Geology of the Maydena, Skeleton, Nevada, Weld and Picton 1:25 000 Scale Map Sheets
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Mineral Resources Tasmania Tasmanian Geological Survey Tasmania DEPARTMENT of INFRASTRUCTURE, Record 2006/04 ENERGY and RESOURCES Geology of the Maydena, Skeleton, Nevada, Weld and Picton 1:25 000 scale map sheets by C. R. Calver, S. M. Forsyth and J. L. Everard CONTENTS General remarks …………………………………………………………………………………………… 5 Parmeener Supergroup mapping (Maydena, Skeleton, Nevada map sheets) …………………………………… 6 Vegetation ……………………………………………………………………………………………… 7 Physiography ……………………………………………………………………………………………… 9 Fold structure province ………………………………………………………………………………… 9 Fault structure province ………………………………………………………………………………… 9 Acknowledgements ………………………………………………………………………………………… 12 STRATIGRAPHY ………………………………………………………………………………………… 13 Proterozoic sedimentary rocks ……………………………………………………………………………… 13 Harrisons Opening Formation (Weld, Picton map sheets)…………………………………………………… 13 Turbiditic lithic sandstone, conglomerate and black phyllite (Phc) …………………………………………… 13 Black slate and phyllite with minor quartzwacke and diamictite (Php) ………………………………………… 13 Clark Group …………………………………………………………………………………………… 16 Clark Group correlate, Jubilee Range area (Skeleton, Nevada map sheets) ……………………………………… 16 Needles Quartzite correlate ……………………………………………………………………… 16 Humboldt Formation correlate …………………………………………………………………… 16 Clark Group correlate, Snake River Valley (Nevada map sheet) ……………………………………………… 19 Clark Group correlate, Gallagher Plateau area (Weld map sheet) ……………………………………………… 19 Orthoquartzite (Pcq) ……………………………………………………………………………… 19 Dolomitic mudstone and siltstone (Pcd) …………………………………………………………… 19 Mudstone and siltstone (Pcmm) …………………………………………………………………… 19 Unit Pcp (probable Clark Group correlate), Manuka Creek area (Weld map sheet) ……………………………… 21 Clark Group correlate, Glovers Bluff inlier (Weld map sheet) ………………………………………………… 21 Orthoquartzite (Pcq) ……………………………………………………………………………… 21 Mudstone, siltstone and intraclastic conglomerate (Pcm, Pcdc, Pcmm)………………………………… 21 Clark Group — age and correlation ……………………………………………………………………… 21 Depositional environments ……………………………………………………………………………… 22 Weld River Group ……………………………………………………………………………………… 22 Conglomerate, sandstone and red mudstone (Pwa) (Skeleton, Nevada, Weld map sheets) ………………………… 23 Pebbly laminated mudstone and sandstone (Pwap) (Nevada map sheet) ………………………………………… 23 Dolostone (Pwt) (Maydena, Skeleton, Nevada, Weld map sheets) ……………………………………………… 23 Fine-grained dolostone (Pwtf) (Nevada, Skeleton, Weld map sheets) ………………………………… 23 Red mudstone (Pwtm) (Nevada map sheet) ………………………………………………………… 24 Dolostone: dominantly oolitic grainstone (Pwtg) (Nevada, Skeleton, Weld map sheets) ………………… 24 Dolostone, diamictite, mudstone and sandstone (Cotcase Creek Formation) (Nevada, Weld, Picton map sheets) ……… 25 Predominantly massive, fine-grained dolostone (Pwcd) (Nevada, Weld, Picton map sheets) …………… 25 Predominantly black dolomitic diamictite (Pwcx) …………………………………………………… 27 Predominantly black mudstone and quartz sandstone (Pwcm) ……………………………………… 27 Predominantly pebbly laminated dolomitic siltstone and mudstone and pale grey dolomitic diamictite … 27 Silicification in dolostones of the Weld River Group ………………………………………………………… 29 Tasmanian Geological Survey Record 2006/04 1 Early diagenetic quartz cement …………………………………………………………………… 29 Boxwork and massive to vuggy silicification………………………………………………………… 29 Altered dolostones of the Weld River Group, Glovers Bluff area (Pwts, Pwtq, Pwtqo) (Weld map sheet) …………… 31 Magnesian skarn (Pwts) …………………………………………………………………………… 31 Secondary quartzite, quartzitic breccia and opaline silica (Pwtq, Pwtqo) ……………………………… 35 ‘Silica-clay zone’ of Forster Prospect area …………………………………………………………… 35 Weld River Group……………………………………………………………………………………… 36 Depositional environments………………………………………………………………………… 36 Age and correlation ……………………………………………………………………………… 36 ?Early–Middle Cambrian rocks ……………………………………………………………………………… 38 Correlates of Ragged Basin Complex (Maydena, Skeleton, Weld, Glen Huon map sheets) …………………… 38 Micaceous lithic sandstone, mudstone and chert (Ccwl) ……………………………………………………… 38 Chert, with minor mudstone (Ccwc) ……………………………………………………………………… 38 Dolostone, mudstone and chert (Ccwd) …………………………………………………………………… 40 Basalt (Ccwb) ………………………………………………………………………………………… 41 Maynes Hill and near Pine Hill (Maydena map sheet) ……………………………………………… 41 Glovers Bluff inlier (Weld map sheet) ……………………………………………………………… 42 Arve Plains inlier (Weld, Glen Huon map sheets) …………………………………………………… 42 Volcanic breccia (Ccwbb) (Maynes Hill, Maydena map sheet) ………………………………………………… 42 Lithic sandstone and conglomerate (Calc, Calct, Cals, Cdi) (Maydena, Nevada, Weld, Picton map sheets) ……… 43 Polymict conglomerate, lithic sandstone and shale (Calc) (Nevada, Weld map sheets) …………………………… 43 Feldspathic sandstone (Cdi) (Nevada map sheet) …………………………………………………………… 44 Talc-hematite-chlorite altered rocks of unit Calc (Calct) (Weld map sheet) ……………………………………… 44 Turbiditic lithic sandstone, etc. (Cals) (Maydena, Nevada, Weld, Picton map sheets) …………………………… 45 Eastern slopes of Mt Mueller (western Maydena map sheet, eastern Adamsfield map sheet) …………… 45 Huon River (Picton map sheet) …………………………………………………………………… 46 Weld River (Nevada map sheet) …………………………………………………………………… 47 Denison Group …………………………………………………………………………………………… 47 Tim Shea Sandstone (COlt) (Maydena map sheet) ………………………………………………………… 47 Florentine Valley Formation (COucf) (Maydena map sheet) ………………………………………………… 47 Gordon Group……………………………………………………………………………………………… 47 Karmberg Limestone (Olk) (Maydena, Picton map sheets) ………………………………………………… 48 Cashions Creek Limestone (Olc) (Maydena, Picton map sheets) …………………………………………… 48 Benjamin Limestone (Olb) (Maydena, Picton map sheets)…………………………………………………… 48 Parmeener Supergroup……………………………………………………………………………………… 49 Lower Parmeener Supergroup …………………………………………………………………………… 49 Truro Tillite correlate (Ptx)……………………………………………………………………………… 49 Lower unit ……………………………………………………………………………………… 51 Upper unit ……………………………………………………………………………………… 52 Weld and Picton map sheets ……………………………………………………………………… 53 Discussion ……………………………………………………………………………………… 53 Basal conglomerate (Plbc) ……………………………………………………………………………… 53 Woody Island Siltstone correlate (Plw) …………………………………………………………………… 53 Weld and Picton map sheets ……………………………………………………………………… 57 Bundella Formation correlate (Pln) ……………………………………………………………………… 57 New mapping. …………………………………………………………………………………… 58 Picton sheet ……………………………………………………………………………………… 60 Faulkner Group correlate (Pfk)…………………………………………………………………………… 60 New mapping …………………………………………………………………………………… 61 Weld and Picton map sheets ……………………………………………………………………… 62 Deep Bay Formation and Nassau Formation correlate (Puh) ………………………………………………… 62 New mapping …………………………………………………………………………………… 63 Upper beds ……………………………………………………………………………………… 65 Picton map sheet ………………………………………………………………………………… 65 Minnie Point Formation correlate (Pun) ………………………………………………………………… 66 New mapping …………………………………………………………………………………… 66 Picton map sheet ………………………………………………………………………………… 68 Risdon Sandstone correlate (Pui) ………………………………………………………………………… 69 Picton map sheet ………………………………………………………………………………… 70 Abels Bay Formation correlate (Pub) ……………………………………………………………………… 70 Picton map sheet ………………………………………………………………………………… 71 2 Tasmanian Geological Survey Record 2006/04 Upper Parmeener Supergroup. …………………………………………………………………………… 72 Cygnet Coal Measures correlate (Pwtq) …………………………………………………………………… 72 Quartz sandstone sequence ……………………………………………………………………………… 73 Upper Parmeener Supergroup (undifferentiated) (Tr) ……………………………………………………… 74 Quaternary deposits………………………………………………………………………………………… 74 Dolerite topples (Qptf) …………………………………………………………………………………… 74 Deeply weathered dolerite boulder deposits including till (Qpdb) …………………………………………… 74 Weathered till (Qpgw) …………………………………………………………………………………… 75 Till of undissected moraines (Qpgm) ……………………………………………………………………… 75 Periglacial non-vegetated scree deposit (Qptnv) …………………………………………………………… 75 Talus (Qpt) ……………………………………………………………………………………………… 75 Siliceous lag and colluvium (Qss) (Weld map sheet) ……………………………………………………… 76 Siliceous lag and colluvium including silica flour (Qs) (Maydena map sheet) ………………………………… 77 Alluvial gravel, sand and clay (Qa, Qaf, Qpao) …………………………………………………………… 77 Marsh and swamp deposits (Qhab). ……………………………………………………………………… 78 Man-made deposits (Qhmm). …………………………………………………………………………… 78 IGNEOUS ROCKS ………………………………………………………………………………………… 79 Cambrian mafic and ultramafic igneous rocks ……………………………………………………………… 79 Amphibolite (Ccwba) (Nevada map sheet) ………………………………………………………………… 79 Serpentinite (Cspla) (Maydena, Skeleton map sheets) ……………………………………………………… 79 Basaltic rocks (Ccwb) (Maydena, Skeleton, Weld map sheets) ……………………………………………… 79 Petrography ………………………………………………………………………………………… 79 Maydena area …………………………………………………………………………………… 79 Skeleton map sheet ……………………………………………………………………………… 79 Arve Plains inlier ………………………………………………………………………………… 79 Geochemistry ………………………………………………………………………………………… 80 Summary ………………………………………………………………………………………… 80 Analytical methods and data interpretation ………………………………………………………… 81 Major elements …………………………………………………………………………………… 81 Trace elements …………………………………………………………………………………… 83 Tectonomagmatic discrimination diagrams ………………………………………………………… 88 Possible correlates in western Tasmania …………………………………………………………… 89 Lamprophyres, Glovers Bluff inlier ……………………………………………………………………… 95 Petrography ……………………………………………………………………………………… 95 Geochemistry …………………………………………………………………………………… 95 Jurassic dolerite ……………………………………………………………………………………………