THE STRATIGRAPHY and GEOCHEMISTRY of the GRANITE GNEISSES, BROKEN HILL, N.S.W. by IAN D. BLUCHER Department of Mining and Minera

THE STRATIGRAPHY AND GEOCHEMISTRY

OF THE . GRANITE GNEISSES, BROKEN HILL, N.S.W.

IAN D. BLUCHER

Department of Mining and Mineral Sciences, w.s. & L.B. Robinson University College, University of New South Wales.

MARCH, 1983. This thesis contains no material which has been accepted for the award of any other degree or diploma in any Tertiary Institution; nor does it contain any material previously published or written by any other person except where due reference and acknowledgement is made in the text.

I.D. BLUCHER. ACKNOWLEDGEMENTS

I would like to thank my supervisors Ors. K.D. Tuckwell and P.C. Rickwood for their advice and help during the preparation of this thesis. The analytical expertise of both Dr. T. Hughes of Melbourne University and

The Zinc Corporation, Limited assay laboratory is greatly appreciated.

The financial support provided by the Broken Hill Mining Managers'

Association, the geological staff of both The Zinc Corporation, Limited and North Broken Hill Limited for specimens, maps and helpful discussions and the technical expertise of Mr. J. Vaughan, Mrs. K. Goldie, Ms. J. Gray and Mrs. J. Day all contributed to the successful completion of this study. Abstract

The Granite gneisses located at Broken Hill have been examined in order to establish their internal stratigraphy, the significance of any chemical trends present and also an origin for these gneisses.

Mineralogically these gneisses,which are chemically indistinguish able from one another can be divided into garnet-bearing or garnet-absent, quartz-feldspar-biotite gneisses, and an aplitic-textured quartz-feldspar rich fels. The first two gneiss types may in places be rich in feldspar augen and grade vertically into augen-poor or layered gneisses. Augen are interpreted as premetamorphic crystal relicts and the presence of garnet in stratigraphically distinct zones is believed to be due to the local, premetamorphic, mobilization of Na and K from original feldspars and clays.

These alkali-deficient sites could then generate garnet when metamorphosed.

The aplitic fels lllarks the stratigraphic top of the whole Granite Gneiss sequence. It is present within the lllain granite gneiss body and, although texturally and chemically distinct from the other two gneiss types exhibits similar chemical trends and ratios which indicate its close affinities with these gneisses.

The origin andlllOde of deposition proposed for these gneisses is that they were felsic, calcalkaline, crystal-rich volcanic material of dacitic composition, deposited in an aqueous environment as a series of debris or turbidite flows. Physical conditions prevailing during the deposition of this -volcanic sedilnent developedgrainsize abundance, density and total grainsize grading as well as layering features resembling those of

Bouma sequences. The forward motion of these debris flows was sufficient to cause ablation ,t.o ..take place of the finer grained material from the outer surface, this material settled out of suspension and eventually formed what is now the aplitic quartz-feldspar fels. The development of these features has led directly to a chemical signature which closely resembles an igneous fractionation pattern even though it is the sole result of sedimentological processes. Table of Contents

Page No.

1. Introduction 1

1.1 Terminology 1

2. Granite gneiss stratigraphy

2.1 Introduction 4

2.2 Methodology 4

2.2.1 Stratigraphic Synthesis 7

2.3 Stratigraphic reconstruction

2.3.1 Upper Granite Gneiss 9

2.3.2 Lower Granite Gneiss 14

2.4 Layering 15

2.5 Description of Gneiss types

2.5.1 Aplitic textured quartz-feldspar fels (Ap) 15

2.5.2 Feldspar biotite garnet gneiss (Fbg) 18

2.5.3 Feldspar biotite gneiss (Fb) 18

2.5.4 Green-grey aplite (Gap) 19

2.5.5 Quartz augen rocks 19

2.5.6 Amphibolite 21

3. Mineralogy 24

3.1 Metamorphic conditions 24

3.2 Aplitic textured quartz-feldspar fels (Ap) 25

3.3 Feldspar biotite garnet gneiss (Fbg) 26

3.4 Feldspar biotite gneiss (Fb) 29

3.5 Green-grey aplite (Gap) 29

3.6 Quartz augen rocks 30

4. Granite gneiss chemistry 31

4.1 Sample analysis 31

4.2 Analytical results 33

4.2.1 Harker-style variation diagrams 33

4.2.2 Trace- and interelement variation 41 (cont.) Table of Contents (cont.)

Page No.

4.3 Multivariate data analysis 52

4.3.1 Principal components Analysis 53

4.3.2 Cluster Analysis 55

4.3.3 Results of Multivariate data analysis 56

4.3.4 Kolmogorov-Smirnov two sample test 62

5. Petrology 65

5.1 Alteration 66

5.2 Petrological character 71

5.2.1 Alkaline vs. subalkaline composition 72

5.2.2 AFM variation 72

5.2.3 An-Ah-Or projection 75

6. Discussion 77

6.1 Origins of Granite gneiss 77

6.2 Depositional mechanisms for the Granite gneisses

6.2.1 Air fall tuffs 79

6.2.2 Mass flow 80

6.3 Feldspar augen and megacryst formation 84

6.4 Garnet formation in the Granite gneisses 86

6.5 Geochemical trends in relation to a mass flow model 87

6.6 The significance of non-Granite gneiss lithologies 89

7. Conclusions 93

References 96

Appendices 101 List of Figures

Figure Description Page No.

1 Locality plan of study area and major structural Appended elements.

2a-d Unfolded diamond drill sections showing the Appended relative position of stratigraphic and mineralogical variations in the Upper and Lower Granite Gneisses from the Northern Leases and Southern Extensions.

3 & 4 Small scale mapping depicting the relationships 5, 7, present between Quartz augen rocks, amphibolites and Granite 9neiss in the Lower Granite Gneiss.

5 Schematic, cutaway block reconstruction of the Appended Upper and Lower Granite Gneisses.

6a-i Harker style plots of sio2 vs. Tio2 , A1 203 , Fe2o3 , 42-45 MnO, MgO, CaO, K20, Na2o and P 205 .

7a,b,c Plots of K20 vs. Rb, Ba and Na20. 46

8a,b Plots of Fe2o3 vs. Ti02 and MgO. 47

9a,b,c Plots of Ti02 vs. Zr, y and er. 48

lOa,b,c Plots of Ni vs. Cr, V and MgO. 49

lla,b Plots of Zr vs. Y and Ce. 50

12a,b,c Plots of niggli mg vs. niggli si, niggli er and 51 niggli ni.

13 Principal Component analysis results for Fbg, Fb 58 and Ap Granite gneiss types.

14 Cluster analysis dendrograph of Northern Leases 60 Granite .gneiss, based on chemistry.

15 Cluster analysis dendrograph of Northern Leases 61 Granite gneiss, based on mineralogy.

16 Plot of K2o_+ Na2o vs. Si02 for Northern Leases 73 Granite gneisses.

17 AFM diagram for Northern Leases Granite gneisses. 74

18 An-Ab-Or projection for Northern Leases Granite 76 gneisses.

19 Postulated method of deposition for the Granite 83 gneisses. List of Tables

Table Description Page No.

1 Average volume fraction analyses for Granite gneisses 27 and associated rock types.

2 Analytical results for USGS G-2, AGV-1. 32

3a Aplitic textured quartz-feldspar fels chemistry. 34 3b Feldspar biotite garnet gneiss chemistry. 35 3c Feldspar biotite gneiss chemistry. 36 3d Quartz augen and related rock types chemistry. 37 3e Amphibolite, Biotite selvage, and Green-grey aplite 38 chemistry.

4 Principal components for all Fbg, Fb and Ap gneiss 57 types.

5 Kolmogorov-Smirnov two sample comparison between Fbg 63 and Fb gneisses.

6 Average composition of rock types used in Barth Standard 68 Cell calculations.

7 Changes in Barth Standard Cell needed to convert Arkose, 69 Sillimanite Gneiss, Dacite and Rhyolite to Granite gneiss type lithologies.

8 Chemical characteristics of Granite gneiss types with 70 respect to all possible parents. List of Plates

Plate Description Page No.

1 Feldspar-biotite gneiss clasts in Feldspar-biotite, 11 and Feldspar-biotite-garnet gneiss.

2 Feldspar augen grain size and abundance decreasing 12 stratigraphically upwards.

3 Aplitic textured fels and feldspar augen-bearing 13 Feldspar-biotite gneiss.

4 Amphibolite and biotite-selvage layers within 16 Feldspar-biotite gneiss.

5 Fine grained layering developed in Feldspar-biotite 17 and Feldspar-biotite-garnet gneisses.

6 Mottled and fragmental, layered Green/grey aplite and 20 layered quartz augen rock.

7 Amphibolite textures representing possible premetamorphic 23 flow top breccias and infilled vesicles. 1

CHAPTER 1

1. Introduction

The Willyama Complex of New South Wales contains a number of coarse grained, quartzo-feldspathic gneisses which are locally termed granite or granitic gneisses. At Broken Hill two bodies of gneiss crop out sporadically in two parallel zones on the eastern and western sides of the Broken Hill ore bodies from Kellys Creek, 10 kms to the south west of Broken Hill, to beyond Piesses Nob, 15 kms to the northeast (Fig. 1).

It is this close proximity to the ore zone which has caused the origins of these bodies of gneiss in particular to be subject of considerable contro versy and debate. The aim of this study is to resolve if possible, through an examination of the spatial variations of geochemistry and mineralogy, a likely mode of origin for these gneisses and the method by which they arrived at the stratigraphic position they now occupy.

Willyama Complex stratigraphy has been firmly established by

Stevens et al. (1979). These workers place the granite gneiss at the top of Suite 3~ a metamorphic/stratigraphic group of rocks which consists largely of abundant feldspathic psai:nopelitic metasediments, amphibolites and bodies of granite gneiss. Suite 4, which overlies Suite 3 and contains all of the major lead-zinc mineralization in the Willyama Complex, consists predominant ly of interlayered metapsammites and pelites, psammopelites and amphibolites.

No granitic gneisses are present in Suite 4, although a fine to medium grained garnet-rich quartz-feldspar-biotite gneiss locally known as "Potosi

Gneiss" occurs in the vicinity of mineralization. Thus on a local scale the granite gneisses under study here are a "basement" to Suite 4 lithologies.

1.1 Terminology

The body of gneiss which lies to the west of the Broken Hill ore bodies is known as the Upper Granite Gneiss and the body on the eastern side of the Broken Hill antiform,as the Lower Granite Gneiss. Both bodies possess a simple mineralogy of quartz, feldspar, biotite and garnet with minor accessory sillimanite, however a variety of subtypes can be recognised which may possess varying abundances of feldspar augen, or are garnet-free, 2

or are very fine grained and exhibit an aplitic texture. Abundant amphibo

lite horizons are rare,metapelitic horizons may also be present as internal

features. It is current geological practice at Broken Hill to refer to these

granite gneiss bodies as the Upper and Lower Granite Gneiss without genetic

or structural connotations. This is despite the work of Laing et al. (1978) which places both granite gneiss bodies in the Broken Hill mines area in the

one stratigraphic horizon and so, even though this study provides chemical

and mineralogical evidence in support of this, the terms Upper and Lower

Granite Gneiss will be retained here as an aid in referencing each body.

Historically the terminology relating to the Upper and Lower

Granite Gneisses has varied with geological fashion and although confusing

can be summarized as follows: The first worker to study these gneisses was

Andrews (1922) who used the general term "Platy Gneiss" for both bodies and

referred to the western outcrop in particular as the "Hanging Wall Gneiss".

The stratigraphic reconstructions by Gustafson et al. (1950),

King and Thomson (1953) and King and O'Driscoll (1953), placed both the

eastern and western bodies in the same horizon, above the ore bodies. It

followed therefore that an appropriate tenn for these gneisses was "Hanging

Wall Gneiss", a term also favoured by Dewar (1968). However Carruthers and

Pratten (1961) placed the eastern horizon stratigraphically below the ore bodies and the eastern horizon stratigraphically above the ore bodies and so

introduced the terms "Lower Granitic Gneiss" and- "Upper Granitic Gneiss".

A variety of terms have been subsequently introduced and include1

"Upper and Lower Hanging Wall gneiss" (Lewis et al., 1965), "Footwall and

Hanging Wall granitic gneiss" (Phillips and Ransom, 1970), "quartz-alkali

feldspar-plagioclase-biotite gneisses (Vernon, 1969) and also "Upper and

Lower quartzofeldspathic gneisses (Stone, 1973).

Samples of diamond drill core used in this study were obtained

from North Broken Hill Ltd's. (NBH) Northern Leases and from The Zinc

Corporation (Z)-New Broken Hill Consolidated (N) mine and Southern Extensions 3

leases. This sampling programme is additional to, and compliments those carried out by Stone (1973), Shaw (1974), Plimer (1976) and Klingner and

McConachy (1975); consequently a comprehensive geochemical and mineralogical coverage of the whole strike length of the Upper and Lower Granite Gneisses has now been achieved.

Each core sample referred to in the text is prefixed by mine name, followed by hole number and the depth, in original measurement units, at which it was obtained, e.g. NBH 2058/3194'. Surface samples are prefixed by sand referred to by number, e.g. Sl2, thin sections of all samples are prefixed t.s •• The results of all Granite gneiss intersections logged by the author are presented in Appendix A, and brief descriptions of material sampled, in Appendix B. All samples are stored at the w.s. & L.B. Robinson

College, University of New South Wales, Broken Hill and will be transferred at a .l.ater date to the Kensington campus of the University of New South

Wales. 4

CHAPTER 2

2. Granite gneiss Stratigraphy

2.1 Introduction

The original mapping of the Upper and Lower Granite Gneisses by

Andrews (1922) clearly demonstrated the presence of an aplitic textured phase in the Upper Granite Gneiss and the presence of numerous arnphibolite layers in parts of the Lower Granite Gneiss. With the exception of Stone (1973) and

Stevens et al. (1979) past authors have reported that the granitic gneisses are typically quartz-orthoclase-plagioclase-biotite gneisses with accessory garnet and have ignored the mineralogical and textural variations which are present in surface outcrops.

Mineralogical work carried out by Stone (1973) indicated that it was possible to distinguish between Upper and Lower Granite Gneisses on the presence or absence of alkali feldspar~ however, the geochemical studies carried out by Shaw (1973), the detailed surface mapping of Stevens et al.

(1979) as well as this study, indicates that this conclusion is not warranted and may be due to limited sampling. Despite relatively poor out crop the mapping of Stevens et al. (1979) has demonstrated that variations in both bodies of Granite gneiss can be represented by simple textural criteria based on the relative size of feldspar augen or megacrysts. Thus they have presented a scheme where granite gneiss can be classified on grainsize alone, such that there are coarse (BC) and medium grained (BM) varieties which have a varying biotite content. Garnet is not critical to this scheme and may be present or absent in either type.

2.2 Methodology

The technique of mapping mineralogical variations within the one general rock type, in a similar manner to Stevens et al. (1979), is used here. Due to the poor outcrop of both bodies of gneiss and the availability of diamond drill core over the majority of each bodies' strike length, a combination of surface mapping of selected areas (Figs. 3, 4), general

reconnaissance traverses as well as extensive core logging (Appendix A) have been used to produce a series of cross sections (Figs. 2a, 2b, 2c, 2d). The 5

Figure 3: Quartz augen rocks and amphibolite contact.

(For location of area, see Figure 1). -

...... ____

Gradational'

25m

1,500

0 0

1'11

l~•n90N

Scole

"'~Fooo,

""'

gneiss

biotite

sample

ougen

Quartz

Alluvium

Amphibolite

Feldspar-

Foliation

Surface

')..__

,.-'..,',

\j-'-

"~l.,..J

~ ~

LEGEND 6

Figure 4: Structural and lithological relationships between

Quartz augen rocks and Granite gneiss.

(For location of area, see Figure 1).

I I

1•2500 1•2500

0 0

Scale Scale

/ /

gneiss gneiss

garnet garnet

gneiss gneiss

-biotite -biotite

sample sample

augen augen

Surface Surface

Foliation Foliation

Alluvium Alluvium

Amphibolite Amphibolite

Quartz Quartz

Feldspar-biotite-

Feldspar Feldspar

@ @

~I',,'~ ~I',,'~

'?:,j '?:,j

,,(r ,,(r

D D

[SJ [SJ

EJ EJ

[2'.j [2'.j

~ ~

0 0

,,, ,,,

I~/ I~/ ___lmeoN ___lmeoN 7

sections reproduced here on which all mapping details have been recorded are North Broken Hill and Zinc Corporation-New Broken Hill mine drilling sections which have been structurally inverted so that all mapping is "right way up".

The mineralogical criteria which has proved to be the most useful for subdividing the Granite gneisses is the presence or absence of garnet1 thus two major subtypes of Granite gneiss, feldspar-biotite garnet gneisses and feldspar-biotite gneisses can be shown to exist. A third subtype which also is defined by a general absence of garnet but more typically through its characteristic texture, is an aplitic-textured feldspar quartz rock, locally known as "aplite". Two other, minor gneiss types found in the Lower Granite Gneiss (Figs. 2c, 2d, 3, 4) and associated diamond drill intersections, and which are probably closely related to amphibolites, are also defined here as they occupy discrete horizons within the stratigraphy of the Lower Granite Gneiss. These minor types consist of a greenish/grey aplitic textured feldspar-chlorite-biotite rock and a fine grained quartz rich rock containing numerous quartz porphyroblasts, the former is referred to here as a "green-grey aplite" and the latter as a "quartz augen rock".

The lack of quartz in the naming of the first two gneiss types, which are the most extensive of the five, is a result of it not being immediately visible in biotite-rich specimens and so is not considered important as a classification tool. The lateral extent of a horizon of either of the two major subtypes is at least 15 km, whereas the remaining three ~ypes are limited to less than 5 km in strike length.

2.2.1 Stratigraphic Synthesis

The stratigraphic reconstruction of both the Upper and Lower

Granite gneisses as depicted in'l?i-g,ires 2a-d and the synthesis of these semi-isometric projections (Fig. 5) is based on the current structural inter pretation proposed by Laing et al. (1978). This interpretation places the

Upper Granite Gneiss in the core of the "Hanging Wall Synform" with the Lower

Granite lying to the south-east of the "Broken Hill Synforrn" (Fig. 1), 8

situated between these two synforms is the "Broken Hill Antiform".

Sedimentary facings of the type used by Laing et al. (1978) to produce the above details do not exist in Granite gneiss lithologies, however the presence of foliation vergences in the Upper Granite Gneiss at Block 10

Hill, and also in the Lower Granite Gneiss (Fig. 4), demonstrates the presence of major fold hinges within both gneiss bodies.

In constructing the stratigraphic sections presented here, the stratigraphic top of both gneisses have been used as local arbritary datums, which has resulted in all sections being presented with horizontal upper and lower surfaces (Figs. 2a, b, c, d).

It is clear from Figure 1 that large portions of the Upper

Granite Gneiss in particular have been affected by major fold structures and thus can be expected to be attenuated in hinge zones. Thisat:tenuation which could not be reliably assessed, affects the positioning of the trace of a drill hole on an unfolded section and so each trace must be considered as only a best estimate. Thus while most holes are represented as vertical traces, long holes such as N2550 and N2570 which pass through the axis of the "Hanging Wall Synform", are depicted with curved traces. Each trace present on a section is a schematic log of theintersections recorded in

Appendix A at a vertical scale of 10 mm.: 25~., within section horizontal scale is also 10 mm.: 250m. and the between section horizontal scale is

10 mm.: 250 m. Two further complications exist in these reconstructions; where large scale shears are present in the Upper Granite Gneiss, e.g. Round

Hill Section and Section 226, the stratigraphy has been interpreted through them, and secondly, due to the structural attitude of both Granite gneiss bodies, their horizontal extremities cannot be observed. Despite these constraints, schematic block diagrams have been constructed (Fig. 5) which in conjunction with Figures 2a, b, c, d can be used to evaluate the internal morphology of both Granite gneisses. 9

2.3 Stratigraphic reconstruction

2.3.l Upper Granite Gneiss

The mapped distribution of rock types (Figs. 2a, b, c, d) and their interpreted distribution (Fig. 5) indicates that each rock type occurs as a thin, laterally extensive horizon which, when combined with the other horizons present, produces a layer cake-like stratigraphy. The Upper

Granite Gneiss can be divided on mineralogical grounds into three distinct, extensive, units and incorporating a metasedimentary horizon which is confined to the northern extremity of the body.

The three major units located in the Upper Granite Gneiss are a quartz-feldspar-rich aplitic fels (Ap}, where fels is used in the sense of

Winkler (1976), a feldspar-biotite-garnet gneiss (Fbg) and a feldspar-biotite gneiss (Fb). The Ap-unit lies at the stratigraphic top of the Upper Granite

Gneiss, extending northwards as a thin sheet from the vicinity of Section 92 to Imperial Ridge Section where it reaches a thickness of approximately 200 m.

From this point it thins rapidly both laterally and in a northerly direction to a more typical thickness of 20 m. As well as this major unit of aplitic fels a number of thinner replicas are present within the Upper Granite Gneiss, particularly from Section 226 to Kelly's Creek Section.

Beneath the Ap-unit is an interval of up to 400 m of Fbg gneiss which contains within it a large lensoidal body of Fb gneiss and a metapelitic horizon. The Fb gneiss within the Fbg gneiss reaches a maximum thickness of

200 m.on Section 30 and rapidly thins southwards as Section 244 is approached, but thins only gradually in a northerly direction. Between Round Hill and

Flying Doctor Sections, there is a metapelite horizon separating the Fb and

Fbg units which reaches a maximum thickness of 150 m. on the Flying Doctor

Section.

North and South of Section 30 the overlying Fbg gneiss onlaps or wedges out against the major thickening in the Fb gneiss and thins even further in a northerly direction beneath the overlying Ap-unit. The Fbg horizons which envelop the central Fb horizon appear to be separate horizons, 10

at least to Section 226 where they coalesce, however no criteria could be established which would discriminate between the two horizons. Amphibolite horizons and biotite schist/selvage horizons are sporadically distributed throughout the Upper Granite Gneiss but show a general increase in abundance south of Block 10 Hill.

Two features which are unique to the Upper Granite Gneiss as a whole are the presence of rare clasts of Granite gneiss and a regular variation in feldspar augen size and abundance. The clasts, which reach a maximum length of 0.08 m., have only been observed in N4270, Nl640 and Nl760, located on

Sections 226, 240 and 292 respectively. Only one surface occurrence has been located at G.R. 6461000N 534100E approximately 250 m. north of the Kannandah

Road abattoir. Clast mineralogy is the same as that of Fbg or Fb gneiss, in as much as they are composed of feldspar-biotite and/or garnet, with the biotite defining a gneissosity which parallels that of the surrounding gneiss.

Clast boundaries are defined by abrupt grain boundary terminations resulting in a generally lenticular outline, these boundaries are not necessarily parallel to the gneissosity of the surrounding gneiss (Plate l).

Within vertical stratigraphic intervals ranging in thickness from

25 to 150 m. in either Fbg or Fb gneiss, feldspar augen and tabular feldspar megacrysts can be observed to decrease in size and/or abundance in a strati graphically upwards sense, Thus it is possible to progress from an Fbg or Fb gneiss containing up to 30% feldspar augen and megacrysts, through to a medium to fine-grained Fbg or Fb gneiss containing few or no augen or megacrysts.

This transition in grainsize and abundance also occurs across Fbg-Fb gneiss boundaries, and so where it occurs in an interval which terminates in an Ap unit, the overall effect of fining upwards is further enhanced (Plates 2, 3).

No regular variation of size and abundance of augen or megacrysts was observed in the Lower Granite Gneiss, although this may be more a function of the presence of numerous amphibolites and biotite selvages breaking the

continuity of such trends, rather than their absence. In both the Upper and

Lower Granite Gneisses it is connnon to observe intervals within Fbg or Fb 11

Plate 1: Upper - Surface outcrop of Feldspar-biotite clast

in Feldspar-biotite-garnet gneiss.

1 scale division= 20 mm.

Lower - Feldspar biotite clasts (arrowed) in N2550A

at 2876', 2942', 3057' and 3272 (From left to right).

1 scale division= 20 mm.

Plate 2: Upper left - Feldspar augen grainsize decreasing

stratigraphically upwards in Feldspar-biotite gneiss.

N4740, 39', 52', 59', 62' (Left to right).

l scale division= 20 mm.

Upper right - Feldspar augen abundance and grainsize

decreasing stratigraphically upwards in Feldspar-biotite

and Feldspar-biotite-garnet gneiss, N2870, 2957',

3l72', 3302', 3424', 3574' and 3680' (Left to right).

l scale division= 20 mm.

Lower - Feldspar augen grainsize decreasing strati

graphically upwards in Feldspar-biotite and Feldspar

biotite-garnet gneiss, N2000, 252', 338', 415', 522',

581' (Left to right). 1 scale division= 20 mm.

Plate 3: Upper~ Aplitic textured fels, showing fine grainsize,

low biotite content and weak or absent foliation.

Z3010A, 517-520 m. 1 scale division= 20 mm.

Lower - Feldspar-biotite gneiss with coarse sparsely

distributed feldspar augen. N2870, 3635-3645'.

material consisting of evenly distributed augen and megacrysts of the same general size which exhibit little variation in size or abundance. This is despite the occurrence of either side of such intervals of material with wide disparities in augen or megacryst abundance, and/or grainsize, and/or texture.

2.3.2 Lower Granite gneiss

A "layer-cake" stratigraphy also exists in the Lower Granite

Gneiss but is confined to a region north of approximately midway between No. 3 and Cosgroves Sections. The units which define this stratigraphy are, in general, laterally impersistent and of variable strike length (1-5 km).

Combined field data and drill hole interpretation indicates that this portion of the Lower Granite Gneiss consists of an upper Ap-unit which is underlain in turn by Fb, Fbg, Gap, Fbg and Fb gneisses. This succession overlies a sericite-garnet metapelite, which in drill core appears as a medium to fine grained (~ 1 mm) mafic, granoblastic biotite-feldspar-quartz sericite gneiss. Underlying the metapelite horizon are Fb gneiss horizons, which in places are in turn underlain by thin (c. 10 m) horizons of quartz augen rocks. The whole of the above sequence is underlain by approximately

200 m of Fbg gneiss (Figs. 2c, 2d, 3, 4, 5).

Amphibolites up to 10 m. thick are quite sparsely distributed in this section of the Lower Granite Gneiss. Outcrop patterns indicate that these amphibolites are discontinuous pods and lenses confined to discrete, individual stratigraphic intervals. With few exceptions, these rocks are typically found at, or in close proximity to, the boundaries between the individual units listed above. Southwards of this area, the overall character of the Lower Granite Gneiss changes rapidly from a type containing few widely spread amphibolites to one with an abundance of amphibolites in a wide and long horizon ranging in thickness from 100 to 200 m. This horizon is under lain intermittently by Fb gneiss and in places is overlain by Fbg gneiss, both of which are up to 25 m. thick and generally free of amphibolites and biotite selvages (Figs. 2c, d). Closely associated with the abundant amphibo lites are numerous biotite-(chlorite)-rich selvages which occur either as 15

marginal phases to retrogressed or sheared amphibolites, or as discrete layers showing no evidence of retrogression or shearing (Plate 4).

2.4 Layering

As described above, both the Upper and Lower Granite Gneisses possess very coarse layering on a scale in excess of 10 m. Within this broader framework there exists a second type of layering, ranging in thick ness from less than 0.1 m to 0.5 m which in isolated instances may occur at any stratigraphic level within Fb or Fbg horizons, but never in Ap units.

Any one particular small scale layer is usually found in association with one or more layers resulting in a clearly defined zone of small scale layers.

Mineralogically this type of layering is distinct from both Fb and

Fbg gneisses, being invariably quartz-rich with minor feldspar and accessory biotite. Garnet, feldspar augen and/or quartz porphryoblasts are absent and the grainsize is generally less than 15 mm. Foliation definition within these layers is usually weak or absent due to the low biotite content (Plate 5).

Examination of drill core and surface outcrop indicates that fine scale layering is a wide, and fairly evenly spread phenomena over the whole strike length of both granite gneisses. Along-strike continuity of individual layers or zones of layers is uncertain, although at Block 10 Hill, fine scale layering can be traced along strike for over 100 m (Plate 5).

2.5 Description of gneiss types

2.5.1 Aplitic textured quartz-feldspar fels (Ap)

This rock has a medium to fine grained equigranular texture composed almost entirely of quartz and feldspar with a little, subordinate biotite and/or sericite. Biotite plates and wispy sericite up to 4 mm in length are weakly aligned, forming a poorly defined foliation (?S1) which parallels the gross layering of the surrounding gneisses. Shearing within this gneiss type produces sericite which forms linear subparallel masses rather than discrete wisps (Plate 3).

Garnet occurs only very rarely in this gneiss type and is invari ably less than 5 mm in diameter and is invariably undeformed (e.g. NBH2003/ 16

Plate 4: Upper - Amphibolite layers (top and middle) and

biotite selvage in Feldspar-biotite gneiss.

N2550A, 3011', 3200', 3233' (Top to bottom).

1 scale division= 20 mm.

Lower - Felsic layering in amphibolite in Feldspar

biotite gneiss. Z2660, 1044', 1053', 1071', 1055'

(Left to right). 1 scale division= 20 mm.

Plate 5: Upper - Fine grained Feldspar-biotite layering

in Feldspar-biotite-garnet gnerss (To left of

hammer} at Block 10 Hill.

Lower~ Feldspar-biotite and Feldspar-rich layering

in Feldspar-biotite gneiss, N2550A, 3013', 3173', 2550'

(Left to right). 1 scale division= 20 mm.

1570). These garnets may be partially or completely retrogressed thus adding further, minor, amounts of biotite to that already defining the

-foliation (e.g. NBH834/581; NBH952/171).

2.5.2 Feldspar biotite garnet gneiss (Fbg)

Garnet-bearing types of Granite gneiss are by far the most common of the three types examined. From Table 1 it can be seen that garnet content is quite variable, ranging from 2.7 to 18.3%, This estimate is complicated by the occurrence of elongate garnets parallel to the biotite foliation (S1) up to 45 mm in length (e.g. NBH837/301), whereas the more common form is as rounded to subhedral or semi-rounded and ragged porphyroblasts 5-7.5 mm in diameter, Partial retrogression of garnets to biotite, resulting in biotite rims or haloes (e.g. N2770) is common, although complete retrogression is uncommon (e.g. NBH2003/1627).

Sillimanite, when present occurs as thin elongate masses which are often partially sericitized. Sericite derived from this breakdown or from feldspar is typically white or cream in colour which contrasts to the rounded, greenish masses of sericite up to 10 mm in diameter which also occur sporad ically in both the Fbg and Fb gneisses. These clot-like masses are surrounded by quartz and feldspar, and are undeformed and show no preferred distribution

(e.g. NBH836/1392; NBH837/301),

Texturally this gneiss is dominated by a pronounced biotite folia tion which is accompanied by minor to trace quantities of sillimanite. This foliation is super-imposed upon a granoblastic mosaic of medium to coarse grained feldspar, quartz and garnet. The garnets are typically slightly elongate, whereas quartz and feldspar generally combine to form lenticular aggregates. Within these aggregates feldspars form augen-like porphyroblasts up to 10 mm in diameter, or in isolated instances, tabular megacrysts up to

2 5 mm in length.

2.5.3 Feldspar--biotite gneiss (Fb)

Granite gneiss in which garnet is lacking or extremely rare, closely resembles the Fbg gneisses texturally with the possible exception of 19

having a lower sillimanite content and fewer green sericite clots. Feldspar

and quartz have the same habit in the Fb gneisses as observed in the Fbg

gneisses, i~e. they form granoblastic mosaics with sporadic, larger, augen

like porphyroblasts or tabular megacrysts. One feature of Fb gneisses which was not observed in Fbg gneisses, is that in augen and biotite-poor zones, a

light and dark grey mottled effect is produced by the abundance of equi granular quartz and feldspar,

2.5.4 Green-Grey Aplite (Gap)

This rock has the most striking appearance of all gneisses examined.

It is characteristically a mottled grey and/or green unfoliated rock of medium grainsize (0.5-3 mm) containing quartz, chlorite, feldspar and minor biotite. The melting is developed by discrete grains of feldspar and quartz

set in a matrix of green chlorite (NBH3186/892; NBH3186/970). A further feature of this rocktype is the presence of numerous finer grained layers or layers containing coarse angular feldspar fragments, both of which may range

in thickness from 20 mm to 200 mm. The fine-grained layers have a general grainsize of less than 1 mm. However, they resemble the main rock mass in all other respects. The fragmental feldspar layers are composed almost

entirely of feldspar fragments up to 10 mm across which are typically pink or orange in colour (NBH3186/892) (Plate 6).

2.5.5 Quartz augen rocks

Quartz augen rocks are confined to the northern most outcrops of the

Lower Granite Gneiss (Figs. 2c, d) and have not been observed in drill inter

sections. The overall appearance of this rock is that it is very fine

grained (i.e. <0.5 mm) dark grey to black, unfoliated and contains porpyro

blastic grains and aggregates of quartz, and less commonly feldspar, up to

5 mm in length which are set in a matrix of hornblende and finer grained

quartz. Biotite and chlorite are present in insufficient quantities to

produce a foliation in outcrop, however, the weak parallel alignment of

elongate quartz porphyroblasts is sufficient to impart a weak linear fabric

to the rock. The general size of the porphyroblasts diminishes and 'their 20

Plate 6: Upper - Mottled and fragmental layered texture of

Green-Grey aplite. NBH3186, 852', 973', 976',

1280 1 (Top to bottom). 1 scale division= 20 mm.

Lower - Quartz augen rock with angular grains or eyes

of quartz and well developed layering (S9).

Scale= 20 mm.

distribution becomes more sparse towards the stratigraphic top of this rock type (Plate 6).

All outcrops of this rock type grade vertically into and/or laterally from amphibolite over very short distances and generally contain thin epidote and quartz-rich layers up to 0.2 m thick which probably represent relict layering (Fig. 3). Very fine scale layering or laminations (c. 1 mm thick) composed largely of epidote grains, have also been observed (S6), but are uncommon (Plate 6).

Rare clasts composed of identical material to the main rock type up to 0.5 m in length are also present. The observation of these clasts is at best, difficult, as the boundaries are typically defined by grainsize differ ences or by disor.ientated layering. This problem is partially relieved through the differential weathering of zones with varying grainsize.

2.5.6 Amphibolite

The mafic gneisses which occur within the Upper and Lower Granite

Gneisses appear little different from those found elsewhere in the vicinity of Broken Hill, Due to the relatively narrow stratigraphic interval of granite gneiss studied here, it is possible to document a number of amphibol ite-related features. The particular features described below occur pre dominently in Lower Granite Gneiss amphibolites and have not been previously documented.

Within the Lower Granite Gneiss there is a strong stratigraphic control over the distribution of pyroxene-bearing amphibolites, in as much that amphibolites containing abundant pyroxene (c. 20 volume%) are found towards the stratigraphic base of the Lower Granite Gneiss and those with little or no pyroxene occur at higher stratigraphic levels. The presence of pyroxene is readily recognized through its characteristic red-brown weather ing in surface outcrop and in drill core by an overall khaki colour (Nl810).

In both cases, amphibolite-rich exposures or intersections are typically dark green to black.

A number of amphibolites in the northern portion of the Lower 22

Granite Gneiss are characterized by a distinctive felsic-mafic mottling of

their stratigraphic uppermost portions. This mottling takes the form of

either rounded to elongate clusters of amphibole and/or biotite to 20 mm in

diameter or slabs of amphibolite up to 60 mm in length, set in a matrix of

feldspar. Where this feature is well developed, it forms a pellet-like or

blocky, fragmented texture (e.g. Sl3, Plate 7).

Boundaries between granite gneiss and amphibolite horizons have a

number of forms other than the biotite selvage-effect described earlier, and may also be garnet and/or feldspar rich as well as grading gradually or

abruptly into granite gneiss. Combinations of any of these forms can occur

on the top and bottom boundaries, although these features are generally only observed in drill core due to their small scale and the effects of weathering on surface outcrops.

One unique feature, found only in one location (G.R. 646475N,

534813E) consists of a 1 m. thick amphibolite horizon which has a groundmass

composed essentially of green hornblende and minor interstitial feldspar which shows evidence of a slight lineation. Dispersed throughout this fine

grained matrix are numerous, discrete, semi-spheriodal masses of feldspar up

to 25 mm in diameter (Plate 7). The lack of feldspathic layering in this particular amphibolite, together with the discrete nature of each feldspar mass indicates that they are not boudins, therefore it is probable they

represent premetamorphic, zeolite-filled vesicles, implying that this amphib

olite was either a basaltic flow or sill. 23

Plate 7: Upper - Pellet-like or blocky texture in

amphibolite (Sl3). Scale= 20 mm.

Lower - Coarse albite masses in fine grained felsic

amphibolite representing possible premetamorphic

infilled vesicles (Sl7). Scale= 20 mm,

Chapter 3

3. Mineralogy

The petrology of each rock type has been determined by examination of thin sections, with volume estimates being provided with the aid of a

Swift electromechanical point counter, the results of which are sunnnarized in Table 1. Although these figures provide a complete overview of the variability present in these gneisses, they suffer from the large size range present in feldspar grains which has led to a probable overestimate of its presence.

3.1 Metamorphic Conditions

In the vicinity of Broken Hill, gneisses of the Willyama Complex have been involved in three recognizable metamorphic events, the first two of which were prograde and attained upper amphibolite/lower granulite facies grade. The third period of metamorphism was a retrograde event which reached lower amphibolite facies {Binns, 1964, 1968; Phillips, 1978). Prograde metamorphism was accompanied by two deformational episodes which generated

F1 and F2 structures, the latter of which was superimposed on an inverted stratigraphic succession formed as a consequence of F1 deformation {Laing, et al., 1978). Within the Willyama Complex, prograde metamorphism can be divided into four zones on the basis of the mineral assemblages of pelitic and mafic rock types. These zones are Andalusite-Muscovite, Sillimanite

Muscovite, Sillimanite-K-feldspar and a two pyroxene zone {Phillips, 1978), in which Broken Hill is located. Retrograde metamorphism was accompanied by a third period of deformation as well as the development of extensive shear zones {Rutland and Etheridge, 1975).

Rubidium-Strontium whole rock isotopic dating indicates that prograde metamorphism was initiated at about 1700 m.y. ago {Pidgeon, 1967; Shaw, 1968) and probably continued for a further 60 m.y. (Shaw, 1968). Further work by

Pidgeon (1968) has placed the occurrence of the retrograde event at about 25

. . 87 06s . . d" . 500 m.y. ago. Initial Sr1 r ratios in icate that the metasediments enclosing the Broken Hill ore bodies were formed about 1820 + 60 m.y. ago

(Shaw, 1968). During prograde metamorphism pressure-temperature conditions have been estimated to be in the vicinity of 3.5-8kb and 400-800°c, with

Hewins, 1975; Phillips et al., 1976; Scott PH20

The preservation of sedimentary features such as lithological layering and graded bedding in metapsammites and pelites and also in chemical sediments such as banded iron formations, implies that chemical mobility during both prograde and retrograde metamorphism was generally quite low.

Quantitative assessment of observations similar to these enabled Stanton and

Williams {1978) to demonstrate the discrete chemical characteristics of individual banded iron formation layers. Similarly Ransome {1969) and also

Elliott (1979) have shown, that with the exception of retrograde shear zones, retrogression was isochemical and of an incipient pseudomorphous nature.

Within shear zones, retrogression was allochemical, with large losses and gains being recorded (Stillwell, 1959; Plimer, 1975).

3.2 Aplitic textured quartz-feldspar fels {Ap)

The lack of appreciable biotite and the presence of only minor sericite in Ap fels types produces a texture dominated by all grain boundary relationships of quartz and feldspar, which typically occur as anhedral, equidimensional grains with serrate to straight or lobate common boundaries.

As the proportion of straight to lobate boundaries increases, so too does the occurrence of triple point junctions, producing an excellent granoblastic mosaic (NBH952/171). A weak discontinuous linear fabric defined by elongate, compact wisps of sericite, upwards to 1 mm in length is also present, which together with sporadically distributed flakes of biotite, parallel the foliation of the surrounding gneisses. 26

All sections of this rocktype examined exhibited varying degrees of retrogression which is indicated by the presence of very fine particulate sericite "clouding" of feldspar. Sericite is only abundant when shearing has occurred (NBH847/416) and is more normally developed from the retrogres sion of cordierite and sillimanite when these minerals are present; retro gressed biotite in this rock type forms pale green chlorite.

Orthoclase and minor microcline (e.g. NBH847/47; NBH15N4/2549) are more dominant than plagioclase which has an average composition of An44

(Michel-Levy method). Rim zoning may also be present in both alkali and plagioclase feldspars (e.g. NBH962/1294), with the former also exhibiting film perthite and/or myrmekite (e.g. NBH813/518).

Trace amounts of sphene, zircon, apatite, epidote, ilmenite, biotite and an unidentified carbonate may also be present. The first three of these minerals typically occur as subhedral to euhedral grains interstit ial to the larger quartz and feldspar grains, whereas epidote and ilmenite are anhedral. Biotite is generally greenish-brown and may exhibit crystal lographically aligned apatite (e.g. NBH952/171). Cordierite is present as slightly to completely pinitized anhedral grains.

3,3 Feldspar-biotite-garnet gneiss (Fbg)

The macroscopically prominent biotite foliation described above for Fbg-lithologies, also dominates the microscopic field of view. The biotite comprising this fabric is typically straw yellow to deep fox red

(e.g. NBH961/1866, NBH15N4/1747) and forms linear masses of interlocking plates. This generation of biotite is optically distinct from that biotite formed from the breakdown of garnet or the interaction of magnetite with alkali feldspar; in both cases this biotite is deep brown to black and forms irregular felted masses. Elongate masses of garnet consisting of rounded to anhedral subgrains or isolated and discontinuous bundles of sillimanite and long to 1 mm) wisps of sericite which often possess elongate, acicular cores of ilmenite, may also accompany the biotite foliation. 0.6

o.s

0.1

0.1-

0.2-3

Cordierite

1.2

0.2 0.1

Magnetite

0.2-5

0.1

Epidote

0.1-2

0.3

0.1

Sphene

0.1-

0.2 0.3

0.1

0.0 0.1

0.1 0.2

0.1

0.1-

Apatite

0.6

0.3 0.6 0.4

0.1

0.2

0.3 0.1

0.1

0.2

Zircon

0.1- 0.2-

0.2-

0.5

1.4

3.8

1.1

0.5

0.2 o.s

3.0

Ilmenite

0.3-

0.2-

2.3-

0.0-

0.2

centers.

31.4

blende Horn-

0.3-5

28.6-34.1

rocks.

0.5*0.5

Gap

14.7

Chlorite

8.6018.0 0.2-0.3

and

0.2

5.1

3.4

augen

o.o

0-12.1 o-

1.9-10.6

approximately

0.1-0.5

Sericite

Quartz

6.2

3.8

7.6

1.9

counter

Silli-

3.6-20.4

1.0-

1.9-

manite

0.5-3

lithologies,

0.2

5.2

o.o

1-8

Garnet

2.7-18.3

gneiss

electro-mechanical

8.7

8.1

14.8

16.l

Granite

6.2-10.4

Biotite 8.5-24.6

3.2-15.1

0.1-0.3

10.6-20.4

Swift

for

0.0

l\)

5.4

8.9

8.6

23.3

20.4

clase

using

2.2- Plagio-

3.7-16.2

0.6-17

0.2-1

8.1-36.5

18.9-27.7

out

fractions

26.5

22.0

21.6

33.8

feldspar

9.7-36.3

Alkali- 6.1-43.1

0.5-18

carried

12.0-34.2

22.2-32.8

volume

was

50.7

40.1

45.7

42.0

22.4

Average

Quartz

0.2-3

35.2-68.8

25.4-53.3

36.2-56.1

41.1-42.8

16.1-33.9

Counting

5683

6984

4790

2048

3067

Table

Points

Counted

Note:

augen

Range(nan)

type

Gneiss

IIAnge

AP-fels IIAnge

Fbg

Range

IIAnge

Range

Quartz

Gap

Grainsize 28

The interfolial volume consists of granoblastic, serrate to smooth lobate or reniform mosaics of quartz and feldspar plus minerals present in minor or trace quantities. Alkali-(orthoclase) and plagioclase feldspars

(average composition An45) are present in equal abundance overall, however alkali feldspars dominate to the exclusion of plagioclase in distinctive fine grained garnet and biotite-poor layers (e.g. NBH951/120; NBH3186/2141). As in the Ap fels types rim zoning is observed in both feldspar species together with myrmekite and film perthite development in the alkali feldspars, however, by comparison these features are not particularly common. Instead, the occurrence of perthitic twinning in alkali feldspars and Carlsbad-Albite twinning and inclusions of quartz and biotite in both alkali- and plagioclase feldspar and apatite aligned in the Murchinson direction (e.g. NBH837/301;

NBH3105/2380) are notable features. Where Carlsbad-Albite twinning occurs in larger feldspar grains, the twin planes exhibit evidence of kinking and distortion (e.g. NBH962/900; NBH3186/2042). Less common types of inclusions observed are optically orientated grains of plagioclase, and also rim zoned plagioclase (NBH813/438; NBH838/924) in an alkali feldspar matrix. Partic ular features exhibited by quartz not found in the Ap fels types are: symplectic quartz-biotite intergrowths (NBH837/389; NBH3186/2175) and discrete, very elongate (>0,5 mm) grains of quartz which, while retaining their external structure, have completely recrystallized into subgrains.

(NBH834/35; NBH834/389).

The garnet present in Fbg-gneisses typically contains fibrolite inclusions and may also feature biotite-rich rims or biotite filling internal fractures. This biotite is of the second generation mentioned above, and may further break down into masses of pale green chlorite or sericite. Inclusions of zircon (NBH3074/4214), first generation biotite (NBH962/764) and quartz

(NBH3105/2380) may also be present. Zircon, with associated pleochroic haloes, occurs in first generation biotite, where it may also be accompanied by crystallographically aligned lattices of apatite (NBH3186/2111) or granules of apatite in the near vicinity. Sphene, which may also possess a carbonate 29

haloe (.NBH3186/1700}, zircon,rare pinitized cordierite, and very minor

quantities of pyrrhotite form the remaining constituents of this gneiss tYPe.

The effects of retrogression in the Fbg gneisses are not as notice

able as in the Ap fels rocks. Fine-grained, sporadically-distributed

sericite is developed in most feldspars but is best developed by the break down of sillimanite, biotite and cordierite, all of which exhibit varying

stages of retrogression. It is these three latter minerals which are respon

sible for the formation of these sericite wisps and clots which do not possess elongate, acicular ilmenite cores. It is possible that sericite masses with

ilmenite cores are relicts of an earlier generation of biotite.

3.4 Feldspar-biotite gneiss (Fb)

Microscopically there is little or no textural and/or mineralogical difference between the Fb and Fbg gneisses, except that garnet is lacking in

the former type. Thus, as is found in the Fbg gneisses, the Fb gneisses possess a strong biotite foliation which is customarily accompanied by varying proportions of quartz, alkali-(microcline) and plagioclase- (average An41)

feldspars plus minor to rare amounts of zircon, sphene, apatite, magnetite,

ilmenite and pyrrhotite. Myrmekite, film perthite, rim zoning of feldspars,

symplectic quartz-biotite intergrowths and the recrystallization of the larger

and more elongate quartz grains are also common features in this gneiss.

_Layering is also well defined by decreasing grain size and the general lack

of biotite, whereas quartz and/or alkali-feldspar and/or plagioclase may be present in abundance.

3.5 Green/grey aplite (Gap)

This rock type consists almost entirely of discrete, angular grains

of orthoclase, plagioclase (An45) and quartz set in a matrix of green chlor

ite and very subordinate biotite, Granoblastic, reniform or lobate textures

such as are found in the Fbg and Fb gneisses are generally uncommon and are

developed best in the more quartz rich zones.

There is only a weak linear fabric developed in this rock and

defined by biotite, the chlorite invariably is present as irregularly 30

oriented sheaves and felted masses. It appears that this chlorite is not

developed as an alteration product of biotite as it coexists with the little

biotite that is present, exhbiting sharp mutual boundaries and showing no

evidence of any transition zones. Alternatively this chlorite may have

originated through the complete breakdown of a pre-existing amphibole phase

although no evidence was found to support this. The feldspars present

possess a small range of features in comparison to those found in the Granite gneisses; in that there is no myrmekite developed and the alkali feldspars

are largely untwinned, however plagioclase may exhibit Carlsbad-Albite and

albite twinning and also minor rim zoning.

3.6 Quartz augen rocks

Quartz augen rocks consist primarily of quartz with variable prop

ortions of hornblende and plagioclase (av. composition An68) and exhibit a

blastoporphyritic texture composed of a very uniform, granoblastic serrate

to smooth mosaic of grains with a size range of 0.1-0.3 mm. Contained within

this ground mass are discrete, elongate grains of quartz from 0.4 to 0.8 mm

in length, the larger of these grains are composed of a number of internal

subgrains, and may in hand specimen reach 5 mm in length and show a general

tendency for the long axis of the grain to be aligned parallel to the weak

layering and biotite foliation, if present.

The only evidence of retrogression present in this rock type is

the isolated occurrence of zoisite formed from the breakdown of plagioclase

and possibly the presence of ilmenite along the cleavage planes of some

hornblendes. It is considered here that the abundance of hornblende (Table

1), the calcic plagioclase present and the intimate field relations that

exist between this rock type and amphibolites provide good evidence that

these two rock types are related. Chapter 4

4. Granite gneiss Chemistry

During the logging of diamond drill core, a number of specimens

were selected to study the chemistry of the various Granite gneiss

types. In order to obtain a reasonable sample population representative of

both the Upper and Lower Granite gneisses, it was found necessary to include

analytical results obtained by Shaw (1973), Stone (1973), Klingner and

McConachy (1975), Plimer (1975) and Elliott (1979). Results from these

authors were only utilized when the mineralogy of the relevant samples could

be determined; those analyses which have been included in this study are

listed in Appendix c.

The major oxide analyses used here were produced by a variety of

X-Ray Fluoreseence (XRF') techniques in a number of different laboratories.

Despite this, it would appear from the results obtained from principle com

ponent analysis (Fig. 13), that no obvious differences exist between samples

analysed by different laboratories and that the rocks analysed have a uniform composition.

Material analysed for this study was selected on the basis that the

samples had only undergone pseudomorphous retrogression and did not include

pegmatitic segregations or shearing. From examination of the sites from

which samples were obtained by the above authors, it is apparent that they

have used similar criteria.

4.1 Sample Analysis

The sampling procedure used here was to take up to 0.75 kg of

rock,drill core or surface sample, and crush it to - 10 mm by jaw crusher

before fine grinding in a tungsten-carbide Siebtecnik ring grinder. Suffic

ient material was retained from each sample for thin sectioning and reference

purposes.

The method used for preparing the samples obtained from North

Broken Hill's drill core is outlined in Haukka and Thomas (1977) and also

Thomas and Haukka (1978). This method is based on a low dilution (1:2) 32

Table 2: Analytical results for USGS G-2, AGV-1

oxide USGS G-2 USGS AGV-1 (%)

SiO 70.46 (69.19) 59.99 (58.99) 2 Ti02 0.49 ( 0.53) 1.06 ( 1.08) Al203 l5.58 (15.34) 17.43 (17.01) Fe2o3 2.66 2.76) 6.79 6.80) MnO 0.03 0.03) 0.10 0.09) MgO 0.78 o. 78) l. 57 1. 49) CaO l.91 1. 98) 4.90 4. 98)

K20 4.5l 4.5l) 2.96 2.89) Na2o 4.l5 4.l5) 4.37 4. 33) P205 O.l4 0.14) 0.51 ( o. 48) so3 0.33 0.07) 0.32 ( 0.15) LOI 0.26 0.56) 0.62 1. 34) Total 101. 30 (100. 04) 100.62 (99.63)

Trace elements (ppm)

Cu 14 (11) 57 (64) Zn 88 (75) 88 (112) er 8 ( 9) 7 (13) Ni 10 6) 19 (18) Co 6 5) 16 (16) Rb 176 (234) 75 (89) Sr 489 (463) 670 (657) y 22 (12) 29 (25) Zr 314 (316) 235 (227)

V 35 (37) 116 (121) Cl 43 (108) 117 (184) Nd 26 N.A 15 N.A Sc 2 ( 4) 6 (13) Ga 12 (20) 11 (18) Ce 147 (166) 73 (76) Ba 1843 (1950) 1201 (1410)

Note; All iron analysed as Fe O. Values in brackets are the preferred values of Flannagan (1913f. N.A - Not analysed. 33

sample to lithium metaborate mix, fused at 1000°c and cast into a glass disc.

Disc preparation and analysis was carried out by Dr. T. Hughes of Melbourne

University, using a Siemens sequential SRS-1 XRF with a TlAP analysing crystal. Reference standards used for analysis by this method included USGS

G-2, AGV-1, as well as natural and synthetic standards as outlined in Thomas and Haukka (1978), results obtained for G-2 and AGV-1 are presented in

Table 2.

In addition to the North Mine samples analysed, a further ten samples were analysed using the method of Norrish and Hutton (1969) at The

Zinc Corporation's Assay laboratory. These analyses are presented in Tables

3a-e, and are prefixed z, Nor S.

4.2 Analytical Results

The major oxide and trace element chemistry for the three Granite gneiss types, the green-grey aplite, quartz augen rocks, and related material are presented in Tables 3a, b, c, d, e. A l"ist of the sample numbers, loca tions and rock-types of the analyses obtained from other sources is presented • in Appendix C. With the exception of the work of Klingner and McConachy

(1975) which is a C.R.A. internal report and is on closed file, all other material is located in the Mining Managers Association library, w.s. & L.B.

Robinson College, University of New South Wales, Broken Hill.

These two sets of information have been combined to produce Harker style plots and Principle Component Analysis, whereas only the analyses obtained during this study have been used in Cluster Analysis and petrological discriminant diagrams. This approach has been used in the former case to define broad scale trends and characteristics of the Granite gneisses as a whole and in the latter case to examine the relationships which exist between individual rock-types whose mineralogical composition is known.

4.2.1 Harker-style variation diagrams

From plots of major oxides against s102 content (Figs. 6a-i) it is apparent that:

1) For the whole sample population, there is ·a very wide range in the 34

Table Ja: Aplitic textured Quartz-Feldspar Fels chemistry

Hole 2003 847 952 3167 813 3074 S20 S12 KC5 Depth 1570 416 143 4642 518 5053 307972 307982 682 Section No. 3 Cos. Imp. Pot. RH. FD. KC Oxide (%)

Si02 82.22 74.98 73.74 77.94 72.62 76.67 74. 72 74.06 73.24 TiO 0.24 0.15 0.19 0.19 0.25 0.24 0.19 0.29 0.27 2 Al203 9.40 13.49 13.38 14.30 14. 77 13. 37 14.70 14.18 13.46 Fe2o3 1. 36 2.48 1.61 2.02 2.29 1. 52 0.68 1.41 2.08 MnO 0.04 0.06 0.03 0.02 0.03 0.02 0.03 0.05 0.03 MgO 0.36 0.25 0.31 0.35 0.40 0.39 0.15 0.45 0.36 cao 1. 36 1.07 1.33 1.01 0.74 1. 32 4.88 7.83 0.41

K20 2.81 3.32 3.17 3.47 4.86 2.36 0.39 0.11 7.55 Na2o 1.20 2.33 3.18 2.54 2.30 2.72 3.21 0.74 1.52 P205 0.03 0.15 0.12 O.ll 0.12 0.07 0.13 0.13 0.11 so3 0.03 0.03 0.03 0.03 0.05 0.03 <0.01 <0.01 <0.01 LOI 0.05 0.07 0.26 0.19 0.49 0.66 Total 99.10 98.38 97.25 102.J.7 98.92 99.38 99.09 99.21 99.04 Trace elements (ppm) Cu 14 11 7 9 11 10 <80 <80 <80 Pb 68 35 37 34 120 97 <93 <93 <93 Zn 87 85 59 68 70 86 <80 <80 <80 er 15 2 6 6 11 6 Ni 15 8 8 9 12 5 <79 <79 <79 Co 111 62 90 116 84 41 Rb 70 92 69 87 84 52 Sr 119 98 256 133 141 179 Ba 540 593 865 483 667 427 1012 <90 324 y 25 38 49 35 45 39 Zr 207 75 103 87 117 109 V 16 7 11 8 16 12 Cl 271 295 288 153 140 80 Nd 9 7 10 7 12 9 Th 13 11 15 12 6 8 Sc 2 6 6 4 4 5 Ga 7 9 9 9 11 11 La 34 9 27 17 32 25 Ce 40 20 33 28 46 36 Nb 8 11 18 17 16 12 35

Table 3b: Feldspar-biotite-garnet gneiss chemistry

Hole 2003 2003 834 837 962 962 820 813 3105 3074 961 15N4

Depth 1627 2153 389 301 900 764 2609 438 2380 4814 1866 1747

Section No.3 No.3 Cos. Cos. Imp. Imp. Pot. RH. RH. FD. Globe carb.

Oxide (%)

Si02 70.46 70.05 68.12 66.13 70.86 67.71 69.88 67.42 65.44 67.60 67.33 65.03

Ti02 0.54 0.54 0. 57 0.95 0.60 0.56 0.55 0.62 0.72 0.63 0.64 0.54

Al 2o3 13. 20 13.89 15.46 17.75 15.12 15.54 14.34 15. 79 '15.58 14.99 15.73 14.74

Fe2o3 5.86 4.30 5. 74 6.41 5.67 4.61 3.42 6.55 6.67 6.17 5.47 5.64

MnO 0.21 0.03 0.16 0.06 0.10 0.06 0.06 0.11 0.12 0.14 0.06 0.09

MgO 0.49 o. 79 0.91 1.42 1.05 1.14 0.91 1.07 1.19 1.17 0.96 0.90 cao 2.42 0.85 3.10 1.47 1.82 1.19 2.95 1.15 1.85 1.46 1.58 2.41

K20 3. 53 7.32 1.59 3.67 2.65 4.64 2.45 3.91 3.22 3.52 3.98 3.30

Na 2o 1.98 1.27 3.37 2.29 2.28 1.96 3.38 2.14 2.59 2.68 2.36 2.33

P205 0.16 0.15 0.16 0.15 0.11 0.16 0.18 0.13 0.13 0.14 0.12 0.14

503 0.04 0.04 0.03 0.03 0.02 0.03 0.03 0.22 0.05 0.04 0.24 0.40

LOI 0.12 0.07 0.12 0.06 0.25 0.17 2.06 0.56 0.25 0.08 0.68 3.99

Total 99.01 99.33 99.3310 0.4810 0.39 97.80 99.67 97.81 98.62 99.15 99.5110 0.21

Trace elements (ppm)

Cu 22 38 13 12 5 14 13 22 8 15 34 so

Pb 44 49 27 26 15 13 29 35 59 71 62 61

Zn 127 120 64 119 71 107 72 100 124 129 91 85

Cr 14 16 23 53 27 28 15 31 34 31 30 19

Ni 14 18 16 24 17 17 13 20 20 21 21 16

Co 128 75 76 93 79 80 98 63 66 47 65 110

Rb 95 186 49 97 73 89 92 101 88 87 85 84

Sr 330 389 398 114 240 123 325 90 161 169 140 259

Ba 870 1193 363 699 527 881 475 624 715 918 828 680 y 68 61 76 69 71 51 so 83 81 72 87 87

Zr 204 216 310 350 253 226 198 261 351 287 392 315

V 34 28 33 72 39 38 40 45 45 44 41 36

Cl 434 325 279 352 167 273 179 191 207 141 273 310

Nd 23 19 36 42 27 24 20 32 37 31 39 32

Th 22 33 39 44 25 20 22 32 33 32 38 36

Sc 9 8 7 9 9 6 7 10 8 8 6 8

Ga 11 11 12 14 11 12 10 10 12 12 13 11

La 62 43 78 100 67 72 30 94 103 83 95 66

Ce 94 78 157 174 109 103 75 144 177 132 173 141

Nb 21 19 27 32 25 20 19 21 25 22 25 26 36

Table 3c: Feldspar-biotite gneiss chemistry

Hole 2003 834 95]. 3074 15N4 3J.J.3 Depth J.904 476 38 3977 1670 24 Section No. 3 Cos. Imp. FD. Carb. Carb. Oxide (%) SiO 73.60 66.23 67.10 66.49 73.2]. 67.83 2 TiO O.l5 0.73 0.74 0.75 0.28 0.64 2 Al203 13.54 15.66 .15.32 15.16 13.23 15.ll Fe2o3 2.13 5.93 6.16 6.04 2.40 6.09 MnO 0.02 0.08 0.07 0.05 0.04 0.08 MgO 0.72 l.05 l.05 J.. 20 0.46 .1 • .10 cao 0.32 l.35 2.02 .1. 43 l.43 .1. 44 K20 6.J.9 4.59 2.87 3.40 5.40 3. 9.1 Na20 0.99 2.19 3.38 2.20 2 • .19 2.40 P205 0.06 0 • .13 0 • .lJ. O.J.4 0.14 0.10 so3 0.04 0.07 0.26 0.22 0.04 0.08 LOI 0.78 0.83 0.20 0.84 0.30 0.28 Total 98.54 98.84 99.28 97.92 99 • .12 99.06 Trace element (ppm) Cu 20 20 .J.2 28 19 17 Pb 53 42 38 82 35 34 Zn ll6 114 207 165 55 l.16 Cr 2 33 29 34 8 27 Ni .10 24 is l.3 12 l.7 Co 78 307 66 63 133 87 Rb 173 ll8 J.00 l.12 ll6 106 Sr .123 89 l.l.7 146 2l.5 l.22 Ba 790 756 33.l. 741 626 677 y 22 77 lll. 62 41 75 Zr 93 383 395 328 l.29 302 V 4 49 47 5l. 19 38 Cl 45.l 404 263 4l.6 l.07 l.50 Nd 2 42 34 36 ll 33 Th 12 44 37 33 .18 34 Sc 4 7 8 7 5 9 Ga 10 l.3 l.2 10 9 11 La 2 101 90 100 10 72 Ce 3 178 144 156 40 l.45 Nb J.4 32 33 23 16 28 37

Table 3d: Quartz augen and related rock type chemistry

S3 S9 Sl6 S6 SB

Sample 307978 307981 307985 307979 307980 Oxide {%) Si02 71.12 72.34 63.80 53.18 44.97 TiO 0.55 0.52 0.98 0.93 0.62 2 AJ.203 l3.58 l3.6l l3. 83 20.99 22.l2 Fe2o3 4.86 3.53 8.65 6.87 l0.58 MnO O.l2 0.06 0.20 0.09 0.14 MgO l.03 0.91 2.01 0.66 0.15 cao 5.45 6.82 8.l2 10.01 l7.68

K2 0 1.07 O.Sl 0.52 0.38 O.l6 Na20 l.32 0.67 l.00 5.26 l.57 P205 0.09 O.ll O.ll O.l3 O.l2 so3

Note: 307978) 307981) Quartz augen rock with+ garnet 307985) 307979 -Weakly layered feldspar-epidote rock with+ acicular magnetite needles 307980 -Epidote-feldspar-magnetite rock. Magnetite occurs as cubic masses to 0.04 cm. Field locations are shown on Fig. 4. 38

Table 3e; Amphibolite, Biotite Selvage and Green-grey Aplite Chemistry

Hole 3198 3186 3.186 3ll3 Depth 1555 307973 3079.74 3079.75 307977 307984 892 l.283 l687 Section Imp. FD. FD. Carb. Oxide (%)

Si02 4l.53 46.58 50.09 60.34 49..36 62.90 60.66 60.22 72.33 TiO 0.91 J.. 38 0.99 J..J.8 J.. 37 0.96 0.47 0.66 2 a.so A1203 l3.95 l.5.l.5 J.5.97 .J.3.86 J.4.59 l.4.37 l.8.75 l.8.87 l.4 .l.8 Fe2o3 17.96 l.3.78 J.l.. 93 ll.25 J.5. 22 8.56 3.27 3.09 3.22 MnO 0.33 0.21 0.20 0.23 0.24 O.l.9 0.04 0.03 0.05 MgO l.0.30 8.29 6.45 2.90 5.9J. 2.32 2.82 4.61 0.90 CaO 4.62 ll.61 ll. 7.1. 7.44 9.83 8.06 l.l.2 0.53 l. 83 K20 5.57 0.56 0.68 0.59 0.90 0.44 0.38 0.32 0.80 Na20 0.24 l..09 l.08 0.99 l..40 l..40 8.76 8.60 5.06 P205 0.12 0.07 0.03 O.ll 0.05 0.12 O. l.7 0.20 0.15 so3 0.02 0.35

Table 3e (.contd.) :

Note: NBH3l98/J.555 Biotite-chlorite selvage 307973 Felsic amphibolite containing pyroxene-rich patches (fragments?) 307974 Vesicular (?) amphibolite containing isolated, spherical masses of albite to 2 cm in diameter 307975 - Felsic amphibolite containing angular fragments(?) of amphibolite set in a matrix of feldspar (Z2660/525, Section 30) 307977 - Felsic amphibolite 307984 - Felsic amphibolite containing lenticular masses of feldspar up to 25 cm in length NBH3l86/892, NBH3l86/J.283, NBH3J.l3/l687 - Green-grey aplite Nomenclature used for Tables 3a-e: With exception of drill hole KC5, all diamond drill samples used here were obtained from North Broken Hill Ltd. KC5 is from the Southern Extensions. S20, SJ.2 are surface samples and have corresponding Zinc Corporation sample numbers of 307972 and 307982. Drilling Section abreviations: No. 3 No. 3 Shaft Section Cos. Cosgroves Section Imp. Imperial Ridge Section Pot. Potosi Section RH Round Hill Section FD Flying Doctor Section Carb. Carbonate Ridge Section KC Kellys Creek Section

Fe2o3 Total iron

LOI Loss on ignition

"-" Not analysed 40

amount of Si02 present, however, the very similar ranges exhibited by both Fb and Fbg-types are quite distinct from those present in the Ap

type gneisses.

2) For each of Al2o3 , Ti02 , Fe2o3 , MgO and to a lesser extent MnO and CaO,

there is a marked, negative linear relationship with Sio2 , such that with

increasing Si02,each of these oxides decreases in abundance in Fb and Fbg-type gneisses. The Ap-type gneisses diverge strongly from these

trends, exhibiting either flat or slightly positive linear relationships

with Si02 • The remaining oxides, Na 2o, K20 and P2o5 , do not possess any

obvious relationship with increasing Si02 in any of the three gneiss types.

3) Each oxide which exhibits a linear relationship with sio2 has a wide sample population range, however the variation in that oxide at any

particular value of Si02 is low. The Ap fels, by comparison, exhibit a

narrow spread of oxide values over the whole range of Si02 • 4) Despite the wide range of oxide values present in both the Fb and Fbg-type

gneisses, no obvious criteria exists which would enable either of these

gneiss populations to be distinguished on a chemical basis.

5) Although the number of quartz augen rocks analysed is very small (n = 3)

in comparison with the sample population size for Fb gneisses (n = 27)

and Fbg gneisses (n = 54), the above conunents regarding the linear rel

ationships between all oxides and Sio2 remains valid. However in terms

of relative oxide abundances quartz augen rocks are enriched in Tio2 ,

Fe2o3 , MnO and cao, and depleted in Al2o3 , Na 2o and K20 with respect to both Fb and Fbg-types.

61 No valid comparisons can be drawn between the three Gap rocks analysed

and either the quartz·~augen rocks or the Fb and Fbg gneisses, due in this

particular case, to the small sample population.

In addition to the above points and although not shown here, the

same data have been plotted in a further three ways, i.e. a) in terms of

belonging to either the Upper or Lower Granite gneiss horizon, orb) with 41

regard to position along strike, and cl the relative stratigraphic position of each sample.

For the Fb and Fbg-type gneisses, none of these criteria produced discernable groups which could enable individual horizons or stratigraphic positions to be determined. However, for the Ap fels with the exception of

S12 which is from the Lower Granite Gneiss, there is some evidence for along strike and stratigraphic variations in chemistry. Table 3a demonstrates that the Northern Leases' Ap samples have a fairly uniform composition which contrasts with that of S20 {from Block 10 hill), taken from the same horizon some 10 kms to the south, and also with that of KCS/682 obtained from a thin, orange, Ap-fels horizon in the lower part of the Upper Granite Gneiss on

Kelly's Creek section. This contrast in chemistry arises from higher CaO and lower K20 values for S20 and higher K2o and lower CaO for KCS/682 t~an is found in the Northern Leases Ap fels. There is insufficient data to determine the spatial significance of the Gap and quartz augen rock types sampled, even though they belong to single horizons within the Lower Granite Gneiss.

4.2.2 Trace- and interelement variation

There is little information in the literature regarding trace and/or interelement behaviour of the Broken Hill Granite gneisses, Of the 20 trace elements analysed in this study only Ni, er, V, Ba, Rb, Zr, Y and Ce are used below in Figs. 7-12 in preference to Cu, Pb, Zn, Co, Cl, Nd, Th, Sc, Ga, La and Nb as the former have been shown to be useful petrological and geochemical discriminants in altered or metamorphosed rocks {inter alia Kamp (1965);

Pearce and Cann (1970, 1973); Garcia (1978)) and are used in conjunction with

MgO, Fe2o3 , K20, Ti02 and Niggli mg and si, or as trace element vs. trace element plots in an effort to further define the characteristics of individual gneiss types.

Plotting of K2o against Rb (Fig, 7a), Fe2o3 against Ti02 (Fig. Ba), and MgO U'ig. 8b), Tio2 against zr, Y and er (Figs. 9a-c), Ni against er, V and MgO (Figs. lOa-c) and Zr against Y and Ce (Figs, lla, b) reveal that the individual components of each pair show well defined positive trends. A 42

Figure 6a: % Ti02 vs. % Sio2 .

(. D = Fbg gneisses, •= Fb gneisses, 0= Aplitic fels,

A= Gap gneisses, 0= Quartz augen rocks). 60

0 D D D

D •

0 0 0 0 0 0 -· co

• 0 re D 0

D c1 ~~ "t 0 ,. ~ :\·II' 0 0 D D ~- f 0 ~ 0 0 <:t 00 0 0 ...

0 d' • 0 D

0 0 0 0 0 0 0

65 70 75 -~;:;---80 ~% S10i! 43

Figure 6d: % MnO vs. % Si02.

Figure Ge: % MgO vs. Sio2 •

C. O= Fbg gneisses, •= Fb gneisses, 0 = Aplitic fels,

~ = Gap gneisses, O = Quartz augen rocks) • D 6d ¾MnO

025 D

D D 0 20 0

D [Jt D 015 • D • D •o D 4J D D (IJ 0 010 OD D D D D o o~o o• !D D [I] ~· omD D D oOJ •m •o~ 0 005 D D .. D •0 .. • D 0 .. • D D • •0 • 0 0 0 • ••• 0 0 0

¾MgO

D D

20 •O

'.l 0 .Q:J 15 D• D D et, G! o0 D • o .51eo 0 ~ 10 • ~B~ om cB D D ~- 0 coo ~ Do • D • 05 D • • ~o• ~'- 0 0 0 0 Oo

60 65 70 75 80 ¾Si02 44

Figure 6f: % cao vs. % Sio2 .

Figure 6g: % Na2o vs. % sio2 •

(. D= Fbg gneiss, •= Fb gneiss, 0= Aplitic fels,

-' = Gap gneisses, 0 = Quartz augen rocks) • 61 %COO

8 0 0

D D 0 D 4 D D • D D D[ll D D D jJ tl) • • D D D ~c:P 'tP c::f3(b D • 2 • D ,::i D • OD • 0 1' ~~OD ~ 0 D •o 0 •• • c510 • • •o 0 0 D De 0 a. D • o• '

%Not) 6g

D • D 4 D O D D Q]c:P 0 0 •C9 0 D D CJ.B• • D ' • 0 0 cticf€. sif. ~B • ~ • CX) 2 • • D • d' D 0 0 0 D •o D 0

60 65 70 75 80 %S102 45

Figure 6h: % K2o vs. % Sio2 .

( D= Fbg gneisses, •= Fb gneisses, O= Aplitic fels, •= Gap gneisses, 0= Quartz augen rocks). 6h

8 D

6 •

4 0 0 D D 0 D 0 2 • • 0 0 • 0 0

D 0 2 A 0 0 • D • 0 D • D 0 00 o• D • 0 0 OD • 0 .. 0 0 £j • D D .. 0 0~ OIJO ~(I] D • 0 fJ O D• 0 00 OD • De i.oom oD 0 0 01 D D • 0 0

0 •

60 65 70 75 80 %Si02 46

Figure 7a: %K2o vs, Rb (ppm.).

Figure 7b: %K 2 O vs. Ba (ppm.) •

Figure 7c: %K20 vs. %Na 2o

( 0= Fbg gneisses, e = Fb gneiss, 0 = Aplitic fels,

, = Gap gneisses, O = Quartz augen rocks) • CJ 7a

%K20 6 • • 0 CJ • 4 CJ CJ • CJ~ Orn • CJ Oo • 0 ·O 2

......

50 100 150 Rb ppm

KC5/682 CJ 7b ¾KzO bat KzC= 7·55%

6 • • 0 CJ • CJ 4 0 \J 0 CJD r:+J. 0 o 8cf 2 • CJ ·, 0 0 S20 0 0

"'"' 500 1000 1500 2000 Ba ppm

0 KCS/682 7c %K20 6at KzO = 7·55%

6 • • 0 o•

4 CJ oCe CJ~OOCJ 0 0 CJ • 0 0 2 0 0

0 0 S20 0 0 41,,. 2 3 4 5 6 7 8 9 %Na20 47

Figure Ba: %Fe 2o3 (total iron} vs. %Ti0 2.

Figure Bb: %Fe 2o3 (total iron) vs. %Mg0.

( D= Fbg gneisses, •= Fb gneisses, 0= Aplitic fels,

~ = Gap gneisses, 0 = Quartz augen rock•) • %Fe2o 3 Ba

0 8

D D D 6 De 8 D D D ••• 0 OD 4 • 0 i 0 0 2 0 otcs/682 • 0 8 OS11 s20O

02 0·4 06 08 %Ti02

%Fa2o 3 Bb

0 8

oo D 6 D .. 'ii l'.:tfl OD D 4 ~

2 O ~KCS/682 %s11 S20 0 •

1·0 2·0 3,0 4·0 %Mg0 48

Figure 9a: %Ti02 vs. Zr (ppm).

Figure 9b: %Ti02 vs. Y (ppm.}.

Figure 9c: %Ti02 vs. (Cr (ppm.}

( D= Fbg gneisses, ei= Fb gneisses, 0 = Aplitic fels,

~ = Gap gneisses} • %T10z 9c

0·8 ,. • D • •

0·6 D OD cP• D ,. 00° ,. D 0·4

00 • 0 0·2 0 0 0 •

100 200 300 400 Zr ppm

¾TiOz 9b

0·8 • •o ,. • o• DO 0·6 D D cP,.,. D D D

0·4

0 0 • 0 0·2 0 0 • 0

50 100 150 Y ppm %Ti02 9c

0·8 • ,. • •o 06 D • og D ,. 00 D D ,. 0

0·4

0 • 0 0 0·2 00 ~

10 20 30 40 Cr ppm 49

Figure lOa: Ni (ppm.) vs. Cr (ppm.).

Figure lOb: Ni (ppm.) vs. V (ppm.).

Figure lOc: Ni (ppm.} vs. %Mg0.

( 0= Fbg gneisses, •== Fb gneisses, 0= Aplitic fels,

£= Gap gneisses). Ni ppm I0a 25 •

DO 20 0 0

0 ooe

0 0 • 0 15 0 0 0 • • 0 10 • 0 • • 0 0

5 0 •

10 20 30 40 50 Cr ppm

Ni I0b ppm • 0

0 0 20 0 0 • C] 0 -11 15 0 0 0 • 0 • j, 10 • 0 • • 0 0

5 0

25 50 75 V ppm

Ni ppm I0c • 0

0 0 20 0 0

C] r,D• OJ 15 0 0 0 cx:a • 10 .. • 0 • CX>

1·0 2·0 3-0 4·0 % MgO 50

Figure lla: Zr {ppm.) vs. Y (ppm.).

Figure llb: Zr (ppm.) vs. Ce (ppm.).

( 0= Fbg gneisses, •= Fb gneisses, 0= Aplitic fels, A= Gap gneisses). Zr ppm Ila 400 • 0 • 0 0

• eD 0 300 0 0 0 0• • 0 0 0 200 D A

• 0 100 0 0 • 0

20 40 60 80 100 Y ppm Zr ppm II b 400 • o.

cjl. • 300 D 0 D 0 D & 0 0 200 • 0

00• O 100 e 0 0

40 80 120 180 220 Ce ppm 51

Figure 12a: Niggli mg vs. niggli si.

Figure 12b: Niggli mg vs. er. (ppm.}.

Figure 12c: Niggli mg vs. Ni (ppm.).

l 0= Fbg gneisses, •= Fb gneisses, 0 =Aplitic fels, • = Gap gneisses). 12a 0

Si 600

500 0 0 0 0 • 0 • 400 oO ·o D 300 r:Jj.-!, ~ 0 D ,. ,. & 200 015 025 035 045 0·55 0·65 mg

Cr 12b ppm 0 50

0 • 30 D DO • D ~ • 0 20 0 D QJ,. 10 0

0 0 • 0 0 • 0·15 0·25 0·35 0·45 0·55 0·65 mg

Ni 12c 25 • 0

[I] 20 D 0

• D •o D DO 15 OJ • 0 • 10 0 • 0 0

5 0

0-15 0·25 0·35 045 055 065 mg 52

similar relationship also exists between K20 and Ba U'ig. 7b) but is more diffuse and less well defined than the above examples, however, the reverse situation exists between K2o and Na2o where an increase in K2o values is matched with a corresponding decrease in Na2o (Fig. 7c). The relationships between Niggli si and Niggli mg and Cr and Ni with Niggli mg (Fig. 12a-c) are not very well defined due to a narrow range of mg-values, although in each case there exists a slight negative relationship between variables.

A dominant feature of Figures 7a, 7b, Ba, 8b, 9a-c, lOa-c and lla, llb is the ability of each element-element or element-oxide pair to separate the Ap samples from the majority of the Fb and Fbg samples. As is demonstrated in these diagrams, this split arises from lower total abundances of the element or oxide pairs concerned, rather than any change in interelement ratios in the

Ap fels in relation to the Fb or Fbg gneisses. The immediate conclusion to be drawn here is that Ap ::fels are exhibiting the same elemental behaviour patterns as the Fb and Fbg gneisses, but on a much reduced scale.

Of equal importance with the above observation is the following; in none of these diagrams U'igs, 6-12) is there any criteria which would allow the Fb and Fbg gneisses to be distinguished from each other. This contrasts with trends present in the Gap rocks, where interelement/oxide relationships can, with few exceptions, be represented by horizontal trends which diverge widely from those expressed by the Fb and Fbg gneisses. Of the oxide/element pairs examined, only these involving K2o, Rb and Ba (Figs. 7a, b), Ti02 and Zr, Y and Ce (Figs. 9a, b, c) show any similarity to the Fb and Fbg gneisses.

The quartz augen rocks on the other hand, exhibit Fe2o3 - Ti02, Fe 2o3 - MgO relation ships which are very similar to, apart from K2o-Ba, K20-Na2o values which contrast markedly with; those present in the Fb and Fbg gneisses.

4.3 Multivariate data analysis

It has been clearly demonstrated in the preceeding sections that

there is no simple method, based on chemistry, which will distinguish

between the two major gneiss types using binary plots. Principal Components

Analysis (l'CA} and Cluster Analysis are two multivariate analysis techniques 53

which enable items with numerous attributes to be compared together as whole

individuals instead of component parts of individuals. In this particular

case the individual items are the samples studied and their attributes, their

component chemistry.

PCA is used here on all of the samples examined to evaluate the

interrelations which may exist between their major oxides. Cluster analysis

however, is only used here on the Northern Leases samples for which there is major oxide, trace element and mineralogical data available, Both methods of

analysis are summarized below together with the implications of the displayed

results.

4.3.l Principal Components Analysis

Principal Components Analysis is a multivariate technique in which a

large sample population, each sample of which possesses a number of variables,

can be examined for any underlying distinguishing features. The concept of

PCA is such that a linear transformation of a number of variables measured on

a set of samples can be generated which will successively account for as much

of the variation present in the sample population as is possible, It is the

process of transformation which is termed PCA. The following explanation and

description of the fundamentals behind PCA has been derived from Wahlstedt

and Davis (1968).

One problem encountered in many multivariate statistical procedures

applied to geological situations is that the data does not possess the desired

degree of independence between variables. It is more usual for the reverse to

be true, with each variable measured on a sample being interdependent on the

majority of the other variables measured, The transformation of raw data into

principal components achieves this objective of independence of variables.

The large number of manipulations required to produce the principal

components of a sample population are best carried out by computer and the

computer program used for this study was developed by Wahlstedt and Davis

(1968), using the Jacobi algorithm which is outlined below. The initial step 54

is to produce an m x m matrix of covariances or correlations, where m is the number of observed variables. A covariance matrix is calculated by:

m m m Aij = Iaijl = n E E x.x E x.x ) i=l j=l i j i=l i j (Equation 1) , n (n-11 where a,.= array A element of row i, column j 1] n = number of samples. similarly a correlation matrix can be calculated by:

m m m m Aij = [rij] = n E E x.x E X .r X X i=l j=l i j i=l i j=l j (Equation 2) ,

m m m 2 /n; x2 - ( E X) ).(n r x2 - ( E X) 2) i=l i=l j=l j=l

The difference between the two matrices is that a correlation matrix is equivalent to a covariance matrix of standardized variables. A standardized variable is one where the raw data are expressed as a measure of their varia tion from the population mean of each variable in units of the standard varia tion of that population, i.e. z(standardized variable)= (X(variable measured)

X(population mean))/s(standard deviation). A standardized variable is a dimensionless quantity as it is independent of the original units used. This aspect of a covariance matrix is important in geological problems as it allows major oxides with widely differing ranges, to be directly compared and/ or allows major oxides and trace element data, between which exists a large disparity in abundance levels, to be compared. For these reasons only stand ardized variables have been used in the PCA and Cluster Analysis results presented below.

Associated with every square matrix [A] is a characteristic function;

f(>.) (Equation 3), 55

which has the property of fO.l = 0, From this matrix equation, m roots, called eigenvalues can be extracted. Each eigenvalue has an associated eigenvector which is a column vector {Xi], with the property [A-A]. (xi] = 0.

If the eigenvalues of a matrix are nonidentical, then the associated eigenvec tors are independent. It is these vectors that are the transformed variables or principal components. The sum of the diagonal elements (trace) of the matrix, which is equivalent to the sum of the eigenvalues, represents either the total variance or correlation in the matrix.

4.3.2 Cluster Analysis

Cluster analysis is a multivariate classification technique which allows mutual elemental and intersample relationships in a set of samples to be examined. The basis of this method is the calculation of similarity co efficients between each pair of samples and then grouping or linking, i.e.

"clustering" the sample pairs according to their level of similarity. Gradual ly more sample pairs are admitted to the original cluster as the similarity level is lowered. Eventually other clusters are initiated and enlarged until all sample pairs and individual clusters are linked.

Three methods of clustering are favoured; weighted pair-group average linkage, unweighted pair group average and single linkage. The computer program used here (Mccammon and Wenninger, 1970) to perform cluster analysis on the Northern Leases samples uses the unweighted pair-group average method.

This program also produces a dendrograph as the final product, which is a two dimensional hierarchial representation of the relationships between sample pairs and individual clusters. Substantial modifications were carried out on the original program to facilitate the calculation of a covariance matrix and euclidean distance measures from the raw data.

Several authors, notably Rhodes (1969), Hesp and Rigby (1972) and also Joyce (1973), point out that the use of euclidean distance as a measure of correlation assumes that all variables are orthogonal, and so non-correl ated. This is rarely the case with geochemical data, for instance Rhodes

(1969) and Joyce (1973) show that the geochemistry of granites frequently 56

exhibit a high degree of inter-element correlation. The use of correlated variables in cluster analysis amounts to a concealed weighting of the vari ables, giving those variables with high correlations, a greater weighting than the weakly correlated variables.

4.3.3 Results of multivariate data analysis

Principal Components Analysis results for all the Fbg, Fb and Ap gneisses studies and a plot of the first two components or factors extracted

(Table 4, Fig. 13) indicate that the first two eigenvalues account for over

92% of the total variance in the sample population as a whole. The first eigenvalue, accounting for 82.3% of the population variance, consists of a vector representing increasing Si02 and decreasing Al2o3 and Fe2o3 . An increase in Cao and Na 2o and a decreasing K20 content constitute the second vector with a corresponding eigenvalue which accounts for 9.9% of the popul atio.n variance, These two vectors can be represented simply as Si02/(A12o3+

Fe2o3) and _(Ca0+Na2o)/K2o. The ability of the first two components to account for almost all of the variance in the original data indicates that little importance needs to be attached to the variability of Ti02 , Mn0, Mg0 and P2o5 • That the first component is geologically feasible is readily seen from Figure 6b, 6c where both

Al 2o3 and Fe2o3 are shown to have a strong negative relationship with Si02. Mineralogically this component can be quantified by an increase in quartz at the expense of feldspar, garnet and biotite (Table 1). Of less significance and therefore exerting less influence over the variation in the chemistry of these samples the second component can also be demonstrated to be real in both chemical and mineralogical terms. This is shown in Figure 7c where K2o decreases with increasing Na2o and in Table 1 as a general decrease in K feldspar with increasing plagioclase.

If each sample of the original data is converted to a "score", i.e. each component part of the analysis of a sample is multiplied by the corres ponding element of an eigenvector, these sample points can then be projected Table 4: Principal Components for all Fbg, Fb and Ap gneiss types

Vector Eigenvalue Total variance (%) Cumulative variance (%) 1 15.2 82.274 82.274 2 1.82 9.851 92.125 3 0.612 3. 313 95.438 4 0.439 2.376 97. 814 5 0.224 1.213 99.027 6 0.129 0.698 99. 725 7 0.0452 0.245 99.970 8 0.0042 0.023 99.993 9 0.0008 0.004 99.997 10 0.0007 0.003 100.000

Eigenvector Variable 1 2 3 4 5 6 7 8 9 10

Si0 2 0.8715 0.1202 0.1273 -0.2438 -0.2133 -0.3236 -0.0111 -0.0050 0.0025 0.0007 Ti0 2 -0.0434 0.0159 -0.0393 -0.0292 -0.0356 -0.0620 -0.1162 -0.9874 -0.0380 0.0217 Al2o3 -0.2788 -0.0284 0.8634 -0.0230 -0.0214 -0.3948 -0 .1372 -0.0129 0.0081 -0.0062 Fe 2o 3 -0.3744 -0.0247 -0.3422 -0.4801 -0.5837 -0.3918 -0.1047 0.0770 0.0255 -0.0005 MnO -0.0079 0.0032 0.0013 -0.0233 -0.0084 -0.0056 -0.0163 0.0373 -0.9980 -0.0402

MgO -0.0912 0.0207 0.0899 -0.1396 0.0139 -0.0752 0.9701 0.1243 -0.0081 0.0337 cao -0.0903 0.5252 -0.2295 -0.1088 0.6428 -0.4827 -0.0628 0.0238 0.0049 -0.0267

Na20 -0.0074 0.2532 -0.1226 0.8123 -0.3640 -0.3435 0. 0968 0.0318 -0.0134 -0.0049 K20 0.0642 -0.8022 -0.2094 0.1304 0.2566 -0.4743 0.0198 0.0115 -0.0053 -0.0135 P205 -0.0005 0.0032 -0.0066 0.0070 0.0186 -0.0198 -0.0378 0.0197 -0.0390 0.9979

u, -.J 58

Figure 13: Principal components for Fbg, Fb and Ap Granite

gneiss types, . 0= Fbg gneiss, •= Fb gneiss, 0= Aplitic fels, U = Upper

Granite Gneiss, L = Lower Granite Gneiss samples). 10

DL ou

9 ... 0

0 0

0 7

c9b eu DL {§'1l _u [.]' eu ou eu 6 ou rnie~~u

~uu .L eu C eu O lu eu ~u 0 !5 eu

4 -----;;------~-;;;-----7,;------~s!o~u____ 40l 45 50 ---;6;5::=~--;1'00 55 Component I. 59

onto pairs of principle axes, such as in Figure 13. The overall distribution of sample points is little different from that presented in Figures 6-12, in as much that the Fb and Fbg gneisses remain undifferentiated one from the other and the Ap fels variants are well separated from the other two gneiss types. It is quite clear from Figure 13 that samples obtained from the Upper

Granite Gneiss horizon cannot be distinguished from those obtained from the

Lower Granite gneiss, and although not shown, no lateral (i.e. north-south) variation could be detected in the distribution of points.

The results obtained from Cluster Analysis are presented in a manner which demonstrates the interrelated nature of the chemistry of the Northern

Leases Ap, Fbg and Fb gneisses (Fig, 14) and secondly how these gneisses actually relate to each other (Fig. 15). The chemistry of these gneisses has produced a dendrograph which can be divided into what is essentially a mafic portion (left hand side) and a felsic portion (right hand side). This sub division can be best explained in terms of the abundance of biotite-ilmenite magnetite-zircon on the left hand side and both plagioclase and K-feldspar as well as garnet on the right hand side, A similar mineralogical inference could also be drawn from the numerous bivariate plots of Figures 6-12. There fore Figure 14 can be considered as a general "precis" of the chemical rela tionships present in these gneisses.

Inter-gneiss relationships are demonstrated in Figure 15 and it is apparent that this diagram can also be used to summarize the sample distribu tions found in Figures 6-12. The main feature of Figure 15 is that the majority of the Ap fels samples and the Gap rocks form discrete clusters which are chemically separated from the majority of the other rock types. Despite this and the fact that some Fb and Fbg gneisses form discrete clusters on their own, there is no distinct separation into garnet-rich and garnet-poor varieties, The discrete individual clusters of Fb and/or Fbg gneisses are interpreted here as representing the wide chemical variability which is present in both of these gneisses, 60

Figure 14: Cluster analysis dendrograph of Northern Leases

Granite Gneiss samples, based on chemistry.

( 0 = Fbg gneisses, e = Fb gneisses,

0 = Aplitic fels, A= Gap gneisses) 0 0 (,JI 6 ui

Ce Euclidean distance ____r--- Nd - La - Zr ,-. Th - Fe2o3 .... Nb ,__ y

Ni -

MgO ..... Cr - V

Ti02 ... Ga

A1 20 3 ,__ Sc MnO - P205 - Zn - CaO - Na20 - Cl - Cu .._

Co ...... Sr - Pb - Si02

Ba Rb I K20 I 61

Figure 15: Cluster analysis dendrograph of Northern Leases

Granite Gneiss samples, based on mineralogy.

D= Fbg gneisses, e = Fb gneisses, 0= Aplitic fels,

A= Gap gneisses, NBH3167/4642 = North Broken Hill Ltd.

diamond drill hole sample). I\) .i:- en (X) 0 0 0 0 0

NBH 3113124 • NBH 813/438 0

NBH 3105/2 380 0 I ,___

NBH I5N4/1747 0 NBH 961/1866 0 - .__ ,___ NBH 837/301 0 NBH 3074/ 3977 • NBH 834/476 - ---- NBH 2003/1627 NBH 952/143 § I NBH 3074/4814 I NBH 962/764 0

NBH 2003/2153 0

NBH 962/900 0 NBH 820/2609 0 NBH 884/389 0 I--

NBH 15N4/2I54 NBH 951/38 • NBH 2003/1904 •

NBH 847/416 0 NBH 2003/1570 I NBH I5N4/ 1670 NBH 813/518 ~ NBH 3074/5053 0 I NBH 3167/4642 0

NBH 3113/1687 ...

NBH 3186/1283 • I NBH 3186/892 0 62

4.3.4 Kolmogorov-Smirnov two sample test

From the results of the bivariate chemical plots and Principal

Components Analysis, it is apparent that both the Fb and Fbg gneisses are chemically very similar. The nature of this similarity can be tested by comparison of individual oxide frequency curves from each gneiss-type using the Kolmogorov-Smirnov two sample test. This test indicates the level of confidence that can be placed on the assumption that two sets of data were drawn from the same sample population,

To perform this test, the two sets of data are first divided into the same class intervals and the absolute difference between the same class interval frequencies for each gneiss is then calculated. The maximum absolute difference obtained is tested against the critical value for accept ance of the hypothesis that the two sample sets were drawn from the one popul ation. At the 95% level of significance, the critical value is calculated as:

D < I 1.36* t(m+n)/mnl (Equation 4), where D is the maximum mn mn absolute difference between the two frequency curves, and m, n are the size of the two sample sets. For this exercise, m (size of the Fbg sample set) =

54 and n (size of the Fb sample set) = 27, and so D = 0.3206. mn The Kolmogorov-Smirnov two sample test was applied to the frequency distribution curves of each major oxide of the Fbg and Fb gneisses and the maximum absolute differences between each curve tabulated in Table 5. It is probable that the high absolute differences found between Si02 , Ti02 and Mn0 are ·a function of insufficient Fb samples rather than a significant result as this test was primarily designed for data sets containing at least 20 samples.

This comment arises from the fact that in order to achieve a balance between class intervals containing similar numbers and intervals which were chemically reasonable, class widths for each oxide were established at approximately la intervals,

It appears justified to conclude here that the Kolmogorov-smirnov two sample test indicates that both the Fbg and Fb gneiss samples were derived 63

Table 5: Kolmogorov-Smirnov two sample comparison between Fbg and Fb gneisses.

Oxide Dmn

Si02 0.3148

Ti02 0.3148

Al203 0.2963

Fe2o3 0.1482

MnO 0.3148

MgO 0.0370

cao 0.0926

Na2o 0.0741

K20 O.llll

P205 0.0925

Note: The critical value at a level of 95% significance which Dmn must exceed is 0.3201. Above this point the data sets are considered to have been drawn from different populations. 64

from the same population, This conclusion supports the inferences which have

already been derived from the bivariate chemical plots and Principal Components

Analysis. This test cannot be applied between the Ap fels and Fbg-Fb gneisses, or the Ap and Gap rocks or the Gap-rocks and Fbg-Fb gneisses as the sample populations of both the Ap and Gap-rocks are too small. 65

Chapter 5

5. Petrology

Petrological discriminant diagrams are used with the Northern

Leases samples to examine the similarities which may exist between these rocks and those with known igneous origins. These comparisons provide a measure of the igneous-like nature of the Northern Leases samples and so a

starting point from which their origins can be examined.

The three whole rock petrological discriminant diagrams discussed below were developed for use in evaluating essentially unaltered igneous rocks and their use here infers; a) the gneisses under examination had

igneous premetamorphic precursors and b) that they are relatively unaltered.

Although the former assumption that Granite gneiss lithologies were igneous in origin cannot be quantitatively justified at present, the strong linear nature of the relationship between Si02 and Al2o3 , Ti02 , Fe2o3 , MgO and possibly MnO resemble igneous fractionation trends. This observation is in apparent conflict when trace elements such as Y and Zr, which may be enriched

in the latter stages of a fractionation cycle, are compared from Fbg and Fb

Granite gneiss types and the Ap fels which occupy the stratigraphic upper most portions of granite gneiss horizons. Y and Zr are depleted in the Ap

fels relative to the other Granite gneiss types, yet still retain the same

elemental ratios.

If significant alteration has occurred in this suite of rocks

either prior to, during, or after metamorphism it would be reasonable to

expect that this would be reflected in their chemistry. At a qualitative

level, if alteration has affected some of the rocks examined it is expected

that any changes occurring would be represented by discontinuities in the

binary plot trends already observed in these rocks (Figs. 6-12). It

follows then that unless alteration has taken the form where all the element

al/oxide pairs examined have been effected in the same manner, that it is

probable any alteration which may have occurred was incapable of disrupting

the chemical attributes of these rocks to any great degree. 66

5,1 Alteration

A semi-rigorous method for evaluating losses and gains occurring during alteration is the Barth Standard Cell (Barth, 1948), which is based on the ideal of a standard cell or unit of rock containing 160 oxygens, with the sum of all associated cations being approximately equal to 100. The basic assumption underlying this method is that any alteration which may have occur red, has taken place without a change in volume. As well as alteration studies, the Barth Standard Cell (BSC) comparison is considered here to be an appropriate tool with which the tectonic regime under which a rock was prod uced, could be assessed. This latter point arises from the concept that a total analysis of a rock is characteristic of the tectonic regime the rock was generated in (Jakes and White, 1971, 1972), thus a useful by-product of a

BSC comparison is an indication of the provenance of the rock being examined,

Alteration studies based on the BSC method require a "parent" from which the altered end result can be produced and also, that an isovolurnetric ideal is maintained. A selection of "parents" are presented in Table 6, together with average Granite gneiss compositions; averages are used for all

"parents" and Granite gneiss types rather than specific analyses, in order to arrive at a generalized conclusion for the whole Granite gneiss sample population, instead of specific results for each analysis. The various

"parental" materials were selected in order to accommodate a variety of possible precursors which have been postulated by previous authors and which fall broadly into either sedimentary or igneous/volcanic categories. There fore the "parents" used in BSC evaluations of the Granite gneisses are arkose

(c.f. King and Thomson (1953); Thomas (1960); Carruthers (1965), and Lewis et al. (1965)) and dacite or rhyolite (c. f. Shaw (1973), Stanton (1976),

Plimer (1977) and Stevens et al. (1979)), Dacite and rhyolite from both an

active continental margin and also an island arc setting, have been specific

ally selected as "parents" in order to test the assumption of Stanton (1976)

that the Granite gneisses were generated in an island arc setting. The remaining "parent", sillimanite gneiss, is included to cover the possibility 67 that the granite gneisses were derived from the in situ mobilization of local gneisses.

The maintenance of an isovolumetric ideal through the whole of the granite gneisses' history is difficult to establish, however, as previously mentioned (c.f. Chapter 3.7), mineralogical evidence indicates chemical mobility during metamorphism was insignificant.

Having calculated BSC's for the average compositions presented in

Table 6, it is possible to calculate the cation changes required to convert a postulated "parent" BSC into the resulting Granite gneiss type BSC (Table 7).

The resultant cation sums for each comparison indicate whether the conversion involved a net gain (+ ve sum) or a net loss (-ve sum). It follows therefore, that the closer the cation sum is to zero, the greater the similarity between the "parent" precursor and the material being examined. A second corallary of low cation sums is that if the tectonic regime of the "parent" is known then a similar regime may be inferred for the material being compared.

The changes required in the BSC conversions of selected "parents" into Granite gneiss rock types and the resultant sums are presented in Table

7. This method has characterized the Ap fels, Fbg and Fb gneisses as being most chemically similar to arkose, active continental margin rhyolite and active continental margin dacite respectively. The overall changes required for each cation in individual comparisons is generally small, particularly when compared to the results of BSC studies carried out by Spitz and Darling (1975) on altered felsic volcanics. Despite these relatively small changes there are however, a number of consistencies in the behaviour of some individual cations

irrespective of the "parent" chosen or which are specific to either Ap or

Fb-Fbg gneiss types. In this particular case, consistent behaviour is defined

to be where the majority of the differences for a particular cation for the

range of "parents" chosen are of the same sign. The behaviour of each cation

with respect to all "parents" for each gneiss-type conversion is sUimnarized

in Table 8.

The ~hernical characteristics of each Granite gneiss type presented Table 6: Average composition of rock types used in Barth Standard Cell calculations.

Oxide(%) 1 2 3 4 5 6 7 8 9

Si02 76.86 67.67 69.40 64.35 69.61 64.41 73.67 66.80 74.22

T:i,0 2 0.20 0.65 o. 53 0.81 0.44 o. 72 0. 21 0.23 0.28

Al203 13.23 15.46 14.86 19.78 12.83 16.37 13.62 28.24 l3.27

Fe2o3 1. 72 5.49 4.52 5.21 3.61 3.64 1.48 1.92 1.90

MnO 0.03 0.10 0.07 0.03 0.06 0.08 0.06 0.06 0.05

MgO 0.32 1.15 LOO 1.96 1. 73 2.39 0.45 1.50 0.28

cao 1..14 2.38 2.00 0.28 2.67 4.68 1.24 3.17 1.59

Na2o 2.53 2. 77 2.66 2.10 3.07 4.15 3.69 4.97 4.24

K20 3.43 3.35 3.64 4.09 2.75 2.31 4.36 .1. 92 3 • .18

P205 0 . .1.1 0 . .14 0.13 0 . .10 0 • .14 0.16 0.08 0.09 0.05

Note: Rock types and sources -

1 - Average Ap fels (7), table 3a, this study 2 - Average Fbg gneiss (54), table 3b, this study 3 - Average Fb gneiss (27), table 3c, this study 4 - Average Sillimanite gneiss (63) (Shaw, 1973) 5 - Average Arkose (26) (Kamp et al, 1976, table 5) 6, 7 - Active Continental Margin average dacite (6) and rhyolite (7), compiled from Siegers et al. (1969), Zeil and Pichler (1969), Guest and Sanchez (1970) , and Gunn and Mooser (1971) 8, 9 - Island Arc dacite {Jakes and White, 1971), Island Arc Rhyolite (25), Ewart and Stipp (1968)

Numbers in brackets, e.g. (63) represent the number of analyses used to calculate the average. Table 7: Changes in Barth's Standard Cell needed to convert Arkose, Sillimanite Gneiss, Dacite and Rhyolite to Granite Gneiss type lithologies.

Aplitic textured Fels Feldspar-biotite-garnet Gneiss Feldspar biotite Gneiss Cation ARK SG ACMD ACMR IAD IAR ARK SG ACMD ACMR IAD IAR ARK SG ACMD ACMR IAD IAR

Si +6.15 +8.40 +9.18 +1.15 +6.77 +1.05 +0.49 +5.42 +3.52 -4.51 +1.11 -4.61 +3.17 +5.42 +6. 20 -1.83 +3.79 -1.93 Ti -0.19 -0.38 -0.43 -0.01 -0.03 -0.07 -0.19 0.00 -0.05 +0.37 +0.35 +0.31 +0.11 -0.08 -0.13 +0.29 +0.27 +0.23

Al +0.38 -7.46 -3.63 -0.61 -5.67 -0.40 +3.24 -4.60 -0.77 +2.25 -2.63 +2.56 +3.42 -4.42 -0.59 +2.43 +2.63 +2.56

Fe -1.23 -2. 41 -1.58 +0.04 -0.33 -0.15 +l. 36 +0.18 +l.01 +2.63 +2.26 +2.44 +1.42 -0.33 +0.50 +2.12 +l.75 +2.44

Mn -0.02 0.00 -0.04 +0.03 -0. OJ. -0.02 +0.04 +0.06 +0.02 +0.03 +0.05 +0.04 +0.02 +0.04 o.oo +0.01 +0.03 +0.02

Mg -1.81 -2.21 -2.74 -0.18 -1. 57 +0.04 -0.69 -1.09 -1. 62 +0.94 -0.45 +l.16 -0.81 -1.21 -1. 74 +0.82 -0.57 +1.04

Ca -1.40 +0.75 -2.36 -0.10 -1.95 -0.44 -0.19 +1.96 -2.15 +1.11 -0.74 -0.77 -0.45 +2.70 -2.41 +0.85 -1.00 +0.51

Na -0.90 +0.56 -2.87 -2.02 -4.32 -2.97 -0.32 +l.14 -2.29 -1.44 -3.74 -2.39 -0.29 +l.17 -2.46 +1.41 -3. 71 -2.39

K +0.73 -0.91 +1.16 -1.09 +1.58 +0.21 +0.79 -0.85 +1.22 -1.03 +1.64 +0.27 +1.33 -0.31 +1. 76 -0.49 +2.18 -1.03 p -0.03 +0.01 +O.Ol +0.02 0.00 +0.04 +0.01 +0.05 +0.05 +0.06 +0.04 +0.08 -0.06 -0.02 -0.02 -0.01 -0.03 +0.06

Total +1.68 -3.65 -3.30 -2.77 -5.53 -2. 71 +4.92 +2.27 -1. 06 +O. 41 -2.11 -0.91 +7.86 +2.96 +1.11 +2.78 +5.34 +1. 51

Note: ARK - Average arkose, SG - Average sillimanite gneiss, ACMD - Average active continental margin dacite, ACMR - Average active continental margin rhyolite, AID - Average island arc dacite, IAR - Average island arc rhyolite. 70

Table 8: Chemical characteristics of Granite Gneiss types with respect to all possible "parents".

Cation Ap Fbg Fb Postulated Source of characteristic

Si Enhanced Enhanced Enhanced Original

Ti Depleted Enhanced Enhanced Original

Al I I I Original C?l

Fe Depleted Enhanced Enhanced Original

Mn Depleted Enhanced Enhanced Original (?)

Mg Depleted Depleted Depleted Original

Ca Depleted I I Original C?)

Na Depleted Depleted Depleted Alteration/Original (?)

K I I I Original C?)

p r Enhanced Depleted Original

Note: I - Inconsistent cation variation between "parents" to enable a specific trend to be established. Original/Alteration - Premetamorphic origin of cation characteristic. 71

in Table 8 can be regarded as either fundamental features of the granite gneisses or as derivatives of alteration processes. A solution to this problem is suggested by the bivariate plots of Figures 6-12, which demonstrate the generally regular nature of the variations in oxide to oxide relationships.

Although this may be so for Si, Ti, Fe and Mg it is clearly not so for Na 2o.

The behaviour of this particular oxide is very erratic and exhibits only a weak relationship with either K2o or sio2 , these features and the depleted cation values with respect to all "parents" suggests either; 1) Na may have been removed from the Granite gneisses, or 2) Na was only present in minor quantities originally. Similarly it could also be argued that the overall enhancement of Si and depletion of Mg were products of alteration were it not for the demonstrably close ties these cations have with other cations and trace elements (Figs. 6-12), Therefore it is probable that the levels and behaviour of Si, Ti, Fe, and Mg reflect the unaltered premetamorphic chemistry of the Granite gneisses. Through similar reasoning the same conclusion appears valid for Al, Mn, Ca, Kand P although at a quantitative level their behaviour remains equivocal. It is quite possible that the foregoing evalu ation of BSC comparisons between Granite gneiss lithologies and postulated

"parents" yields realistic results, however two features of this method indicate that caution should be used when applying these answers:

1) Large positive or negative cation changes in the one rock type

could balance out and bring the total close to zero.

2) Small, relatively insignificant changes in a number of elements

could yield a large positive or negative total.

Both of these problems have been catered for here in a general way with the comparisons being performed on a number of differing "parents" and then assessing and summarizing the dominant trends present (Tables 7 and 8).

5,2 Petrological character

Use of the BSC comparison has provided semiquantitative evidence that the Fbg and Fb gneisses are similar to volcanic rocks, and so it should be possibie then to examine their chemistry in relation to standard petrolog- 72

ical discriminants, The Northern Leases samples are used here specifically, as this is the data set on which the most physical and chemical information is available. The three discriminants used here are; alkaline vs. subalkal ine compositons (Fig. 16), variation in the components A (Na2o + K2o), F(total iron as FeO) and M(MgO) all as weight% (Fig, 17) and a ternary pro jection of the components An-Ab-Or in cation% (Fig. 18). All three discrim inants are used in the revised form proposed by Irvine and Baragar (1971).

5.2.l Alkaline vs. subalkaline composition

Plotting weight% (Na 2o + K20) against Si02 enables volcanic rocks to be classified as being either alkaline or subalkaline in composition.

When the granite gneisses and associated rock-types are plotted on such a diagram (Fig. 16), all samples excepting the Na2 o-rich Gap rocks fall in the subalkaline field. For comparison purposes the same "parental" material used in the BSC comparisons are also plotted here and in Figures 17 and 18.

The main features of Figure 16 are that both the Fbg and Fb gneisses plot in close proximity to each other, but are distinct from the Ap fels and also that both the Fbg and Fb gneisses possess Na2o + K2o contents similar to all of the postulated precursor rock types, This relationship does not hold for most of the Ap fels and the Quartz-augen rocks due to their low Na 2o + K20 contents (cf. Table 3a).

5.2.2 AFM variation

The AFM diagram is used to distinguish between rocks belonging to the tholeiitic series and those of the calcalkaline series as is shown in

Figure 17. Use of this diagram here indicates that the granite gneiss variants are precominantly calcalkaline in nature, despite a considerable spread along the A-F axis. All the Granite gneiss samples plotted here exhibit an A:M ratio which is consistently higher than that of all postulated percursor rock types excepting that of the Active Continental .Margin Rhyolite and the Island arc Rhyolite. The higher A:M ratios in the Granite gneisses are due to the generally low MgO content of these gneisses rather than elevated Na 2o + K20 73

Figure 16: % (K20 + Na 20] vs. %Si02 • ( O= Fbg gneisses, •= Fb gneisses, 0= Aplitic fels, A= Gap gneisses, O = Quartz augen rocks. Alkaline-Subalkaline

division after Irvine and Baragar (1971). Details relating to

the average rock types ACMD, ACMR (Active Continental Margin

Dacite and Rhyolitel, IAD, IAR (Island Arc Dacite and Rhyolite),

Sill G (Sillimanite gneiss} and Arkose are listed in Table 6). .. Alkaline oKC5 Sub Alkaline 9 ..

er *ACMR

• I IAR 0 • 7~ *IAO • D it ACMD e D 0 N 0 ~ De ltSG + D •o 0 0 N ARK1D .& ~ D :,l1 0 D 0 D

5 D D 0

4 0

OS20

3 1 ~s16 1 1 s3?"-~s9 is12 1 1 60 65 70 75 80 %Si02 1·52 2·39 1·18 0·85 74

Figure 17: AFM diagram for Northern Leases Granite gneisses.

0= Fbg gneisses, •= Fb gneisses, 0= Aplitic fels,

A= Gap gneisses, O= Quartz augen rocks,

A = Na 2o + K20, Fe= FeO (total iron), M = MgO. Calcalkaline-thoelitic division after Irvine and

Baragar (1971). Details relating to the average

rock types ACMD, ACMR (Active Continental Margin Dacite

and Rhyolite), IAD, IAR (Island Arc oacite and Rhyolite)

Sill G (Sillimanite gneiss) and Arkose are listed in

Table 6).

60M 60M

M M

A A

Colcolkoline Colcolkoline

' '

SG SG

ACMD ACMD

I-

ARK ARK

~ ~

DO/ DO/

0 0

60F 60F

~· ~·

'1 '1

D D

• •

IAD IAD

/2~~-D /2~~-D

AD AD

D D

oo oo

0 0

/ /

' '

D D

0 0

00 00

*tAR& *tAR& 0 0

1-ACMR 1-ACMR A A 75

values, as Figure 16 demonstrates that this component is similar to that found in all postulated precursors.

The spread of data along the A-F axis expressed by the granite gneisses is slightly more extensive than that of the postulated precursors and is due to the wide variation in iron content of the Ap fels compared to that of the Fbg and Fb gneisses. This variation effectively distinguishes the Ap fels from the majority of the Fbg and Fb gneisses, however the vari ation in all three components (A, F and M) is insufficient to enable the Fbg and Fb gneisses to be separated.

5.2.3 An-Ab-Or projection

The An-Ab-Or projection used here (Fig. 18) is in the form modified by Spitz and Darling (1975) , such that the field for volcanic rocks of average potassium-content has been superimposed over the fields occupied by sub alkaline rocktypes. The majority of the Ap fels, Fbg and Fb gneisses plotted on this projection form a compact group which straddles the boundary between rhyodacites and rhyolites.

The clustering present here illustrates the similarities which exist between the three variants and the actual location of the cluster indicates that the granite gneisses, on the whole, are richer in Or (i.e. K) than "average" volcanics rocks and also the postulated· precursor rock types excepting the Arkose and Sillimanite Gneiss. Contrasting with the K-rich nature of the granite gneiss variants is the Ab-rich (i.e. Na-rich, K-poor)

Gap rocks and the An-rich, Ab-Or-poor nature of the Quartz augen rocks. Figure 18: An-Ab-Or projection for Northern Leases Granite Gneisses

( D= Fbg gneisses, •= Fb gneisses, O= Aplitic fels,

..= Gap gneisses, O= Quartz augen rocks. After Irvine

and Baragar (1971) where An, Ab and Or correspond to normative

anorthite, albite and orthoclase. Details relating to the

average rock types ACMD, ACMR (Active Continental Margin

Dacite and Rhyolite), IAD, IAR (Island Arc Dacite and

Rhyolite), Sill G (Sillimanite gneiss) and Arkose are listed

in Table 6). Or

•

K-Rhyolite

l'sm

D •

Rhyodocife

'ti

g I

I~'\

•

ACMR

Rtlite

Rhyolite

volcanic-...,,.._

rocks

"Average"

IAR

Ab 77

Chapter 6

6. Discussion

The detailed examination of the Granite gneiss horizons at Broken

Hill during this study has revealed that:

a) On mineralogical grounds these horizons can be divided into

distinct laterally extensive zones of garnet-rich, garnet-poor

Granite gneiss. This stratigraphy is defined by: a general

grainsize fining upwards of the whole sequence which is expressed

by size and abundance grading of feldspar augen; the presence

of localized layering and the presence of aplitic horizons

internal to, and capping the sequence.

b) The presence of a recognizable stratigraphy within the Granite

gneisses is not paralleled by changes in geochemistry, even

though the chemistry of the granite gneisses as a whole exhibits

very regular trends. Thus it is not possible to distinguish

chemically between garnet-rich and garnet-poor Granite gneisses

nor is it possible to assign an unique stratigraphic position to

a sample on the basis of its chemistry.

These observations appear to be mutually exclusive, however, the largely coherent relationships which are present between the individual components of the geochemical data used, the similarities which have been established between the granite gneisses and possible volcanic precursors and the stable, low pH20 conditions prevailing during metamorphism indicate that these features are directly related to premetamorphic events. This being the case, it is relevant to examine postulated origins for these gneisses and also develop a model which adequately caters for the physical and chemical features of the granite gneisses.

6.1 Origins of Granite gneisses

Origins postulated for the Granite gneisses have varied with geologic fashion from granitic sill, to arkose, to calcalkaline pyroclastics.

The opinion that the origin of the Granite gneisses could be explained by 78

means of post-metamorphic sill-like intrusions was put forward by Browne

(J922) and supported by Gustafson et al. (]950), however this idea received

little support from King and Thompson (]953), Thomas ()960), Carruthers ()965)

or Lewis et al. ()965) who all favoured a metamorphosed arkosic sediment as

the most likely source material. This argument was effectively countered by

Plimer (]977), who pointed out that the high stratigraphic position occupied by these gneisses within the Willyama Complex and the lack of any spatially

related granitic rocks precluded an origin based on arkosic material.

An igneous parentage for these gneisses was reintroduced by Binns

(J964), who suggested that the Granite gneisses were compositionally similar

to calcalkaline granites. This point was also made by Shaw ()973) and

Stanton (]976) who recognized the calcalkaline affinities of those gneisses,

and together with Plimer (]977) and Stevens et al. ()979), they regard the precursors to.the Granite gneisses to be sediments of dacitic to rhyodacitic

composition, probably pyroclastic in origin.

This study has quantitatively demonstrated that the stratigraphic

uppermost part of the Granite gneiss (i.e. the Ap fels) closely resembles

arkoses in composition, whereas the Fbg and Fb gneisses appear similar to

dacites or rhyolites. Although the BSC method used here will distinguish

between sediments and igneous rocks, it is not capable of distinguishing

extrusive/pyroclastic material from entirely intrusive rocks as it is based

solely on chemical criteria. Field evidence such as the lack of any observ

able crosscutting relationships with the enclosing metasediments; the

absence of xenolithic inclusions not related to the Granite gneisses; the

presence of laterally extensive, layer parallel metasedirnentary horizons;

and no evidence of metamorphic effects present in the surrounding metasedi

ments implies that an intrusive mode of emplacement for these gneisses is

unlikely.

Despite being classified in part here as arkoses and partly as

volcanic, all the Granite gneisses studied are demonstrably chemically

related; it follows therefore that all the gneiss types examined were 79

initially derived from the one source. Thus as there is little or no evid ence of the effects of alteration, the varying chemical and physical charac teristics found in the granite gneisses can be directly attributable to a depositional mechanism.

There are two possible means whereby volcanic material can be emplaced into a sedimentary environment, either as airfall tuffs and ash or as a mass flow of debris. The physical location of the source of this volcanic material will not be speculated on here as it has no direct bearing on this study, however the lack of recognizable vents or volcanic rocks with in the Willyama Complex suggests that the volcanic material under examination here is well removed from its source.

6.2 Depositional mechanisms for the Granite gneisses

6.2.1 Air Fall tuffs

The occurrence of volcanoclastic air-fall deposits in marine sequences is a rarely documented phenomena (Niem, 1977), however, in the instances where they have been examined they have been shown to possess very uniform characteristics over vast distances from their source (c.f. Sparkes and Huang, 1980). One such study by Sparkes and Huang (1980) on several thin (i,e. < 2m.) ash layers in Mediterranean showed that samples taken from

layers proximal to the source consist of a lower, coarse unit and a finer upper unit. Distal sampling showed evidence of a decrease in the grainsize of the coarser fraction, whereas the finer fraction showed little or no

evidence in size variation from the source. The distances involved in this

study were of the order of up to 1500 km. from the source. Sparkes and Huang

(op. cit.) acknowledged that marine processes such as differential settling

turbidity currents, slumping and grain flow would further enhance the sorting of an already well sorted ashfall, but conclude that the grainsize bimodality

is a primary volcanic feature only slightly distorted by marine processes.

In comparison with volcanogenic debris deposited by a mass trans port mechanism, water-laid airfall tuffs are generally thin, extensive uni

form bodies lacking in thickness changes. It would be less likely for the 80

internal stratigraphy of an airfall deposit to be interrupted by non air fall components as it would be in the mass transport situation where the high energies involved could induce the mass transport and deposition of unrelated material in the near vicinity.

6.2.2 Mass Flow

The mass mo~ement of volcanogenic debris within an aqueous environ ment is the more common mechanism whereby this type of material reaches its final point of deposition. This conclusion is justified by the observation of features within volcanogenic sequences which are directly analogous to those found in nonvolcanic sediments.

The main features which may be recognized in such sequences are a variety of grain size variations and include normal or total-size grading involving a gradual, upward decrease in the whole grainsize population, coarse-fraction grading generated through an upward decrease in the grainsize of only the coarse fraction and also coarse-fraction frequency grading arising from an upward decrease in the abundance of the coarse fraction (Cas, 1979).

Mass flow debris deposits studied by Cas (1979) where the above grainsize gradations were observed also contained some massive ungraded units which underlay the graded units and also overlying thinly laminated beds. This whole sequence was believed by Cas (op. cit.) to be a direct equivalent to the Bouma sequence with the c 2 division absent, i.e. there are no current ripple laminations or crossbeds towards the top of the sequence.

The hydrodynamic parameters required to produce these characteris tics in a debris flow as summarized by cas (1979) consist predominently of variations in the rate of sediment deposition and concentration level of sediment within the current. According to Cas, massive units are generated through a high sediment load of largely granular material which promotes an increasing depositional rate once deposition has been initiated. At high rates of deposition, tractional movement is suppressed and so related struc tures such as parallel lamination and crossbedding are not produced.

Normal or total-size grading within an individual sedimentation 81

unit results from the layer by layer deposition, or suspension fallout, from currents with a low sediment concentration, whereas coarse-fraction grading occurs as a result of deposition from high concentration density currents.

Such grading is presumed to be due to the limitation of particle freedom caused by high sediment concentration.

In addition to the above types of grading observed by Cas (op. cit.), a debris unit may also consist of a sequence of doubly-graded beds (Fiske and

Matsuda, 1964), composed of two cycles of normal or total-size fraction grading where one cycle encompasses the whole depositional unit in as much as the over all grainsize decreases from the base upwards and the second cycle involves numerous (often l00's) of normally graded beds contained within the first depositional unit. Each successive bed of the second cycle is progressively more finer grained than the succeeding bed, which gives rise to the character istics of the first cycle.

This type of grading is believed to develop through the differential settling rates of coarse and fine material from a submarine eruption column

(Fiske and Matsuda, 1964) and forms a lag-fall deposit (~iles, 1982). During deposition the coarser material settles at a greater rate than the finer material until the deposit becomes unstable and moves off downslope as a turbidity current, settling out into a graded bed. This process is repeated with finer and finer material for as many as 200 cycles (Fiske and Matsuda,

1964), where each individual cycle consists of a crystal-rich base which grades upwards into a pumice and shard-rich top.

The above features are not exclusive to the emplacement of cold volcanogenic debris into an aqueous environment as deposition of material from pyroclastic flows also produces lithologies with very similar character istics. Niem (1977) and Sparks et al. (1980a, b) believe that pyroclastic subaqueous flows form from tuffs derived from highly explosive eruptions of vesiculating magma which produced large volumes of superheated particles and gas and then flowed as largely coherent bodies of steam and gas inflated slurry down a submarine slope. An example documented by Niem (1977) which 82

he believed formed in this manner developed thick density graded, pumaceous vitric-crystal tuffs which were rapidly followed by a number of smaller density flows depositing a bedded pumaceous tuff. The waning stage of the volcanic event was marked by the continuous settling of fine ash, forming a thick, fine grained vitric tuff layer.

It is possible that Niern's example is not the product of three distinct events, but a combination of the Bouma structures described by Cas

(1979) summarized above and the model of subaqueous pyroclastic flow develop ment postulated by Sparks et al. (1980b). The model suggested by Sparks et al.

(op. cit.) depicts the interaction of a subaqueous pyroclastic flow as it flows down slope with the enveloping water as mainly one of shearing along the upper surface of the flow which in turn generates a turbulent cloud of fine material. This fine material may in turn develop into a turbidity current in its own right as is depicted in Figure 19 and finally settle out as an ash turbidite horizon.

Even though the process whereby volcanic debris entered the aqueous environment was initially separated above into air fall deposits and subaqueous flow deposits there is probably very little to indicate what the original dep ositional mechanisms were, after the volcanic material has reached its final resting place. Such a situation could arise in regions of volcanic activity where unconsolidated air fall deposits could be induced to move from their initial point of deposition and travel via debris flows or turbidity currents to another des·tination. An airfall deposit transported in this manner would be indistinguishable from a volcanogenic debris flow deposit which did not have a primary air fall component.

The features documented here for volcanogenic debris flows, provide an attractive model with which the physical and possibly also the chemical features found in the Granite gneisses can be compared with. Such a comparison would be relatively straight forward were it not for the high metamorphic grade of these gneisses.

Therefore the importance or otherwise of the location and distrib- 83

Figure 19: Postulated method of deposition for the Granite gneisses,

A) Debris flow moving downslope and developing a fine grained

cloud of material which eventually may form a turbidity current

in its own right(B). Eventually this material falls out of

suspension, forming a finer grained deposit on top of the debris

flow (C). Fine grained ( Turbulent

Direction of movement water of unknown depth

Turbidity

Fine groined Turbidite I c. 84

ution of feldspar augen and megacrysts, the significance of the chemical trends present, and also the presence or absence of garnet must be established before a debris flow model of deposition can be considered as a realistic means through which all those features can be generated.

6.3 Feldspar augen and megacryst fonnation

The fonnation of augen (or porphyroblastic) textures are still matters of speculation. However, the features observed in the granite gneisses examined here have been observed in similar gneisses from British Guiana (Cannon,

1964), Uruguay (Saenz and Gubser, 1971), France (Demange, 1975) and various areas in Norway (Ohta, 1969, 1972, Petersen, 1977).

There are two popular methods by which augen are believed to have formed, i.e. metasomatism on a massive scale (e.g. Jones, 1961) or alternatively the deformation of pre-existing large feldspar idioblasts and the subsequent growth of porphyroblasts through coalescence of the granulated material (Ohta,

1969). Large scale metasomatic events involving the supply of large quantities of material can only be invoked to explain porphyroblast growth when an obvious source is available (Petersen, 1977), even if this source was available, the production of granite-like rocks will only occur in the near vicinity of a granitic magma and then only on a restricted scale (Winkler, 1976).

Postulating fluid or vapour activity as the means of transporting augen-forming material would require high pressure gradients or abrupt changes in these gradients in order that material could be transferred from one site to another. As Phillips (1978) has demonstrated, neither situation exists at

Broken Hill as the pressure gradients across the Willyama Complex change slowly and the contribution of water to the total pressure was generally small. It appears unlikely then that augen formation was the result of metasomatism on

a large scale, particularly as this would involve an unidentifiable source, which according to Vernon (1977, 1978) is a solution to be viewed with suspi

cion.

It is possible however, to explain the growth of augen or megacrysts

in terms of local or mosaic equilibria and variations in alkali/H+ activities 85

(Wintsch, .1975a, b). Wintsch Cl975a) believes that equilibrium developed between metamorphic crystallization reactions and intergranular solutions is attained over ·areas of varying size. Cation exchange between muscovite and the intergranular fluid will shift the alkali/H+ a~tivity of the solution into the stability field of feldspar (Equations 5 and 6). + + KA13Si03010(0H)2+6Si02+2K = 3KA1Si308+2H (Equation 5)

KA1 3sio3o10 (0H 2)+6Si02+3Na+ = 3NaA1Si3o8+K+2H+ (Equation 6)

Variations in starting materials, P 0 , and strain rate will affect H2 both the size and the number of porphyroblasts which develop, thus the system can be considered to be open on the scale of centimetres, but closed on the scale of metres (Wintsch, 1975a). It has been established previously (Chapter

3.7) that P was low, therefore it is hard to envisage large relative dif- H20 ferences in P on the scale found here, let alone the mechanisms which may H2o have induced such differences, Likewise where the scale is too large for variations in P O to be developed, it is probably too small to develop vari H2 ations in the strain rate.

Of the three possibilities for augen and megacryst growth it is the variations in starting materials which appears to be the most applicable in this particular case. To form feldspar augen at a particular location,the probable sequence of events that took place was that primary feldspar pheno crysts were altered to clays after deposition and during metamorphism these clays were progressively metamorphosed to micas, then into domains of feldspar which then may have coalesced into larger feldspar grains and megacrysts (Eqn.

7) •

Primary feldspar phenocrysts +clays+ micas+

domains of small feldspars+ coalescence of small feldspars to form

megacrysts (Equation 7).

With this mechanism,and given that no evidence has been found for any large scale alteration of these rocks,it is probable that augen have formed at the site of original feldspar phenocrysts and so the abundance and distrib ution of augen and megacrysts pseudomorphs the original, premetamorphic distrib ution of feldspar. 86

6.4 Garnet formation in the Granite gneisses

Given that the chemistry of both the Fbg and Fb Granite gneiss types is identical and that they both have undergone the same metamorphic processes; it is likely that events prior to metamorphism influenced the final formation of garnets in the locations where they now occur. Equations 8 and 9 cater in a general way for the observed metamorphic mineralogical variations present in both the Fbg and Fb gneisses and although they deal only with pure end member species and yield ideal situations they illustrate that rocks with differing mineral ogical make up can be produced from the same starting material.

4 quartz+ 3 biotite + 2 sillimanite - 2 biotite + 2 garnet+ 4Si02 + 3KFe3AlSi3o10 (0H)+2AlSi05 - 2KFe 3AlSi3o10 (0H)+2Fe3Al2si3o12 1 K feldspar (Equation 8) + KA LS'i 2o8

4 quartz+ 4 biotite + 2 sillimanite + 1 K feldspar - 3 biotite + 4Si02 + 4KFe3AlSi3o10 (0H)+2AlSi05 + KALSi 3o8 - 3KFe3AlSi3o10 (0H) 2 garnet+ 2 K feldspar (Equation 9) 2Fe3Al2si3ol 2+2KALSi3o8 As well as both sides of Equations 8 and 9 being chemically equival ent, the two equations are themselves equivalent as they can be reduced to

Equation 10.

4 quartz+ 1 biotite + 2 sillimanite - 1 K feldspar - 2 garnet. 4Si02 + KFe3AlSi3010(0H)2+2Al2Si05- KAISi308 _ 2Fe3Al2si3o12 (Equation 10)

The implication of Equation 10 is that a deficiency of K feldspar, or the removal of the precursor of this metamorphic feldspar from the presence of the precursor assemblage of quartz, biotite and sillimanite is sufficient to enable an equivalent proportion of garnet to form. This situation could take place at the stage in Equation 7 where clays have formed at the expense of the original feldspars through the removal of Kand/or Na from the clays present.

Sites at which this removal had taken place would be relatively enriched in Al and depending on the surrounding mineralogy would form garnet, sillimanite and/ or biotite upon metamorphism.

The results of the BSC comparisons (Table 8) which indicate a general deficiency in Na2o for all Granite gneiss types as well as the inverse relation- 87 ship exhibited between Na2o and K20 (Fig. 7c) suggest that cation exchange + + + + between Na and K and the subsequent relocation of either Na or K on a local scale is a possible method for the generation of garnet. It is proposed therefore that garnet generation takes place at locations which were the sites of leach ing of Na+ from plagioclase and/or clays and its replacement in whole or in part with K+ leached in a similar manner within freshly deposited debris. It is the local chemical imbalances generated during this exchange which are the points at which garnets form on metamorphism.

Such a model requires sufficient water and porosity which will allow + + some fluid movement to enable the initial mobilization of Na and K and the + relocation of some of the Na. The former requirement can be met by the physical behaviour of a debris flow moving downslope as all the outer surface would be in a state of turbulent motion and so water would be incorporated within the near surface of the flow. In the latter case, the large grainsize variations which are postulated as an original feature of Granite gneiss pre cursors, would provide the required porosity.

Therefore it is possible to speculate that the Pb-variants, although possessing similar porosities to that of the Fbg precursors, are located away from the edge of a debris flow and so do not possess excessive volumes of incorporated water. Conversely if the Ap-fels are considered as the fine grained suspension fallout of a turbulent flow, their original grainsize would be small and as a result, porosity low.

6.5 Geochemical trends in relation to a mass flow model

If the Granite gneisses examined here were in fact deposited as the result of a turbulent flow composed of volcanic debris, it is unlikely that any of the original magma chamber zonations which may have been present, would be preserved as a stratigraphically related feature. With respect to the preceeding evaluation of garnet formation in the Fbg variants, both the Fb and

Fbg gneisses can be considered chemically and mineralogically identical at the time of deposition. It follows therefore, that the distribution and abundance of feldspar, quartz and biotite must directly reflect the distribution of precursor mineralogy and likewise the observed chemical variations within the 88

Granite gneisses.

Modal analysis of the Fbg and Fb variants (Table 1) demonstrates that the abundance of feldspar is generally higher and more variable than that of quartz and more variable than that of biotite, whereas the Ap variants consist essentially of quartz and feldspar, this quantitative assessment is in agreement with the field observations depicted in Figures 3 and 4. These observations support the conclusion that it is the abundance and distribution of feldspar augen, grains and megacrysts which is directly responsible for the majority of the chemical variations found in these gneisses. This fundamental control over Granite gneiss chemistry is generated through the wide variation in original grainsize of feldspar grains and crystals which would be more likely to show the effects of sedimentological processes rather than the apparently more even grained quartz grains and fragments.

The Ap fels types are demonstrably chemically related to the Fbg and Fb gneiss by similar element and oxide ratios, despite the generally lower levels of most oxides excepting Si02 , and to a lesser extent K2o and Na 2o. This depletion-enhancement effect could be generated from the turbulent ash cloud suspension fall out model proposed for the Ap fels through the differ ential settling of component particles: It is likely that minerals such as clays, micas and glass fragments, present i~ or formed in the debris after primary deposition would, during mass movement, be thrown into the overlying water column. Quartz and feldspar would also be placed into suspension, however by virtue of their larger grainsize are redeposited at a greater rate than the clays, micas and any glass present. Therefore the resultant sediment is enhanced in quartz and feldspar, i.e. Sio2 , K2o and Na 2o and depleted in clays, micas and glass which would be the main sources of Ti, Mn, Zr, Y and

Nb in the granite gneiss precursor.

This possible mechanism for Ap fels formation also adequately accounts for the BSC classification of these rocks as arkoses in preference to having an igneous parentage due to the lack of Fe-Ti-Mg-rich minerals. One other alternative for explaining an arkosic precursor is that the Ap fels 89

represent an in situ reworking of the upper portions of a Granite gneiss hori

zon. This idea is not favoured as this implies time breaks in Granite gneiss deposition to allow reworking to take place and possibly sedimentation from other sources to recommence. In the case of the internal Ap fels horizons to the S.E. this has not occurred and conversely in the Northern Leases where

stratigraphic breaks are represented by metasedimentary horizons, these hori

zons are not underlain by Ap fels.

Although the above explanation for the development of the geochemical

trends in the Granite gneisses is speculative, it is a simple solution to an

intriguing problem. To the best of the authors knowledge only one other example of sedimentary-derived 'fractionation-trends' has been documented on a geochemical basis by Ricci and Sabatini (1976). This work demonstrates that compositionally uniform volcanic material subjected to granulometric and gravi metric processes during deposition in aqueous environment will yield differ entiation trends similar to those developed during igneous fractionation.

6.6 The significance of non-Granite gneiss lithologies

Within both Granite gneiss bodies examined there are a number of mineralogically and chemically distinct lithologies which are locally, later ally extensive, but are confined to narrow vertical intervals. Of the four horizons referred to here, viz. amphibolites/biotite selvages, metapelites,

Gap rocks and Quartz augen rocks the latter two are exclusively confined to the Lower Granite Gneiss whereas metapelite horizons occur at the northern extremities of both the Upper and Lower Granite Gneisses. Amphibolites and biotite-rich selvage horizons, however, are similarly distributed in both bodies of granite gneiss where they increase in abundance in a southerly direction and in general decrease in abundance from the base upwards at the same time. This vertical decrease in amphibolite abundance terminates midway through the Lower Granite Gneiss sequence to yield an arnphibolite-free zone.

The presence of the metapelite horizons within both Granite gneiss bodies at their northern extremities, at a similar level indicates that there were at least two episodes of granite gneiss deposition. If this is so, then 90

the break in deposition was of sufficient length to allow a pelite horizon to

be deposited, although in this case the local nature of this particular horizon

suggests that its deposition was spatially controlled.

Quartz augen rocks also exhibit spatial control as they are direct

vertical and lateral equivalents of amphibolite horizons and are localised

towards the base of the Lower Granite Gneiss at its northern extremity. Gap

horizons have no direct stratigraphic correlatives either within the Granite

Gneisses or elsewhere in the Willyama Complex, however they bear some compari

son with the Quartz augen rocks and also the Granite gneisses in general through

their felted grey green chloritic matrix, their large grainsize variations and

also their distinctive layering.

Amphibolites, on the other hand, appear in three general forms; i.e.

as discrete discontinuous stratigraphic horizons composed of one or more indiv

idual intervals such as are found in the Northern Leases (Fig. 2d) and on

Section 30 (Fig. 2c), or as delicate layering interbanded with granite gneiss

(Plate 4) and also as biotite selvages which are chemically similar to amphib

olites (Table 3e) and are considered here to represent retrogressed or altered

amphibolites. The distribution of all three forms, regardless of whether or

not they occur associated with the other forms, appears to be stratigraphic

ally controlled, This is clearly demonstrated by Figs. 2a, b, c, d which show distinct zones that are amphibolite/biotite selvage-free. The presence of

isolated features resembling amygdales and flow-top breccias (Plate 7), coupled with the interlayered nature of some amphibolites, their apparent

stratigraphic control and the lack of any crosscutting features in relation to

the Granite gneisses, indicates that an origin based on basic sills or dykes

for these rocks is unlikely. These field relations do favour however origins

based on basic tuffs or debris with a minor flow component.

Between all four non-Granite gneiss lithologies, regardless of

likely precursor rock types, there is the common denominator of their distrib

ubion being spatially controlled either in a horizontal and/or vertical sense.

As these rocks occur in what has been inferred to be a relatively high energy 91

environment, occurring over a very short time span, severe restraints on

possible modes of formation can be immediately imposed. Given that the meta

pelites, Gap rocks, the more massive amphibolite horizons and the Quartz augen

rocks represent time gaps in the deposition of Granite gneiss precursors,

then the deposition/formation of these rocks would also have been rapid. In

this particular case normal suspension fall-out type deposition fails to

account for the localized nature of the metapelite horizons, massive amphibo

lite and the Gap rocks as they should form widespread blanket-like deposits.

Therefore it is postulated that these three rocktypes were deposited from

turbiditic flows, with a minor contribution to massive amphibolites from

basic flows.

Turbidite-derived deposition for these rocks in general and the

layered amphibolites, biotite selvages and Quartz augen rocks in particular is

the simplest mechanism possible which would account for the observed features

exhibited by each lithology. Such a model requires no further, specialized

mechanisms, (for which there is no evidence) is also compatible with the

general style of deposition invoked for the Granite gneisses; and provides

possible solutions to the origins of biotite selvages, Gap and Quartz augen

roeks, As turbidite deposits are often characterized by extraneous rock

fragments and slabs which have been incorporated into the passing debris

flow; it is quite feasible to regard the majority of the biotite selvage

horizons as consolidated amphibolite-precursor material which has been picked

up by the Granite gneiss debris flow. The Gap rocks could also have a similar

origin in as much that the passage of a Granite gneiss precursor flow over

this rock could produce a mixing situation where unconsolidated mafic material

was combined with varying proportions of granite gneiss before being redepos

ited. The Quartz augen rocks by virtue of their field relations with amphibo

lites and their amphibole-rich matrix possibly represent the amphibolite

equivalent of the finer density graded portions of the Granite gneisses. In

this situation it is envisaged that a debris flow of amphibolite-precursor

'material composed of amphibolites, pyroxenes, iron oxides, quartz, feldspar 92

and probably a glassy component, underwent a simple density gradation during

its forward motion and so depending on which section of this deposit is viewed

and the point at which this activity was arrested, so the Quartz augen material

lies adjacent to, or on top of the parent amphibolite.

The localization of non-Granite gneiss lithologies in the north

western portion of the reconstructed horizon (Fig. 5), indicates that the

source of this and Granite gneiss precursor material lies further to the north

west. The abundance of amphibolite/biotite selvage horizons located ih the

part of this horizon exposed as the Lower Granite Gneiss is probably due to

the inability of the granite gneiss debris flow to carry the majority of this material as slabs or fragments into the region now known as the Upper Granite

Gneiss,

Other evidence for a source area lying to the northwest provided by

Figure 5 is that the major aplitic fels unit at the stratigraphic top of the

Upper Granite Gneiss develops its greatest thickness in the northern part of

this body before dying out to the south as the other metasedimentary horizons

do. In addition to this sedimentological change, the interpreted distribution

of garnet indicates that Fb gneisses do not persist to the south. In the

debris flow model proposed here, this can be explained through the greater

quantity of water likely to have been incorporated into the flow the further

it travels and which in turn is more likely to induce local small scale alter

ation to form garnets on metamorphism. 93

Chapter 7

7. Conclusions

Detailed field, geochemical and petrological studies of the Upper and Lower Granite Gneisses at Broken Hill has revealed a very uniform, laterally extensive sequence of augen and felsic gneisses which exhibit regular mineralogical variations in the vertical sense, The gneisses examined here, which have reached Upper Amphibolite facies, possess a simple mineralogy composed essentially of K-feldspar with varying abundances of plagioclase, quartz, garnet and biotite, Based on the presence or absence of garnet, a classification scheme for all varieties of these gneisses; excepting several biotite-poor, garnet-absent horizons possessing an aplitic texture, has been erected. Under this scheme three varieties of Granite gneiss have been recog nized; a feldspar-biotite-garnet gneiss, a feldspar-biotite gneiss and the aplitic phases, each of which occur as distinct mappable units. The former two gneiss-types possess anhedral to augen-like megacrysts which locally decrease in abundance and/or physical size stratigraphically upwards and feldspar-quartz-rich layering. In localities where megacrysts are not prev alent, an overall fining upwards of grainsize may occur. The third Granite gneiss variety, termed an aplitic fels, possesses no augen, garnet or layering, has an even grainsize distribution throughout and predominates at the strati graphic top of the northern part of the Upper Granite Gneiss. Elsewhere the aplitic fels occur as discrete internal horizons within the Granite gneiss sequence, in each case it is believed that these units mark the stratigraphic top of a granite gneiss depositional interval,

The distinction between the augen-bearing, garnet-rich plus garnet poor Granite gneisses and the aplitic fels, is further highlighted by the

occurrence in the former of horizons consisting of amphibolite, biotite selv

ages, metapelitic material and also amphibolite-garnet gneiss mixtures. A

number of the amphibolites examined exhibit possible premetamorphic vesicles

and textures which resemble flow top breccias. Field evidence indicates that 94

to the surrounding metasediments; structural and mineralogical evidence link both the Upper and Lower Granite Gneisses together as the same horizon result ing in horizontal dimension in excess of 30 km wide and 20 km long.

The metasediments enveloping the Granite gneiss horizon and also the internal metasedimentary horizons show no evidence of contact metamorphism or alteration and so coupled with the internal physical attributes of the granite gneisses outlined above it is believed that the granite gneisses were deposited as an integral part of a sedimentary sequence. The presence of frequency and physical size grading of augen/megacrysts and local layering signifies that the style of sedimentation was similar to that in which Bouma sequences are developed, i.e., a mass debris flow or turbidite-like mechanism.

During the passage of such a debris flow downslope the upper surface may suffer erosion and fine grained material may be thrown upwards into the overlying water column and subsequently may settle slowly out of suspension to form a uniformly textured, blanket-like deposit. The close correspondence of the features of this mechanism and the characteristics of the aplitic fels, provides good evidence for considering this material as the final stage in the deposition of an individual granite gneiss horizon,

Very regular and uniform chemical variations are present in all granite gneiss variants, such that when the major oxides are plotted against

Sio2 , a trend resembling igneous differentiation is developed. The major flaw with this assumption is that the more siliceous material, which is predominently composed of aplitic fels, has been depleted in elements such as Zr and Y which would be enriched in the final stages of differentiation.

Despite this, the aplitic fels possess element-element ratios which are the same as the garnet and non-garnet bearing Granite gneisses. The style of sedimentation which deposited the Granite gneisses produced size and frequency graded horizons grading from feldspar-rich, quartz-poor at the base to relat ively quartz-rich, feldspar-poor at the top. Thus if sufficient random geo chemical sampling is carried out on these horizons a differentiation trend produced by Bed±we:ntol.Qgical processes will result. 95

Even though a working mineralogical classification scheme based on the presence of garnet has been erected, chemically this has no significance, on both the feldspar-biotite-garnet and the feldspar-biotite gneisses possess identical chemistry. The development of garnet at the locations at which they are found is believed to be the result of the local breakdown of original feldspars in the sediment due to the presence of excess poor water, High pore water concentrations can be generated in a debris flow at the turbulent zone of interaction between the sediment-water column interface of the moving debris flow.

Using qualitative petrological discriminants, the.granite gneisses are demonstrably subalkaline in nature and resemble calcalkaline dacites and rhyolites with respect to normative feldspar content. Precursor rock type classification was assessed using the more rigorous Barth Standard Cell, which also indicated a dacitic to rhyolitic parent which was more likely to have been derived from an active continental margin than an island arc setting.

The Barth Standard Cell also indicated that these gneisses have a low sodium content which is inferred to be an original feature, rather than one resulting from alteration. 96

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From To Description

No. 3 Shaft Section

DDH 2003

1493' Sillimanite bearing metapelite.

1493' 1575' Aplitic textured, sericitic feldspar-quartz-(biotite)

fels. Rare garnet. Sampled at 1570'.

1575' 1601' Sillimanite bearing metapsammite.

1601' 1770' Weakly foliated feldspar-garnet-biotite quartz gneiss.

Sampled at 1627'.

1770' 2126' Weakly foliated, sericitized feldspar-biotite-gneiss.

Sampled at 1904'.

2126' 2147' Moderately foliated feldspar-garnet biotite gneiss.

Sampled at 2135'.

2147' 2293' Weakly foliated pink feldspar-biotite-(garnet) gneiss.

Sampled at 2153'.

2293' 2392' Moderately foliated sericitized biotite-feldspar gneiss

Amphibolite from 2382'-2390'.

2392' Sillimanite bearing metapelite.

DDH 2058

3170' Sillimanite-garnet metapsammite.

3170' 3203' Weakly foliated feldspar-biotite-(garnet) gneiss.

Garnets small, usually less than 3 mm diameter.

Sampled at 3194'.

3203' Sillimanite-garnet metapsammite.

DDH 3094

769' Sheared, sericitic feldspar-biotite gneiss. Feldspar

augen-like.

769' 789' Moderately foliated feldspar-biotite gneiss. Sampled

at 787'.

789' 806' Moderately foliated feldspar-biotite gneiss with

sporadic biotite clots, probably representing retrogressed

garnet. Sampled at 800'. 102

DOH 4018

3411' Sericitic shear zone.

3411' 3544' Moderately foliated feldspar-biotite gneiss. Pegmatite

from 3518'-3531'. Srurpled at 3497'.

3544' 3546' Aplitic textured feldspar-quartz fels.

3546' Interlayered meta psarnrnite/pelite sequence.

Cosgroves Section

DOH 834

20' 383' Well foliated feldspar-biotite-garnet gneiss. Sampled

at 35'.

383' 410' Weak to moderately foliated feldspar-biotite-(garnet)

gneiss containing scattered wisps of sericite.

Sampled at 389' •

410 I 568' Strongly foliated feldspar-biotite-quartz gneiss.

Biotite- rich selvage from 538'-542'. Sampled at 476'.

568' 1144 I Weak to moderately foliated garnet-biotite-feldspar

sericite gneiss containing sporadic clots of chlorite.

Dolerite from 677'-677.5' and 700'-703'. Sampled at

581'.

1144' 1161' Aplitic textured, fine grained, feldspar-quartz fels

containing rare garnets. Very weakly foliated. Up

hole contact gradational. Sampled at 1159'.

1161' Metapeli te.

DOH 837

20' 45' Strongly foliated garnet-biotite gneiss.

45' 48' Aplitic textured, fine grained quartz-feldspar-(biotite)

fels. Sampled at 47'.

48' 202' Strongly foliated biotite-feldspar gneiss.

202' 768' Moderately to strongly foliated garnet-biotite-feldspar

gneiss, containing sporadic clots of chlorite. Sampled

at 301'. 103

768' 920' Sericitized garnet-biotite-feldspar gneiss. Very

sheared in places.

920' 923' Quartz-feldspar pegmatite.

923' 1147' Moderately foliated garnet-feldspar-biotite gneiss.

1147' 1167' Aplitic textured, fine grained quartz-feldspar fels.

1167' Metapelite.

DOH 838

898' Amphibolite.

898' 980' Moderately foliated garnet-biotite-feldspar gneiss

containing sporadic chloritic clots. Sampled at

924'.

980' Metapelite.

DOH 844

461' 821' Extensively sheared feldspar-biotite gneiss. Augen

to megacryst-like feldspars. Sampled at 500'.

DOH 847

154' Moderately foliated feldspar-biotite-(garnet) gneiss

containing numerous chloritic clots. Garnets elongate

parallel to Sl. Sampled at 150'.

154 I 172' Moderately foliated feldspar-biotite-garnet gneiss.

Garnets elongate parallel to s 1 . Sampled at 170'.

172' 180' Moderately foliated feldspar-biotite-(garnet) gneiss

containing numerous chloritic clots.

180' 232' Moderately foliated feldspar-biotite-garnet gneiss. . Garnet elongate parallel to s1 • 232' 418' Aplitic textured feldspar-quartz-(biotite) fels

containing numerous wisps of sericite. Sampled at

416'.

418' Sillimanite-biotite-garnet metapelite. Feldspars

augen-like. 104

Imperial Ridge Section

DOH 836

1172' Garnet-sillimanite bearing meta psammite/pelite.

1172' 1242' Moderately foliated feldspar-garnet-biotite-sillimanite

gneiss containing sporadic clots of chlorite. Sampled

at 1208'.

1242' 1493' Moderately foliated feldspar-biotite-garnet gneiss,

tending pegmatitic over last 3'. Sampled at 1392'.

1493' Garnet-sillimanite bearing metapsammite.

DDH 951

23 I 104' Well foliated feldspar-biotite gneiss. Sampled at

38'.

104' 155' Weakly foliated feldspar-biotite-garnet-(sillimanite)

gneiss containing sporadic clots of chlorite. Sampled

at 120'.

155' 246' Moderately foliated feldspar-garnet-biotite-sillimanite

gneiss. Sampled at 243'.

246' 346' Aplitic textured, sericitic quartz-feldspar-(biotite)

(garnet) fels. Sampled at 331'.

DDH 952

7' 133' Weakly foliated garnet-feldspar-biotite gneiss containing

sporadic clots of chlorite. Sampled at 109'.

133' 299' Aplitic textured feldspar-quartz fels. Garnet-biotite

rich zone from 155'-177'. Sampled at 143' and 171'.

299' Sericitized metapelite.

DOH 960

O' 156' Weakly foliated garnet-feldspar-(biotite) gneiss

containing sporadic clots of chlorite and rare

sillimanite. Sampled at 135' .

.156~ 233' Moderately foliated biotite-feldspar-(garnet)-(sericite)

gneiss. Sampled at 210 1 • 105

233' 434' As for between 156'-233', but with sericite content

increasing down hole.

434' Amphibolite.

DDH 962

760' Metapelite.

760' 769' Weakly foliated feldspar-garnet-(biotite) gneiss

containing sporadic clots of chlorite. Sampled at 764'.

769' 800' Moderately foliated feldspar-biotite-(sillimanite)

(garnet) gneiss. Sampled at 787'.

800' 850' Moderately foliated, sericitic feldspar-biotite gneiss.

Sampled at 831'.

859' 923' Moderately foliated biotite-feldspar-garnet gneiss.

Sampled at 900' •

923' 1020' Garnet-biotite-feldspar gneiss containing minor sillimanite.

Sampled at 94 7' •

1020' 1197' Moderately foliated biotite-garnet-feldspar-sericite

gneiss. Sampled at 1126'.

1197' 1328' Aplitic textured feldspar-quartz-(biotite) fels. Sampled

at 1294 I•

1328' Sericitic biotite feldspar meta pelite.

DDH 3198 (m)

1264 Sericitic meta psammite.

1264 1624 Weakly foliated, fine to medium grained, well layered

feldspar-biotite-(garnet)gneiss.

1371.5-1372 Biotite selvage

1441 -1448 Chloritic biotite selvage

1454 -1456 Chloritic biotite selvage, brecciated

lower boundary

1506.5Ll5301 Amphibolite, sharp upper boundary,

lower boundary intercalated with quartz

feldsoa thic crneiss. 106

1538 -1541 Biotite selvage.

1548 -1555.5 Biotite selvage with intercalated

gneiss.

1600 -1602 Biotite selvage.

Section sampled at 1263.7, 1289.6, 1350.7 1444.5,

1460.8, 1470.3, 1501.4, 1555.5.

1624 I Arnphiboli te.

Potosi Section

DDH 804

61' No core.

61' 148' Well foliated feldspar-biotite gneiss. Last 18'

sheared. Sampled at 74'.

DDH 820

1962' Sericitic meta pelite/psarnrnite.

1962' 2196' Weak to moderately foliated feldspar-biotite-sillimanite

(garnet) gneiss. Minor fine grained interlayers.

Sampled at 1971'.

2196' 2322' Shear zone~

2322' 2436' Moderately foliated garnet-biotite-feldspar gneiss

containing sporadic clots of chlorite. Sampled at 2354'.

2436' 2632' Moderately foliated feldspar-biotite-sillimanite-garnet

gneiss. Sampled at 2609'.

2632' EOH Weakly foliated feldspar-biotite-garnet gneiss, minor

sillimanite. Sampled at 2697'.

DDH 3167

2045' Sericite-garnet metapsammite.

2045' 2345' Weakly foliated feldspar-biotite-garnet gneiss, medium

grained with an aplitic texture. Sampled at 2205'.

2345' 3897' Sillimanite-biotite-(garnet) rnetapelite.

3897' 3930' Moderately foliated feldspar-biotite-garnet-(sillimanite).

gneiss. Sampled at 3919'. 107

3930' 3944' Aplitic textured feldspar-quartz-biotite fels.

3944' 4060' Moderately foliated feldspar-biotite-garnet-(sillirnanite)

gneiss.

4060' 4069' Arnphibolite. Uphole boundary sharp, downhole boundary

garnetiferous and gradational.

4069' 4096' Moderately foliated feldspar-biotite-garnet-(sillirnanite)

gneiss.

4096' 4111' Arnphibolite. Uphole boundary sharp, downhole boundary

gradational.

4111' 4119' Quartz-feldspar-rnuscovite pegrnatite.

4119' 4639' Moderately foliated feldspar-biotite-garnet-(sillirnanite)

gneiss.

4639' 4710' Aplitic textured quartz-feldspar-(biotite) fels. Sampled

at 4642'.

4710' Sillimanite rnetapsarnrnite.

Round Hill Section

DDH 813

426' Sillirnanite-biotite-garnet meta psarnrnite.

426' 514' Moderately foliated feldspar-biotite-garnet-sillimanite gneiss.

Garnets elongate parallel to s1 . Sampled at 438'. 514' 561' Sericitic, aplitic textured feldspar-quartz-(biotite)

fels. Sampled at 518'.

DDH 3105

2310 I Metapelite.

2310' 2657' Moderately foliated feldspar-garnet-biotite gneiss

containing sporadic chloritic clots. Garnet content

increases downwards. Sampled at 2380'.

2657' 2788' Moderately foliated feldspar-biotite gneiss. Garnets

present towards base of unit.

2788' 3258' Moderately foliated feldspar-garnet-biotite g~eiss 108

Flying Doctor Section

DOH 3074

3972' Sillimanite-biotite metapsammite.

3972' 4101' Moderately foliated feldspar-biotite-quartz gneiss.

Sericitised in part. Sampled at 3977'.

4101' 4694' Metapsammite.

4694' 5025' Weak to moderately foliated feldspar-biotite-garnet

gneiss containing isolated calcite rich zones.

Sampled at 4814'.

5025' 5093' Aplitic textured quartz-feldspar fels containing very

little biotite. Interval finishes in a shear.

Sampled at 5053'.

DDH 3186

821' Metapelite.

821' 982' Greenish-grey aplitic textured fels containing numerous

layers of fragmented feldspars. Sampled at 892',

970.3'.

982' 1230' Moderately foliated K-feldspar (pink)-quartz-biotite

gneiss. Both fine grained mineralogical banding and

layers of feldspar fragments are common. Biotite selvage

from 986'-989'. Sampled at 1036', 1097'.

1230' 1251' Greenish-grey aplitic textured quartz-feldspar fels

containing numerous layers of fragmented feldspars.

1251' 1273' Moderately foliated K-feldspar (pink)-quartz-biotite

gneiss. Mineralogical banding and layers of feldspar

fragments common. Sampled at 1251'.

1273' 1353' Greenish-grey aplitic textured quartz-feldspar fels

containing numerous layers of fragmentedfeldspars.

Sampleq at 1283'. 109

1353' 1478' Moderately foliated feldspar-biotite-garnet gneiss.

Garnet content decreasing in a downhole direction.

Sampled at 1448'.

1478' 1484' Arnphiboli te.

1484 1 1665' Moderately foliated feldspar-biotite-(garnet) gneiss

containing numerous fine grained bands. Porphyroblastic

feldspars give rock a mottled appearance- from 1615 '-

1665'. Sampled at 1659'.

1665' 1675' Greenish-grey aplitic textured quartz-feldspar fels.

1675' 2158' Moderately foliated feldspar-biotite-(garnet)

2158' 2320' Weakly foliated, fine grained, well layered feldspar-biotite

gneiss. Sampled at 2175'.

2320' 2405' Metapelite/psarnrnite.

2405' 2451' Quartz-feldspar-sericite pegrnatite.

2451' 2570' Biotite metapsarnrnite.

2570' 2627' Weakly foliated, fine grained feldspar-biotite gneiss.

Arnphibolite from 2616-2619', downhole boundary very

gradational.

2627' 2687' Quartz-feldspar pegmatite. Feldspars chloritic in part ,

849m numerous cavities present throughout. Sampled at 2637'.

849m 906m Weakly foliated, pegrnatitic textured feldspar-(biotite)

gneiss. Sampled at 905.5m.

906m 1043m Weak to moderately foliated, fine grained feldspar

biotite-quartz gneiss. Sampled at 983.8m.

934937m Biotite-rich arnphibolite

976.5-987m Cavenous feldspar-sericite-carbonate rock.

1001.5-1003m Cavenous feldspar-sericite- carbonate

rock.

1043m 1068m Garnet-epidote metapsammite. 110

1068m 1323m Weak to moderately foliated, very fine to medium grained

feldspar-biotite-quartz gneiss. Numerous fine grained

layers.

1323m 1398m Shear zone.

1398m Feldspar-rich-garnet metapsamrnite.

Globe Section

DDH 961

1863' Garnet-bearing amphibolite.

1863' 1883' Moderately foliated feldspar-(biotite)-sillimanite

(garnet) gneiss. Sampled at 1866'.

1883' Garnet-bearing amphibolite grading down hole to feldspar

sillimanite-garnet metapelite.

Carbonate Ridge Section

DDH 15N4

0 9M' Moderately to strongly foliated feldspar-biotite-(garnet)

gneiss. 53'-74' Biotite selvage. Uphole boundary

consists of feldspar breccia, lower boundary sharp.

85'-123' Garnet free zone.

148'-245' Garnet free zone.

178'-214' Quartz-feldspar pegmatite.

245'-290' Quartz-feldspar pegmatite.

331'-358' Quartz-feldspar pegmatite.

382'-386' Quartz-rich metapsammite (?), sampled

at 384'.

408'-426' Quartz-feldspar pegmatite.

717'-736' Biotite selvage, mafic psammopelite

inter layer.

799'-814' Aplitic textured feldspar-quartz

(biotite) fels, sampled at 801'. 111

893'- 900' Quartz-feldspar pegmatite.

989' 992' Quartz-feldspar pegrnatite.

992' 1649' Very fine grained biotite rich, aplitic textured meta

psarnrnite.

1649' 1663' Metapsammite/pelite, biotite selvage.

1663' 1700' Weakly foliated, slightly sericitized feldspar-biotite

gneiss. Sampled at 1670'.

1700' 1987' Weakly foliated feldspar-biotite-garnet gneiss.

1701'-1703' Arnphibolite, sharp upper and lower

boundaries.

1710'-1723' Quartz-feldspar pegrnatite.

1746'-1754' Biotite spotted and flecked unfoliated

zone. Sampled at 1747'.

1800'-1832' Quartz-feldspar pegmatite.

1909'-1916' Shear zone.

1916'-1931' Quartz-feldspar pegrnatite.

1950'-1956' Quartz-feldspar pegrnatite.

1987' 2034' Quartz-feldspar pegrnatite with intercalations of feldspar

biotite-garnet gneiss.

2034' 2119' Weak to unfoliated feldspar-quartz-garnet-(biotite)

gneiss. Sampled at 2040'.

2119' 2137' Grey-green mottled, unfoliated quartz-feldspar-(garnet)

gneiss. Sampled at 2124'.

2137' 2139' Biotite-rich amphibolite, sharp uphole boundary,garnet

iferous transitional lower boundary.

2139' 2157' Feldspar-quartz fels containing ragged clots of chlorite,

possibly after garnet.

2157' 2383' Weak to moderately foliated feldspar-garnet-biotite

gneiss. Sampled at 2345'. 112

2187'-2188' Biotite selvage.

2288'-2291' Chlorite spotted layer similar to that

between 2139'-2157'.

2355'-2368' Quartz-feldspar pegmatite.

2383' 2419' Grey-green mottled quartz-feldspar-(garnet) gneiss.

2419' 2517' Moderately foliated, sericitized feldspar-biotite

gneiss. Sampled at 2509'.

2445'-2454' Quartz-feldspar pegmatite.

2469'-2483' Biotite, chlorite-rich amphibolite,

sharp upper, diffuse garnetiferous lower boundary.

Lower boundary is intercalated with feldspar

biotite-gneiss.

2517' 2530' Carbonate-rich quartz-feldspar pegmatite. Sampled at

2525'.

2530' 2560' Weakly foliated, aplitic textured, sericitic feldspar

quartz-(biotite) fels. Sampled at 2549'.

2560' Sericitic metapelite.

DDH 3113

20' 35' Well foliated feldspar-biotite gneiss. Sampled at 24'.

35' 382' Very weakly foliated feldspar-(biotite) gneiss.

152'- 153' Quartz-feldspar pegmatite.

189'- 189.5' Quartz-feldspar pegmatite.

237'- 247' Quartz-rich zone in gneiss. Sampled

at 239'.

266'- 297' Biotite content increases although

foliation remains weak.

382' 413' Slightly sheared mafic quartz-biotite gneiss exhibiting

a granular texture in parts.

413' 485' Well foliated feldspar-biotite gneiss. 113

485' 839' Well foliated feldspar-(biotite) gneiss. Mottled

appearance in parts.

839' 899' Slightly sheared mafic quartz-biotite gneiss exhibiting

a granular texture in parts.

899' 920' Weak to moderately foliated feldspar-biotite gneiss.

mottled appearance in parts.

920' 1020.5' Zone of pegmatites with intercalations of well foliated

feldspar-(biotite) gneiss.

1020.5' 1022' Garnet bearing amphibolite. Sharp upper boundary,

garnet-rich, transitional lower boundary.

1022' 1145' Moderately foliated feldspar-biotite-garnet gneiss

containing sporadic epidote rich patches. Sampled at

1042'.

1067'-1070' Biotite selvage.

1070'-1085' Well foliated, mafic biotite-quartz

rich gneiss. Sampled at 1082'.

1099'-1130' Biotite, chlorite-rich selvage,

containing fragmented feldspars.

Sampled at 1112'.

1130'-1132' Amphibolite.

1145' 1168' Weak to moderately foliated feldspar-biotite gneiss.

Layers of fragmented feldspars plus an overall mottled

appearance.

1168' 1173' Mafic biotite-quartz-rich gneiss.

1173' 1675' Well foliated feldspar-biotite-(garnet) g~eiss.

1236'-1240' Quartz-feldspar pegmatite.

1357'-1363' Sericite mass, sampled at 1360'.

1467'-1547'Quartz-feldspar pegmatite with inter-

calations of feldspar-biotite-(garnet) 114

1675' 1849' Moderately foliated greenish-grey feldspar-biotite

gneiss possessing a mottled appearance.

1849' 1918' Moderately foliated feldspar-biotite-garnet gneiss.

1918 1932' Quartz-feldspar pegmatite.

1932' 2068' Weakly foliated, aplitic textured feldspar-quartz

biotite gneiss. Sampled at 2068'.

2001'-2027' Quartz-feldspar pegmatite.

2068' Sericitic metapsammite. 115

Appendix Al: Sample Descriptions.

No. 3 Shaft Section

DOH 2003

1570' Very weakly foliated, aplitic textured feldspar-quartz

fels. Rare fine grained biotite. Sericite occurs as

wisps up to 3 mm long. Rare anhedral garnets. s1 = 15°. 1627 1 Unfoliated feldspar-biotite-garnet gneiss. Garnets

completely retrogressed to biotite.

1904' Weakly sericitic foliated feldspar-biotite-sericite

gneiss. Sericite occurs as wisps. Isolated feldspar

0 porphyroblasts to 4 mm diameter. s1 = 10 •

2135 I Moderately foliated feldspar-biotite-garnet gneiss. Garnets

elongate parallel to s1 , feldspar porphyroblasts to 1 cm

0 common. s 1 = O.

2153' Weakly foliated pink feldspar-biotite-sericite gneiss.

0 Sericite occurs as wisps to 1 cm long. s1 = 150.

DDH 2058

3194' Weak to moderately foliated feldspar-biotite-(garnet) gneiss.

Garnets retrogressed to biotite.

DDH 3094

787 Moderately foliated feldspar-biotite-(sericite) gneiss.

0 s1 = 110 •

800 Weakly foliated feldspar-rich gneiss with minor biotite

0 clots. s1 = 30 •

Cosgroves Section

DDH 834

35' Well foliated, sericitic feldspar-biotite-garnet gneiss.

Garnets e 1 ongate para 11e 1 to s1 • s1 = 30,o s 2 = 135°.

0 389' Weakly foliated feldspar-biotite-garnet gneiss. s1 = 120 •

476' Moderately foliated, slightly sericitized feldspar-biotite

0 gneiss. s1 = o • 116

581' Fine grained aplitic textured, mafic quartz-feldspar-garnet

rock. Garnets undeformed and completely retrogressed to

biotite.

1159' Weakly sericitized, weakly foliated, medium grained aplitic

textured quartz-feldspar-(biotite) gneiss.

DDH 837

47' Slightly sericitized, fine grained quartz-feldspar-fels.

301' Weak to moderately foliated feldspar-biotite-garnet gneiss

with sporadic chloritic clots. Garnets very elongate

0 parallel to s1 • s1 = 150.

DDH 838

924' Moderately foliated feldspar-biotite-garnet gneiss.

Garnets elongate parallel to s1 • Feldspars augen-like,

minor sillimanite throughout. s1 = 90°.

DDH 844

500' Sheared, sericitic feldspar-biotite gneiss. Feldspars

angular and appear fragmented. s 1 = s 2 = 150°.

DDH 847

150' Moderately foliated feldspar-biotite-garnet-(sillimanite)

gneiss. Garnets slightly retrogressed to biotite.

0 Numerous chloritic clots. s1 = 45. 170' Weak to moderately foliated feldspar-biotite-garnet gneiss.

Garnets elongate parallel to s1 , feldspars equant in part. 416' Very weakly foliated quartz-feldspar fels. Sericitic

0 wisps. Minor biotite. s1 = o. Imperial Ridge Section

DOH 836

1208' Moderately foliated feldspar-biotite-garnet gneiss containing

0 sporadic chloritic clots plus minor sillimanite. s1 = 120. 1392' Moderately foliated feldspar-biotite-(sericite) gneiss.

0 s1 = 90. 117

DOH 951

0 38' Well foliated feldspar-biotite gneiss. s1 = 120 •

120' Moderately foliated feldspar-biotite-garnet-sillimanite

gneiss containing chloritic clots.

243' Moderately foliated feldspar-garnet-biotite-(sillimanite)

gneiss. Garnets elongate parallel .to S 1• S 1 = 20°.

331' Aplitic textured quartz-feldspar fels. Minor sericite and

0 garnet. s1 = 90.

DOH 952

109' Weakly foliated feldspar-biotite-quartz gneiss. s1 = 115°.

143' Aplitic textured quartz-feldspar-sericite fels.

171' Coarser grained variant of sample at 143'; Containing

garnet retrogressed to biotite and minor biotite.

DOH 960

135' Moderately foliated feldspar-biotite-garnet gneiss. Minor

sillimanite and chloritic spotting. Garnets elongate

parallel to s 1 • s 1 = 30°.

210' Moderately foliated biotite-feldspar-quartz gneiss.

DOH 962

764' Strongly foliated feldspar-biotite-garnet (-silltmanite)

0 gneiss with chloritic spotting. s1 = 90 • 787' Moderately foliated feldspar-(sillimanite) gneiss. Garnets

0 elongate parallel to s1 • s1 = 145 • 831' Moderately foliated feldspar-biotite gneiss. Slightly

sericitized. Feldspars slightly elongate to platy.

0 0 Mottled appearance in places. s 1 = 90, s 2 = 45. 900' Moderately foliated feldspar-biotite-garnet gneiss.

0 s1 = 60 • 947' Aplitic textured, weakly foliated (sillimanite foliae);

Biotite-quartz-feldspar interlayer.

1126' Well foliated Biotite-feldspar-quartz gneiss. s = o0 • 1 118

1194' Sericitic, aplitic textured quartz-feldspar-(biotite)

0 fels. S 1 = S 2 = 60 . DOH 3198

1263.7 Weakly foliated feldspar-quartz-garnet-(biotite) gneiss.

0 s1 = 35 • 1289. 6 Weakly foliated feldspar-biotite-quartz gneiss. Sericite-

0 0 quartz layer present. s0 = 105 , s1 = 135. 1350. 7 Well foliated and layered feldspar-quartz -biotite gneiss.

Interlayer composed of finer grained aplitic material.

Possible top downwards facing in interlayer. s = s = 0 1 150°.

1444.5 Biotite-feldspar breccia.

1460.8 Fine grained, well foliated and layered, aplitic textured

biotite-feldspar-quartz gneiss. Layering is monominerallic

in feldspar. S = S = 35°. 0 1 1470.3 Biotite-poor, feldspar-rich layer in contact with a well

foliated biotite feldspar-quartz gneiss. s 0 = s 1 = 30°. 1501. 4 Fine grained, weakly foliated feldspar-quartz-biotite,

0 aplitic textured fels. so= 45.

1555.5 Biotite salvage.

Potosi Section

DOH 804

74 I Moderately foliated feldspar-biotite gneiss. s1 = 120°.

DOH 820

1971' Moderately foliated feldspar-biotite-garnet gneiss.

0 Garnets elongate parallel to s 1 , s1 = 150. 23 54' Weakly foliated feldspar-biotite garnet gneiss. Garnets

0 ragged to elongate. s1 = 130 • 2609' Weakly foliated feldspar-biotite gneiss with very minor

0 sillimanite. s1 - o • 2697' Weakly foliated feldspar-biotite-(garnet) gneiss, very

minor sillimanite. Garnet elongate parallel to s 1• s 1 = 30°. 119

DDH 3167

2205' Weak to unfoliated feldspar-biotite-garnet gneiss. Garnets

small, generally retrogressed.

3919' Moderately foliated feldspar-biotite-garnet-(sillimanite)

0 gneiss. Garnets elongate parallel to s1• s1 = 120.

4642' Aplitic textured, sericitic quartz-feldspar-(biotite) fels.

0 Weak foliation developed by sericite. s2 = 30. Round Hill Section

DDH 813

438' Moderately foliated feldspar-biotite-garnet gneiss containing

minor sillimanite. Garnet parallel to s1• Isolated large

0 porphyroblasts of feldspar. s1 = 90 o

DDH 3105

2380' Feldspar-biotite-garnet gneiss, moderately foliated,

0 containing minor sillimanite. s 1 = 90. Flying Doctor Section

DDH 3074

3977' Moderately foliated feldspar-biotite-(sericite) gneiss.

s = 120°. 1 4814' Weak to moderately foliated feldspar-biotite-garnet-

(sillimanite) gneiss. Garnets elongate parallel to s1 •

5053' Sericitic, aplitic textured, quartz-feldspar fels containing

minor biotite. s1 = s2 = 40°. DDH 3186

892 1 Unfoliated to weakly foliated aplitic textured quartz-K

feldspar-(pink)-biotite gneiss. s0 = 90°.

970 1 Quartz-rich variant of 892'. Faint mineralogical layering,

low biotite content.

1036 1 Mineralogically layered quartz+ feldspar/biotite+quartz+

feldspar. Sporadic fresh and retrograde garnets. s 0 = s1 =

150°.

1097' Well layered gneiss with quartz or biotite-rich layers. 120

Biotite layer well foliated. Feldspar porphyroblasts

to 1 cm in biotite layer.

1148' Moderately foliated quartz-biotite-feldspar gneiss

containing sporadic retrograde euhedral garnets. s1 = 40°. 1251' Contact between quartz+biotite+feldspar, unfoliated layer

with foliated K-feldspar (pink)-quartz-biotite gneiss.

1263' Aplitic textured, chloritic-K-feldspar gneiss.

1659' Mottled, moderately foliated biotite-feldspar-quartz

gneiss. s1 = O. 1700' Weakly foliated, weak mineralogically layered quartz-

0 feldspar-biotite gneiss. s1 = 150 •

0 2042' Well foliated biotite-feldspar-quartz gneiss. s1 = o.

2111' Moderately foliated, layered quartz-feldspar-biotite

gneiss containing retrogressed garnets.

2141' Moderately foliated, layered gneiss consisting of biotite

and biotite-quartz rich layers. Garnets are sheathed in

biotite. s0 = s1 = 160°. 2175' Well layered quartz-biotite-feldspar-(garnet) gneiss with

quartz-rich interlayers. Garnet is slightly retrogressed.

2637' Chloritic, vuggy pegmatite.

866m Brecciated feldspars in a chlori tic-bioti te matrix.

905m Chlorite (?) vein.

983m Vuggy, quartz feldspar pegmatite.

0 998m Weakly foliated feldspar-quartz-biotite gneiss. s1 = 45 • 1097m Fine grained unfoliated aplitic textured quartz-feldspar

biotite gneiss.

Globe Section

DDH 961

1866' Well foliated, feldspar-biotite-sillimanite gneiss.

0 Sillimanite sericitized. s1 = 160 • 121

Carbonate Ridge

DDH 15N4

384' Aplitic textured quartz-feldspar-garnet fels. Garnet

retrogressed.

556 1 Layered aplitic quartz-feldspar fels with interlayer of

feldspar-(biotite) gneiss. 20°. s 0 = s 1 =

732 1 Layered mafic aplitic quartz-feldspar gneiss witha sericitic

feldspar-biotite-quartz layer.

801' Unfoliated feldspar-biotite rock. Feldspar porphyro-

blastic to 0.5 cm, biotite, unorientated.

1670' Weakly foliated layered gneiss consisting of feldspar

biotite gneiss interlayered, with a feldspar-rich layer

containing rare biotite. S 0 - S 1 = 30°. 1747' Unfoliated feldspar-biotite-(garnet) gneiss.

2040 1 Very weakly foliated feldspar-biotite-garnet gneiss.

Garnets numerous, generally less than 2 mm diameter.

2345' Very similar to sample at 2040, some garnets retrogressed

to biotite. s1 = 30°.

2509' Garnet-biotite/chlorite-(feldspar) schist (?). Retrograde

0 amphiboli te (?) • s1 = 45.

2525 I Feldspar-quartz-carbonate pegmatite.

2649' Weakly foliated, fine grained feldspar-biotite gneiss.

Feldspars porphyroblastic to 0.5 cm. Minor wisps of

sericite.

3024' Weakly foliated feldspar-garnet-quartz-(biotite) gneiss.

Feldspars mottled in part.

3054' Aplitic textured feldspar fels plus retrogressed garnet,

now chloritic clots to 1 cm.

DDH 3113

24' Moderately foliated, weakly layered feldspar-biotite

crneiss. S = q = ,~ 0 122

Appendix B; Diamond drill logs for Zinc Corporation, New Broken Hill Consolidated and Southern Extension intersections

Section 30 DDH Z296

1676' Sheared biotite-sericite schist i676~ 2004' Weakly foliated feldspar-biotite gneiss. s1 at 10°. 1777-1817 Abundant feldspar augen 1821-1822 Sericite shear 1843-1846 Quartz-feldspar pegmatite.

E.O.H.

DDH Z631

820' Garnet-biotite-sillimanite metapelite.

820' 876' Weakly foliated feldspar-biotite+sillimanite gneiss. - 0 Numerous quartz-feldspar segregations. s1 at 65

876i 879' Amphibolite.

879' 930.5' Weakly foliated feldspar-biotite gneiss with minor amphibolite and biotite-rich layers.

930.5' 932' Quartz-feldspar pegmatite.

932' 958' Weakly foliated feldspar-biotite gneiss.

E.O.H.

DDH Z653

558' Felsic biotite-garnet-rich amphibolite. Sharp lower boundary.

558' 686' Weak to moderately foliated feldspar-biotite-garnet gneiss. Garnet content decreasing downhole. s1 at 60 . 650' Biotite-rich zone.

686' 809' Weakly foliated, quartz-rich feldspar-biotite gneiss with numerous quartz-feldspar segregations throughout. 0 s1 at 60.

E.O.H.

DDH Zl330

660' Feldspar!biotite-sericite metapsammite. Abrupt downhole boundary.

660' 1016' Moderately foliated feldspar-biotite gneiss, with s1 varying from 40-90° and s2 at 20° to core axis. Abundant quartz-feldspar segregations, biotite selvages and amphibolite-rich layers. Amphibolites reach 3 ft. in width and possess abrupt boundaries. Fragmented feldspar 123

textures are also present in some amphibolites. Meta quartzite layer at 956'.

1016' Quartz-feldspar layered amphibolite.

DDH Z2560

761' Sericitic garnet-biotite-feldspar:sillimanite metapelite.

761' 845' Weakly foliated feldspar-biotite-garnet gneiss with minor feldspar-rich layers. Garnets are rounded and up to 1 cm diameter.

845' 1070' Strongly foliated feldspar-biotite gneiss containing zones of elongate feldspars. Interval tends to be slightly sheared in places and biotite selvages are common.

1070' 1127' Weakly foliated feldspar-biotite gneiss with zones rich in feldspar and numerous feldspar breccia zones.

1127' 1156' Sheared felsic amphibolite. ll56' 1160' Sericitic, sheared feldspar-biotite gneiss. Down hole boundary gradational.

1160' Sheared, sericitic garnet-biotite-feldspar metapelite.

DOH Z2660

682.4m Sillirnanite-biotite-garnet metapelite. Note: Amphibolite at 529.7 m with a mottled or? Fragmental texture.

682.4 724 Moderately foliated feldspar-biotite+garnet gneiss. Uphole boundary gradational. -

724 830.4 Moderately foliated feldspar-biotite-garnet gneiss with numerous biotite selvages to 0.2 m thick. 759-760.5 m Amphibolite interlayered with quartz-feldspar gneiss. 763 Amphibolite interlayered with quartz-feldspar garnet gneiss. 0 765.2 s 0 = s 1 = ~o , s 2 defined by sericite at 45° to core axis. 765.2 - Numerous amphibole-rich and biotite-rich 830.4 selvages. Foliation reversal in arnphibolite at 794.5 m. 0 sa0 = s 1 cut by s 2 at o at 774.4 m, and at 30° t 815.6 m.

830.4 865.2 Weakly foliated and mottled feldspar-biotite gneiss. Generally fine grained with feldspar augen reaching 0.8 cm. Numerous weakly layered chloritic-biotite-garnet arnphibol ite interlayers with s0 at 60-90° to core axis. Abrupt downhole termination.

865.2 l028.5 Sheared sericitic biotite-garnet feldspar metapelite inter layered with arnphibolite layers.

l028.5 1212 Finely layered, mottled, fine grained feldspar-biotite 124

gneiss interlayered with numerous finely layered amphibolite horizons. Layering shows evidence of numerous foliation reversals. Minor siderite and ptygmatic veining present.

1212 Sheared, sericitic feldspar-garnet metapelite interlayered with amphibolite layers.

DDH N2840

4659 Biotite-feldspar-sillimanite metapelite.

4659 4764 Quartz-feldspar, aplitic-textured fels, containing sericitic sillimanite-biotite-rich layers. Uphole contact gradational.

4764 4954 Weakly foliated feldspar-biotite gneiss, feldspar very abundant in places. Minor quartz-feldspar segregations. 0 s1 at 70-90 to core axis. 4928-4954 Feldspars with a "blebby" habit.

E.O.H.

DDH N2960

0 254m Weak to moderately foliated feldspar-biotite gneiss. 0 - 54.4 Medium grained with numerous feldspar augen 54.4- 85.7 Fine grained, biotite-poor. 230.3-254 Very felsic in places, foliation indistinct.

254 258.4 Aplitic textured quartz-feldspar fels, uphole boundary gradational.

258.4 272.6 Sheared, sericitic feldspar-biotite-garnet metapsammite. s0 at 30°, S at o0 to core axis. 2S6.l-268.2 Quartz-feldspar pegmatite.

272.6 293.2 Well foliated, mottled feldspar-biotite gneiss with feldspar augen to 2.5 cm. s1 _at 90°, s 2 (sericitic shearing) at 0.20° to core axis. 286- 287.2 Quartz-feldspar pegmatite.

293,2 335.9 Aplitic textured quartz-feldspar+sericite fels with minor iron staining derived from pyrrhotite. Downhole boundary abrupt. 309.6-310.6 Quartz-feldspar pegmatite 330.6-331.8 Quartz-feldspar pegmatite.

335.9 Quartz-feldspar metapsammite with sillimanite-garnet biotite interlayers.

DDH Z3010A

0 90.3m Weak to moderately foliated feldspar-biotite gneiss, biotite content decreases towards end of interval. 70,l- 73.0 guartz-teldspar-muscovite pegmatite. 125

90.3 220 Aplitic textured quartz-feldspar fels with numerous quartz feldspar segregations. Abrupt downhole boundary.

220 Feldspar-quartz!biotite=sericite metapsanunite.

Section 84

DOH N359

1621' Biotite-sillimanite-garnet metapelite with numerous quartz-feldspar segregations.

1621' 1628' Moderately foliated feldspar-biotite gneiss with numerous quartz-feldspar segregations and minor chlorite. s1 at 70° to core axis.

1628' 1659' Moderately foliated feldspar-biotite-garnet with numerous quartz-feldspar segregations and minor amphibolite-rich bands.

1659' 1666' Amphibo li te •

1666' 1632' Moderately foliated feldspar-biotite-garnet gneiss containing minor pyrrhotite, with abundant amphibolite rich layers and biotite selvages throughout. s1 at 60-70° to core axis.

E.O.H.

DOH N482

2143 1 Sericitic garnet-sillimanite-feldspar metapelite. Down hole boundary gradational.

2143' 2647' Moderately foliated feldspar-biotite-garnet gneiss. Abundant biotite selvages and amphibolite-rich layers throughout. s1 generally at 70-90° to core axis. 2299-2315 Felsic amphibolite with feldspar biotite-garnet gneiss interlayers. Uphole boundary gradational, downhole sharp. 2477-2479 Muscovite-feldspar pegmatite. 25l7L2522'Quartz-feldspar pegmatite.

2647' 2682' Very fine grained feldspar-biotite gneiss containing numerous biotite selvages and amphibolite layers. Down hole boundary gradational.

2682' Felsic biotite-sericite metapelite.

DOH N2310

2155 Sillimanite-biotite-feldspar-garnet metapelite, inter layered feldspar..-quartz metapsanunite.

2l50' 2432' Fine grained, weakly foliated feldspar-biotite-sericite gneiss. Sericite appears to have been derived from garnet. Interval is well layered, individual layers 126

being composed of quartz+feldspar+biotite, are very fine grained and seldom exceed 2 cm in-thickness. This layering is distinct from the quartz-feldspar segregations which also occur throughout the interval. Biotite-rich selvages and amphibolite layers are common, particularly from 22l7' onwards.

2432' 2437' Weakly foliated feldspar-biotite gneiss containing minor pyrrhotite and interlayered with biotite-rich selvages.

2437' Sillimanite-sericite-biotite-feldspar-quartz metapsammo pelite.

Section 92

DDH N250

0 1788' Moderately foliated feldspar-biotite-garnet gneiss with numerous quartz-feldspar pegmatitic segregations through out. Slat 60-70° to core axis throughout interval.

1788' Sericitic feldspar-quartz-biotite metapsammite, uphole boundary abrupt.

DDH N305

0 136' Moderately foliated feldspar-biotite gneiss.

J.36' 215' Weak to moderately foliated feldspar-biotite-garnet gneiss.

215' Sericitic feldspar-quartz-biotite~sillimanite metapsammite, uphole boundary abrupt.

Section llO

DDH N2550

0 426' Weak to moderately foliated feldspar-biotite-garnet gneiss. Interval contains abundant. Feldspar augen to 2 cm in length. s1 at 45° to core axis. 17- 32 Amphibolite.

426' 431' Quartz-feldspar pegmatite with minor, sporadic pyrrhotite.

431' 450 1 Weak to moderately foliated feldspar-biotite gneiss. s1 at 60° to core axis.

450' 503' Quartz-feldspar pegmatite containing minor pyrrhotite.

503' 765' Weak to moderately foliated feldspar-biotite-garnet gneiss with green chloritic clots scattered throughout. s1 at 526 '· .,_ o0 , changing to 30° at 685' • 765' Quartz-feldspar pegmatite with minor pyrrhotite.

785' Weak to moderately foliated feldspar-biotite-garnet gneiss. ioo9-l0l3 1\Illphibolite with sharp upper and lower boundaries. 10l3~068 Interval containing green chloritic clots. ~0Sl, Dolerite. l068-l073 1303-l404 Interval with numerous amphibolites and biotite selvages.

2609' 4065' Weak to moderately foliated feldspar-biotite gneiss. 2604-2608 Metaquartzite. 2632-2644 Fine grained feldspar+quartz-rich interval with well developed layering. 2715-2793 Biotite-:chlorite selvage. 2853-2858 Quartz-feldspar pegmatite. 2858-2870 Chloritic shear zone. 1998-3000 Fine grained quartz-feldspar-rich layering.

DDH N2550A

2547' 2698' Moderately foliated feldspar-biotite+garnet gneiss. Feldspar augen very tabular. -

2698' 3774' Moderately foliated feldspar-biotite gneiss containing sporadic feldspar augen. 2794-2797' Chloritic amphibolite 2885 Chloritic biotite selvage 2893 Biotite selvage 2939-3035 Sporadic chloritic biotite selvages with fine grained feldspar-rich interlayers. 3226-3229 Biotite selvage. 3240-3244 Felsic biotite selvage. 3699-3703 Fine grained quartz-feldspar-rich interval.

3774' Sericitic metapsammite, uphole boundary very gradational.

Section l20

DDH N2000

0 378' Augen-rich feldspar-biotite gneiss. Feldspars possess a platy habit which becomes less pronounced downhole. Sampled at 5'.

378' 596' Weak to moderately foliated feldspar-biotite-garnet gneiss. 55l- 596 Garnet and biotite content decreasing.

596' Biotite-feldspar-sillimanite metapsammite, uphole boundary abrupt.

DDH N4740

0 32m Weakly foliated feldspar-biotite gneiss, augen to 3 cm, minor quartz-feldspar segregations. 1~

32 47.3 Mottled feldspar-rich feldspar-biotite gneiss. Feldspars appear brecciated in places.

47.3 62 Very fine grained, layered feldspar-biotite gneiss with rare augen,

62 68.5 Aplitic textured, weakly foliated quartz-feldspar+biotite fels. Interval ends in a sericitic shear. -

Section 155

OD Nl810

0 296' Well foliated feldspar-biotite-garnet+sillimanite gneiss. Garnets attenuated parallel to S at -35 0 to core axis. Feldspar augen are sporadically aistributed and reach 2cm in length. 47- 56' Mottled felsic amphibolite. 139- l40' Quartz-muscovite-feldspar pegmatite.

296' Sericitic sillimanite-biotite-garnet metapelite, uphole boundary abrupt.

Section 175

DOH N2060

0 207' Tabular augen-rich feldspar-biotite gneiss.

207' 210' Biotite selvage; probably retrogressed amphibolite.

210' 548' Moderately foliated augen-rich feldspar-biotite-garnet gneiss, downhole boundary gradational.

548' Sericitic feldspar-rich metapsammite.

DOH N2450

2044' Interlayered feldspar-garnet, biotite-sillimanite-garnet metapsammite-metapelite.

2044' 2107' Well foliated feldspar-biotite-garnet gneiss. Garnets are elongate parallel to s1 , interval is lacking in feldspar megacrysts and also contains sporadic chloritic clots and minor pyrrhotite.

E.O.H.

DOH N2870

0 Well foliated feldspar-biotite-garnet gneiss, garnets elongate parallel to s1 . Minor chloritic clots throughout. 187' 193' Very fine grained dolerite with minor feldspar.

193 1 236' Moderately foliated feldspar-biotite gneiss with minor sericite. Feldspar possess a tabular to "blebby" habit and may reach 2 cm in length. 129

236' 754' Moderately foliated feldspar-biotite..-.garnet gneiss. Garnets retrogressed to biotite and feldspars tend ''blebby" in places. 3l9- 434 Garnets present in only minor proportions. 434-· 564 Interval contains numerous garnets pyrrhotite derived iron staining. at 25-30° to core axis.

754' 926' Interlayered metapelite-metapsarnrnite interval composed of quartz-feldspar and garnet. Pyrrhotite stained throughout.

926' l940' Moderately foliated feldspar-biotite..-.garnet gneiss with minor pyrrhotite. Garnets reach 2 cm diameter and feld spars, 1.5 cm. Feldspar megacrysts tend to become larger and more numerous downhole. 1650-1714 Prominent zone of shearing. l715 Biotite rich selvage. 1938-1940 Quartz-feldspar pegmatite.

1940 1 1959' Weakly foliated quartz-feldspar-(biotite) gneiss.

1959' 2639' Moderately foliated feldspar-biotite-garnet gneiss with minor pyrrhotite. 2194-2l99 Amphibolite, sharp upper and lower boundaries. 2269-2365 Zone of weak to strong shearing. 2530-2532 Chlorite-rich amphibolite, gradational boundaries. 25-37-2539 Sheared felsic arnphibolite.

2639' 2643' Weakly foliated quartz-feldspar-(biotite) gneiss.

2643' 3633' Moderately foliated feldspar-biotite-(garnet) gneiss. Weakly layered throughout. 2740-2741 Quartz-feldspar pegmatite. 3336-3338 Metaquartzite. 3355-3366 Metaquartzite.

3633 3170 Well foliated weakly layered, fine grained feldspar biotite gneiss, with minor pyrrhotite and sporadic large feldspar megacrysts.

3720 Biotite-quartz-garnet metapsarnmo-pelite, uphole, boundary garnet and pyrrhotite-rich.

Section 226

DDH Nl560

0 187' Moderately foliated, interrnittantly layered feldspar biotite+sillirnanite gneiss sporadic quartz-feldspar pegmatitic segregations. s1 at 45° to core axis from 0-130 1 , 60° to core axis 130-187'. ll9- l22 Quartz~feldspar pegmatite. 129- 132 Quartz-feldspar pegmatite. -133~ 134 Quartz-feldspar pegmatite. 145- 147 Quartz""'.feldspar pegmatite. ~54- 168 Garnet-bearing amphibolite. 175- 187 Interval containing interlayers of 130

amphibolite and feldspar-biotite gneiss.

N.B. Quartz-feldspar-biotite gneiss clasts occur in the upper part of this interval.

187' l94' Aplitic textured quartz-feldspar+biotite fels, weakly foliated with slat 45° to core axis.

194' 270' Moderately foliated, medium to coarse grained feldspar biotite gneiss containing numerous quartz-feldspar pegmatitic segregations. s1 at 45° to core axis.

270' 320' Moderately foliated feldspar-biotite-garnet gneiss. Garnets are elongate parallel to s1 at 45° to core axis.

320' 340' Fine grained, aplitic textured, weakly foliated feldspar quartz fels. s1 at 45° to core axis.

340' 867' Moderately foliated feldspar-biotite-garnet gneiss containing numerous biotite- or amphibole-rich interlayers. Quartz-feldspar pegmatitic segregations throughout. s1 at 45° to core axis.

867' l012' Weakly foliated feldspar-biotite gneiss, exhbiting a mottled texture in part and sporadic banding.

10l2 2325 Feldspar sericite sillimanite metapelite.

2325 3232 Weakly foliated feldspar biotite garnet gneiss. Sporadic pyrrhotite-iron staining and occasional quartz-feldspar segregations. Feldspar-augen decrease in size downhole. 2663' Chlorite-biotite amphibolite 3005'-3015' Sericitic shear 3015'-3021' Quartz-feldspar pegmatite.

3232 3554 Moderately foliated feldspar biotite gneiss. Rare feld spar augen to 1 cm. 3270' Felsic amphibolite, sharp hole boundary, biotite rich downhole boundary. 3320 -3325' Amphibolite.

3554 Sheared sericite feldspar garnet metapsammite.

DDH N2460

1242' Sericitic, pyrhotite-bearing feldspar-garnet-sillimanite metapelite. Downhole boundary very gradational.

1242' 2072' Moderately foliated, pyrhotite-bearing feldspar-biotite garnet (-sillimanitel gneiss. Garnets elongate parallel to s1 . 1336 - 1339 Felsic amphibolite with very gradational garnetiferous uphole boundary and intercalated with feldspar-biotite-garnet gneiss on downhole boundary. -1339 - .1346 Feldspar-rich zone, 1.3 46 - J.3 50 Very felsic amphibolite, gradation al boundaries. 131

l803 - 1806 Very fine grained, sheared dolerite. 1943 ~ 1954 Very fine grained feldspar (pink} biotite gneiss with minor, thin quartz-feldspar (pink) segregations.

2072' 1093' Very fine grained, aplitic textured quartz-feldspar (sericitel fels.

DOH N2530

3252' Interlayered sillirnanite-garnet-feldspar metapsarnrnite pelite.

3252 3358 Moderately foliated feldspar-biotite-garnet gneiss containing minor pyrrhotite and sporadic green chlorite clots. 3292 Arnphibolite, uphole boundary garnet rich. 3298 - 3299 Interval containing intercalated feldspar-biotite gneiss and fine grained arnphibolite. 3304 - 3306 Quartz-feldspar pegrnatite. 3342 Arnphibole-rich gneiss layer, uphole boundary gradational.

3358 3487 Very weakly foliated quartz-rich feldspar-garnet:biotite gneiss. Garnets are elongate parallel to s1 . E.O.H.

Section 244

DOH N4270

0 35.8m Moderately foliated feldspar-biotite-garnet gneiss, with garnets elongated parallel to s1 . Both garnets and feld spar are up to 3 cm in length, with the feldspars often present in a tabular form. Minor chloritic clots through out interval. Last five metres are pyrrhotite stained. 19.3- 20.8 Quartz-feldspar pegmatite.

35.8 78.5 Moderately foliated feldspar-biotite-garnet+sillimanite gneiss containing trace pyrrhotite. -

78.5 106 Well layered, very fine grained feldspar-biotite-quartz gneiss containing sporadic clasts of feldspar-biotite gneiss. Individual layers may also contain isolated feldspar augen to 1.5 cm. 89.8 - 106 Layering becomes less pronounced and interval takes on a "mottled" appearance.

106 l99.4 Feldspar-biotite-garnet gneiss, moderately to strongly foliated with garnets, reaching 2 cm, elongated parallel to s1 . Numerous quartz-feldspar pegmatitic segregations.

199.4 222.4 Weak to moderately foliated feldspar-biotite gneiss contain sporadic tabular feldspars. 132

222,4 268 Weakly foliated, "mottled" feldspar-biotite-garnet gneiss, garnets are typically rounded with, retrogressed, biotite rich rims. Sporadic chloritic clots throughout interval. 240.3 Arnphibolite, uphole boundary gradational. 248,7- 250.2 "Mafic" feldspar-biotite-garnet gneiss, containing amphiboles and porphyroblastic feldspars. Garnets are fine grained, generally less than 0.5 cm diameter. 265, 267,0 Arnphibolite, sharp up and downhole boundaries.

268 Fine grained garnet-feldspar-biotite rnetapsammite containing sericite-sillimanite interlayers.

DDH N4270A

251.8 268 Weakly foliated "mottled" feldspar-biotite-garnet gneiss, containing feldspar augen to 3 cm in length. 265,5- 266.5 Arnphibolite with gradational down hole, sharp uphole boundaries.

268 704,6 Biotite-feldspar-guartz-sericite+garnet metapsammite, 0 - S0 = 70, Sl = l0 to core axis. Abrupt uphole boundary.

704,6 785.6 Weakly foliated, feldspar augen-rich feldspar-biotite gneiss. Rare finer grained layers are also present. Sporadic quartz-feldspar pegmatitic segregations. Interval becomes very felsic and quartz-rich over last 0,5 metres.

785.6 Feldspar-biotite-sericite metapsammite, uphole boundary gradational.

Section 262

DDH Nl640

0 333' Weak to moderately foliated feldspar-biotite-garnet gneiss with very minor sillimanite. Garnets are elongate parallel to s1 at 50° to core axis. Minor chloritic clots are sporadically distributed throughout the interval. Layering is moderately well developed. 292 - 293 Biotite-garnet amphibolite.

333' Biotite-garnet amphibolite, followed by sillimanite-garnet biotite metapelite at 35l'.

DDH N2630

0 513 Weakly foliated, fine grained feldspar-biotite-garnet gneiss. 2l4 .,.. 222 1 Arnphibolite with interlayered feldspar-biotite gneiss. Both boundaries are sheared; uphole boundary intercalated with quartz .... feldspar-rich material. 133

20. 242 Fine grained amphibolite, both boundaries sharp. 246 513 Biotite-chlorite selvages common; numerous quartz-feldspar segreg ations. 304 - 350 Distinctive interval where Sl parallels core axis and s2 is at 90° to core axis. 379_ 380,5 Chlorite-biotite-rich amphibolite, both boundaries sharp. 49J ... 490.5 Chlorite-biotite-rich amphibolite, both boundaries sharp. 4ll ... 4l6 Amphibolite with interlayered quartz-feldspar-rich gneiss. 429 - 502 Interval containing nmnerous thin layered amphibolites, which may be interlayered with quartz-feldspar rich gneiss and possess sharp upper and lower boundaries.

5l3 728 Moderately foliated feldspar-biotite gneiss with minor sericitic patches. Strongly sheared in places. Nmnerous biotite-rich selvages and chlorite-biotite-rich amphibol ites.

728 758 Moderately foliated feldspar-biotite-garnet gneiss.

758 763 Quartz-feldspar pegmatite.

763 Interlayered feldspar-biotite-garnet metapsalllillite and fine grained layered amphibolite. Garnets anhedral to 2 cm diameter.

Section 292

DDH Nl760

O' 266' Weak to moderately foliated feldspar-biotite-garnet gneiss with minor sillimanite. Interval contains rare feldspar biotite gneiss clasts. 65' Biotite-garnet selvage. 20l - 266 Layering becoming more dominant S0 = s1 = 45° to core axis. 266' 309' Moderately foliated feldspar-biotite-garnet gneiss inter layered with sillimanite-garnet-biotite metapelite.

309' Amphibolite containing quartz-feldspar layers grades to sillililanite-garnet-biotite metapelite at 3ll'.

DOH N2290

l135' Blue quartz-sericite-garnet metapsammite. Downhole boundary gradational. ll35' 4090 1 Weakly foliated feldspar-biotite-garnet gneiss. Minor pyrhotite and rare sillimanite throughout, garnets elongate parallel to S..J.. Nmnerous quartz-feldspar pegmatite zones- to O. 5 m. 134

_ll62 I -_J_J.66 '· ;Felsic amphibolite, sharp upper and lower boundaries • ll83 1 ....n90• Quartz-feldspar pegmatite. 2338' -2340' Pink feldspar..-quartz-(biotitel pegmatite. 2349' -2349.5' Felsic amphibolite, sharp upper and lower boundaries. 2JJ.0' -2Jll' Amphibolite, sharp upper and lower boundaries. 27.J.2 '· -2768' Felsic amphibolite with inter calations of feldspar-biotite garnet gneiss. Uphole boundary sharp, garnet-rich. Downhole boundary sharp with a "breccia" texture. Sampled at 2765.5'. 285l' -2864' Amphibolite, sharp uphole bound ary, gradually becoming more felsic downhole. 3052' -3056' Amphibolite, sharp uphole bound ary, intercalations of feldspar biotite gneiss increasing down hole. 3203' -3231' Fine grained quartz-rich feldspar biotite gneiss zone with minor biotite selvages. 3320' -3348' Garnet and sillimanite rich feld spar-biotite-garnet gneiss zone, abundant biotite selvages. Interval ends pyrrhotite-rich. 3597' -3604' Fine grained amphibolite with garnet-rich contacts. 3604' -3620 1 Similar interval to 3320-3348'. 3634' -3638' Fine grained amphibolite with garnet-rich contacts. 3678' -3684' Amphibolite with coarse garnet rich gradational contacts. Up hole boundary intercalated with fine grained feldspar-biotite garnet gneiss. 3698' -3703' Amphibolites with garnet-rich boundaries, feldspar-biotite garnet gneiss at 3699.5-3701. 3703' -3904 1 Interlayered sequence of feldspar biotite-garnet gneiss, quartz feldspar and feldspar-biotite gneisses. 3904 1 -3908' Garnet-rich amphibolite, down hole boundary gradational. 3908' -4058' Augen-rich feldspar-biotite garnet gneiss zone. Augen are up to 3 cm. . 4058' -4062 1 Quartz-feldspar pegmatite, 4062· -4090 1 Biotite retrogressed garnet zone in feldspar-biotite-garnet gneiss. 40901 -4092 '· Quartz-feldspar pegmatite.

4092 Pyrrhotite-bearing feldspar-biotite-richmetapelite, 135

Kellys Creek Section

DOH KC4

0 l92 1 Moderately foliated feldspar-biotite-gneiss, garnets are elongate parallel to Si at 45° to core axis. Sporadic green chloritic clots and minor pyrrhotite..-staining occurs throughout interval, Strongly developed shear at 80'; 0 • s2 = to core axis.

l92' Interlayered sillimanite-garnet..-.feldspar metapelite metapsammite.

DOH KC5

0 467' Strongly foliated and sheared feldspar-biotite-garnet gneiss containing minor sillimanite and pyrrhotite. Garnets are elongate parallel to Sl. Feldspar occurs as augen to 2 cm in length. lOO - ll0' Finely layered amphibolites with feldspar-biotite garnet gneiss inter layers. Uphole boundaries sharp, downhole boundaries brecciated, biotite-chlorite-rich. -1.28' Chlorite-garnet selvage. 2l3 Quartz-feldspar-pegmatite.

467 473 1 Aplitic textured quartz-feldspar fels with minor sericite and rare biotite.

473 I 502 I Strongly foliated feldspar-biotite-garnet gneiss.

502' 505 1 Aplitic textured quartz-feldspar fels with minor sericite and epidote.

505 1 633' Strongly foliated feldspar-biotite-garnet gneiss. 593 - 595 1 Quartz-feldspar pegmatite. Pyrrhotite rich downhole boundary.

633 1 64l' Aplitic textured quartz-feldspar fels with minor sericite. 638' Quartz-feldspar pegmatite.

64l' 649 1 Strongly foliated feldspar-biotite-garnet gneiss.

649' 658 1 Fine grained dolerite.

658' 678' Strongly foliated feldspar-biotite-garnet gneiss.

678 1 684' Aplitic textured quartz-pink feldspar (?orthoclase} fels. Sampled at 682' •

684 1 722 1 Strongly foliated feldspar-biotite-garnet gneiss.

722 1 728 1 Very fine grained aplitic textured quartz..-.feldspar-fels with minor serj.cite,

728 1 -1.583 I Strongly foliated feldspar-biotite-garnet gneiss contaming sporadic fine grained thin (2 cm} feldspar-biotite layers. 862 1 - 868 1 Strongly retrogressed (?I amphibolite, sharp lower- and brecciated, 136

biotite-rich upper boundary. 878' Garnet-biotite-rich selvage. 878' -l306' Interval is relatively more mafic with higher biotite and quartz content. Numerous quartz-feldspar segregations. -1256'· -1288' Amphibolite with sharp upper and lower boundaries. l483' -J.488' Quartz-feldspar pegmatite,

.1583 • Layered quartz-feldspar-garnet metapsammite •

DDH N2770

0 189' Weakly foliated feldspar-garnet-biotite gneiss. Very garnet rich with garnets to 2 cm, often with biotite rims. Weak foliation is very variable from 0-60° to core axis. Rare pyrrhotite staining. Sporadic, weakly developed quartz feldspar segregations.

l89' 476' Weakly foliated feldspar-biotite-garnet gneiss, foliation (S1 1 at 40° to core axis. Interval contains numerous amphibolites ranging from 4 cm to 0.5 m in width. 220' - 222' Garnet-free interval, feldspar-rich, tending aplitic-like in texture. 289' s1 reversal in Granite Gneiss. 351' s1 reversal in layered, felsic amphibolite. 387' Coarse breccia-texture developed by feldspar-biotite gneiss and biotite garnet amphibolite. 433' - 437' Quartz-feldspar-muscovite pegmatite.

476' 478' Brown-green, felsic, equidimensional, fine grained pyroxene- bearing amphibolite. Sampled at 476.5'.

478' 796' Very confused interval consisting mainly of feldspar-biotite+ garnet gneiss. Weakly foliated at 60° to core axis. Augen - are only weakly developed. Numerous quartz-feldspar segregations and biotite-chlorite selvages throughout. Fine grained quartz-feldspar layers, narrow amphibolites and mottled or brecciated textures become progressively more abundant downhole.

796' Massive amphibolite containing numerous biotite-feldspar breccia layers, --.I

I-'

3.08 2.

2. 1.32

5.65

0.16 0.16

0.51

0.67

Fbg

99.00

2209

15.83

66.13

N482

2.92

3.08

5.99

2.23

0.10 0.20

0.88

1. 0.63

Fbg

14.33

67.94 99.05

2190

N482

2.30

1.10 2.89 3.62

0.08 0.15

0.68

4.70 0.85

Fbg

2175

68.

15.23

N482

100.29

3.06

3.03

0.85

0.10 4.37 0.48

Fbg 0.43

0.19

1.19

70.82

N482

15.48

100.00

3.22 2.97

3.99

2.14

0.55 0.93

0.37

0.16

2150 2160

69.11 99.33

15.82

.10

4.91 1.23

0.94

0.25 0.07 0.08

0.72 4.11 0.31

0.69

Fbg Fbg

2108

68.25

99.09

N482 N482

78 study

651

3.59

1.06 0.15 0.27 2.16

0.00

0.03 0.14

76.42

13.88

N2000

99.48

this

456

3.43 3.76

0.39

o.oo

0.07

0.64 4.97

Fbg

1.51

72.54

14.48

N2000

used

101.90

380 3.25

2.79

0.46 a.so

0.23

Fbg

3.75

1.82

71.08

14.50

N2000

99.89

analyses

rock

311

0.38

2.97 2.50

5.36

0.61

Fb 0.25

0.05 0.06 0.17 0.15 0.17

1.48

71.

14.16

N2000

99.71

whole

234

0.40

3.03 Fb 2.49

0.23

0.04 0.18

0.61

4.07

1.32

72.

14.30

N2000

99.24

(1973)

Unpublished

198

0.58

4.03 0.38

2.53

5.09

0.06 0.16

0.93

1.69

N2000

69.54

14.83

99.82

Shaw

Type

DDH

Depth

Appendix Source:

Ti0 sio

FeO

MgO

Nai°

cao

MnO P205

Total Appendix C: Unpublished whole rock analyses used in this study (cont.)

Source: Shaw (1973)

DOH N482 N482 N482 N482 N482 N482 N482 N482 N482 N482 N482 N482 Depth 2246 2262 2279 2301 2331 2364 2382 2404 2433 2472 2437 2727 Type Fbg Fbg Fbg Fbg Fbg Fbg Fbg Fbg Fbg Fbg Fb Fb

Si0 2 64.65 70.68 60.21 61.68 67.35 68.46 66.30 68. 96 65.70 64.02 73.63 63.22

Ti0 2 0.82 0.51 1.02 0. 96 0.73 0.62 0.75 0.65 0.93 0.88 10.41 0.75

Al 2o3 16.00 14.49 17.07 16.73 15.25 15.09 15.86 15.39 16.35 16.98 13.95 19.51

Fe 2o 3 o. 77 0.22 0.76 0.42 0.52 0.76 0.85 0.47 0.80 o. 71 0.38 1.46

FeO 6.20 3.80 8.54 7.86 5.32 4.42 5.59 5.04 4.64 6.51 2.28 5.58

MnO 0.11 0.08 0.31 0.17 0.11 0.09 0.13 0.09 0.07 0.14 0.06 0.15

MgO 1.65 0.83 2.30 1.63 1.35 1.26 1.27 1. 21 1.55 1.53 0. 72 1.99

cao 3.33 2.28 4.22 4.01 2.97 2.24 3.40 3.94 4.50 3.14 3.69 2.12

K20 2.18 4.79 2.48 2.57 3.21 4.30 2.37 1.32 1.93 2.65 1.59 1.43

Na2o 2.85 2.52 2.49 2.97 2.61 2.53 2.94 2.69 2.75 3.06 2. 72 2.07

P205 0.15 0.16 0.10 0.21 0.13 0.11 0.17 0.16 0.14 0.11 0.11 0.10 Total 98. 71 100.33 99.50 99.21 99.58 99.88 99.61 99.02 99.36 99.73 99.54 98.38

I-' w OJ I-' w

I.O

26 24

Ap 0.15

0.02 1.28 0.

0.51 0.02 2.34 5.30

0.11

75.25

NBH3176

13.

98.38

0.54

3.00 0.87 Fbg 4.52 0.08 3.66 0.17

0.13

Surface 69.23

14.95

98.48

3.89 Fbg 0.67

0.64

0.03 1.08

3.23 4.31

1.93

Surface

67.00

15.63

98.58

0.65

Fbg 4.88

0.06

3.07 3.18

1.29 1.50

67.57

Surface

16.00

0.62

Fbg 5.61 0.12 0.42 0.34 2.02

3.28

1.20

0.11 0.14 0.17

KCS

66.11

1062

16.18

98.44 98.68

94 76

0.66

4.92 0.58 0.03

1.02 4.76

1. 1.22 0.12

Surface

66.12

16.39

98.

(cont.)

study

Fb Fb 0.48

2.67 a.so

0.04

2.74 4.01

0.16

71.

14.23

this

Fb 0.14

0.02

1.57 0.34 0.83 3.23 0.70

5.20

0.20

73,94

13.41

98.76 98.98

used

Fb 0.15

0.04

0.01 0.01 1. 0.36

0.61 5.42

73.41

Surface Surface Surface

13.60

99.19

analyses

rock

0.59

0.30 5.27

3.55

1. 3.15 3.68

0.13 0.14

1.96

8180 Nl560

66.96

15.00

98.52

whole

Fbg 0.92

7.31

0.58 0.11 0.11 3.60 2.58 3.28

1.44

0.13

2300

N482

62.90

15.

98.62

(1973)

Unpublished

619

0.31

2.80 0.05

0.02

0.44

4.56 3.21

1. 0.16

NBH3113

72.

13.44

98.92

Stone

2 0

Appendix Source:

DDH Depth Type

Si0

Ti0

Al Fe

FeO

MnO

MgO K cao

Na P205 Total

I-' I-'

,i,. ,i,.

0 0

(cont.) (cont.)

study study

this this

in in

used used

analyses analyses

rock rock

0.62 0.62

2.91 2.91

0.06 0.06

4.18 4.18

0.53 0.53

0.92 0.92

Fbg Fbg 4.27 4.27

0.11 0.11

1.55 1.55

67.91 67.91

Surface Surface 15.36 15.36

98.42 98.42

whole whole

0.69 0.69

0.25 0.25

4.61 4.61

2.89 2.89

0.04 0.04

0.12 0.12

4.54 4.54

1.91 1.91

1.05 1.05

15.41 15.41

67.18 67.18

Surface Surface

98.68 98.68

(1973) (1973)

Unpublished Unpublished

0.60 0.60

670 670

0.78 0.78

Fbg Fbg Fbg 4.53 4.53

2.33 2.33

0.07 0.07

0.12 0.12

4.46 4.46

1.08 1.08

1.60 1.60

N2550 N2550

67.52 67.52

15.41 15.41

98.50 98.50

C: C:

Stone Stone

3 3

0 2 2

2 2

o o

0 0

Type Type

Depth Depth

Source: Source:

DDH DDH

Appendix Appendix

Si0

Ti0

cao cao

P205 P205

FeO FeO

K Fe

MgO MgO

MnO MnO Total Total 141

Source: Klingner and McConachy (1975) This data is confidential and is on closed file at The Zinc Corporation Ltd., Broken Hill. It is used with the permission of Mr. T.W. Dickson. The location and mineralogy of the data used is as follows:

DDH Depth Type

N2870 60 Fbg

N2870 152.4 Fbg

N2870 304,8 Fbg

N2870 457.2 Fbg

N2870 609.6 Fbg

N2870 762.0 Fbg

N2870 914.4 Fbg

N2870 1066.8 Fbg

Nl640 45.7 Fbg

N2060 64.0 Fb

N2060 152.4 Fb

N2000 60.9 Fb

N2000 106.7 Fb

N2000 167.6 Fbg

N2550 106.7 Fbg

N2550 304.8 Fbg

N2550 442.0 Fb

N2550 594.4 Fbg

N2550 746.7 Fbg

N2550 899.2 Fbg

N2550 1051.6 Fbg

N2550 1203.9 Fbg

ZJ.330 225.3 Fb

N2310 656.2 Fb

N2310 685.8 Fb

N2310 705.3 Fb

Z2620 343.2 Fb