Northwest Queensland Research Articles

Effect of herbage in Astrebla spp. pastures in northwest Queensland on lamb survival

SUMMARYExtensive grazing experiments were conducted over four summer breeding seasons in north-west Queensland between 1984 and 1989. Ewes in the last third of pregnancy were grazed on Mitchell grass (Astrebla spp.) pastures of varying forb (herbaceous plant other than a grass) content. Pastures of low forb content (F-) were attained by stocking paddocks heavily with wethers prior to the experiment, or by selecting paddocks which already contained pastures of low forb content. Pastures of high forb content (F+) were kept without animals prior to the experimental period. Pastures comprised a range of forb biomass (29–828 kg DM/ha) and percentage forbs in total biomass (3–49%). Lamb marking percentage was found to be dependent on the biomass of forbs and proportion of forbs in the pasture, in two experiments. Ewes which grazed F+ pastures had lower lamb marking percentages than those grazing F- pastures.Twenty pasture species collected during the experiments were analysed for the ratio of 13C: 12C and photosynthetic pathway was determined. Five forb and all three grass species had C4-dicarboxylic acid pathways, ten forbs had Calvin-C3 pathways and two forbs had crassulacean acid metabolism pathways.Estimates of the proportion of C3 and C4 species in the diet were determined by analysing the ratio of 13C:12C in faeces. The apparent high proportion of Calvin-C3 pathway forbs in the diet of ewes compared to the proportion in the total pasture biomass indicated that ewes preferentially select C3 forbs in the diet, although there was no dependence of lambing percentage on the estimated proportion of C3 forbs in the diet. Management strategies that may improve lambing percentage in the Mitchell grass areas of north-west Queensland are discussed.

Managing Sheep for Optimum Productivity in Astrebla Pastures in North-West Queensland.

A yearly management program for sheep in north-west Queensland has increased lambing percentage by > 20% compared with the district average. Greasy wool production of ewes over 4 years (1988-91) averaged 4.3 kg and wethers over 2 years (1990-91) averaged 5.7 kg. Managing sheep using this program increased wool production of the flock compared with the district average. The economic advantages of running breeding ewes or wethers was influenced by wool and sheep markets. During low wool prices ($2.82/kg net selling costs, 1990; $2.44/kg net selling costs, 1991) it was estimated that a 65% lamb weaning rate was needed for returns from the ewe and wether flock to be equal. Gross margins ($/DSE) for the ewe flock were 21.80, 17.07, 8.53 and 5.42 in years 1988, 1989, 1990, 1991 respectively and 5.82 and 5.01 for wethers in 1990 and 1991 respectively. Gross margin ($/DSE) of combined ewe and wether enterprises on properties representing the district, averaged 16.50, 14.20, 8.00 and 5.00 in years 1988, 1989, 1990 and 1991 respectively. The management program implemented at Toorak generated higher gross margins than the district average particularly during the years of higher wool prices.

Geological Mapping Capabilities of the QUESTEM Airborne Electromagnetic System for Mineral Exploration — Mt. Isa Inlier, Queensland

Airborne electromagnetic (AEM) surveys are now being flown to assist in geological mapping programs. In areas of varying electrical conductivity AEM data provide significant information that can be used in conjunction with aeromagnetic and ground geological data to build up a three-dimensional interpretation of the geology. Image presentations enable interpretation and mapping of the geology.A QUESTEM airborne geophysical survey was flown over the Lady Loretta deposit in the Lawn Hill Platform, north-west Queensland, with the aim of mapping the geology, using both AEM and airborne magnetics. The survey area comprises folded and faulted Middle Proterozoic sediments unconformably overlain by Cambrian sediments in the east of the area.High electrical conductivity contrasts between the different stratigraphic units has enabled a detailed geological interpretation to be made from the AEM data. For example, the Esperanza and Gunpowder Creek Formations are strongly conductive relative to overlying and underlying formations allowing fold structures and faults to be mapped. The Upper Lady Loretta Formation includes strongly conductive pyritic shale that hosts the lead-zinc mineralisation. In addition broad subtle changes in conductivity enable different lithologies to be distinguished. The aeromagnetic data does not provide the detail seen in the AEM data due to the lack of magnetic susceptibility contrast within the Proterozoic sediments. Faults interpreted from the aeromagnetic data generally correlate with those evident in the AEM.In the eastern part of the survey area conductive units can be traced below the Cambrian sandstone. These may represent areas of further exploration interest.

Maramungee; a Proterozoic Zn skarn in the Cloncurry District, Mount Isa Inlier, Queensland, Australia

The significant but subeconomic (1.8 Mt4.4% Zn) Maramungee deposit is 90 km south-southeast of Cloncurry in northwest Queensland. It lies in the Eastern fold belt of the Proterozoic Mount Isa inlier within rocks of the Maronan Supergroup that also hosts the large Pb-Zn-Ag deposits at Cannington and Pegmont. The Maramungee deposit is a product of a series of processes that occurred during the metamorphic evolution of the Eastern fold belt and the brittle structures that host sulfide mineralization are likely to have been active after the emplacement of the late to post-tectonic granites of the Williams batholith.Maramungee is hosted by upper amphibolite (sillimanite-K feldspar zone) gneisses, exceptionally iron-rich metabasites, and foliated granite. Mineralization was restricted to an elongate embayment in the margin of the Maramungee Granite pluton created by the antiformal part of a steeply inclined parasitic F 2 fold. A major photolinear feature lies immediately west of the hinge in both the granite and its host rocks. This structure was initiated by fabric intensification during attenuation of the adjacent fold limb. Mineralization was further localized by a heterogeneous altered rock package including (1) potassic rocks (generally foliated) with large amounts of microcline and/or biotite, (2) skarns (partly discordant) including both manganoan hedenbergite + Fe-Mn-rich grossularite + quartz + apatite rocks and Ca-rich almandine + or - clinopyroxene-bearing metabasites, and (3) a range of compositionally intermediate assemblages distinguished by the coexistence of Fe-Mn, Ca-, and K-bearing metamorphic silicates. Graphite commonly occurs at levels of several modal percent in the altered rocks but magnetite and zincian spinel are absent. The most strongly altered rocks have a chemical component derived from the metasedimentary gneisses and possibly reflect alteration of a unit which previously contained carbonates. This alteration would have involved reduction producing graphite coupled with differential addition of K, Fe, Mn, P, and F.The potassic and skarnoid rocks are distinctive components of a regional pattern of metasomatism that exploited steeply inclined D 2 structures. Early metasomatic fluids in equilibrium with graphite at Maramungee are unlikely to have been evolved from the magnetite-bearing pluton. Sulfides (mainly sphalerite, pyrrhotite, and pyrite) occur in veinlets and microbreccia matrices that overprint all the earlier rock types and alteration assemblages. They are associated with the development of retrograde (hydrous) and comparatively oxidized secondary minerals including Cl- and Fe-rich amphiboles, chlorite, scapolite, calcite, albite, epidote, and muscovite. Hematite is present in the youngest alteration assemblages. Retrograde phase relationships suggest that sulfide deposition was induced by reduction of the infiltrating fluid, initially occurred at temperatures of 450 degrees to 500 degrees C, and may have continued through a significant cooling interval.Zn is the only economically significant metal present, although Pb, Ag, Cu, Cd, and Sb are commonly anomalous and there are sporadically elevated amounts of Au, As, and Mo. Molybdenite is associated with fluorite and enrichments of Rb, Ba, U, Th, and light REE in the early potassic alteration. With the exception of Zn and Cd there is little overall correlation among the chalcophile elements. There is a crude zoning toward higher Cu/Zn ratios in the southern part of the prospect and there are sporadic occurrences of Cu-Fe sulfide mineralization that have no clear relationship to the main Zn zone associated with silicification, muscovite-chlorite alteration, and variably anomalous Au, Ag, Se, Co, REE, and U.

Reply to discussion: Tectono‐metamorphic evolution of the Mary Kathleen fold belt, northwest Queensland: A reflection of mantle plume processes?

Reply to discussion: Tectono‐metamorphic evolution of the Mary Kathleen fold belt, northwest Queensland: A reflection of mantle plume processes?

Identification of a rock-wallaby population from 'Lawn Hill', northwest Queensland, as Petrogale lateralis purpureicollis: a significant range extension.

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Geological note: Documentation and significance of a major unconformity in the Wonga Belt of the Mt Isa Inlier, northwest Queensland

(1992). Geological note: Documentation and significance of a major unconformity in the Wonga Belt of the Mt Isa Inlier, northwest Queensland. Australian Journal of Earth Sciences: Vol. 39, No. 5, pp. 671-673.

Discussion: Tectono‐metamorphic evolution of the Mary Kathleen fold belt, northwest Queensland: A reflection of mantle plume processes?

Discussion: Tectono‐metamorphic evolution of the Mary Kathleen fold belt, northwest Queensland: A reflection of mantle plume processes?

Effect of Haemonchus contortus on productivity of ewes, lambs and weaners in a semi-arid environment

SUMMARYLactating ewes, ewes that had lambed but subsequently lost their lambs (dry) and weaners were either artificially infested with 2000–3000 third-stage Haemonchus contortus larvae (parasitized) or drenched with levamisole (treated) and run under extensive grazing conditions in north-west Queensland. Worm egg counts in parasitized lactating, dry and weaner sheep ranged from 860–2830 eggs per gram of faeces. These levels of infestation significantly (P < 0·01) reduced liveweight gain of all three sheep classes, milk yield of ewes and wool growth of weaners compared to their treated counterparts. The lower milk yield of the parasitized ewes significantly (P < 0·01) reduced lamb growth rate. Survival of lambs to weaning was 26% higher in the treated group. The experiments showed that moderate levels of H. contortus, that did not produce clinical signs of infestation, reduce productivity of sheep in this semi-arid environment.

The Walford Creek Prospect — An Exploration Overview

alford Creek is a Zn, Pb, Cu, Ag prospect located in northwest Queensland at 17° 48¢S, 138° 17¢E. Both stratiform mineralisation and stratabound breccia style mineralisation are present but not in sufficient quantity to make the deposit economic. The base-metal occurrences are closely associated with a much larger body of stratiform massive pyrite. This massive pyrite body has a shallow southerly dip, a strike length of six kilometres, and a typical width of 1500 m. The classic geological setting and similar geophysical signature to some economic deposits make it a useful case history. The mineralisation is hosted by the mid-Proterozoic Mt Les Siltstone on the northern margin of the Lawn Hill Platform. It lies immediately to the south of the Fish River Fault, under thin alluvial cover. The prospect was originally targeted by Western Mining Corporation on conceptual geological grounds, with the aid of government geological mapping. Until recently the prospect was thought to have no surface expression, and exploration has been primarily advanced by the use of electromagnetic techniques. The stratiform mineralisation is intimately associated with a series of three gently dipping and vertically stacked synsedimentary massive pyrite horizons. It comprises an overprinting diagenetic impregnation of coarse-grained sphalerite and galena. The stratabound breccia mineralisation is hosted by a series of dolomite talus breccias adjacent to the Fish River Fault. It is a later, discordant style of mineralisation consisting of sphalerite, galena and chalcopyrite. The coincident-loop TEM method has been the primary geophysical exploration tool. The host shale package to the mineralisation is not graphitic, and the TEM results have successfully mapped the extent and gross geometry of the upper pyrite lens. Gravity has been shown to be a useful exploration aid at both the regional and prospect scales. Airborne magnetic surveys have successfully mapped the main basin structure controlling the mineralisation. Airborne TEM and a large fixed-loop survey have been tested over a part of the mineralized system.

Geophysics of the Century Zinc-Lead-Silver Deposit, Northwest Queensland

The Century Zn-Pb-Ag deposit, located about 250 km north-northwest of Mount Isa, Queensland, was discovered by CRA Exploration in 1990 following several years of regional area selection studies and initial reconnaissance field work. The field work focussed attention on a zinc soil geochemical anomaly, which was delineated on one of two regional gravity, ground magnetic and soil sample traverses. No anomalous response was detected on the gravity or magnetic data.Follow-up grid-soil sampling delineated an area about 1.5 km square of enhanced zinc anomalism, located adjacent to the Termite Range Fault, a major northwest trending structure. However, concurrent magnetic and SIROTEM surveys failed to reveal any targets to support the immediate drill testing of the geochemical anomaly.Subsequent siting of the discovery drillhole was based largely on the observed geochemical anomaly, and recognition of near-surface leaching of zinc elsewhere in the Century area. Post-discovery drilling has outlined a resource containing 116 Mt of 10.3% zinc, 1.5% lead, and 35 g/t silver.Geophysical techniques have been applied at Century since the discovery to help define the limits of mineralisation, map lithologic boundaries and structure, provide data for ore reserve estimates and mine planning, and to aid ongoing exploration in the area. Methods used have been gravity, ground and airborne magnetics, ground and airborne electromagnetics, IP/resistivity, downhole geophysical logging, and reflection seismic. The most useful technique to date has been IP/resistivity, which has assisted in mapping the extent of mineralisation beneath limestone and younger cover to depths of at least 150 m.

Geophysical Characteristics of the Eloise Cu-Au Deposit North-West Queensland

The Eloise Cu?Au deposit is located approximately 60 km south-east of Cloncurry in northwest Queensland. It is hosted within interpreted Early to Middle Proterozoic metasediments of the Soldiers Cap Group, and comprises a number of steeply plunging, structurally complex mineralised zones. The deposit is overlain by between 50 and 70 m of highly conductive, flat-lying Mesozoic age sediments. Geophysical methods assumed leading roles in the discovery of the Eloise deposit. The systematic evaluation of linear aeromagnetic trends using moving-loop transient EM (TEM) profiling led to the initial recognition of the Eloise anomaly. Fixed-loop TEM surveying detailed a strong bedrock conductor broadly coincident with a moderately intense magnetic ridge. Drillhole END17, sited to test the conductive source, intersected 20 m of chalcopyrite?pyrrhotite mineralisation. The geometry of the deposit limited the extent to which surface TEM methods could confidently define targets for subsequent drilling. As a consequence, downhole TEM was identified as an effective tool to guide exploration drilling. This technique proved extremely useful, both in detecting additional mineralised bodies and in helping to define the dip extent of the deposit. Lines of gravity and dipole?dipole IP have also been completed over the deposit to further characterise its response. In both instances sizeable anomalies were recorded, attributable in part to a significant mafic alteration system associated with the mineralisation.

The history and current status of geophysical exploration at the Osborne Cu & Au deposit, Mt. Isa

The Osborne deposit lies within the Trough Tank project area, situated some 190 km south-east of Mt Isa, in northwest Queensland. Copper and gold mineralisation occurs within a magnetite-rich Proterozoic ironstone sequence, possibly equivalent to the Mt Norna Quartzite unit of the Soldier’s Cap Group.Mineralisation occurs within two shallow north-easterly dipping ironstone units, beneath 20 to 40 m of flat lying mesozoic siltstone. Based on 396 drillholes completed to the end of 1991, the total diluted resource was calculated at 36 Mt at 2.0% Cu and 1.0 g/t Au, using a 1% Cu-Au equivalent cut-off.Results of early geophysical surveys (magnetics, IP and TEM) have been described by Gidley (1988). Although initial interpretation of magnetic data failed to recognise the likely influence of demagnetisation effects, subsequent modelling efforts incorporating a qualitative demagnetisation correction effectively sited drillholes to test the ironstone sequence. Quantitative interpretation of the magnetic response in the area of the deposit, including demagnetisation effects, is the subject of a current M.Sc. study by a co-author (Logan).Fixed and moving loop TEM surveys subsequently defined a strongly conductive zone within the southern portion of the ironstone trend. The next drilling phase tested this position and intersected encouraging thicknesses of sub-economic mineralisation within massive ironstone. Downhole TEM surveys, in conjunction with resistivity logging and physical property measurements, established that conductivity variations within the ironstone relate to the content and degree of remobilisation of magnetite as well as sulphide content. Continuing use of TEM for detection of high-sulphide lenses within the ironstone conductive host was therefore questionable.Step-out reverse circulation drilling continued to confirm the presence of a large mineralised system, although no coherent high-grade intersections were achieved. Vertical derivative enhancement and further modelling of ground magnetic data contributed to the development of structural models for the prospect, which were tested with further drilling programmes, but still failed to reveal any high-grade mineralisation. The first economic drill intersection came after 28 diamond-cored and approximately 70 reverse circulation holes had been completed on the project.Moving-loop coverage of the grid area was completed after drilling had established the presence of high-grade material down-dip from the magnetic anomaly position, in areas poorly coupled with the earlier fixed-loop transmitter loops. This coverage outlined a small conductive zone within the northern high-grade mineralisation.Subsequent geophysical surveys have included gravity, down-hole magnetics, mise-à-la-masse and magnetometric resistivity. Gravity results closely reflect the known distribution of ironstone, and borehole magnetometry has confirmed the inferred orientation of the total field after demagnetisation. Additional electrical techniques have confirmed the conductive zones outlined in TEM data and further indicated that the conductivity of ironstones is not directly related to mineralisation. This is attributed in part to the increase in silica content in high-grade material, at the expense of magnetite, reducing the interconnection of sulphide and magnetite grains.Recent tests with the borehole Radio Imaging Method (RIM) have indicated that this technique may help to confirm inferred correlations of mineralisation between diamond drillholes at separations of up to 70 m. Conductivity of mineralisation at the employed radio frequency (50 kHz) appears to be more coherent than is observed for the TEM technique.

Reply to discussion: Nature and timing of early extensional structures in the Mitakoodi Quartzite, Mount Isa Inlier, northwest Queensland

Reply to discussion: Nature and timing of early extensional structures in the Mitakoodi Quartzite, Mount Isa Inlier, northwest Queensland

Discussion: Nature and timing of early extensional structures in the Mitakoodi Quartzite, Mount Isa Inlier, northwest Queensland

Discussion: Nature and timing of early extensional structures in the Mitakoodi Quartzite, Mount Isa Inlier, northwest Queensland

New records of the Julia Creek dunnart, Sminthopsis douglasi (Marsupialia : Dasyuridae)

The Julia Creek dunnart, Sminthopsis douglasi, previously known from only four specimens, the last of which was collected in 1972, has been found alive. The number of known localities has been increased from three to eleven, and its range in the 'downs country' of north-west Queensland extended.

Tectono‐metamorphic evolution of the Mary Kathleen fold belt, northwest Queensland: A reflection of mantle plume processes?

The Proterozoic Mary Kathleen Fold Belt is one of the most intensely deformed fold belts within the Mt Isa Inlier (northwest Queensland), and contains key evidence for both extension and shortening, as well as a protracted thermal history culminating in a high temperature, low pressure amphibolite facies metamorphism. An early phase of extension (1780–1730 Ma) may have initially been responsible for basin development, and was subsequently associated with intense ductile shearing and multiple magma injection in a lower plate, and minor folding, extensional fracturing and emplacement of discrete intrusions in a more brittle upper plate. The subsequent regional deformation (D2) and metamorphism (1600–1500 Ma) involved east‐west directed compression, locally producing a variety of fold interference patterns by overprinting of F1 folds. This deformation resulted in tight folding of the early zone of high D1 strains into a large anticlinorium (the Wonga Belt). East of this zone, the effects of D2 dominate. The ...

Surface gravity and magnetic responses of mineralization, Mt. Isa, northwest Queensland, Australia

Surface gravity and magnetic surveys around the giant copper‐silver‐lead‐zinc mine at Mt. Isa in northwest Queensland have shown that each type of mineralization presents characteristic responses which are anomalous within the perspective of the host rocks. The responses reflect the entire mineralization‐alteration package and not simply the economic ore. Copper mineralization and associated alteration products, including “silica dolomite,” are not significantly magnetized, but the mineralization across a depth range of 1000 m produces a positive gravity anomaly of more than 2.5 mGal. The related alteration products are associated with large negative anomalies of up to 8 mGal in both hanging wall and footwall host rocks. Silver‐lead‐zinc mineralization is moderately magnetic (about 0.001 cgs). It is also denser and shallower and generates larger gravity anomalies. Negative secondary alteration effects, while significant, are equivalent in magnitude to the mineralization effect. Sites mineralized comparably to Mt. Isa would be located by semiregional surveys with a station spacing of 200 to 400 m and survey precision of better than 0.4 mGal, although there are limits to resolution of individual parts of the mineralization.

Thesis Abstract: Prehistoric Settlement Patterns and Artefact Manufacture at Lawn Hill, Northwest Queensland

(1989). Thesis Abstract: Prehistoric Settlement Patterns and Artefact Manufacture at Lawn Hill, Northwest Queensland. Australian Archaeology: Vol. 29, No. 1, pp. 75-78.

The intra-cratonic evolution of the central eastern Mount Isa Inlier, northwest Queensland, Australia

The central eastern part of the Mount Isa Inlier can be subdivided into three major tectono-stratigraphic domains, from west to east: (i) the Mitakoodi Anticlinorium, a tight, northeast-plunging, composite anticline, which is developed within subaerial to shallow-marine, continental-rift facies lithologies; (ii) the Marimo-Staveley Block, in which tight to isoclinal folds are developed within a marine shelf; (iii) the central part of the Soldiers Cap Group belt, which is dominated by a series of metaturbidites, and which hosts a fold nappe refolded about N-S to NE-SW trending axes. The transition from subaerial sediments in the west through marine shelf sediments to turbidites in the east has been one of the main arguments used by advocates for a Proterozoic continental margin at this locality. Here, however, it is argued that folding and differential uplift along late fault and shear zones led to the juxtaposition of different stratigraphic levels, and to the apparent deepening of palaeobasins from subaerial in the west to deep water in the east. The age of the Soldiers Cap Group is poorly constrained, but it is likely to be older than that of rocks cropping out in the Marimo-Staveley Block. The Marimo-Staveley Block lithologies overlie those of the Mitakoodi Anticlinorium, so here time-transgression rather than eastward deepening may be deduced. Thus, a palinspastic reconstruction based on an eastwards progressive deepening, is not justified. This adds to other evidence that refutes the continental margin model previously proposed for the eastern margin of the Mount Isa Inlier. Instead, the lithostratigraphic sequences reflect several stages of intra-continental rifting, all without formation of oceanic crust. The pervasive post-depositional deformational event is associated with regional low-P-facies metamorphism, which indicates a further ensialic history.