Advanced Geophysical Operations and Services Inc. (AGCOS) participated in the Near-Surface Asia Pacific Conference 2015 which was held at Hilton Waikoloa Village, Waikoloa, Hawaii, USA from July 7 to 10, 2015. As a part of the technical program of the conference, AGCOS presented the following papers:
Measurement optimization of three orthogonal components of the alternating magnetic field of the earth in mining and geothermal exploration
In the middle of the last century, surface multiturn coils and quartz variometers served as sensor components of the alternating magnetic field. Later, they were replaced by fluxgate sensors measuring the alternating magnetic field against its constant component and induction sensors reacting only to the variable component. Thanks to a wide frequency range and a low level of generated noise, induction sensors became the main instrument, converting alternating magnetic field into an electric signal. However, there are significant difficulties when it comes to their installation at survey sites, particularly for the vertical component (Hz). This process is first of all, very labour intensive and, second, at times simply impossible due to local conditions, such as rocks, slopes, sand, snow and ice. A solution has been found in utilizing custom designed tripods, which are used not only to accurately align the sensors but to also easily transport them. These are currently mass produced and easily accessible on the market. In recent years, many successful mining geophysics projects have been completed with both geological and economic success in large part due to the use of these tripods. In some cases, these projects were only possible as a result of tripod application since they allow carrying out successful field surveys with AMT, MVP and CSAMT methods on any terrain and soil conditions.
Ways to improve the efficiency of multifunction electroprospecting instruments for mining exploration
The idea of developing a multifunction EM instruments implementing many ground EM methods with a common ideology of processing and interpreting the data has been held by geophysicists from the 1980s of the last century. At the turn of the 1980s and 1990s several companies (Phoenix, Zonge) managed to achieve positive results. However, the equipment of the time remained bulky, heavy, was expensive and low productive. The modern development of electronics and computer technology allows to fully realize the idea of versatility and combine in a single instrument seemingly not possible to be joined in the past MT and VES functions. Portable, multifunction equipment is offered based on 4- and 8-channel EM receivers, with flexible configuration of magnetic and electrical channels. Equipment can effectively implement virtually all ground electroprospecting methods (excluding ground penetrating radar). A set of equipment includes all the necessary elements of hardware and software for productive field work including field recording, processing of field data and interpretation (including complex). That is, system may include one or more wideband EM receivers, wideband current source (transmitter), wideband sensors of electric and magnetic field components, precision tripods for mounting magnetic sensors, set of accessories, and set of software for the operation of equipment, processing, and interpretation of the field data.
Seabed EM surveys in shallow water environments have a number of specific particularities. Specifically, there is difficulty with hermetical sealing of EM instruments and the necessity of overcoming electromagnetic noise caused by underwater currents and sea surface disturbances. Another problem is the inability to employ large ocean going vessels in many areas, while the use of small vessels increases the demands on the size and weight of the equipment. There are also certain positive aspects in this, pertaining to the ability to use reliable acoustic communication between the marine EM instrument positioned on the seabed and the sea surface, as well as the use of beacons for identifying the location of the bottom apparatus. In this paper, discussed is a shallow marine EM data acquisition equipment complex that allows efficient use of standard ground EM instruments for carrying out investigations at a sea depth interval of 0-200m. This complex consists of 2x – 4x – 5-channel marine EM systems.