Postgraduate Report
THE APPLIED STRUCTURAL GEOLOGY FOR
MINERAL EXPLORATION & MINING
INTERNATIONAL SYMPOSIUM
Karla Olvera
ANU, ACT
2002 AIG Postgraduate Bursary Winner
First, I wish to thank to the Australian Institute of Geoscientists for giving me the
opportunity, through the Student Bursary Program, to attend the Applied Structural
Geology for Mineral Exploration and Mining International Symposium at Kalgoorlie on
the 23rd to the 25th of September this year. Thanks also to the sponsors to make the
Student Bursary Program exist. This experience allowed me to meet, talk and share
ideas with scientists and exploration geologists from Australia and other countries. The
talks programmed in the diverse sessions provided me with a significant knowledge on
the diverse types of structural controls acting on different types of mineral deposits.
Research Project Overview
Geological setting
Bendigo is located within the Bendigo-Ballarat zone of the Palaeozoic Lachlan Fold
Belt of Eastern Australia (Gray, 1988). The bedrock at Bendigo is comprised of Lower
Ordovician marine sediments and metasediments, which constitute a sequence of
turbidite sandstones, siltstones and mudstones, known as the Castlemaine Supergroup
(Cas and VanderBerg, 1988). The Lachlan Fold Belt has an orogenic history stretching
from Late Ordovician (~450 Ma,) through early Carboniferous times, recording arccontinent collision, marine sedimentation, folding and faulting, volcanism, igneous
intrusion and regional metamorphism (Foster and Gray, 2000). The deformational event
produced a regular north-south train of open to tight folds, which are cut by east and
west- dipping reverse faults. The major gold mineralisation occurs in quartz veins
developed in or adjacent to reverse faults (Cox et al, 1991).
The aims and advances
My research project is focused in exploring how deformation processes during folding
and faulting in the Bendigo goldfield has controlled the development of fluid pathways
during gold mineralisation. Specifically, how lithology and the mechanics of folding
have influenced the localisation of bedding-parallel slip and related development of
saddle reefs, related reverse faults and vein systems which host gold mineralisation.
With the new underground exposures along the Swan Decline, built by Bendigo Mining
N.L., we are being able to access and map faces along strike of the main anticlines, and
therefore we are documenting the changes in geometry of bedding parallel veins and
related saddle reefs, as well as other fault related structures. At this stage of my project,
and with the access to drill cores and new underground exposures (Sheepshead and
Deborah anticline) a very high-resolution understanding of the stratigraphy at Bendigo
is being attained, with the refinement of stratigraphic columns and the localization of
slip movement horizons through the sequence using the drill cores.
Victoria Goldfields Background
The Symposium represented the perfect scenario to meet and talk with scientists who
have done research at the Bendigo Goldfields and other adjacent areas in Victoria in
recent years. Peter Schaubs was one of them. Peter’s research was focused in
understanding folding and faulting controlling mineralisation along the Deborah
anticline in Bendigo. I was pleased to get directly from him one of the reprints of his
published research paper. He mentioned that by the time he worked in Bendigo, he only
could have access to the Deborah Anticline underground workings. We agreed that the
fact that I am now having direct access also to the Sheesphead anticline, undoubtedly
will allow me to obtain a wider record not only in stratigraphy facies changes, but also
in bedding parallel veins and saddle reefs geometry changes across and along strike of
both anticlines. Peter’s findings and interpretations represent a good reference to my
research.
On the other hand, the talks presented by people from CRC School of Earth Sciences of
the University of Melbourne, like John Miller and Chris Wilson, also provided me with
a substantial feedback on having the “broad picture” of the Victoria Goldfields. Their
research on the gold lodes in the Western Lachlan Fold Belt (LFB), specifically in the
Wonga Mine and the Golden Gift lodes in Stawell, represent a good example to
understand timing and mineralisation variation across the LFB.
Complementary Projects
I found a very encouraging environment at Kalgoorlie, knowing geoscientists and
listening to ideas and suggestions that are already taking effect in my research. Such
was the case of meeting and talking with Simon Dominy, from James Cook University,
at Towsnville. Simon is currently leading a project on ore grading, sampling and
resources estimation at Bendigo. His talk and clue ideas about geological continuity are
definitely complementary to my own observations at the Bendigo’s stratigraphy and
structure, since it seems that most of the structures like bedding parallel veins and
saddle reef development is controlled by specific stratigraphical packages across the
entire sequence. Changes of facies, along strike and across the anticlines in the turbidite
sequence at Bendigo, or otherwise, their continuity, must be taken into account in order
to understand localized mineralised structures. A good predictive model cannot be
attained without this essential factor: geological continuity. Is important to mention that,
as the result of the discussions at the Symposium, and since our research projects are
strongly linked, we are now thinking on complementing our research for future papers,
or presentations in up coming conferences.
References
Cas R.A.F., and VanderBerg, A.H.M., 1988, Ordovician: Geological Society of
Australia Special Publication 5, p. 63-102.
Cox, S.F., Etheridge, M.A., Cas, R.A.F., and Clifford, B.E., 1991, Deformational Style
of the Castlemaine area, Bendigo-Ballarat zone: Implications for evolution of crustal
structure in Central Victoria: Australian Journal of Earth Sciences, v.38, p.151-170.
Gray, D.R., 1988, Structure and tectonics: Geological Society of Australia, Special
Publication 5, p. 1-33.
Foster, D.A. and Gray, D.R., 2000: Evolution and Structure of the Lachlan Fold Belt
(Orogen) of Eastern Australia, Annu. Rev. Earth Planet Sci. 28:47-80.