Geology and mineral resources of the

Ahmad M and Munson TJ (compilers)

Northern Territory Geological Survey Special Publication 5

Chapter 6: Arnhem Province

BIBLIOGRAPHIC REFERENCE: Ahmad M and Munson TJ, 2013. Chapter 6: Arnhem Province: in Ahmad M and Munson TJ (compilers). ‘Geology and mineral resources of the Northern Territory’. Northern Territory Geological Survey, Special Publication 5.

Disclaimer While all care has been taken to ensure that information contained in this publication is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of its information. The Northern Territory of gives no warranty or assurance, and makes no representation as to the accuracy of any information or advice contained in this publication, or that it is suitable for your intended use. You should not rely upon information in this publication for the purpose of making any serious business or investment decisions without obtaining independent and/or professional advice in relation to your particular situation. The Northern Territory of Australia disclaims any liability or responsibility or duty of care towards any person for loss or damage caused by any use of, or reliance on the information contained in this publication. Arnhem Province Current as of May 2011

Chapter 6: ARNHEM PROVINCE M Ahmad and TJ Munson

INTRODUCTION %XNXGDO*UDQLWHDQGIHOVLFDQGPD¿FG\NHVDOVRLQWUXGH the formation. The Arnhem Province (previously known as Arnhem Inlier) The Grindall Formation is best exposed in the south forms basement to sedimentary and minor volcanic rocks RIWKH$UQKHP3URYLQFHDORQJWKHHDVWHUQÀDQNRIWKH of the McArthur Basin succession in northeastern Arnhem Coast Range and on some islands in BLUE MUD BAY1 Land (Figures 6.1, 6.2). The stratigraphic succession of (Figure 6.2c). Widespread clasts of Grindall Formation in the province is summarised in Table 6.1. It comprises the basal units of the McArthur Basin succession indicate pre-Nimbuwah Event metasedimentary and anatectic that the unit is probably extensive in the subsurface. The rocks of the Bradshaw and Mirarrmina complexes, and thickness of the unit is uncertain, as the base and top of the turbidite-dominated Grindall Formation. These are WKH IRUPDWLRQ DUH QRW GH¿QHG EXW +DLQHV et al (1999) possibly equivalent to the Cosmo Supergroup of the Pine estimated in excess of 1000 m. Island outcrops of the Creek Orogen (P4 interval of Ahmad 2000). Intruding these Grindall Formation are relatively unmetamorphosed and units are granites and coeval felsic volcanic rocks, which consist of rhythmically intercalated red-brown to grey- were divided by Budd et al (2002) into the Bradshaw and green sandstone and mudstone that have been tightly to Giddy suites. The ca 1865 Ma ‘Bradshaw Suite’ was an openly folded (Figure 6.3 7KH¿QHWRPHGLXPVDQGVWRQH informal name for intrusive rocks dominated by restite-rich, is thinly to thickly bedded and sandstone beds have sharp garnet-bearing S-type granite and migmatite that are now EDVHVEXWFRPPRQO\JUDGHXSZDUGVLQWR¿QHUOLWKRORJLHV included within the Mirarrmina and Bradshaw complexes. 3ODQDU DQG FURVVODPLQDWLRQV DUH SUHVHQW LQ WKH ¿QHU The ca 1835 Ma Giddy Suite includes the Bukudal, Giddy, tops of sandstone beds and water-escape structures are Garrthalala and Dhalinybuy granites and comprises Fe- also present. Contact- and regionally metamorphosed rich, relatively anhydrous fayalite-bearing granite. equivalent strata from mainland localities consist of metasandstone interbedded with phyllite and quartz- PALAEOPROTEROZOIC sericite schist. The metasandstone is apparently coarser than that on the islands and the beds are thicker or occur in Grindall Formation amalgamated packets (Haines et al 1999). The succession The Grindall Formation (originally Grindall is also more tightly folded, has common quartz veins and Metamorphics; Plumb and Roberts 1992) is a deformed exhibits a steeply dipping northwest-trending foliation and locally metamorphosed succession of interbedded LQ¿QHUOLWKRORJLHV+DLQHVet al interpreted the Grindall sandstone and mudstone (Figure 6.3), which is Formation as representing a turbidite succession, probably unconformably overlain by various units of the McArthur deposited in a rapidly subsiding marine basin, with Basin. The formation is intruded by granite of the mainland exposures in the west probably representing Bradshaw Complex, but may be contiguous with and a more proximal facies. partial protolith of the metamorphic component of the 1 Names of 1:250 000 and 1:100 000 mapsheets are in large and complex (Pietsch et al 1997a, Haines et al 1999). The small capital letters, respectively, eg BLUE MUD BAY, CALEDON.

131° 132°133° 134° 135° 136° 137°

12° Money Shoal Basin d a Darwin Arafura Basin Carpentaria Basin Jabiru b

13° Pine McArthur Basin Creek Orogen c

Alyangula NORTHERN 14° TERRITORY Carpentaria Basin Carpentaria Basin

A09-266.ai Palaeo-Mesoproterozoic Mesozoic-Cenozoic Archaean basins Palaeo-Mesoproterozoic 0 100 km Neoproterozoic-Palaeozoic Arnhem Province orogens Figure 6.1. Regional geology of Arnhem Province. NT geological regions from NTGS 1:2.5M geological regions GIS dataset. Boxes show locations of maps in Figure 6.2.

Geology and mineral resources of the Northern Territory 6:1 Special publication 5 Arnhem Province

acARNHEM GOVE KOOLATONG BLANE

McArthur Nhulunbuy Basin Carpentaria Basin

ARNHEM GOVE BLUE MUD BAY BAY BLUE MUD BAY BICKERTON

0 25 km

DURABUDBOI CALEDON

d Carpentaria Basin Fault

Gwakura Fault

Fault

Fault

Ranges Fault ?

Fault Ritarango

Gali

Frederick

? Mitchell ?

Donydji Fault

? BLANE GREY

?

Range

Fault ?

Fault Coast 0 50 km

Fault

Sheridan Range

Fault BLUE PORT Bath

MUD BAY LANGDON Koolatong Lela

0 50 km Mitchell-Flinders Fault Normal High-angle Thrust Belt fault reverse fault Fault, inferred

MIRRNGADIA MITCHELL b RANGES Arafura Basin

Palaeoproterozoic 1:100 000 mapsheet Bukudal Granite Giddy Granite McArthur Giddy Suite 1:250 000 mapsheet Basin Garrthalala Granite

Dhalinybuy Granite Location of Figure 6.7 ARNHEM BAY Mirarrmina Complex Melville Bay Metamorphics Drimmie Head Granite Bradshaw Complex Undivided Bradshaw Complex

Grindall Formation

Arnhem Province (under shallow Cenozoic cover) FLEMING KOOLATONG 0 10 km

A09-267.ai Figure 6.26LPSOL¿HGJHRORJ\RI$UQKHP3URYLQFHRYHUODLGRQ17*60JHRORJLFDOUHJLRQV*,6GDWDVHW6HHFigure 6.1 for locations of maps and legend for geological regions. (a–c) Outcrop maps derived from GA 1:1M geology GIS dataset. (d) Principle faults in eastern Arnhem /DQGDUHDLQWHUSUHWHGIURPPDSSLQJDQGJHRSK\VLFDOGDWDDQGORFDWLRQRI0LWFKHOO)OLQGHUV7KUXVW%HOW PRGL¿HGIURP5DZOLQJV 

Geology and mineral resources of the Northern Territory 6:2 Special publication 5 Arnhem Province

A minimum age for the Grindall Formation is Bradshaw Complex. The Melville Bay Metamorphics in provided by a U-Pb SHRIMP zircon date of 1837 ± 4 Ma the north comprises granulite-facies rocks, whereas the for the Bukudal Granite which intrudes the formation. undivided Bradshaw Complex to the south is mainly of The Grindall Formation is lithologically similar to and is amphibolite-facies grade. The protolith for the Bradshaw tentatively correlated with the Burrell Creek Formation Complex is at least partially represented by the Grindall (Finniss River Group) of the PCO; this unit overlies the Formation, which outcrops in BLUE MUD BAY to the Gerowie Tuff, which which has a SHRIMP U-Pb zircon south (Haines et al 1999). age of 1863 ± 3 Ma (Lally and Worden 2004). The Bradshaw Complex is intruded by Giddy Suite granites and by dykes and sills of microgranite and Bradshaw Complex dolerite. It is overlain by the Spencer Creek Group of the McArthur Basin, and by Cretaceous and Cenozoic The Bradshaw Complex comprises a continuum of deformed sedimentary rocks and laterite. The complex has been granite, granitic gneiss, migmatite and paragneiss, and is given a peak metamorphic age of 1867 ± 12 Ma, on the poorly exposed in northeastern and eastern basis of SHRIMP U-Pb zircon dating of a sample of (Figures 6.2a, 6.4). Several informal subdivisions of the Drimmie Head Granite (Rawlings et al 1997), and this complex were recognised by Plumb and Roberts (1992) corresponds to an interval of regional deformation and DQG0DGLJDQDQG5DZOLQJV  ZKLFKZHUHVLPSOL¿HG metamorphism (Nimbuwah Event) in the Pine Creek by Rawlings et al (1997) into three units: the Melville Bay Orogen. A broad span of post-peak and retrograde Metamorphics, Drimmie Head Granite and undivided metamorphism from 1855 to 1845 Ma is indicated by

Unit /Age Lithology Relationships Diagnostic Features ARNHEM INLIER Garrthalala *UDQLWHPHGLXPWR¿QHJUDLQHGSRUSK\ULWLF Intrudes Bradshaw Complex, coeval with K-feldspar megacrysts; fayalite- Granite (P5) massive, distinctive reddish brown weathered Bukudal Granite. Intruded by 1710 Ma bearing. White xenoliths of 1833 ± 3 Ma surface, composed of quartz, K-feldspar, rhyolite dykes. thermally metamorphosed SODJLRFODVHID\DOLWHDQGELRWLWH¿QHWRPHGLXP Bradshaw Complex. grained white granite xenoliths. Bukudal Granite Granite, massive, white to pink, equigranular, Intrudes Bradshaw Complex, coeval Reddened spherical inclusions; (P5) medium- to coarse-grained, composed of quartz, with Garrthalala Granite. Intruded by fayalite-bearing. 1837 ± 4 Ma K-feldspar, plagioclase, biotite and fayalite; ca 1710 Ma rhyolite dykes. locally sheared. Dhalinybuy Granite, pink to green, medium- to coarse- Inferred to intrude the Bradshaw K-feldspar megacrysts; localised Granite (P5) grained, equigranular to porphyritic, composed of Complex; overlain unconformably by foliation and mylonite. quartz, K-feldspar and biotite; locally sheared and Spencer Creek Group. Intruded by foliated, local mylonite. dykes of Yanungbi Volcanics. Giddy Granite Granite, pink to grey, medium- to coarse- grained, Inferred to intrude the Bradshaw K-feldspar megacrysts; fayalite- (P5) massive, equigranular to porphyritic, composed Complex. Inferred to be intruded by bearing. 1836 ± 4 Ma of quartz, K-feldspar, plagioclase, biotite and Latram Granite (1712 ± 10 Ma). fayalite; locally sheared. undivided A continuum of amphibolite-facies gneiss, Intruded by Bukudal and Garrthalala Amphibolite-facies mineral Bradshaw PLJPDWLWHJUDQLWLFJQHLVVDQGJUDQLWH¿QHWR granites. assemblages. Complex coarse-grained, foliated to massive. Drimmie Head Leucogranite and granitic gneiss, medium- to Derived from and intruded into the /HXFRJUDQLWHPD¿FJUDQXOLWH Granite (P4) coarse-grained, massive to foliated, composed Melville Bay Metamorphics. enclaves. 1867 ± 12 Ma of quartz, garnet, plagioclase, cordierite and K -feldspar; abundant enclaves including psammitic and pelitic gneiss, calc-silicate KRUQIHOVDQGPD¿FJUDQXOLWH Melville Bay Banded granulite, alternate dark pelitic layers and Intruded by Drimmie Head Granite. Relict sedimentary layering; Metamorphics white felsic layers, medium- to coarse-grained granulite facies assemblages. (P4) with localised veins and pods of coarse-grained, garnetiferous leucogranite. Grindall 6DQGVWRQHUHGEURZQWRJUH\JUHHQ¿QHWR Oldest known component of the Arnhem Deformed and locally Formation (P4) medium grained, thin to thick bedded, graded, Inlier. Intruded by the granites of the metamorphosed turbidite interbedded with red-brown to grey-green Bradshaw Complex and Bukudal Granite. sequence. mudstone. MIRARRMINA INLIER Mirarrmina ‘Older’ component: metasedimentary gneiss, ‘Older’ high-grade metamorphic and Amphibolite facies assemblages; Complex (P4) migmatite, granite, minor cataclasite; mineral anatectic rocks intruded by ‘younger’ retrogressed along shear-zones assemblage - garnet, quartz, orthoclase, biotite, felsic and mafic dykes. Probably to greenschist facies. Garnet- plagioclase, cordierite and retrograde muscovite unconformably overlain by Dhunganda dominated. and sericite; commonly foliated. Formation (Donydji Group). ‘Younger’ component: porphyritic microgranite, rhyolite, dolerite, minor hybrid rock.

Table 6.1. Summary of stratigraphic succession of Arnhem Province (after Rawlings et al 1997, Haines et al 1999). P4–P5 terminology after Ahmad (2000).

Geology and mineral resources of the Northern Territory 6:3 Special publication 5 Arnhem Province ages determined from lower-grade parts of the complex magnetite, biotite and zircon. It is peraluminous, has (Rawlings et al 1997). a relatively narrow range in silica (68.19–73.92%) and is generally low in Fe O (0.57–4.88%). The granite 2 3 Melville Bay Metamorphics is massive for the most part, but local alignment of The Melville Bay Metamorphics occur in the northeast of K-feldspar crystals does occur. Minor shear zones and the Arnhem Province on Bremer Island and Wargarpunda extensive pegmatite zones are also present. The granitic Point near Nhulunbuy (Figure 6.2a). They are intruded gneiss is medium to coarse and can be distinguished by irregular pods and veins of leucogranite of the from the granite by the presence of orthopyroxene and Drimmie Head Granite (Rawlings et al 1997), and are blocky sillimanite. It contains abundant schlieren, as overlain by Quaternary sediments and alluvium. The ZHOODVPHWDVHGLPHQWDU\DQGPD¿FHQFODYHV (Rawlings metamorphics consist mostly of banded garnetiferous et al 1997). granulite with alternate dark pelitic layers, and white Pelitic enclaves comprise garnet, K-feldspar, felsic layers (Figure 6.5). The pelitic layers are medium- cordierite, sillimanite, quartz, and accessory minerals. to coarse-grained and contain cordierite, garnet, Calcsilicate and psammitic enclaves are equigranular, sillimanite, K-feldspar, biotite and accessory spinel, ¿QHJUDLQHGDQGPDVVLYHDQGDUHSHWURORJLFDOO\VLPLODU magnetite, ilmenite, zircon, plagioclase and monazite. to enclaves from the undivided Bradshaw Complex. Felsic bands comprise either garnet, quartz, plagioclase, 0D¿FHQFODYHVDUH¿QHWRPHGLXPJUDLQHGDQGFRQVLVWRI orthopyroxene, sillimanite, cordierite and K-feldspar, orthopyroxene, clinopyroxene, plagioclase (bytownite), with accessory magnetite, biotite, ilmenite, zircon and titanite and biotite (Rawlings et al 1997). spinel, or calcite, scapolite, quartz, clinopyroxene, The Drimmie Head Granite is a syn-metamorphic wollastonite, plagioclase, sphene with accessory zircon, leucogranite that was probably derived from the magnetite and monazite. These layers were referred to as inhomogeneous melting of a metasedimentary protolith ‘quartzite’ by Plumb and Roberts (1992), but are probably that included the Melville Bay Metamorphics (Rawlings better described as metapsammite and calcsilicate rock et al 1997). (Rawlings et al 1997). Pressure and temperature estimates for the Melville Bay Metamorphics have been determined to be in WKH UDQJHV ௘±௘ž& DQG ௘±௘ NEDU UHVSHFWLYHO\ (IR Scrimgeour, NTGS, pers comm in Rawlings et al 1997).

Drimmie Head Granite The Drimmie Head Granite is exposed as sheets and plutons around the Melville Bay area in the northeast of the Arnhem Province to the west of Nhulunbuy (Figure 6.2a). The granite intrudes the Melville Bay Metamorphics and is overlain by Cretaceous and Cenozoic sediments, and by Quaternary alluvium. It comprises garnetiferous leucogranite and granitic gneiss with abundant enclaves of granulite-facies Figure 6.4. Migmatite gneiss of Bradshaw Complex showing anastomosing leucosome development (GOVE, CALEDON: PHWDVHGLPHQWDU\DQGPD¿FURFNV7KHPDLQURFNW\SHLVD (53L 687100mE, 8590300mN, small island southeast of Mount medium to coarse leucogranite, which consists of quartz, Alexander). Sledge hammer is 1 m long. Photo courtesy of garnet, plagioclase, cordierite, K-feldspar and accessory DJ Rawlings (formerly NTGS).

Figure 6.3. Steeply dipping sandstone and mudstone beds at the Figure 6.5. Layered granulite of Melville Bay Metamorphics Grindall Formation type section on eastern Morgan Island (BLUE exposed on beach at Gove near NABALCO processing plant MUD BAY, BLANE: (53L 619500mE, 8510300mN). Width of (GOVE, GOVE: 53L 683600mE, 8652400mN). Lens cap is 5 cm in section is about 20 m. Photo courtesy of DJ Rawlings (formerly diameter. Photo courtesy of DJ Rawlings (formerly NTGS). NTGS).

Geology and mineral resources of the Northern Territory 6:4 Special publication 5 Arnhem Province

Undivided Bradshaw Complex granitoid basement; intrusive equivalents of the Donydji Undivided Bradshaw Complex forms an elongate northeast- Group; structurally intercalated strips of the Donydji and trending belt in the east of the Arnhem Province in CALEDON probably Parsons Range groups; and relatively young and GOVE (Figure 6.2a) and consists of amphibolite- dolerite dykes. This structural complex thus incorporates facies paragneiss, migmatitic gneiss, migmatite, granitic elements of the McArthur Basin as well as basement gneiss and granite (Rawlings et al 1997). It is intruded by rocks that are equivalent to those of the Arnhem Province. the Bukudal and Garrthalala granites of the Giddy Suite Rawlings et al (1997) further described the complex as (Budd et al 2002), and by dykes and sills of microgranite occupying the sole thrust zone of the Mitchell-Flinders and dolerite. Undivided Bradshaw Complex is overlain by Thrust Belt (Figure 6.2d), a “north-northeast-trending Cretaceous sedimentary rocks and by Cenozoic laterite. region of thrust duplexes and imbricate stacks, separated by Paragneiss occurs mostly as enclaves within steep oblique ramps”, extending from northwestern BLUE migmatitic gneiss, granitic gneiss and granite. There is MUD BAY to the Melville Bay area. This thrust belt is an apparent continuum between deformed paragneiss part of the Walker Fault Zone (see McArthur Basin) and

DQGPLJPDWLWLFJQHLVVGH¿QHGE\GLIIHUHQWGHJUHHVRI was formed during D2 (Plumb 1994), which is equivalent partial melting. Migmatitic gneiss is characterised by an to the ‘Post-Nathan Shortening’ event of Haines et al anastomosing compositional partitioning into leucosomes (1999). The age of this deformation is poorly constrained and melanosomes, and migmatite is mainly stromatic, between ca 1600 and ca 1430 Ma (Rawlings et al 1997). although some may be nebulitic. Granitic gneiss is All components of the Mirarrmina Complex, except the commonly deformed and contains abundant enclaves and younger dykes, have been overprinted by deformation schlieren. Enclaves are also common within migmatitic related to this event. Deformational products range from gneiss and granite, and include pelitic schist and gneiss, weak to intense cataclasite or mylonite, in which almost all and calcsilicate (Figure 6.6 SVDPPLWLFDQGPD¿F primary fabric has been destroyed. Basement rocks of the rocks. Granite is abundant in the complex and is mostly complex are presumed to be overlain unconformably by the light to dark grey, medium to coarse grained, massive, Donydji Group, although the contact is not exposed. and equigranular to porphyritic. Overall, the undivided Mirarrmina Complex basement rocks that are equivalent Bradshaw Complex exhibits a mineralogy characterised to the Bradshaw Complex comprise foliated metasedimentary by the presence of andalusite, sillimanite and cordierite, rocks and granite gneiss. The metasedimentary rocks suggesting that it formed under Buchan-style metamorphic include an amphibolite-grade granofels that has been locally conditions (see Hietanan 1967) of low to moderate pressure retrogressed to lower greenschist-grade quartz-sericite schist and high temperature. Paragneiss, migmatite and granite and phyllonite along shear zones. The granofels contains are intimately associated, suggesting that the complex mineral assemblages that are consistent with those of the formed by heterogeneous melting of a sedimentary protolith Bradshaw Complex to the east. Foliated gneiss and granite (Rawlings et al 1997). comprise porphyroblastic garnetiferous gneissic granite and granite gneiss, augen gneiss, banded gneiss and migmatite, Mirarrmina Complex and minor quartz monzonite and granodiorite. However, relationships between these rock types are obscured by poor The poorly exposed Mirarrmina Complex is distributed exposure. The garnetiferous gneissic granite is distinctly over a small area (<450 km2) along the western margin of the S-type and resembles that of the coeval Bradshaw Complex. Mitchell Ranges, centred on the Aboriginal community of Compositionally, the gneiss and granite are quite uniform, Donydji in southwestern ARNHEM BAY and northwestern consisting of microperthitic K-feldspar, quartz, biotite BLUE MUD BAY (Figures 6.2b, 6.7). Rawlings et al and garnet. Grainsize varies from medium to coarse, and (1997) and Haines et al (1999) described the complex as fabrics range from massive to foliated, and equigranular a composite unit comprising metamorphic and anatectic to porphyroblastic. Rawlings et al (1997) interpreted the mineralogy of these basement rock types as representing an aluminous sedimentary protolith, which probably included equivalents of the Grindall Formation to the southeast and the PCO succession to the west. Metamorphism of these basement rocks is presumed to be equivalent to the peak metamorphic event effecting the Bradshaw Complex to the east (Rawlings et al 1997), which corresponds in age to the Nimbuwah Event in the Pine Creek Orogen. The younger intrusive units of the Mirarrmina Complex include porphyritic rhyolite, megacrystic microgranite and dolerite/gabbro. Rhyolite and microgranite form the more resistant outcrop and occur as vertical dykes intruding the older gneiss and metasedimentary rocks. They are probably stratigraphically equivalent to the nearby Fagan Volcanics Figure 6.6. Calcsilicate enclave within granitic gneiss of (Donydji Group). undivided Bradshaw Complex, cut by late stage pegmatite veins (GOVE, CALEDON: 53L 683300mE, 8586300mN; one of the SHRIMP U-Pb geochronology of zircons of anatectic Three Hummocks, a group of small islands southeast of Mount basement rocks from the complex have yielded an Alexander). Photo: DJ Rawlings (formerly NTGS). interpreted metamorphic age of 1870 ± 8 Ma, similar to the

Geology and mineral resources of the Northern Territory 6:5 Special publication 5 Arnhem Province age of the Bradshaw Complex, whereas the younger felsic granite. It is exposed over a wide area in the east of the intrusive rocks are dated at 1705 ± 10 Ma, similar to the age Arnhem Province from BLANE to CALEDON, including of the Fagan Volcanics (Rawlings et al 1997). a number of offshore islands (Figure 6.2a). The granite contains quartz (35-45%), K-feldspar (microcline and Giddy Suite orthoclase) (35%), plagioclase (10%), biotite (5%) and garnet (10%), with minor fayalite, orthopyroxene, clinopyroxene The Giddy Suite granites were emplaced after the main DQG KRUQEOHQGH DQG DFFHVVRU\ ÀXRULWH VSLQHO PDJQHWLWH deformation and metamorphic event to effect the Arnhem zircon and rutile. Secondary minerals include sericite, Province and are essentially undeformed. They are muscovite, chlorite and epidote. The Bukudal Granite has correlated with the Cullen Supersuite in the PCO, but have an SiO range of 68.15–75.39% and is more felsic when 2 little associated mineralisation. The granites have undergone compared to the Garrthalala Granite. It is low in Fe O and 2 3 fractionation to a high level of Rb content that reaches about CaO and high in K O, when compared to the Giddy and 2 500 ppm at a SiO2 concentration of 75%. Two granites (Giddy Garrthalala granites, and to average I-type granites with Granite and ‘Caledon Granite’) were originally differentiated similar silica contents. In comparison to I-type granites, it by Dunnet (1965) and Plumb and Roberts (1992), but LV DOVR KLJK LQ 5E %D /D &H =U DQG *D $ VLJQL¿FDQW Rawlings et al (1997) revised this into four new units (Giddy, feature is the higher than normal Ga concentration, varying *DUUWKDODOD%XNXGDODQG'KDOLQ\EX\JUDQLWHV 7KH¿UVW from 20 to 28 ppm (average 25 ppm). three are essentially coeval, with indistinguishable SHRIMP Miarolitic cavities and granophyric intergrowths are U-Pb zircon ages in the range 1833–1837 Ma (Rawlings common in the Bukudal Granite and are indicative of et al 1997). The Dhalinybuy Granite is undated, but was high-level emplacement. Petrological and geochemical regarded by Rawlings et al as being probably comagmatic GDWDVKRZWKDWWKHJUDQLWHKDV$W\SHDI¿QLWLHV 5DZOLQJV (if not connected at depth) with the Giddy Granite. A et al 1997). minimum age for this granite of about 1710 Ma is given by an unconformable or nonconformable relationship with the Dhalinybuy Granite overlying Yanungbi Volcanics of the Spencer Creek Group The Dhalinybuy Granite is exposed as rounded tors and (basal McArthur Basin). These granites were all included in boulders of pink to green, medium to coarse, equigranular the Giddy Suite by Budd et al (2002). to porphyritic granite in a small area in eastern ARNHEM BAY (Figure 6.2a). It is inferred to intrude the Bradshaw Bukudal Granite Complex and is overlain by the Yanungbi Volcanics or Gove The Bukudal Granite intrudes the Bradshaw Complex and Sandstone of the Spencer Creek Group (McArthur Basin) LVDZKLWHWRSLQN¿QHWRFRDUVHHTXLJUDQXODUDQGPDVVLYH and by Cenozoic sediments. There are also numerous

135.5° 135.8° -12.6° Cenozoic sand, soil, alluvium

Gulbuwangay River Neoproterozoic–Cambrian Arafura Basin 40 Buckingham River Goulburn and Wessel groups Palaeoproterozoic McArthur Basin Balma Group

Parsons Range Group 15 Donydji Group FAULT FAULT Arnhem Province Mirarrmina Complex

85 Maidjunga River dip and strike of strata

FAULT 20 70 foliation, measured

FAULT foliation, vertical

FAULT 25 GALI fault river

70 FAULT road

DONYDJI RITARANGO 65 RANGES 55 5 -13°

0 5 10 km 5

KOOLATONG Koolatong River NORTHERN 10 TERRITORY

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MIRARRMINA A08-297.ai Figure 6.7*HRORJLFDOPDSRIWKH0LUDUUPLQD&RPSOH[DQGVXUURXQGV VLPSOL¿HGIURP3LHWVFKet al 1997b). Location shown in Figure 6.2d.

Geology and mineral resources of the Northern Territory 6:6 Special publication 5 Arnhem Province

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Geology and mineral resources of the Northern Territory 6:7 Special publication 5 Arnhem Province

Dunnet D, 1965. Arnhem Bay-Gove, Northern Territory map series explanatory notes, parts of SD 53-07, 08, 11, (First Edition). 1:250 000 geological map series 12. Northern Territory Geological Survey, Darwin. explanatory notes, SD 53-03, 04. Bureau of Mineral Pietsch BA, Rawlings DJ, Haines PW and Madigan TLA, Resources, Australia, Canberra. 1997b. Arnhem Bay-Gove, Northern Territory Haines PW, Rawlings DJ, Sweet IP, Pietsch BA, Plumb (Second Edition). 1:250 000 geological map series, KA, Madigan TLA and Krassay AA, 1999. Blue Mud SD 53-03, 04. Northern Territory Geological Survey, Bay, Northern Territory (Second Edition). 1:250 000 Darwin. geological map series explanatory notes, SD 53-07 (and Plumb KA, 1994. Structural evolution of the McArthur part of SD 53-08). Northern Territory Geological Survey, Bain, NT: in Hallenstein CP (editor) ‘Au st ralian Darwin and Australian Geological Survey Organisation, mining looks north – the challenges and choices.’ Canberra (National Geoscience Mapping Accord). 1994 AusIMM Annual Conference, Darwin Hietanan A, 1967. On the facies series in various types of 5–9 August 1994, Technical Program Proceedings. metamorphism. Journal of Geology 75, 187–214. The Australasian Institute of Mining and Metallurgy, Lally JH and Worden K, 2004. Geochronology in the Pine Melbourne, 139–145. Creek Orogen – new results from NTGS: in ‘Ann u al Plumb KA and Roberts HG, 1992. The geology of Geoscience Exploration Seminar (AGES) 2004. Record Arnhem Land, Northern Territory. Bureau of Mineral of abstracts.’ Northern Territory Geological Survey, Resources, Australia, Record 1992/55. Record 2004-001. Rawlings DJ, 2001. Tectonostratigraphy of the McArthur Madigan TL, and Rawlings DJ, 1994. Low-pressure Basin. 1:1 000 000-scale map. Northern Territory regional metamorphism in the Bradshaw Complex, Geological Survey, Darwin. northeast Arnhem Land, Northern Territory, Australia. Rawlings DJ, Haines PW, Madigan TLA, Pietsch BA, Geological Society of Australia, Abstracts 37, 260. Sweet IP, Plumb KA and Krassay AA, 1997. Arnhem Needham RS, Stuart-Smith PG and Page RW, 1988. Bay–Gove, Northern Territory (Second Edition). Tectonic evolution of the Pine Creek Inlier, Northern 1:250 000 geological map series explanatory notes, Territory. Precambrian Research, 40/41, 543–564. SD 53-03, 04. Northern Territory Geological Survey, Pietsch BA, Rawlings DJ and Haines PW, 1997a. Groote Darwin and Australian Geological Survey Organisation, Eylandt Region, Northern Territory. 1:250 000 geological Canberra (National Geoscience Mapping Accord).

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