3D Interpretation of geological, 3D seismic, and conventional geophysical data for brownfields exploration targeting
On March 2, we presented the Darlot Gold Mine Area case study at the annual KEGS Symposium. The presentation summarized the results of an ongoing technical collaboration between Mira Geoscience, Red5 Limited, and HiSeis, and outlined workflows and interpretational considerations required to implement an integrated geological, petrophysical, seismic, and non-seismic geophysical program to effectively support brownfields targeting in hardrock environments.
Caption: The figure illustrates the Darlot 3D seismic cube with a selected fence section used to cross-check the geological interpretation. Geological wireframes interpreted from the seismic cube (partially transparent light blue) represent a dolerite sill (host to the mineralization), and a major structure offsetting the dolerite sill. Positioned above the seismic cube is the measured magnetic response (reduced to pole), measured gravity (first vertical derivative) and the geological map (hashed green domain corresponds to the wireframes. The correlations between the mapped geology, synclines inferred from the seismic, and measured potential field responses are evident.
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Case study: Darlot Gold Mine Area, Australia
The modern capability of 3D seismic surveys to image formational contacts and structures in hardrock environments can have a game-changing impact on the effectiveness of brownfields exploration programs because the geometry of mineralized systems can be directly imaged over large volumes of ground. Furthermore, the formational and structural geometry revealed by 3D seismic also provides primary control on the physical property variations that magnetic, gravity, and electrical or EM methods respond to. Seismic interpretation thus provides ideal constraints and guidance on the interpretation of other geophysical data. This is particularly valuable when an objective of geophysical interpretation is imaging of second-order controls on physical property variation, such as the effects of alteration.
Darlot is an Archean orogenic gold deposit located in the world-class gold and nickel terrain of the Yandal granite-greenstone belt, part of the Yilgarn Craton in Western Australia. A 3D seismic survey was acquired with the objective of improving lithological and structural interpretation, and to generally extend understanding of the 3D mineralized system to support targeting. The processed seismic volume shows numerous interpretable contacts and structures. Seismic interpretation tools in GOCAD Mining Suite have been used to create an initial wireframe formational and structural model. We used the 3D model interpreted from drilling and seismic interpretation as a geometrical constraint on the interpretation of other geophysical data. This provides a means to validate and refine seismic interpretation of geometry, interpret parts of the volume that are too shallow to be effectively resolved from the seismic survey, and image physical property variations within formations that may have a bearing on targeting decisions.
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