THE BHP AIRBORNE TEM AND MAGNETIC SURVEY (1997) OVER THE CARRICKMACROSS, NEWBRIDGE, SUMMERHILL, TULLAMORE WEST, TULLAMORE EAST AND LISHEEN AND NAVAN

Transcription

1 THE BHP AIRBORNE TEM AND MAGNETIC SURVEY (1997) OVER THE CARRICKMACROSS, NEWBRIDGE, SUMMERHILL, TULLAMORE WEST, TULLAMORE EAST AND LISHEEN AND NAVAN TEST AREAS December 2001

2 Department of the Marine and Natural Resources THE BHP AIRBORNE TEM AND MAGNETIC SURVEY (1997) OVER THE CARRICKMACROSS, NEWBRIDGE, SUMMERHILL, TULLAMORE WEST, TULLAMORE EAST AND LISHEEN AND NAVAN TEST AREAS Compiled by Orla Dardis EXPLORATION AND MINING DIVISION MINERALS PUBLICATION MP 16/01 DECEMBER 2001 Exploration and Mining Division 2001 Published by authority of the Minister for the Marine and Natural Resources

3 TABLE OF CONTENTS INTRODUCTION 1 SURVEY EQUIPMENT AND SPECIFICATIONS 2 PROCESSING OVERVIEW AND MAP GENERATION 3 Magnetics Processing Sequence 3 Electromagnetics Processing Sequence 3 Grid and Map Generation 4 DATA LISTING 4 Geosoft polygon files of survey boundaries 4 Parameter table files 4 Anomaly Listings 4 Databases 5 Processed GEOTEM and Magnetic Data (Geosoft GDB) 5 Raw GEOTEM Data (ASCII XYZ) 5 Grids 6 Maps 6 Supplied by BHP 7 Supplied by EMD on Ordnance Survey base 8 Company reports 8 GEOSOFT DATABASE CHANNEL LISTING 1 9 Carrickmacross, Newbridge, Summerhill, Tullamore East, Tullamore West 9 GEOSOFT DATABASE CHANNEL LISTING 2 11 Lisheen and Navan Test Areas 11 SURVEY LOCATION 13 Figure 1. Location of the survey areas on a simplified geology map of Ireland. _ 13 Figure 2. The Carrickmacross survey area on a 1:250,000 Ordnance Survey base.14 Figure 3. The Newbridge survey area on a 1:250,000 Ordnance Survey base. 14 Figure 4. The Summerhill survey area on a 1:250,000 Ordnance Survey base. 15 Figure 5. The Tullamore East survey area on a 1:250,000 Ordnance Survey base. 15 Figure 6. The Tullamore West survey area on a 1:250,000 Ordnance Survey base.16

4 INTRODUCTION In July 1996 BHP Minerals International Inc flew a 7075 line km magnetic and electromagnetic survey over seven areas encompassing approximately 1645 km 2 (Figure 1). Two small areas, Lisheen and Navan, were flown as test areas. Block Line km Approx. Area (km 2 ) Carrickmacross Newbridge Summerhill Tullamore East Tullamore West Lisheen 15 6 Navan 20 4 This survey is the sixth in a series of surveys, acquired over four years ago, which are due for public release in fulfilment of the Open Skies policy of the Exploration and Mining Division (EMD). The Division acknowledges the cooperation of BHP Minerals International Inc and the assistance of PGW Europe Ltd. Block Prospecting Licences covered by Survey Carrickmacross 2828, 2023, 3819, 3609, 1171, 3825, 3579, 3732, 3278 Newbridge 3330, 3331, 3332, 3434, 3792, 2824, 1607, 1604, 1608, 1632 Summerhill 3152, 1322,1323, 1325, 2778, 2779, 3621, 1332, 1500 Tullamore East 3232, 2676, 1179, 2757, 2675, 3583 Tullamore West 481, 1111, 1110, 1377, 1378, 2563, 2860, 2881, 2781, 2782, 3147 Lisheen 3262, 2258 Navan 1380R, 1489R At this time EMD is primarily concerned with prompt data release and no attempt was made to reprocess or correct survey data. Data is released as submitted and no liability is accepted on the part of the EMD for data quality or accuracy. However, to facilitate ease of use, several grids are provided with an Ordnance Survey base map for ease of geographical reference. Geoterrex conducted the survey using a towed bird magnetometer and the GEOTEM dual-coil electromagnetic system. This consists of 2 receiver coils, the x-coil axis along the flight direction and a vertical z-coil axis. Time domain electromagnetic (TDEM), magnetic, radar altimeter and navigation data was acquired during the survey. All processing was carried out by Geoterrex, which is now part of Fugro Airborne Surveys. The survey specifications, and data acquisition and processing procedures used are outlined in the Geoterrex report. The survey results are discussed in the Ireland Zinc Program Geophysics report by BHP. A listing of all digital and hardcopy data (databases, grids, maps and company reports) lodged with the Exploration and Mining Division is included in this publication and outlined below in the data listing section. 1

5 SURVEY EQUIPMENT AND SPECIFICATIONS Flight Line Spacing 250m Flight Line Direction Carrickmacross 90 Newbridge 144 Summerhill 146 Tullamore East 146 Tullamore West 0 Lisheen 144 Navan 90 Tie Line Spacing m Mean Terrain Clearance 120 m Nominal Survey Speed 120 knots ( 62 m/s ) Total Survey Area km 2 Total Line Km 7075 line km Magnetometer Sensitivity Sample Rate Mounting Sensor Height above ground TEM Receiver TEM Transmitter Cycle rate Pulse width Pulse Delay Off-Time Sample Rate Mounting Sensor Height above ground Cesium Vapour 0.01 nt 10 samples /sec Towed Bird 75 m Horizontal & vertical coils Vertical axis loop 75 Hz msec msec msec 4 samples/sec Towed Bird 64 m Below are the window mean delay times (in milliseconds), from the end of the transmitter pulse, for a 75 Hz base frequency as listed in the Geoterrex report and readme file. em em em em em em em em em em em em em em em em em em em em

6 PROCESSING OVERVIEW AND MAP GENERATION The information provided in this section was taken from the Geoterrex report and readme file for the survey (included on CD) and from examination of the data. Magnetics Processing Sequence A system lag correction of 3.6 seconds was applied followed by noise editing (de-spiking) and filtering. Appendix A of the Geoterrex Report outlines the field processing sequence in more detail. The long wavelength component (greater than 40 seconds) of the diurnal field was removed from the data. The regional magnetic field (IGRF) was also removed from all areas except the test areas. The data was resampled to 5 samples per second for inclusion in the final database. A proprietary algorithm, to improve trends along anomalies, was applied. The data was then microleveled and gridded using a modified Akima spline interpolation. For the test areas, no tie lines were flown and only the raw magnetics channel is included in the database. Electromagnetics Processing Sequence A system lag correction of 4.5 secs was applied followed by drift corrections to the off-time channels 5 to 20 and on-time channel 1. Each EM transient decay curve was de-spiked and the data was then noise filtered and smoothed. Appendix A of the Geoterrex Report outlines the field processing sequence in more detail. No corrections for flight direction asymmetry (de-herringboning) were applied. The data was resampled to 5 samples per second for inclusion in the final database EM Decay Constant Calculation The EM early to middle time decay constant was calculated from the z-coil data by fitting channels 8 to 14 (mean delay times msec) to a single exponential function. The EM middle to late time decay constant was calculated from the z-coil data by fitting channels 12 to 18 (approx msec). A slow rate of decay gives a high decay constant which indicates a better conductor. EM Anomaly Selection EM anomalies were located by an automatic anomaly picking routine, using channel 12 (mean delay time msec) as a reference. X coil channels 9 to 20 were then fitted to the vertical plate model to extract conductance and depth information. 3

7 Grid and Map Generation Grids were submitted with the survey data in grid exchange format (gxf) (see Grids section). Grids were produced in EMD for the Lisheen and Navan test areas using a minimum curvature interpolation and are identified by an emd label in the filename. All grids have a grid cell size of 50m. The original submitted grids were used to generate the all EMD maps on an Ordnance Survey base. All digital and hardcopy products are in the Irish National Grid (ING) coordinate system: Datum: TM65 / Airy Modified 1849 Ellipsoid: Airy Modified 1849 Major axis: Eccentricity: /f: Projection Transverse Mercator Central Meridian Latitude of origin False Northing: 250,000 m False Easting: 200,000 m Scale factor: DATA LISTING Geosoft polygon files of survey boundaries Geosoft polygon files (*.ply) for each survey area are included on the CD. The files are in ASCII format and can be opened in any text editor to view survey boundary coordinates (in ING). Parameter table files Geoterrex supplied waveform parameter table files, one for each survey flight, in ASCII format. These files provide information on the system geometry, the channel positions in time and the reference waveform. The waveform is used to remove the effects of the primary field on the received secondary signal. Anomaly Listings No anomaly listings in digital form were provided. Hardcopy x-coil anomaly maps were provided for each area and scanned in EMD. Anomaly listings for all areas were provided as a separate appendix (G) with the Geoterrex report. This volume of anomaly listings is available for viewing in the EMD. The BHP Geophysics report highlights and describes 32 anomalies for ground follow-up. 4

8 Databases The raw and processed data was supplied by BHP in ASCII format and imported into Geosoft Database format (GDB) by EMD. Geoterrex readme files with channel listings are included on the CD and summarised on pages 9 to 12. The processed magnetics and EM data is released on CD in Geosoft format. The raw EM data is available on CD in zipped ASCII format. The processed data files submitted for Lisheen and Navan contained only a raw magnetics channel and no final magnetics channel. Processed GEOTEM and Magnetic Data (Geosoft GDB) Database Number of Channels Approx. Size (Mb) Carrickmacross carric Newbridge newb Summerhill summ Tullamore East tulle Tullamore West tullw Lisheen test area lish_test Navan test area nav_test File Name (.gdb) Raw GEOTEM Data (ASCII XYZ) ASCII Data File No of columns Approx. Size (Mb) File Name (.zip) Carrickmacross macraw Newbridge newraw Summerhill sumraw Tullamore East tuleraw Tullamore West tulwraw Lisheen test area lishraw Navan test area navraw 5

9 Grids The following grids were submitted by BHP (in ASCII gxf format) and reproduced where required by EMD (in Geosoft grid format) as no grids were submitted by BHP for the test areas. All grid cell spacings are 50m. Block Grid Grid Name Carrickmacross tfmac.gxf Newbridge tfnew.gxf Total Magnetic Field (IGRF Summerhill tfsum.gxf removed) Tullamore East tftule.gxf Tullamore West tftulw.gxf Lisheen lisheen_tmi_emd.grd Raw Total Magnetic Field Navan navan_tmi_emd.grd Carrickmacross Newbridge Summerhill Tullamore East Tullamore West Carrickmacross Newbridge Summerhill Tullamore East Tullamore West Lisheen Navan Carrickmacross Newbridge Summerhill Tullamore East Tullamore West Lisheen Navan Total Magnetic Field (IGRF removed, culture edited) Early-Middle time decay constant (zcoil ch 8 to 14) Middle-Late time decay constant (zcoil ch 12 to 18) editmac.gxf editnew.gxf editsum.gxf edittule.gxf edittulw.gxf Taue mac.gxf tauenew.gxf tauesum.gxf tauetule.gxf tauetulw.gxf lisheen_etau_emd.grd navan_etau_emd.grd taulmac.gxf taulnew.gxf taulsum.gxf Taultule.gxf taultulw.gxf lisheen_ltau_emd.grd navan_ltau_emd.grd Maps BHP submitted no digital or hardcopy maps for the Lisheen and Navan test areas. All hardcopy maps submitted by BHP for this release were scanned and stored in a compressed TIFF format, to keep file sizes manageable. Compression was carried out using Imaging for Windows, which is available under the Accessories menu in Windows. Black and white images were compressed using CCIT Group4 compression, which can be opened in all standard packages. Colour TIFF images were compressed using LZW compression option and can be opened and/or exported into Imaging for Windows and the Geosoft Oasis Montaj 5.0 free viewer. This LZW compression is not supported by Arcview 3.2 but the Geosoft viewer can be downloaded free of charge and gives the option to save compressed 6

10 TIFF files in other formats. Maps produced in EMD, on an Ordnance Survey 1:50,000 base, are available on the release CD as uncompressed images in JPEG format, or in hardcopy format on request. Supplied by BHP Block Map Title Filename Scale Carrickmacross Geology Map bhp :50000 Carrickmacross Processed TMI Drape with sun from west bhp :50000 Carrickmacross Residual Magnetic Contour Map bhp :50000 Carrickmacross Late time decay constant calculated from z-coil channels bhp :50000 Carrickmacross EM x-coil anomalies bhp :50000 Carrickmacross XCHO8 draped over processed TMI with W sun angle bhp :50000 Carrickmacross Interpretation Overlay of XCHO8 draped over TMI with W sunangle bhp :50000 Newbridge Geology Map bhp :50000 Newbridge Processed mag drape with NW sun angle bhp :50000 Newbridge Residual magnetics Contour Map bhp :50000 Newbridge Late time decay constant calculated from z-coil channels bhp :50000 Newbridge EM x-coil anomalies bhp :50000 Newbridge XCHO8 draped over processed magnetics with NW sunangle bhp :50000 Newbridge Interpretation Overlay of XCHO8 draped over Magnetics bhp :50000 Summerhill Geology Map bhp :50000 Summerhill Geology Map including amendments from GEOTEM interpretation bhp :50000 Summerhill Processed magnetics with NW sunangle bhp :50000 Summerhill Residual Magnetics Contour Map bhp :50000 Summerhill Late time decay constant calculated from z-coil channels bhp :50000 Summerhill EM x-coil anomalies bhp :50000 Summerhill XCHO8 draped over processed magnetics with NW sunangle bhp :50000 Summerhill Interpretation Overlay of XCHO8 draped over Magnetics bhp :50000 Tullamore East Geology Map bhp :50000 Tullamore East,West,Centre Geology map based on EM interpretation bhp :75000 Tullamore East Processed TMI with NW sunangle bhp :50000 Tullamore East Residual Magnetics Contour Map bhp :50000 Tullamore East EM Late time decay constant bhp :50000 Tullamore East EM x-coil anomalies bhp :50000 Tullamore East XCHO8 draped over processed Magnetics with NW sunangle bhp :50000 Tullamore East Interpretation Overlay of XCHO8 draped over processed Magnetics bhp :50000 Tullamore West Geology Map bhp :50000 Tullamore West Processed TMI drape with N sunangle bhp :50000 Tullamore West Residual Magnetics Contour Map bhp :50000 Tullamore West Late time decay constant calculated from z-coil channels bhp :50000 Tullamore West EM x-coil anomalies bhp :50000 Tullamore West XCHO8 draped over processed TMI with sun from N bhp :50000 Tullamore West Interpretation Overlay of XCHO8 draped over processed Magnetics bhp :

11 Supplied by EMD on Ordnance Survey base Block Map Filename Scale Carrickmacross carric_tmi_emd 1:50000 Newbridge newb_tmi_emd 1:50000 Total Magnetic Field Summerhill summ_tmi_emd 1:50000 (IGRF removed, culture edited) Tullamore East tulle_tmi_emd 1:50000 Tullamore West tullw_tmi_emd 1:50000 Carrickmacross carric_etau_emd 1:50000 Newbridge newb_etau_emd 1:50000 Early-Middle time decay constant Summerhill summ_etau_emd 1:50000 (z-coil ch 8 to 14) Tullamore East tulle_etau_emd 1:50000 Tullamore West tullw_etau_emd 1:50000 Carrickmacross carric_ltau_emd 1:50000 Newbridge newb_ltau_emd 1:50000 Summerhill Middle-Late time decay constant summ_ltau_emd 1:50000 Tullamore East (z-coil ch 12 to 18) tulle_ltau_emd 1:50000 Tullamore West tullw_ltau_emd 1:50000 These maps are available, on an Ordnance Survey 1:50,000 base, as jpeg images on CD or in hardcopy format on request. Company reports The Geoterrex Logistics and processing report and a survey report by BHP are included on the release CD. Report Title Filename (.pdf) No. of pages Ireland Zinc Program Geophysics Report. Geotem surveys over Galmoy, Carrickmacross, Newbridge Summerhill, Tullamore East, Tullamore West. Logistics and Processing Report of the Airborne magnetic and Geotem electromagnetic multicoil survey in the Republic of Ireland over the Tullamore East, Tullamore West, Carrickmacross, Newbridge and Summerhill Blocks and the Lisheen and Navan test areas bhpr3_1 129 bhpr3_

12 GEOSOFT DATABASE CHANNEL LISTING 1 Carrickmacross, Newbridge, Summerhill, Tullamore East, Tullamore West CHANNEL NAME DESCRIPTION UNITS FLT Flight number FID Fiducial seconds x 10 EASTING Easting metres NORTHING Northing metres MAG_RAW Total field magnetics (raw) nt x 100 MAG_FINAL Total field magnetics (final) nt x 100 DIURNAL Diurnal magnetics nt x 100 MAG_CULT Culture edited magnetics nt x 100 RAD Radar altimeter metres BARO Barometric altimeter metres X1 Em channel X1 ppm X5 Em channel X5 ppm X6 Em channel X6 ppm X7 Em channel X7 ppm X8 Em channel X8 ppm X9 Em channel X9 ppm X10 Em channel X10 ppm X11 Em channel X11 ppm X12 Em channel X12 ppm X13 Em channel X13 ppm X14 Em channel X14 ppm X15 Em channel X15 ppm X16 Em channel X16 ppm X17 Em channel X17 ppm X18 Em channel X18 ppm X19 Em channel X19 ppm X20 Em channel X20 ppm RAW_X2 Raw Em channel X2 ppm RAW_X3 Raw Em channel X3 ppm RAW_X4 Raw Em channel X4 ppm Z1 Em channel Z1 ppm Z5 Em channel Z5 ppm Z6 Em channel Z6 ppm Z7 Em channel Z7 ppm Z8 Em channel Z8 ppm 9

13 Z9 Em channel Z9 ppm Z10 Em channel Z10 ppm Z11 Em channel Z11 ppm Z12 Em channel Z12 ppm Z13 Em channel Z13 ppm Z14 Em channel Z14 ppm Z15 Em channel Z15 ppm Z16 Em channel Z16 ppm Z17 Em channel Z17 ppm Z18 Em channel Z18 ppm Z19 Em channel Z19 ppm Z20 Em channel Z20 ppm RAW_Z2 Raw Em channel Z2 ppm RAW_Z3 Raw Em channel Z3 ppm RAW_Z4 Raw Em channel Z4 ppm ZTDC_EARLY Em early decay constant from Z usec ZTDC_LATE Em late decay constant from Z usec PRIMARY_FIELD Em primary field uv XPOWERLINE_MONITOR Powerline monitor uv RMS_X Decay fitting RMS error from X ppm RMS_Z Decay fitting RMS error from Z ppm IGRF IGRF correction nt x 100 COMPENSATION Tie-line levelling correction nt x

14 GEOSOFT DATABASE CHANNEL LISTING 2 Lisheen and Navan Test Areas CHANNEL NAME DESCRIPTION UNITS FLT Flight number FID Fiducial seconds x 10 EASTING Easting metres NORTHING Northing metres MAG_RAW Total field magnetics (raw) nt x 100 DIURNAL Diurnal magnetics nt x 100 RAD Radar altimeter metres BARO Barometric altimeter metres X1 Em channel X1 ppm X5 Em channel X5 ppm X6 Em channel X6 ppm X7 Em channel X7 ppm X8 Em channel X8 ppm X9 Em channel X9 ppm X10 Em channel X10 ppm X11 Em channel X11 ppm X12 Em channel X12 ppm X13 Em channel X13 ppm X14 Em channel X14 ppm X15 Em channel X15 ppm X16 Em channel X16 ppm X17 Em channel X17 ppm X18 Em channel X18 ppm X19 Em channel X19 ppm X20 Em channel X20 ppm RAW_X2 Raw Em channel X2 ppm RAW_X3 Raw Em channel X3 ppm RAW_X4 Raw Em channel X4 ppm Z1 Em channel Z1 ppm Z5 Em channel Z5 ppm Z6 Em channel Z6 ppm Z7 Em channel Z7 ppm Z8 Em channel Z8 ppm Z9 Em channel Z9 ppm Z10 Em channel Z10 ppm 11

15 Z11 Em channel Z11 ppm Z12 Em channel Z12 ppm Z13 Em channel Z13 ppm Z14 Em channel Z14 ppm Z15 Em channel Z15 ppm Z16 Em channel Z16 ppm Z17 Em channel Z17 ppm Z18 Em channel Z18 ppm Z19 Em channel Z19 ppm Z20 Em channel Z20 ppm RAW_Z2 Raw Em channel Z2 ppm RAW_Z3 Raw Em channel Z3 ppm RAW_Z4 Raw Em channel Z4 ppm ZTDC_EARLY Em early decay constant from Z usec ZTDC_LATE Em late decay constant from Z usec PRIMARY_FIELD Em primary field uv XPOWERLINE_MONITOR Powerline monitor uv RMS_X Decay fitting RMS error from X ppm RMS_Z Decay fitting RMS error from Z ppm 12

16 SURVEY LOCATION THE BHP AIRBORNE TEM AND MAGNETIC SURVEY (1997) CARRICKMACROSS, NEWBRIDGE, SUMMERHILL, TULLAMORE WEST AND TULLAMORE EAST BLOCKS 6.1 Carrickmacross 2 Newbridge 3 Summerhill 4 Tullamore E 5 Tullamore W Figure 1. Location of the survey areas on a simplified geology map of Ireland. 13

17 Figure 2. The Carrickmacross survey area on a 1:250,000 Ordnance Survey base. Figure 3. The Newbridge survey area on a 1:250,000 Ordnance Survey base. 14

18 Figure 4. The Summerhill survey area on a 1:250,000 Ordnance Survey base. Figure 5. The Tullamore East survey area on a 1:250,000 Ordnance Survey base. 15

19 Figure 6. The Tullamore West survey area on a 1:250,000 Ordnance Survey base. 16