3D, probabilistic and numerical modelling - Tools in assessing mineral resource potential under cover

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Scott, Margaretha۱; Feltrin, Leonardo۲; Dixon, Owen۱; Blake, Paul۱; Fitzell, Melanie۱; Purdy, David۱; Oliver, Nick۲; McLellan, John۲
Holding Date 15 September 2008

The Late Devonian-Carboniferous northern Drummond Basin region is one of Australia’s more prospective areas for epithermal vein and stockwork style gold deposits, hosting both low and high sulphidation epithermal mineralisation. Despite this fact, the controls acting on mineralisation are not well understood. 3D-GIS reconstructions, probabilistic modelling (WOFE) and numerical modelling (UDEC, FLAC 3D) are used here to explore basin and local-scale controls on the genesis of these deposits.
The northern Drummond 3D model was constructed with the objective of: providing a visual model of the basin; establishing spatial associations between key datasets; and refining conceptual models of the region. An initial review of existing data sets and conceptual models highlighted a number of unresolved issues and inconsistencies. As a consequence, the re-evaluation of stratigraphic and magmatic frameworks and constraints to the architecture of the basin, became a prerequisite to the numerical modelling phases.
The key interpretations derived from this work indicate that:(1) the Drummond Basin is underlain by a number of basement elements;(2) basement boundaries coincide with structural domains that reflect the partitioning of deformation across the northern Drummond Basin;(3) there is an association between known low sulphidation occurrences and intrusive bodies;and (4) areas of potentially younger silicic pyroclastic deposits equivalent to Permian volcanic units known to host high sulphidation epithermal mineralisation in the adjacent Bowen Basin are present.
These observations allow us to propose that there was a change in age and style of epithermal Au from 345 Ma (low sulphidation epithermal) to 300 Ma (intermediate-high sulphidation epithermal), reflecting a transition from localised rift to caldera volcanism. At camp scale, gold localisation appears to be governed by the interplay between intrusive bodies and the local structural architecture. The basin is considered here as a series of rift segments distinguished on the basis of their structural characteristics and separated by major accommodation zones. Extensional strain is thought to be accommodated differently between domains, involving primarily strike-slip movement and listeric faulting or dip-slip tilt blocks.
Following on from this work, 2.5D coupled thermal-fluid flow and 3D coupled deformation-fluid flow modelling is being used to develop an understanding of the role of key basement structures and the impact of basement anisotropy in focusing hydrothermal activity. UDEC process modelling of the interaction of faults, rock types and pore fluid pressure is providing data on failure and dilation sites. Outputs from this will be compared with probabilistic results generated using WOFE. These techniques are aimed at quantifying the character of mineralising processes operating in the northern Drummond, and improving exploration targeting strategies under cover.