Geochemical characterization of some tin-mineralizing granites of New South Wales

Geochemical characterization of some tin-mineralizing granites of New South Wales

Journal of Geochemical Exploration, 11 (1979) 321--333 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands GEOCHEMICAL ...

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Journal of Geochemical Exploration, 11 (1979) 321--333 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

GEOCHEMICAL CHARACTERIZATION GRANITES OF NEW SOUTH WALES

321

OF SOME TIN-MINERALIZING

D.N. JUNIPER and J.D. KLEEMAN Department of Geology, University of New England, Armidale, N.S.W. 2351 (Australia)

(Received and accepted May 30, 1979}

ABSTRACT Juniper, D.N. and Kleeman, J.D., 1979. Geochemical characterization of some tin-mineralizing granites of New South Wales. J. Geochem. Explor., 11: 321--333. The granites of three areas of Sn mineralization in the New England Area of New South Wales have been analysed to determine whether geochemical discriminants may be used to distinguish between granites which produce Sn mineralization, and those which do not. Neutron activation analyses of Sn are consistent with reports elsewhere that Snmineralizing granites have Sn concentrations of 15--30 ug/g, whereas granites which do not produce mineralization typically have about 5 ug/g Sn. Furthermore, Sn-mineralizing granites form compact groups, distinct from granites not responsible for mineralization, when plotted on ternary diagrams of SiO2--CaO+MgO+FeO--Na20+K20+A1203, Na + K--Fe--Mg and Ca--Na--K. We conclude that the Sn-mineralizing granites can be geochemically characterized.

INTRODUCTION T h e r e has b e e n c o n s i d e r a b l e c o n t r o v e r s y c o n c e r n i n g t h e g e o c h e m i c a l chara c t e r o f granites r e s p o n s i b l e f o r S n - m i n e r a l i z a t i o n . M o s t c o n t r o v e r s y concerns t h e c o n c e n t r a t i o n o f Sn in w h o l e r o c k samples. While B a r s u k o v (1957), Ianova (1963) and Rattigan (1963, 1964) propose that the whole r o c k Sn a b u n d a n c e is higher in granites p r o d u c i n g S n - m i n e r a l i z a t i o n t h a n in t h o s e w h i c h d o n o t , H o s k i n g ( 1 9 6 8 ) a n d F l i n t e r ( 1 9 7 1 ) argue against this. T h e l a c k o f reliable d a t a as n o t e d b y B o n d ( 1 9 7 0 ) , S c h m i d t ( 1 9 7 1 ) a n d G o o d m a n ( 1 9 7 3 ) has c o n t r i b u t e d t o t h e d i l e m m a . Tin is a d i f f i c u l t e l e m e n t t o analyse, especially in a r o c k m a t r i x . R a t t i g a n ( 1 9 6 4 ) , K l o m i n s k i and G r o v e s ( 1 9 7 0 ) and S t e m p r o k ( 1 9 7 0 ) have a t t e m p t e d s o m e c o r r e l a t i o n o f m a j o r e l e m e n t g e o c h e m i s t r y w i t h Sn-mineralizing granites, b u t little w o r k has b e e n p u b l i s h e d o n granites as Sn-mineralizing using g e o c h e m i c a l criteria. This w o r k is an a t t e m p t t o g e o c h e m i c a l l y c h a r a c t e r i z e s o m e granites f r o m t h e N e w E n g l a n d area w h i c h h a v e given rise t o S n - m i n e r a l i z a t i o n a n d t h u s distinguish t h e m f r o m t h o s e w h i c h h a v e n o t . T o a c c o m p l i s h this c o m p a r i s o n

322 104 analyses from three Sn-mineralizing and seven Sn-barren granites were used. The term "Sn-mineralizing granite" is here taken to mean a granite which has given rise to Sn mineralization, while a Sn-barren granite is one which has not, even though superimposed lode Sn deposits may occur within it. NEW ENGLAND TIN-MINERALIZING GRANITES The New England Sn-mineralizing granites belong to the New England Batholithic Suite (Wilkinson, 1969; Flood, 1971). These are the Gilgai Granite, the Mole Granite and the R u b y Creek Granite. For detailed descriptions of the R u b y Creek Granite see Phillips (1969), Olgers and Flood (1970), Robertson (1970a, b, 1972) and Weber (1974) and of the Mole Granite see Weber (1974). The Gilgai Granite Previous mapping of the Gilgai Granite has been of an incidental and reconnaissance nature (Chestnut, 1971; Chestnut et al., 1973 ; Pogson and Hitcherts, 1973). New detailed mapping (Fig. 1) was necessary to establish geological boundaries and field relations, since there has been some dispute whether the Tingha Adamellite, or an "acid granite" has been responsible for the Sn mineralization. The name Gilgai Granite is proposed to supersede the inappropriate name " A c i d " Granite previously used (Cotton, 1909). Gilgai is the only town in the exposed mass and is close to the type location ( G R 1 8 0 9 6 3 analysis no. 1). The more or less equigranular, leucocratic Gilgai Granite has intruded the porphyritic Tingha Adamellite, exhibiting a chilled margin and xenolithic contact at a few locations. Small exposures of Gilgai Granite occur within the Tingha Adamellite mass. Spatial relationships in mineshafts indicate that the Gilgai Granite has been emplaced under the Tingha Adamellite at other points. The Tingha Adamellite is intruded by dykes of a fine-grained phase of the Gilgai Granite at other locations. The Gilgai Granite is bounded on the west by the Oakey Creek Granite (Cotton, 1909) of the Bundarra Suite of the New England Batholith, against which it exhibits an unusually extensive chilled margin. Dykes from the Gilgai Granite penetrate the Oakey Creek Granite at two locations. Dykes of the Gilgai Granite also intrude an undifferentiated granite at its southwest boundary. It appears that the r o o f of the Gilgai Granite is just being exposed and the occurrence of chemically equivalent porphyries which have been intruded by the Gilgai Granite substantiate this. The porphyries are considered to be the extrusive equivalent of the Gilgai Granite. Tin mineralization occurs as lodes in both the Gilgai Granite and Tingha

l i pgg~ Undifferentioted gronite$

I p p ~ Porphyry

~Pto ] Tingho Adomelii~e

~--~

//"--'~7.~]/.i

Tv

INVERELL

I ~

! p

TINGHA 8

Mine estoblilhed Geo4ogicotboundory inferred Rood I

Pro

IOROUGH

P-Cl

ILGAI

-~:

Pgo

j/

Pro

Pgg

~

• ....

~'~Tv

I

/

Pgg

Pgg ~

' j

Pug

i

pgg

Pto

N•" I ' I

Pgg

km

@

740

~

O0

pp

co_

90

PrO

GRANITES OF THE GILGAI- TINGHA AREA I

o

Tv

Pug

.~ /Y " P-Cs ,~ Rgo ~/ / f

Tv

~ J ~

pgg

j

.-

Tv

G

)

PO0

Fig. 1. Map of Gilgai Granite south of Inverell, New South Wales, Australia.

~.Cp[p_csI S~limentsondhorflfels /

P

Volconicsond their derived sediments

: ~g-g~ Gilgoi Gronite

T [~

03 t~ O3

324 TABLE I Gilgai Granite -- average modal and mesonormative composition Average modal composition

Average mesonormative composition

Quartz K-feldspar Plagioclase Biotite

Q Or Ab An C Bi Ho Wo Mt He Ap

24.9 60.7 12.5 1.9

35.8 23.2 33.3 3.5 0.7 0.7 {1.7)* (0.1)* 0.2 0.8 0.1

Total

100.1

*Mesonormative compositions of Ho refer to three samples, and Wo to two samples only.

Adamellite and as alluvial or "deep lead"-type deposits, mainly along Copes Creek. These latter have been comprehensively described by Came (1911) and Weber (1974). Early workers (Andrews, 1907a, b; Cotton, 1909; Benson, 1913) writing at the time of great mining activity, considered the Gilgai Granite as the Snmineralizing granite. It appears that subsurface evidence available from mines at the time helped towards drawing this conclusion. Hesp (1973) and Hesp TABLE II Gilgai Granite -- major element analyses 1 SiO~ TiO 2 Al203 Fe203 FeO MnO MgO CaO Na20 K20 P2Os H~O÷ H~OCOs To~l

2

3

4

5

6

7

8

74.91 0.12 12.21 1.35

77.81 0.09 11.70 0.70

79.60 0.07 11.89 0.87

80.47 0.11 11.64 0.72

77.53 0.09 11.69 1.02

78.77 0.12 11.10 1.00

69.65 0.49 13.97 2.67

78.75 0.09 11.59 1.23

0.03 0.24 0.69 4.98 5.38 0.01 0.08

0.03 0.56 4.36 4.65 0.02 0.08

0.01 0.03 0.48 3.78 3.18 0.01 0.08

0.01 0.03 0.56 4.24 2.13 0.01 0.08

0.02 0.03 0.80 4.12 4.61 0.01 0.08

0.01 0.04 0.53 3.61 4.72 0.02 0.08

0.06 1.62 2.74 3.59 4.08 0.13 1.00

0.02 0.04 0.52 3.59 4.09

100.00

100.00

100.00

100.00

100.00

100.00

100.00

100.00

0.08

Analysts/source: Analyses 1--13, Juniper (this work); 14, 15, Rattigan (1964); 16, H.P. White in Came (1911); 17, Flinter (1972). Sample locations are shown in the Appendix.

325 a n d R i g b y ( 1 9 7 2 , 1 9 7 3 , 1 9 7 4 ) a c c e p t e d this, b u t W e b e r ( 1 9 7 4 ) has caut i o n e d against u n q u e s t i o n e d a c c e p t a n c e . I t is clear t h a t t h e Gilgai G r a n i t e is t h e Sn-mineralizing p l u t o n , as t h e s a m e s t r u c t u r a l p a t t e r n o f joints p e r v a d e s b o t h it and the T i n g h a A d a m e l l i t e . T h e earliest possible ore e n t r y is f o l l o w i n g t h e solidification and j o i n t i n g o f t h e u p p e r p o r t i o n s o f the Gilgai G r a n i t e . As l o d e Sn m i n e r a l i z a t i o n is usually f o u n d within its s o u r c e p l u t o n or its r o o f a d e e p e r s o u r c e t h a n the Gilgai G r a n i t e is d i s c o u n t e d . Aplite d y k e s in b o t h p l u t o n s d e m o n s t r a t e t h a t t h e Gilgai G r a n i t e has filled t h e joints w i t h a l a t e r fluid.

Petrological and chemical description. T a b l e I s h o w s an average m o d a l and m e s o n o r m a t i v e c o m p o s i t i o n f o r the Gilgai G r a n i t e . Analyses f o r the Gilgai G r a n i t e are given in T a b l e II. M e s o n o r m a t i v e C o l o r I n d e x {Color I n d e x derived f r o m t h e M e s o n o r m s ) ranges f r o m 0.87 t o 1 1 . 3 8 w i t h 3.7 average. Average ( m o d a l ) C o l o r I n d e x is 1.9. Average n o r m a t i v e plagioclase c o m p o s i t i o n is AnT. P o t a s s i u m f e l d s p a r c a n o c c u r as p h e n o c r y s t s or g r o u n d m a s s . F r e q u e n t t w i n n i n g is c a r l s b a d or c r o s s h a t c h e d . M i c r o p e r t h i t e s are c o m m o n . G r a n o p h y r i c i n t e r g r o w t h s o f q u a r t z and p o t a s s i u m f e l d s p a r o f t e n r e p l a c e t h e r i m s o f t h e p o t a s s i u m f e l d s p a r crystals. Plagioclase is usually e u h e d r a l and can c o n t a i n inclusions o f b i o t i t e and allanite. B i o t i t e is r e p r e s e n t e d b y green, Fe-rich and b r o w n , Ti-rieh varieties, a n d it m a y be e u h e d r a l or c o r r o d e d . I r o n o x i d e s a n d zircon are o f t e n associated. In s o m e cases t h e b i o t i t e is w h o l l y or p a r t i a l l y altered t o chlorite. T h e Gilgai is classified u n e q u i v o c a b l y a granite u n d e r t h e s y s t e m s o f b o t h

9

10

11

12

13

14

15

16

17

79.37 0.05 11.53 1.30

77.92 0.06 12.07 1.14

75.25 0.23 12.89 2.40

76.67 0.19 12.30 0.77

78.70 0.11 12.05 1.35

76.45 0.20 11.41

76.51 0.13 12.77

70.20 0.38 14.70

0.06 0.03 0.74 3.62 3.22

0.03 0.25 1.11 3.54 4.05 0.17 0.08

0.01 0.22 0.99 3.24 5.59 0.04 0.08

0.02 0.04 0.59 3.83 3.22 0.01 0.08

2.19 0.05 0.15 0.65 3.98 4.56 0.20

1.01 0.10 0.17 0.71 3.50 4.94 0.14

0.08

0.01 0.03 0.56 4.20 3.80 0.13 0.08

71.27 0.24 13.40 1.11 1.89 0.07 0.79 2.46 3.08 4.91

100.00

100.00

100.00

100.00

100.00

0.18 0.32 0.03 99.82

99.98

99.75

2.45 0.06 0.84 1.85 2.80 5.07 0.13 0.07

98.55

326 Nockolds (1954) and C h a y e s ( 1 9 5 7 ) . The Mole and R u b y Creek Granites are petrologically similar. By comparison, the Tingha Adamellite, representative of the Sn-barren granites, is a biotite adamellite which plots close to the granodiorite boundary (Chayes, 1957). GEOCHEMICAL CHARACTERIZATION OF THE GRANITES

Source of data Major element data are from analyses reported by Came (1911), SaintSmith (1911), Rattigan (1964), Phillips (1968) and Flinter et al. (1972) and unpublished analyses conducted at the University of New England by H.R. Butler, A.G. Connor, D.N. Juniper and G.I.Z. Kalocsai. Full details of all these analyses are available from the authors on request. Trace Sn determinations were carried out by the authors using neutron activation analysis. The ~- decay of l:lSn formed by 12°Sn (n,7) was used. Following thermal neutron irradiation, sample fusion, solution, and a radiochemical separation and ignition was used to isolate Sn as the oxide. Chemical yields were determined with an inactive Sn carrier, and standardization was with spectroscopically pure Sn foil. Activities were determined by an end-window Geiger-Miiller detector and counter, and radiochemical purity was checked by following decay of preparations through one or several halflives. The m e t h o d of neutron activation analysis is particularly suitable for the analysis of Sn in a rock matrix due to its selectivity, accuracy and sensitivity. Other methods are often unreliable at low concentrations in silicate rock matrix.

Methods of approach to geochemical characterization of tin-mineralizing granites Geochemical attempts to characterize Sn-mineralizing granites have taken t w o lines of investigation. The first being to determine the absolute Sn concentration of the rock (SnR) and that of the constituent minerals (SnM) in order to determine if there is a relation between a particular granite as Snmineralizing and either or both Sn R and Sn M. The second approach is the consideration of the distribution of other elements in both the whole rock and constituent minerals. In both methods a comparison must be made with Sn-barren granites.

Tin content of granite. Barsukov (1957) and Ianova (1963) have determined that Sn-mineralizing granites have a greater SnR than Sn-barren granites. Barsukow (1957) found Sn-mineralizing granites to contain 16--30 pg/g Sn compared with 3--5 pg/g Sn for Sn-barren granites.

327 Ianova (1963) found that in the tin-tungsten belt of Eastern Transbaikaliya the Sn-mineralizing Durulguyev Granite Massif had an average of 23.4 pg/g Sn while the Sn-barren Tsagan-Olvi and Kondui Granites had 5 ug/g Sn. The sensitivity of the analytical method did not permit detection below 5 gg/g. In northeast Queensland {Australia) Sheraton and Black (1973) found that only the Sn-mineralizing granites (Elizabeth Creek, Mareeba, Finlayson and Esmerelda Granites) had mean SnR values greater than the stated detection limit of 4 pg/g. The average SnR being 5 ug/g. Rattigan (1963, 1964) reports a considerable difference between Australian Sn-mineralizing granites and Sn-barren granites. The Sn-mineralizing granites (Rattigan, 1964) have a range of 4--45 t~g/g Sn (mean 20 ug/g) and the Sn-barren a range of 2--5 pg/g (mean 3.1 pg/g). A plot (Fig. 2) of Sn R against frequency of occurrence for Russian {data

50 I- l--

- ] T i n - barren

40 I-

I

Tin-

mineralizing

30 I--

c:

20 -

0"

10

II

I0

20 Tin concentration

30

(pg/g)

40

Fig. 2. Frequency distribution of Sn content of Australian and Russian granites. Data from Rattigan (1963, 1964) and Ianova (1963).

328

from Ianova, 1963) and Australian (data from Rattigan, 1963, 1964) granites shows that the Sn R of the Sn-mineralizing granites is higher, though not uniformly so, than Sn-barren granites. Hosking (1968) claims that there is or should be no relation between Sn R and the potential of a granite to give rise to Sn mineralization. Flinter (1971), Hesp (1971) and Flinter et al. {1972) state that, " . . . the Sn content of a granitoid has no bearing on the presence of mineralization...".

Tin content of New England granites. Table III shows the Sn R for some New England granites. The respective representative values for SnR of 25 and 24 pg/g for the Sn-mineralizing Gilgai and Mole Granites compared with 5 ~g/g for the Sn-barren Tingha Adamellite demonstrate that the SnR of New England Sn-mineralizing granites can be expected to be 4 - 5 times that of Sn-barren granites. Major element geochemical characterization. A ternary plot, SiO:--CaO+ MgO+FeO--Na:O+K20+A120~ suggested by Stemprok (1970) after Greig (1927) can be used to define a Sn-mineralizing rock field with only a few points falling outside. Rattigan (1964) used the ternary plots Na+K--Fe--Mg and Na--K--Ca to infer a trend of magmatic evolution. These have been used to define Snmineralizing rock fields. Si02--CaO+MgO+FeO--Na20+K20+AI203. Fig. 3 shows that Sn-mineralizing and Sn-barren fields can be described on this plot. Na+K--Fe--Mg. Fig. 4 shows that very clear Sn-mineralizing and Sn-barren rock fields can be defined.

TABLE III Tin content o f some New England granites as determined by neutron activation analysis Class

Rock

Sample

SnR (ug/g)

Tin-mineralizing granite

Mole Granite

21 47

17 31

Ruby Creek Granite

48

6

3 8 9 4 1 2

21 8 26 30 21 11

71 73 77

28 6 5

Gilgai Granite

Tin-barren granite

Tingha Adamellite

329

Field of tin-mineralizing

Si02 A • Tin-mineralizing rocks

17 75

5

No2 O+ K2 0 + A I 2 0 5

CoO+MgO+FeO

Fig. 3. System SiO:--CaO+MgO+FeO--Na20+K20+AI~O 3 for New England granites.

FQ

Field of 1'in-mineralizing granites -.

NQ+K 5

50/<

• Tin-mineralizmg rocks rocks

Mg

Fig. 4. System Na+K--Fe--Mg for New England granites.

o

/

/

/

0

0

0

2

Ca

=o

0 t-

o

o

o

m

I0

2O

50

60

Fig. 6. Mesonormative Color Index against Differentiation Index for New England granites.

57

• Tin-mineralizing rocks o Tin-barren rocks / Field of Tin Mineralizing < granites

Fig. 5. System Na--K--Ca for New England granites.

/

12

[

Na

0

7

'%0°o

) /



.....

A

K

o

8

o

o

O

80 Differentiation

©

°°°~%

oOo

Index

I00

• Tin-mineralizing rocks o T i n - b a r r e n rocks

331

Na--K--Ca. In Fig. 5 a Sn-mineralizing granite field is well defined with only a small a m o u n t of overlap from one field to the other. Relation of Mesonormative Color and Differentiation Indices. Fig. 6 shows that there is a broad negative correlation between the Mesonormative Color Index {based on mineral compositions calculated by a Mesonorm) and the Differentiation Index and that a field of Sn-mineralizing granites can be described. A second criteria need only be used where the first is insufficient to characterize the rock. APPLICATION OF GEOCHEMICAL CRITERIA

Several geochemical criteria have been determined which have application in exploration for Sn. It has been substantiated that Sn R is 4--5 times as high in Sn-mineralizing than in Sn-barren granites. However, there is a need for the development of a rapid, precise and accurate analytical technique to take advantages of these findings. The major element geochemical characterization can be used on the basis of normal whole rock analysis. Only seven elements need be analysed for the ternary plots, while a complete major element analysis is required for the Mesonormative Color Index--Differentiation Index plot. As 90--95% of samples fall in the appropriate field only a small number of representative samples need be used.

Acknowledgements Thermal neutron irradiations were performed in the H I F A R reactor of the Australian Atomic Energy Commission Research Establishment at Lucas Heights, New South Wales, and funded by a grant from the Australian Institute of Nuclear Science and Engineering. The Mesonorm computer program was supplied by Dr. N.C.N. Stephenson. We thank Mr. M. Bone for drafting assistance, and Mrs. R. Vivian for typing the manuscript. APPENDIX L o c a t i o n o f a n a l y s e d s a m p l e s o f Gilgai G r a n i t e Analysis No. 1 2 3 4 5 6 7

Location

Analysis No.

Location

180963 363912 271883 271883 324878 383889 190868

8 9 10 11 12 13

084848 176873 163893 293962 305821 346921

L o c a t i o n grid r e f e r e n c e s are t h e A u s t r a l i a n 1 0 0 0 m m a p grid, z o n e 56. T h e same grid is u s e d in Fig. 1.

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