Open File Report 1
Atlas of weathered rocks
Robertson, I.D.M. and Butt, C.R.M.
Determining bedrock type from its weathered counterpart is one
of the chief problems encountered by exploration geologists, particularly
newly qualified geologists, when working in intensely weathered
This report is an Atlas which makes use of some of the magnificent
sectional exposures generated by open pit gold mining in the Yilgarn.
It introduces regolith terminology, the principles of weathering
and its attendant mineralogical changes. The main part of the Atlas
illustrates the fabric and mineralogical changes that take place
as rocks weather. The Atlas is presented in hard cover, loose-leaf
format and contains 136 annotated colour photographs with detailed
descriptions. Many of these are in pairs so as to relate petrographic
detail to what can be seen with a hand lens.
It also records the changes in major and trace element contents
which occur in the weathered profile, backed by tabulated geochemical
data. The Atlas discusses the use of 'immobile' elements to identify
rock types and introduces multivariate methods and discriminant
Improved identification of rock types in the weathered zone will
assist interpretation of geochemical data. Being able to recognise
the position in the weathered profile from weathering fabrics will
lead to a better understanding and prediction of geochemical dispersion.
Lithogeochemistry, fabrics, petrography, immobile elements, multivariate
statistics, bedrock identification, regolith terminology, regolith
classification, posl lateritic modification, truncation, cementation,
soil, lag, initiation of weathering, weathering reactions, mineral
stability, colour, mineralogy, geochemistry, phyllite, Beasley Creek,
granite, Trial Hill, Barr Smith Range, QAZ cement, Dam Bore, silcrete,
aluminosilicate cement, Tammin, sandplain, Bottle Creek, Lights
of Israel, Ora Banda, primary fabrics, secondary fabrics, voids,
mica relics, palimpsest fabrics, accordion fabrics, void fill fabrics,
duricrust fabrics, Reedy, foliation, saprock, saprolite, plasmic
zone, kaolinite blasts, quartz segregation fabrics, porphyry, Mt
Percy, ultramafic, mafic.
Last updated: Friday, December 24, 1999 09:30 AM