Documents

Chubby Bear Logistic Report [PDF | 0.3MB].
Geochemical Results from the Chubby Bear Soil Grid [PDF | 1.6MB].

Location:
The project area is located in the Cariboo mining district north of Quesnel along the 1300 road off Highway 26. Figure 1 below shows the location of the Chubby Bear project. The grid was accessible by vehicle via logging road.



A total of 3 lines were marked out at 200m intervals with an approximate azimuth of 51 degrees for the survey. Pickets were placed every 25m along the line. Stations were labeled with the west end at 5300E and the east end at 7000E for a total length of 1700 meters. See the figure below for line information.

The total survey line kilometers of the Chubby Bear project is 5 km. The topographic relief of the grid is about 125m.

Survey lines of Chubby Bear project

Field Work and Instrumentation:

The SJ Geophysics Ltd. crew consisted of three SJ Geophysics employees: Lauran Devlin (geophysical technician), John Wilkinson (technician) and Trevor Stapleton (helper); the client provided local helpers, Stuart Alec, Chris Spicer, Jeff Wannop, and Colby Doherty to assist with the survey.

Data acquisition occurred on June 28th, 2006 starting on line 75N, and progressed to the south to line 25N. The overall IP production was 5000 m/day. For the entire survey the array consisted of a modified pole-dipole configuration that was used with a combination of 12 dipoles of 10x100m and 2x300m dipoles for a total array length of 1600m. Current shots were made at a interval of 50m. For all the current shots injected the remote current was placed off to the east for reading half of the line and to the west for half.

For the entire IP survey, all data was collected using SJV 24 Full Waveform Digital Receiver (Rx). The current was injected with a 2 seconds on, 2 seconds off duty cycle into the ground via a transmitter (Tx). A GDD Tx II 3.6 KW transmitter was utilized during the duration of the survey program.

The dipole array was implemented using standard 8 conductor cables configured with 50m takeouts for the potential rods. At each current station, the electrodes used consisted of 5/8" stainless steel rods of approximately 1m in length. For the potential line, the electrodes consisted of 3/8" stainless steel "pins" of 0.5m in length.

The exact location of the remote current is used in the geophysical calculations. The location data was collected by using 12 channel hand held Garmin GPS's at position accuracy of 5-6m. Location coordinates were in UTM projection with datum of NAD 83.

The IP readings from each day's surveying were downloaded to a computer and entered into a database archive every evening. Survey data quality control, processing and data backup were done on daily basis.

Geophysical Techniques:
IP Method:

The time domain IP technique energizes the ground surface with an alternating square wave pulse via a pair of current electrodes. On most surveys, such as this one, the IP/Resistivity measurements are made on a regular grid of stations along survey lines.

After the transmitter (Tx) pulse has been transmitted into the ground via the current electrodes, the IP effect is measured as a time diminishing voltage at the receiver electrodes. The IP effect is a measure of the amount of IP polarized materials in the subsurface rock. Under ideal circumstances, IP chargeability responses are a measure of the amount of disseminated metallic sulfides in the subsurface rocks.

Unfortunately, there are other rock materials that give rise to IP effects, including some graphitic rocks, clays and some metamorphic rocks (serpentinite for example). So from a geological point of view, IP responses are almost never uniquely interpretable. Because of the non-uniqueness of geophysical measurements it is always prudent to incorporate other data sets to assist in interpretation.

Also, from the IP measurements the apparent (bulk) resistivity of the ground is calculated from the input current and the measured primary voltage. IP/resistivity measurements are generally considered to be repeatable to within about five percent. However, they will exceed that if field conditions change due to variable water content or variable electrode contact.

IP/resistivity measurements are influenced, to a large degree, by the rock materials nearest the surface (or, more precisely, nearest the measuring electrodes), and the interpretation of the traditional pseudosection presentation of IP data in the past has often been uncertain. This is because stronger responses that are located near surface could mask a weaker one that is located at depth.

Geophysical Techniques: 3D-IP Method:

Three dimensional IP surveys are designed to take advantage of the interpretational functionality offered by 3-D inversion techniques. Unlike conventional IP, the electrode arrays are no longer restricted to in-line geometry. Typically, current electrodes and receiver electrodes are located on adjacent lines. Under these conditions, multiple current locations can be applied to a single receiver electrode array and data acquisition rates can be significantly improved over conventional surveys.

In a common 3D-IP configuration, a receiver array is established, end-to-end along a survey line while current electrodes are located on two adjacent lines. The survey typically starts at one end of the line and proceeds to the other end. A typical 12 dipole array normally consists of one 300m dipole, followed by one 200m dipole and then nine 100m dipoles, and a 200m dipole at the end of the array. In some areas these spacings are modified to compensate for local conditions such as inaccessible sites, streams, and overall conductivity of ground. Current electrodes are advanced along the adjacent lines, starting at approximately 1000m from the center of the array and advancing approximately 1000m through the array at 100m increments. At this point, the receiver array is advanced 600m and the process is repeated down the line. Receiver arrays are typically established on every second line (400m apart) thereby providing subsurface coverage at 200m increments.

Geophysical Techniques: Inversion Programs:

"Inversion" programs have recently become available that allow a more definitive interpretation, although the process remains subjective. The purpose of the inversion process is to convert surface IP/Resistivity measurements into a realistic "Interpreted Depth Section." However, note that the term is left in quotation marks. The use of the inversion routine is a subjective one because the input into the inversion routine calls for a number of user selectable variables whose adjustment can greatly influence the output. The output from the inversion routines do assist in providing a more reliable interpretation of IP/Resistivity data, however, they are relatively new to the exploration industry and are, to some degree, still in the experimental stage

The inversion programs are generally applied iteratively to evaluate the output with regard to what is geologically known, to estimate the depth of detection, and to determine the viability of specific measurements.

The Inversion Program (DCINV3D) used by the SJ Geophysical Group was developed by a consortium of major mining companies under the auspices of the UBC-Geophysical Inversion Facility. It solves two inverse problems. The DC potentials are first inverted to recover the spatial distribution of electrical resistivity, and, secondly, the chargeability data (IP) are inverted to recover the spatial distribution of IP polarizable particles in the rocks.

The interpreted depth section maps represent the cross sectional distribution of polarizable materials, in the case of IP effect, and the cross sectional distribution of the resistivity, in the case of the resistivity parameter.