Territory Stories

Pine Creek orogen : field excursion guide. Chief Government Geologists Conference, 28 April - 2 May 2003

Details:

Title

Pine Creek orogen : field excursion guide. Chief Government Geologists Conference, 28 April - 2 May 2003

Creator

Ahmad, M; Lally, JH; Ahmad, M; Lally, JH

Issued by

Northern Territory Geological Survey; Northern Territory Geological Survey

Collection

E-Publications; E-Books; PublicationNT; NTGS Record; Australia 1:250 000 Geological Map Series Pine Creek SD5208

Date

2003; 2003

Location

Australia 1:250 000 Geological MapPine Creek SD5208; Australia 1:250 000 Geological MapPine Creek SD5208

Notes

Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System; Made available via the Publications (Legal Deposit) Act 2004 (NT)

Language

English

Subject

Geology; Pine Creek Orogen

Publisher name

Northern Territory Government; Northern Territory Government

Place of publication

Darwin

Series

NTGS Record; Australia 1:250 000 Geological Map Series Pine Creek SD5208

Volume

2003-003

File type

application/pdf

ISBN

724570608; 0724570608

ISSN

1443-1149; 1443-1149

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government; Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/; https://creativecommons.org/licenses/by/4.0/

Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/82420 [GEMIS]; https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/82420

Parent handle

https://hdl.handle.net/10070/794266; https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/82420

Citation address

https://hdl.handle.net/10070/794285

Page content

20 (LMS), upper-mine (UMS) and hanging-wall sequences (HWS) by Geopeko geologists (Eupene et al 1975) during the exploration phase and this terminology is still in use at the mine. Quartz-feldspar-tourmaline pegmatite intruded mine sequence rocks after formation of the schistosity, but before mineralisation, and this has been dated at 1847 1 Ma (Annesley et al 2002) An important feature is the presence of thrust faults at a low angle to bedding and schistosity, which produced zones of strain slip cleavage and chevron folding that postdate the main schistosity. These structures have acted as conduits during mineralisation (Savory 1994). No.1 orebody The No.1 orebody within the LMS is confined to massive chlorite schist and lenticle schist, the latter being characterised by aligned lenticular nodules of chlorite. In this lower mine unit, chert and chert breccia are also present and both may contain some mineralisation. The UMS is about 500 m thick and has been altered to quartz-chlorite rock in the mineralised zone. Graphitic schist within the central disturbed zone hosts high-grade uranium mineralisation (>1% U3O8). A U-Pb isochron on pitchblende gives an age of 1737 20 Ma for the Ranger uranium mineralisation (Ludwig et al 1987). This is considerably older than those obtained from other uranium deposits (Jabiluka, Nabarlek and Koongarra), which are in the range 1614-1650 Ma (Maas 1989). Within the No.1 orebody, ore-grade mineralisation is confined to a discrete synformal structure, formed as a result of the thinning of carbonates associated with thrusting of mine sequence over footwall sequence. In the synformal structure, there are two styles of mineralisation (Kendall 1990). The first type occurs as veins averaging 1% U3O8 and is recognisable by intense brecciation and chloritisation within the upper mine sequence. The second type is patchy in the lower and upper mine sequences and averages 0.15% U3O8. Uraninite and pitchblende are the major ore minerals of both styles, but coffinite and brannerite are also present as minor phases (Kendall 1990, Savory 1994). Minor gold is present. Uranium mineralisation is accompanied by pervasive chloritisation, with sericitisation and hematitisation. No.3 orebody The No.3 orebody lies 1500 m to the north along strike from the No.1 orebody. The UMS is a monotonous succession of thinly laminated quartz-chlorite schist containing a few thin (<1 m thick) chert bands. LMS rock types include banded chert, chloritic Ranger 1 No.1 V V V V V V V V V Mamadawerre Sandstone Pegmatite Upper Cahill Fm Lower Cahill Fm - metapelite Lower Cahill Fm - carbonate Namambu Complex Ranger 1 No.3 0 500 1000 2000 3000 m Ranger 1 No.5 Ranger 1 No.2 Ranger 1 No.4 Steeply dipping normal fault Low angle reverse fault V N Pit outline Airborne radiometric anomaly To Jabiru To Jabiru Figure 13. Surface geology of the area surrounding the Ranger Uranium Deposits.