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.