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Short Course for Northern Star Resources YILGARN REGOLITH AND LANDSCAPE Mehrooz F Aspandiar Department of Applied Geology Western Australian School of Mines The Yilgarn Craton surface regolith Image: Churhward & Anand, 2000 Regolith-landforms: Variable Regolith Lateritic residuum Fe saprolite Mottled saprolite saprolite Cenozoic sediments Mottled saprolite Photograph & Concept C. Butt Relict – Erosional – Depositional Scheme R – lateritic gravel and duricrust dominated terrane E – Saprolite, shallow soil and bedrock dominated terrane D – Sediment dominated terrane Remote Sensing & Regolith-landforms 20 km Tertiary sediments Interface saprolite saprolite Regolith-landforms of Northern Yilgarn From Anand & Butt (2010) Main Phanerozoic Sediment relationships – Transported regolith 5. Miocene to 4. Miocene gravelly Pliocene gravelly to 6. Quaternary sand sand sand variable dunes sediments Saprolite Bedrock 3. Miocene Perkolli 1. Permian boulder 2. Paleocene shale (clays & clays, grits, sandstone Wollabur gravel & lenses of gravel) sandstone From Anand & Butt (2010) Stratigraphy of transported regolith in the Yilgarn Lithology Interpreted depositional Age Regolith Unit Description environment Sandy clay to clay Aeolian, fluvial, Pleistocene Hardpan sand with Fe gravel colluvial Pliocene Nodular ferricrete Sandy clay with clay Overbank deposits spherites Fe gravel + clay Granule to pebble, Fluvial, colluvial hematite + maghemite White to cream clay Early Eocene Megamottled Overbank – with quartz, kaolinite, to clay shallow wetland lignite Mid Miocene Grey clay with Fe pisolitic kaolinite, smectite clay Fe gravel & sand, Gravel + sand vein quartz Fluvial channel Mottled mudstone Mudstone to Permian sandstone with Glacial outflow Sandstone conglomerate base Archean Saprolite Compiled from Dusci (1994), deBrokert (2002), Anand et al. (2013) Weathering history and landscape evolution - 1 Late Permian to Cretaceous – extension weathering with stable landsurface conditions Late Cretaceous to Eocene – drop in sea-levels (base level change) caused inset valleys to develop in the landscape with erosion After Anand & Butt (2010) Weathering history and landscape evolution - 2 Mid Eocene - Miocene filling of inset valleys due higher sea-levels Saprolite Bedrock Mid-Miocene –stable conditions favouring weathering Late Miocene –to current – local erosion and sedimentation and onset of aridity – drop in water tables Yilgarn Inset valley paleochannel fills Salt lakes Paleodrainage Trunk inset valley fill Trunk inset valley fill (inferred) After de Brokert (2002), compiled from Kern & Commander (1993) Yilgarn Inset Valley Paleochannels - Magnetics RTP – southeast of Laverton 1VD – 30 km southeast of Laverton 6 km 6 km Paleochannel sediments that have maghemite bearing pisolites show up on magnetic survey images – distributary channel form Paleochannels (Inset-valley

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