The blueberry (iron nodule) from the Shark Bay area, Western Australia and its implication to the genetic environments of iron nodules on Mars

Fist-sized iron nodules, extensively found on the ground of Western Australia, were investigated by element analysis (XRF, ICP-MS and ICP-AES), electron microscopes, X-ray diffraction and Mossbauser spectroscopy. Loosely-packed pisoidic structures of a few to > 10 mm in size were observed in the cross-section of nodules. Chemically, the nodules are majorly made of O, Si, Fe and Al, and share similar REE pattern with the loess sourced Greatford concretions from New Zealand. Angular quartz particles, nano-sized goethite and hematite are found to be the major mineral phases. Other minerals, such as detrital zircon, barite and Ce-containing particles can also be observed but of very low abundance. No detectable carbonate or amorphous silica implies that these nodules have experienced little underground fluid alteration. The quartz particles showing particularly three sections of fractal size-distributions, together with their extensive broken features and conchoidal fractures, strongly suggest in situ fragmentation of the host rock with minimum later dynamic sorting. These observations indicate the genetic environment of those nodules is always close to the surface of the tectonically stable ground since their formation. Because of the similarity of climatic and geological features, the genesis and preservation environment of these nodules in Western Australia may provide clues on the formation of Martian iron concretions.