A product with a focus on the shallow geology within the top 2km below the surface. HiSeis Pty Ltd adapted a conventional processing flow to the acquisition parameters, survey objectives and geology known to exist in this area. Parameter testing was conducted and the results of these tests determined an optimum flow in order to image the complex structural geology for each of the two products: regional processing and shallow processing. While care must be taken interpreting 2D sections because reflections that are observed may not originate from directly below the survey line and may be distorted due to the 3D complexity of the earth, initial results suggest all of the major gold-copper deposits in proximity to line 101 are associated with northward-verging thrust faults which extend down to about 13 kilometres depth. There are also a number of thrusts without expression at the surface, and these have no known mineralization, but where the thrusts are known at the surface, there is a positive correlation with mineralization. The survey also imaged many more felsic intrusives than were expected. A major sub-horizontal boundary is clearly visible at approximately 20km depth and represents the top of a different seismic domain which may be analogous to the top of the Ooratippra Seismic Province defined on the line 09GA-GA1 (Georgina Basin-Arunta Region) located 210km to the South East. A washed-out zone above this domain represents the basement on which the Warramunga Formation and younger units were deposited. The links between gold-copper mineralization, felsic intrusives and thrust faults have long been postulated for the Tennant Creek Mineral Field but this data provides the first validation of the concept and should permit exploration to focus on previously unknown thrusts.