Student exercise
Interpretation of visible-near to shortwave infrared reflectance drill core
data from a channel iron deposit in the Hamersley Province (WA)
Introduction
Channel iron deposits (CIDs) are the second most important source for iron production in
WA, after the bedded iron deposits (BIDs). CIDs developed along tertiary palaeochannels,
where these crosscut banded iron formations (BIFs) or for several kilometres downstream,
above metabasalt and metasedimentary rocks (Morris and Ramanaidou, 2007). CIDs consist
of a mixture of Fe-(oxyhydr-)oxide pelletoids and ferruginised wood fragments, cemented in
a goethite matrix. Detrital components, including quartz grains, BIF fragments or clays are
rare. Many of the pelletoids are ooids, with a hematite or goethite core, surrounded by onionlike goethite shells (Fig. 1).
Fig. 1 Typical CID mixture of Fe-(oxyhydr-)oxide pelletoids and ferruginised wood fragments, cemented in a
goethite matrix (From Morris et al., 1993)
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CIDs throughout the Hamersley Range have a similar stratigraphy within the palaeochannel,
as shown in Fig. 2 for the palaeochannel hosting the series of Yandi CID.
Fig. 2 Stratigraphy of the Yandi CIDs in the Marillana Creek (from Kneeshaw in Ramanaidou et al., 2003)
The CID can vary internally between different ore types of which some pure endmember
forms are depicted in Fig. 3. Vitreous goethite received its name thanks to its typical
shininess. It is a massive form of goethite, often (but not always) associated with silica and its
reflectance spectrum has a characteristic wide crystal field absorption beyond 900 nm and a
steep reflectance slope between 1400 and 1800 nm. Ochreous goethite is a more common
form of goethite, being often powdery and having a characteristic strong yellow colour.
Ochreous goethite is very often associated with AlOH-type clays, like for example kaolinite.
This form of goethite is distinguished in the USGS library as limonite. The ‘original’ CID can
have many different appearances, but should always be built up by goethite (and mostly
hematite) pelletoids, mixed with ferruginised wood fragments in a goethite matrix.
In the lower CID at Yandi (Fig. 2), ochreous goethite is extensively developed and believed
to a product of weathering below the water table. Vitreous goethite at Yandi is more often
developed closer to the surface as a hardcap covering the iron ore body (Ramanaidou et al.,
2003).
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Fig. 3 Common ore types in CID
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Kaolinite is the most common clay
in CIDs. In many of the CIDs both
well- and poorly-crystalline
kaolinite are developed (Fig. 4).
Well-crystalline kaolinite (upper
spectrum in Fig. 4) is thought to be
the result of in-situ weathering of
basement rocks or neoformation of
kaolinite below the water table in
more acidic conditions. Poorlycrystalline kaolinite (lower
spectrum in Fig. 4) can be the
result of neoformation in alkaline
conditions (above the water table)
or transport of kaolinite.
Fig. 4 Kaolinite crystallinity, dependent on intensity of
Distinctions of well- and poorlyabsorption at ~2165 nm (intensity ~ crystallinity)
crystalline kaolinite have proven to
be powerfull indicators for
delineating palaeochannel boundaries (Haest et al., 2012).
References
Haest, M., Cudahy, T., Laukamp, C., and Gregory, S., 2012b, Quantitative mineralogy from visible to
shortwave infrared spectroscopic data: (II) 3D mineralogical characterisation of the Rocklea Dome channel iron
deposit in Western Australia: Economic Geology, v. 107.
Morris, R. C., and Ramanaidou, E. R., 2007, Genesis of the channel iron deposits (CID) of the Pilbara region,
Western Australia: Australian Journal of Earth Sciences, v. 54, p. 733-756.
Morris, R. C., Ramanaidou, E. R., and Horwitz, R. C., 1993, Channel Iron Deposits of the Hamersley Province,
AMIRA Project P75G - Restricted Report 399R, CSIRO Exploration and Mining, p. 208.
Ramanaidou, E. R., Morris, R. C., and Horwitz, R. C., 2003, Channel iron deposits of the Hamersley Province,
Western Australia: Australian Journal of Earth Sciences, v. 50, p. 669-690.
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Exercise 1: annotate spectra
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Identify minerals and classify in function of lithology or ore type
Order the spectra in function of depth, starting from 1 at the surface
Indicate position of drill core on the profile in Fig. 2
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Exercise 2
TSG file called RKD_5-7-9 contains hyperspectral diamond drill core data for RKD 5, 7 and
9 at 1 cm spatial resolution. These drill cores are aligned E-W along a profile through a CID.
Coordinates, RL and bottom of drill hole depths are provided in Table 1.
Table 1 Drill hole data
Hole ID
RKD005
RKD007
RKD009
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Easting
Northing
547505.9 7475596
547901.7 7475596
548192.1 7475593
RL
461.6
456.8
458.6
Bottom of hole depth
42.4
48.5
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Create in TSG scalars to extract the mineralogical information from the hyperspectral
data, using the profile function
Plot extracted parameters as a function of depth for each drill hole in the scatterplot
window (select specific drill hole using the class masking tool)
Group data for all drill cores manually in a profile (possibly using powerpoint, although
any real drawing program will do)
Delineate the different zones in the channel
An example of what is expected is shown below + describe in detail why you put the
boundaries at a certain depth:
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Exercise 3
TSG file called RC_data contains hyperspectral RC drill core data for 180 holes, sampled at a
1 m resolution. Auxiliary data include easting and northing for all drill cores, allowing to plot
any results up as a map in TSG using the scatterplot and full XRF assays to validate the
hyperspectral results.
-
-
Extract the mineralogy from TSG, copy-processing the scripts from the RKD_5-7-9
TSG file
Validate the hyperspectral-based mineralogy results against the provided XRF data, if
possible
Map the CID channel at the surface (scope in scatterplot limited by depth interval 0-1
m), in particular the palaeochannel boundary and if possible the local mineral content.
Can you recognise zones of high clay/carbonate/Fe-(oxyhydr-)oxide abundance?
Experiment with maps at different depths to explore for buried CID ore and see how
this ore zone at depth corresponds to your palaeochannel outline mapped at the
surface.
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