THE RIO ALGOM/IVERNIA WEST AIRBORNE TEM AND MAGNETIC ... · 75 Hz base frequency as listed in the...

THE RIO ALGOM/IVERNIA WEST AIRBORNE TEM AND MAGNETIC SURVEY (1998) OVER THE FERBANE AND

LOUGH DERG 2 AREAS

December 2002

Department of Communications, Marine and Natural Resources

Department of Communications, Marine and Natural Resources

THE RIO ALGOM/IVERNIA WEST AIRBORNE TEM AND MAGNETIC SURVEY (1998) OVER THE FERBANE AND

LOUGH DERG AREAS

Compiled by Orla Dardis

EXPLORATION AND MINING DIVISION MINERALS PUBLICATION MP 20/02

DECEMBER 2002

Exploration and Mining Division 2002 Published by authority of the Minister for Communications, Marine

and Natural Resources

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 Anomaly Listings ____________________________________________________________ 4 Databases __________________________________________________________________ 5

Processed GEOTEM and Magnetic Data (Geosoft GDB) _________________________ 5 Grids ______________________________________________________________________ 5 Maps ______________________________________________________________________ 6

Supplied by Rio Algom/Ivernia West _________________________________________ 6 Supplied by EMD on Ordnance Survey base ___________________________________ 8

Company reports _____________________________________________________________ 8 GEOSOFT DATABASE CHANNEL LISTING 1 _____________________________________ 9

Ferbane and Lough Derg2 Electromagnetics Database________________________________ 9 GEOSOFT DATABASE CHANNEL LISTING 2 ____________________________________ 11

Ferbane and Lough Derg2 Magnetics and EM Database _____________________________ 11 GEOSOFT DATABASE CHANNEL LISTING 3 ____________________________________ 11

Ferbane and Lough Derg2 Conductance Database __________________________________ 11 SURVEY LOCATION _________________________________________________________ 12

Figure 1. Location of the survey areas on a simplified geology map of Ireland.________ 12 Figure 2. The Ferbane survey area on a 1:250,000 Ordnance Survey base. ___________ 13 Figure 3. The Lough Derg 2 survey area on a 1:250,000 Ordnance Survey base._______ 14

1

INTRODUCTION

Between February and March 1998 Rio Algom Exploration Inc. and Ivernia West Plc. flew a 1961 line km magnetic and electromagnetic survey over two areas encompassing approximately 748 km2 (Figure 1).

Block Line km Approx. Area (km2) Prospecting Licences covered/partially covered by Survey

Lough Derg 2 97 241 2564, 3425, 3426, 3670, 3677, 3678, 3898

Ferbane 651 1720

480, 481, 505, 506, 619, 1108, 1110, 1111, 1113, 1117, 1226, 1244, 1345, 1353, 1377, 1378, 1919, 2105, 2561, 2695, 2781, 2786, 2860, 2861, 3129, 3163, 3266, 3527, 3528, 3529, 3530, 3531,3583, 3588, 3589, 3652, 3813, 3814, 3877

This survey was acquired over six years ago and is available to the general public in fulfilment of the ‘Open Skies’ policy of the Exploration and Mining Division (EMD). The Division acknowledges the cooperation of Rio Algom Exploration Inc. (now BHP-Billiton). 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 GEOTEMIII electromagnetic system. This consists of 3 receiver coils, the x-coil and y-coil axes along and perpendicular to 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 acquisition and processing procedures are outlined in a Geoterrex report. An interpretation is also provided as part of the report, which is included in the CD release. 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 listings section.

2

SURVEY EQUIPMENT AND SPECIFICATIONS

Flight Line Spacing Ferbane 400m Lough Derg2 400m Flight Line Direction Ferbane 325° Lough Derg2 90° Tie Line Spacing Ferbane 3000-4000m Lough Derg2 3000-4000m Mean Terrain Clearance 120 m Nominal Survey Speed 120 knots ( 62 m/s ) Total Survey Area 748 km2 Total Line Km 1961 line km Magnetometer CS-2 Cesium Vapour Sensitivity 0.001 nT Sample Rate 10 samples /sec Mounting Towed Bird Sensor Height above ground 75 m TEM Receiver Horizontal & vertical coils TEM Transmitter Vertical axis loop Cycle rate 75 Hz Pulse width 2.082 msec Pulse Delay 0.104 msec Off-Time 4.480 msec Sample Rate 4 samples/sec Mounting Towed Bird Sensor Height above ground 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.

em1 -1.953 em11 1.146 em2 -1.562 em12 1.407 em3 -0.989 em13 1.693 em4 -0.416 em14 2.005 em5 0.163 em15 2.344 em6 0.235 em16 2.709 em7 0.365 em17 3.073 em8 0.521 em18 3.464 em9 0.703 em19 3.880 em10 0.912 em20 4.297

3

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. Pages 5 to 7 and Appendix A of the Geoterrex report outline the processing sequence in more detail. The long wavelength component (greater than 25 seconds) of the diurnal field was removed from the data. The data was leveled, microleveled and gridded using a minimum curvature interpolation (grid cell spacing 100m). The regional magnetic field (IGRF) was also removed and various filters were applied to the final gridded data to remove cultural noise (see Geoterrex report page 7). Electromagnetics Processing Sequence Appendix A and pages 7 to 9 of the Geoterrex report outlines the processing sequence in more detail. A system lag correction of 4.0 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. The data was resampled to 5 samples per second for inclusion in the final database. The final decay constant and apparent conductivity grids have grid cell spacings of 100m and were created using the Akima interpolation method. Corrections for flight direction asymmetry (de-herringboning) and cultural noise were applied to the final decay constant and apparent conductance grids. EM Decay Constant Calculation The EM time decay constant was calculated from the z-coil data by fitting channels 9 to 17 (approx. 0.703 – 3.073 msec) to a single exponential function. 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 0.1407 msec) as a reference. X-coil channels 9-20 were then fitted to the vertical plate model to extract conductance and depth information. Anomaly listings for the two areas are provided in Appendix G of the Geoterrex reports and as digital files on the release CD. Hardcopy anomaly maps were provided and scanned in EMD. Apparent Conductance Calculation The apparent conductance was computed from the x and z-coil data using both the on and off-time channels and is based on a thin sheet model.

4

Grid and Map Generation Rio Algom lodged grids in grid exchange format (gxf), which were created with a 100m cell spacing. Many of the grids and maps for this release also include merged data from two previous Rio Algom/Ivernia West surveys flown in 1996 and 1997. The 1996 Lough Derg 1 survey and the 1997 Portumna survey have been released and the CD’s are available from EMD. The final magnetics (CULT_MAG) and decay constant (ZTAU_EDIT) channels were re-gridded by EMD using a minimum curvature interpolation (100m grid cell spacing) and are identified by an ‘emd’ label in the filename. The original submitted magnetic and decay constant grids (culture edited) were used to generate the 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: 6377340.189 Eccentricity: 0.081673374 1/f: 299.3249646

Projection Transverse Mercator Central Meridian -8.00.00.000 Latitude of origin 53.30.00.000 False Northing: 250,000 m False Easting: 200,000 m Scale factor: 1.000035

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). Anomaly Listings Anomaly listings for the two areas are provided in Appendix G of the Geoterrex report and also as digital files on the release CD.

5

Databases The raw and final data was supplied 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 11. The processed magnetics and EM data is released on CD in Geosoft format. Processed GEOTEM and Magnetic Data (Geosoft GDB)

Database Number of Channels

Approx. Size (Mb)

File Name (.gdb)

Ferbane magnetics & EM 17 7.5 ferbane_mag_em Ferbane EM 64 26.3 ferbane_em Ferbane conductance 4 3.1 ferbane_cond Lough Derg2 magnetics & EM 17 2.8 lderg2_mag_em Lough Derg2 EM 64 6.3 lderg2_em Lough Derg2 conductance 4 2.0 lderg2_cond

Grids As mentioned above, many of the grids and maps for this release also include merged data from two previous Rio Algom/Ivernia West surveys flown in 1996 and 1997. The 1996 Lough Derg 1 survey and the 1997 Portumna survey have been released and the CDs are available from EMD. The following grids in gxf format were submitted by Rio Algom and reproduced where required by EMD to provide a grid produced using a minimum curvature interpolation in Geosoft grid format (grd).

Block Grid Grid Name Grid cell spacing (m)

Format

Ferbane ferbedit 100 gxf

Lough Derg2 Residual magnetic field (culture edited) ld2edit 100 gxf

Ferbane ferbtauz 100 gxf

Lough Derg2 Decay constant (z-coil ch 9-17, culture edited) ld2tauz 100 gxf

Ferbane & Portumna fp 100 gxf

Lough Derg1 & 2 Merged residual magnetic field

ld 100 gxf

Lough Derg1 & 2 lcond 100 gxf

Ferbane & Portumna Merged apparent conductance (culture edited) fpcond 100 gxf

Lough Derg1 & 2 ltauz 100 gxf

Ferbane & Portumna Merged decay constant (z-coil ch 9-17, culture edited fptauz 100 gxf

Ferbane ferbane_tmi_emd 100 grd

Lough Derg2 Residual magnetic field

lderg2_tmi_emd 100 grd

Ferbane ferbane_ztau_emd 100 grd

Lough Derg2 Decay constant (z-coil ch 9-17)

lderg2_ztau_emd 100 grd

6

Maps All colour hardcopy maps submitted by Rio Algom for this release were scanned and stored in a compressed TIFF format, using LZW compression to keep file sizes manageable, and can be opened in most standard packages. Compression was carried out using Imaging for Windows, which is available under the Accessories menu in Windows. LZW compressed TIFF images can only be viewed in Geosoft when they are imported as a GeoTIFF file. Black and white images were compressed using CCIT Group4 compression, which can be opened in all standard packages. Maps produced in EMD, on an Ordnance Survey 1:50,000 base, with permission from Ordnance Survey Ireland, are available on the release CD as uncompressed images in JPEG format, or in hardcopy format on request. Supplied by Rio Algom/Ivernia West

Block Map Title Filename Scale L. Derg, Ferbane Total Magnetic Intensity Reduced to Pole NW Illumination rio11.1.01c 1:100000 L. Derg, Ferbane, Portumna

Residual Magnetic Field (Culture Edited) Contour Map (sheet 2 of 7)

rio11.1.02c 1:25000

L. Derg, Ferbane, Portumna


rio11.1.03c 1:25000



rio11.1.04c 1:25000



rio11.1.05c 1:25000



rio11.1.06c 1:25000



rio11.1.07c 1:25000



rio11.1.08c 1:25000


EM Early-Mid Time Decay Constant Contour Map (Z-Coil Ch 9-17) sheet 1of 7

rio11.1.09c 1:25000


EM Early-Mid Time Decay Constant Contour Map (Z-Coil Ch 9-17) sheet 2 of 7

rio11.1.10c 1:25000


EM Early-Mid Time Decay Constant Contour Map (culture edited) (Z-Coil Ch 9-17) sheet 3 of 7

rio11.1.11c 1:25000



rio11.1.12c 1:25000



rio11.1.13c 1:25000



rio11.1.14c 1:25000



rio11.1.15c 1:25000


Residual Magnetic Contour Map (Sheet 1 of 7) rio11.1.16c 1:25000

7













Ferbane Mid-Late Time Constant Decay rio11.1.23c 1:50000 Ferbane Residual Magnetic Field Culture Edited b/w rio11.1.24c 1:50000 L. Derg, Ferbane, Portumna

Apparent Conductance (culture edited) Contour Map (Sheet 1 of 7)

rio11.1.25c 1:25000



rio11.1.26c 1:25000



rio11.1.27c 1:25000



rio11.1.28c 1:25000



rio11.1.29c 1:25000



rio11.1.30c 1:25000



rio11.1.31c 1:25000

L. Derg Calculated Vertical Gradient of Culture Edited Magnetics (Sheet 1of 7)

rio11.1.32c 1:25000

L. Derg Calculated Vertical Gradient of Culture Edited Magnetics (Sheet 2 of 7)

rio11.1.33c 1:25000


Calculated Vertical Gradient of Culture Edited Magnetics (Sheet 3 of 7)

rio11.1.34c 1:25000

Ferbane, Portumna Calculated Vertical Gradient of Culture Edited Magnetics (Sheet 4 of 7)

rio11.1.35c 1:25000


rio11.1.36c 1:25000


rio11.1.37c 1:25000


rio11.1.38c 1:25000

L. Derg, Ferbane Total Magnetic Intensity rio11.1.39c 1:100000 L. Derg, Ferbane Total Magnetic Intensity Reduced to Pole rio11.1.40c 1:100000 L. Derg, Ferbane Total Magnetic Intensity Reduced to Pole E Illumination rio11.1.41c 1:100000 L. Derg, Ferbane Total Magnetic Intensity (Transparency) b/w rio11.1.42c 1:100000

8

Supplied by EMD on Ordnance Survey base

Block Map Filename Scale

Ferbane ferbane_tmi_emd 1:100,000

Lough Derg2 Processed magnetic intensity (culture edited)

lderg2_tmi_emd 1:50,000

Ferbane ferbane_ztau_emd 1:100,000

Lough Derg2 Decay constant (z-coil ch 7-19) (culture edited)

lderg2_ztau_emd 1:50,000

These maps are available, on an Ordnance Survey 1:50,000 base, as scanned images (jpeg format) or in hardcopy format (Ordnance Survey Permit DNE 001001). Company reports The Geoterrex logistics and processing report for both areas, which includes an interpretation, is included on the release CD. Report Title Filename (.pdf) No. of pages

Geoterrex Logistics, Processing and Interpretation Report of the Airborne Magnetic & GEOTEM Electromagnetic Multicoil Survey over Lough Derg 2 and Ferbane Blocks

Rior11_1 161

9

GEOSOFT DATABASE CHANNEL LISTING 1

Ferbane and Lough Derg2 Electromagnetics Database

CHANNEL NAME DESCRIPTION UNITS

X Easting metres

Y Northing metres

FID Fiducial seconds after midnight

POWERLINE_MONITOR Powerline monitor uV

X1 Em channel X1 ppm

RAW_X2 Raw Em channel X2 ppm



















Y1 Em channel Y1 ppm

RAW_Y2 Raw Em channel Y2 PV/m2



Y5 Em channel Y5 PV/m2






10











Z1 Em channel Z1 PV/m2

RAW_Z2 Raw Em channel Z2 ppm



Z5 Em channel Z5 ppm
















11


Ferbane and Lough Derg2 Magnetics and EM Database


X Easting metres

Y Northing metres

FID Fiducial seconds

RAD Radar altimeter feet

GPS GPS elevation Metres x 100

DIURNAL Diurnal magnetics nT x 100

RAW_MAG Raw magnetics (after lag, spike editing & filtering) nT x 100

DIURNAL_MAG magnetics (before leveling)

LEV_MAG Levelled magnetics nT x 100

IGRF_MAG Leveled magnetics (IGRF removed) nT x 100

COMP Leveling compensation nT x 100

CULT_MAG Cultured edited magnetics nT x 100

GRAD RF vertical gradient nT/km x 100

ZTAU Decay constant from z-coil (ch 9-17) µsec

ZTAU_EDIT Culture edited decay constant from z-coil (ch 9-17) µsec

PRIMARY_FIELD Em primary field uv

POWERLINE_MONITOR Powerline monitor uv


Ferbane and Lough Derg2 Conductance Database


X Easting metres

Y Northing metres

FID Fiducial seconds

CONDUCTANCE Apparent conductance mS x 1000

12

SURVEY LOCATION Figure 1. Location of the survey areas on a simplified geology map of Ireland.

DUBLIN

CORK

GALWAY

BELFAST

DERRY

DuncormickZn, Pb

Tynagh

Barite

AbbeytownPb, Zn

TatestownOldcastleZn, Pb

KeelZn, Pb, Barite

KilrootSalt

Sandy BraesPerlite

GlangevlinGypsum

Kingscourt

RossmoreCoal

BallingarryCoal

Calcite

Barite

Cu, Ag

Ball Clay

Clonakilty Barite

AllihiesCu

CharlestownCu

WestportTalc

ArignaCoal

BunmahonCu

BenbulbenBarite

BennettsbridgeDolomite

Kish BasinCoal

CrumlinLignite

BallymoneyLignite

TomduffAndalusite

AvocaCu

Curraghinalt Au

CavanacawAu

ClontibretAu, Sb

LecanveyAu

CregganbaunAu

Kilmacoo Au

Gold MinesRiver Au

Au

Mallow

Ballyvergin

Ballymacadam

Cu, Ag

Zn, PbMoyvoughly

Carnew

Gypsum

BallinalackZn, Pb

Pb, Zn, Cu, Ag,

Harberton BridgeZn Pb,

Zn, PbNavan

Zn, Pb

PortroeSlate

Kilbreckan Cu

LIMERICK

CourtbrownZn, Pb Cu, Ag, Hg

Gortdrum

BallynoeLisheen

KedrahDolomiteAherlow

Zn, Pb

SilverminesZn, Pb, Ag

Zn, PbGalmoy

13.1

THE RIO ALGOM/IVERNIA WEST AIRBORNE TEM AND MAGNETIC SURVEY (1997) FERBANE AND LOUGH DERG 2 AREAS

13.1 Ferbane 2 Lough Derg 2

Industrial mineral depositCoal deposit

Active mineCity

Base metal deposit

Disused mine

Gold deposit

13.2

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Figure 2. The Ferbane survey area on a 1:250,000 Ordnance Survey base.

(Ordnance Survey Permit DNE 001001).

14

Figure 3. The Lough Derg 2 survey area on a 1:250,000 Ordnance Survey base.

(Ordnance Survey Permit DNE 001001).

THE RIO ALGOM/IVERNIA WEST AIRBORNE TEM AND MAGNETIC ... · 75 Hz base frequency as listed in the...

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