WA Regolith Example
The
WA_Regolith is a demonstration data set of spectra from a deeply
weathered hole from the West Australian goldfields. There is also
an additional dataset 'Custom Library 01' which contains data from a project
in a similar geologic environment situated about 350km from this project
area, these data can be used as a custom library to help identify
the spectra in this data set.
Download
the WA_Regolith zip file to your PC and then unzip it. There are two
data sets and six files in the zip file, WA_Regolith.tsg,
WA_Regolith.bip and WA_Regolith.ini, and Custom Library 01.tsg, .bip and
.ini. For each data set all three files are required to be in the same
directory for you to successfully open the TSG file.
The
spectral data in WA_Regolith.tsg comes from an exploration drill hole in
an Archean Greenstone gold environment. The TSG file already contains a
variety of scalars as well as imported Au data. The following notes have
been adapted from a report on this spectral data.
Common
throughout the region are deeply weathered profiles of felsic and mafic
units which can be difficult for geologists to visually log in RC/RAB
samples. Spectral data was collected to assess whether these could aid
the exploration program.
This data
set consists of 66 metres of RC drill hole samples (in chip trays) that
were measured with a PIMA at 1 metre sample intervals. The fact that
these deeply weathered felsic and mafic units are difficult for
geologists to visually log was demonstrated by the lack of detail in the
original drill log and is one of the main reasons for the almost total
reliance on geochemical data in this region. These samples are deeply
weathered to about 60m where the first recognisable chips of altered
basalt occur.
Have a
look at the results of the Custom Library search using the Floater and
the results displayed in the Log Screen. To do this attach the custom
library tsg file using the Attach Aux function in the File
drop down menu. You can then overlay the spectra in the custom library,
or view the search-match results in the Floater screen (when it is in
Aux match mode). For more information on how to use the custom
libraries please look up the Custom libraries section under
Auto Mineral ID in the TSG user manual.
A
comparison of the spectral data and gold grade show that there are some
important associations between these data sets. Gold mineralisation in
this hole is associated with three factors that can be recognised in the
spectral data:
-
The contact between mafic and overlying felsic units occurs between
40-41m and is indicated by a decrease in kaolinite response and a
marked increase in smectite (nontronite ~2290nm) at 40 to 41m. There
is also a corresponding peak in Au near to this contact;
-
Sericite (illite) alteration, in felsic (34m) and in mafic (67m)
units is associated with small increases in Au. Indicators include
decreasing wavelength of AlOH absorptions, decreased kaolinite
response, increased sericite response, as well as local decreases in
the hydroxyl (~1400nm) and the water (~1900nm) features and
shoulders near 2196nm on the main kaolinite related AlOH
absorptions;
-
Fe carbonate alteration, most easily recognised from an increase in
the effect of Fe2+ in the low wavelength region of the
reflectance spectra (i.e. no hull correction) is associated with the
main Au mineralisation towards the base of the hole (between 71 and
90m). This alteration probably starts near to 61m.
