3D structural-stratigraphic modelling supporting mineral discovery
in the Purcell Basin, southern BC
By Eric de Kemp, Ernst Schetselaar, Mike Hillier, John Lydon, Mike Thomas, Jamel Joseph
Conatct:
edekemp@nrcan.gc.ca
ABSTRACT
The core notion of this project is that we want to develop the practice of 3D geologic data
interpretation beyond the head frames of mines. Modern exploration in the 21’st century combines
the best of 3D geologic modelling and data integration technologies, geophysical inversion tools,
as well as 3D geostatistical property mapping. This project will use these methods in a way which
supports mineral discovery by creating a single georeferenced ‘knowledge cube’ in which all
relevant data and interpretations can be inspected and reconciled. Currently however, many of
these techniques used in 3D modelling for hard rock applications are done at the data rich mine
site for local reserve extension, targeting and support for ore grade calculations. We would like to
go more regional, in the challenging domain where 3D sub-surface information is much more
limited. Here we need to lever our information through surface and subsurface data reconciliation
in 3D and better use of structural observations to interpolate and extend geologic features of
interest.
The initial test site will focus on modelling the Purcell Anticlinorium and its main target horizon the
Lower to Middle Aldridge Formation contact (LMC), hosting the world class Sullivan Pb, Zn, Ag
deposit. The focus will be on applying and testing structural interpolation and stratigraphic
modelling methods using geological map, geophysical and drill-hole data. The focus will be on
estimating the 3D regional extent of the LMC in several large fault blocks beyond the Sullivan
deposit. Stratigraphic thickness estimation of marker bounded units within the Middle Aldridge will
be attempted, but of course will remain dependent on the abundance and accuracy of drill hole and
surface observations. This is why we are actively encouraging local exploration experts to support
us in gathering the relevant data constraints especially from historical drill records so the best 3D
picture can emerge. Potentially these models will provide a geometric framework for modelling
other internal properties (geochemical, lithofacies and geophysical) of the associated “Sullivan
Time” sequence. In addition the delineation of structural discontinuities (normal, strike-slip and
thrust faults) in 3D and where possible the major fault network offsets will be estimated in order to
make a coherent regional structural-stratigraphic 3D model.
Currently we have developed a 3D data store which has all surface and sub-surface data in a
common coordinate system (UTM Zone 11 NAD83). All regional 50K map based information from
previous compilations have been converted into a 3D GIS comprising of 4500 lithology records and
12,000 structural observation points. Reprocessed seismic profiles, 45 predominantly 3 second
lines from previous TGI3. BC TRIM based DEM and other surface reference features are all in 3D.
Surface and a significant amount of subsurface markers including the Sullivan horizon (LMC) from
approximately 754 Drill holes, more than 100 Sullivan time piercing points and near 200 Middle
Aldridge subsurface markers. From this data we have developed various constrained LMC horizon
models the latest of which can be seen in Figure 1 for the St. Mary's block, host to the Sullivan
deposit. This year will focus on incorporation of more historical drill core from this block and
validation of the model through consultation with industry experts. Ongoing is the methodology
development for 3D structural and stratigraphic interpolation with Structural Field Interpolation (SFI)
as well as using Radial Basis Functions (RBF) for fast horizon development. Next year 2013 we
expect to produce a preliminary 3D data and model release for the St. Mary's block region and
apply our new methods to specific areas of interest in the region.
We believe that the future of mineral exploration will be in the hands of those who know how to
better interpret beyond the head frame and who can reduce risk when drilling deeper geologic
targets. To do this we need to know how to make 3D models with less data, and better use
existing, albeit sparse, complimentary data for mutual support. There is a growing realization in the
mining exploration industry that integrated 3D geologic-geophysical model driven targeting is
essential to accomplish more efficient and successful deep mineral exploration (> 400 m). To do
this 3D modelling will need to be undertaken beyond the head frames of mines in more challenging
regions. A critical interpretive support needed to develop these areas are tools to estimate spatial
continuity or ‘trends’ of subsurface geological features which are often limited to subjective and
highly hypothetical subsurface representations. This is an underdeveloped area of research in
which we can make an innovative and high impact contribution. If these features can be better
interpreted and spatially integrated with other 3D data (potential fields, seismic, bore hole)
increased opportunities will emerge for generating reproducible subsurface models of mineral
system components (structure, lithostratigraphy and lithofacies) enhancing effective exploration.
Figure 1 - preliminary model St. Mary's block Lower-Middle Aldridge Contact (LMC) as red surface.