Territory Stories

Woodgreen, Northern Territory : explanatory notes

Details:

Title

Woodgreen, Northern Territory : explanatory notes

Issued by

Northern Territory Geological Survey

Collection

E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series

Date

2007

Location

Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310

Map scale

1:100 000

Notes

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

Language

English

Subject

Geology; Georgina Basin; Arunta Region

Publisher name

Northern Territory Government; Northern Territory Government

Place of publication

Darwin

Edition

1st ed.

Series

Australia 1:100 000 Geological Map Series

File type

application/pdf

ISBN

9780724571321

ISSN

0811-6296

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government

License

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

Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]

Parent handle

https://hdl.handle.net/10070/794795

Citation address

https://hdl.handle.net/10070/794807

Page content

22 t he s he e t a r e a , i s i nt e r pr e t e d t o i ndi c a t e s ubs t a nt i a l vol um e s of c onc e a l e d gr a ni t e (not Woodgr e e n gr a ni t e com pl e x, a s out c r ops of t he s e uni t s a r e not a s s oc i a t e d w i t h Bougue r a nom a l y l ow s , t hus t he y a r e not a s f e l s i c a s t he c onc e a l e d body ). the hi ghe s t Bougue r gr a vi t y va l ue s a r e a s s oc i a t e d w i t h out c r oppi ng a nd i nt e r pr e t e d de l ny me t a m or phi c s a nd undi vi de d m e t a m or phi c r oc ks i n s out he r n Woodgreen. gEologIcAlhIStory the ol de s t ba s e m e nt i n Woodgreen c om pr i s e s m e t a s e di m e nt a r y a nd m e t a - i gne ous r oc ks of t he ar unt a re gi on. the ol de s t r oc ks a r e l i ke l y t o be t he pr e c ur s or m e t a s e di m e nt s t o t he ani r a me t a m or phi c s , de l ny me t a m or phi c s a nd ma pa t a gne i s s . the s e a r e l i ke l y t o be equivalent to either the 18101800 Ma Bonya Schist and de e p Bor e me t a m or phi c s (ong e va pa c ka ge of sc r i m ge our 2003) or the 18501820 Ma Lander package. A period of gr a ni t e i nt r us i on , pr oba bl y a c c om pa ni e d by m e t a m or phi s m , i s i nf e r r e d t o ha ve oc c ur r e d dur i ng t he ya m ba h eve nt a t 17801770 Ma, and included the intrusion of the Crooked H ol e gr a ni t e . exhum a t i on a nd e r os i on f ol l ow e d t he ya m ba h eve nt , w i t h de po s i t i on of qua r t z s a nd of t he ut opi a Q ua r t z i t e on t he e xhum e d ba s e m e nt . the 1 730 1 700 ma st r a n gw a ys or oge ny l e d t o r e gi ona l a m phi bol i t e - t o gr a nul i t e - f a c i e s m e t a m or phi s m , de f o r m a t i on a nd i nt r us i on of gr a ni t oi ds . H i gh- t e m pe r a t ur e , l ow - pr e s s ur e m e t a m or phi s m i n t he nor t he a s t e r n ar unt a re gi on a t t hi s t i m e ha s be e n a t t r i but e d t o m a gm a t i c a dve c t i on of he a t a s s oc i a t e d w i t h a m a nt l e - de r i ve d t he r m a l pe r t ur b a t i o n, r e s ul t i ng i n r e gi ona l a ur e ol e m e t a m or phi s m a c c om pa nyi ng c om pr e s s i ona l de f or m a t i on (sc r i m ge our et al 200 1 ). the Woodgr e e n gr a ni t e com pl e x i s l i ke l y t o ha ve be e n ge ne r a t e d by e xt e ns i ve c r us t a l melting during this event. No record of the 15901570 Ma Chewings Orogeny has yet been identified in Woodgreen, a l t hough s t udi e s i n s ur r oundi ng r e gi ons s ugge s t t he l i ke l y e xi s t e nc e of a t he r m a l a nd/ or upl i f t e ve nt i n t he a r e a a t t hi s time. Local ultramafic intrusion occurred at some time after r e gi ona l m e t a m or phi s m , but t he a ge of t hi s e ve nt i s poor l y c ons t r a i ne d. de pos i t i on i n t he ge or gi na Ba s i n w a s i ni t i a t e d a t around 800 Ma as part of a then more widespread entity, t he ce nt r a l i a n supe r ba s i n. H ow e ve r , t he e a r l i e s t hi s t or y of t he ba s i n i s not pr e s e r ve d i n Woodgreen. in t hi s l a t t e r a r e a , t he ol de s t e l e m e nt of t he ge or gi na de pos i t i ona l s uc c e s s i on i s t he Bok o For m a t i on, de pos i t e d dur i ng a r e gi ona l gl a c i a l episode, inferred to have occurred around 600 Ma. During a nd a f t e r i c e s he e t r e t r e a t , gl a c i a l de br i s w a s r e w or ke d by fluvial action and deposited as the Oorabra Arkose, overlying l oc a l r e l i c t s of pr oxi m a l t i l l (Bok o For m a t i on) a nd gl a c i a l l y e r ode d ba s e m e nt . a s ubs e que nt m a r i ne t r a ns gr e s s i on l e d t o t he de pos i t i on of t he el yua h , gr a nt Bl uf f a nd ce nt r a l mount st ua r t f or m a t i ons unde r s ha l l ow - m a r i ne a nd de l t a i c c ondi t i ons . dur i ng de pos i t i on o f t he ce nt r a l mount st ua r t For m a t i on, a bunda nt de t r i t us w a s c a r r i e d by r i ve r s f r om upl i f t e d r e gi ons t o t he nor t hw e s t s ync hr onous l y w i t h t e c t oni c c ont r ol of a c c om m oda t i on s pa c e i n f a ul t - c ont r ol l e d t r oughs . thi s t e c t on i c e ve nt i s br oa dl y c oe va l w i t h t he Pe t e r m a nn or oge ny . at l e a s t t w o m a r i ne t r a ns gr e s s i ons a r e r e c or de d w i t hi n t he Woodgreen a r e a dur i ng t he ca m br i a n. it i s l i ke l y t ha t de pos i t i on c ont i nue d e pi s odi c a l l y t hr ough t o t he m i d- or dovi c i a n, a s i n a dj a c e nt a r e a s , but t he r e c or d i s not pr e s e r ve d. com pr e s s i ona l de f or m a t i on a s s oc i a t e d w i t h t he al i c e spr i ngs or oge ny c om m e nc e d a t a r ound 450440 ma (sc r i m ge our a nd ra i t h 200 1 , H a i ne s et al 200 1 ). de f or m a t i on dur i ng t he al i c e spr i ngs or oge ny w a s dom i na t e d by w e s t - nor t hw e s t - t r e ndi ng, s out h- di ppi ng, hi gh- a ngl e r e ve r s e f a ul t s a nd s he a r z one s t ha t upl i f t e d ba s e m e nt t o t he s out h a nd l oc a l l y j uxt a pos e d ba s e m e nt a ga i ns t ge or gi na Ba s i n s e di m e nt a r y r oc ks . Fol di ng of t he ge or gi na Ba s i n oc c ur r e d dur i ng t hi s e ve nt , w i t h m onoc l i ne s de ve l ope d, a s s oc i a t e d w i t h s out h- s i de - up r e ve r s e f a ul t s . it w a s a t t hi s t i m e t ha t t he ce nt r a l i a n supe r ba s i n w a s s e gm e nt e d a nd t he ge or gi na Ba s i n be c a m e a s e pa r a t e e nt i t y . For e l a nd de pos i t i on c ont i nue d s ync hr onous l y w i t h t e c t oni s m , but t he r e c or d of s uc h s ynor oge ni c s e di m e nt a t i on i s not pr e s e r ve d i n Woodgreen. duc t i l e s he a r i ng of t he ba s e m e nt m a y ha ve be e n c om pl e t e d by t he e nd of t he de voni a n, a nd a l l de f or m a t i on i n t he al i c e spr i ngs or oge ny c e a s e d by t he e nd of t he ca r boni f e r ous . no r e c or d of e ve nt s be t w e e n t he l a t e Pa l a e oz oi c a nd ce noz oi c i s pr e s e r ve d i n Woodgreen; although the area i s l i ke l y t o ha ve unde r gone s l ow e r os i on w i t h s e di m e nt s t r a ns por t e d e l s e w he r e . dur i ng t he ce noz oi c , l oc a l s ubs i de nc e led to deposition within the lacustrine/fluvial TiTree Basin a nd w i t hi n br oa d t r i but a r y c ha nne l s t ha t dr a i ne d nor t hw e s t i nt o t he ba s i n f r om r e l a t i ve l y e l e va t e d a r e a s t o t he s out h and east. Deep weathering profiles and silcrete developed over flat and gently domed areas of basement. Alluvial fans de ve l ope d a r ound m a j or r a nge s c om pos e d of ge or gi na Ba s i n s e di m e nt a r y r oc ks . a r e ne w e d pha s e of e r os i on up t o t he pr e s e nt t i m e ha s l e d t o pa r t i a l di s s e c t i on of e a r l i e r ce noz oi c de pos i t s a nd l a ndf or m s . EconoMIcgEology Coppe r, l e ad, z inc In 1965, prospectors discovered widespread malachite and a z ur i t e - s t a i ne d, gr e y- gr e e n s i l t s t one a nd l oos e nodul e s containing chalcocite between 9.5 km and 3 km north of mount ski nne r t r i gonom e t r i c s t a t i on i n w ha t i s now r e c ogni s e d a s t he tops me m be r of t he ce nt r a l mount st ua r t For m a t i on (Figure21). Youles (1965) visited the area on be ha l f of t he nor t he r n te r r i t or y gove r nm e nt a nd c ol l e c t e d a grab sample that assayed 2.5% Cu. He optimistically e xt r a pol a t e d t he ge nt l y di ppi ng c upr i f e r ous i nt e r va l ove r a n a r e a of a t l e a s t 1 00 s qua r e m i l e s . an or i e nt a t i on s t udy by ke nne c ot t expl or a t i on e s t a bl i s he d t ha t s oi l s a m pl i ng w a s un r e l i a bl e i n l oc a t i ng s ur f a c e cu m i ne r a l i s a t i on. Wor k t he n c onc e nt r a t e d on s ubs ur f a c e e xpl or a t i on a nd s e ve n c os t e a ns w e r e bu l l doz e d across a strike length of 9.5 km. Host rocks were identified as r e duc e d s i l t s t one w i t hi n a t hi c k i nt e r va l of r e d- br ow n a r kos i c s a nds t one a nd s i l t s t one . mi nor l e ns e s of c ha l c opyr i t e i n t he s ha l l ow s ubs ur f a c e c or r e l a t e d t o t he m i ne r a l i s e d out c r op a nd visible mineralisation was generally confined to within 5 m of the surface. The highest value obtained from trench floor s a m pl i ng w a s 7200 ppm cu ove r 45 c m i n tr e nc h c. thr e e percussion holes (BH1 to 3) totalling 600 m were drilled, but the first two failed to reach their target depths because of water inflow. The highest metal intercept reported was