Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Ferricretes, or indurated iron oxides, are a common regolith material found in mineral prospective areas around the word,
including Australia. On Kangaroo Island, they are the dominant regolith material and they are being studied to determine
their usefulness as a sample media for geochemical exploration. Before they can be effectively used as an exploration tool
their formation must be understood. There are a number of different scales that can be looked at, here we are looking at the
microscopic level. From work conducted on the Microprobe SXFive at Adelaide Microscopy, element maps were obtained
that enable us to see microscopic processes at work in the ferricretes, and better understand the larger scale processes that
form them. We have been able to see the transition from weathered saprolite, with fabric still evident, to the pisoliths with
multiple growth stages and the intricacies of the matrix which show several stages of formation. The conclusions of this
being that ferricrete formation is not one single event, but a constantly evolving process and needs to be placed in a
broader landscape context when used as a sample media.
Project #3.2 Using microscopic images to better understand
sample media for geochemical exploration.
Katherine Stoate1, David Giles1, Steve Hill2, Justin Payne3
1DET CRC, The University of Adelaide, South Australia
2Geological Survey of South Australia (GSSA), DSD, Adelaide, South Australia 3TRaX, University of Adelaide, South Australia
Different Ferricrete Morphologies Ferricrete samples have been divided into two broad categories, in situ and
transported ferricretes. The in situ ferricretes are primarily ferruginised bedrock or
saprolite (Figure 1). The transported ferricretes are dominated by pisolitic (Figure
2), nodular and vermiform (Figure 3) ferricretes.
Figure 1: Element maps of ferruginised saprolite, showing remnant fabric.
Figure 2: Element maps of an individual pisolith, showing different stages of rind growth.
Si Al
K Fe
Si
K
Al
Fe
Si
K
Al
Fe
Figure 3: Vermiform ferricrete, where the pisoliths have been remobilised and then re-cemented in a matrix, which has similar characteristics to the pisoliths.
Different Ferricrete Morphologies and Mineral
Exploration We have found that formation of in situ ferricretes involves a
greater component of vertical elemental and mineralogical
reworking and will thus have a greater chance of carrying a
signature of proximal buried mineralisation. Whereas
transported ferricretes, the formation of which is dominated
by distributive lateral processes, are likely to give a broader
and more diffuse geochemical signature.