MRD-AusAID-AGSO Project

	MINERAL RESOURCES DEPARTMENT
Ministry of Lands & Mineral Resources and ALTA Government of Fiji.		Last modified :
AIRBORNE GEOPHYSICAL SURVEY – FIJI
DATA RELEASE Summary: Data acquired by a regional airborne geophysical survey covers the major portion of the Fiji landmass and prospective offshore basins. The flight line spacing over the island group is 400 m, and offshore 800 m. Flying height in both instances was 80 m. A combination of helicopter and fixed wing aircraft was used to fly the survey with a total of 160, 000 line kilometers of data acquistion (~80,000km per aircraft type) Flying commenced in April of 1997 and was completed in September. Survey flying and data acquisition were closely supervised by the Australian Geological Survey Organisation (AGSO). The survey was flown by Kevron Geophysics who was also responsible for data processing. The project was initiated by the Government of Fiji and funded by the Government of Australia through the Australian Agency for International Development (AusAID). The Fiji Mineral Resources Department (MRD) on behalf of the Government of Fiji owns and has copyright over the Fiji digital airborne geophysical data. AGSO besides supervising and managing data acquisition and interpretation supported the training of MRD staff in data handling, archiving and basic processing and interpretation of collected data. The project in addition provided relevant hardware and software to manage the above tasks including digital data reproduction (utilising both tape and CD-ROM media) for sale. This project was part of a major initiative by the Fiji Government to upgrade available geological data and strengthen related institutional arrangements in Fiji’s mineral sector in recognition of its significant future potential to Fiji’s economy. A complementary project also funded by AusAID is presently aimed at institutional strengthening of MRD. The results of the geophysical survey are being released as a comprehensive data package that includes point-located and gridded digital data, image maps, flight path maps and interpretation maps. The digital data is available on both magnetic tape (exabyte) and CD-ROM. Details: The Fiji Airborne Geophysical Survey Project is a regional airborne geophysical survey over the majority of the Fiji land mass plus significant parts of offshore Fiji funded by the Australian Agency for International Development (AusAID). The Fiji Mineral Resource Department (MRD) is the Fiji Government agency corresponding to the project and has the responsibility for the archiving, distribution and the ongoing usage of the results. The coverage of the survey, which acquired airborne magnetic and gamma-ray spectrometric data and digital elevation data, is shown in Figure 1. The Australian Geological Survey Organisation (AGSO), acting as project managers under contract to AusAID, designed and supervised this survey, which was flown during the period from April to August 1997, and subsequently processed by Kevron Pty Ltd who won the acquisition component under a competitive bidding process. AGSO has produced an initial interpretation of the survey results The objective of the survey is to provide a database to stimulate mineral and petroleum exploration in Fiji as well as to aid geological mapping, land use studies, geohazard evaluations and groundwater exploration in Fiji. Data from the survey becomes publicly available on June 2, 1998. Survey Specifications The survey acquired magnetic, airborne gamma-ray spectrometric and digital elevation data. The data were recorded using a fixed-wing twin-engine aircraft over offshore areas and low-lying islands (approximately 80 000 kilometres) and two helicopters over the rugged terrain of the major islands (approximately 80 000 kilometres). The survey elevation was 80 metres above the land and sea. The helicopter lines have a spacing of 400m and are oriented at 330 degrees from true north and the tie lines have a spacing of 4000m oriented 60 degrees east of true north. The fixed wing aircraft lines have a spacing of 800m over water and 400m over the low lying islands with tie line spacings at ten times the line spacing. For all of the fixed wing surveying except over the northern Lau Group of islands the line and tie line orientations are the same as for the helicopter surveys. Over the northern Lau Group the traverse lines are oriented at 45 degrees and the tie lines at 315 degrees due to the different orientation of the geology of this island chain. Click on Map to view Colored version (37K)

Total magnetic intensity was recorded with an acceptable noise envelope of 0.2 nanoteslas. The radiometric (gamma-ray spectrometer) data were acquired with a 33 litre crystal over the full spectrum of 256 channels. The simultaneous recording of GPS elevations of the survey aircraft and the ground clearance as measured by a radar altimeter allowed the production of a digital elevation model.

AGSO applied in-field quality-control techniques that required the contractor to demonstrate the integrity of the data. Further verification checks were made during the processing phase, which included micro-leveling of data to ensure that the digital data sets would be suitable for high-quality image processing.

Data Processing

Images and contour maps have been produced for the various parameters recorded. These have been chosen to illustrate the main information content of the data. The various maps and images produced that are available for purchase are listed below.

Survey Results

An initial interpretation of the survey results has been completed by AGSO. This interpretation has allowed the refinement of the surface geological mapping of Fiji as published in various geological maps. The interpretation has also defined many previously unknown fault systems. The most significant aspect from a mineral exploration perspective is that the geophysical data identifies characteristic signatures over known epithermal gold and porphyry copper deposits and that similar signatures are recognisable in areas where no deposits have yet been discovered. The interpretation has been able to delineate the subsurface extents of various major intrusions that appear to be genetically linked to the formation of the epithermal gold and porphyry copper deposits. In many situations volcanic vent systems have been mapped overlying these intrusions. Depth to magnetic source estimates have been produced for the offshore sedimentary basins to assist with evaluation of the hydrocarbon prospectivity of these areas.

Geophysical Data Products

The results of the survey are available as a comprehensive data package, which is available from the Fiji Mineral Resources Department (MRD) in Fiji. The MRD owns the airborne geophysical data and has copyright over the Fiji data package.

The data package comprises the following products:

point-located digital data

* total magnetic intensity (micro-levelled)
* terrain clearance
* terrain height
* total count (air absorbed dose rate nGh-1 )
* equivalent potassium percentage
* equivalent uranium ppm
* equivalent thorium ppm

gridded digital data

* total magnetic intensity
* total magnetic intensity reduced to the pole
first vertical derivative of total magnetic intensity reduced to the pole
* digital elevation model
* total count (air absorbed dose rate nGh-1 )
* equivalent potassium percentage
* equivalent uranium ppm
* equivalent thorium ppm

image maps

* total magnetic intensity reduced to the pole, north sun-angle (colour)
* 1st vertical derivative, reduced to the pole, north sun-angle (grey-scale)
* 1st vertical derivative, reduced to the pole in grey-scale (north sun-angle) superimposed over TMI in colour with no illumination (colour)
* 1st vertical derivative, reduced to the pole, east sun-angle (colour)
* ternary gamma ray (colour)
* equivalent potassium (colour)
* digital elevation model with a NE sun angle (colour)

contour maps

* total magnetic intensity reduced to the pole contours
* total count (air absorbed dose rate nGh-1 ) contours
* equivalent potassium (percentage) contours
* equivalent uranium ppm contours
* equivalent thorium ppm contours
* digital elevation model (metres) contours

flight-path maps

interpretation maps and interpretation report

* Geophysical interpretation maps showing solid geology indicated by the geophysical results, major faults and structures, plus the distribution of major intrusions occurring beneath the surface. Depth to magnetic source estimates are supplied for the offshore basins. A report is available describing the methodology used to produce this map and the most significant features identified by the interpretation.

To purchase data contact:

Bhaskar Rao (Director), Mineral Resources Department, Private Mail Bag, Suva, Fiji. Telephone: +679 3381 611 , Facsimile: +679 3370 039. Email: brao@mrd.gov.fj.

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MINERAL RESOURCES DEPARTMENT

AIRBORNE GEOPHYSICAL SURVEY – FIJI