Technical papers Stratigraphic revision of the Warrawoona and Gorge Creek Groups in the Kelly greenstone belt, Pilbara Craton, Western Australia by L. Bagas1 variable than previously thought (Van Kranendonk et al., 2002). The Abstract following review and reinterpret- ation of the stratigraphy of the Kelly Mapping in the Kelly greenstone belt in the eastern part of the East greenstone belt is based on mapping Pilbara Granite–Greenstone Terrane of the Pilbara Craton indicates that and geochronology resulting from the stratigraphy of the Warrawoona Group requires significant revision. the National Geoscience Mapping Four stratigraphic revisions are proposed. The Warrawoona Group now Accord (NGMA) projects on the includes the redefined Salgash Subgroup and the newly defined Kelly SPLIT ROCK * (Bagas and Van Subgroup. The felsic volcanic rocks of the c. 3325–3320 Ma Wyman Kranendonk, in prep.), MOUNT EDGAR Formation conformably overlie the Euro Basalt and are now included in (Williams and Bagas, in prep.), and the Warrawoona Group. The 3324 ± 4 Ma Kelly porphyry, previously NULLAGINE (Bagas, in prep.) 1:100 000 thought to be a felsic volcanic interbed in the Euro Basalt, is now sheet areas. recognized as intruding the Euro Basalt and is associated with the overlying Wyman Formation. The Charteris Basalt, previously included in the Gorge Creek Group, is now included with the Kelly Subgroup and it conformably overlies the Wyman Formation. The redefined East Pilbara Granite– Warrawoona Group is unconformably overlain by sedimentary rocks of Greenstone Terrane the c. 3308 Ma Budjan Creek Formation and dominantly clastic sedimentary rocks of the 3240–2940 Ma Gorge Creek Group (locally The EPGGT is characterized by large redefined to exclude the Charteris Basalt). ovoid granitoid complexes forming domes that are surrounded by KEYWORDS: Archaean, Pilbara Craton, stratigraphy, East Pilbara synformal greenstone belts or Granite–Greenstone Terrane, Kelly greenstone belt. unconformably overlain by volcanic and sedimentary rocks of the Fortescue Group (Fig. 2). The greenstone belts commonly dip at moderate to steep angles away from granitoid complexes, and are typically metamorphosed to greenschist facies, although higher grades are reached near the Introduction granite–greenstones of the Kelly complexes. greenstone belt form part of the The Archaean Pilbara Craton in c. 3655–2830 Ma East Pilbara Table 1 summarizes the former and the northwest of Western Granite–Greenstone Terrane current stratigraphic nomenclature Australia contains well-exposed (EPGGT) of the northern Pilbara of the EPGGT, and Table 2 shows granite–greenstones that are Craton (Hickman, 2001; Fig. 1). the geochronological data for the unconformably overlain by volcanic Kelly greenstone belt. and sedimentary rocks of the Hickman (1983, 1984) provided a c. 2770–2400 Ma Hamersley Basin, regional lithostratigraphic which around the Kelly greenstone interpretation of the EPGGT based belt are part of the 2770–2630 Ma on 1:250 000-scale reconnaissance Stratigraphy of the Kelly Fortescue Group (Trendall, 1990; geological mapping during the greenstone belt Thorne and Trendall, 2001). The 1970s. Subsequent investigations broadly confirmed the continuity The southern part of the Kelly 1 [email protected] between greenstone belts of the greenstone belt outcrops between * Capitalized names refer to standard 1:100 000 EPGGT, but have also shown that the Corunna Downs Granitoid map sheets. the greenstones are more laterally Complex (CDGC) to the west and 53 Geological Survey of Western Australia 2001–02 Annual Review 20° 117° 118° 119° 120° 121° INDIAN OCEAN ? ? 100 km TERRANE WEST PILBARA GRANITE–GREENSTONEZONE 21° MOUNT CENTRAL PILBARA TECTONIC EDGAR WPGGTMB GRANITOID TERRANE COMPLEX MB EAST PILBARA GRANITE–GREENSTONE EPGGT Mosquito Creek Basin 22° Figure 2 LB132a 25.09.02 Mesoproterozoic–Phanerozoic rocks MB Mallina Basin LOCATION MAP Hamersley Basin GGT Granite–greenstone terrane MAP AREA Terrane and/or tectonic zone boundary PILBARA Northern Pilbara Inlier CRATON CAPRICORN OROGEN Mallina Basin YILGARN Greenstone CRATON PERTH Granitoid 500 km Figure 1. Regional geological setting of the East Pilbara Granite–Greenstone Terrane the Fortescue Group to the east, and were emplaced approximately with the Euro Basalt and Wyman the northeastern part of the belt lies contemporaneously with felsic Formation in the Kelly Subgroup between the McPhee Dome and the volcanic rocks of the Wyman of the Warrawoona Group. Mount Edgar Granitoid Complex Formation and the Budjan Creek (Fig. 2). In both areas the belt Formation (Bagas et al., 2002). Another change not shown in comprises dominantly greenschist- Table 1 is that the 3324 ± 4 Ma facies volcanic rocks of the Salgash Kelly porphyry, previously and Kelly Subgroups of the Warrawoona Group thought to be a correlative of the Warrawoona Group. The Following detailed mapping and Panorama Formation (Hickman, Warrawoona Group is unconform- geochronological studies in the Kelly 1983) or a felsic volcanic interbed in ably overlain by the dominantly greenstone belt, three major the Euro Basalt (McNaughton et al., sedimentary sequences of the stratigraphic revisions have been 1993), is now recognized as Budjan Creek Formation (Noldart made for the Warrawoona Group intruding the Euro Basalt and and Wyatt, 1962; Lipple, 1975), (Tables 1 and 2): associated with the overlying which in turn is unconformably • The Kelly greenstone belt is now Wyman Formation. overlain by the dominantly clastic subdivided into the redefined sedimentary rocks of the Gorge Salgash Subgroup and the newly Salgash Subgroup Creek Group (Noldart and Wyatt, defined Kelly Subgroup. 1962; Ryan and Kriewaldt, 1964; • The felsic volcanic rocks of the The Salgash Subgroup, which Hickman and Lipple, 1978; c. 3325–3320 Ma Wyman formerly included the Towers Hickman, 1983), and the Fortescue Formation conformably overlie Formation, Apex Basalt, Panorama Group (Bagas and Van Kranendonk, the Euro Basalt and are now Formation, and Euro Basalt in prep.; Table 2). included in the Warrawoona (Hickman 1990), now comprises the Group. Apex Basalt (not in the Kelly Granitoid rocks in the CDGC (Fig. 2) • The Charteris Basalt, which was greenstone belt), Panorama mostly range in age from about 3317 previously included in the Gorge Formation, and Strelley Pool Chert to 3307 Ma (Nelson, 2001, 2002), and Creek Group, is now included (Table 1). 54 Technical papers Fortescue Group MOUNT Gorge Creek Group Ultramafic rock EDGAR Corunna Downs Granitoid Complex Budjan Creek Formation Boobina Porphyry Charteris Basalt C Wyman Formation Kelly Porphyry B Kelly Subgroup Euro Basalt 21°30' Mount Edgar Granitoid Complex Strelley Pool Chert Panorama Formation 3433±2 Ma Salgash Apex Basalt Subgroup Warrawoona Group Duffer Formation Talga Talga Subgroup 80 Spinaway Mine Anticline 5 60 D Point referred to in text 70 70 3324±4 Ma Geochronology site McPhee Way-up indicator, pillow structure Dome 15 Bedding, showing strike and dip Plunging anticline Plunging syncline 70 NULLAGINE 1: 100 000 map sheet 3317±2 Ma 65 3321±4 Ma Unconformity Copper Hills Fault c. 3346 Ma 3308±5 Ma Road 3325±3 Ma Track 3315±4 Ma NULLAGINE Figure 2. Geology of the Kelly greenstone belt 50 35 The Panorama Formation (Lipple, previously interpreted as the 1975) consists of felsic Towers Formation (Hickman, volcaniclastic rocks, with 1983). The Strelley Pool Chert subordinate felsic lavas and chert. consists of silicified chert, 120°00' The formation outcrops in the sandstone, and intraformational northeastern part of the Kelly breccia. The chert commonly has Kellys greenstone belt and is intruded by pseudomorphs after barite and granitoid rocks of the CDGC. It gypsum, and wavy to domal 3324±4 Ma was previously interpreted as the laminates with local conical 15 c. 3470–3465 Ma Duffer Formation stromatolites. The base of the unit 50 (Hickman, 1983). Three samples of shows evidence of relict 3325±4 Ma SPLIT volcanic breccia from the topography and differential Cookindina ROCK formation at Sandy Creek were erosion of the underlying Syncline dated at 3433 ± 2 Ma (Nelson, Panorama Formation, with a A 2000), and 3428 ± 4 and 3427 ± corresponding pinching and 3323±3 Ma 2 Ma (Nelson, 2001). These dates swelling of the chert along strike are consistent with the age of the and the filling of palaeochannels in 40 D E Panorama Formation elsewhere in places (Williams and Bagas, in the EPGGT. prep.). 30 N The Strelley Pool Chert (Lowe, Deposition of the Strelley Pool 1983) is a discontinuous unit Chert reflects a hiatus in volcanism 15 conformably overlying the recognized over 220 km across the 5 km Panorama Formation in the EPGGT (Van Kranendonk et al., northeastern part of the Kelly 2002) and is thought to represent LB140 07.10.02 greenstone belt, and was the final hydrothermal phase of 55 Geological Survey of Western Australia 2001–02 Annual Review Table 1. Stratigraphy of the East Pilbara Granite–Greentone Terrane. Units in the Kelly greenstone belt are here shown in bold, and the stratigraphic nomenclature for units outside of the belt is taken from Van Kranendonk et al. (2002) Hickman (1990) This paper Lalla Rookh Sandstone De Grey Group De Grey Group Lalla Rookh Sandstone (s) Budjan Creek Formation Pyramid Hill Formation (sh) Honeyeater Basalt Honeyeater Basalt Cleaverville Formation Paddy Market Formation (sh, BIF) Corboy Formation Corboy Formation Subgroup Pincunah Hill Formation Soanesville (sh, BIF) Gorge Creek Group Gorge Creek Group Subgroup Soanesville