Geological and Atmospheric Sciences Publications Geological and Atmospheric Sciences

2-1988

Structure and metamorphic setting of base metal mineralisation in the Kanmantoo Group, South Australia

Paul G. Spry Iowa State University, [email protected]

Jeffrey C. Schiller C. R.A. Exploration Pty. Ltd.

Ross A. Both The University of Adelaide

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This Conference Proceeding is brought to you for free and open access by the Geological and Atmospheric Sciences at Iowa State University Digital Repository. It has been accepted for inclusion in Geological and Atmospheric Sciences Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Structure and metamorphic setting of base metal mineralisation in the Kanmantoo Group, South Australia

Abstract Base metal mineralisation occurs at several locations within the regionally metamorphosed Kanmantoo Group on the southeastern flank of the Mount Lofty Ranges between Kanmantoo and Strathalbyn, 50 km southeast of Adelaide. Sulphide mineralisation is of three main types (Seccombe et al.,1985): 1. copper deposits, at the Kanmantoo and Bremer mines, South Hill prospect and several minor occurrences 2. lead- zinc deposits at Aclare, Wheal Ellen, Strathalbyn, St. Ives, Scott's Creek, and Glenalbyn mines 3. pyrite- pyrrhotite mineralisation of the Nairne pyrite deposit and many other pyritic schist units within the Kanmantoo Group.

Disciplines Geology | Geomorphology | Mineral Physics | Sedimentology | Stratigraphy

Comments This proceeding is published as Spry, P.G., Schiller, J.C., and Both, R.A., 1988, Structure and metamorphic setting of base metal mineralisation in the Kanmantoo Group, South Australia. The AuslMM Bulletin and Proceedings, v. 293, p. 57-65. Posted with permission.

This conference proceeding is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ ge_at_pubs/359 Structure and metamorphic setting of base metal mineralisation in the Kanmantoo Group, South Australia

By PAUL G. SPRY', JEFFREY C. SCHILLER1 AND ROSS A. BOTH3, Associate Member

INTRODUCTION Base metal mineralisation occurs at several locations within the regionally metamorphosed Kanmantoo Group on the N o"---k-'--m__ 10 southeastern flank of the Mount Lofty Ranges between Kanman­ I too and Strathalbyn, 50 km southeast of Adelaide. Sulphide I mineralisation is of three main types (Seccombe et al.,1985): I ,... 1. copper deposits, at the Kanmantoo and Bremer mines, South I Hill prospect and several minor occurrences l 2. lead-zinc deposits at Aclare, Wheal Ellen, Strathalbyn, St. Ives, Scott's Creek, and Glenalbyn mines I \ 3. pyrite-pyrrhotite mineralisation of the Nairne pyrite deposit \ and many other pyritic schist units within the Kanmantoo Group. Syntheses of folding, metamorphism and stratigraphy of the Kanmantoo Group were given by Kleeman and Skinner (1958), .,:1 Oftler (1960, 1963), Offler and Fleming (1968), Marlow (1975), Mancktelow (1979) and Parker (1986). Studies of the general rela­ Kantnt tionships of mineralisation to structure in the Kanmantoo area •- .1v=· 1B:. were given by Grasso and McManus (1954), Mirams (1962), Poole C ··. (1969), and Lindqvist (1969). ; _mer mine lare I Several conflicting views on the origin of mineralisation in the ine Kanmantoo Group have been proposed. Thomson (1975) consi­ dered much of the mineralisation as a late-stage product of .Wheal Ell~," mine tsilll]Alluvlum CAMBRIAN regional metamorphism and he, like Parker (1986) and Lambert 1 ~Garnet andalusite et al. (1987), stressed the importance of major lineaments as an UIILJ schist ,'\..~ Strathalbyi;ne □Quartz feldspar/ ore control. However, Lindqvist (1969) and Verwoerd and Y.~p::,• mica schists Cleghorn (1975) tentatively suggested a syn-sedimentary origin / mine ~ Pyrltlc schist to the Kanmantoo copper deposit and Jensen and Whittle (1969) and Seccombe et al. (1985) on the basis of sulphur isotope data . i;:ssauartz feldspar schist ~TEROZOIC proposed a bacteriogenic sulphur source and a sedimentary origin . for sulphides in the Nairne pyrite deposit. The latter suggested I that most copper deposits represent stockwork, vein or dissemi­ ,.,.,, Fault nated zones within subsurface vents whereas massive minerali­ sation at Wheal Ellen and Aclare mines probably accumulated Flo. I - Map of regional geology on the ocean floor. This paper presents new geological information on the struc­ tural and metamorphic setting of the base metal deposits and at­ (1972). The Bremer mine is located highest in the Tapanappa For­ tempts to relate this information to previous regional studies of mation, just above the base of the Brown Hill Subgroup. The the Kanmantoo Group. Estimates of pressure and temperature Nairne pyrite deposit may be as much as 3-4 km stratigraphically of peak metamorphic conditions based on silicate mineral sta­ below the level of the base metal mineralisation in the Tapanappa bilities are considered in relation to various silicate and sulphide Formation (Daily and Milnes, 1972) within the underlying Talisker geothermometers which have not previously been applied to rocks calc-siltstone. in the Kanmantoo Group. Four main lithologies and a number of minor rock types are associated with base metal mineralisation. Descriptions of the GEOLOGICAL SETTING main lithologies follow. The Kanmantoo Group consists of a thick succession of region­ (i) Quartz-mica schist is composed of quartz, biotite, musco­ ally metamorphosed pelites and greywackes of Cambrian age vite, feldspar and trace amounts of apatite and zircon. Bio­ (Sprigg and Campana, 1953) and overlies Proterozoic metasedi­ tite and muscovite impart a weak schistosity and, along with ments of the Adelaide System (Daily and Milnes, 1972) as in quartz and feldspar, define original bedding on a scale of Figure 1. All the mineralised areas, with the exception of the I mm to several metres in thickness. Quartz-mica schist is Nairne pyrite deposit, lie within the upper part of the Tapanappa the most common rock type on the southeastern flank of Formation of the Inman Hill Sub_group of Daily and Milnes the Mount Lofty Ranges between Kanmantoo and Strathal­ byn and hosts mineralisation at Strathalbyn, Wheal Ellen, Aclare and South Hill. prospect. ' Assistant Professor, Department of Earth Sciences, Iowa State Univer­ (ii) Biotite schist. Interlayered with quartz-mica schist are sity, Ames, Iowa, U.S.A. 5001 I metapelitic bands of biotite schist which predominantly con­ • Geologist, C. R.A. Exploration Pty. Ltd., Box 467 P.O., Kalgoorlie, WA, 6430, Australia sist of biotite, quartz, and muscovite with minor garnet, 3 Reader, Department of Geology and Geophysics, The University of staurolite and andalusite. The high mica content produces Adelaide, Box 498 G.P.O., Adelaide, SA, 5001, Australia a prominent schistosity and preserves crenulations related Original manuscript received 10th June 1987. to later deformational episodes (Fig 2a). Mineralisation at

The AuslMM Bulletin and Proceedings, Vol. 293, No. 1, February 1988 57 P. G. SPRY, J.C. SCHILLER ANO R. A. BOTH

andalusite-biotite schists have abundant coarse andalusite, in a matrix of biotite, muscovite, quartz and garnet with minor staurolite, fibrolite and chlorite (Fig 2b). One visual variant of the garnet-andalusite-biotite schist is associated with the northeast portion of the main orebody at Kanman­ too. This rock type, referred to here as the poikiloblastic schist, is present between the chlorite-rich lode rocks and the more typical garnet-andalusite-biotite schist. Although chemically and mineralogicaJJy similar to garnet-andalusite­ biotite schist, it contains poikiloblasts of andalusite, garnet, staurolite, biotite and rare cordierite. (iv) Chlorite-rich lode schist. Sulphide mineralisation at Kan­ mantoo and South Hill prospect is contained within this unit. The most common mineral assemblage in these schists is quartz-chlorite-garnet ± pyrrhotite ± chalcopyrite. Other common assemblages are: quartz-chlorite-garnet-biotite ± chalcopyrite FIG. 2a-Crenulated biotite schist at South Hill prospect. The hammer staurolite-biotite-garnet ± pyrrhotite ± chalcopyrite is lying on the dominant S, schistosity surface. Crenulation lineation (L.) staurolite-biotite-garnet-chlorite ± chalcopyrite is indicated and crenulation lineation (L,) parallels the handle of the staurolite-chlorite-magnetite ± pyrrhotite ± chalcopyrite hammer. Unlike the three aforementioned schists, andalusite is a rare component of the chlorite-rich lode schist. Mineralisa­ tion and the chlorite-rich lode schists at the Kanrnantoo mine are grossly discordant to relict bedding in garnet-andalusite­ biotite schists. It is suggested that the late schists represent the metamorphosed alteration product from the walls ad­ jacent to a hydrothermal event. Minor rock types include pyritic schists, calc-silicate schists and cordierite-bearing rocks. Bulk compositions of some rock types associated with mineralisation in the Kanmantoo-Strathalbyn region are included in Table I.

STRUCTURE The base metal deposits discussed here are associated with rocks with a prominent schistosity and a steeply plunging mica linea­ tion. the textures of silicate minerals surrounding and intergrown with the sulphide bodies reveal a structural history not apparent in associated sulphide minerals even though they have been F10. 2b-Garnet-andalusite-biotite schist interlayered with quartz-mica metamorphosed and deformed. schist at Kanmantoo mine. Note the axial plane schistosity (S,) parallels A comprehensive study of the relationships between folding the handle of the hammer. and metamorphism in the Mount Lofty Ranges by Offler and Fleming (I 968) recognised the effects of four separate deforma­ Strathalbyn, Bremer and South Hill prospect is associated tion episodes. The first, and most intense, recognised by these with these rocks. authors produced a widespread, penetrative schistosity which was (iii) Garnet-andalusite-biotite schist. These schists are spatially subsequently deformed by two crenulation producing episodes. associated with mineralisation at Kanmantoo, Wheal Ellen, According to Offler and Fleming (1968), the first of the crenula­ South Hill, St Ives and Scott's Creek areas. Garnet- tions has an east-west axial plane and folds of all scales were

TABLE 1 Whole-rock analyses of rock types associated with base metal mineralisation

2 3 4 5 6

SiO1 64.73 60.55 58.44 65.71 58.88 37.52 Al,O, 15.46 17 .73 19.86 13.69 19.52 31.73 Fe,O,x 10.60 11 .04 12.80 7.86 13.38 16.62 MnO 0.06 0.06 0.23 2.24 0.19 0.32 MgO 3.20 3.36 3.05 1.96 3.86 5.95 CaO 1.58 1.35 0.18 0.42 0.37 0.76 Na,O 1.43 1.14 0.13 0.54 0.20 0.19 K,O 3.68 4.60 3.86 5.50 3.50 6.10

TiO1 0.65 0.71 0.82 0.66 0.81 1.19 P,O, 0.12 0.13 0.14 0.10 0.12 0.39 Cu 0.00 0.04 0.00 0.00 0.01 0.01 Pb 0.01 0.00 0.00 0.00 0.02 0.01 Zn 0.01 0.01 0.00 0.00 0.10 0.19 Total 101.71 100.72 99.51 98.68 100.96 101.00 Loss 1.90 2.57 0.97 1.13 0.75 0.75

1. and 2. Andalusite schist, South Hill prospect; 3. Andalusite schist, Kanmantoo mine; 4. Quartz-mica schist, Kanmantoo mine; 5. and 6. Pyritic schist, South Hill prospect; x Fe measured as Fe,O,; Loss represents the sum of H,O•, S, C, H,o-, Fe''-Fe''

58 The AuslMM Bulletin and Proceedings, Vol. 293, No. 1, February 1988 MINERALISATION IN THE KANMANTOO GROUP

produced, whereas the second crenulation episode produced only The inclusion trails consist mainly of elongated, rounded quartz mesoscale and microscale folds with a north-south axial plane. grains which are finer grained than the matrix quartz grains. Other The intensity of development of both crenulation sets varies spa­ minerals defining S, are biotite, muscovite and ilmenite at Wheal tially throughout the Mount Lofty Ranges and although crenu­ Ellen and South Hill and, at Kanmantoo include chalcopyrite, lations are present in the areas discussed in this paper, their effects pyrite and pyrrhotite also. The inclusion trails in andalusite can are minor. The fourth and final deformation produced sporadic have various trends in thin section but typically are discordant kinking of the regional schistosity. Several subsequent studies in to a well developed S2 schistosity which wraps around the host the Mount Lofty Ranges and Kangaroo Island (Daily and Milnes, andalusite. S, inclusion trails extend to the edge of the host an­ 1973; Flint and O'Grady, 1979) supported this deformational dalusite grains where they usually abut against S, at a high angle history. (Fig 3a). Where it is at a high angle to S2, S, is commonly curved In the area studied here, the earliest fabric recognised is planar or sigmoidal. Sigmoidal S, inclusion trails appear to have deve­ inclusion trails (denoted S,) in porphyroblasts, which are com­ loped by rapid overgrowth of incipient F2 crenulations by monly discordant to the matrix schistosity (denoted S,) wrapping andalusite. the porphyroblasts. Our S, and S, are equivalent to S, and S, Recent microfabric studies by Bell (1985, 1986) and Bell et al. of Mancktelow (1979) who proposed, as a result of a structural (1986) suggest that most porphyroblasts do not rotate during duc­ study of the southern Mount Lofty Ranges, that the widespread tile deformation. These studies support the concept that inclu­ regional schistosity was S,, and that S, only developed in some sion trails in andalusites are the result of an early deformation areas, of which our study area is one. Our S, is believed to corre­ event and not due to rotation of andalusite during one period late with Offler and Fleming's first schistosity and if so, the in­ of deformation. ternal fabrics must be attributed to an earlier event. Curviplanar S, inclusion trails are more common in andalu­ sites near the western deposits, Wheal Ellen and South Hill, than The D, deformation at the Kanmantoo mine, where planar trails are ubiquitous. It Garnet-andalusite-biotite schist which is closely associated with would apppear that andalusite porphyroblasts in the Kanman­ the orebodies at Kanmantoo. Wheal Ellen and South Hill has too mine area usually grew over essentially uncrenulated S, proven to be a key lithology in unravelling the structural history whereas at South Hill and Wheal Ellen andalusites grew over in­

of the Mount Lofty Ranges for it preserves abundant evidence cipient F2 crenulations. Within some andalusite porphyroblasts of D, as planar and curviplanar inclusion trails (S,) within an­ at South Hill and Wheal Ellen (but not at Kanmantoo mine) are dalusite porphyroblasts. Adjacent quartz-mica and biotite schists small andalusite-rich clots which appear to have developed before with considerably fewer porphyroblasts exhibit only D, structures. the inclusion trails, for the trails wrap around them.

FIG. 3a-Quanz-muscovite-biotite inclusion trail (S 1) in a pre-S, andalusite porphyroblast (Wheal Ellen Mine). Note the discordancy of S, to S, which FIG. 3b-S, crenulation produced in quartz-mica schist (South Hill is produced by quartz (q), muscovite (m), biotite (b) and fibrolite (f). prospect). Note the recrystallised muscovite (m) as indicated by polygonal Plane-polarised light. apices. Crossed nicols.

The AuslMM Bulletin and Proceedings, Vol. 293, No. 1. February 1988 59 P. G. SPRY, J.C. SCHILLER AND R. A. BOTH

F10. 3c-Inclusion-filled cordierite (c) intergrown with gedrite (ge) and FIG. 3d-Gahnite (gn), chlorite (ch), apatite (a) rock from Strathalbyn garnet (g) in a cordierite-gedrite-anthophyllite rock (Wheal Ellen mine). mine. The opaque is pyrite. Plane polarised light. Plane polarised light.

The D2 deformation the pyritic schists. The S3 cleavage is defined by quartz-rich hinges At the D, stage a fine-grained schist had formed which con­ and muscovite or a muscovite-biotite-rich intergrowth in the limbs tained small andalusites at Wheal Ellen and South Hill, but ap­ (Fig. 3b). The mica flakes have polygonal apices indicating parently not at Kanmantoo mine. During the D2 stage, the S, recrystallisation after crenulation. The symmetrical crenulations schistosity began to crenulate in the western area, and at an early range in wavelength from 0.2 to 4 mm while the amplitude varies stage in the development of these crenulations coarse-grained an­ between 1 and 8 mm. The larger wavelength and amplitude of dalusite apparently grew rapidly relative to the rate of folding, F, crenulations occur in the pyritic schist. preserving a mildly crenulated S, in the western deposits, but F, crenulations are sporadically developed in the Kanmantoo­ generally uncrenulated S, around the eastern deposits, that is Kan­ Strathalbyn region, but have been observed at Kanmantoo mine, mantoo and Bremer mines. In the western deposits, some of the Wheal Ellen mine and South Hill prospect. The main orienta­ coarse-grained andalusite nucleated on pre-existing andalusite tion of the crenulation lineation is approximately 60° towards grains. As well as andalusite, garnet, biotite, staurolite, musco­ 100° at South Hill and at Wheal Ellen (Fig 4a and b). Lindqvist vite, fibrolitic sillimanite and kyanite began growing early in D2. (1969) and Poole (1969) considered the mineral lineation (L2) and As the intensity of 0 2 increased, the domainal crenulation the crenulation lineation (referred to here as L3) to be produced cleavage (S2) was formed with a mica lineation L2. A period of in the same deformational event. The mean orientations, for the grain size increase accompanied 02. two lineations, are clearly different; in one outcrop, where both Stereographic plots of structural elements for Kanmantoo mine are present, an 18° difference in pitch was observed. No small (Fig. 4a), South Hill prospect and Wheal Ellen mine (Fig. 4b) or large scale F, folds were evident in the Strathalbyn-Kanmantoo show that the orientations of S, and L2 do not vary significantly area. between these deposits. ln all cases, S, trends north-northeasterly and dips steeply to the south-southeast. Table 2 compares the The D. defor ma lion angle (8) between the average fold axis orientation and the L2 A second crenulation, observed only at South Hill prospect, extension direction with the tightness of folds for several deposits. also develops a nonpenetrative crenulation cleavage (S.). The For the eastern deposits (Kanmantoo, Aclare, Scott's Creek and wavelength ranges from 1 to 5 cm and the amplitude is about Bremer mines) 8 is higher and the folds more open than those 1 cm. As with the S, crenulation, quartz concentrates in the hinge associated with South Hill prospect and Wheal Ellen mine. This and biotite-muscovite in the limbs. The mean orientation of the variation is inferred to reflect greater strains associated with the crenulation lineation (L.) is 35° to 170°. Class la mesoscopic F. western deposits compared with those further east. folds (Ramsay, 1967) are rare but present in the biotite schist at The D, deformation South Hill prospect.

A nonpenetrative crenulation cleavage (S3) is developed parallel The relative timing of the 0 3 and o. events is based upon the to the axial plane of the crenulation in the schists, particularly overprint of L. on L3 in road cuttings at South Hill prospect.

60 The AuslMM Bulletin and Proceedings. Vol. 293, No. 1, February 1988 MINERALISATION IN THE KANMANTOO GROUP

KANMANTOO MINE POLES TO So (548) POLES TO S2 (504)

5a·52 INTERSECTIONS MINERAL LINEATIONS a (77) L2 (112) Fto. 4b-Point diagrams of structural data for South Hill prospect and Wheal Ellen mine. F10. 4a-Contour diagrams of structural data for Kanmantoo mine. AH figures are lower-hemisphere, equal-area projections. Numbers of meas­ urements are indicated. Poles to So contour interval: 0.74, 1.48, 2.95, throughout the area; however, kyanite has been recorded just 5.91, and 11.820/o per 10/o area; poles to S, contour interval: 3. 73, 7 .46, north of Wheal Ellen (Offler and Fleming, 1968; Mancktelow, 14.91, 29.82, and 59.650/o per lOJo area; S.-S, intersection contour in­ 1979) and at Shephard Hill (5 km north of Nairne) in the Nairne tervals: 1.35, 2.70, 5.41, 10.81, and 21.620Jo per I OJo area; and L, mineral Pyrite deposit (Skinner, 1958). Experimental results on the sta­ lineation contour intervals 4.50, 9.00, 17.99, 35.99, and 71.970Jo per I 0/o bility field of the alurninosilicates (Richardson et al., 1969; Hold­ area. away, 1971) plus reactions involving the stability of the assemblage staurolite-quartz can be used to place constraints on Marlow (1975) observed two sets of crenulations north of PH,o - T conditions (where PH,o = P,01a1). Strathalbyn which appeared to overprint the other. He concluded Thermodynamic considerations suggest that the aluminosili­ that the two sets developed during the same deformational period. cate triple point of Holdaway (1971) is to be preferred; however, A difference in style and observation of L. consistently distort­ Bickle and Archibald (1984) indicated that natural assemblages ing L3 are the reasons for suggesting the existence of two separate commonly support the triple point determined by Richardson et deformations. al. (1969). The apparent conflict between these studies may in part be resolved by the recent findings of Salje (1986) who redeter­ The D, deformation mined thermodynamic equilibrium between sillimanite and an­ dalusite using new heat capacity measurements on andalusite, D kinks were found only at Wheal Ellen and Kanmantoo mines 5 bulky sillimanite, and fibrolite. Whereas the aluminosilicate phase and South Hill by Poole (1969). These kinks are generally asym­ diagram of bulky sillimanite is in agreement with the experimen­ metric and appear to form interlacing sets, but are not conjugate tal brackets of Holdaway (1971), that of fibrolite is closer to the sets because the sense of movement across the kinks is always results of Richardson et al. (1969). upper half toward the east. The kink axial planes (S,) lie at low Assuming equilibrium, the widespread coexistence of stauro­ angles and are variable in orientation. lite, quartz, andalusite, and fibrolite and the limited presence of kyanite and coarse sillimanite, P-T conditions in the Kanmantoo­ METAM ORPHIC GRADE IN THE KANMANTOO REGION Strathalbyn area are primarily within the andalusite-phase field Mineral assemblages in the Kanmantoo region correspond with close to the aluminosilicate triple point. P-T conditions of 530°- those of the andalusite-staurolite zone of the almandine­ 5600C and 2.2-3.2 kb and 530°-630°C and 2.2-5.4 kb are obtained amphibolite facies (Offler and Fleming, 1968) and the fibrolite assuming the triple points of the Holdaway (1971) and Richard­ zone of Mancktelow (1979). Andalusite and fibrolite are common son et al. (1969), respectively (Fig. 5).

TABLE 2 A comparison ofthe relative finite strain associated with mineral deposits in the Kanmantoo Group. The classification of Ramsay (1967) is used for fold tightness

Sulphide li=angle between Tightness of deposit F, and L, F, folds Data source

Wheal Ellen o· isoclinal Spry (1976) South Hill o• isoclinal Spry (1976) Kanmantoo so• open-close Schiller (in preparation) Scott Creek 30° approximately close tight Askin5 (1968), Poole (1969) Aclare 35° approximately close Askins (1968), Poole (1969) Bremer 35° approximately close Poole (1969) l ~e Aus!MM Bulletin and Proceedings, Vol. 293, No. 1, February 1988 61 P. G. SPRY, J. C. SCHILLER AND R. A. BOTH

vist 1969; SchiJier unpubl. data) and a biotite schist from Wheal Ellen mine (Spry unpubl. data). Garnets appear to exhibit zoning 7 which is typical of growth during a prograde metamorphic event (Tracy, 1982). 6 3 Garnet-cordierite geothermometry 5 For a cordierite-garnet-anthophyllite rock from the Wheal Ellen area (Fig. 3c) and a quartz-mica schist from the Kanmantoo mine, Pkb the geothermometer yields temperatures of 525 ° and 511 °, respec­ 4 tively (Table 3). These temperatures are likely to be minimum temperatures due to compositional zoning in garnet and because of a probable error in the low temperature end of Thompson's 3 calibration which, according to Holdaway and Lee (1977) is low by 30°C.

2 Sphalerite geobarometry The barometer has been applied to seven samples from Wheal 1 Ellen mine and one from Aclare mine. Most sphalerites analysed touched hexagonal pyrrhotite and pyrite at triple point junctions; however, some coexisted with hexagonal pyrrhotite and were en­ 0 L---,r------'lr-----'-tl-'--'----,-~-...... - capsulated in pyrite. Although hexagonal pyrrhotite was dominant 200 8 0 in all sections, as verified by magnetic colloid, minor amounts 400 ToC 600 of monoclinic pyrrhotite were also present. Care was taken to Fm. 5-P-T conditions as deduced by silicate stabilities, sphalerite ge­ analyse sphalerite coexisting with hexagonal pyrrhotite only. The obarometry and various sulphide and silicate geothermometers. (1) aluminosilicate diagram after Holdaway (1971) TABLE 3 (I') aluminosilicate diagram after Richardson et al. (1969) Garnet-biotite and garnet-cordierite geothermometry (2) sphalerite geobarometer (3) sphalerite-galena sulphur isotope geothermometer (4) garnet-biotite geothermometer (average of all samples in Table 3, except Temperature estimates (0 C) sample 22347, using the calibration of Ferry and Spear (1978) for P = 3.5 kbar). Sample (5) garnet-cordierite geothermometer no. Ko 2 3 (6) arsenopyrite geothermometer (7) chalcopyrite-pyrite sulphur isotope geothermometer Garnet-biotile geothermometry (8) The shaded area represents the stability field of staurolite + quartz 5l7-133t 7.556 493 484 528 478 (Bickle and Archibald, 1984) 517-148t 7.711 489 503 517-149t 9.678 444 423 468 517-2870t 7.104 507 401 506 517-004t 7.360 499 491 510 Garnet-biotite geothermometry 517-024t 7.536 494 485 507 517-049t 7.751 488 477 497 The garnet-biotite geothermometer has been applied to eight­ 517-055t 7.335 501 493 509 een new pelitic and semipelitic samples from the Kanmantoo mine 517-057t 7.525 496 487 502 and to seven samples from 6.5 km northeast of Dawsley using 517-112t 7.008 510 505 532 Fleming's (1973) distribution coefficients for Fe and Mg between 517-163t 5.677 563 575 616 garnet and biotite in seven pelitic and semipelitic rocks (Table 517-177t 7.354 499 491 520 3). Note that analyses of garnet from Kanmantoo were obtained 517-059t 7.590 493 483 503 from rims rather than centres. We have chosen to use the calibra­ 517-060t 8.318 473 459 476 517-061t 7.910 484 472 495 tions of Thompson (1976), Ferry and Spear (1978), and Pigage 5 I 7-076t 7.702 489 479 508 and Greenwood (1982). At Kanmantoo, average temperatures of 517-077t 7.548 494 485 504 495°C, 485°C, and 510°C are obtained using calibrations of 517-203t 7.881 485 473 497 Thompson, (1976) Ferry and Spear (1978) at 3.5 kbars, and Pigage 22336• 9.667 440 424 460 and Greenwood (1982) at 3.5 kbars respectively (Table 3). At 22338• 6.712 525 519 578 Dawesley, average temperatures of 511 °C, 509°C, and 564°C are 22339• 6.327 535 536 606 obtained using the same geothermometers. Sample 22347 from 22342• 6.736 518 520 545 Dawesley was not included because it yielded apparently high tem­ 22346• 6.457 530 532 608 peratures. For comparison, Mancktelow (1979) obtained temper­ 22347• 3.289 804 807 879 22348• 6.690 519 521 atures of 500°C and 483°C for one sample from Wheal Ellen 588 K mine using the calibrations of Thompson (1976) and Ferry and 0 = (Fe/Mg)bio/(Fe/Mg)101 Spear (1982), respectively. Compositions determined by Flem­ Garnet-cordierite geothermometry ing (1973) were obtained by x-ray fluorescent spectrography, 501-!0lt 12.349 525 flame photometry and atomic absorption spectrophotometry tech­ 517-055t 13.201 511 niques and those on Kanmantoo mine samples were obtained K = (Fe/Mg)bio/(Fe/Mg)crd utilising the University of Melbourne's JEOL electron 0 microprobe. The temperatures obtained on garnet-biotite pairs are minima because of compositional zoning in garnets observed tKartmantoo mine, analyses determined utilizing an ARL-EMX electron microprobe at the University of Melbourne; in rocks within the Kanmantoo Group including the cordierite­ tWheal Ellen mine, analyses determined by N. Mancktelow utilizing an anthophyllite rock analysed by Mancktelow (1979) from Wheal Elec Autoprobe at the Australian National University; Ellen. Garnet in this rock shows a decrease in Ca with a cor­ •oawesley (after Fleming, 1973); calibration from I. Thompson (1976), responding increase in Fe from core to rim. Increases in Mn and 2. Ferry and Spear (1978) using P = 3.5 kb, and 3. Pigage and Green­ decreases in Fe have been reported from Kanmantoo mine (Lindq- wood (1982) using P = 3.5 kb.

62 The AuslMM Bulletin and Proceedings, Vol. 293, No. 1, February 1988 MINERALISATION IN THE KANMANTOO GROUP

TABLE 4 Chemical composition of sphalerite

Sample Mole "lo FeS Wt. "lo Wt. "lo Wt. "lo Wt. "lo Wt. "lo Total Location No. in sphalerite Zn Fe Cd Mn s WT. o/o

Wheal Ellen 501-035t 15.4 57.1 9.0 0.0 0.6 33.0 99.8 Wheal Ellen 501-036t 15.1 57.7 8.8 0.0 0.3 32.8 99.6 Wheal Ellen 501-037t 15.2 57.6 8.9 0.0 0.3 32.9 99.7 Wheal Ellen 501-038t 15.4 57.6 9.0 0.2 0.3 32.7 99.8 Wheal Ellen 501-06lt 15.2 57.6 8.9 0.2 0.3 32.9 99.9 Wheal Ellen 501-064t 15.2 57.7 8.8 0.0 0.3 33.0 99.8 Wheal Ellen 501-1 l0t 15.1 57.5 8.8 0.0 0.2 32.8 99.8 Aclare Acl-OOlt 15.2 57.4 8.8 0.2 0.3 34.0 100.7 Shephard Hill Sl-1 • 15.3 55.1 9.0 0.2 2.3 Shephard Hill Sl-1 • 15.1 55.0 8.8 0.2 2.5

tAnalyses determined using a JOEL electron microprobe at the Australian Mineral Development Laboratory, Fr,wville, with elemen­ tal standards and an ARL-EMX electron microprobe at the University of Toronto with synthetic chalcopyrite, sphalerite, CdS, and MnS as standards. composition of sphalerite coexistin&_ with hexagonal pyrrhotite shears do not appear to have mobilised and localised ore bodies and pyrite was measured by Skinner (1958) for two samples from at Wheal Ellen and Strathalbyn as was envisaged by Parker the Nairne Pyrite deposit at Shephard Hill and the data are in­ (1986). A 2.5 m wide shear extends 50 m between the Middle Air cluded in Table 4 along with data from the present study. The and Spence Shafts at Wheal Ellen; however, there is no surface average mole percent FeS in sphalerite for each of the three lo­ expression of the shear beyond this distance. No shear zones were calities (Wheal Ellen mine, Aclare mine and Nairne Pyrite deposit) observed by us at Strathalbyn. is 15.2. Using equation 1 of Hutchison and Scott (1981), this yields Lambert et al. (1987) in citing the work of Parker (1986) a pressure of 4.1(±0.3) kb. claimed there was no firm evidence that the mineralisation at Kan­ mantoo preceded deformation and that it was possibly formed Arsenopyrite geothermometry in favourable structural and lithological sites during the Delamerian Orogeny. However, Seccombe et al. ( 1985) have X-ray analyses of two grains from a galena-sphalerite­ shown that the Kanmantoo mineralisation and associated alter­ tetrahedrite-arsenopyrite-pyrrhotite-secondary pyrite sample from ation zone were deformed by F, and subjected to the amphibolite­ the Aclare mine yielded values of 33.20 atomic percent As which grade metamorphic event. Banding between chalcopyrite and pyr- corresponds to a temperature of 500°C (Kretschmar and Scott, 1976). This temperature should be considered a minimum tem­ perature due to recent experimental and theoretical work of Sharp et al. (1985), who supported the views of Clark (1960), that the arsenic content of arsenopyrite is also pressure dependent.

Sulphur isotope geothermometry A detailed sulphur isotopic study of base metal mineralisation in the Kanmantoo Group was recently completed (Seccombe et al., 1985) and thirty-four coexisting sulphide mineral pairs were analysed isotopically as a test of equilibrium and the applicabil­ ity of the sulphur isotope geothermometer. The important con­ clusion from their study was that isotopic equilibrium is rarely achieved, although four pyrite-chalcopyrite pairs give a range from 476° to 786° (average 680°C), using recommended frac­ tionation factors of Ohmoto and Rye (1979). Such a range is con­ sistent with large errors involved in using this pair ( + 250°, - 170°) at a temperature of 600°C. Two sphalerite-galena pairs at Wheal Ellen mine give temperatures of 379°C with an error of ± 60°C F10. 6a-Massive chalcopyrite (C) with bands of pyrrhotite (P) produced at 380°C and may have reequilibriated below this peak. during deformation of Kanmantoo orebody.

DISCUSSION In a regional study of copper deposits in South Australia, Lam­ bert et al. (1987) proposed that mineralisation in the Kanman­ too Trough was related to a north-south trending lineament. Lambert et al. (Fig. 6, p. 119) suggested that this lineament passed through the Kanmantoo and Kapunda deposits. Although not stated by these workers, it is significant that this trend is parallel to, but 7km west of, the extensive Bremer Fault. This fault, which also parallels the axial plane of F1 folds in the Kanmantoo Group near Kanmantoo, extends for over 100 km in a north-south direc­ tion. Despite this feature, none of the other deposits in the Kan­ mantoo Trough appears to show any spatial association with· major lineaments or shears. Field evidence to support a northwest­ trending zone from Bremer mine through Kanmantoo mine to Brukunga (Thomson, 1965) was not obtained in this study. Although minor shears produced during F, appear to have been Flo. 6b-Massive·sphalerite-galena ore from Wheal Ellen mine; note the important in localising ore-bearing fluids of Aclare and Bremer, euhedral porphyroblasts of pyrite in the sample on the left.

The AuslMM Bulletin and Proceedings, Vol. 293, No. 1, February 1988 63 P. G. SPRY, J. C. SCHILLER AND R. A. BOTH

TABLE 5 and fibrolite between Kanmantoo and Strathalbyn and rare oc­ Representative gahnite analyses• currences of kyanite at Shephard Hill and north of Wheal Ellen suggest conditions close to the aluminosilicate triple point. Using the stability of the assemblage staurolite-quartz and assuming con­ 2 3 ditions close to the andalusite-sillimanite boundary, temperatures MgO 2.66 1.70 2. 10 between 530° and 630°C and pressures between 2.2 and 5.4 kb AI,O, 56.21 58.70 56.76 are obtained. Further agreement was found in the temperatures SiO, 0.01 0.o7 0.32 of 495°-565°C, 511 °-525°C and 500°C derived from garnet­

TiO1 0.00 0.04 0.00 biotite, garnet-cordierite and arsenopyrite geothermometry, even MnO 0.35 0.18 0.30 though they should be considered minima, and a pressure of 4.1 FeOt 7.27 9.49 7.11 ( ± 0.3) kb from sphalerite geobarometry is in good agreement ZnO 33.11 29.94 33.58 with silicate stabilities. Temperatures derived from pyrite­ Total 99.61 100.12 100. 17 chalcopyrite sulphur isotope thermometry (average 680°C) should Number of atoms in formula (oxygen basis 24) be treated with caution. Two temperatures of 379°C as obtained Mg 0.710 0.527 0.553 from sphalerite-galena sulphur isotope geothermometry are low Al 11.846 12.106 11.614 compared to silicate stabilities and .may be attributed to a lack Si 0.002 0.012 0.056 of quenching in the sphalerite-galena system. Ti 0.000 0.005 0.000 Two deformations (D, and D.) followed the peak metamorphic Mn 0.054 0.026 0.043 episode and produced nonpenetrative crenulation cleavages. D, Fe 1.086 1.388 1.032 followed late in the history and produced kinking, faulting and Zn 4.370 3.867 4.305 Total 18.068 17.931 17.601 minor shearing.

I. 532-801 Wheal Ellen mine; 2. PGS-58 St. Ives mine; 3. RI0557 Strathal­ REFERENCES byn mine. *Determined using an ARL-EMX electron microprobe (University of Askins, P. W., 1968. Geochemical exploration around the Aclare Mine Toronto) utilizing natural and synthetic spinel standards. and mineral deposits of the surrounding region. B.Sc. (Hons.) thesis tFe content measured as FeO. (unpubl.), Univ. Adelaide. Bell, T. H., I 985. Deformation partitioning and porphyroblast rotation in metamorphic rocks: a radical reinterpretation. J. Metam. Geo!., rhotite at Kanmantoo (Fig. 6a) is clearly the product of 3:109-118. deformation. Bell, T. H., 1986. Foliation development and refraction in metamorphic Parker (1986) suggested that there is a common association of rocks: reactivation of earlier foliations and decrenulations due to shift-· mineralisation with the intersection of pyritic sedimentary ing patterns of deformation partitioning. J. Metam. Geo/., 4:421-444. horizons and fracture zones. Despite this suggestion, there is no Bell, T. H., Rubenach, M. J. and Fleming, P. D., 1986. Porphyroblast field evidence to support it. Sulphur isotope studies by Seccombe nucleation, growth and dissolution in regional metamorphic rocks as et al. (I 985) suggest that there is a genetic relationship between a function of deformation partitioning. J. Metam. Geo(., 4:37-67. the pyritic sedimentary horizons rather than a structural relation­ Bickle, M. J. and Archibald, N. J., 1984. Chloritoid and staurolite sta­ bility: implications for metamorphism in the Archean Yilgarn Block, ship. It is believed by them that sulphur within the base metal Western Australia. J. Metam. Geo/., 2:179-203. mineralisation was partially derived from the pyritic schists. Base Clark, L.A., 1960: The Fe-As-S system:variations of arsenopyrite com­ metal mineralisation could be accounted for by subsurface position as a function of T and P. Carnegie Inst. Wash., Yearb., (copper) and sea-floor (lead-zinc) accumulations from hydrother­ 59:127-130. mal fluids circulating to or expelled from depths of at least 3 to Daily, B. and Milnes, A. R., 1972. Revision of the stratigraphic nomen­ 4 km within the Kanmantoo Trough. Sites of upwelling may have clature for the Cambrian Kanmantoo Group, South Australia. J. Geo/. been partially controlled by the tectonic lineaments in the un­ Soc. Aust., 19: 197-202. derlying basement. Daily, B. and Milnes, A. R., t973. Stratigraphy, structure and metamor­ The metamorphism of the base metal deposits is reflected by phism of the Kanmantoo Group (Cambrian) in its type sections east of Tunkalilla Beach, South Australia. Trans. Roy. Coe. S. Aust., the coarse nature of the sulphides, the development of euhedral 97:213-242. porphyroblasts of pyrite (Fig. 6b) and arsenopyrite, the equilibra­ Ferry, J. M. and Spear, F. S., r978. Experimental calibration of the par­ tion of sphalerite and arsenopyrite with iron sulphides that have titioning of Fe and Mg between biotite and garnet. Cont rib. Mineral. compositions consistent with peak metamorphic conditions and Petrol., 66: 113-11 7. the development of gahnite in the Strathalbyn (Fig. 3d), Wheal Fleming, P. D., I 973 . Mg-Fe distribution between coexisting garnet and Ellen, and St Ives deposits. Gahnite is commonly found in biotite, and the status of fibrolite in the andalusite-staurolite zone metamorphosed base metal deposits elsewhere in the world. The of the Mt. Lofty Ranges, South Australia. Mineral. Mag., 109:477-482. composition of gahnite (Table 5) is typical of zincian spine! that Flint, D. J. and O'Grady, A. E., 1979. Structural geology of the Kan­ has formed by the desulphidation of sphalerite during metamor­ mantoo Group sediments between West Bay and Breakneck River. Trans. Roy. Soc. S. Aust., 103, 45-56. phism (Spry and Scott, 1986). Grasso, R. and McManus, J. B., 1954. The geology of the Callington area. B.Sc. (Hons.) thesis {unpubl.), Univ Adelaide. SUMMARY Holdaway, M. J., 1971. Stability of andalusite and the aluminium sili­ Three types of mineralisation (copper.lead-zinc and pyrite­ cate phase diagram. Am. J. Sci., 271:97-131. Holdaway, M. J and Lee, S. M ., 1977. Fe-Mg cordierite stability in high­ pyrrhotite) are contained within a group of metasediments that grade pelitic rocks based on experimental, theoretical, and natural were originally a greywacke-shale sequence with flysch-like observations. Coritrib. Mineral, Petrol., 63:175-193. characteristics in the Kanmantoo-Strathalbyn area. These sedi­ Hutchison, M. N. and Scott, S. D., 1981. Sphaleritc geobarometry in ments were involved in five deformation episodes and appear to the Cu-Fe-Zn-S system. Econ. Geo/., 76:143-1 53. have the following metamorphic histories. Sediments reached Jensen, M. L. and Whittle, A. W. G., 1969. Sulphur isotopes of the Nairne middle amphibolite grade of metamorphism during the early pyrite deposit, South Australia. Mineral. Deposita, 4:241-247. stages of the Delamerian Orogeny as shown by the presence of• Kleeman, A. W. and Skinner, B. J., 1958. The Kanmantoo Group in pre-S2 andalusites. An internal S, fabric in pre-S2 andalusites is the Strathalbyn-Harrogate Region, South Australia. Trans. Roy. Soc. discordant to the external S2 fabric and is evidence of a defor­ S. Aust., 82:61-71. mation prior to that producing the dominant schistosity. Peak Kretschmar, U. and Scott, S. D., 1976. Phase relations involving ar­ senopyrite in the system Fe-As-S and their application. Can. Mineral., metamorphic conditions apparently were reached during and just /4:364-386. after the production of S, as shown by the development of syn-S, Lambert, I. B., Knutson, J., Donnelly, T. H. and Etminan, H., 1987. andalusite, staurolite, garnet, cordierite and fibrolite and post-S, Stuart Shelf-Adelaide geosyncline copper province. Econ. Geo(., andalusite and garnet. The widespread occurrence of andalusite 82:108-123 .

64 The AuslMM Bulletin and Proceedings, VOi. 293. Na. 1, February 1988 MINERALISATION IN THE KANMANTOO GROUP

Lindqvist, W. F. L., 1969. Geology and metamorphic history of the Kan­ Salje, E., 1986. Heat capacities and entropies of andalusite and sillimanite: mantoo copper deposit, South Australia. Ph.D thesis (unpubl.), Univ. the influence of fibrolitization on the phase diagram of the Al,SiO, London. polymorphs. Am. Mineral., 7/:1366-1371. Mancktelow, N. W., 1979. The structure and metamorphism of the Seccombe, P. K., Spry, P. G., Both, R. A., Jones, M. T. and Schiller, southern Adelaide Fold Belt. Ph.D thesis (unpubl.), Univ Adelaide. J.C., 1985. Base metal mineralisation in the Kanmantoo Group, South Marlow, P. C., 1975. Structural investigations of the Kanmantoo Group Australia: a regional sulfur isotope study. Econ. Geo/., 80,:1824-1841. metasediments near Macclesfield, South Australia. M.Sc. thesis Sharp, Z. D., Essene, E. J. and Kelly, W. C., 1985. A re-examination (unpubl.), Univ. Adelaide. of the arsenopyrite geothermometer: Pressure considerations and ap­ Mirams, R. C., 1962. The geology of the Mount Barker-Callington area. plications to natural assemblages. Can. Mineral., 23:517-534. S. Aust. Dep. Mines Rev., 117:9-16. Skinner, B. J ., 1958. The geology and metamorphism of the Naime Pyritic Offler, R., 1960. The structure, petrology and stratigraphy of the Strathal­ Formation, a sedimentary sulphide deposit in South Australia. Econ. byn Anticline, South Australia. B.Sc. (Hons.) thesis (unpubl.), Univ. Geo/., 53:546-562. Adelaide. Sprigg, R. C. and Campana, B.B. 1953. The age and facies of the Kan­ Offler, R., 1963. Structural geology of the Strathalbyn Anticline, South mantoo Group. J. Geo/. Soc. Aust., 16: 12-14. Australia. Trans. Roy. Soc. S. Aust., 87:199-208. Spry, P. G., 1976. Base metal mineralization in the Kanmantoo Group, Offler, R. and Fleming, P.D., 1968. A synthesis of folding and metamor­ S.A.: The South Hill, Bremer and Wheal Ellen areas. B.Sc. (Hons.) phism in the Mt. Lofty Ranges, South Australia. J. Geo/. Soc. Aust., thesis (unpubl.), Univ. Adelaide. /5:245-266. Spry, P. G. and Scott, S. D., 1986. The stability of zincian spinels in Ohmoto, H. and Rye, R. 0., 1979. Isotopes of sulfur and carbon, in sulfide systems and their potential as exploration guides for metamor­ Barnes, H. L. ( ed.), Geochemistry of Hydrothermal Ore Deposits. phosed massive sulfide deposits. Econ. Geo/., 81:1446-1463. 2nd edn. pp. 509-567 (John Wiley and Sons: New York). Thompson, A. B. , 1976. Mineral reactions in pelitic rocks: 11. Calcula­ Parker, A. J., 1986. Tectonic development and mctallogeny of the Kan­ tion of some P-T-X(Fe-Mg) phase relations. Am. J. Sci., 276:425-445. mantoo Trough in South Australia. Ore Geology Reviews, /:203-212. Thompson, B. P., 1975. Kanrnantoo Trough-regional geology and com­ Pigage, L. C. and Greenwood, H .J. 1982. Internally consistent estimates ments on mineralisation, in Knight, C. L. (ed.) Economic Geology of pressure and temperature: the staurolite problem. Am. J. Sci., ofAustralia and Papua new Guinea-I. Metals. pp. 555-560, 5 (Aus­ 282:943-969. tralas. Inst. Min. Metall., Monogr). Poole, L. E., 1969. The structural geology of an area south of Kanman­ Tracy, R. J., 1982. Comppsitional zoning and inclusions in metamorphic too, South Australia. B.Sc. (Hons.) thesis (unpubl.), Univ. Adelaide. minerals, in Ferry, J. M. (ed.) Characterization of Metamorphism Ramsay, J.G., 1967. Folding and Fracturing of Rocks. (McGraw-Hill: through Mineral Equilibria. Reviews in Mineralogy. pp. 357-397, 10 New York). (Mineral. Soc. Arn.) Richardson, S. W., Gilbert, M. C. and Bell, P . M., 1969. Experimental Verwoerd, P. J. and Cleghorn, J. H., 1975. Kanmantoo copper orebody, determination of kyanite-andalusite and andalusite-sillimanite in Knight, C. L. (ed.) Economic Geology ofAustralia and Papua New equilibria: the aluminium silicate triple point. Am. J. Sci., 267:259-272. Guinea. pp. 560-565, 5 (Australas. Inst. Min. Metall., Monogr).

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