Uranium ore-forming systems of the - Geoscience Australia

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Uranium ore-forming systems of the Lake Frome regionAccording to Quasar Resources and Alliance Resources mineralisation at the Four Mile deposit ishosted by fluviatile sands of the Upper Eyre Formation within an area defined as the Four MileEmbayment (Figs. 5.3, 5.4). The NE trending embayment is confined to a structural zone betweenthe Paralana Fault in the west and the Poontana and Wooltana Fault zone in the east. The easternmargin of the embayment represents a horst-like structure (Poontana Inlier). It is possible that theFour Mile Embayment itself represents a Paleogene paleochannel trending NE.The Eyre Formation at the Four Mile deposit is generally composed of mature sands that are richerin carbonaceous material and pyrite than the Beverley Sands. The sands of the Eyre Formationare interlayered with fine grained silt and coarse grained gravels. The sediments were deposited ina braided river environment. Within the Eyre Formation mineralisation tends to be localisedtowards the lower contact with a diamictite unit (Alliance Resources, 2009). The diamictiteoverlies fractured basement rocks (possibly Proterozoic rocks of the Mt Painter Inlier).The Eyre Formation sands are capped by silcrete (
Uranium ore-forming systems of the Lake Frome regionMineralisation is predominantly localised in the basal aquifer of the Eyre Formation that directlyoverlies altered basement. The lower sandy aquifer in the Eyre Formation is locally pyrite-rich(average 2.6%, estimated on the basis of sulfur analysis by Bampton et al. (2001), and averaging7% as cited in Southern Cross Resources (2000)) and contains an average 0.3% carbonaceousmatter. The organic material is in the form of lignite and fragments of plant and woody material(Bampton et al., 2001; Skidmore, 2005). The clast-supported sand is interlayered with gravelunits. The upper parts of the basal sands are enriched in carbonaceous material which includescoarse lignitic wood fragments. Clayey intervals dominate both middle and upper parts of the EyreFormation in the Honeymoon area.Figure 5.5: General stratigraphy at Honeymoon deposit. Uranium mineralisation is predominantlylocated in the lowermost sandy aquifer in the Eyre Formation (Skidmore, 2005).5.3.2 Geometry of Yarramba PaleochannelAccording to Skidmore (2005), the geometry of ~115 km long Yarramba Paleochannel is stronglycontrolled by the stratigraphy and structure of underlying basement. The orientation of thenorthwest- to north-trending paleochannel system is interpreted to have been controlled by faultsactive during deposition of the Eyre Formation (Skidmore, 2005). Mineralisation at Honeymoon islocated at a major bend in the paleochannel where it traverses a basement ridge evident in gravitydata (Fig. 5.6). Graphitic metapelitic rocks in the basement ridge may have been more resistant toweathering and erosion than adjacent metaevaporite-bearing rocks of the Bimba Formation. TheYarramba prospect (north of Honeymoon) occupies a similar position on a bend (see Fig 6.2 inReport by Southern Cross Resources (2000)). An important feature of the main channel is thepresence of branches and tributaries. Some of these tributaries have catchments covering basementwith uranium-rich felsic rocks. For example, a drill hole in the upstream part of a tributary close tothe Honeymoon deposit intersected syenogranite containing up to 75 ppm uranium (Skidmore,2005).Page 62 of 151
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