Deep penetrating Sampo -geophysical survey
The survey shows clearly that the anomalous region coincides with the same geological structure where the Silver Mine mineralisation is situated. Results of the Sampo method show a strong electromagnetic anomaly situated at the continuity of the Silver Mine mineralisation and extending to depths of 1 000 m am 1 000 m in the strike.
Figure 1 below: Exploration targets below known deposit down to 1 000 meter's depth along the strike.
Sotkamo Silver commissioned a deep penetrating electromagnetic survey from Geological Survey of Finland (GTK) in autumn 2011. The purpose of this survey was to explore the assumed continuities of the Silver Mine orebody between 600-1 000 m levels.
Two methods were chosen for the survey and teams from GTK's Kuopio and Rovaniemi units performed the measurements. First applied method was an audiomagnetotelluric survey (AMT). Two survey lines were measured perpendicular to the strike of the assumed continuation of the Silver Mine mineralisation. Figure 1. below shows the location of the survey lines (blue dots). Basemap is an electromagnetic anomaly map obtained from low altitude aerogeophysical survey performed by GTK in the year 2005. Also in the map is presented the projected outline of the assumed continuation of the deep extending mineralisation (red raster).
Figure 2 below: AMT-survey lines
Results from the AMT-survey show clearly an anomalous region which coincides the same geological structure where the Silver Mine mineralisation is situated. In the southernmost survey line, the anomaly is situated between 800-1 000 m levels. In the northernmost line, the anomaly is situated between 600-800m levels. Results from the southernmost survey line are shown in figure 3.
Figure 3 below: Vertical cross section showing the deep anomaly on the southernmost AMT-survey line
The second geophysical method chosen to explore the assumed continuity of the Silver Mine mineralisation was Gefinex 400S also known as Sampo-method. This method is also a deep penetrating electromagnetic survey, and it is developed by the Geological Survey of Finland. Survey grid is shown in figure 4. Survey grid was located mostly parallel to the geological structures and also parallel to the strike of the Silver Mine mineralisation. In the northernmost corner of the survey area, a small grid perpendicular to the geological structure was also measured.
Figure 4 below: Measuring grid used in the Gefinex 400S survey
Results of the Sampo method show a strong electromagnetic anomaly situated at the continuity of the Silver Mine mineralisation and extending to depths of 1 000 m. This electromagnetic anomaly is characterised by low resistivities, between 500-1500 Ωm. These resistivities are similar to the known Silver Mine mineralisation and thus strengthen the Sotkamo Silver's view that Silver Mine mineralisation extends at least to 1 000 m level below the surface. Gefinex survey also shows that the anomalous region lies between 600-1 000m levels and its strike length is at least 1 000 m. True nature and quality of this geophysical anomaly have to be verified by diamond drilling. Diamond drill testing of the anomaly is tentatively planned to be performed during 2015.
Figure 5 below: shows the electromagnetic anomaly obtained by Gefinex 400S survey. Also in the picture can be seen the existing ore solids in red and the mine decline. Resistivity values in the anomalous zone vary from 500 Ωm to 1500 Ωm.
Sotkamo Silver also commissioned a drill hole geophysical survey from Ageos Oy in autumn 2011. Ageos surveyed some selected surficial and underground drill holes at Silver Mine area. The drill hole survey included measurements of IP (induced polarisation), susceptibility, density, Wenner resistivity and TEM (transient electromagnetic measurement). Data obtained from drill hole geophysical logging was used in the planning of the survey grid for the Gefinex survey and also in the interpretation of the Gefinex survey results.