3D MAGNETIC INVERSION OF A VTEM SURVEY. (Nicol Block) Submitted to: NORTHSTAR GOLD CORP. PRESENTED BY

Transcription

1 3D MAGNETIC INVERSION OF A VTEM SURVEY (Nicol Block) Submitted to: NORTHSTAR GOLD CORP. PRESENTED BY OLIVIER BOULANGER, PHD, P.GEO. MARC BOIVIN, P.Geo NOVEMBER 2009 Created by jbrouillard

2 TABLE OF CONTENTS 1. THE MANDATE NICOL BLOCK SURVEY MAGNETIC DATA FOR THE INVERSION DATA PROCESSING AND SUPPLIED PRODUCTS RESULTS... 7 LISTE DES FIGURES FIGURE 1. GENERAL LOCATION OF THE NICOL BLOCK SURVEY... 1 FIGURE 2. NTS MAPS 41P09 AND 41P FIGURE 3. TOPOGRAPHY, RIVERS AND LOCATION OF THE SURVEY... 3 FIGURE 4. 3D VIEW OF THE MAGNETIC SUSCEPTIBILITY FROM THE 3D INVERSION... 7 FIGURE 5. TOPOGRAPHY IN M FOR THE NICOL BLOCK SURVEY FIGURE 6. OBSERVED MAGNETIC DATA AND PREDICTED DATA FOR THE NICOL BLOCK PROJECT FIGURE 7. PLAN VIEW AND VERTICAL CROSS-SECTION OF THE PREDICTED MAGNETIC SUSCEPTIBILITY DATA FOR THE NICOL BLOCK SURVEY D magnetic inversion Page i Nicol Block VTEM survey

3 1. THE MANDATE PROJECT ID GENERAL LOCATION CLIENT REPRESENTATIVE Nicol Block Survey Our reference: MBG Earlton, Ontario, Canada. Northstar Gold Corp Att: M. George Pollock M. Marc Boivin, P. Geo, Geophysicist (MB GEOsolutions.) M. Olivier Boulanger, P. Geo, PhD, Geophysicist (OB Geophysics.) SURVEY TYPE 3D magnetic inversion of airborne VTEM data Nicol Block Survey FIGURE 1. GENERAL LOCATION OF THE NICOL BLOCK SURVEY. 3D magnetic inversion Page 1 Nicol Block VTEM survey

4 2. NICOL BLOCK SURVEY LOCATION Earlton, Ontario, Canada. Nicol Block: latitude 47 36' 58 N, longitude 80 39'54 W NTS sheets: 41P09 and 41P10 FIGURE 2. NTS MAPS 41P09 AND 41P10 NEAREST SETTLEMENT ACCESS GEOMORPHOLOGY CULTURAL FEATURES SURVEY GRID COORDINATE SYSTEM Nicol Block: 65 km to west of Earlton From North Bay take highway 61 in north direction then turn left on highway 65 in west direction. At Elk Lake turn left on road 560 and drive for about 21 km to reach the Nicol Block. The area has topography ranging from 344 to 442 m. Several lakes surround the survey block (see Figure 2A) Nothing on the prospect. Nicol Block was flown at 100 m traverse line spacing with flight directions of N45 E. Projection: Universal Transverse Mercator Datum: NAD 83 Central Meridian: 73ºW (UTM zone 17N) 3D magnetic inversion Page 2 Nicol Block VTEM survey

5 FIGURE 3. TOPOGRAPHY, RIVERS AND LOCATION OF THE NICOL BLOCK SURVEY. 3D magnetic inversion Page 3 Nicol Block VTEM survey

6 3. MAGNETIC DATA FOR THE INVERSION SURVEY TYPE The magnetic data used for the 3D inversion come from a helicopter-borne VTEM survey flown in January 2009 by Geotech Ltd., for Northstar Gold Corp. The magnetic readings were generally taken at 65 meters from ground along N45 0 flight lines spaced of 100m. The input data file derived from interpolated grid file using 15 meters cell size. PERSONNEL ORIGINAL MILEAGE Olivier Boulanger, PhD, P.Geo. : 3D Inversion and report Marc Boivin, P.Geo : Data processing and report Nicol Block: line-km PROCESSED MILEAGE Subset database: line-km PARAMETERS OF THE ORIGINAL GRID (WITH A ROTATION OF -45 ) Increment in x-direction: Increment in y-direction: Number of points: Minimum value of the magnetic field: Maximum value of the magnetic field: Minimum value of the data elevation: Maximum value of the data elevation: Minimum value of the topography elevation: Maximum value of the topography elevation: X minimum: X maximum: Y minimum: Y maximum: Difference beetween topography and data elevations: 15 m 15 m nt nt m m m m m m m m m PARAMETERS OF THE TOTAL MAGNETIC FIELD Original ( Inclination: Declination: IGRF: Latitude: Longitude: Reduced to the pole Inclination: Declination: IGRF: nt 47 36'58 N 80 39'54 W nt 3D magnetic inversion Page 4 Nicol Block VTEM survey

7 4. DATA PROCESSING AND SUPPLIED PRODUCTS PRE-INVERSION PROCESSING - Extracting data from the original file. - Data interpolated on regular mesh of 15m. - Reduction to the pole - Creating a subset database in order o create a rectangular grid file INVERSION PROCESSING - Calculation of the residual anomaly by removing a regional trend using a 1st order polynomial. - Upward continuation of the interpolated data to a datum located at 520 m. - Inversion of magnetic data with topography NOTE: Inversion of data on a datum taking into account the topography TOTAL MAGNETIC FIELD (TF) PARAMETERS FOR THE INVERSION File name: Increment in x-direction: Increment in y-direction: Number of points: Number of point in X direction: Number of point in Y direction: Minimum value of the TF : Maximum value of the TF Data elevation (datum): upward_magnetic.dat 15 m 15 m nt nt 520 m MESH PARAMETERS Origin (X0, Y0, Z0) : Number of cells (X,Y,Z): Padding cells: Increment (X,Y,Z) : m, m, 442 m 372, 372, m, 15 m, 15 m 3D magnetic inversion Page 5 Nicol Block VTEM survey

8 SUPPLIED PRODUCT Directory \original data - Full_data.xyz Directory \inversion Final Results - Calculated data (Nicol_Block_data_calculated.dat) - Observed data (Nicol_Block_data_observed.dat or Nicol_Block_upward_magnetic.dat) - UBC mesh (Nicol_Block_mesh.ubc) - UBC model (Nicol_Block_model.ubc) - Ground elevation data (Nicol_Block_topo.dat - Inversion model data (Nicol_block_model.xyz) - 3D view (nicol_block_3dview.bmp) SOFTWARE AND DATA SOFTWARE INTERPRETATION GRAVMAG3D, version 2.0 3D gravity/magnetic inversion developped by Olivier Boulanger Olivier Boulanger Geophysics 5140 Beaconsfield Montreal, QC, H3X 3R8, Canada Tel: (514) NUMERICAL DATA All magnetic data and 3D inversion results can be viewed with the UBC-GIF softwares (gm-data-viewer.exe for the magnetic data and MeshTools3d.exe for magnetic inversion (mesh and model)) and in ASCII format *.xyz. RESULTS VISUALISATION To view the results of inversion, launch the application MeshTools3d.exe UBC-GIF ( in Section Software and Utility codes). Import Mesh and Model files in the Load Model sheet and find files with the 'Browse' button. Click OK. Then choose 'Yes' to ignore the fixed cells -1 for magnetic susceptibility or -100 for density (corresponding to air cells) 3D magnetic inversion Page 6 Nicol Block VTEM survey

9 5. RESULTS During this project, an inversion model (with topography) was generated from reduced to the pole magnetic data and placed in a constant flight altitude of 520 m for the Nicol Block project. Figure 4 shows the 3D distribution of the magnetic susceptibility for the inversion of the Nicol Block. Top of the inversion mesh is located at 442 m and north is indicated by the arrow. The inversion result gives a magnetic susceptibility ranging from 0 to 0.4 SI. In Figure 4, the magnetic susceptibility is limited to 0.1 SI to highlight the anomalies of lower amplitude. Figure 5 shows the topography on the block Nicol. Figure 6 shows the observed data and the predicted data calculated at the last iteration. FIGURE 4. 3D VIEW OF THE MAGNETIC SUSCEPTIBILITY IN SI FROM THE 3D INVERSION FOR THE NICOL BLOCK DATASET AT A DATUM OF 520 M. 3D magnetic inversion Page 7 Nicol Block VTEM survey

10 FIGURE 5. TOPOGRAPHY FOR THE NICOL BLOCK SURVEY. 3D magnetic inversion Page 8 Nicol Block VTEM survey

11 FIGURE 6 OBSERVED MAGNETIC DATA AND PREDICTED DATA IFOR THE NICOL BLOCK SURVEY 3D magnetic inversion Page 9 Nicol Block VTEM survey

12 FIGURE 7 PLAN VIEW AND VERTICAL CROSS-SECTION OF THE PREDICTED MAGNETIC SUSCEPTIBILITY DATA FOR THE NICOL BLOCK SURVEY Respectfully submitted, Olivier Boulanger, PhD, P.Geo (OGQ #1274). Geophysicist, OB Geophysics Marc Boivin, P.Geo (OGQ #351) Geophysicist, MB Geosolutions 3D magnetic inversion Page 10 Nicol Block VTEM survey