Enhanced geological modelling of the Upper Elsburg reefs and VCR to optimize mechanized mine planning at South Deep Gold Mine
K Osburn, H Pretorius, D Kock, N King, R Pillaye, M Hlangwane
South Deep Gold Mine, owned by Gold Fields Ltd., is situated near
Westonaria in the Gauteng Province of South Africa and mines the
conglomerate bands of the Upper Elsburg reefs (Mondeor Conglomerate
Formation) of the Witwatersrand Supergroup and the Ventersdorp
Contact Reef (VCR) of the Ventersdorp Supergroup. The stoping and
underground developments are mechanized. The Upper Elsburg reefs are
mined by a variety of mining methods, including mechanized drift and
fill, modified drift and bench, longhole stoping, and low-profile mining.
Optimal mine design and scheduling for deep-level mechanized mining
are complex, and success is highly dependent on detailed, robust, and
accurate geological and geostatistical models.
Geological structures significantly influence the sedimentological
characteristics, distribution, and preservation of the Upper Elsburg reefs
and VCR. Accordingly, particular emphasis is placed on the generation of
a mine-scale structural model that accommodates the relationships
between the older north-trending fault systems (West Rand and
Panvlakte faults) and younger east-trending dextral wrench faults.
Results from underground mapping, borehole intersections, and highresolution
three-dimensional seismic data have been integrated to
produce coherent three-dimensional geological models.
The Upper Elsburg reefs suboutcrop against the VCR and comprise an
easterly diverging clastic wedge, thickening from the suboutcrop
position, to approximately 130 m at the mine’s eastern boundary. The
Upper Elsburg reefs are characterized by conglomerate and quartzite
bands forming multiple, stacked, upward-fining unconformity-bounded
couplets. Palaeocurrent directions are dominantly from west-northwest
to east-southeast, indicating that the more proximal deposits are
preserved close to the suboutcrop, with distal facies to the east.
Sedimentological modelling is applied to individual stratigraphic units
and caters for facies definition. This is achieved through channel width
(CW) kriging and fitting of type sections to borehole and mapping data.
Homogenous geological geozones for each stratigraphic unit are thus
defined within individual structural blocks on the basis of those
sedimentological parameters that have been found to have a positive
spatial correlation to gold concentration. These geozones then serve as
constraints to the evaluation of the orebody.
This contribution presents a summary of the modelling processes that
are currently applied in the development of high-confidence, timeously
produced geological models that are essential input for mineral resource
estimation and mechanized mine planning and scheduling.
Keywords: Witwatersrand Basin, West Rand Goldfield, South Deep Gold Mine,
Upper Elsburg reefs, VCR, geological modelling, mine planning and
scheduling, gold distribution, channel width.