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Case Studies - Mineral Exploration
Sunrise Deposit, NWT, Canada
| The survey area is located approximately 90 kilometres northeast of Yellowknife, Northwest Territories and is contained within the Beaulieu River Supracrustal Belt of the Slave Province. The Sunrise Deposit is an Archean polymetallic Zn-Ag-Pb-Au banded massive sulphide lens within a sequence of intermediate to felsic volcanics. This lens dips at 60-65 degrees to the east, and plunges steeply (60 degrees) to the north. |
Location Map
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The originally defined limits of the ore zone were a 160 metre strike length, with an average thickness of 3 to 3.5 metres and a down dip projection of 700 metres, while the airborne data suggests an even greater strike length of 400 metres.
The airborne data were collected by the Aerodat, now Fugro Airborne Surveys, helicopter electromagnetic (HEM) system towed 30 metres above terrain. Data were also recorded from a high sensitivity Scintrex cesium magnetometer and a two station Herz VLF-EM sensor, both towed at 50 metres above terrain.
The Aerodat HEM unit is a four-frequency system consisting of two vertical coaxial coil pairs operating at 935 and 4600 Hz and two horizontal coplanar coil pairs operating at 4175 and 33,000 Hz. The coils are mounted in a Kevlar "bird" at a separation of 7 metres. The ground data illustrated has been collected by an HLEM system operating at 4080 Hz with a coil separation of 100 metres.
Horizontal Loop Electromagnetic Profile
coil separation=100m; frequency = 4080 Hz |
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Helicopter Electromagnetic Profiles
frequencies=4600Hz coaxial, 4175 Hz coplanar |
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| The comparison of HEM data with Ground HLEM and the geology and drill hole cross section are presented courtesy of Cominco Ltd., Aber Resources Ltd., Hemisphere Development Corp. and Noranda Exploration Company, Ltd. It is evident from this comparison that there is a strong correspondence between the HLEM and HEM coplanar data. |
Cross Section 3 + 60S |
Horizontal Loop Electromagnetic Profile
coil separation = 100m; frequency = 1080 Hz
Helicopter Electromagnetic Profiles
The advantage of the airborne system is the ability to rapidly collect data from multiple frequencies and coil orientations simultaneously to provide geometric and conductivity / resistivity analysis of conductors. The 4600 Hz coaxial coil pair and the 4175 Hz coplanar coil pair indicate the dip of the conductor as seen in this example. The coaxial coil pair provides a maximum peak directly over the conductor with a displaced side lobe while the coplanar data provides a peak in the down dip direction.
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Case Studies
Mineral Exploration