Scale Model Studies of a Transient Electromagnetic Prospecting System Using an Interactive Minicomputer
Scale models have been used for over thirty years in studying the electrical and electromagnetic techniques of geophysical prospecting, and are particularly useful when mathematical or numerical methods are unreasonably difficult. A model study facility has been set up at Macquarie University, Sydney, Australia, to study the transient electromagnetic method of geophysical prospecting. The basic unit in the facility consists of a 35Kword INTERDATA minicomputer which controls the timing and waveform of the transmitted pulse as well as subsequent data collection and processing. A wide-band amplifiler provides an interface between the computer and the small multiturn loops used for model studies. Input and output data are fed via the computer to a teletypewriter. The use of an interactive technique between the computer and operator enables optimum timing and amplifier settings to be easily determined for each model. A model of a uniformly conductive half-space was used to validate the experimental arrangement, and excellent agreement was found between theoretical and model results. A model study of an orebody enabled estimates of bulk conductivity to be made.
Interpretation and design of time domain EM surveys in areas of conductive overburden
The TEM method is being increasingly used for mineral exploration and geological mapping in Australia. The techniques can be divided into one-loop and coincident-loop systems (MPPO-1, MPP-3, SIROTEM) and two-loop systems (Pulse EM, Newmont EMP, SIROTEM, UTEM) which exhibit markedly different responses over the conductive surface layers that cover much of Australia. Successful exploration in the 1980s will depend to a large extent on developing methods of quantitative interpretation of anomalies caused by variations in the surface layer. The response of both one-loop and two-loop systems to variations in the conductivity and thickness of a conductive surface layer or host rock has been investigated. The response of a homogeneous ground is relatively simple for a one-loop configuration, but becomes much more complex as the transmitting and receiving loops are separated and form a two-loop configuration. For a two-loop configuration the response changes sign at a time which depends on the loop separation and ground conductivity. In resistive terrains the sign reversal is usually not observed, but in areas with conductive surface layers the sign reversal can occur at quite late times. Variations in the conductivity of the overburden can cause complex anomalies which are difficult to interpret intuitively and to distinguish from anomalies caused by conductive bedrock sources. This problem holds for both one-loop and two-loop configurations, but is further complicated by the sign changes in a two-loop configuration. These features are seen in Pulse-EM data from Cobar. Interpretation of two-loop data is further complicated by the fact that the response of a finite conductor in a resistive host rock will also exhibit sign changes which depend on depth of burial or conductivity. Thus for ease of interpretation, a one-loop configuration is recommended. This can be approximated in a two-loop system by locating the receiver in the centre of the transmitter loop (sometimes called "in-loop" or "frame-loop" configuration). Limits on the detection of mineral deposits in conductive terrains have been investigated by studying the modelled response of the Elura and Roxby Downs deposits using an interactive mini-computer analogue model system. The TEM response is determined for a variety of loop sizes, depths of burial, and conductivities of the deposits and host rocks. The limits of detection depend on all of these factors. In general, the optimum loop size is larger than the body in resistive terrain but should be smaller than the body in a conductive terrain to minimise coupling with the host rock. For both the Elura and Roxby Downs model studies, it was found that the optimum time range for measurement was between 1 and 50 ms. Measurements at earlier and later times, however, give useful information on conductive host rock or overburden.
First Insights into the Draft Genome Sequence of the Endophyte Paenibacillus amylolyticus Strain GM1FR, Isolated from Festuca rubra L.
ABSTRACT Paenibacillus amylolyticus strain GM1FR is an endophyte isolated from aerial plant tissues of Festuca rubra L. Here, we report the draft genome sequence (7.3 Mb) of GM1FR containing 6,241 protein-coding genes, some of which are potentially involved in plant growth promotion and biocontrol.