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

1 1 i n w e a t h e r e d o u t c r o p s . I n m a n y w e a t h e r e d o u t c r o p s , a b i o t i t e - r i c h p h a s e , w h i c h i s s o m e t i m e s p o r p h y r i t i c , s h o w s a s t r o n g , n o r t h w e s t - t r e n d i n g s t e e p f o l i a t i o n . F r e s h o u t c r o p s s h o w l i t t l e o r n o f o l i a t i o n a n d i t i s u n c l e a r i f t h e f o l i a t i o n h a s b e e n s t r o n g l y e n h a n c e d b y w e a t h e r i n g , o r i f t h e r e i s a s t r o n g l y f o l i a t e d p h a s e t h a t i s p r e f e r e n t i a l l y w e a t h e r e d . P e g m a t i t e s a r e a b u n d a n t t h r o u g h o u t t h e a r e a , b u t m o s t a r e t o o s m a l l t o d i s t i n g u i s h o n t h e m a p . T h o s e i n t h e s o u t h a r e t y p i c a l l y r i c h i n t o u r m a l i n e . T h e g r a n i t e s i n t r u d e a m p h i b o l i t e n e a r t h e U t o p i a t a n t a l i t e p r o s p e c t , b u t o t h e r w i s e t h e r e l a t i o n s h i p w i t h o t h e r u n i t s i s u n k n o w n . T h e g r a n i t e s t y p i c a l l y h a v e a l o w t o m o d e r a t e ( u p t o 1 0 0 0 x 1 0 - 5 S I s u s c e p t i b i l i t y ) m a g n e t i c r e s p o n s e . T a b u l a r b o d i e s o f f r e s h l a y e r e d c a l c - s i l i c a t e r o c k a r e p r e s e n t w i t h i n t h e g r a n i t o i d a b o u t 4 k m e a s t - n o r t h e a s t o f ne w B o r e . T h e c a l c - s i l i c a t e r o c k s a r e c o m p o s i t i o n a l l y v a r i a b l e a n d i n c l u d e f e l s i c , e p i d o t e - r i c h a n d a m p h i b o l e - r i c h v a r i e t i e s . F e l s i c r o c k s a r e r i c h i n p l a g i o c l a s e a n d q u a r t z , w i t h l e s s e r e p i d o t e , t i t a n i t e , a c t i n o l i t e a n d c l i n o p y r o x e n e . T h e s e a r e i n t e r l a y e r e d w i t h r o c k s t h a t a r e r i c h i n g r o s s u l a r g a r n e t , t o g e t h e r w i t h v e r y e p i d o t e - r i c h r o c k s t h a t c o n t a i n t h e a s s e m b l a g e e p i d o t e , p l a g i o c l a s e , t i t a n i t e , c l i n o p y r o x e n e , g r o s s u l a r a n d q u a r t z . H o r n b l e n d e a m p h i b o l i t e , w i t h c o m m o n t i t a n i t e a n d c o a r s e p h e n o c r y s t s o f p l a g i o c l a s e , m a y h a v e a m e t a - i g n e o u s o r i g i n . T h e t w o m a i n o u t c r o p s ( 4 3 3 4 0 0 m e 7 5 5 3 7 6 3 m n, 4 3 2 3 0 0 m e 7 5 5 4 0 0 0 m n) b o t h h a v e a s i m i l a r n o r t h w e s t e r l y t r e n d a n d m a y b e l i n k e d b e n e a t h c o v e r . gi v e n t h e c a l c - s i l i c a t e c o m p o s i t i o n o f t h e r o c k , i t i s m o s t l i k e l y a l a r g e r a f t o f m e t a s e d i m e n t a r y c o u n t r y r o c k . I t h a s m i n e r a l o g i c a l s i m i l a r i t i e s t o t h e a m p h i b o l i t e n e a r U t o p i a t a n t a l i t e p r o s p e c t a t 4 4 4 8 0 0 m e 7 5 4 1 7 0 0 m n a n d m a y h a v e a s i m i l a r o r i g i n . T h i s i s a l s o i n d i c a t e d b y s i m i l a r U - pr e dom i na nt r a di om e t r i c s i gn a t ur e s . P r e l i m i na r y S H rI M P U - P b zircon g e o c h r o n o l o g i c a l d a t a ( J C l a o u e L ong , ge oc i e nc e A us t r a l i a ) i ndi c a t e s t ha t t he M ol l i e gr a ni t e C om pl e x i nt r ude d dur i ng t he S t r a ngw a ys e ve nt . u ndi v ide d gr anitoid r ocks (LP g) ne a r t he c e nt r a l n or t he r n bor de r of W ood gr e e n, t he gr a nt B l uf f F or m a t i on ove r l i e s a m e di um - gr a i ne d, e q ui gr a nul a r , l e uc oc r a t i c m us c ovi t e gr a ni t e . T hi s gr a ni t e i s e f f e c t i ve l y non- m a gne t i c . M os t out c r ops a r e s t r ongl y w e a t he r e d. T he gr a ni t e i s w hi t e i n c ol our a w a y f r om t he unc onf or m i t y , but i s not a bl y r e dde ne d w i t hi n t e ns of m e t r e s of t he unc onf or m i t y s ur f a c e . S i m i l a r gr a ni t e on t he s out he r n m a r gi n of B A rroW C reeK i nt r ude s t he L e da n S c hi s t ( H a i ne s et al 1991) . S e ve r a l l ow out c r ops o f de e p l y w e a t he r e d a nd f e r r ugi ni s e d ( but no n- m a gne t i c ) m e di um - gr a i ne d e qui gr a nul a r gr a ni t e a r e f ound a r ound 400800m e 7540800m n, s out h of M ount H a r pe r . A r ound 444592m e 7532298m n, w e a kl y f ol i a t e d pi nk m us c ovi t e - be a r i ng l e uc oc r a t i c m i c r ogr a ni t e i s ove r l a i n by ge or gi na B a s i n r oc ks . I t i s a l m os t non- m a gne t i c ( m a xi m um s us c e pt i bi l i t y 66 x 10 - 5 S I ) , w i t h a m ode r a t e r a di om e t r i c r e s pons e . A t f our l oc a l i t i e s ( 429772m e 7517459m n, 432000m e 7517000m n, 434900m e 7515400m n, 433600m e 7515200m n) , s m a l l f ol i a t e d gr a ni t oi d bodi e s i nt r ude t he de l ny M e t a m or phi c s . T he e a s t e r nm os t of t he s e out c r ops m a y be s l i ght l y m a gne t i c ; t he ot he r s a r e non- m a gne t i c . T he r oc ks a r e s t r ongl y l a ye r e d a nd, i n pl a c e s , m i gm a t i t i c , w i t h di s c r e t e bi ot i t e - r i c h a nd l e u c oc r a t i c z one s . P e t r ogr a phi c e xa m i na t i on shows significant deformation, recrystallisation and epidote a l t e r a t i on. A n u m b e r o f o u t c r o p s o f w e a t h e r e d g r a n i t e a r e p r e s e n t t o t h e w e s t o f M o u n t S k i n n e r t r i g o n o m e t r i c s t a t i o n a n d n e a r K u n o t h K n o b . M o s t a r e m e d i u m g r a i n e d , l e u c o c r a t i c a n d non-magnetic. A small, relatively fresh outcrop of fine to m e d i u m b i o t i t e g r a n i t e i s p r e s e n t a t 4 4 1 6 4 8 m e 7 5 3 3 6 3 1 m n. T h i s r o c k i s n o m o r e t h a n w e a k l y m a g n e t i c ( m a x i m u m s u s c e p t i b i l i t y 1 8 8 x 1 0 - 5 S I ) , a l t h o u g h m u c h o f t h e u n e x p o s e d b a s e m e n t i n t h e v i c i n i t y ( i n t e r p r e t e d a s L P g w 3 ; s e e a b o v e ) a p p e a r s t o b e h i g h l y m a g n e t i c . I t i s p o s s i b l e t h a t a l l t h e s e g r a n i t e s b e l o n g t o t h e W o o d g r e e n gr a n i t e C o m p l e x , b u t p e n d i n g m o r e d e t a i l e d s t u d i e s , t h e y r e m a i n u n d i v i d e d . gr a n i t e b a s e m e n t ( e s s e n t i a l l y n o n - m a g n e t i c ; s e e Geoph y sic s) h a s a l s o b e e n i n t e r s e c t e d b e n e a t h ge o r g i n a B a s i n s e d i m e n t a r y r o c k s i n d i a m o n d d r i l l h o l e s C M S 2 , C M S 3 a n d C M S 4 . ultramafic intrusive rock (px) A 3 0 m - di a m e t e r c i r c ul a r body of c oa r s e - gr a i ne d pyr oxe ni t e i s pr e s e nt w i t hi n t he de l ny M e t a m or phi c s a t 431 178m e 7517459m n a nd i s i nt e r pr e t e d a s a pi pe - l i ke i nt r us i on. T he r oc k ha s l a r ge l y r e c r ys t a l l i s e d t o s e c onda r y m i ne r a l s , but a ppe a r s t o ha ve c om pr i s e d or t hopyr oxe ne , c l i nopyr oxe ne , magnetite and possibly olivine. Abundant, late fibrous Figu re 1 1 . W oodg r e e n gr a ni t e C om pl e x ( L P gw 5 ) . T ypi c a l e xpos ur e of da r k por phyr i t i c pha s e . 433994m e 7517 894m n, 4 km w e s t - nor t hw e s t of U gna da B or e .