GST IN THE MT ISA INLIER, 1961-1993

- 32 YEARS OF VALUE ADDING

 

 

G.M.Derrick

(G.M.Derrick and Associates)

 

"The new search springs from optimism and wealth ..... Mt Isa has become the pulse of Australia's zone of mineral expansion."

 

Whilst this quotation may well have come from any of Australia's major explorers in the 1990s, it is in fact from Geoffrey Blainey's "Mines in the Spinifex" ca. 1960; at this time annual mineral production from the Inlier was valued at about $45,000,000, mainly from Mt Isa Mines, a figure which has since expanded to about $1,300 million per annum in 1992 , with MIM still the major wealth generator, with contributions from Cyprus/Arimco and their Starra operations.

 

With the hope of renegotiated freight rates, and the blessing of better metal prices in the future, all this is about to change, with a plethora of new players and newly discovered or revitalised projects awaiting feasibility study and possible development (Table 1 and Figure 2) - BHP's Cannington and Eloise, CRA's Century and Dugald River, WMC-Hunter-Savage (+MIM) at Ernest Henry, and Placer's Osborne deposit, for example. Overall, the exposed portion of the Mt Isa Inlier contains in known or previously mined deposits about 42 million tonnes (mt) of zinc, 25 mt of lead, 10 mt. of Cu and 2.5 million ounces of gold in a variety of geological settings, and valued in 1992 dollars and metal prices at A$100 billion (Derrick, 1992). Not surprisingly, this degree of metal endowment has stimulated geological and geophysical exploration of the two-thirds (or 100,000 km2) of the Inlier which is unexposed, and where several discoveries have already been made at depths of 30-50m.

 

Whilst a GST may be politically dead for the moment, there is ample evidence of its presence and its contribution to value-adding in the Mt Isa Inlier. Consider....

 

G - geologists, geophysicists, geochemists, geosynclines, geochronology, gravity, G.I.S., granites, growth faults, geodynamics, garnet, gypsum,.....and

S - stratigraphy, sedimentation, structure, shearing, shorelines, spoon faults, shales, second-order basins, saline fluids, skarns, syn/diagenesis

and T - tectonics, TEM, thrusts, temperature, third-order basins, thematic mapper, Tick Hill, transpression....

 

as just a small sampling of the various geoscientific elements which have contributed to our present understanding of the Mount Isa Inlier.

 

The seminal work of Carter, Brooks & Walker (1961) is, or should be, emblazoned into the psyche of most workers in the Mt Isa Inlier, and it remains a key reference for the region, completed at a time when Land Rover was king, when the Mt Isa - Cloncurry road was but a goat track, and the Inlier was experiencing its one (and only ?) boom in uranium exploration, with Mary Kathleen the prime discovery. This first BMR/GSQ program completed the 1:250,000 mapping in the period 1950-54, and from this came BMR Bulletin 51 in 1961, a readable, informed and informative publication whose production is all the more remarkable for the fact that a fire in the old BMR building in Canberra destroyed most of the project field notebooks before final writing and data assembly commenced.

 

A second period of 1:100,000 mapping/research by BMR/GSQ in the period 1969-80, and synthesised by Blake (1987), modernised the geology of the Inlier in the form of various reports and a set of excellent 1:100,000 geological maps, which arguably represent one of the most important Federal/State government initiatives in geoscientific infrastructure development of the past fifty years.

 

The State Mines Department in 1968 also carved for itself a special niche in Mt Isa geological history by commissioning the first, and still a most superior, set of colour photography at 1:20,000 scale covering the Mary Kathleen 1:100,000 sheet area. This initiative set the scene for subsequent colour coverage by the Commonwealth of the entire Inlier at 1:25,000 scale, a factor which figured strongly in the overall success of the 1:100,000 mapping program.

 

From 1983 to the present, BMR (now AGSO) and BMR-supported university workers (J.C.U.N.Q., U of Q, Monash, and Utrecht, for example) conducted more detailed structural, petrological, sedimentological and geochronological studies (Stewart & Blake, 1992) in an east-west transect between Cloncurry and Mt Isa, and AGSO is currently preparing digital datasets (geochemical, geophysical, geochemical, metallogenic) for integration with G.I.S. Industry has strongly supported various studies throughout the Inlier at various prospects/projects, and recently through EGRU and the Key Centre at James Cook University has supported a detailed mapping program covering much of the Maronan Supergroup south of Cloncurry.

 

 

GEOLOGICAL OUTLINE (Blake, 1987; Page, 1988; Stewart & Blake, 1992)

 

The Mt Isa Inlier is probably part of an intraplate, ensialic crustal setting, in which most sedimentation and volcanism are related to crustal extension. Oldest rocks form part of the Barramundi Orogen (1900-1870 Ma), which is overlain by rift/sag sequences (collectively described as cover sequences) of various age and geographic distribution. At least four periods of rifting may be present, and at least 4 cover sequences (Figure 1). Rift phases are represented by an abundance of bimodal volcanics (felsic to mafic) and coarse clastics, whereas sag phases are dominated by finer clastics and carbonates, and are commonly more areally extensive.

 

Cover sequence 1 (1870-1850 Ma) equates with the extensive felsic ignimbrites/volcanics of the Leichhardt Volcanics; cover sequence 2 (?1800-1730 Ma) contains basal felsic/basic volcanics mixed shallow water clastics, subaerial basalts and carbonates, and apart from the Quilalar sag phase was deposited largely within the aulacogen-like Leichhardt River Fault Trough. A series of smaller scale rifting episodes are newly postulated for the period 1730-1680 Ma, prior to or accompanying deposition of cover sequence 3 (1680-1650 Ma?) comprising basal volcanics and clastics, overlain by fine clastics and carbonates (e.g. Mt Isa, McNamara Groups). An additional cover sequence 4 is postulated in the east of the Inlier, to include the 1620 Ma Beacon (or Tommy Creek) Beds (Derrick, 1991; Hill et al, 1992), which are in thrust contact with Corella Formation (pre-1740 Ma), and are here postulated to be equivalent to the Soldiers Cap Group in the far east of the Inlier.

 

Granites were emplaced at 1860 Ma, 1800 Ma, 1740-1720 Ma, 1670 Ma and 1500 Ma, and are largely I-type with some A-types represented (Wyborn, 1988; Wyborn et al., 1988). The largely extensional regime with associated normal faulting and synsedimentary (growth) faulting during the period of cover sequences 2 & 3 was terminated by the compressive Isan Orogeny (1600 Ma to 1500 Ma), simplistically described as comprising an early phase of thrusting and folding (D1), a later phase of east-west compression, peak metamorphism and major upright N-S folding (D2, 1550 Ma), followed by retrograde metamorphism with late wrenching (D3; 1500 Ma), which also produced some further normal ("negative flower") and reverse faulting subsidiary to the main wrenching.

 

 

GEOLOGICAL DEVELOPMENTS AND MUSINGS

 

The recent publication of AGSO Bulletin 243 (Stewart and Blake, 1992) is an admirable summary of recent detailed work within the Mt Isa transect between Mt Isa and Cloncurry, introducing some of us to BP3 , DH1 , DK3 , uniaxial constriction, low-angle listric detachment, flow field perturbation in vergent folds, and riders in the footwall; in the field of sedimentation and sequence analysis, there are stacked channel sequences, fan head entrenchment, subaqueous mass flow fan deposits, CU and FU heterolithic facies, transgressive systems tracts and shoaling storm-dominated outer shelves.

 

While this new work adds another dimension to our understanding of the Inlier, it will always remain important in my view to place such work within a regional perspective, to see the larger picture incorporating, for example, data from those areas outside the transect which are less deformed, less metamorphosed and where relationships may be clear and unequivocal. In all parts of the Inlier there remain many unsolved geological problems, and certain myths and/or bones of contention are still perpetuated. Some matters also require reiteration as being of fundamental truth, and a selection of these problems, myths, and truths are mused upon below.

 

The Leichhardt River Fault Trough (LRFT) is a fundamental tectono-stratigraphic unit (Glikson et al, 1976; Derrick, 1982) within the Inlier, displaying a long-acting eastern margin with associated west-facing fan wedges (Quilalar Arch), and an internal subsidiary horst-like structure (or series of listric fault blocks), the Mt Gordon Arch, across which various units are condensed in thicknesses, and which increase in thickness west of the Arch. The true nature of the western boundary of the LRFT is obscured by younger cover, but filtered gravity data suggests the presence of a linear north-trending belt of dense crust (?basalt/basic rock), possibly another rift feature, parallel to the main LRFT and extending southwards in the subsurface from Century for over 200 km.

 

The correlation of Argylla Formation and Magna Lynn Metabasalt with Myally Subgroup and Eastern Creek Volcanics respectively, as shown in BMR/AGSO maps and publications since Blake (1987), is a stratigraphic and palaeoenvironmental aberration for which there is no strong evidence. The Argylla Formation/Magna Lynn Metabasalt bimodal suite are best thought of as a correlative of the Bottletree Formation forming a geochemically discrete and possibly diachronous basement to the LRFT, and ranging in age from 1800 to 1780 Ma. Clasts of Bottletree Formation (= Argylla Formation) are common in clastic wedges and debris flows at the base of the Haslingden Group.

 

Growth or synsedimentary faulting (Smith, 1969; Derrick, 1982) is now a firmly established characteristic of the LRFT, and detailed work shows that it occurs at many stratigraphic levels and may be of varying orientation, e.g. E-W trending, south-verging extensional faulting in ECV, prior to Surprise Creek Formation; NW-SE trending depocentres in Myally Subgroup related to basement shear; N-S trending transpressional flower structures with rim-syncline pebbly beds; eastward-block tilting (i.e. E edge of Mt Gordon Arch); N-S trending fault scarps (e.g. Hero Fault and Hero fan wedge complex at the base of the Mt Isa Group); west-verging, low-angle thrusting affecting only Moondarra Siltstone and containing some dolerite, and south-block down movement on E-W structures in lower Mt Isa Group forming clastic wedges in siltstone (Nijman et al, 1992a,b). Some north-block down E-W trending faults are also present. Growth faults are firmly established east and NE of Mt Isa, and are now documented to the south and SW of Mt Isa (Proffett, 1990, Connors et al, 1992) - one is an extensional fault which predates the region-wide Surprise Creek Formation unconformity, and which shows a reconstructed northerly dip of 25o-30o; and a younger growth fault was active in lower Mt Isa Group time, also downthrown to the north, and with older rocks inferred to have been steep-dipping to overturned before erosion and deposition of the overlying conglomerates.

 

The largely transgressive shallow-water Quilalar Formation/Mary Kathleen Group sag phase of cover sequence 2 represents a major thermal relaxation event across two thirds of the exposed Inlier from NW to SE, and ultimately allowed reasonably precise correlation of units across the Kalkadoon- Leichhardt basement block ; previously positive areas in LRFT time, such as the Kalkadoon-Leichhardt Block, became a focus for a number of trough and tidal shelf-dominated shallow water and continental palaeoenvironments (Jackson et al., 1990). Saline evaporites in the Corella Formation were likely sources of scapolite and NaCl-rich metamorphic fluids in later D2-D3 Cu-Au mineralising event(s), in the Eastern fold belt in particular.

 

Newly identified extensional events post-Mary Kathleen Group but pre-Mt Isa Group (Holcombe et al., 1992) include intrusion of Wonga and Burstall Granites at 1730-1740 Ma, and extrusion of Fiery Creek Volcanics at 1680 Ma; fluviatile clastics of the Mt Albert Group in the east are considered equivalent to shallow shelf coarse clastics of the Surprise Creek Formation in the west, and are underlain by a significant regional unconformity. These large fluviatile sand bodies may be associated with extension-related graben formation across the Corella shelf.

 

Not all metamorphism is limited to the Isan Orogeny; significant contact metamorphism to diopside-wollastonite grade is present adjacent to the 1730-1740 Ma Burstall Granite; such metamorphism may explain the sudden appearance of coarse muscovite in the disconformably overlying Mt Albert Group/Surprise Creek Formation.

 

The Maronan Supergroup/Soldiers Cap Group is probably allochthonous, rafted onto the Mt Isa terrane from the Diamantina Orogen to the east or southeast (Laing, 1991); however, Laing's proposal to extend the thrust zone further westwards to include Mt Albert Group is rejected, as is his suggestion that the Mt Norna Quartzite was once Mt Norna dolomite, and that some of the persistent ironstones plus Ba-F exhalites in the Maronan Supergroup, e.g. Monakoff, are mylonitic replacement zones. Some of these BIF-exhalite zones contain layers or beds of "garnet sandstone", confirming the overall similarity of the Cloncurry terrane to that of Broken Hill.

 

Beacon beds (or Tommy Creek beds) dated at 1620 Ma are postulated to be equivalent to the Soldiers Cap Group, on the basis of a unique exhalative mineralisation style in both areas viz barite-fluorite-carbonate + base metal association with black shale, metabasalt and other shallow shelf carbonates. The Beacon beds in addition contain abundant felsic volcanics, graded pebbly wackes and intermediate tuffaceous metadacites. The Beacon Beds, Soldiers Cap Group, etc. are similar in age, tectono-stratigraphic setting and mineralisation style to the Broken Hill Group (N.S.W.).

 

Re-evaluation of old (1975) BMR air photo interpretation and mapping in Alsace and Prospector 1:100,000 sheets suggests that the upper half of the 1740 Ma? Corella Formation may include equivalents of the Bigie Formation clastic-carbonate suite associated with the Fiery Creek rift phase at about 1680 Ma. Zn-anomalous shale basins at Deighton Pass and Dugald River thought to be upper Corella Formation by BMR (Derrick et al., 1977), and Mt Isa Group by CRA (Sheppard and Main, 1990), may in fact be of Fiery Creek age, e.g. 1680 Ma.

 

Throughout the Inlier, a cautious approach is recommended before declaring certain major concordant stratigraphic contacts as "conformable". Whereas many contacts between cover sequences are undisputably angular and unconformable or disconformable within the LRFT, because of an abundance of synsedimentary faulting and rotated listric fault blocks, equivalent contacts between the various cover sequence cycles outside of the LRFT and in the eastern fold belt tend to be subparallel, and either conformable or disconformable. The contact between 1860 Ma Leichhardt Volcanics and 1780-1800 Ma Argylla Formation volcanics is concordant for over 200 km, with only sporadic development of conglomerate above the older Leichhardt Volcanics to indicate an 80 Ma age difference. The relationship was ultimately clarified by geochronology. Similar problems may arise with cover sequence 3 quartzites (Knapdale, Deighton, Surprise Creek) of possible 1680 Ma age resting concordantly on 1740 Ma sag phase of the Mary Kathleen Group/Quilalar Formation.

 

Bell's "folded D1 thrust duplex" model to explain the repetition of greenstone - Mt Isa Group sequences within the LRFT is being strongly challenged (Stewart, 1992; Nijman et al, 1992a,b) on the basis that many of the east-west faults are younger than main-phase ("D2") upright folding, and are themselves folded by later events ("D3", "D4"). E-W trending folds adjacent to the E-W faults, formerly considered as D1 structures, are now young drag synclines produced by the S-verging extension. This pattern of faulting was described as an extensional "spoon fault" domain by Dunnet (1976), although there are timing differences between the extension models of Dunnet and Nijman (1992a,b).

 

Overall, it appears that the thrust imbricates of Bell are in fact normal fault graben. Should the shibboleth of Bell's D1 thrusting model be found wanting, then usage of terms such as Meerenurker thrust (= roof thrust) and Kokkalukkernurker duplex may thankfully be reduced, if not expunged.

 

Carbonate breccias, most common in the Corella Formation, but also present in other carbonate-bearing units (e.g. Beacon beds, Soldiers Cap Group) are largely of tectonic origin, with those associated with the Soldiers Cap Group east of Cloncurry the most problematical. Earlier workers (Carter et al, 1961), Glikson, 1972) quite reasonably declared the Corella Formation breccias to rest unconformably on Soldiers Cap Group. More detailed work by Ryburn et al (1988) suggested that breccias of 2 ages are present - an older Corella breccia may be in tectonic contact with other units, and shows effects of D1/D2 deformations. A younger but lithologically similar breccia, the Gilded Rose breccia, postdates the second major metamorphism and deformation, and includes fragments of Soldiers Cap Group and granite. The breccias are albitised, as is the granite, and Ryburn suggests the Gilded Rose Breccia is a product of late (?1500 Ma) granite intrusion of older Corella beds causing fluidisation and mobilisation of breccia which subsequently intrudes as diatremes and associated outflows, the whole process accompanied by soda metasomatism.

 

The entire stratigraphic column is characterised by alternating and contrasting lithologies and by an abundance of syndepositional structural features - unconformities, disconformities, various faults (growth, extensional, thrust etc), and a myriad of permeable zones such as conglomerate wedges and basaltic flow tops. All of these features at some time or another, either during times of diagenesis, compaction and basin dewatering, or during the post-depositional Isan Orogeny, provide important foci and pathways for potentially mineralised hydrothermal fluids of mixed meteoric, metamorphic, and/or magmatic origin; with reactivation of the various planar elements during late deformation comes the physico-chemical gradients, the dilatancy and, in some favourable sites, big gobs of mineralisation. One ignores the stratigraphic column and its various planes of potential reactivation at one's peril.

 

 

OVERVIEW OF MINERALISATION (Figure 2; Table 1)

 

Mineralisation types include syn/diagenetic Pb-Zn sediment-hosted deposits of Isa-Century type, common in areas of growth faulting and abundant pyritic and carbonaceous shales, and which are subject to recrystallisation during later shearing and metamorphism (e.g. Mt Isa, Dugald River); granite-related skarn-Cu-U-F at 1730 Ma, again subject to resetting or remobilisation at 1500 Ma (Mary Kathleen); Cu-only, Au-only and numerous Cu-Au shear-related deposits throughout the Inlier allied to the Isan Orogeny (1600-1500 Ma) and circulating saline metamorphic fluids, the latter being very efficient carriers of base metals and Au to a lesser extent, especially in the eastern fold belt. Major Cu-Au-magnetite deposits of the Osborne-Ernest Henry type may be products of an especially fertile association of hot saline metamorphic fluid and magmatic fluid derived from fractionating Williams Batholith (Wyborn et al., 1988) at about 1500 Ma.

 

A distinctive Cu-Mo-U-Au (D2-D3?) association with granofels and black shale is moderately typical of Williams Batholith element association, but in fact is developed along the 1730-1740 Ma Wonga-Burstall belt south of Mary Kathleen, adjacent to the Pilgrim Fault. This setting resembles that at the Au-only Tick Hill deposit along strike 75 km to the south, which occurs in highly strained quartz-veined pinkish granofels and in which mineralisation may in fact pre-date peak metamorphism.

 

The probable allochthonous Soldiers Cap belt contains BIF-exhalite-related Pb-Zn mineralisation of the Broken Hill type at Cannington, Pegmont, etc., characterised by low S, high silicate and high Fe, Mn, P geochemistry, and apparently predating major deformation and metamorphism i.e the mineralisation may have been subject to D1 thrusting and nappe development (Newbery, 1991). Ba-F-BIF-associated exhalites (Beacon, Milo, Monakoff) may be part of this mineralised exhalative package, which occurs mainly within and stratigraphically adjacent to the Mt Norna Quartzite unit in the Soldiers Cap Group. Some magnetic zones in this stratigraphy relate to both magnetite and pyrrhotite-rich shear zones hosting significant Cu-Au mineralisation e.g. Eloise (Brescianini et al., 1992).

 

 

Reasons are diverse for the spate of major Cu-Pb-Zn-Au discoveries in the Inlier in the period 1989-92; apart from good luck, they include the Australia-wide preoccupation by many companies with gold exploration in the early to mid 1980s, evidenced by a lack of major base metal discoveries in this period, and an associated decrease in the proportion of budgets allocated to base metal exploration viz. from 60% in 1982 to 15% in 1988. The penny began to drop at this time in 1987-88 that shortages of base metal, and consequent higher commodity prices, were a likely scenario for the near future; added to this was an emerging research program from 1986 on Proterozoic Au-Cu mineralisation in iron oxide-dominated hydrothermal systems (Tennant Creek/Starra), and their relation to granites and deformation and possibly sea-floor processes, the production start-up at Starra in 1987 which showed that success was possible even after 30 years of prior exploration, the on-going efforts by Placer/Billiton at Osborne/Trough Tank, and an explosion of geophysical imaging technology, especially in airborne magnetics; and a realisation that the DCF/NPV for Cu-Au deposits remained quite attractive even under 30 to 50m of Mesozoic cover.

 

In those areas and deposit types where magnetics were NOT a major factor in exploration, the push for base metals in the late 80s relied a little more on solid conceptual thinking utilising known deposits and the ready availability of that most precious exploration commodity - detailed geological maps. With the aid of geochemistry and conceptual thinking CRA found Century and WMC found Walford Creek; WMC were kind enough to state that the deposit was "targeted on conceptual geological grounds, with the aid of government geological mapping" (Webb & Rohrlach, 1992). Within-lease or "brownfields" exploration expanded the reserves at Hilton North and Dugald River, the latter deposit confirming the role that D2-D3 deformation and metamorphism could play in the upgrading of a known resource (Sheppard and Main, 1990). And if D3 events can upgrade a resource, why not create the resource, as is proposed by Perkins (1991) for the Mt Isa Cu-Pb-Zn pyrite deposit ? One wonders which way this particular geological domino may fall.....

 

Recent discoveries east of Cloncurry include the "Lorena" lode near Pumpkin Gully - a WNW-trending, steep and south-dipping quartz vein in silicified grey siltstone of the upper Toole Creek Volcanics contains an arsenopyrite-rich lode zone to 8m thick and 200m long with gold assays locally exceeding 1,000g/t. The lode quartz is veined by a later tourmaline-bearing quartz vein stockwork which contains fragments of a fine-grained felsic ?intrusive. A late granite-gold association is suspected, and the lode is planned to be mined by a local syndicate.

 

Elsewhere, the success of SXEW Cu processing at Gunpowder mine in particular, and Mount Isa, is no doubt influencing other groups in considering the toll treatment of suitable ores throughout the area, although carbonate gangue in many deposits renders these ore types less suitable to leaching.

 

CONCLUDING REMARKS

 

The discovery of Lorena simply says that there is room for everyone in the Mt Isa Inlier, large company or small. The stage is now set for considerable economic growth in the area; the geoscientific data base is in place and being refined month by month; the exploration skills have been honed by recent discoveries, and there is good reason to expect that a few more major deposits will be found in the next decade. Exploration success may not be a function of technical inputs, but of which land areas may be available for testing, and the nature and extent of compensatory agreements enacted through the area in the name of Mabo. More positively, the visionaries have a small piece of the ear of government, and the Carpentaria and Mt Isa Mineral Province Study Group, chaired by Mr A. Paton in 1992-93, foresees the union of natural gas and mineral resource projects in the next two decades or so, producing $2.5 billion of new capital investment, 2,000 new permanent jobs in the Province and up to $30 billion in new export revenue, notwithstanding the recent naive and uninformed remarks of the new Leader of the Australian Democrats. Mt Isa City is destined to grow apace, but between all this enthusiasm spare a thought also for Cloncurry, the premier copper field of the Commonwealth in 1916, and described by Blainey in 1960 as "sleepy Cloncurry, the town of more unfulfilled promises than any other town in Australia".

 

This time, one feels that fulfilment is nigh.

 

REFERENCES

 

Beardsmore, T.J., Newbery, S.P., and Laing, W.P., 1988 The Maronan Supergroup: an inferred early volcanosedimentary rift sequence in the Mt Isa Inlier, and its implications for ensialic rifting in the Middle Proterozoic of northwest Queensland. Precambrian Research, 40/41, 487-507.

 

Bell, T.H., 1983 Thrusting and duplex formation at Mt Isa, Queensland, Australia.

Nature, 304, 493-497.

 

Blainey, G., 1960 Mines in the Spinifex - the story of Mt Isa Mines. Angus and Robertson, Sydney.

 

Blake, D.H., 1987 Geology of the Mt Isa Inlier and environs, Queensland and Northern Territory. BMR Bulletin 225 83 pp.

 

Brescianini, R.F., Aston, M.W., and McLean, N., 1992 Geophysical characteristics of the Eloise Cu-Au deposit, northwest Queensland. Exploration Geophysics , 23, 33-42

 

Carter, E.K., Brooks, J.H., and Walker, K.R., 1961 The Precambrian mineral Belt of northwestern Queensland. BMR Bulletin 51

 

Connors, K.A., Proffett, J.M., Lister, G.S., Scott, R.J., Oliver, N.H.S., and Young, D.J., 1992 Geology of the Mount Novit Ranges, southwest of Mt Isa mine. in Stewart, A.J., and Blake, D.H.,(Eds), Detailed Studies of the Mt Isa Inlier. AGSO Bulletin 243, 137-160.

 

Derrick, G.M., 1992 Brothers-in-Arms: the interaction of geology and geophysics in the Mount Isa Inlier. Exploration Geophysics, 23, 117-122.

 

Derrick, G.M., 1991 Field Conference, Mt Isa Inlier - Guidebook, 8-10 June 1991. Geol. Soc. Aust. (Qld division)

 

Derrick, G.M., 1982 A Proterozoic rift zone at Mt Isa Queensland, and implications for mineralisation. BMR Jour. Aust. Geol. Geophys., 7, 81-92.

 

Derrick, G.M., Wilson, I.H., Hill, R.M., Glikson, A.Y., and Mitchell, J.E., 1977 Geology of the Mary Kathleen 1:100,000 sheet area, northwest Queensland. BMR Bulletin 193.

 

Derrick, G.M., Wilson, I.H., and Sweet, I.P., 1980 The Quilalar and Surprise Creek Formations - new Proterozoic units from the Mt Isa Inlier, their regional sedimentology and application to regional correlation. BMR Jour. Aust. Geol Geophys. 5, 215-223

 

Dunnet, D., 1976 Mt Isa - reconstruction of a faulted orebody. Philosophical Transactions of the Royal Society of London, A283, 333-344.

 

Glikson, A.Y., 1972 Structural setting and origin of Proterozoic megabreccias, Cloncurry region, northwest Queensland. Jour. Geol. Soc. Aust., 19, 53-63

 

Glikson, A.Y., Derrick, G.M., Wilson, I.H., and Hill, R.M., 1976 Tectonic evolution and crustal setting of the middle Proterozoic Leichhardt River Fault Trough, Mt Isa region, northwest Queensland. BMR J. Aust. Geol. Geophys., 1 (2), 115-129.

 

Hill, E.J., Loosveld, R.J.H., and Page, R.W., 1992 Structure and geochronology of the Tommy Creek Block, Mt Isa Inlier in Stewart, A.J., and Blake, D.H.,(Editors), Detailed Studies of the Mt Isa Inlier. A.G.S.O Bulletin 243, 329-348.

 

Holcombe, R.J., Pearson, P.J., and Oliver, N.H.S., 1992 Structure of the Mary Kathleen Fold Belt, in Stewart, A.J., and Blake, D.H.,(Editors), Detailed Studies of the Mt Isa Inlier. A.G.S.O Bulletin 243, 257-287.

 

Jackson, M.J., Simpson, E.L., and Eriksson, K.A., 1990 Facies and sequence stratigraphic analysis in an intracratonic thermal-relaxation basin; the Early Proterozoic, Lower Quilalar Formation and Ballara Quartzite, Mount Isa Inlier, Australia. Sedimentology, 37, 1053-1078.

 

Laing, W.P., 1991 Base metal + gold mineralisation styles in the Cloncurry terrane, in Base Metal Deposits Symposium, EGRU Contribution 38, 77-88.

 

Newbery, S., 1991 Iron formation-hosted base metal mineralisation of the Cloncurry terrane, Mt Isa Inlier, in Base Metal Deposits Symposium, EGRU Contribution 38, 89-99.

 

Nijman, W., van Lochem, J.H., Spliethoff, H., and Feijth, J., 1992a Deformation model and sedimentation patterns of the Proterozoic of the Paroo Range, Mt Isa Inlier, Queensland, Australia. in Stewart, A.J., and Blake, D.H.,(Editors), Detailed Studies of the Mt Isa Inlier. A.G.S.O Bulletin 243, 29-74.

 

 

Nijman, W., Mijnlieff, H.F., and Schalkwijk, G., 1992b The Hero fan delta (lower Mt Isa Group) and its structural control: deformation in the Hero/Western Fault zone at Paroo Range compared, Proterozoic Mount Isa Inlier, Queensland, Australia. in Stewart, A.J., & Blake, D.H.,(Eds.), Detailed Studies of the Mt Isa Inlier. AGSO Bulletin 243, 30-75.

 

Page, R.W., 1988 Geochronology of Early to Middle Proterozoic fold belts in northern Australia - a review. Precambrian Research, 40/41, 1-19

 

Proffett, J., 1990 Some new observations on the geological structure southwest of Mount Isa. in Mt Isa Inlier Geology Conference, Monash University/VIEPS, Nov. 1990 (abs)., 29-31.

 

Ryburn, R.J., Wilson, I.H., Grimes, K.G., and Hill, R.M., 1988 Cloncurry, Qld: 1:100,000 Map Commentary, BMR, Australia.

 

Smith, W.D., 1969 Penecontemporaneous faulting and its likely significance in relation to Mount Isa ore deposition. Geol. Soc. Aust. spec. Publ. 2, 225-235.

 

Stewart, A.J., & Blake, D.H., 1992 Detailed studies of the Mt Isa Inlier. AGSO Bulletin 243.

 

Webb, M., and Rohrlach, B., 1992 The Walford Creek Prospect - an exploration overview. Exploration Geophysics , 23, 407-412.

 

Wyborn, L.A.I., 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

 

Wyborn, L.A.I., Page, R.W., and McCulloch, M.T. 1988 Petrology, geochronology and isotope geochemistry of the post-1830 Ma granites of the Mt Isa Inlier: mechanisms for the generation of Proterozoic anorogenic granites. Precambrian Research, 40/41, 509-541.

* Competition No.3, Clue No.5 and Question:
Which Australian geologist, listed in the bibliography above is renowned for her work on granites and what was the title of her jointly authored paper to the SMEDG-AIG '93 Symposium?
E-mail answer to THE JUDGE
The Judge's decision final, no correspondence entered into except for humorous purposes or exchanges of views of no consequence whatsoever. Well done on getting this far!