An interpretation of some recent Geophysical Data of Wolfe Creek Crater, south of Halls Creek, Kimberly region, Western Australia
by Louis A G Hissink MSc. Consulting Diamond Geologist December 2002 (Updated 23 Jan 2016)
Wolfe Creek Crater, aerial view, looking north (Image Credit WA Museum and Kevron Aerial Surveys)
Wolfe Creek Crater was first discovered in 1947 from an aerial survey, but was previously known to the local Aborigines as “Kandimalal”. The crater is circular and has a diameter of 880 metres, with the floor of the crater some 60 meters below the rim. It lies 90 kilometres south of Halls Creek on the edge of the Great Sandy Desert in Western Australia. Figure 1 is an aerial image of the crater while Figure 2 is a recent satellite image of the crater, showing the nearby Wolfe Creek drainage system. The satellite image is skewed to the right.
It is conventionally interpreted as a classic meteorite crater and dated some 300,000 years BP. Fragments of the meteorite which created the crater have been found and unusual iron rich shale balls also occur around the crater rim, containing fragments and veins of iron-nickel metal and an iron-phosphide, Schreibersite.
In July 2002 UTS Geophysics flew a geophysical survey over Wolfe Creek Crater for Geoscience Australia. Airborne Magnetic, radiometric and digital terrain data were collected. The author purchased the final digital data from the Department of Minerals and Resources of Western Australia . The geophysical data is displayed on the Department’s web site and shows various images of the data.
Satellite Image of Wolfe Creek Crater (Google Earth 2016)
The following are images computed from a GIS system of the Reduced to Pole magnetics, Total Radiometric Count and the digital terrain model of the crater.
Reduced to Pole Magnetics (Crater is large circular feature in centre of image)
The magnetic response of the crater is fairly weak, with a thin annulus magnetic high corresponding to the crater rim, and a very small high in the centre or the bull’s eye in the crater. The regional magnetic field slopes from west to east.
The next image (Figure 4) is a composite of the Radiometric Total count, the Digital terrain contours, and the position of the section line AB. The most striking feature here is the concentration of the radioactive elements (Uranium, Thorium and Potassium) around the crater rim together with a south west-to-west concentration away from the crater itself.
However closer inspection of the elevation contours shows that the crater rim is somewhat asymmetric in shape in that the south west crater rim is thicker and of a shallower slope than the steeper north-eastern part of the rim. This, coupled with the regional topographical slope to the southwest, suggests that the splay of radiometric material is probably related to subsequent erosion of the crater rim towards Wolfe Creek to the west.
There is however a strong correlation between the radiometric counts with the crater rim.
DTM on TC-radiometrics showing Section AB
Figure 5 below is a composite profile along section AB showing the topography from the DTM data, (bottom profile), the Total count of the radiometric data and the RTP (Reduced to Pole) magnetic data over Wolfe Creek crater. There is good correlation between the geophysics and crater rim, and the radiometric total count is quite anomalous.
The meteorite inferred to have formed the Wolfe Creek Crater has been described as an iron meteorite and the shale balls interpreted as deeply rusted (or highly weathered) remains of the iron meteorite. The structural relationship of the country rock to the crater is typical for an impact crater. The country rock is a quartzite capped with laterite, and often layers of laterite can be seen sandwiched in between the contorted quartzite, putting the impact as post laterite development. This has been confirmed in the field by the author in 1999 and 2000.
The uranium abundance in meteorites is typically as 0.008 ppm, and that for the earth’s crust 1.4 ppm, and often 50 ppm in some granites, and in the percent range for uranium ore deposits (Briefing paper No 78, 2002, The Cosmic Origins & Geological Role of Uranium, Uranium Information Centre, Melbourne Victoria, Australia).
It is difficult to explain the anomalous concentration of radioactive uranium, thorium and potassium as the result of the catastrophic melting of the Wolfe Creek Meteorite itself on impact, given the extremely low abundance of uranium in meteorites.
Composite profile of Magnetics, Radiometric Total Count and Digital Terrain model (A is on left B on right, looking NW)
Experience elsewhere in this region shows that elevated radiometric counts are often associated with surface laterite deposits, one such example occurring on Nookanbah Station hundreds of kilometres to the west where a similar geophysical survey was conducted by the author on behalf of a client over a tenement hosting igneous intrusions known as lamproites during 2001. However the clear association of the radiometric anomaly at Wolfe Creek Crater with the crater rim itself, discounts any association with the known laterite at the crater. All that could be said is that the radiometric anomaly is associated with the crater rim, but is not derived from the meteorite itself since these meteorites don’t have enough uranium in the first instance to create the measured anomaly. Unless the Wolfe Creek Crater meteorite was a rare one, which did have elevated levels of uranium, but there is little data to form this interpretation, if any.
Aboriginal myths about Wolfe Creek Crater are unusual and the one published by the West Australian Museum mentions the local story of two rainbow snakes, whose sinuous paths across the desert formed the nearby Sturt and Wolfe Creeks, and the crater marks the place where one of those rainbow snakes emerged from the ground.
Another aboriginal myth relates this crater to the morning star, though the reference is anecdotal. None the less if ancestral Aborigines had observed this crater being formed then either it is sheer coincidence as the aborigines are assumed to have arrived 40,000 years ago, or the geological dating is problematical.
Giving the Aboriginal myth some credence, it is possible that what their ancestors could have described was an enormous electrical discharge between the earth and some other cosmic body. Such electrical discharges would have occurred over some hours of duration, and such a novel physical phenomenon would tend to be described by technologically unsophisticated nomadic hunter-gatherers in terms of an aboriginal metaphor, or a snake, hence the term “rainbow snake”. This suggests that the Wolfe Creek Crater is a discharge crater, not a meteoritic impact crater.
Australia’s Meteorite craters, Alex Bevan and Ken McNamara, West Australian Museum, December 1993
Logistics report for a Detailed Airborne Magnetic, Radiometric and Digital Elevation survey for the Wolfe Creek Crater Project, July 2002, UTS Geophysics, for Geoscience Australia.