N S W D P I Quarterly Notes G e olo gic al Sur vey of New S o u th Wale s Januar y 2006 No 119 The Willyama Supergroup in the Nardoo and Mount Woowoolahra Inliers ABSTRACT The Nardoo and Mount Woowoolahra Inliers are 100 km north and 90 km north-northwest, respectively, of Broken Hill, in far western New South Wales. Both inliers contain rocks which belong to the Palaeoproterozoic Willyama Supergroup. Geological mapping of the inliers shows that they both contain graphitic to non-graphitic psammitic, psammopelitic and pelitic metasediments. The Nardoo Inlier contains a significant amount of pegmatite and intermixed pegmatite and granitoid while Mundi Mundi type granite is common in the Mount Woowoolahra Inlier. Structural fabrics and metamorphic mineral assemblages within the inliers are consistent with those observed in the nearby Broken Hill and Euriowie Blocks. The metasediments are considered to form part of the Paragon Group. However, it is not clear if they can be correlated with other occurrences of the Paragon Group in the Broken Hill and Euriowie Blocks, or whether they are a separate (stratigraphically higher) part of the Paragon Group. The recent finding that the Paragon Group in the Broken Hill Block is a time equivalent of stratigraphic units which host significant Pb–Zn deposits in the Mount Isa Inlier in Queensland, increases the prospectivity of the Paragon Group. Understanding its distribution and characteristics has, hence, become important. Keywords: Nardoo Inlier, Mount Woowoolahra Inlier, Paragon Group, Willyama Supergroup, Broken Hill, lead–zinc–silver mineralisation, prospectivity INTRODUCTION AUTHOR The Nardoo and Mount Woowoolahra Inliers are 100 km north and 90 km north-northwest, respectively, of Broken Hill, in far Gary Burton western New South Wales (Figure 1). Both inliers contain rocks Senior Geologist belonging to the Palaeoproterozoic (Statherian) (Plumb 1992) Geological Survey of New South Wales, Willyama Supergroup and are surrounded by Adelaidean cover NSW Department of Primary Industries rocks. [email protected] The geological mapping of Cooper et al. (1975) has been, until now, the best available for showing the distribution of In 2004 the former Department of Mineral Resources was incorporated into the Department of Primary Industries (DPI). We apologise for delays in Willyama Supergroup exposure in the areas of the Nardoo and producing publications while completing our restructure and relocation. Mount Woowoolahra Inliers. Their mapping, however, did not Quarterly Notes are once again being produced on schedule. differentiate the constituent rocks within the inliers. The aim Simone Meakin of this paper is to describe the rock types which occur within Geological Survey Editor both inliers. The work is based on mapping carried out in 1997, as part of the Broken Hill Mapping Project undertaken by the Geological Survey of New South Wales. Both inliers were mapped at 1:25 000 scale using enlargements of originally 1:60 000 scale Land and Property Information (NSW Department of Lands) black and white aerial photographs, which had been taken in 1965. The geological mapping is lithological in nature, being consistent with the style adopted Papers in Quarterly Notes are subject to external review. by Stevens and Willis (1983) for mapping the Willyama External reviewer for this issue was Paul Ashley. His Supergroup rocks of the Broken Hill Block and Euriowie Block. assistance is appreciated. The mapping of Cooper et al. (1975) was used as a guide. All Quarterly Notes is published to give wide circulation to coordinates in this paper refer to AMG Zone 54, AGD 66 and all results of studies in the Geological Survey of New South azimuths are with respect to true north. Wales. Papers are also welcome that arise from team studies with external researchers. Contact: [email protected] ISSN 0155-3410 CONTENTS GEOLOGICAL HISTORY OF THE WILLYAMA SUPERGROUP AND ABSTRACT 1 ADELAIDEAN ROCKS IN WESTERN NEW INTRODUCTION 1 SOUTH WALES GEOLOGICAL HISTORY OF THE WILLYAMA SUPERGROUP AND An account of the regional geological history is summarised ADELAIDEAN ROCKS IN WESTERN NEW SOUTH WALES 2 here to place the geology of the Nardoo and Mount Woowoolahra Inliers into a regional context. THE NARDOO INLIER 5 The Willyama Supergroup in the Broken Hill and Euriowie Mapped rock units 5 Blocks in western New South Wales is interpreted as having Stratigraphy 8 been deposited within a deepening intracratonic rift (Willis, Brown et al. 1983; Stevens et al. 1988) between approximately Structure 8 1710 Ma and 1640 Ma (Page, Stevens et al. 2000). Figure 2 illustrates the stratigraphic column of the Willyama Supergroup Alteration 8 as constructed by the Geological Survey of New South Wales. Adelaidean rocks 8 The Thackaringa Group and equivalents and lower units are interpreted to have been deposited in a subaerial/fluvial to THE MOUNT WOOWOOLAHRA INLIER 9 evaporitic environment (Stevens et al. 1988). The Alma and Rasp Ridge Gneisses are interpreted as having been emplaced as Mapped rock units 9 granitic sills at 1704±3 Ma and 1682±3 Ma respectively (Page, Stratigraphy 9 Stevens et al. 2000; Stevens & Barron 2002). The Broken Hill Group, which hosts the Broken Hill Main Lode, is interpreted Structure 12 to have formed within a shallow marine environment (Stevens et al. 1988) and is characterised by the presence of Alteration 12 quartzofeldspathic gneiss, some calc silicate rocks and such Exploration pits 12 lode rocks as quartz–gahnite and garnet–quartzite. Basic gneisses within the Broken Hill Group and lower stratigraphic Adelaidean rocks 12 units have been interpreted as representing doleritic sills and dykes (Stevens & Barron 2002). The Sundown Group PROSPECTIVITY OF THE PARAGON GROUP 12 represents deepwater turbiditic sedimentation (Stevens et al. SPATIAL RELATIONSHIP BETWEEN THE WILLYAMA SUPERGROUP 1988) and the Paragon Group was interpreted as a deepwater AND ADELAIDEAN ROCKS AND POSSIBLE EXTENT OF PARAGON turbidite sequence by Willis, Brown et al. (1983) — though GROUP BENEATH ADELAIDEAN COVER 14 the Cartwrights Creek Metasediments and the Bijerkerno Metasediments may be shallow marine deposits (Stevens et CONCLUSIONS 14 al. 1988). The Paragon Group in the Broken Hill and Euriowie ACKNOWLEDGMENTS 15 Blocks is characterised by graphitic pelitic schists and fine- grained psammites which tend to be rich in albite (Stevens et REFERENCES 15 al. 1988). The King Gunnia Calc-silicate Member, a distinctive graphitic calcsilicate unit, is present in the upper part of the Editor: Richard Facer Cartwrights Creek Metasediments. Geological Survey editor: Simone Meakin Geospatial information: Cheryl Hormann The Willyama Supergroup was metamorphosed during the Design: Nicole Irvine Olarian Orogeny at approximately 1600 Ma (eg, Page & Laing Layout: Simone Madigan 1993; Page, Stevens et al. 2000). During this event the lower parts of the sequence reached granulite facies (sillimanite+K• feldspar assemblages in metasediments and two-pyroxene assemblages in mafic rocks), while Paragon Group rocks reached amphibolite facies and commonly contain andalusite/ chiastolite (Phillips 1980; Stevens et al. 1988). Marjoribanks et al. (1980) described the structural fabric of the central part of the Broken Hill Block. The following account is based on that work, which probably applies to the entire The information contained in this publication is based on knowledge and understanding at Willyama Supergroup in western New South Wales. the time of writing (December 2005). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of New South Wales Department of Primary Industries or the user’s independent adviser. 2 January 2006 REFERENCE Cainozoic Palaeozoic Adelaidean Mundi Mundi type granite Willyama Supergroup Figure 4 Nardoo Inlier Figure 5 Mount Woowoolahra Inlier Woowoolahra Trigonometric Station N 0 10 km Euriowie Block Broken Hill Bourke Block Cobar Broken Hill Dubbo Broken Hill New South Wales Sydney ACT Canberra 0 25 km 2004_12_0099.ai Figure 1 Location of the Nardoo and Mount Woowoolahra Inliers and simplified regional geology (modified from Cooper et al. 1975). Quarterly Notes 3 Adelaidean rocks 1596 +_ 3 Post-folding granite intrusions 1591 +_ 5 (including Mundi Mundi type granites) Texas Bore gneissic leucogranite (Euriowie Block) Dalnit Bore Metasediments <1642_ +_ 5 Bijerkerno Metasediments <1656_ +_ 5, <1657_ +_ 4 King Gunnia Calc-silicate Member Cartwrights Creek PARAGON GROUP Metasediments SUNDOWN GROUP _<1670 to 1680 Hores Gneiss Silver King 1686 +_ 3 Formation 1689 +_ 5 Freyers Metasediments <1780 Parnell Formation 1693 +_ 5, >1676 +_ 7 Allendale Metasediments BROKEN HILL GROUP <1691_ +_ 3 Ettlewood Calc-silicate Member Rasp Ridge Gneiss 1682 +_ 3 Himalaya Formation _<1710 to 1700 >1690 _+ 11 Cues Kyong Formation Formation (Euriowie Alders Tank REDAN SUB-BLOCK Block) Formation Alma Gneiss Farmcote Gneiss _ 1704 +_ 3 THACKARINGA GROUP >1704 + 3 Lady Brassey Formation <1705_ +_ 5 _<1710, >1704_ +_ 3 Mulculca Formation Thorndale Composite Gneiss Ednas Gneiss Clevedale Migmatite Redan Gneiss 1704 Age in million years 2004_12_0096 Figure 2 Stratigraphic subdivision of the Willyama Supergroup within the Broken Hill and Euriowie Blocks as established by the Geological Survey of New South Wales. Geochronology from Page, Stevens et al. (2000), Stevens (2000) and Page et al. (2005). Modified from Stevens and Barron (2002). 4 January 2006 Prograde deformation associated with the Olarian Orogeny is Veevers 2000) and during the Delamerian Orogeny, at about defined as two events — 1D and D2. D1 deformation produced 520 Ma (Harrison & McDougall 1981). Further retrogression may nappe-style folds (F1), which caused overturning of parts of have occurred during the Kanimblan/Alice Springs Orogeny at the stratigraphic succession. These folds have an associated about 350 to 325 Ma (Scheibner & Basden 1998). axial planar foliation, S1, defined by prograde metamorphic Adelaidean rocks unconformably overlie the Willyama minerals, which is mostly parallel to bedding.