Exploration, Discovery, and Geology of the Ntaka Hill Nickel Sulfide DepositsA Potential New Proterozoic Nickel District in the Nachingwea Area, Mozambique Belt, Tanzania

Author(s):  
P. A. Tirschmann ◽  
C. S. MacDougall ◽  
G. R. Katchen
Geophysics ◽  
2001 ◽  
Vol 66 (3) ◽  
pp. 824-835 ◽  
Author(s):  
David Johnson ◽  
Elena Cherkaev ◽  
Cynthia Furse ◽  
Alan C. Tripp

The finite‐difference time‐domain method is used for high‐resolution full‐wave analysis of cross‐borehole electromagnetic surveys of buried nickel sulfide deposits. The method is validated against analytical methods for simple cases, but is shown to be a valuable tool for analysis of complicated geological structures such as faulted or layered regions. The magnetic fields generated by a wire loop in a borehole near a nickel sulfide deposit are presented for several cases. The full‐wave solution is obtained up to 200 MHz, where quasi‐static methods would have failed. The dielectric response is included in the solution, and the diffractive nature of the field is observed. The sensitivity of each receiver in a vertical line in the cross borehole is presented and analyzed to provide an optimal weighting for receivers that can be applied to an experimental study.


1981 ◽  
Vol 76 (6) ◽  
pp. 1550-1564 ◽  
Author(s):  
M. J. Donaldson ◽  
G. J. Bromley

Geophysics ◽  
2012 ◽  
Vol 77 (5) ◽  
pp. WC123-WC132 ◽  
Author(s):  
Milovan Urosevic ◽  
Ganesh Bhat ◽  
Marcos Hexsel Grochau

The greenstone belts of the Yilgarn Craton, Western Australia, host numerous Archaean gold, nickel, and iron ore deposits. These deposits typically are found in complex geologic structures hidden by a deep, heterogeneous, and often conductive regolith profile. This added complexity limits the depth of penetration for the potential field methods, but at the same time opens new revenue possibilities through the application of seismic methods. To explore this opportunity, we acquired high-resolution, experimental, 3D seismic data over Lake Lefroy in Kambalda, Western Australia. The main objective was to map exceptionally complex, deep structures associated with Kambalda dome. Survey design used 3D ray tracing to improve the distribution of the common reflection points across ultramafic-basalt contacts which host numerous small, high-grade nickel sulfide deposits. A combination of small explosive sources, high-shot/receiver density, and exceptionally good coupling over the ultrasalty lake surface produced seismic data of very high quality. Processing focused on computation of accurate static and dynamic corrections, whereas imaging was helped by the existing geologic model. Advanced volumetric interpretation supported by seismic forward modeling was used to guide mapping of the main lithological interfaces and structures. Forward modeling was carried out using rock properties obtained from ultrasonic measurements and one borehole, drilled in the proximity of the 3D seismic volume. Using this information, geometric constraints based on the typical size of ore bodies found in this mine and a simple window-based seismic attribute, several new targets were proposed. Three of these targets subsequently have been drilled and new zones of mineralization were intercepted. The case study presented demonstrates that high-quality, high-resolution, 3D seismic data combined with volumetric seismic interpretation could become a primary methodology for exploration of deep, small, massive sulfide deposits distributed across the Kambalda area.


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