Issuu

Geological Society of Australia

ABSTRACTS Number

Insights into volcanic processes, mantle sampling | and gems Specialist Group in Geochemistry, Mineralogy and Petrology Central Victoria September -

October 2003

Geological Society of Australia

ABSTRACTS Number 71

Insights into volcanic processes^ mantle sampling and gems Editor: Ian Graham

Specialist Group in Geochemistry, Mineralogy and Petrology Central Victoria September - October, 2003

Produced by Ian Graham Geodiversity Research Centre Australian Museum 6 College Street, Sydney NSW 2010

September 2003

ISSN 0729 01IX

TABLE OF CONTENTS Page Cohen, B.E., Vasconcelos, P.M., and Knesel, K.M. Tracking Oligocene Volcanism across Southeast Queensland.

Green, M.G. An integrated geochemical and geochronological study of the Tanami granites: a suite approach to Palaeo-Proterozoic evolution.

Mollis, J.D., and Pogson, R.E. Former hydrothermal systems in Victoria's Spa Country: some surprises?

Joyce, E.B. The young volcanic province of southeastern Australia: physical volcanology and eruption risk.

Pandit, M.K. Neoproterozoic crustal evolution of the NW Indian craton: clues from acid magmatic events.

Pandit, M.K., and Shekhowat, L.S. Geochemistry of metabasic volcanics from Aravalli Supergroup in NW India: implications on tectonic evolution of a Palaeo-Proterozoic rift basin.

Sutherland, F.L., Schwarz, D., and Webb, G. Basaltic gem fields, eakem Australia: Sapphire-ruby characteristics and connections.

Tracking Oligocene Volcanism across Southeast Queensland Benjamin Eric Cohen*, Paulo Marcos Vasconcelos, and Kurt Michael Knesel Department of Earth Sciences, University of Queensland St Lucia 4072 •Email: b.cohen@niai]box.uq.edu,au

Introduction Evaluation of proposed models for the origin of Cenozoic intraplate magmatism in eastern Australia requires knowledge of the distribution of volcanism in space and time. K-Ar dating, chiefly on whole-rock samples, have yielded disperse results, where individual bimodal volcanic centres and basaltic lava fields display age ranges of up to 15 million years (Duncan and McDougall, 1989).

This dispersion may reflect in part

inaccurate ages due to inherited Ar, K loss, or Ar loss during weathering or devitrification. Therefore, uncertainty regarding the accuracy and precision of the K-Ar ages precludes confident deduction of the duration and temporal sequences of volcanic activity in eastern Australia. For example, a plot of K-Ar age with latitude for southeast Queensland has a large scatter, and a barely discemable southward age progression with latitude (Figure 1). To improve our knowledge of the age of these rocks, we have applied the ^ W W method to a bimodal suite of extrusive and intrusive igneous rocks from - 28^S in southeastern Queensland (Figures 2, 3) previously dated by the K-Ar technique (Figure 1). Most samples were analysed by laser incremental-heating of either mineral separates or whole-rocks, except for sanidine mineral separates, which were analysed by laser total fusion. Details of analytical methods and full results will be reported in Cohen et al (in prep.). Representative results are shown in Figure 4. Most samples yielded plateaus containing more than 50% of the ^Âr released, with no evidence of Ar or K losses due to weathering. However, some of the step-heating results show older ages for the lowtemperature steps, possibly revealing the presence of excess ^Âr or partial ^Âr recoil loss from poorly crystalline or devitrified sites during neutron bombardment.

45 40

•

Figure 1: K-Ar age versus latitude for locations 1-5 in figure 3. Data from: Webb et al (1967), Green & Webb (1974), Green & Stevens (1975), Evans (1976), Murray et al (1980), Ewart (1982), Messenger (1986), and A. Ewart pers. comm. (2002).

y = -0.78X + 4 7 . 5 9 R2 = 0 . 0 2

a> §> 3 0

•1

20 15

. 25.0

26.0

27.0

28.0

Latitude

Figure 2

^igurg 3

Figure 2: Distribution of Cainozoic volcanic rocks in eastern Australia, after Johnson (1989), with the location of the study area. Figure 3: Detailed map of southeast Queensland, with the study locations of: (1) Eraser Island, (2) Noosa area, (3) Maleny, (4) Glasshouse Mountains, and (5) Flinders Peak. Numbers 6, 7, and 8 represent the large-volume volcanic centres in southeast Queensland of the Tweed Shield Volcano, Main Range, and the Bunya Mountains, respectively.

step-Heating Spectrum for Q74 (anorthoclase, Mt Blaine) a: 40-

Age Probability Plot for Q74 (anorthoclase, Mt Blaine)

(a)

0.1 »

25.9 ± 0.3 Ma* -

Integrated Age-27.95 ±0.20 Ma

Cumulative % ^^Ar Released

Age (Ma)

Step-Heating Spectrum for Q29 (whole-rock comendite, Mt Coolum) 80^

Age Probability Plot for Q68 (sanidine, Mt Ngungun) :

( d )

/ 26.76

• = 20

I,. i2 o

i Integrated Age - 27.81 ±0.07 Ma

1 ^

Cumulative % ^^Ar Released

26.79 ±0.17 30

Age (Ma)

Figure 4: (a) Step-heating spectrum for an anorthoclase grain from a metaluminous trachyte, with high % radiogenic argon, and low-temperature steps with older ages representing trapped argon, (b) Age-probability plot for the same sample with a well-defined maximum at 25.67 Ma, within error of the plateau age. There is also a smaller peak at 28.93 Ma representing trapped argon, (c) Step-heating spectrum for a whole-rock comendite with high % radiogenic argon and K/Ca ratios, and a near-ideal step-heating spectrum, (d) Age-probability plot for sanidine from a comendite. The outlier at ~ 44 Ma with a large error represents a grain that did not fuse during laser heating.

Silicic activity occurred over a relatively short period of time (29.5 - 27.5 Ma around Noosa, and 27.5 - 26.5 Ma in the Glasshouse Mountains). Mafic volcanic activity occurred at least as early as 30 Ma; the full range of mafic activity will be known when analyses of the stratigraphically highest and lowest flows are completed. These age relationships are consistent with petrologic and geochemical evidence indicating that

most of the silicic magmas are derived from mafic parents via fractional crystallisation (Ewart, 1982; Cohen, 2002). ^^Av/^^Av dating also confirmed an Oligocene age for two previously undated intrusions of peraluminous

rhyolite. These rhyolites have

geochemical signatures indicating an origin by crustal melting, rather than crystal fractionation from a basaltic parent (Ewart, 1982; Ewart et al, 1985; Cohen, 2002), and suggest that the influx of mantle-derived magma during the Oligocene was locally intense enough to melt the crust.

Our ^Âr/^Âr results show a clear age progression with latitude (R^ of 0.8, Figure 5a). Seven "^Âr/^Âr ages from the Ebor volcano, 300 km to the south of the study area (Ashley et al, 1995), lie on a very similar regression line, with a substantially better correlation coefficient (R^ of 0.97, Figure 5b). Together these data yield a migration rate for the Australian plate of 51 mm/yr. This estimate is slower than those of Wellman and McDougall (1974) and Duncan and McDougall (1989) of 66 ± 5 and 65 ± 3 mm/yr, respectively, obtained from K-Ar studies of the last 40 million years of east Australian volcanism. Our estimate is, however, consistent with models where the migration rate of the Australian plate has changed throughout the Cainozoic. Some authors suggest that plate migration rates for Australia may have been as low as 53 mm/yr for the period from 43 - 20 Ma, and 51 mm/yr for 10 - 20 Ma, only increasing to <73 mm/yr after 10 Ma (Weissel and Hayes, 1971). Therefore, ^Âr/^Âr analyses for other east AustraHan Cenozoic volcanic provinces may further refine plate migration rates at different times during the Cenozoic.

34 (a)

32 CD

0 < 28

30 •

26 •

t 3 3 M y = -2.2x + 85.7 R2 = 0.8

I 1

24 25

l \ J

Latitude (degrees south)

5 1

26 y = -2.26x+88.04

R^ = 0.97

1 18

Latitude (degrees south)

Figure 5: ^^Ar/^^Ar age with latitude: (a) for southeast Queensland (this study), and (b) for southeast Queensland (this study) and Ebor volcano (Ashley et al 1995). Numbers are the same as for figure 3.

References Ashley, P.M., Duncan, R.A., and Feebrey, C.A., 1995. Ebor Volcano and Crescent Complex, northeastern New South Wales: age and geological development. Australian Journal of Earth Sciences, 42, 471 -480. Cohen, B.E., 2002. Geochronology and geochemistry of southeast Queensland Tertiary volcanism. B.Sc. (Hons.) thesis (unpublished),University of Queensland, Brisbane. Duncan, R.A., and McDougall, I., 1989. Volcanic time-space relationships. IN: Johnson, R.W., editor, Intraplate Volcanism in Eastern Australia and New Zealand: Cambridge, Cambridge University Press, pp. 43-53. Evans, R., 1976. A study of the basic volcanic rocks of the Maleny-Mapleton area, southeast Queensland. BSc. (Hons) thesis (unpublished). University of Queensland, Brisbane. Ewart, A., 1982. Petrogenesis of the Tertiary anorogenic volcanic series of southern Queensland, Australia, in the light of trace element geochemistry and O, Sr and Pb isotopes. Journal of Petrology, 23, 344-382. Ewart, A., Chappell, B.W., and LeMaitre, R.W., 1985. Aspects of the mineralogy and chemistry of the intermediate-silicic Cainozoic volcanic rocks of eastern Australia. Part 1: introduction and geochemistry. Australian Journal of Earth Sciences, 32, 359-382. Green, D.C., and Stevens, N.C., 1975. Age and stratigraphy of Tertiary volcanic and sedimentary rocks of the Ipswich District, southeast Queensland. Queensland Government Mining Journal, 76, 148-150. Green, D.C., and Webb, A.W., 1974. Geochronology of the northern part of the Tasman Geosyncline. IN: Denmead, A.K., Tweedale, G.W., and Wilson, A.F. (editors). The Tasman Geosyncline - a symposium. Geological Society of Australia Incorporated, Queensland Division, 275-291. Johnson, R.W., 1989. Intraplate Volcanism in Eastern Australia and New Zealand: Cambridge, Cambridge University Press. Messenger, P.R., 1986. Geology and geochemistry of the central Glass House Mountains, southeast Queensland. BSc. (Hons) thesis(unpublished),University of Queensland, Brisbane. Murray, C.G., and 13 others, 1980. Regional Mapping, TN: Queensland Department of Mines Annual Report 1980, 79-82.

Webb, A.W., Stevens, N.C., and McDougall, L, 1967. Isotopic age determination on Tertiary volcanic rocks and intrusives of south-eastern Queensland. Proceedings of the Royal Society of Queensland, 79, 79-92. Weissel, J.K., and Hayes, D.E., 1971. Asymmetric seafloor spreading south of Australia. Nature, 231, 518-522. Wellman, P., and McDougall, L, 1974. Cainozoic igneous activity in eastern Australia. Tectonophysics, 23, 49-65.

An integrated geochemical and geochronological study of the Tanami granites: a suite approach to Palaeoproterozoic evolution Michael G Green Northern Territory Geological Survey PO Box 8760, Alice Springs, NT 0871 Email: michael.green@nt.gov.au

Introduction Interpretation of magnetic and gravity data suggests that more than half of the Palaeoproterozoic basement in the Tanami region, northern Australia, is composed of granite. Poor exposure of the basement, however, has severely hampered geological studies in the area. Herein, the Tanami granites are examined using the suite classification of White et al (2001) to identify petrogenetically related rocks. Coupled with precise geochronological data, the suite approach is used to constrain the persistence and evolution of Palaeoproterozoic tectonic processes in the North Austrahan Craton. White et al (2001) based the suite classification on field, then petrographical and finally geochemical data. In contrast, whole-rock geochemical data were used primarily to classify the Tanami granites and thus incorporate the widest selection of samples from previous studies (159 felsic magmatic samples from Blake 1974, Blake et al 1979, Tunks 1996, Dean 2001). Despite all of the Tanami samples showing some degree of postmagmatic alteration, 83 samples have been interpreted to adequately preserve primary magmatic compositions and have been used here.

The Tanami granites are predominantly monzogranite to granodiorite and have restricted Si02 contents (65 to 77 wt%; 4 samples at 57 to 65 wt%). Seventy-four samples are peraluminous, whereas the other 9 samples are slightly metaluminous. More than half of the samples have >1 % normative corundum, consistent with biotite as the dominant accessory mineral. Hornblende and muscovite are present in the metaluminous and strongly peraluminous samples, respectively. A positive correlation between ASI and Si02 suggests that aluminium enrichment was controlled by fractionation. Most elements define broad linear trends on variation diagrams, which reflect typical magmatic

processes. Hence, CaO, FeO(totai)? P2O5, Ba and Sr were compatible and Na20, K2O and Rb were incompatible. A change of trajectory for Zr reflects a change from incompatible to compatible behaviour. The absence of linear trends for La, Nd and Y reflects their strong control by accessory minerals. Relative to average upper continental crust (UCC), the Tanami granites have flat to moderately steep patterns with a broad range of positive and negative anomalies. Most samples with precise REE measurements have large negative Eu anomalies.

The Tanami granites are divided into The Granites, Frederick and Birthday Suites according to geochemical differences (Table 1). The Birthday Suite is restricted to the northeastern Tanami region, whereas The Granites and Frederick Suites are geographically coincident. Indeed, components of The Granites and Frederick Suites form parts of the same plutons. Each suite defines a discrete fractionation trend for certain crucial elements and has a distinct UCC normalised trace element pattern. However, compositional differences between the Tanami suites are not great and probably reflect subtle variations and combinations of source composition, melting depth and fractionating assemblage. Hence, a general model should sufficiently explain the petrogenesis of the Tanami granites.

Suite Birthday

Major elements highest K2O, FeO(totai) and Ti02 define good P 2 O 5 trend

Trace elements Age (Ma) moderately steep UCC norm 1825-1815 strong negative Sr slight positive Nb, Zr variable Ba strong negative Eu (n = 2) Frederick less K2O than Birthday, flat UCC norm 1815-1787 but more than The strong negative Y moderate positive Th, La, Ce Granites large positive and large most aluminous negative Eu define good P 2 O 5 trend The low K2O, Na20, high CaO low Y, except for D 1821-1791 positive Nb, P, Rb Granites weak to no P 2 O 5 trend variable Sr, can be quite low large positive and large negative Eu Tab le 1: Summary of major geoc lemical differences between suites.

Felsic magmatism in the Tanami region followed deposition of the <1840 Ma Tanami Group and Mount Charles Formation, but preceded deposition of the Pargee Sandstone and Birrundudu Group. Interpretation of precise U-Pb zircon analyses constrains magmatism between 1825 and 1787 Ma (Table 1), with no defined pattern of spatial distribution of ages. In general, the three suites are coeval, and so the petrogenetic processes which formed each suites must have operated concurrently. Moreover, granite emplacement was broadly coincident with regional deformation and peak metamorphism, and thus, this period marked a significant tectonothermal episode in the Palaoproterozoic evolution of the Tanami region.

Most of the Tanami granites contain abundant inherited zircon, including many Archaean grains. Comparison of integrated zircon age spectra of 23 Tanami granites and 4 Killi Killi Formation sediments (uppermost Tanami Group) shows significant overlaps at approximately 1860 and 2500 Ma, but at markedly different relative abundances. It is likely that the Tanami Group contributed some zircon to the magmas by assimilation, but additional contribution of 2500 Ma material is required to explain the relatively high proportion of late Archaean zircon in the granites.

Granite suites with restricted high Si02 contents, such as in the Tanami region, are typically interpreted to have formed by fusion of crustal rocks because extended fractionation of mantle-derived magmas should form a spectrum of samples with much lower Si02 contents. In addition, the presence of abundant inherited zircon has been interpreted in Palaeozoic granites to reflect fusion of pre-existing basement, the source of zircon, at relatively low temperatures (Chappell et al 1998). The trace element behaviour of P, Ce, Y and Th is also remarkably similar to those of low-temperature I-type granite suites (Chappell et al 1998, Chappell 1999). It follows that the Tanami granites probably formed by low-temperature fusion of a pre-existing crust. /

The high ASI values of the Tanami granites suggest a highly aluminous melting source and, in such a case, the Tanami granites may be classified as S-type (Chappell and White

1974). However, there is little evidence to corroborate this classification as aluminous minerals such as garnet, sillimanite, andalusite and cordierite have not been identified in the Tanami granites. Moreover, the metaluminous granites contain modal hornblende and are linked to the peraluminous granites along broad magmatic trends. Therefore, the strongly peraluminous Tanami granites probably formed by extended fractionation. In this case, the Tanami granites are classified as I-type (Chappell and White 1974) and thus were derived from fusion of pre-existing crust which had not been modified by weathering. Crustal fusion can also account for various trace element behaviour, such as Y and Eu depletion. Inherited zircon grains provide further clues about the source rocks as the great abundance of --^2500 Ma inherited zircon cannot be readily attributed to assimilation of Tanami Group sediments alone. Instead, -2500 Ma zircon must have been derived from the melting source, in this instance, extensions of Late Archaean felsic gneisses which outcrop sparsely in the Tanami region (Page et al. 1995).Deciphering the tectonic setting from granitic rocks alone can be problematic because granites are typically mixed rocks with complicated tectonic fingerprints. Nevertheless, Wybom (1988) proposed 5 possible tectonic settings for Australian Palaeoproterozoic granites: • • • • •

highly fractionated mantle-derived melts, a combination of mantle-derived melts, contemporaneous subduction, remelting of a major Lower Proterozoic mafic underplate, and reworking of Archaean crust through partial melting.

The first three of these settings seems unlikely as there is little evidence for mantle contributions to the Tanami granites and there is no spatial or temporal variation of Tanami ages or compositions as expected at subduction zones. Moreover, the interpretation that the Tanami granites were derived from partial fusion of late Archaean felsic gneisses precludes reworking of a mafic underplate. However, further evidence of

the magmatic source, such as radiogenic isotopes, are poorly constrained.

Given that reworking of Archaean crust seems to account for the formation of the Tanami granites, then the Palaeoproterozoic tectonic setting requires a significant heat source. Scrimgeour and Sandiford (1993) show that peak metamorphism was broadly synchronous with deformation and was followed by isobaric cooling. Such a tectonothermal evolution can be explained by crustal thickening due to convergent tectonics, perhaps with the introduction of mantle-derived mafic magmas into the lower crust. Given the unlikelihood of contemporaneous subduction, continent-continent collision is more likely with pronounced thickening of the crust. Following from work in the Lamboo Complex (Halls Creek Orogen), which interprets a northwesterly dipping subduction zone beneath the Kimberley Craton at -1865 Ma (Sheppard et al 1999), the Tanami region can be explained as later inboard deformation recording the collision of Kimberley and North Australian Craton. Such an event is also broadly coeval with mafic magmatism in the Arunta region to the south (Johannsen Metagabbro, Mount Hay and Enbra Granulites, 1812-1805 Ma, Hoatson et al 2002) and so the thermal perturbation may have been widespread.

References Blake DH, 1974. Shallow stratigraphic drilling in The Granites-Tanami region. Northern Territory and Western Australia, 1971-73. Bureau of Mineral Resources Record, 1974/104. Blake DH, Hodgson IM and Muhling PC, 1976. Geology of The Granites-Tanami region. Bureau of Mineral Resources Bulletin, 197. Chappell BW, 1999. Aluminium saturation in I- and S-type granites and the characterisation of fractionated haplogranites. Lithos, 46, 535-551. Chappell BW and White AJR, 1974. Two contrasting granite tj^^es. Pacific Geology, 8, 173-174. Chappell BW, Bryant CJ, Wybom, D, White AJR and Williams IS, 1998. High- and lowtemperature I-type granites. Resource Geology, 48, 225-235.

Dean AA, 2001. Igneous rocks of the Tanami region. Northern Territory Geological Survey Record, GS 2001-0003. Hoatson D, Claoue-Long J and Sun S-s 2002. Event chronology and prospectivity of the mafic magmatic systems in the Arunta province. IN: AGES 2002 Record of Abstracts, Northern Territory Geological Survey Record, 2002-0003. Page R, Sun S-s and Blake D, 1995. Geochronology of an exposed late Archaean basement terrane in The Granites-Tanami region. Australian Geological Survey Organisation Research Newsletter, 22, 19-20. Scrimgeour I and Sandiford M, 1993. Early Proterozoic metamorphism at The Granites gold mine, Northern Territory: implications for the timing of fluid production in hightemperature, low-pressure terranes. Economic Geology, 88, 1099-1113. Sheppard S, Tyler IM, Griffin TJ and Taylor WR, 1999. Palaeoproterozoic subductionrelated and passive margin basalts in the Halls Creek Orogen, northwest Australia. Australian Journal of Earth Sciences, 46, 679-690. Tunks AJ, 1996. Structure and origin of gold mineralisation, Tanami mine, KT, Ph.D thesis (unpublished). Centre for Ore Deposit Research, University of Tasmania, Hobart. White AJR, Allen CM, Beams SD, Carr PF, Champion DC, Chappell BW, Wybom D and Wybom LAI, 2001. Granite suites and supersuites of eastern Australia. Australian Journal of Earth Sciences, 48, 515-530. Wybom LAI, 1988. Petrology, geochemistry and origin of a major Australian 1880-1840 Ma felsic volcano-plutonic suite: a model for intracontinental felsic magma generation. Precambrian Research, 40/41, 37-60.

Former hydrothermal systems in Victoria's Spa Country: some surprises? Julian D Hollis^'^ and Ross E Pogson^ ^ 33 Park Street, Trentham 3458, Victoria 2

Geodiversity Research Centre Australian Museum 6 College Street, Sydney NSW 2010

Introduction Recent volcanic activity in the West-Central highlands of Victoria is indicated by young scoria cones at mounts Buninyong, Franklin and Warrenheip. These are too young to be dated by K-Ar, Rb-Sr or fission-track methods, but are within the range for C^'^ (Oilier and Joyce, 1964). A small crater northeast of Mount Franklin appears to be a very young phreatic centre and may have formed from an eruption witnessed by local aboriginals (Parker, 1854). The region around Daylesford is renowned for its C02-bicarbonate rich mineral springs. These are described by McLaughlin and Macumber (1968), Lawrence (1969), Wishart and Wishart (1990) and Cartwright et al (2002). The springs are 'cold' issuing at ambient groundwater temperatures. However, locally high geotherms have been recorded (Purss and Cull, 2001). The Central Leads United Mine, south of Ullina, attempted to follow the Berry United Lead through a large maar system. A westerly drive at 30 metres depth became so hot that work had to be abandoned, whilst in 1972 a bore for stock water immediately southeast of Mount Kooroocheang encountered warm water ('- 25^C) (Bernard Righetti, property owner, pers.comm.). It would be expected that sporadic hydrothermal activity accompanied volcanism. An initial search for possible sites in the Spa Country and adjacent areas has identified at least 8 locations showing calcareous tufa deposits, hydrothermal breccias and lahaar deposits (Figure 1). Previously, Condon (1951) described hot spring sites in the Werribee Plains, west of Melbourne. However, none have been described from the adjacent highlands where volcanic activity was so extensive over the last 8 million years (Graham eVal, 2003).

Figure 1. Location of probable hydrothermal deposits from the West-Central Highlands.

1. Tufa deposits around existing mineral springs 'Ulrichs Springs' (BU 467 747): Ulrich (1866) recorded a 'small patch of freshwater limestone, its margins consisting of a breccia of slate and quartz cemented by lime', near the head of Limestone Creek, north of Mount Franklin. This is associated with two active mineral water springs. There are five patches of calcareous breccia consisting of matrixsupported ferruginised Ordovician siltstone and slate fragments in a hard concrete-like cement. Irregular cavities are lined with small calcite crystals. The deposits resemble typical tufa systems deposited by recent hot spring and geyser activity. The southern spring is surrounded by partly exposed crusts of grey tufa, suggesting a particularly young age. Mineral water seeps are rich in CO2 and FeCOs but they are 'cold' and not depositing CaCOs. However, they are clearly related to original tufa-depositing systems. Lime Kilns (BU 461 768): A commercial mineral water spring at 'Lime Kilns', beside the Midland Highway was also mapped by Ulrich in 1866. 'Freshwater limestone' was roasted at this site at the time. The site shows accretionary pale grey rocks resembling tufas, in a basin structure some 50 metres across. This forms a raised flat area above Limestone Creek. On the south and west sides there are tufa breccias, similar to those at Ulrichs Springs, perhaps the result of geyser activity.

Interestingly, there are no carbonate rocks in the Ordovician of this region and the source of the CaCOa may be unusual. We suggest a deep source, probably related to magmatic systems such as carbonatites. Wishart and Wishart (1990) allude to calcium carbonate deposits associated with springs in the Loddon River near Lyonville. A tufa-like limestone showing cone-in-cone structure was figured from the Just-in-Time Mine, Daylesford by Willman et al (2002). 2. Sinter deposits not associated with springs 'North Frenchmans' (BU 469 662): A complex mineralised axial zone in the Ordovician has been worked in the nearby mine. Slopes northwards have been extensively sluiced towards the Hepburn Spa area and expose a channel-fill sheet of leached sinter-breccias up to 0.7 metres thick, overlying Ordovician bedrock. The sinters are grey, moderately compact siliceous claystones that appear to have been deposited from hot springs along the adjacent fracture systems. Rock fragments are angular and unsorted and include small fragments of vegetable carbon. Similar deposits have been described from hydrothermal systems by Laznicka (1988) and Wohletz and Heiken (1992). White Hill, Campbells Creek (BU 519 912): Intensive surface gold workings on the west side of the ridge east of Campbells Creek show veins and 'blows' of clayey, siliceous breccia similar to North Frenchmans. A 0.3 metre thick channel fill of grey clayey sinter is preserved downslope, overlying White Hills Gravel (post-Mesozoic). The site is 2 kilometres SSE of the probable location for a breccia pipe at Diamond Gully, of Newer Volcanics age. 3. Hydrothermal slurry deposits Stony Creek Basin (BU 460 610): Grey silty to sandy clays locally containing highly altered, matrix-supported clasts, form an irregular ridge around the eastern sector of the Stony Creek Basin. The basin is a probable volcano-collapse structure (Macdonald, 1972) and has been described by Hart (1904), Orr (1927) and Coulson (1950). It post-dates nearby basalts, dated near 1.7 Ma (Sniderman et al, 2003) and is occupied by a sequence of carbonaceous claystone. These are overlain by the ridge deposits. Along the east side there are a series of pits to which the deposits appear to be related. We suggest that these were slurries of hydrothermal origin derived from geyser activity that emanated via the peripheral basin fractures. Fission-track ages for zircons from the clays include a significant number of zero results, indicating very recent resetting. In 2002, Monash University excavated black shales for palynological studies. They exposed a v-shaped surface pit widening to 1 metre, filled with a scatter of hard hematitic nodules showing concretionary structure, palagonitic clays, baked shale and inertinite fragments. An elongate fracture or pipe extended downwards containing gray clay with bleached clay fragments. The surrounding black shales have been partly bleached. We suggest that this structure may have been a fumarole or hot spring vent.

Green Gully Lead (BU 533 740): A significant 'blind' lead yielded large gold nuggets. Near its southern termination, blocks of an unusual matrix-supported clastic sediment occur on mine waste heaps. These show quartz-rich sandy-silty clays with angular quartz fragments and carbon flakes. There are also courses and crusts of magnesite and nontronite. The material is closely similar to hydrothermal breccia as seen from the Waimangu 1917 hydrothermal explosions in New Zealand and is clearly not a normal alluvial deposit. This raises the possibility that the gold nuggets have a hydrothermal accretionary origin, otherwise their provenance is inexplicable. Newbury Crater (BU 594 550): An ovoid, flat-bottomed crater some 300 metres across lies on the divide at Kearney's Road, Newbury. It has a low rim of red 'soil' containing sporadic, irregularly oriented fragments to large blocks of local Ordovician and basalt origins. The Ordovician in the adjacent dam is deeply leached to soft clays. The feature is clearly not of direct magmatic origin and we suggest that it may have formed from recent hydrothermal explosive activity. It also lies on a major WNW linear feature that runs from Tullamarine to Evansford, and hosts numerous phreatic and volcanic systems, including the Stony Creek Basin. The lagoon at North Blackwood (BU 655 572) is also a crater, although this appears to be a volcano-collapse structure. There is a low rim of red 'soil' around the west and north sides that may be of hydroclastic origin. 4. Lahar deposits Extensive trenching for the Trentham sewerage scheme in 2001-02 exposed a peculiar red clay-soil cover that appears to be derived from the southwest. Previously mapped as 'basalt', the red clays are not related to basalts in the vicinity of Trentham. They contain zircon and ilmenite showing alluvial abrasion, scattered angular fragments of quartz and sporadic blocks of silcrete conglomerate up to one meter across. The blocks are matrixsupported and some are irregularly oriented. The clays are identical to those seen at the Newbury Crater, suggesting that they were a lahar flow deposit from that source. Small relics of similar deposits occur south of Newbury, also showing heavy minerals identical to those of the Newbury Crater. The mineralogy of the various hydrothermal systems described above is presented in Table 1. It is likely that many more sites of hydrothermal activity will be identified in this region of Victoria.

Table 1. Relative mineral abundances from probable hydrothermal rocks, West-Central Victoria (XRD analysis, Australian Museum). Sample N.o Qtz la lb 2 3a 3b 4 . 5 6 7

Illite

Kaolinite

CalciteAlbite Montmorillonite

-f-

• •

•

-f

4+ +

•

-f +

+ •

•

+ + 4+

G Goethite

+ + •

+ +

Key: • = major, • = moderate, + = minor,. = not detected Localities la Stony Creek Basin, Daylesford: grey clay with soft clasts from probable hydrothermal explosion deposits. lb Stony Creek Basin, Daylesford: brown clay with baked shale clasts from probable fiimarole system. 2 'Ulrichs Springs', head of Limestone Creek: tufa deposits around existing springs, now cold. 3a Lime Kilns, Limestone Creek: tufa-breccia resembling a geyser deposit. 3b Lime Kilns, Limestone Creek: limestone from probable thermal lake. 4 White Hill, Campbells Creek: grey siliceous sinter downslope from former hot springs. 5 Parwan Crater, Mouyong: layered tufa with fragments of basalt from side of volcanocollapse system. 6 North Frenchman's, Hepburn Springs: grey clay-sinter breccia with leached countryrock fragments. 7 Base of Trentham Falls: grey clay from beneath 5.7 Ma mugearite flow. A lahar or ash deposit.

Acknowledgment We would particularly like to thank Rod Kirby for his observations and fieldwork support.

References Cartwright, L, Weaver, T., Tweed, S., Aheame, D., Cooper, M., Czapnik, K., and Tranter, J., 2002. Stable isotope geochemistry of cold C02-bearing mineral spring waters, Daylesford, Victoria, Australia: sources of gas and water and links with waning volcanism. Chemical Geology, 185, 71-91. Condon, M.A., 1951. The geology of the lower Werribee River, Victoria. Proceedings of the Royal Society of Victoria, 63, 1-24. Coulson, A.L., 1950. The origin of the Stony Creek Basin, Daylesford, Victoria. Proceedings of the Royal Society of Victoria, 60, 156-162. Graham, I.T., Hollis, J.D., Sutherland, F.L., and Joyce, E.B., 2003. Insights into the Newer Volcanics Province of Victoria, Specialist Group in Geochemistry, Mineralogy and Petrology Field Guide, Geological Society of Australia. Hart, T.S., 1904. Note on the Stony Creek Basin, Daylesford. Proceedings of the Royal Society of Victoria (New series), 17, 366-370. Lawrence, C.R., 1969. Hydrogeology of the Daylesford Mineral District with special reference to the mineral springs. Geological Survey of Victoria, underground water investigation, Report 12, Melbourne. Laznicka, P., 1988. Breccias and coarse fragmentites. Petrology, environments, associations, ores. Developments in Economic Geology, 25, Elsevier. Macdonald, G.A., 1972. Volcanoes, Prentice-Hall, pp. 510. McLaughlin, R.J.W., and Macumber, J.J., 1968. Mineral springs of the Daylesford district. Proceedings of the Royal Society of Victoria, 81, 143-148. Oilier, C.D., and Joyce, E.B., 1964. Volcanic physiography of the western plains of Victoria. Proceedings of the Royal Society of Victoria, 77, 357-376. Orr, D., 1927. The Stony Creek Basin and the Corinella Dyke. Proceedings of the Royal Society of Victoria, 40, 26-33. Parker, E.S., 1854. Letter to the Royal Society of New South Wales. Royal Society of New South Wales archives, Sydney. Purss, M.J.B., and Cull, J., 2001. Heatflow data in western Victoria. Australian Journal of Earth Sciences, 48, 1-4. Sniderman, J.M.K., O'Sullivan, P.B., Hollis, J.D., and Kershaw, A.P., 2003. Late Pliocene vegetation and climate change in the Western uplands of Victoria, Australia. Proceedings of the Royal Society of Victoria, in press.

Ulrich, G.H.F., 1866. Geological Survey of Victoria Quarter Sheet No 15SE. Willman, C.E., Bibby, L.M., Radojkovic, A.M., Maher, S., Haydon, S.J., Hollis, J.D., and Osborne, C.R., 2002. Castlemaine 1: 100 000 map area geological report. Geological Survey of Victoria, Report 121. Department of Natural Resources and Environment, Victoria, pp. 170. Wishart, E., and Wishart, M., 1990. The Spa Country: A field guide to 65 mineral springs in the Central Highlands, Victoria. Spa Publishing, Daylesford, pp. 192. Wohletz, K., and Heiken, G., 1992. Volcanology and Geothermal Energy, University of California Press, pp. 432.

The young volcanic province of southeastern Australia: physical volcanology and eruption risk Bernard Joyce School of Earth Science The University of Melbourne Vic 3010

Introduction The Newer Volcanic province can be divided into three main sub-provinces. The Western Plains sub-province and the Mt Gambier sub-province in southeastern South Australia is a broad plain, while the Western Uplands sub-province forms the elevated east-west spine of Western Victoria, with the Great Divide running along its crest. About 5 Ma both the Uplands and the Plains gave birth to a new volcanic province, and nearly 400 small, monogenetic, Strombolian/Hawaiian scoria cones, maars and lava shields have been built up, with fluid basalt flows spreading laterally around vents, and often southwards for many kilometres down stream valleys. Where the lava has blocked drainage, lakes and swamps have formed, and on the plateau-like flow surfaces collapse depressions have produced further lakes and swamps.

The Western Plains subprovince The Western Plains consist of a major volcanic plain, often called the Western District Volcanic Plains, and a generally level coastal plain. The latter is a depositional surface left by the final retreat of a series of Tertiary-Quaternary transgressions, and later modified by fluvial and aeolian erosion and deposition. This depositional surface also underlies the Volcanic Plains. The Western District Volcanic Plains are generally less than 200 m in elevation and form the major portion of the Newer Volcanic Province of southeastern Australia, which extends northwards into the Western Uplands. This total province consists of 15 000 km^ of thin lava flows and small ash deposits with nearly 200 scoria cones (commonest in the Western Uplands) and about 200 lava volcanoes, mostly on the northern part of the Western Plains (Oilier and Joyce 1964; Joyce 1975). There are also about forty maars, concentrated on the southern edge of the plains, along with the youngest scoria cones, over the axis of the underlying Tertiary basin (Oilier and Joyce, 1964). Mt Elephant, near the centre of the plains, is the highest volcano. It rises a striking 240 m above the plains to an elevation of 393 m, with a crater 90 m deep, and is comparable in size to Mt Kooroocheang, the highest volcano in the Western Uplands. The youngest lava flows form 'stony rises' with a characteristic relief of up to 20 m. They have sharp boundaries, commonly stepping down onto the surrounding plain by up to 15 m, and are readily recognisable by their characteristic irregular stony surfaces, thin soils

and woodland cover. These young lava flows have a shallow, brown to black clay soil through which boulders protrude on the slopes and in depressions. Basalt outcrops occur on the rises. The stony rise flows form extensive areas around individual volcanoes (e.g. Mt Eccles, Mt Napier, Mt Rouse), spreading radially as a series of lobes which overlap to give a sheet of lava. The outbreak of tongues of liquid lava from the outer lobes and the collapse of the original surface over the evacuated area formed the irregular hummocks, ridges and sinuous or basin-like depressions of the stony rises. Around Mount Pomdon there are extensive plateau areas, with irregular collapsed areas further from the vent and distinct lobes at the outermost edge of the lava field, where the flows run out on to the floor of Lake Corangamite. K-Ar and radiocarbon dates indicate ages of less than 1 Ma for stony rise flows, and many eruptions are less than a few hundred thousand years old. Most flows on the plains are thin, from 2 to 10 m, but they may be composed of individual layers as little as 0.5-1 m thick. Valley flows are often mappable for long distances, for example the Harman Valley flow from Mount Napier extended 20 km (Oilier and Joyce, 1973) and a valley flow from Mount Eccles travelled 50 km. The somewhat older subdued stony rise flows from Mount Rouse, now dated as about 300 000 years old, followed pre-existing valleys for 60 km to the coast. In each case the lava probably remained fluid by flowing within a lava tube through the interior of the flow. Ash deposits are not generally extensive in the province, but are prevalent around maar volcanoes in the Colac-Camperdown region, such as Bullenmerri and Gnotuk. Ash may extend downwind (east) from vents for up to 8 or 10 km, as at Tower Hill, some 33,000 years old, near Warmambool. The effects of the basalt flows on the pre-emption drainage system include the displacement of streams laterally, the ponding of streams against flow edges (e.g. Buckley's Swamp northeast of Mt Napier), and the formation of lakes, swamps and disordered drainage on the flows themselves. In some cases, for example at Geelong and along the course of the Curdies River south of Mount Pomdon, lateral stream valleys have successively been filled with lava, developing further lateral streams. On the plains, the low relief has allowed only shallow and poorly integrated drainage systems to develop, except for the major incised valleys of the Moorabool-Barwon and the Hopkins - Mt Emu Creek river systems, with their terraces and floodplains. On the volcanic plains, lava flows have been faulted along the Rowsley Fault Scarp and warped on the nearby Lovely Banks Monocline, north of Geelong. Mt Clay (189m) is a tuff volcano which sits on an uplifted block of Tertiary sediments northwest of Portland. The Staughtons Hill volcanic complex, south of Terang, consists of a maar, several broad scoria mounds and a small, spatter-rimmed crater, sitting on a block of Tertiary sediments elevated some 60 m and now marked by solutional sinkholes (Joyce, 1988). The uplift probably occurred at about the same time as the volcanic emption. Domal uplift has also occurred in South Australia around the Mt Gambier volcano, which empted some 5 000 years ago.

Little seismic activity is on record for the Western Plains over the past 80 years, since the major Warmambool earthquakes of 1903 and the offshore Kingston/Beachport (South Australia) earthquake of 1897.

The Western Uplands subprovince In the southern and central parts of the Dissected Uplands, the activity of over 250 scoria and lava volcanoes has produced valley flows and small lava plains on a previously uplifted and dissected upland. The flows filled valleys at least as deep as the present valleys, and the thickness of the lava, often more than 100 m, allowed slow cooling and the development of columnar jointing, exemplified by the Organ Pipes just north of Melbourne. Continued eruption in places buried the original dissected topography to give small lava plains, for example in the Ballarat-Creswick area. Mt Kooroocheang, also known as Mt Smeaton, north of Creswick, is the largest volcano in the Uplands, rising 200 m above the plain to an elevation of 676 m. Mt Warrenheip and Mt Buninyong are large young cones near Ballarat. The valley-filling lavas preserved the underlying alluvium as deep leads, for example along the Campaspe and Loddon drainage systems. The Campaspe lava flow is over 85 km long, making it possibly the longest recorded flow in Victoria. Some of the deep leads contained gold, and these were extensively mined in the 19th century. The mining records have allowed reconstruction of the pre-eruption drainage patterns, which are in general very similar to the present stream systems. North of Ballarat the divide between north- and south-flowing drainage may have been moved some 20 km southwards by the volcanic activity of the extensive Ballarat-Creswick lava plain. Post-eruption incision at the edges of valley flows has formed deep gorges, plateaus and in places twin lateral streams, such as Goodmans Creek and Pyrites Creek, on each side of the 3.48-Ma Mt Bullengarook flow, which now forms a plateau north of Bacchus Marsh. The Guildford Plateau, southwest of Castlemaine, is a remnant of a flow with incised lateral streams. Waterfalls often develop on the edge of lava plateaus, for example Trentham Falls, Lai Lai Falls and Turpins and Mitchells falls (near Barfold). Near Bacchus Marsh, at the eastern margin of the Western Uplands, intermittent movement on the Rowsley Fault has produced a scarp from 90 to 270 m high and caused strong rejuvenation of the Lerderderg and Werribee rivers and Parwan Creek. This incision produced spectacular gorges in the resistant Palaeozoic sediments and granites, and wide valleys in soft Tertiary sediments underlying Newer Volcanic lava flows along Parwan Creek and lower course of the Werribee River. Up to three sets of river terraces were also formed. Lava flows dated at 4 Ma are folded monoclinally across the fault (Joyce, 1975), indication that movement may have begun in the late Pliocene, and probably continued into the Quaternary. Earthquakes are associated with the Rowsley Fault. For example, the ML 4.7 Balliang earthquake of 2"^ December 1977 was felt over a wide area in central Victoria and caused local minor damage. Another concentration of earthquake activity in the Western

Uplands extends from Bendigo southwest towards Ballarat. Overall however, the area is seismically much quieter than the Eastern Uplands.

Dating and volcanic risk Some lava flows have been dated by K/Ar and radiocarbon, and changes in landforms, drainage, and soil and regolith development, using new airborne geophysical imagery, can be used to build up a detailed chronosequence of lava flows through the Quaternary (Joyce, 1999). The youngest dated eruption is that of Mt Gambier in nearby southeastern South Australia, at 4000-4300 B.P. by radiocarbon, and perhaps a dozen volcanoes may eventually be found to have erupted within the last 20,000 to 30,000 years (Table 1). If activity had been regularly spaced, there would have been an eruption every 12,500 years. However, recent work using soil and regolith landform mapping has assigned ages to otherwise undated flows, and also helped distinguish cycles of activity through time, notably a period of more concentrated activity in the late Quaternary in far Western Victoria. It is now generally agreed amongst Australian volcanologists that further eruption is likely, and may well be overdue. Eruptions to be expected are maar crater formation with ash falls for several kilometres downwind i.e. to the east, and cinder/scoria cone formation by fire-fountaining with associated long valley flows. Maar activity would provide particular problems if upwind of a town or either of the two cities. Lava flows would follow the general southerly slope and pre-existing valleys. Among likely problems arising are evacuation planning, effects on farm animals and crops, water pollution, stream derangement, diversion or control of valley flows, effects on roads and railways, and grassfires. A draft hazard map has been prepared (Figure 1; Joyce 2001), suggesting where a future eruption might occur, and the extent of its effects. There is a need for public education, both of the local community and of planners within local government.

Table 1. Estimates of eruption age for some Newer Volcanic volcanoes using radiocarbon, K/Ar, Cosmogenic Chlorine-36 and fission track dating

Mt Gambier

4,300 yrs B.P.

East Basin

>5,200

Red Rock

>7,800 & <15,200

Lake Gnotuk

>9,200

West Basin

>10,000

Lake Bullenmerri

>16,800

Mt Schank

18,100

MtLeura

>21,100 & <25,300

Mt Eccles

>27,500 & <19,300

Lake Keilambete

>29,100

Mt Napier

-32,000 & >7,200

Tower Hill

33,000 & >23,000

Lake Wangoom

>200,000

Lake Terang

>350,000

Mt Rouse

300,000

Mt Pomdon

300,000 or-59,000

Mt Franklin

470,000

The Sisters

570,000

Mt Warmambool

>570,000

Mt Fraser or Hayes Hill

810,000

Pejark Marsh

>980,000

Mt Warrenheip

-1,000,000

Anakie volcanoes

-1,500,000

A preliminary volcanic risk and hazard map for the Newer Volcanic Province of Southeastern Australia

Key Eruption type

Age of eruption

A »comcofM» A tayA%li<«ld o maar crKtf

9 200j000 yn • pn»«nl • IMa 200 000yt« • 3*1 M«

Volcanic rink

O Q

Vbteanic hazard O t y p i c a i ama covewJ lyyMli

Population centre

• cily^lown

medium

O tow

Figure 1. Preliminary volcanic risk and hazard map for the Newer Volcanics Province.

References Oilier, C.D. and Joyce, E.B., 1964. Volcanic physiography of the Western Plains of Victoria. Proceedings of the Royal Society of Victoria, 77,357-376. Olher, C.D. and Joyce, E.B., 1973. Chapter 12. Geomorphology of the Western District volcanic plains, lakes and coastline, IN: McAndrew, J., and Marsden, M.A.H. (editors). Regional Guide to Victorian Geology. University of Melbourne, School of Geology (2nd Edition), pp. 100-113 Joyce, E.B., 1975. Quaternary volcanism and tectonics in southeastern Austraha. The Royal Society of New Zealand Bulletin, 13,169-176. Joyce, E.B., 1988. Cainozoic volcanism in Victoria, Chapter 8. IN: Clarke, 1. and Cook, B. (editors), Victorian Geology Excursion Guide. Australian Academy of Science, Canberra, pp.71-80.

Joyce, E. B. 1999. A new regolith landform map of the Western Victorian volcanic plains, Victoria, Australia, IN: Taylor, G, and Pain, C. (editors), Regolith '98, Australian Regolith & Mineral Exploration, New Approaches to an Old Continent, Proceedings, Australian Regolith Conference, Kalgoorlie, 2-9 May 1998. CRC LEME, Perth, pp.117 -126. Joyce, B.J., 2001. The young volcanic province of southeastern Austraha: volcanic risk evaluation and the community. IN: Stewart, C., (editor). Proceedings of the Cities on Volcanoes 2 Conference, Auckland, New Zealand, 12-14 February 200L Institute of Geological and Nuclear Sciences Information Series 49, p.70.

Neoproterozoic crustal evolution of the NW Indian craton: clues from acid magmatic events M. K. Pandit Department of Geology, University of Rajasthan, Jaipur 302004, India mpanditJpl @jp 1 .sanchamet.in

Introduction The Precambrian crustal evolution of the Aravalli craton in the northwestern territory of the Indian Shield was centred along two major accretionary fold belts (the Aravalli and Delhi belts) developed over a basement, commonly referred to as the Banded Gneissic Complex (BGC). The Delhi Fold Belt, forming the most important geomorphic feature of this terrain, records prominent granitic activity which can be grouped into two age clusters (1800 - 1700 and --SOO Ma). The temporally distinct granitoids also show a spatial discrimination; the older granitoids being restricted to the northern segment and the younger granitoids to the southern segment. There have been a series of tectonically diverse acid magmatic events following the closure of the Delhi Basin, represented by the syn-tectonic Erinpura granite, late-tectonic Abu (also Godhra) granite, and anorogenic magmatism (predominantly acid volcanics) of the Malani Igneous Suite (MIS). The Precambrian acid magmatism in Rajasthan has a well-documented geochronological record with a Sm - Nd age of 3.3 Ga (Gopalan et aL, 1990) and single zircon evaporation age of 3.2 Ga (Roy and Kroner, 1996). The younger granitoids, intrusive into these gneisses (Berach granite), with closely comparable ages (2.6 Ga) mark the end of Archaean acid magmatism in this region. The Proterozoic accretionary cover sediments developed over the crystalline basement (BGC) record 2.0 - 1.8 Ga old (Darwal, Anjana) granites marking the end of the Aravalli orogeny. This talk presents a critical evaluation of the 1000 - 750 Ma granitoids, representing a continuum from orogenic to anorogenic (subduction-related) magmatism in order to characterize the Neoproterozic evolution of NW India.

Sendra Granite In the Sendra area (southern segment of the Delhi Fold Belt), five variably deformed granitoid plutons cut across carbonate-rich metasedimentary rocks of the Delhi Supergroup. The largest of these bodies, the Chang pluton, consists of monzogranitic gneisses. U-Pb zircon dating (TIMS method) of a biotite granite gneiss from the Sendra Granite yielded a weighted mean ^^^Pb/^^^Pb age of 967.8 ±12 Ma, interpreted as the time of magmatic crystallization (Pandit et al, 2003). Initial isotopic ratios (at 968 Ma) for Chang pluton granitoids are compatible with source materials similar to the Archaean amphibolitic rocks of the Banded Gneiss Complex. These rocks represent the products of convergent margin processes during the Early Neoproterozoic.

The most voluminous acid magmatism in the southern segment of Delhi Fold Belt, the Erinpura Granite, has been attributed to a single thermal event at around 850 Ma. This syn-tectonic event is followed and overlapped by the Godhra granite, Abu granite and the anorogenic Malani Igneous Suite (MIS). The Erinpura Granite is extremely variable in texture, ranging from porphjnroblastic to gneissic (with granophyric and myrmekitic intergrowth of quartz and feldspar). The mineralogical variation in the Erinpura granites leads to their classification as granite to granodiorite. Overlapping I- and S-type characteristics of the Erinpura Granite have led to contradictory source composition models, ranging from an igneous protolith (Bhushan, 1995) to meta-sedimentary parent material (Gangopadhyay and Lahiri, 1984). The Erinpura granites are a result of complex petrogenetic history involving variable sources and processes.

Malani Igneous Suite The Malani Igneous Suite, represents predominantly acidic, polyphase magmatism characterized by an initial felsic (bimodal in places) volcanism followed by emplacement of granites and acid to basic dykes. These are undeformed and unmetamorphosed rocks with well-documented intrusive relationships to the older Delhi metasediments and Erinpura Granite. The occurrence of conglomerate and their linear disposition suggests that the volcanic activity took place along roughly N - S, subparallel fracture systems. A significant observation is that the Sindreth bimodal volcanics have a strong similarity and

coevality with Malani rocks rather than the highly deformed and metamorphosed Delhi rocks (Van Lente, 2001). Chemically, the felsic rocks can be described as peraluminous (biotite - hornblende, K-feldspar - albite) and peralkaline (riebeckite - arfVedosnite perthite) types. Recently published and more precise U - Pb zircon ages indicate that the Malani magmatism commenced at 770 - 750 Ma with outpouring of lavas and coeval emplacement of granites and dykes (Torsvik et al, 2001). Mineralized granites The western mineralized granitoids (Balda, Degana and Sewariya granites) occur as a linear belt along the western flank of the Delhi Fold Belt. The Balda Granite (intrusive into the 'Erinpura granite'; Chattopadhyay et al, 1982) is equigranular, while the Degana Granite is porphyritic with large K-feldspar phenocrysts. The Balda Granite has been described as a leucogranite with essential quartz, K-feldsapr, albitic plagioclase and muscovite, and biotite, tourmaline, topaz and opaques as the accessories (Chattopadhyaya et al, 1982). The preponderance of muscovite and the occurrence of biotite as an accessory phase is in strong contrast to the overall biotite-rich character of the 'Erinpura granite'. The Degana pluton shows textural heterogeneity, ranging from coarse-grained hypidiomorphic to fine-grained porphyritic types. The Degana Granite has A-type affinity, as defined by enrichment in HFSE, high Ga/Al ratios and other trace element parameters (Chattopadhyay et al, 1994). The Sewariya Granite is a composite body, predominantly biotite granite with subordinate leucogranite, both welldifferentiated, high-level, peraluminous, S-type granites that host W and Li mineralization, respectively. No geochronological data is available on these mineralized granitoids. Conclusions The above observations can be summarized to conclude that: • The Neoproterozoic acid magmatic events are distinctfiromeach other in terms of tectonic setting. The Ga collisional event resulted in increased thermal gradient and partial melting of BGC amphibolites to produce the Sendra Granite.

•

The 850 Ma, Erinpura Granite represents closing of the Delhi Orogeny in the southern sector.

•

There was a period of shearing and strong fluid activity that resulted in W (± Sn, ± Li) mineralisation.

•

The 770 -750Ma Malani magmatism appears to be coeval with similar magmatic activity in the Seychelles and Madagascar, substantiating their spatial conjugate position forming the western margin of Rodinia.

References Baneqi, S. and Pandit, M. K., 1995. Current Science, 69, 252-256. Bhushan, S. K., 1995. Memoirs of the Geological Society of India, 34, 339-353. Chattopadhyaya, B., Mukhopadhyaya, A. K., Singhal, R. K., Bhattachaijee, J. and Hore, M. K., 1982. Symposium on Metallogeny, Bangalore, pp.115-132. Chattopadhyaya, B., Chattopadhyaya, S. and Bapna, V.S., 1994. Mineralogy and Petrology, 50, 69-82. Gangopadhyaya, P. K. and Lahiri, A., 1984. Indian Journal of Earth Sciences, Special Issue, 92-112. Gopalan, K., Macdougall, J. D., Roy, A.B. and Murali, A. V., 1990. Research, 48, 287-297.

Precambrian

Pandit, M. K., Carter, L.M., Ashwal, L.D., Tucker, R.D., Torsvik, T.H., Jamtveit, B. and Bhushan, S.K., 2003. Journal of Asian Earth Sciences, (in press). Roy, A. B. and Kroner, A., 1996. Geological Magazine, 133, 333-342. Torsvik, T. H., Carter, L. M., Ashwal, L. D., Bhushan, S. K., Pandit, M. K. and Jamtveit, B., 2001. Precambrian Research, 108, 319-333. Van Lente, B., 2001. Geology, geochemistry and geochronology of volcanic rocks of Punagarh and Sindreth Groups, NW India. M.Sc thesis (unpublished), Rand Afrikaans University, Johannesburg.

Geochemistry of metabasic volcanics from Aravalli Supergroup in NW India: implications on tectonic evolution of a Palaeoproterozoic rift basin M. K. Pandit^ and L. S. Shekhawat^ ^ Department of Geology, Univeristy of Rajasthan, Jaipur 302004, India

mpandit jp] @sanchamet.in ^Training Institute, Zawar Centre, Geological Survey of India, Jhalana Dungari, Jaipur 302004, India

The Precambrian geological evolution of the NW Indian shield includes the development of two Palaeo- and Mesoproterozoic tectonostragraphic units (the Aravalli and Delhi Supergroups), deposited over an Archean basement (BGG - Banded Gneissic Complex). The Aravalli Supergroup represents an ensialic rift basin fill which includes a shelf sequence in the eastern segment and deep-sea facies in the western one. The basal part of Aravalli Supergroup is characterised by the presence of a continuous horizon of metabasic volcanics associated with quartzite and locally developed conglomerate. The metabasic volcanics occurring in the Salumber region form the target rocks for the present study. At least five different flow units can be recognised on the basis of field observations and textural variations. Although metamorphosed to greenschist facies, the rocks still preserve primary features (circular amygdules, relict pyroxene, etc.). The mineral assemblages include, (a) oligoclase + actinohte + chlorite + epidote and (b) oligoclase + homblende-f chlorite+ biotite + Fe-Ti oxides. The metabasic volcanics show silica and MgO contents from 47 to 57% (basaltic to andesitic) and 3.71 to 12.83%, respectively. Taking into account other geochemical characteristics (e.g. FeO + Ti02, AI2O3 and MgO) these can be subdivided into komatiitic basalt, tholeiitic basalt to tholeiitic andesite. The geochemical variations are generally consistent with a fractionation mechanism, such as the inverse relationship of MgO with silica and alkalis. However, there is some scatter in the data in the case of rocks with <5% MgO, indicating some degree of crustal contamination in the case of these evolved flows. The metabasalts are enriched in incompatible elements and show similarity with continental basalts. However, in the trace element discrimination schemes, they show affinity with MORE and lAT settings. The REE patterns show moderate LREE enrichment (La = 30 - 40 x chondrite, Lu = 2 - 5 x chondrite) with no significant Eu anomalies. The geochemical characteristics suggest a complex evolutionary history. The melt was derived from an enriched source (more than one composition) and some part was contaminated during ascent.

Basaltic gem fields, eastern Australia: Sapphire-ruby characteristics and connections, F.L. Sutherland*, D. Schwarz^ and G. Webb* ^ Geodiversity Research Centre, Australian Museum 6 College Street, Sydney, NSW 2010 ^ Gubelin Gem Lab, 102 Maihofstrasse CH-600, Lucerne, Switzerland

Introduction Many intraplate basalt fields in eastern Australia are sources for gem corundums (Olliver and Townsend, 1993; Sutherland, 1996; Sutherland and Schwarz, 2001). Some fields support commercial mining for sapphires (New England area of NSW, Central Queensland), which includes gem enhancements (Coldham 1992, 2003). Alkaline basaltic rocks typify the corundum carriers, but show no obvious geochemical distinction from such basalts in fields that lack a corundum component (Coenraads, 1994). The corundums (Figure 1) represent xenocrysts and rare corundum-bearing xenoliths that are redistributed into alluvial placers (Robertson and Sutherland, 1992; Oakes et al, 1996).

Figure 1. Gem corundum concentrate showing range of colours and zoning of alluvial sapphires, Tumbarumba field, NSW. Note magmatic corrosion and growth zoning on some crystals, which include magmatic, metasomatic and metamorphic genetic types. Crystals range up to 3mm. (Photo G.Webb, Austrahan Museum).

The volcanic hosts include pyroclastic, lahar and various volcaniclastic deposits and the precise mechanisms of eruption and reworking of corundum deposits have been detailed for New England NSW fields by Pecover (2003). The Australian basaltic gem fields are part of a larger system that extends along the West Pacific continental margin (Figure 2).

Figure 2. Distribution of eastern Australian and West Pacific margin zircon-corundum gem fields in basalt areas. The main gem areas are symbolised by Z.

Gem corundum suites The corundums typically exhibit effects of magmatic corrosion and reaction rim features (e.g. spinel formation), which indicates their conveyance in basaltic melts at temperatures of at least lOOO^'C (Coenraads 1992 a,b; Sutherland et al, 1998b). Sapphire dominates the gem suites, but ruby appears in some fields, particularly in the Harrington, NSW field (Webb, 1997). Corundums from several fields have had detailed trace element (Figure 3) and inclusion studies, e.g. New England, Barrington, Tumbarumba, CudgegongWellington, NSW and Lava Plains, Queensland (Coenraads, 1992b; Sutherland and Coenraads, 1996; Guo et al, 1996; Sutherland et al, 1998 a,b, 2002, 2003). Central Queensland suites require far more study, as do the widespread but scattered Victorian suites (Birch and Henry, 1997) and the little studied NE Tasmanian suite. Trace element and primary mineral inclusion studies have delineated three main genetic associations; 'magmatic*, 'metamorphic' and 'metasomatic' (Table 1). Table 1. Identified corundum genetic types, eastern Australia. MGS 'magmatic' sapphire suite, MGR 'magmatic' ruby suite, MTS 'metamorphic' sapphire-ruby suite, MTR 'metamorphic' ruby suite, MES 'metasomatic' sapphire suite. D dominant, E equal part, P present. Datafi-omcited references and authors unpublished work. Gemfield

Lat'S

Long"E

Corundum types

Proportion

Mt McLean, Qld

15.9

145.7

MGS

Lava Plains, Qld

18.5

144.7

MGS, MTS

D,P

Anakie, Qld

23.5

147.7

MGS

New England, NSW 29.5 (Bingara - Glen Innes) -30

150.5 -152

MGS, MGR MTR

D,P P

Barrington, NSW

151.5

MTS, MGS

E,E

WellingtonCudgegong, NSW

32.3 -33

149 -149.8

MGS MTR

D P

Oberon, NSW

33.7

149.6

MGS

Tumbarumba, NSW 35.7

148.2

MGS, MES, MTR

D,P,P

Carapooee, Vic

36.7

143.4

MGS, MES

D,P

Mymiong, Vic

37.6

144.3

MGS, MGR

D,P

Bass River, Vic

38.5

145.5

MGS, MES?

D,P

NE Tasmania

41.1

147.8

MGS

^Magmatic' sapphire suites A dominant blue-green-yellow sapphire suite is characterised by colour zoning related to interplay of Fe and Ti as chromophores and by a wide range of inclusions, particularly silicates (alkali and plagioclase feldspars, zircon and rare feldspathoid and thorite), NbTa oxides (ferrocolumbite, ilmenorutile, betafite, samarskite), Fe-Ti oxides (spinels, ilmenite, rutile), U oxide (uraninite), sulfides (pyrrhotite) and phosphate (brockite). This suite ranges into white, brown and black less gemmy materials, but the dark material still has value for star stones and carved material (e.g. the USA presidents carved heads). The growth zone features include trapiche-like structures, and with enriched Ga contents in the corundums suggests a magmatic genesis. The great majority of Australian sapphires belong here, defined by a geochemical field having low Cr203/Ga203 (<1) and a wide range of Fe203/Ti02 (5 - 1000) ratios (Figure 3).

1000.00

100.00-

10.00-

Metamorphic fields

o" o

1.00Magmatic fields 0.10-

0.01.

0.10

1.00

10.00

100.00

1000.00

Fe^O^mO^

Figure 3. Trace element chemical characteristics of eastern Australian gem corundums, based on Cr203/Ga203 and Fe203/Ti02 ratios. The 'metamorphic' fields include Wellington-Cudgegong ruby suite (W-C), Barrington ruby suite (B) and Tumbarumba ruby suite (T) in comparison to East Thailand (ET) and Pailin (P) SE Asian ruby suites. The main 'magmatic' sapphire field for all eastern Australian gem fields is symbolised b. The intermediate 'metasomatic' sapphire field from Tumbarumba is symbolised t. The unusual 'magmatic' sapphire-ruby fields include Swanbrook (S) and Mymiong (M). Fields come from the cited literature and the authors unpublished data.

The precise magmatic processes that generate this suite are under debate. They include crystallisation from high pressure fractionation of basanitic magmas into nepheline syenite (phonolite) magmas (Irving, 1986), involvement of hybrid carbonatitic-granitic reactions (Guo et al, 1996), and production of syenitic melts formed after low degree melting of hydrous mantle and lower crustal assemblages (Sutherland et al, 1998a). Recent studies on fluid and melt inclusions and on oxygen isotopes in such sapphires elsewhere mostly favour genesis from alkaline silicate melts under mantle-lower crust conditions, rather than lower temperature carbonatitic-granite reactions (Upton et aL, 1999; Srithai and Rankin, 1999; Limtrauken et al, 2001; Tzen-Fu et al, 2003). The known high pressure coarse corundum-syenite xenoliths (Stephenson, 1990), and common alkali and Na-rich feldspar and zircon inclusions in such Australian corundums suggests that salic syenitic melts were widely operative in their genesis. U-Pb dating of the syngenetic zircon inclusions generally yields formation ages close to host basalt ages (Coenraads et al, 1990; Guo et al, 1996; Sutherland et al, 1998a; Sutherland et al, 2002a,b), suggesting close links existed between syenitic melt generation and subsequent transporting basaltic magmatism. Rarer eastern Australian sapphire suites may originate from nepheline syenitic melts, as proposed for Cudgegong sapphires, which contain syngenetic nepheline and occur near phonolites within adjacent alkali basalts (Sutherland et aL, 2003). In terms of trace elements, Cudgegong sapphires have high Fe203 relative to Ti02. ^Magmatic' sapphire-ruby suites These suites are unusual in combining typical magmatic growth zoning features and Ga levels (> lOOppm) along with significant Cr as a chromophore (Figure 3). They are typical within the Swanbrook, New England, NSW suite, where the Cr enters into a colourful range of violet, purple, orange, pink and red corundums. The larger New England faceted rubies (up to 17 carats) including the spectacular Aurora sapphire with its ruby core (Sutherland, 1991) probably belong with this suite. Such ruby suites are rarely recorded from Australian basaltic fields (or even worldwide). They may be more prevalent than realised, as similar limited suites appear in Victoria (e.g. Mymiong in the Newer Volcanics Province). 'Metamorphic' sapphire-ruby suite These suites show a greater range of 'fancy colours' (violet, mauve, pink, purple, red), mostly with diffuse colour zoning. They carry a simpler set of syngenetic mineral inclusions and are typically depleted in Ga relative to Cr. The inclusions typify metamorphic associations (sapphirine, spinel, Al-rich diopside, scapolite, rutile, calcic pyrope), and the corundums have high Cr203/Ga203 (5 - 200) and range in Fe203/Ti02 (1 - 100) ratios (Figure 3). The blue end of the sapphire spectrum shows different colour absorption characteristics to 'magmatic' blue sapphires (Sutherland et al, 1998b, 2002b). The metamorphic suites vary in detailed characteristics from different areas (Figure 3). Those from the Barrington region contain sapphirine and Cr-bearing spinel intergrowths and tend to higher Fe203/Ti02 ratios. Those from the western Sydney basin (Cudgegong,

Wellington, Bingara) contain Al-rich diopside, meionite and anatase and trend to lower Fe203/Ti02 ratios, while Tumbarumba ruby tends to lower Cr203/Ga203 and intermediate Fe203/Ti02 ratios. Preliminary studies on fluid and melt inclusions from Barrington rubies suggests this metamorphic genesis incorporated some alkali melt interactions (K. Zaw and F.L. Sutherland, unpublished data). ^Metasomiatie' sapphire suites More subdued, pastel coloured sapphires, with pink tinges, are typical of these suites and are best exemplified in the Tumbarumba field (Sutherland et al, 2002b). They are intermediate in geochemical characteristics between the low Cr203/Ga203 (<1) 'magmatic' and high Cr203/Ga203 (>5) 'metamorphic' suites and show Fe203/Cr203 ratios (20 - 110), similar to known metasomatic sapphire values from elsewhere. Syngenetic inclusions include typically small zircons, with U-Pb ages that provide formation ages consistently different to those in the associated 'magmatic' sapphires and host basalts. These suites, like the 'magmatic' suites include examples of trapiche-like radiating growth and exsolution features. Zircon connections The eastern Australian basaltic gem corundum suites, like similar suites elsewhere, are normally accompanied by more prolific zircon megacryst suites. The zircons also exhibit similar magmatic corrosion effects and many suites show crystal morphologies, growth features and inclusion suites indicative of crystallisation from alkaline, salic melts (Hollis and Sutherland, 1985; Coenraads, 1992b; Sutherland, 1996; Sutherland and Fanning, 2001; Sutherland et al, 2002b). The geochemistry of zircon inclusions within the associated sapphires suggests that highly evolved alkaline melts participated in the sapphire crystallisation, but with some overlap with the zircon megacryst-producing melts (Quo et al, 1996; Sutherland et al, 1998a). Zircon and more sporadic corundum crystallisation events punctuated main basaltic magmatic episodes (Sutherland and Fanning, 2001; Sutherland et al, 2002b). However, the gem suites were not always crystallised with a basaltic episode, as some represent palaeo crystallisations, in some cases formed up to 200 million years earlier (Sutherland andKinny, 1990). Regional connections Gem corundum basaltic fields extend along eastern Australia from 16^ S to 41^ S and geochemical characteristics of the corundums along this belt have been studied to at least preliminary stage (authors unpublished data). This major gem corundum belt has evolved during intermittent, repeated intraplate basaltic activity since at least Triassic time (Sutherland and Kinny, 1990; Worden et al, 1996; Sutherland, 1999), which has accompanied rifting, tensional uplift and passage of eastern Australian lithosphere over mantle thermal zones (Sutherland 1996, 1998, 1999). The Austrahan corundum-zircon basaltic fields are part of a more extensive system of such gem fields that border the West Pacific continental margin (Figure 2), from southern New Zealand, through eastern Australia, Kalimantan and the commercial mining fields in SE Asia (Vichit, 1992; Smith,

1995; Sutherland et al, 1998b, 2002a) and China (Guo et al, 1996), and into newly discovered fields in eastern Russia (Vysotskii et aL, 2002). Acknowledgments Help with specimens and preparation for the project came from Ross Pogson, Collection Manager, Dr Ian Graham, Scientific Officer, and Julian Hollis, Research Associate, Australian Museum, and from Cluff Resources Pacific NL, Sydney through Peter Kenewell, Managing Director, and Robert Coenraads, from Sapphex PL Sydney, through Terry Coldham, and from Museum Victoria, through Dr Bill Birch. References Birch, W.D., and Henry, D. (editors), 1997. Gem Minerals of Victoria, Special Publication No 4, Mineralogical Society of Victoria and the Royal Society of Victoria, Melbourne, 121pp. Coenraads, R.R., 1992a. Surface features of natural rubies and sapphires associated with volcanic provinces. Journal of Gemmology, 23, 151-160. Coenraads, R.R., 1992b. Sapphires and rubies associated with volcanic provinces: inclusions and surface features shed light on their origin. Australian Gemmologist, 18 (3), 70-78. Coenraads, R.R., 1994. Evaluation of potential sapphire source rocks with the catchments of Kings Plains Creek and Swan Brook, near Inverell, New South Wales. Records of the Australian Museum, 46 (1), 5-24. Coenraads, R.R., Sutherland, F.L., and Kinny, P.D., 1990. The origin of sapphires: U-Pb dating of zircon inclusions sheds new light. Mineralogical Magazine, 54, 113-122. Coldham, T.S., 1992. The Australian sapphire industry. Australian Gemmologist, 18 (4), 104-107. Coldham, T.S., 2003. The history and importance of heat treatment of Australian sapphire. Australian Gemmologist, 21 (11), 450-462. Guo, J.F., O'Reilly, S.Y., and Griffin, W.L., 1996. Corundum from basaltic terrains: a mineral inclusion approach to the enigma. Contributions to Mineralogy and Petrology, 122, 368-386. Hollis, J.D., and Sutherland, F.L., 1985. Occurrences and origins of gem zircons in eastern Australia. Records of the Australian Museum, 36 (6), 299-311.

Irving, A.J., 1986. Polybaric magma mixing in alkali basalts and kimberlites: Evidence from corundum, zircon and ilmenite megacrysts. Geological Society of Australia Abstracts Series, 16, 262-264. Limtrakun, P., Zaw, K., Ryan, C.G., and Memagh, T.P., 2001. Formation of the Denchai gem sapphires, northern Thailand: evidence from mineral chemistry and fluid/melt inclusion characteristics. Mineralogical Magazine, 65, 725-735. Oakes, G.M., Barron, L.M., and Lishmund, S.R., 1996. Alkali basalts and associated volcaniclastic rocks as source of sapphire in eastern Australia. Australian Journal of Earth Sciences, 43, 289-298. Olliver, J.G., and Townsend, I.J., 1993. Gemstones in Australia. Australian Govemment Publishing Service, Canberra, 72pp. Pecover, S., 2003. The geology and genesis of high-grade sapphire deposits in the New England gemfields, Central Volcanic Province. Ph.D thesis (unpublished). University of Sydney. Robertson, A.D.C., and Sutherland, F.L., 1992. Possible origins and ages for sapphire and diamond from the central Queensland gemfields. Records of the Australian Museum Supplement, 15, 45-54. Smith, C.P., Kammerling, R.C., Keller, A.S., Peretti, A., Scarratt, K.V., Khoa, N.D., and Repetto, S., 1995. Sapphires from southern Vietnam. Gems and Gemmology, 31 (3), 168186. Srithai, B., and Rankin, A.H., 1999. Fluid inclusion characteristics of sapphires from Thailand. IN: Stanley et ah (editors). Mineral Deposits: Processes to Processing, Balkema, Rotterdam, pp. 107-110. Stephenson, P.J., 1990. The geological context of sapphire occurrences in the Anakie region, central Queensland. Geological Society of Australia Abstract Series, 25, 232-233. Sutherland, F.L., 1991. Gemstones of the Southern Continents. Reed Books, Sydney, 256pp. Sutherland, F.L., 1996. Alkaline rocks and gemstones, Australia: a review and synthesis. Australian Journal of Earth Sciences, 43, 323-343. Sutherland, F.L., 1998. Origin of north Queensland, Cenozoic volcanism: Relationships to long lava flow basaltic fields, Australia. Journal of Geophysical Research, 103 (Bll), 27347-27358.

Sutherland, F.L., 1999. Volcanism, geotherms, gemstones and lithosphere, since orogenesis, N.E New South Wales: A synthesis. IN: Flood, P.G. (editor), New England Orogen; Regional Geology, Tectonics and Metallogenesis. Earth Sciences, University of New England, Armidale, NSW, pp. 355-364. Sutherland, F.L., and Coenraads, R.R„ 1996. An unusual ruby-sapphirine-spinel assemblage from the Tertiary Barrington volcanic province, New South Wales. Mineralogical Magazine, 60, 623-638. Sutherland, F.L., and Fanning, C.M., 2001. Gem-bearing basaltic volcanism, Barrington, New South Wales: Cenozoic evolution, based on basalt K-Ar ages and zircon fission track and U-Pb isotope dating. Australian Journal of Earth Sciences, 48, 221-237. Sutherland, F.L., and Kinny, P.D., 1990. Ion probe U/Pb isotopic ages of gemmy zircon from eastern Australia, including Tasmania. Geological Society of Australia Abstract Series, 25, 241-242. Sutherland, F.L., and Schwarz, D., 1991. Origin of gem corundums from basaltic fields. Australian Gemmologist, 21 (1), 30-33. Sutherland, F.L., Hoskin, P.W.O., Fanning, C.M., and Coenraads, R.R., 1998a. Models of corundum origin from alkali basaltic terrains: a reappraisal. Contributions to Mineralogy and Petrology, 133, 356-372. Sutherland, F.L., Schwarz, D., Jobbins, E.A., Coenraads, R.R., and Webb, G., 1998b. Distinctive gem corundum suites from discrete basalt fields: a comparative study of Barrington, Australia, and West Pailin, Cambodia, gemfields. Journal of Gemmology, 26, 65-85. Sutherland, F.L., Boshart, G., Fanning, C.M., Hoskin, P.W.O., and Coenraads, R.R., 2002a. Sapphire crystallisation, age and origin, Ban Huai Sai, Laos: age based on zircon inclusions. Journal of Asian Earth Sciences, 20 (7), 841-849. Sutherland, F.L., Graham, LT., Pogson, R.E., Schwarz, D., Webb, G., Coenraads, R.R., Fanning, C.M., Mollis, J.D., and Allen, T.C., 2002b. The Tumbarumba basaltic gemfield. New South Wales: In relation to the sapphire-ruby deposits of eastern Australia. Records of the Australian Museum, 54 (2), 215-248. Sutherland, F.L., Coenraads, R.R., Schwarz, D., Raynor, L.R., Barron, B.J., and Webb, G., 2003. Al-rich diopside in alluvial ruby and corundum-bearing xenoliths, Australian and SE Asian basalt fields. Mineralogical Magazine, 67, 717-732. Sutthirat, C., Saminpanya, S., Droop, G.R.T., Henderson, C.M.B., and Manning, D.A.C., 2001. Clinopyroxene-corundum assemblages from alkali basalt and alluvium, eastern Thailand: constraints on the origin of Thai rubies. Mineralogical Magazine, 65, 277-295.

Tzen-Fu, Y., Zaw, K., and Limtranken, P., 2003. Oxygen isotope compositions of the Denchai sapphires, Thailand: A clue to its enigmatic origin. Lithos, 67, 153-161. Upton, B.G.J., Hunton, R.W., Aspen, P., Finch, A., and Valley, J.W., 1999. Megacrysts and associated xenoliths: evidence for migration of geochemical enriched melts in the upper mantle beneath Scotland. Journal of Petrology, 40, 935-956. Vichit, P., 1992. Gemstones in Thailand. IN: Piancharoen, C. (editor). Proceedings of a National Conference on Geological Resources of Thailand: Potential for Future Development. Supplementary Volume, Department of Mineral Resources, Bangkok, pp. 124-150. Vysotskii, S.V., Shcheka, S.A., Nechaev, V.P., Soroka, V.P., Barkov, A.V., and Khanchuk, A.I., 2002. First finding of sapphire from Cenozoic alkali-basaltic volcanoes in the Primor'e region. Doklady Akademie Nauk SSR, Earth Science, 387A, 1100-1103. Webb, G., 1997. Gemmological features of rubies and sapphires from the Barrington volcano, eastern Australia. Australian Gemmologist, 19 (11), 471-475. Worden, J.M., Baadsgaard, H., Crackwell, D.N., and Krstic, D., 1996. Major extensional events recorded by zircon xenocrysts from the central Queensland gemfields. Geological Society of Australia Extended Abstracts, 43, 569-573.