Geophysical imaging of a kaolinite deposit at Sylvan, Manitoba, Canada

• Published in: Journal of applied geophysics 1999-02, Vol.41 (1), p.105-129
• Main Authors: Ferguson, Ian J, Ristau, Johannes P, Maris, Virginia G, Hosain, Ifti
• Format: Article
• Language: English
• Subjects: Applied geophysics; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geophysical imaging; Internal geophysics; Kaolinite deposit; Metallic and non-metallic deposits; Sylvan; Useful material except metal geology
• ISSN: 0926-9851; 1879-1859
• DOI: 10.1016/S0926-9851(98)00051-2

A geophysical survey was performed at Sylvan, Manitoba, Canada (51°5′N, 97°22′W) to investigate a Lower Cretaceous kaolinite deposit. The deposit consists of zones of kaolinite, silica sand, and lignitic clay located in a series of channels formed during karsting of the underlying Palaeozoic bedrock and is covered by 3 to 5 m of glacial drift. The aim of the study was to identify cost-efficient electrical and electromagnetic (EM) geophysical methods for locating, mapping, and assessing this target. Methods applied included terrain conductivity (EM31), VLF-EM, time-domain electromagnetics (TEM), DC-resistivity, and shallow seismic refraction. The survey showed that EM methods offer a viable alternative to more expensive seismic reflection surveys in the investigation of small industrial mineral deposits. Comparison of the geophysical survey results with those of a drilling program indicated that VLF-EM and TEM were the best methods for delineating the kaolinite deposit. VLF-EM was the most cost-efficient method for delineating the kaolinite deposit over a ca. 10 ha area and for exploring for further deposits within several kilometers of the main site. Joint interpretation of the in-phase and quadrature response is required for increased reliability in identifying the major kaolinite-filled channels. The TEM method provided more detailed resolution of the deposit than VLF-EM and was the optimal method for assessing its thickness. However, TEM data acquisition is too slow and inefficient for reconnaissance mapping of 10 ha sites. EM31 surveying is useful for defining the palaeokarst surface and overburden thickness in areas surrounding the deposit but cannot be used reliably for mapping the kaolinite deposit itself. The combined geophysical survey results show the kaolinite deposit at Sylvan to be located in a channel which is 100 m wide and about 25 m deep. The deposit has a bulk electrical conductivity between 13 mS m −1 and 25 mS m −1 consistent with low cation exchange capacity values measured for the kaolinite. The palaeokarst surface surrounding the deposit contains a series of sinuous, discontinuous, depressions with a depth variations of several meters.