Geochemistry of Ground Waters From the Great Artesian Basin, Australia

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Journal of Hydrology, 126 (1991 ) 22 5-2 45 225

E l s e v i e r S c i e n c e P u b l i s h e r s B . V . , A m s t e r d a m

[2]

Geochemistry of ground waters from the Great

Artesian Basin, Australia

A . L . H e r c z e g , T . T o r g e r s e n b , A . R . C h i v a s c a n d M . A . H a b e r m e h l d

~Centre Jor Groundwater Studie s and C SI RO Division ~1" W ater Resources, Private Bag No. 2,

Glen Osmond, S.A. 5064, Austral ia

UDepartment of M arine Sciences, University of Connecticut, A veo ' Point, Gro wn, C T 06340, US A

~Research Schoo l o[" Earth Seiences, The Austral ian Nati onal University , G.P.O . Bo x 4, C anberra,

A.C .T . 2601, Austra l ia

dDivision o[" Co ntine ntal Geology, Bureau o [ M ine ral Resources, Ge ology and Geophysics,

G.P.O. B ox 378, Canberra, A.C .T. 2601, Austral ia

(Received 8 December 1989; accepted after revision 11 November 1990)

ABSTRACT

Herczeg, A.L., Torgersen, T., Chivas, A.R. and Habermehl, M.A., 1991. Geochemistry of ground waters

from the Great Artesian Basin, Australia. J. Hydrol., 126: 225-245.

Ground waters from the confined Lower Cretaceous-Jurassic aquifer of the Great Artesian Basin,

Australia (GAB) are characterised by Na-H CO 3 type waters throughout the eastern and central parts o fthe basin and Na-SQ-C1 type waters in the western part. Sodium and bicarbonate increase in concen-

tration from the northeastern margins to the southwestern discharge areas along the regional groundwater

flowlines. A mass-balance and equilibrium model for major dissolved species and stable carbon isotopes

of dissolved inorganic carbon show that the chemical trends observed are caused by mass transfer reactions

involving cation exchange of Na for Ca-Mg, carbonate dissolution and reactions between Na and kaolinite

to form Na-smectite. The stable carbon isotopic composition of dissolved inorganic carbon (DIC)

increases from values of about - 15%o near the basin margins to - 6%o in the interior of the basin. An

inverse relationship exists between 6~3C and DIC indicating addition of enriched carbon as the ground

waters move basinwards. A t2C-~3C mass balance indicates that the trend toward heavier 6~3C values

in the interior of the basin results from bacterial reduction of carbon dioxide to produce methane

rather than dissolution of, and equilibration with, carbona te minerals. The GAB aquifer system is

apparently open to CO~ which is the product of in situ anaerobic fermentation producing CO 2 enrichedin t3C.

The chemical evolution of the major dissolved species and carbon isotope distribution in the eastern and

central par ts of the GAB can then be envisaged as an initial pCO 2 up to several orders of magnitude above

atmospheric level is acquired within the recharge area by plant respiration and oxidat ion of organic matter

in the soil zone. Initially, silicate and carbonate minerals may dissolve, at least in some parts of the basin,

resulting in increased alkalinity, higher Ca and Mg concentrations, and a 6~3C concentrat ion of the DIC

of around - 12%0. Processes such as cation exchange of Na for Ca and Mg in addition to the removal of

some Na by reverse weathering which produces a Na smectite dominate in the interior of the GAB. The

chemistry of ground waters derived from the western recharge areas is controlled by evaporite dissolution

as indicated by very high CI/Br ratios.



2 2 6 A .L . H E R C Z E G E T AL.

I N T R O D U C T I O N

Ge oc h e m ic a l p r oc e s se s oc c u r r in g w i t h in gr ou n d w at e r s an d r e ac t ion s w i t h

aq u i f e r m in e r a l s h ave a p r o f ou n d e f f e c t on w at e r q u a l i t y . Th e r e f or e , t h e

e va lu a t ion o f t h e im p or t an c e o f su c h p r oc e s se s i s e s se n tia l i f gr ou n d w at e rr e s ou r c e s ar e t o b e p r o p e r ly d e v e l o p e d f o r h u m a n c o n s u m p t i o n a n d p a s to r a l

or m in in g ac t iv i t ie s . T h i s p ap e r in ve s t iga te s t h e p os s ib l e p h ys i c a l an d c h e m ic a l

p r oc e s se s a f f e c t in g t h e m aj or e l e m e n t an d s t ab le c ar b on i so t op ic c om p os i t ion

o f g r o u n d w a t e r s f r o m t h e G r e a t A r t e s ia n B a s i n ( G A B ) o f A u s tr a l ia .

T h e G A B i s l oc a t e d in t h e s e m i -ar id an d ar id p ar t s o f e a s t e r n A u s t r a l ia an d

u n d e r l i e s ab ou t 22 ( 1 .7 x 106 k m 2 ) o f t h e A u s t r a l ian c on t in e n t (F ig . 1 ). I t

i s a c on f in e d gr ou n d w at e r b as in c om p ose d o f aq u i f e r s in c on t in e n t a l

q u a r t z o s e s a n d s t o n e s w i t h c o n f i n i n g b e d s o f p a r t l y m a r i n e m u d s t o n e a n d

s i l ts t on e o f Tr ia s s ic , Ju r as si c an d C r e t ac e ou s age u p t o 30 00 m t h ic k ( F ig . 2 ) .R e c h ar ge o f gr ou n d w at e r oc c u r s m a in ly in t h e e as te r n m ar g in a l zon e w i t h

som e m in or in p u t f r om t h e w e s te r n m ar g in . P r e c ip i t a t ion in t h e r ec h ar ge ar e a

ave r age s 6 0 0 m m ye ar ~ an d i s lar ge ly s e ason a l w i t h r e lat ive ly d r y w in t e r s

~ ' ~ ~ ~ ~' ~'

- . . . . .

• t ' f

Fig . 1 . Locat ion o f the Great Ar te s ian Bas in , Aus tra l ia ( ins e t ) and inferred f low l ines bas ed on poten-

t iom etr ic s ur faces ( a f ter Haberm ehl , 1980 ) . Recharge occurs m os t ly on the eas tern and nor theas tern

m arg ins s upp ly ing water to the wes tward and s outhward f lowing reg im es . Som e fur ther recharge occurs

in the wes tern m arg ins . D i s charge v ia upw ard l eakage takes p lace throug hout the bas in through ar te s ian

s pr ings and by d i f fus e d i s charge in the s outhwes tern m arg ina l par t o f the bas in .



GREAT ARTESIA.N BASIN GEOCHEMISTRY 227

- . ~

~ o

~ Cretoceou aquifer

~ C o n fl n L qg b a d - - - - B o u n d e r b e t w e e n c o n fi n e d a q u if e r s P o t O M l O O ~ f r l curface Jurassic aqulf orJ~ Oand conr~mmg l~ds

- -- -- Walertable .. .. Pofont/omotr/C urface duras 4C qul~g,/970durasslc aquifer

Fault o Petroleum exp/orat/on o//

I I B . . . . . , . . . . . T o p o ~ r op h . . . . . f o u r { re ) o b eY * M S L

Fig . 2 . Genera l i s ed cros s - s ec t ion o f the Great Ar te s ian Bas in s howing the Juras s ic aqui fer and the over ly ingconf in ing b ed and cre taceous aqui fer . The s ec t ion re fers lo the l ine A- A ' ( a f ter Hab erm ehl , 1980 ) .



228 A.L. HERCZEG ET AL.

'; ~ 1-/ ~ ~ u _;~ c 'J ; . AI N C ,,.

/ < V l ~ t_ / \ \ .

- t , 1 , , . . . . . . . . . . . ¢ ~ f ~ F , . < ,

Fig. 3. Location o f artesian water wells sampled in May 1985 for this investigation. Sample numbers 73-98

refer to our inte rnal code (see Table 1). The three transects discussed in the text are given here as Line A

(wells 73-77), Line E (wells 78-92) and Line W (wells 93-98).

a n d w e t s u m m e r s . L a r g e -s c a le g r o u n d w a t e r m o v e m e n t is t o w a r d s t h e s o u th -

w e s t e r n a n d s o u t h e r n m a r g i n s ( F ig . 1 ). D i s c h a r g e o c c u r s v ia u p w a r d l e a k a g e

a n d t h r o u g h s p ri n g s a n d d if fu s e d i s c h a rg e in t h e s o u t h w e s t e r n a n d s o u t h e r n

m a r g i n s ( Fi g. 1). T h e p o t e n t i o m e t r i c s u rf ac e o f t h e L o w e r C r e t a c e o u s - J u r a s s ic

a q u i fe r s y s te m i s a b o v e g r o u n d le v e l t h r o u g h o u t m o s t o f t h e b a s in . A q u i fe r s

f r o m t h e U p p e r C r e t a c e o u s r o c k s h a v e m u c h l o w e r w a t e r y ie ld s a n d g r e a t e r

s a li n it y t h a n w a t e r fr o m t h e L o w e r C r e t a c e o u s - J u r a s s i c a q u i f e r s y s te m

( h e r e a f t e r t e r m e d t h e J u r a s s ic a q u i f e r s y s te m ) a n d t h e r e f o r e a r e o f l e ss e r

i m p o r t a n c e f o r e xp l o it a t i o n . T h e g e o l o g y a n d h y d r o g e o l o g y o f t h e G r e a t

A r t e s i a n B a s i n i s d e s c r i b e d i n c o n s i d e r a b l e d e t a i l in H a b e r m e h l ( 19 80 ).

T h i s p a p e r d e a l s e x c lu s i v e ly w i t h g r o u n d w a t e r c o l le c t e d fr o m t h e w i d e l y

e x p l o i t e d J u r a s si c a q u i f e r s y st e m , in p a r t ic u l a r w i t h w a t e r f r o m t h e H o o r a y

S a n d s t o n e a n d its e q u i v a l e n ts w h ic h a r e h i g h l y p r o d u c t iv e , a n d t h e u p p e r

a r te s i a n a q u if e rs in t h e G A B . T h e w a t e r s a re d o m i n a t e d b y N a + a n d H C O 3

t h r o u g h o u t m o s t o f t h e b a s i n w i t h a g e n e r a l i n c r e a s e i n to t a l d i s s o l v e d s o li d s



GREAT ARTESIAN BASIN GEOCHEMISTRY 229

f r o m t h e n o r t h e a s t e r n a n d e a s t e r n m a r g i n s t o w a r d s t h e in t e r io r o f th e b a s in .

W a t e r s o f p r e d o m i n a n t l y N a - C 1 t yp e o c c u r n e a r th e w e s t e r n m a r g i n a l z o n e

w h e r e r e c h a r g e f r o m t h e w e s t d i s so l v e s e v a p o r i t e m i n e r a l s ( H a b e r m e h l , 1 980).

H a b e r m e h l ( 1 98 0, 1 9 8 6 ) a n d C a l f a n d H a b e r m e h l ( 1 98 4) d e a l w i th s o m e

a s pe c ts o f t h e h y d r o c h e m i s t r y o f t h e G A B g r o u n d w a t e rs i n te r m s o f g e n e ra lp a t te r n s t h r o u g h o u t t h e b as in . A d i s c u ss i o n o f t h e e n v i r o n m e n t a l is o t o p e

d i s t r i b u t i o n i n th e g r o u n d w a t e r s b y A i r e y e t al . (1 9 79 ) i n d i c a te s t h a t t h e

w a t e r s a r e e n t ir e l y o f m e t e o r i c o r i g in .

N i n e t e e n c h e m i c a l a n d i s o to p ic a n a l ys e s o f g r o u n d w a t e r s a m p le s w e r e

o b t a i n e d f r o m e x is t in g f l o w i n g a r t e s i a n w a t e r w e l ls in t h e J u r a s s i c a q u i f e r

o f t h e G A B i n 1 9 8 5 . S a m p l e w e l l l o c a l it ie s fo r t h i s s t u d y a r e s h o w n i n F i g . 3.

W e u s e d a c h e m i c a l a n d i s o to p i c m a s s b a l a n c e a n d e q u i l i b r i u m a c t i v i ty

r e l a t io n s h i p s to d e t e r m i n e th e t yp e s o f m i n e r a l - w a t e r i n t e r a c t i o n s t h a t a r e

l ik e ly to t a k e p l a c e. I d e n t i fi c a t io n o f s o l id m i n e r a l p h a s e s a n d t h e i r c h e m i c a lc o m p o s i t io n s w e r e c a r r ie d o u t t o v e ri fy w h e t h e r t h e p r o p o s e d c h e m i c a l

r e a c t i o n s d e r i v e d f r o m t h e r m o d y n a m i c m o d e l l in g a r e f ea s ib l e. A ~3C i s o t o p e

a n d d i ss o l v ed i n o r g a n i c c a r b o n m a s s b a l a n c e p la c e s a d d i t i o n a l c o n s t r a i n t s o n

t h e p r o p o s e d c h e m i c a l r e a c t i o n s i n v o l v i n g p r o t o n t r a n s f e r r e a c t io n s w i t h i n

t h e g r o u n d w a t e r s y s t e m .

ANALYTICAL METHODS

W a t e r s a m p l es w e r e c o l l e c te d i n a c i d - w a s h e d N a l g e n e b o t tl e s f r o m a r t e s ia n

w e l ls t h a t w e r e fl o w i n g c o n t i n u o u s l y a n d h a d b e e n d o i n g s o f o r s e v e r a l y e a r s

o r d e c a d e s . A l l s a m p l e b o t t le s w e r e f lu s h e d w i t h s e v e r a l v o l u m e s o f w a t e r

b e f o r e c h e m i s t r y s a m p l e s w e r e t a k e n . S e p a r a t e 5 0 0 -m l s a m p l e s w e r e ta k e n f o r

c a t i o n s a n d a n i o n s a n d f il te r e d i m m e d i a t e l y t h r o u g h 0.4 5-/~ m M i ll i po r e ®

f il te r s a n d t h e c a t i o n a l i q u o t a c i d i fi e d t o p H < 1 . 5 . A l k a l i n i t y s a m p l e s w e r e

c o l l e c te d i n 1 00-m l W h e a t o n ® b o t tl e s t o w h i c h 1 m l o f s a t u r a t e d H g C 1 2

s o l u t io n w a s a d d e d , a n d a r u b b e r s e p t u m w a s s e c u r ed b y a n a l u m i n i u m

c r i m p e d s e a l . T h e p H w a s m e a s u r e d i n t h e f i e l d u s i n g a p o r t a b l e O r i o n p H

m e t e r c a l i b r a t e d w i t h t w o s t a n d a r d b u f fe r s o lu t i o n s ( p H v a l u e s o f 7 a n d 9 ).

M a j o r c a t i o n s w e re a n a l y s e d by a to m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y .

S u l p h a t e , b r o m i d e a n d f lu o r i d e w e r e d e t e rm i n e d o n a D i o n e x ® i o n c h r o m a -

t o g r a p h . C h l o r i d e w a s d e t e r m i n e d s e p a r a te l y b y p o t e n t i o m e t r i c ti t r a t io n w i th

s il v er n i t ra t e . A q u e o u s s i lic a w a s a n a l y s e d b y a t o m i c a b s o r p t i o n f o l lo w i n g t h e

m e t h o d o f K i s s (1 982 ). A l k a l in i t y w a s m e a s u r e d b y a p o t e n t i o m e t r i c G r a n

t i tr a t i o n i n t h e la b o r a t o r y . T o t a l d i s s o l v e d i n o r g a n i c c a r b o n ( D I C ) w a s

d e t e r m i n e d b y c a l c u l a ti o n f ro m p H a n d a l ka l in i ty d a t a u s in g th e p r o g r a m

P H R E E Q E ( P a r k h u r s t e t a l ., 1 980). F o r d e t e r m i n a t i o n o f 61 3C D Ic, B a C 12 a n d

N a O H w e r e a d d e d t o a b o u t 2 5 0 m l o f w a t e r t o in d u c e p re c i p it a t i o n o f

d i s s o l v e d C O 2 a s B a C O 3 . T h e p r e c i p i ta t e s w e r e a c i d i fi e d i n a v a c u u m l in e a ft e r



2 3 0 A.L. HERCZEG ET AL.

r e t u r n t o t h e l a b o r a t o r y a n d t h e e v o l v e d C O 2 d e t e r m i n e d f o r i t s i so t o p ic

c o m p o s i t i o n o n a m o d i f ie d N u c l i d e M S 1 2 m a s s s pe c t r o m e t e r . P r e c is io n f o r

i s o t o p e a n a l y s e s i s n o m i n a l l y _+ 0.1 % o.

R E S U L T S

R e s u l t s o f c h e m i c a l a n d 6 ~3C a n a l y se s o f g r o u n d w a t e r s f r o m t h e J u r a ss i c

a q u i fe r s in t h e G r e a t A r t e s i a n B a s in a r e p r e s e n t e d i n T a b l e 1. T h e d a t a a r e

g r o u p e d in t o t h r e e t ra n s e c t s ( F ig . 3) w h i c h r e p r e s e n t d o w n g r a d i e n t e v o l u t i o n

f r o m t h e i r re s p e ct iv e r e c h a r g e a r e a s . T h e w a t e r s o n o u r L i n e E t r a n s e c t ( w e ll s

7 8 -9 2 ) a r e d o m i n a n t l y N a - H C O 3 t y p e w i t h t o t a l d i s s o l v e d s o l i d s ( T D S )

c o n t e n t s r a n g i n g f r o m 3 6 2 p p m i n t h e n o r t h e a s t e r n z o n e t o g r e a t e r t h a n

1 6 00 p p m n e a r t h e d i s c h a r g e a r e a s i n th e w e s t e r n a n d s o u t h w e s t e r n p o r t i o n s

o f t h e b a s i n . W e l ls 7 3- 7 7 , w h i c h lie o n a n e a s t - w e s t l i n e t o w a r d s t h e e a s t e r ns id e o f t h e b a s in ( L i n e A ) , t e n d t o h a v e h i g h e r T D S c o n t e n t s t h a n t h o s e

e m a n a t i n g f r o m t h e n o r t h e a s t e r n p a r t o f t h e b a si n . T h e y a r e c h a ra c t e r i s e d b y

h i g h e r N a , H C O 3 a n d C 1 c o n c e n t r a t i o n s t h a n t h e g r o u n d w a t e r s f r o m L i n e E

f u r t h e r t o t h e n o r t h . W a t e r s f r o m t h e w e s t e r n t r a n s e c t , L i n e W ( we lls 9 3- 9 8 )

a r e o f t h e N a -C 1 t yp e a n d h a v e m u c h h i g h e r T D S c o n t e n t s (u p t o 5 835 p p m )

t h a n t h e e a s t e r n t r a n s e c t s .

F i g u r e 4 s h o w s t h e t r e n d s o f c h e m i c a l p a r a m e t e r s a n d ~3C a l o n g t h e t h r e e

t r a n s e c t s d e fi n e d as L i n e s A , E a n d W ( s h o w n i n F ig . 3) f r o m n e a r t h e i n f e r r e d

r e c h a r g e a r e a s t o w a r d s t h e d i s c h a r g e a r e a in t h e s o u t h w e s t e r n p a r t o f t h eb a s i n . T h e r e is a g e n e r a l i n c r e as e i n d i s s o lv e d s o l id s c o n c e n t r a t i o n a l o n g a ll

t r a n s e c t s t o w a r d s t h e i n te r io r o f t h e G A B , w h i c h is a c o m m o n f e a tu r e o f m a n y

l a rg e g r o u n d w a t e r b a s in s . S i m i l a r ly N a c o n t e n t a n d a l k a l i n i ty s h o w s i m i l a r

i n cr e as e s t o t h o s e o f t h e T D S c o n t e n t a n d t h e y d o m i n a t e t h e T D S t re n d .

C h l o r i d e i n c r e a s e s g r a d u a l l y f o r t h e m o s t p a r t ( e x c e p t f o r t h e w e s t e r n

t r a n s e c t ) a n d i n c re a s e s b y a b o u t a f a c t o r o f t h r e e a l o n g L i n e E . T h e r e i s a q u i te

d i s t in c t s e p a r a t i o n o f c h l o r i d e c o n c e n t r a t i o n f o r th e t h r e e t ra n s e c t s a n d r a n g e

o v e r t w o o r d e r s o f m a g n i t u d e . P o t a s s i u m m i m i c s c h l o r id e t o s o m e e x t e n t a s

i t s h o w s a s l i g h t d e c r e a s e a l o n g L i n e E a n d t h e n s o m e in c r e a s e f o r th e l a s t f o u r

w e l ls . C a l c i u m a n d m a g n e s i u m s h o w a m a r k e d d e c r ea s e to a b o u t 30 0 k m t h e n

r e m a i n a t v e r y l o w c o n c e n t r a t i o n s e x c e p t f o r L i n e A w h i c h s h o w s a g e n e r a l

i n c r e a s e , a lb e i t a t a l o w l e v e l. A l k a l i n i t y , D I C a n d 6 ~3C s h o w s i m i l a r p a t t e r n s

f o r L i n e E a s t h e y i n c r e a se s t e a d i ly a lo n g t h e t ra n s e c t . A l k a l in i t y a n d D I C

c o n c e n t r a t i o n s a r e m a r k e d l y h i g h e r fo r L i n e A t h a n t h e o t h e r t r a n se c ts .

X - r a y d i f f r a c t i o n a n a l y s i s o f a q u i f e r s o l i d m a t e r i a l w a s c a r r i e d o u t t o

d e t e r m i n e w h i c h m i n e r a l s w i t h i n t h e b a s i n a r e l ik e ly to i n f l u e n c e t h e w a t e r

c h e m i s t r y . F i f t e e n d e e p d r i l l h o l e ( p e t r o l e u m e x p l o r a t i o n w e l l ) c o r e s a n d

c u t t in g s o f s a n d s t o n e s a n d c o n f in i n g m u d s t o n e s s h o w a u n i f o r m d i s t r ib u t i o n



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GREAT ARTESIAN BASIN GEOCHEMIS TRY 233

TABLE 2

Average sandstone and shale composition from GAB core cuttings collected throughout

the basin

Average GAB sandstone Average GAB shale(n = 7) (n = 8)

% SD % SD

SiO 2 71.1 10.9 60.6 3.54

TiO, 1.17 0.39 1.47 0.24

A120~ 12.9 3.8 16.54 1.34

Total Fe 3.82 2.12 6.17 0.91

MgO 0.89 0.41 1.32 0.21

CaO 2.10 1.52 1.78 0.77

Na~O 1.36 0.22 1.47 0.49K20 1.57 0.22 1.95 0.34

CaCO~ 1.80 2.06 3.45 1.73

Organic C 0.85 0.25 1.09 0.16

o f p r e d o m i n a n t l y qu a r t z , k a o l in i te , i ll i te a n d s m e c t i t e w i th m i n o r a m o u n t s o f

c a lc i te a n d a l b it e . P e t r o g r a p h i c e x a m i n a t i o n o f c o r e c u t t i n g s i n d i c a t e t h a t t h e

p l a g i o c l a s e f e l d s p a r s a r e c o m p l e t e l y s e r ic i ti z e d b u t a l k a l i f e l d s p a r s a n d q u a r t z

a r e e ss e n t ia l ly u n a l t e r e d . T h e c h e m i c a l c o m p o s i t i o n o f th e a q u i f e r m a t e r i a l

( T a b l e 2 ) v e r if ie s t h a t t h e a q u i f e r i s h i g h l y a lt e r e d a n d d e f i c ie n t in b a s e c a t i o n s .

T h e o r g a n i c c a r b o n c o n t e n t o f t h e s a n d s t o n e s is a b o u t 1 % w h i l e C a C O 3

c o n t e n t r a n g e s u p t o 3 .5 % b y w e i g h t .

DISCUSSION

I n c r e a s e i n T D S d o w n g r a d i e n t

T h e i n c r e as in g T D S c o n t e n t d o w n g r a d i e n t o b s e r v e d in th e G A B m a y b e

c a u s e d b y s e v e r a l p r o c e s s e s . T h e s e i n c l u d e : (1 ) m i x i n g o f t h e d i l u t e r e c h a r g e

w a t e r s w i t h s a l in e w a t e r s p r e s e n t w i t h i n d e e p e r p a r t s o f t h e b a s i n ; ( 2 ) i o n -

f i l t ra t io n t h r o u g h s h a le m e m b r a n e s ; (3) d i s s o l u t i o n o f e v a p o r i t e s , c a r b o n a t e

m i n e r a l s o r i n c o n g r u e n t d i s s o l u t i o n o f f e ld s p a r s , m i c a s o r c l a y m i n e r a ls .

T h e o n l y s a li n e w a t e rs t h a t m a y i n fl u e n ce G A B h y d r o c h e m i s t r y a r e n e a r

t h e w e s t e rn m a r g i n w h e r e d i s s o l u t io n o f h a li te a n d g y p s u m o c c u r ( s e e b e l o w )

a n d p o t e n t i a l l e a ka g e f r o m a b o v e o r b e l o w . L e a k a g e is u n l i k e ly t o o c c u r f r o m

t h e o v e r ly i n g C r e t a c e o u s s e q u e n c es b e c a u s e o f t h e n e t u p w a r d h e a d i m p o s e d

b y t h e Ju r a s s ic a q u i f e r b u t d i f fu s i o n o f io n s d o w n w a r d s a g a i n s t t h e h y d r a u l i c

g r a d i e n t m a y o c c u r . T h e r a t e o f u p w a r d m o v e m e n t o f w a te r e xc e e ds th e r a te

a t w h i c h C I a n d N a c a n d i f fu s e d o w n w a r d s , h e n c e t h e i n fl u e n c e o f m o r e s a li n e



234 A.L. HERCZEG ET AL,

1 • . a ) b )

L i n e A

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i s tance k m ) > D i s t a n c e k i n ) )

F ig . 5 . ( a ) - ( d ) P l o t s o f t h e m o l e r a t i o s o f N a / C I , (C a + M g ) / C 1 , C I / B r , a n d S r / C a a l o n g t h e t h r e e t ra n s ec t s

represented in Fig. 3.

w a t e r f r o m t h e U p p e r C r e t a c e o u s a q u i f e r s m u s t b e c o n s i d e r e d t o b e s l i g h t .

S a l i n e w a t e rs f r o m t h e m a r i n e C r e t a c e o u s m u d s t o n e s m a y l ea k in t o t h e

J u r a s s i c a q u i fe r , p a r t ic u l a r l y n e a r t h e d i s c h a r g e a r e a s b u t i t w o u l d n o t a c c o u n t

f o r t h e o v e r a l l c h e m i c a l t r e n d s d e s c r i b e d a b o v e .

T h e G A B w a t e rs a r e p r e ss u r is e d in t h e in t e r io r o f th e b a s i n ( a t m o r e t h a n2 00 b a r ) a n d t h e y a r e o f m e t e o r i c o r i g i n a s d e t e r m i n e d f r o m s t a b le i s o t o p i c

c o m p o s i t i o n o f h y d r o g e n i s o t o p e s in t h e w a t e r m o l e c u l e s (A i r e y e t a l. , 1 979 ).

U sin g 36C1a n d t o t a l c h l o r i d e c o n c e n t r a t i o n s , B e n t le y e t al . (1 9 86 ) c o n c l u d e d

t h a t i o n f i l t r a t io n d o e s n o t o c c u r in t h e G A B b u t t h a t t h e r e is a c o n t r i b u t i o n

o f 'd e a d ' c h l o r i d e in t h e e a s t e r n f lo w r e g im e s , p o s s i b ly f r o m a n u n d e r l y i n g

a q u i fe r th a t c o n t a i n s c o n n a t e w a te r . W e c o n c l u d e t h a t a c o m b i n a t i o n o f

e v a p o t r a n s p i r a t i o n w i th i n t h e r e c h a rg e a r e a s a n d m i n e r a l d i s s o l u t io n p r o v i d e

t h e m o s t p la u s ib l e m e c h a n i s m f o r th e c h e m i c a l t r e n d s o b s e r v e d a l o n g L i n e s

E a n d W . E v a p o r i t e d i s s o l u t i o n a n d e n t r a i n m e n t o f m o r e s a l i ne g r o u n d w a t e r s

a r e n o t i m p o r t a n t c o n t r i b u t o r s e x c e p t i n t h e w e s t e r n a n d s o u t h w e s t e r n

m a r g i n s o f th e b a s in .

P l o t t i n g t h e i o n /C 1 r a t io s a s a f u n c t i o n o f d i s t a n c e a l o n g e a c h t r a n s e c t

a l lo w s u s t o d e l i n e a t e c h e m i c a l p r o c e s s e s t h a t a r e n o t r e l a t e d t o e v a p o t r a n s -

p i r a t i o n v a r i a ti o n s d u r i n g r e c h a rg e b e c a u s e C1 is c o n s e r v e d d u r i n g g r o u n d -

w a t e r e v o l u t io n t h r o u g h o u t m o s t o f th e G A B . S o d i u m / c h l o r i d e r a ti o s t e n d t o

b e v a r i a b le t h r o u g h o u t t h e b a s i n ( F ig . 5 ( a )) b u t g e n e r a l ly in c r e a s e b y a f a c t o r

o f a b o u t t h r e e . S o d i u m / c h l o r i d e m o l e r a t i o s a r e a lw a y s g r e a te r t h a n t w o

( e x ce p t f o r L i n e W ) , d e m o n s t r a t i n g t h a t h a l i te d i s s o l u t i o n o r m i x i n g w i t h



G R E A T A R T E S I A N B A S IN G E O C H E M I S T R Y 2 3 5

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F i g . 6 . S a t u r a t i o n i n d e x o f G A B g r o u n d w a t e r s w i t h r e sp e c t t o c a lc i te ( g iv e n a s t h e ra t i o o f t h e io n i c a c t i v i t y

p r o d u c t d i v i d e d b y t h e e q u i l i b r i u m s a t u r a t i o n v a l u e ) a s a f u n c t i o n o f a l k a l i n i t y . A v a l u e o f z e r o r e p r e s e n t s

s a t u r a t i o n w h i l e v a l u e s le s s t h a n 0 r e p r e s e n t u n d e r s a t u r a t i o n .

t r a p p e d s e a w a t e r b r in e s d o e s n o t c o n t r i b u t e t o t h e i n c r e as e in s o d i u m o b s e r v e d

h e r e . T h e r a t i o o f ( C a + M g ) /C 1 d e c r e a se s m a r k e d l y fo r t h e f ir s t 30 0 k m a l o n g

t r a n s e c t E ( F ig . 5 ( b )) b u t t h e n r e m a i n s a t v e r y l o w le v e ls , t h e r e f o r e C a a n d M g

a r e r e m o v e d f r o m s o l u t io n d u r i n g t h e f i r st o n e - t h i r d p o r t i o n o f th e t r a n se c t .

C h l o r i d e / b r o m i d e ra t io s r a n g e o v e r a fa c t o r o f t w o f o r L i n e s E a n d A

( F ig . 5 ( c)); h o w e v e r , a ll b u t o n e a r e w i t h i n t h e r a n g e o f v a l u e s t h a t c o u l d b e

d e r i v e d f r o m r e c h a r g e o f s e a w a t e r - d e r i v e d c y c li c s a lt . T h e s i m i l a r i ty o f C 1 / B r

r a t io s f o r L i n e s A a n d E t o t h o s e f o u n d i n s e a w a t e r ( 5 5 0 -7 0 0) d e m o n s t r a t e

t h a t n o e v a p o r i t e d i s s o l u t i o n h a s ta k e n p la c e w h i c h w o u l d g e n e r a t e C 1 /B rm o l e r a ti o s m u c h g r e a t e r t h a n a p p r o x i m a t e l y 5 0 0- 70 0. T h e h i g h C 1 / B r r a ti o

m e a s u r e d a t w e l l 83 in d i c a t e s t h a t s o m e m i x i n g o f w a t e r s h a s o c c u r r e d

b e t w e e n w e ll s 8 2 a n d 8 3, p o s s ib l y b y u p w a r d l e a k a g e o f C l - r i c h w a t e r d e r i v e d

f r o m t h e L o w e r P a l a e o z o i c - P r o t e r o z o i c G e o r g i n a B a s in u n d e r l y i n g t h e G A B .

T h e e a s t e r n m a r g i n o f t h e G e o r g i n a B a s i n is l o c a t e d in t h e a re a , a n d a f au l t

s t r u c t u r e is p r e s e n t i n t h e G A B s e q u e n c e i n t h e r eg i o n . C h l o r i d e / b r o m i d e

r a ti o s o f g r o u n d w a t e r s f r o m t h e w e s t e rn m a r g i n a r e m u c h g r e a t e r th a n 1 000

d e m o n s t r a t i n g t h a t t h e y ar e d e r iv e d f r o m e v a p o r i te d i s so l u t io n .

S t r o n t i u m / c a l c i u m r a t io s ( F ig . 5 ( d )) s h o w a g e n e r a l i n c re a s e in L i n e s E a n dW w h i c h c o u l d b e c a u s e d b y l o ss o f C a v i a c a t io n e x c h a n g e . P r e c i p i ta t i o n o f

C a C O 3 is n o t p o s s ib l e b e c a u s e a ll b u t o n e o f t h e w a t e r s f r o m L i n e E a r e

u n d e r s a t u r a t e d w i t h r e s p e c t t o C a C O ~ ( F i g . 6 ) .

Mineral-solution interactions

T h e t y pe s o f m i n e r a l - s o l u t i o n r e a c t i o n s th a t m a y c o n t r o l t h e c o m p o s i t i o n

a n d t r e n d o f h y d r o c h e m i c a l s pe c i es i n o u r t r a n s e c ts A a n d E a r e c a t i o n

e x c h a n g e , d i s s o l u t i o n o f c a lc i te o r f e ld s p a r s o r r e a c t i o n s i n v o l v i n g c la y

m i n e r a ls . I t is i m p o r t a n t t o n o t e t h a t t h e t h r e e t r a n s e c t s d e s c r i b e d a b o v e a ll



23 6 A.L. HERCZEG ET AL.

s h o w d i ff e re n t c h a r a c te r i s ti c s a n d t h e r e f o r e t h e t y pe s o f c h e m i c a l r e a c t io n s

n e e d n o t o p e r a t e t o t h e s a m e e x t e n t in a ll p a r t s o f t h e b a s i n a n d t h e r e f o r e w i ll

b e d i s c u s s e d s e p a r a t e l y .

W e a s s u m e t h a t c h l o r id e io n s b e h a v e c o n s e r v a t iv e l y t h r o u g h o u t L i n e E ,

w i t h p e r h a p s t h e e x c e p t i o n o f so m e a d d i t i o n o f C l - r ic h w a t e r b e t w e e n w e l ls8 2 a n d 83 (s e e a b o v e ) . N o r m a l i s i n g a ll o t h e r c h e m i c a l s p ec i es t o c h l o r i d e a l l o w s

u s to e v a l u a t e t h e t y p e s o f c h e m i c a l p r o c e s s e s a ff e c t in g o t h e r d i s s o l v e d s p e c i e s

w i t h i n t h e G A B t h a t a r e n o t r e l a t e d t o p r o c e s s e s s u c h a s e v a p o t r a n s p i r a t i o n .

C h l o r i d e c o n c e n t r a t i o n s i n r a in f a ll i n r e g i o n s , w h i c h a r e m o r e t h a n 1 00 k m

f r o m t h e c o a s t, f a l l i n t o a n a r r o w r a n g e o f le ss t h a n 1 t o 5 p p m ( B l a c k b u r n a n d

M c L e o d , 1 9 83). T h e s e c o n c e n t r a t i o n s a re a n o r d e r o f m a g n i t u d e o r m o r e

l o w e r t h a n C 1 - c o n c e n t r a t io n s i n e v e n t h e m o r e d i lu t e re g i o n a l g r o u n d w a t e rs

w i t h in t h e G A B ( T a b l e 1). E l e v a t e d c h lo r i d e c o n c e n t r a t i o n s i n t h e g r o u n d

w a t e rs a r e p r o b a b l y c a u s e d b y e v a p o t r a n s p i r a t i o n d u r i n g r e c h a r g e a n d t h ise v a p o t r a n s p i r a t i o n a ffe c ts a ll i o n s e q u a ll y . C y c li c w e t t i n g a n d d r y i n g in t h e

u n s a t u r a t e d z o n e ( e .g . D r e v e r a n d S m i t h , 1 9 78) w i t h i n t h e r e c h a r g e a r e a s i s

n o t i m p o r t a n t b e c a u s e th e r e c h a r g e w a te r s d o n o t e v a p o r a t e t o d r y n e s s w i t h in

t h e s o il z o n e . T h i s p ro c e s s c a n o n l y f r a c t i o n a t e s o d i u m a n d c h l o r i d e i f h a l i t e

f o r m s in t h e so i l z o n e , a n d t h is d o e s n o t o c c u r i n th e G A B r e c h a r g e a r e a s .

T h e t y p e s o f re a c t i o n s p r o p o s e d f o r L i n e E m u s t s i m u l t a n e o u s l y s a ti sf y t h e

o b s e r v e d in c r e a s e s i n N a , a l k a li n i ty a n d D I C a n d a t t h e s a m e t i m e t h e d e c r ea s e

in C a a n d M g . F u r t h e r m o r e , t h e r e la t i ve ly c o n s e r v a t iv e b e h a v i o u r o f a q u e o u s

s il ic a m u s t b e a c c o u n t e d f o r i n a n y r e a c t i o n s i n v o l v i n g s i li c a te m i n e r a l s .T h e r e le a s e o f N a , t o t h e m o r e d i l u t e w a te r s n e a r e r t h e r e c h a r g e a r e a s m a y

b e a c c o m p l i s h e d b y t h e f o l l o w i n g : (i) d i s s o l u t i o n o f N a b e a r i n g m i n e r a l s

( e. g. p l a g i o c l a s e o r o r t h o c l a s e ) ; (ii) c a t i o n e x c h a n g e w h i c h r e l e as e s N a * f r o m

c l ay m i n e r a l s ; (iii) c o n v e r s i o n o f a N a - s m e c t i t e t o k a o l i n i te . I n c o n g r u e n t

d i s s o l u t i o n o f a l b it e re l ea s e s N a a n d H C O 3 i n t o s o l u t i o n in a n a p p r o x i m a t e l y

1 : 1 r a t io a c c o r d i n g t o t h e e q u a t i o n

2 N a A 1 S i 3 O s + l l H 2 0 + 2 C O 2 ~ A 1 2 S i2 O s( OH ) 4 + 2 N a

a l b i t e k a o l i n i t e+ 2 H C O 3 + 4 H 4 S I O 4 ( 1 )

o r

2 . 3 3 N a A 1 S i 3 0 8 + 8 . 6 4 H 2 0 + 2 C O 2 ~ N a 03 3A 1 2 3 3S i 36 7O t0 (O H ) 2

a l b i t e N a - m o n t m o r i l l o n i t e

+ 2 N a + 2 H C O 3 + 3 .3 2 H 4 S I O 4 ( 2)

w h i c h a l s o r e le a se s o n e e q u i v a l e n t o f a l k a li n i ty f o r e a c h e q u i v a l e n t o f N a b u t

a l so r e l e as e s s u b s t a n t i a l a m o u n t s o f d is s o l v e d s il ic a f o r e a c h m o l e o f N a

p r o d u c e d . S i l i c a d o e s n o t r e a c h e l ev a t e d c o n c e n t r a t i o n s a n y w h e r e in t h e G A B



GREAT ARTESIAN BASIN GEOCHEMISTRY 237

and the waters are well undersaturated with respect to amorphous silica.

Precipitation of a-quartz is not likely to be achieved even over the very long

water residence times within the deep aquifer. Fur the rmo re, the Na/SiO2 ratio

actually increases along the transects which is the opposite of that predicted

by the above equations.Exchan ge of cations between the solution an d clays (such as one Ca 2. for

two Na* ions) would increase Na relative to Ca but have no effect on

alkalinity. Therefore, alth ough cation exchange may be an im porta nt process,

it cannot be the sole process responsible for the increase in Na and HCO3.

Dissol ution of carb onate s (calcite or dolomite) can occur within the GAB

as the lower bicarbonate c oncentra tion waters are undersa turated with respect

to calcite (Fig. 6, Table 1). Dissolution may take place via the reaction.

CO 2 q- Ca CO 3 + H20 ~ 2H CO 3 q- Ca (3a)

o r :

2CO 2 + CaMg( CO3) 2 + 2H20 ~ 4HCO3 + Ca + Mg (3b)

which produces Ca, Mg and HC O 3. However, Ca a nd M g decrease mar ked ly

with increasing TDS c ontent and in fact never reach very high concent rati ons

except in waters from Line E near the eastern margin.

Ma ss -ba l a n c e c a l c u l a t io n s

We tested a model based on that proposed by Blake (1989) for the

generation of waters high in Na HC O 3 in the Ot way basin of southeast

Australia. The model hypothesises a three-stage process involving: (1) release

of Ca, Mg and HCO~ via carbonate dissolution; (2) cation exchange of Ca (and

TABLE 3

Thermodynamic data used in calculating mineral-solution equilibria in Fig. 7. H and Grepresent the enthalpy and free energy of formation for each mineral phase in units of

cal tool L. Log K is the equilibrium constant derived from free energy data at 25°C

Mineral H G log K Ref.(cal mol 1) (cal mol 1)

Albite -939.7 -886.3 2. 59 Helgeson t al., 1978Calcite -288.8 -270.1 -8.48 Parkhurst et al., 1980Na-beidellite - 1368.2 - 1277.8 - 7.9 Nesbitt, 1977Kaolinite - 982.2 - 905.6 Helgeson et al ., 1978Gibbsite -309.1 -276.2 10.38 Helgeson t al., 1978

Quartz -217.65 -204.65 -4.01 Helgeson t al., 1978Amorphous s il ica -214.57 -202.89 - Helgeson et al., 1978



2 3 8 A . L . H E R C Z E G E T A L .

12 • , . , • , • , •

10 . ~ l og (a Na /a H) v ' s l o g ( a S l 0 2 )

~ . ~ A l b i t e

Gibbsite

Kaolmfle

J i i i

-5 . 0 -4 .5 -4 .0 -3 .5 -3 .0 -25

l o g a S l 0 2 )

F ig . 7. A c t i v i t y - a c t iv i t y d i a g r a m d e p i c t i n g t h e s ta b i l it y fi el d o f N a m i n e r a l s . T h e r m o d y n a m i c d a t a f o r

c a l c u l a t i o n o f m i n e r a l s t a b i l i t y f ie l d s a r e g i v e n i n T a b l e 3 . T h e s t a b i l i t y fi e ld s a r e g i v e n a t 2 5 ° C w h i l e

a c t iv i ti e s fo r d i s s o l v e d sp e c i e s a r e a t i n s i tu g r o u n d w a t e r t e m p e r a t u r e s ( 3 0 - 9 5 ° C ) . W i t h i n t h i s t e m p e r a t u r e

r a n g e t h e m i n e r a l - w a t e r s t a b i li ty f ie l d s d o n o t c h a n g e s i g n if ic a n t ly f ro m t h o s e d e n o t e d h e r e . T h e w a t e r s

a p p e a r t o b e a t o r n e a r e q u i l i b r i u m w i t h r e s p e c t t o k a o l in i t e , a n d a N a - s m e c t i te . T h e y a r e u n d e r s a t u r a t e d

w i th r e s p e c t to a m o r p h o u s s i li ca a n d c a l c it e a n d s u p e r s a t u r a t e d w i th r e s p e c t to q u a r t z .

M g ) f o r N a o n c l a y m i n e r a l s ite s ; (3) b a c k r e a c t i o n o f N a w i t h k a o l i n i t e to

p r o d u c e a N a b e a r i n g s m e c t i t e . T h i s w o u l d r e s u l t i n a n i n c r e a se i n a lk a l in i t y

t h r o u g h t h e d i s s o l u t io n o f c a r b o n a t e s , e x c h a n g e o f N a f o r C a t o s u p p l y N a ,

a n d e q u i l i b r iu m c o n t r o l s o n N a a n d S i O 2 b y r e a c t io n o f N a w i t h k a o l in i t e t o

f o r m a N a - b e a r i n g s m e c t i t e .

T h e r e a c t io n b e t w e e n s o d i u m a n d k a o l in i t e m a y t a k e t h e g e n e r a l fo r m3 A 1 2 S i2 0 5( O H )4 + N a + + 4 H 4 S i O 4

k a o l i n i t e3Na0.33A12.33SiB67Ot0(OH)2 + H + + 1 1 . 5 H 2 0 ( 4 )

N a - s m e c t i t e

T h e s t o i c h i o m e t r y is s u c h t h a t o n e e q u i v a l e n t o f N a is c o n s u m e d f o r e a c h

e q u i v a le n t o f a l ka l in i ty c o n s u m e d . T h e a m o u n t o f H 4 S iO 4 c o n s u m e d d e p e n d s

s o m e w h a t o n t h e a m o u n t o f S i i n t h e re s pe c t i v e c la ys a n d n e e d n o t b e in t h e

p r o p o r t i o n g i v e n a b o v e b u t i s s o m e w h e r e b e t w e e n 1 a n d 4 m o l e s d e p e n d i n g

o n t h e s t o i c h i o m e t r y o f t h e c la y m i n e r a l s .

I n t h e a b o v e s c e n a r i o , n o e x t e r n a l s o u r c e o f C O2 is re q u i r e d t o d i s s o lv e

C a C O 3 b e c a u s e t h e p r o t o n s n e c e ss a ry fo r c a r b o n a t e d i s s o l u t i o n a re d e r iv e d

f r o m e q n . ( 4) a b o v e , p r o c e e d i n g t o t h e r i g h t . A c t iv i t ie s o f i o n s c a l c u l a te d f r o m

t h e c o m p u t e r p r o g r a m P H R E E Q E ( P a r k h u r s t e t a l. , 1 980) a r e p l o t t e d o n a

m i n e r a l s t a b i l i t y d i a g r a m f o r t h e N a - H - S i O 2 s y s te m in F ig . 7 u s i n g t h e r m o -

d y n a m i c d a t a i n T a b l e 3 . M o s t o f th e w a t e r s a r e e q u i l i b r a t e d w i t h r e s p e ct t o

k a o l i n i t e a n d a N a - m i x e d l a ye r c l a y r e p r e s e n t e d h e r e b y N a - b e i d e l li te . T h e N a

c o n c e n t r a t i o n i n t h e s e w a t e r s m a y t h e r e f o r e b e c o n t r o l l e d b y e q u i l i b r i u m

b e t w e e n k a o l in i t e a n d a N a - s m e c t i te . F u r t h e r m o r e , N a - s m e c t i te s a re p r e s e n t



GREAT ARTESIAN BASIN GEOCHEMISTRY 23 9

TABLE 4

Mass transfer (in mmol kg ~) of Ca, Mg, alkalinity and Na f rom upgrad ient to downgradient

wells as indicated. The calculations were done after normalising all data to chloride (see text).

Positive numbers indicate flux from solid to solution and negative numbers indicate removal

from the aqueous phase

ACa AMg AAIk ANa (mmol kg ~)

(mmolk g i) (mmolk g i) (meqkg i)Measured Calculated

78 --* 79 -0 .2 8 -0 .5 5 -0 . 8 +0.41 +0.86

79 -~ 81 --0.4 --0.85 +1.56 +3. 76 +4.06

81 ~ 82 --0.12 -0 .0 1 +0.4 8 +0.89 +0. 74

82 ~ 83 --0.07 0 -4 .6 5 - 4 . 7 -4. 51

82 ~ 84 -0.0 5 0 -0 .3 -0.1 -0 .2

84 --, 85 +0.01 0 - 3. 0 -2 . 8 - 3. 085 ~ 86 -0 .02 0 + 1.38 + 1.5 + 1.42

86 ~ 87 -0 .02 0 +1.11 +2.1 +1,1 5

87 --, 89 0 0 +4 .5 +4 .0 +4 .5

89 --* 91 0 0 - 3 . 6 - 4 . 0 - 3. 6

91 --, 92 0 0 -4 .0 -3 .0 -4 .0

i n m u c h l a r g e r a b u n d a n c e in t h e a q u i fe r t h a n p r i m a r y p l a g io c l a se ( se e a b o v e )

a n d a r e m u c h m o r e r e a c t iv e .

W e p e r f o r m e d m a s s - b a la n c e c a l c u l a ti o n s a l o n g L i n e E t o d e t e r m i n e t h e

r e la t iv e i m p o r t a n c e o f t h e a b o v e p r o c e s s e s i n c o n t r o l l i n g th e m a j o r i o n

c h e m i s t r y . T h e r e s u l ts a r e p r e s e n t e d i n T a b l e 4 a n d w e r e d o n e i n t h e f o l l o w i n g

s e q u e n c e t o c a l c u la t e t h e b u i l d - u p o f s o d i u m :

(1 ) N o r m a l i s e a l l d a t a i n d o w n g r a d i e n t b o r e t o C 1 c o n c e n t r a t i o n i n

u p g r a d i e n t w e l l .

(2 ) N e t N a g a i n v ia c a t i o n e x c h a n g e a n d u p t a k e o f N a b y N a - s m e c t i t e e q u a ls :

2 × ( A C a + A M g ) + A H C O 3

( 3) I f Y A l k l o s s is g r e a t e r t h a n ( 2 x ( C a + M g ) ) l o ss t h e n n e t N a l o s s t o

N a - s m e c t i t e e q u a l s A A l k .

(4 ) C o m p a r e c a l c u l a te d N a g a i n w i th n o r m a l i s e d N a g a i n d e t e r m i n e d f r o m

t h e a n a l y t ic a l d a t a . T h e r e s u lt s (T a b l e 4 ) s h o w t h a t t h e N a f l u xe s p r e d i c t e d b y

t h e m a s s - b a l a n c e c a l c u l a t i o n s a re g e n e r a l l y s i m i l a r t o t h a t a c t u a l l y m e a s u r e d

( a ft e r n o r m a l i s i n g t o C 1 ). T h i s su g g e s t s t h a t t h e m o d e l a d e q u a t e l y a c c o u n t s f o r

t h e d i s t r ib u t i o n o f th e d i s so l v e d m a j o r i o n s o b s e r v e d a s t h e G A B w a t e r s f r o m

L i n e E p r o g r e s s b a s i n w a r d s . P o s i t iv e fl u xe s a re t h e r e s u lt o f e x c h a n g e o f N a

f o r C a a n d M g w i t h s o m e re m o v a l o f N a v ia f o r m a t i o n o f a N a - sm e c t i te

( r e a c t io n (4 )). N e g a t i v e f l ux e s s u g g e s t th a t e i t h e r m o r e N a is r e m o v e d v i a t h e

c la y r e a c t io n t h a n b y c a t i o n e x c h a n g e o r t h a t n o c a t i o n e x c h a n g e o c c u r s a n d



240 A.L HERC ZEG ET AL.

t h a t o n l y e qn . (4 ) p r o c e e d s t o r e m o v e N a f r o m s o l u t i o n b y c o n v e r s i o n o f

k a o l i n i t e t o N a - s m e c t i t e .

F r o m t h e r e s u l t s p r e s e n t e d a b o v e , t h e r e i s n o a p r i o r i r e q u i r e m e n t f o r a n

e x t e r n a l s o u r c e o f C O 2 to d i s s o l v e s o l i d c a r b o n a t e o t h e r t h a n t h a t p r e s e n t in

t h e r e c h a r g i n g w a te r . I f n o a d d i t i o n a l C O o w e r e to b e a c q u i r e d b y t h e g r o u n dw a t e r d u r i n g i t s t r a v e r se a c r o s s t h e b a s i n , t h e n t h e p H w o u l d r i se t o v a l u e s in

e xc es s o f 8 o r 9 b e c a u s e o f c o n s u m p t i o n o f C O o . R e m o v a l o f H C O 3 v ia

c o n v e r s i o n o f k a o l in i t e to a c a t i o n - b e a r i n g c l a y s u c h a s s o d i u m - s m e c t i t e

i n v o lv e s tr a n s fe r o f h y d r o g e n i o n f r o m c la ys t o s o l u t io n w h i c h c o n s e r v e s D I C

i n t h e w a t e r s b u t d e c r e a s e s a l k a l i n i t y. A n e t i n c r e a s e in a l k a l i n i t y c a n t h e r e f o r e

o n l y b e a c c o m p l i s h e d b y c a r b o n a t e d i s s o lu t i o n b u t m a i n t a i n i n g h i g h p C O 2

v a l u e s m u s t i n v o l v e a n e x t e r n a l s o u r c e o f C O ~. E v i d e n c e f o r a n e x t e r n a l

s o u r c e o f C O 2 is p r e s e n t e d i n th e f o l l o w i n g s e c t io n .

Carbonate chemistry and ;-~C

T h e c o m p o n e n t s o f t h e c a r b o n a t e s y s t e m a n d t h e ' 3C / '2 C r a t io o f t o ta l

d i s s o l v e d C O 2 a r e i n f l u e n c e d b y s e v er a l p ro c e s s e s w i th i n g r o u n d w a t e r

s y s t e m s . T h o s e p r o c e s s e s w h i c h a r e l i k e l y t o b e m o s t i m p o r t a n t w i t h i n t h e

G A B i n c l u d e C O2 r e s p i r a t io n b y p l a n t m a t t e r w i t h i n t h e s oi l z o n e o f t h e

r e c h a r g e a r e a s , d i s s o l u t i o n o r p r e c i p i t a t i o n o f c a r b o n a t e m i n e r a l s s u c h a s

c a lc i t e o r d o l o m i t e , a d d i t i o n o f C O 2 fr o m d e g r a d a t i o n o f o r g a n i c m a t t e r

w i t h in t h e a qu i fe r , a n d m e t h a n e p r o d u c t i o n . A n y o t h e r p r o c e s s t h a t i n v o lv e st h e t r a n s f e r o f p r o t o n s , s u c h a s t h e h y d r o l y s i s r e a c t i o n s i n v o l v i n g c la y

m i n e r a l s , o r t h e t r a n s f e r o f e l e c t ro n s b y b a c t e r i a ll y m e d i a t e d r e d o x r e a c t i o n s

( e . g . , s u l p h a t e r e d u c t i o n ) w i l l i n d i r e c t l y a f f e c t t h e c a r b o n a t e s y s t e m b e c a u s e

a d d i t i o n o r r e m o v a l o f h y d r o g e n i o n s w il l p e r t u r b t h e C O 2 s y s t e m a n d

t h e r e f o r e i n d i r e c t l y p r o m o t e c a l c i t e d i s s o l u t i o n o r p r e c i p i t a t i o n . A l l

c o m p o n e n t s o f t h e c a r b o n a t e s ys te m , t a k e n t o g e t h e r w i t h t h e s ta b le c a r b o n

i s o t o p e d i s t r ib u t i o n , c a n p r o v i d e a c o n s t r a i n t o n t h e p o s s i b l e c h e m i c a l

p ro c e s se s o c c u r r i n g w i th i n t h e g r o u n d w a t e r s y s te m a n d d e t e r m i n e t h e r o le o f

C O 2 i n t h e s e r e a c t i o n s .T h e r e i s a g e n e r a l i n c r e a s e i n t h e a l k a l i n i t y , D I C a n d 6 ' 3 C D , c v a l u e s w i t h

d i s t a n c e a l o n g L i n e E ( F ig s . 4 ( g )- 4 ( i) ) i n d i c a t i n g a d d i t i o n o f is o t o p i c a ll y

e n r i c h e d D I C a l o n g L i n e E . C o n s i d e r th e c as e w h e r e C O2 d e r iv e d f r o m

o x i d a t i o n o f o r g a n i c m a t t e r o r p l a n t r o o t r e s p i r a t io n i n t h e r e c h a r g e a r e a s

r e a c ts w i t h C a C O 3 a c c o r d i n g t o e q n . ( 3a ) ( se e a b o v e ) t o p r o d u c e t w o e q u i v -

a l e n t s o f a l k a li n i ty f o r e a c h n e t m o l e o f D I C p r o d u c e d . I f e q n . ( 3a ) p r o c e e d s

i n s t r ic t s t o i c h i o m e t r i c p r o p o r t i o n s , t h e ~ '3C H co ~ c a n b e g i v e n b y t h e e x p r e s s i o n :

~ ~t~( ~1 3C ( f i C c 0 2 - ]- C a C 0 3) ( 5 )HCO; = 2



G R E A T A R T E S I A N B A S I N G E O C H E M I S T R Y 241

-4

aa . - 6

J

- 1 0

0 -12 • • • ~ ~ A

- 1 4 •

n

- 1 6 . 0 0 .1 0 . 2 0 , 3

1 / D I C

F ig . 8 . 0 ~C t ~ l ~ a s a f u n c t i o n o f t h e in v e r s e o f D 1 C f o r g r o u n d w a t e r s f r o m t h e G A B J u r a s s i c a q u i f e r. T h e

t r e n d o f d a t a r e p r e s e n te d b y t h e d i a g o n a l l i ne i n d ic a t e s a d d i t io n o f a ~ C e n r i c h e d s o u r c e o f D I C w i th a

~ l~ C gl C, c o m p o s i t i o n o f a b o u t 0 %0 .

If the 6~3C concentrat ion of CO~ derived from plant respiration and

Jegradation in the soil zone in semi-arid regions within the recharge areas of

the GAB is estimated to be between - 20 and - 24%0 (Salamons and Mook,

1986) and the 613C concentration of CaCO3 within the aquifer is between 0

and -6%o, which is the range for non-marine carbonates (Salamons and

Mook, 1986), then the resultant bicarbonate produced in a closed system

according to eqn. (5) would be approximately -12%o. Therefore, if only

carbonate dissolution via addition of CO 2 was involved in adding DIC to thewater, then the 613C concentrat ion would evolve to about - 12 + 2%0 given

enough time or a sufficient amount of material and water residence time. Such

a scenario could adequately explain the GAB 613C data for the first 600 km o f

the Line E transect and the data for Line W (Fig. 4(i)). However, this process

does not explain the enriched 6~3C values measured for the last 600 km o f Line

E nor the enriched values in Line A.

On a plot of 6~3C values vs. the inverse of DIC concen tra tion (Fig. 8) we

observe two trends for the data. One group of points appear to be independent

of DIC concentrati on at a 613C value of about - 12 to - 14%o. Another group

of points define a linear trend with increasing ~3C values as I/DIC decreases.

The latter linear trend indicates mixing of DIC derived from two end-

members; one derived from dissolution of carbonate minerals and the other

end-member having an isotopically enriched source with a 6~3C composit ion

of around - 2 to 0%0.

Processes which could provide DIC enriched in '-~C include:

(1) Exchange of carbon atoms between dissolved CO, and calcite which

may ul timately result in a 6~3C concen tra tion of dissolved HCO 3 which is

close to that of the solid material, that is, about 0%o. However, isotopic



24 2 A.L. HERC ZEG ET AL.

e x c h a n g e w o u l d i n c re a se 6 t3C c o n c e n t r a t i o n o f t h e D I C w i t h o u t a c o n -

c o m i t a n t i n c r e a s e i n D I C c o n c e n t r a t i o n , t h e r e f o r e t h i s p r o c e s s c a n n o t b e

i m p o r t a n t i n d e t e r m i n i n g th e o b s e r v e d t r e n d s .

( 2) P r e f e r e n t i a l m e t a b o l i s m o f ~3C e n r i c h e d c a r b o n b y b a c t e r i a d u r i n g

o x i d a t i o n o f o r g a n i c m a t t e r i n a g r o u n d w a t e r s y s te m ( e .g . C h a p p e l l e e t a l. ,19 88). T h e m a g n i t u d e o f th i s e n r i c h m e n t is o f t h e o r d e r o f - 1 0 t o - 1 5 % o

f o r C O2 r e la t iv e t o o r g a n i c m a t t e r w h i c h w o u l d r e s u lt i n a 6 ~3C e n d - m e m b e r

c o m p o s i t i o n o f a b o u t - 1 2% o; t o o l i g h t t o ex p la i n th e G A B d a t a .

(3 ) P r o d u c t i o n o f m e t h a n e v ia C O 2 r e d u c t io n :

C O , + 4 H ~ --* C H a + 2 H 2 0 ( 6 a )

o r b y a c e t a t e f e r m e n t a t i o n :

2 C H 2 0 ~ C H 4 + C O 2 ( 6 b)

B o t h o f t h e se p ro c e s se s in c r ea s e th e D I C c o n c e n t r a t i o n a n d e n r i c h t h e D I C

i n 13C ( G a m e s e t a l ., 1 9 78 ; W h i t i c a r e t a l. , 1 9 86 ). C a r b o n d i o x i d e r e d u c t i o n

a l s o r e s u l t s i n a n e t i n c r e a s e i n D I C b e c a u s e t h e m e t h a n e p r o d u c t i o n s t e p

a lw a y s a c c o m p a n i e s C O2 p r o d u c t i o n v ia o t h e r a n a e r o b i c o x i d a t i o n p r o ce s se s

( K la s s , 1 9 84 ). T h e a m o u n t o f C O 2 c o n s u m e d t o g i v e m e t h a n e is le ss t h a n t h a t

p r o d u c e d b y f e r m e n t a t i v e o x i d a t i o n r e s u l t i n g in a n e t b u i l d - u p o f C O 2 . In

a q u i fe r s w h e r e t h e o r g a n i c c a r b o n c o n t e n t i s l o w , t h e r e d u c t i o n s t e p te n d s t o

d o m i n a t e t h e p r o d u c t i o n o f m e t h a n e ( e .g . G r o s s m a n e t al . , 19 89 ).

D I C w i th 6 L3C c o m p o s i t i o n s o f m o r e t h a n 0%0 h a v e b e e n r e c o r d e d ing r o u n d w a t e r s y t e m s ( e. g. B a r k e r a n d F r i t z , 1 9 81 ; G r o s s m a n e t a l ., 1 9 89 )

w h i c h in d i c a te s t h e i m p o r t a n c e o f m e t h a n o g e n e s i s in t h e D I C m a s s - b a la n c e

o f m a n y c o n f i n e d a n d p h r e a ti c g r o u n d w a t e r s ys te m s . F re e h y d r o g e n , m e t h a n e

a n d o t h e r l ig h t h y d r o c a r b o n s a r e p r e se n t in m o s t p a r ts o f t h e G A B

( H a b e r m e h l , 1 986 ), t h e r e f o r e t h e s e r e a c t i o n s m u s t b e t a k i n g p l a c e . T h e l in e a r

r e l a t i o n s h i p s e e n in F i g . 8 th e n , c a n b e e x p l a in e d b y a d d i t i o n o f C O 2 w i t h a n

i s o to p i c c o m p o s i t i o n w h i c h i s c o n s i s te n t w i th a c o m b i n a t i o n o f a n a e r o b i c

f e r m e n t a t i o n a n d r e d u c t i o n o f C O2 t o p r o d u c e m e t h a n e .

T h e r e l a t i o n s h i p b e t w e e n a l k a l in i t y a n d D I C f o r th e t h r e e t r a n s e c t s ( Fi g . 9)

c a n i n d i c a t e th e e x t e n t o f o p e n - o r c l o s e d - s y s te m b e h a v i o u r w i t h i n t h e a q u i f e r

w i t h r e s p e ct t o C O 2 . E a c h o f th e t r a n s e c t s s h o w l i n e a r r e la t i o n s h i p s , a l t h o u g h

w i t h d i ff e r e n t g r a d i e n t s a n d f o r L i n e s A a n d E a t le a s t, m o r e t h a n 1 m o l e D I C

is p r o d u c e d p e r e q u i v a l e n t o f a l ka l in i ty p r o d u c e d . I f c a r b o n a t e d i s s o l u t io n

w a s t h e o n l y s o u r c e o f D I C t o t h e g r o u n d w a t e rs , t h e n t h e ra t i o o f

A A I k : A D I C w o u l d b e a b o u t 2 : 1. H o w e v e r i f s o m e a l k a l in i t y is r e m o v e d v i a

p r o d u c t i o n o f o n e p r o t o n d u r i n g t h e c o n v e r s i o n o f k a o l in i t e t o N a - s m e c t i t e

( e q n . (4 )) t h e n t h e r a t i o w o u l d a p p r o a c h 1 : 1. T h i s v a l u e c a n o n l y b e

a c h i ev e d i f t h e r e w a s n o n e t p r o d u c t i o n o f N a .



G R E A T A R T E S I A N B A S I N G E O C H E M I S T R Y 243

30

• Un e E ( s l ope = 0 .67)A

O Line A s l o p e = 0.78

O 20 t = L i ne W ( s l ope = 1 .0) o 0

oo~ 0

O

_~m 10 •

&

O 1'0 2'0 30

DIC (mmo l / kg )

F i g . 9 , A l k a l i n i t y v s . D I C f o r al l t h r e e t r a n s e c t s s h o w l in e a r r e l a t i o n s h i p s w i th g r a d i e n t s r a n g i n g f r o m l

t o 0. 6 7. L i n e s A a n d E h a v e m o r e D I C a d d e d p e r e q u i v a l e n t o f a l k a li n it y a d d e d i n d i c a t i n g a s o u r c e o f

a d d i t i o n a l C O , t h a t i s n o t a c c o m p a n i e d b y g e n e r a t i o n o f a l k al in i ty .

B e c a u s e a n a e r o b i c o x i d a t i o n o f c a r b o n c o u p l e d w i t h m e t h a n o g e n e s i s

p r o d u c e s C O 2 w i th l i tt le o r n o c o n c o m i t a n t i n c re a s e in a l k a l i n i ty , w e s h o u l d

s ee m o r e D I C t h a n a l k a li n i ty p r o d u c e d a s t h e w a t e rs e v o l v e v ia t h is p ro c e s s .

T h e a d d e d C O2 i n d u c e s th e d i s s o l u t io n o f c a r b o n a t e s w h i c h i n t u r n i n c r ea s es

a l k a li n i ty a n d D I C i n a 2 : 1 r a t i o . W e d o o b s e r v e t h a t a b o u t 5 0 % a n d 3 0 %

m o r e m o l e s o f D I C a r e p r o d u c e d t h a n e q u i v a l e n t o f a l ka l in i ty fo r L i n e s E a n d

A r e s p e c t iv e l y ( F ig . 9 ). T h e r e f o r e , a d d i t i o n o f C O ~ v i a f e r m e n t a t i v e b a c t e r i a l l y

m e d i a t e d r e a c t i o n s is m o r e i m p o r t a n t t h a n c a r b o n a t e d i s s o l u t i o n t h r o u g h o u t

m o s t o f t h e G A B . T h i s is p a r t ic u l a r l y n o t i c e a b l e t o w a r d t h e b a s i n w a r d w e llsw h e r e in s i t u m i c r o b i o l o g i ca l ly m e d i a t e d f e r m e n t a t i o n r e a c t io n s b e c o m e m o r e

d o m i n a n t in p r o d u c i n g th e a d d e d D I C t o th e G A B w a te rs .

C O N C L U S I O N S

T h e c h e m i c a l e v o l u t i o n o f t h e m a j o r d i s so l v e d sp ec ie s a n d c a r b o n i s o t o pe

d i s t r i b u t i o n i n t h e e a s te r n a n d c e n t r a l p a r t s o f t h e G A B c a n t h e n b e e n v i s a g e d

a s fo l lo w s . A n i n i t ia l le v e l o f p C O 2 u p t o t h r e e o r d e r s o f m a g n i t u d e a b o v e

a t m o s p h e r i c le v e l s o f p C O 2 is a c q u i r e d b y w a t e rs n e a r t h e r e c h a r g e a r e a o w i n g

t o p l a n t r e s p i r a t i o n a n d o x i d a t i o n o f o r g a n i c m a t t e r i n t h e s o il zo n e . I n i t i a ll y ,

s il ic a te a n d c a r b o n a t e m i n e r a l s m a y d i s so l v e , a t l e as t in s o m e p a r t s o f t h e

b a s i n , re s u l t in g i n i n c r e a s e d a lk a l in i t y , N a , C a a n d M g c o n c e n t r a t i o n s a n d

5~3C DIc v a l u e s a r o u n d - 1 2 % o . A s t h e w a t e r s p r o g r e s s b a s i n w a r d s , c a t i o n

e x c h a n g e o f N a f o r C a a n d M g a n d s u b s e q u e n t r e a c t io n i n v o l v in g N a a n d

k a o l i n i t e t o p r o d u c e N a - s m e c t i t e e x e r t s a n i m p o r t a n t c o n t r o l o n t h e d i s -

t r i b u t i o n o f d is s o l v e d s pe c ie s f o r a l a rg e p a r t o f t h e G r e a t A r t e s i a n B a s i n . C l a y

m i n e r a l r e a c t io n s b u f f er a q u e o u s s il i ca c o n c e n t r a t i o n s b e l o w a m o r p h o u s S iO ~

s a t u r a t i o n . C a t i o n e x c h a n g e a n d d i s s o lu t i o n o f c a r b o n a t e m i n e r a l s d o n o t



244 A L HERCZEG ET AL

a p p e a r t o b e i m p o r t a n t a s t h e g r o u n d w a t e r s a p p r o a c h t h e d i s c h a r g e a re a s a s

t h e r e i s n e t N a r e m o v a l f r o m t h e a q u e o u s p h a s e .

A d i s s o l v e d i n o r g a n i c c a r b o n i s o t o p e m a s s b a l a n c e i n d i c a t e s t h a t t h e

g r o u n d w a t e r s y s t em is o p e n t o C O 2 a n d t h a t a d d i t io n o f C O 2 is a c c o m p l i s h e d

b y f e r m e n t a t i o n p r o c e s s es o c c u r r i n g in s it u. S o m e o f t h e a d d e d C O , is ab y - p r o d u c t o f m e t h a n o g e n e s i s in d i c a t e d b y a t3C e n r ic h e d e n d - m e m b e r f o r th e

D I C . T h e a d d i t i o n o f C O2 d r iv e s t h e c a r b o n a t e d i s s o lu t io n r e a c t i o n , t h e r eb y

e x e rt in g a n i m p o r t a n t c o n t r o l o n t h e e v o l u t i o n o f t h e N a - H C O 3 w a t e rs w i t h in

t he G A B .

A C K N O W L E D G E M E N T S

W e t h a n k D . J . G r e g g , M . M a l i k i d e s a n d E . K i s s f o r a s s i s t a n c e w i t h f i e l d

s a m p l in g a n d l a b o r a t o r y a n a l y s is o f w a t e r s . R e v i e w s o f e a r l ie r v e r s io n s o f th i sp a p e r b y E . M a z o r , A . V e n g o s h a n d t h r ee a n o n y m o u s r ef er e es a r e a p pr e c i-

a te d . M . A . H a b e r m e h l p u b l i s h e s w i th t h e p e rm i s si o n o f th e D i r e c t o r , B u r e a u

o f M i n e r a l R e s o u r c e s , G e o l o g y a n d G e o p h y s ic s .

R E F E R E N C E S

A i r e y , P . L , C a l f , G . E . , C a m b e l l , B . L ., H a r t l e y , P . E . , R o m a n , D . a n d H a b e r m e h l , M . A . , 1 9 79 .

A s p e c t s o f th e i s o t o p e h y d r o l o g y o f t h e G r e a t A r t e s i a n B a sin . I n : I s o t o p e H y d r o l o g y ,

V o l . 1 , I A E A , V i e n n a , p p . 2 0 5 - 2 1 9 .

B a r k e r , J. F . a n d F r it z , P ., 1 9 8 1 . T h e o c c u r r e n c e a n d o r i g i n o f m e t h a n e i n so m e g r o u n d w a t e r

f low s ys tem s . C an . J . E a r t h S c i ., 18 : 1802-181 6 .

B e n t l e y , H . W . , P h il li ps , F . W . , D a v i s , S . N . , H a b e r m e h l , M . A . , A i r e y , P . L . , C a l f , G . E . , E l m o r e ,

D . , G o v e , H . E . a n d T o r g e r s e n , T . , 1 9 8 6 . C h l o r i n e - 3 6 d a t i n g o f v e r y o l d g r o u n d w a t e r 1 . T h e

G r e a t A r t e s i a n B a s i n . W a t e r R e s o u r . R e s . , 2 2 : 1 9 9 1 - 2 0 0 1 .

B l a c k b u r n , G . a n d M c L e o d , S . , 1 9 8 3 . S a l i n it y o f a t m o s p h e r i c p r e c i p i t a t io n i n t h e M u r r a y -

D a r l i n g d r a i n a g e d i v i si o n , A u s t r a l ia . A u s t . J . S oi l R e s ., 2 1 : 4 1 1 - 4 3 4 .

B l ak e, R . , 1 9 8 9 . T h e o r i g in o f h i g h s o d i u m b i c a r b o n a t e w a t e r s in t h e O t w a y B a si n, V i c t o r i a ,

A u s t r a li a . I n M i le s D . L . ( E d i to r ) , W a t e r - R o c k I n t e ra c t i o n . B a l k e m a , R o t t e r d a m , p p . 8 3 -8 5 .

C a l f, G . E . a n d H a b e r m e h l , M . A . , 1 9 8 4 . I s o t o p e h y d r o l o g y a n d h y d r o c h e m i s t r y o f th e G r e a t

A r t e s i a n B a si n, A u s t r a l i a . I n : I s o t o p e H y d r o l o g y I A E A , V i e n n a , p p. 3 9 7 - 4 1 3 .

C h a p p e l l e , F . H . , M o r r i s , J .T . , M c M a h o n , P .B . a n d Z e l i b o r , Jr ., J. L . , 1 9 8 8 . B a c t e r ia lm e t a b o l i s m a n d t h e 6 ~3C c o m p o s i t i o n o f g r o u n d w a t e r , F l o r i d a n a q u i f e r s ys t e m , S o u t h

C a r o l i n a . G e o l o g y , 1 6 : 1 1 7 - 1 2 1 .

D r e v e r , J .I . a n d S m i t h , C . I . , 1 9 7 8 . C y c l i c w e t t in g a n d d r y i n g o f t h e s o il z o n e a s a n i n f l u e n c e

o n t h e c h e m i s t r y o f g r o u n d w a t e r i n a r i d t e r r a i n s . A m . J. S c i. , 2 7 8: 1 4 4 8 - 1 4 5 4 .

G a m e s , L . M . , H a y e s , J . M . a n d G u n s a l a s , R . P . , 1 9 7 8 . M e t h a n e p r o d u c i n g b a c t e r i a : n a t u r a l

f r a c t i o n a t i o n s o f th e s ta b l e c a r b o n i s o t o p e s. G e o c h i m . C o s m o c h i m . A c t a , 4 2 : 1 2 9 5 -1 2 9 7 .

G r o s s m a n , E . L . , C o f f m a n , B . K . , F r i tz , S .J . a n d W a d a , H . , 1 9 8 9 . B a c t e r ia l p r o d u c t i o n o f

m e t h a n e a n d i t s i n f l u e n c e o n g r o u n d - w a t e r c h e m i s t r y i n e a s t - c e n t r a l T e x a s a q u i f e r s .

G e o l o g y , 1 7: 4 9 5 - 4 9 9 .

H a b e r m e h l , M . A . , 1 9 8 0 . T h e G r e a t A r t e s i a n B a sin , A u s t r a l ia , B M R J . A u s t . G e o l . G e o p h y s . ,

5 : 9-38.



GREAT ARTESIANBASINGEOCHEMISTR~ 245

H a b e r m e h l , M . A . , 1 9 8 6. R e g i o n a l g r o u n d w a t e r m o v e m e n t , h y d r o c h e m i s t r y a n d h y d r o c a r b o n

m i g r a t i o n i n t h e E r o m a n g a B a s i n . G e o l . S o c . A u s t . S p e c . P u b l . N o . 1 2 , p p . 3 5 3 - 3 7 6 .

H e l g e s o n , H . C . , D e l a n e y , J . M . , N e s b i t t , H . W . a n d B i r d , D . K . , 1 9 7 8. S u m m a r y a n d c r i t iq u e o f

t h e t h e r m o d y n a m i c p r o p e r t i e s o f r o c k - f o r m i n g m i n e r a ls . A m . J . S ci ., 2 7 8 - A : 2 30 .

K i s s , E . , 1 98 2. D e t e r m i n a t i o n o f s i li c a i n g e o l o g i c a l m a t e r i a l s u s in g a t o m i c a b s o r p t i o n s p e c t r o -

p h o t o m e t r y . A n a l . C h i m . A c t a , 1 4 0 : 1 9 7 -2 04 .K l a s s , D . L . , 1 9 8 4 . M e t h a n e f r o m a n a e r o b i c f e r m e n t a t i o n . S c i e n c e , 2 2 3: 1 0 2 1 - 1 02 8 .

N e s b i t t , H . W . , 1 9 7 7 , E s t i m a t i o n o f th e t h e r m o d y n a m i c p r o p e r t i e s o f N a - , Ca-, a n d M g -

b e i d e l l i t e s . C a n . M i n e r a l . , 1 5 : 2 2 - 3 0 .

P a r k h u r s t , D . L . , P l u m m e t , L . N . a n d T h o r s t e n s o n , D.C. , 1 9 80 . P H R E E Q E - - A c o m p u t e r

p r o g r a m t b r g e o c h e m i c a l c a l c u l a ti o n s . U . S . G e o l . S u r v . W a t e r R e s o u r . I n v e st . 8 0- 9 6 ,

210 pp .

P l u m m e t , L . N . , P a r k h u r s t , D . L . a n d T h o r s l e n s o n , D . C , , 1 9 8 3 . D e v e l o p m e n t o f r e a c t i o n

m o d e l s f o r g r o u n d - w a t e r s y st e m s . G e o c h i m . C o s m o c h i m . A c t a , 4 7 : 6 6 5 - 6 8 5 .

S a l a m o n s , W . a n d M o o k , W . G . , 1 9 8 6 . I s o t o p e g e o c h e m i s t r y o f c a r b o n a t e s i n th e w e a t h e r i n g

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Geochemistry of Ground Waters From the Great Artesian Basin, Australia

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