Central NSW Research Articles

Determining The Salt Store and Mobility in the Regolith, Bland Sub-Catchment, Central Nsw

To manage salinity risk for a sub-catchment or a region, quantifying the salt store and degree of salt mobility are two fundamental issues to address. In a thick (e.g. 70 m) and complex aquifer system, where sand bodies are semi-confined to confined within spatially dominating mud and clay, quantifying the salt store and mobility based on information collected from sparsely and unevenly distributed water bores and exploration drill holes is a significant challenge. Airborne electromagnetic (AEM) data, using Fugro?s time-domain TEMPEST fixed wing system, were collected over ~ 1,500 km2 of the Bland sub-catchment in central NSW (Lawrie et. al., 2002). Conductivity responses depict the electrolyte concentrations (mainly sodium chloride) and water content of the regolith and basement rock (Lawrie et al., 2002). Statistical analyses of water content, salinity and electrical conductivity logs show that conductivity is a measure of salt load. Non-porous bedrock is resistive whereas porous and moist sediments with saline pore fluids are conductive. Amongst the sediments, less porous coarse textured palaeo-valley basal gravely sand is less conductive than highly porous clay-rich colluvium and lacustrine mud. Using conductive depth slices (CDI), the spatial salt load distribution was mapped and quantified using ArcGIS (Tan et al., 2005a).

Hyperspectral discrimination of halophytic vegetation as an indicator of stressed arable land

The spectral properties of eleven Australian halophytic grass species were analysed for key spectral characteristics to assist in hyperspectral image interpretation and mapping. Six halophyte species were successfully mapped using hyperspectral imagery over an area suffering from dry‐land salinity in central west NSW. The resultant class map of halophytes was statistically compared to interpolated electrical conductivity data via a confusion matrix. Variations in the spatial abundance of different halophyte species are shown to significantly reflect the level of landscape stress in terms of salt scalding and electrical conductivity. This illustrates the ability of such technology to map environmental stress as indicated by halophyte populations.

Monitoring the hydrological impact of land use change in a small agricultural catchment affected by dryland salinity in central NSW, Australia

Increasing salinity in river systems in the Murray-Darling Basin is a current concern and has the potential to devastate many rural industries. The solution is seen as a move away from traditional agricultural practices which are inefficient water users and lead to high groundwater recharge and toward high water use enterprises that can minimise groundwater recharge. Previous modelling studies have shown that land use change in local groundwater systems has the potential to impact upon groundwater levels and streamflow within a decadal scale time frame, however there are few field based studies to prove the modelling correct. The current study reports on 13 years of groundwater and surface water monitoring on a 129 ha first order catchment in the Boorowa River catchment in NSW, Australia. The land use has changed from annual cropping and pastures to tree belts with perennial pastures. Five years after the land use change, the groundwater levels have fallen dramatically due to almost no recharge, runoff has been significantly reduced and the salt input–output ratio of the catchment has halved. Analysis of the measured components of the water cycle show that the reduction in recharge and runoff are due to the land use change and not merely a reflection of the reduced rainfall since the implementation of the land use change. Numerical groundwater modelling has shown that the reduction in salt affected area in this catchment and the export of salt out of this catchment will reduce for the next few decades.

Effect of some selective herbicide oversprays on newly emerged eucalypt and hopbush seedlings in Central Western New South Wales

Summary Unlike parts of Victoria and South Australia, direct seeding of woody plants has been unreliable in Central Western New South Wales where failures have been attributed to low rates of seedling emergence and competition from herbaceous weeds. We investigated the usefulness of overspraying newly emerged seedlings of eucalypt (Eucalyptus spp.) and Narrow‐leaf Hopbush (Dodonaea viscosa ssp. angustissima) in an existing or potentially weedy seedbed using a grass‐selective herbicide (Fusilade® or Sertin®) and/or a soil‐residual herbicide (Simazine®). These treatments were investigated at two sites over three sowing seasons in Central Western NSW. In most cases, the herbicides failed to enhance seedling survival because grasses were not the main component of the weed species present or because the herbicide damaged the seedlings. Hopbush was relatively tolerant to Simazine but eucalypt seedlings were not, particularly at the site with sandy soils. Grass‐selective herbicides did not appear to damage seedlings. Suggestions for increasing the reliability of direct seeding in this region are presented.

Optimization of partial extraction chemistry for buffered acetate and hydroxylamine leaches

The reaction conditions chosen for most partial geochemical extractions remain largely unjustified in terms of optimizing their ability to isolate element signatures related to the effects of mineralization. This study demonstrates the use of central composite designs to study the effects of variation in temperature, pH and reagent concentrations on metal extraction for a buffered acetate leach and a hydroxylamine leach. These designs have been used on nine soil samples from a traverse over porphyry Cu–Au mineralization in central NSW, Australia. For both leaches, metal extractability varies significantly with reaction conditions and the strongest responses to mineralization are generally provided under a very restricted range of digestion conditions. The optimum extraction conditions at Mandamah for the acetate leach are the low pH of the acetate buffer (3.76) and a high acetate concentration at any temperature. The optimum conditions at Mandamah for the hydroxylamine leach are pH = 0, T = 100°C and a moderate to high hydroxylamine concentration (although not for its ability to reduce metal oxides).

Rutile geochemistry as a guide to porphyry Cu–Au mineralization, Northparkes, New South Wales, Australia

The textures and compositions of accessory minerals formed during hydrothermal alteration in porphyry Cu–Au deposits may reflect those processes. Furthermore, if the accessory minerals are stable during weathering processes, they should be able to be used as a guide to mineralization even when the sulphides have been destroyed by weathering. In the Northparkes district, central western NSW, Australia, several Cu–Au ore deposits occur as disseminated or veined sulphides associated with a number of quartz monzonite porphyries intruded into lower Palaeozoic K-rich trachyandesites. This paper reports results from 2000 analyses of rutile grains from 80 samples of rock and soil from around one of these deposits, the E26N porphyry Cu–Au deposit. Within 100 m of ore, rutile grains are larger (commonly with length × breadth >4000 μm 2 ) than the grains further from ore (length × breadth <1500 μm 2 ). The rutile grains closer to ore also are zoned and contain V-rich portions in which V contents are >0.2% (commonly >0.4%) whereas barren rutile generally contains <0.15% V. Niobium contents of >0.15% occur in rutile in the E26N ore zone and in an altered zone within an adjacent earlier intrusion. Thus, Nb in rutile is not as consistently related to mineralization as V in rutile. Vanadium- (and Nb-) rich rutile is present in both the saprolite and soils derived from mineralized rocks at the deposit. Thus, the V contents in rutile can be utilized as a guide to mineralization even in highly weathered material.

Application of three modelling approaches to simulating tree growth in central NSW, Australia

In Australia, tree planting is being considered for major national catchment planning and management initiatives, especially in low rainfall regions. Models that provide spatial estimates of tree growth and incorporate the effects of climate variability are required to support these initiatives. This study employed three different modelling approaches to assess tree growth for the Lachlan catchment in south-eastern Australia. Firstly, the Physiological Principles for Predicting Growth (3-PG) model was used in ‘grid mode’ with long-term average climate grids to produce surfaces of modelled growth (Model 1) for three scenarios: managed timber plantations, plantations for farm forestry and other purposes, and natural regeneration of native vegetation. Secondly, the 3-PG model was used in ‘point mode’ with 50 years of actual weather records to simulate the effects of climatic variability on tree growth at 30 sites across the region (Model 2). Simulated estimates of growth for these 30 sites (Model 2 outputs) were then regressed against a detailed mean annual rainfall surface and the resulting linear equations were used to develop surfaces for predicted growth across the catchment (Model 3). These three approaches were compared to assess their suitability for developing spatial estimates of tree growth and the effects of climatic variability for catchment assessment and planning. The study confirms that use of long-term average climate data to model tree growth across a region may be misleading and that regional assessments should incorporate the effects of climatic variability on tree growth.

The influence of diurnal temperatures on the hydrochemistry of a tufa‐depositing stream

AbstractAt‐a‐station diurnal variations in carbonate hydrochemistry were measured during four observation periods at Davys Creek, a tufa‐depositing stream in central NSW, Australia. Major ion concentrations and continuously logged measurements of specific conductivity, pH and temperature showed that changes in the amount of CaCO3 deposited upstream of the study reach were directly related to changes in diurnal water temperatures, which control the rate of CO2 efflux to the atmosphere. The greatest upstream losses occurred during the mid‐afternoon water temperature peak, whereas the lowest upstream losses occurred at sunrise, when water temperatures were at their lowest. Cloudy days at all times of the year produced small diurnal water temperatures ranges (c. 2–5°C) and, consequently, relatively small changes in upstream CaCO3 loss (23–50 mg L−1) through the day. Clear sunny days, especially during summer months, produced large diurnal water temperature changes (up to c. 11°C), which in turn triggered diurnal changes in upstream CaCO3 loss of up to 100 mg L−1. By implication, the active reach of tufa deposition must advance downstream and increase in length during the evening and vice versa during the day. Given that the temperature of Davys Creek waters are a function of insolation, changes in the reach of tufa deposition under baseflow conditions are a direct function of the prevailing weather. This has implications for the palaeoclimatic interpretation of fossil tufa deposits. Copyright © 2003 John Wiley & Sons, Ltd.

Tau-p velocity imaging of regolith structure

The tau-p velocity imaging method, first developed for obtaining the velocity field from marine multichannel seismic data, has been applied to refracted waves from the regolith in regional seismic reflection surveys on land. The technique converts travel time picks from the refracted wavefield into two-dimensional velocity models, by transforming from time-offset into the tau-p domain. Each arrival is mapped individually, and the ?true? velocity and position of the ray turning point is obtained by considering reversed raypaths. Thus the data are transformed directly into a depth or two-way time image of the subsurface displayed in seismic velocity. The method is extremely fast and involves no interpretive steps or iteration. Ideal datasets contain the refracted wavefield sampled densely and equally in the shot and receiver domains. It was therefore decided to test the application of the method for mapping the velocity structure of a portion of regolith and to compare the results with those obtained using more conventional methods. The area chosen for study was part of a regional seismic reflection line across the Lachlan River palaeo-valley in central NSW. The data set consisted of the first break picks for 240 channels with receivers spaced every 40 m and vibration points every 40 m. The velocity images were produced as both time and depth sections and compared with one and two layer refractor models from a refraction tomographic approach. A low velocity region on the image corresponds to the deepest part of the refractor model, interpreted as the thickest part of the palaeo-valley. Bedrock velocity variations are also mapped and agree with the changes along the (lowest) refractor velocity profile. While further tuning may be required for land work, the technique has the advantage that velocities can be directly imaged and potentially related to regolith physical properties.

A Geophysical Signature for tin deposits in south-east Australia - revisited

Webster (1984) showed “that hardrock tin deposits in south-east Australia have a characteristic magnetic signature in the vicinity of each deposit”. This magnetic signature was concluded to be due to the high temperature of related granitoids imposing a remanent magnetism on rocks within the metamorphic aureole. The paper also discussed the main granitoid classifications and associated mineralisation in relationship to geophysical parameters and the use of the regional data for geological mapping in New South Wales and Tasmania.The case examples utilised in the original paper have been re-examined using modern airborne geophysical data acquired by Mineral Resources Tasmania (MRT) and the NSW Department of Mineral Resources. The magnetic and radiometric character of the granitoids and local lithology patterns are better contrasted in the new data sets, which allows for mapping of geology and structure to finer resolution.A significant feature of the new MRT data is the magnetic and radiometric aureole, up to 2km wide, now observed to encircle S-type granites, in particular the Meredith Granite. A metamorphic aureole was known from earlier geological mapping, however, the geophysical response was only poorly expressed in earlier datasets. The new data in the vicinity of these tin deposits are presented and profile modelling is used to confirm that remanence effects are involved in the source of the anomalies. The radiometric data sets show complimentary patterns in the vicinity of tin deposits that enhance the recognition of the mineralised target zones.In the central NSW tin-belt the S-type granites are intruded into weakly magnetic Ordovician meta-sediments, however, the zero magnetic response of the granites is well contrasted with the north-south linear fabric of the meta-sediments. The tin and gold deposits generally occur in quartz reefs located along sheared contacts of the granite with the meta-sediments and cross cutting east-west structures appear to be related to the source of the tin and gold mineralisation. The application of the radiometric data is restricted by the lack of outcrop.

Brachiopods of the Orders Protorthida and Orthida from the Silurian of the Yass Syncline, southern New South Wales

The Yass Syncline succession ranges in age from possibly late Wenlock to earliest Devonian, with reasonable correlation based on conodonts and graptolites for the late Ludfordian through Prídolí to earliest Lochkovian (i.e. uppermost Black Bog Shale to Elmside Formation). Numerous brachiopods have been recorded from the succession, but there are no published descriptions of protorthides or orthides. In this paper nine species are described, of which two (Skenidioides thrinax and Salopina mediocostata) were originally described from the late Wenlock of Canberra, while five are new: Dolerorthis exatripalude, Isorthis (Arcualla) salicipontis, Salopina pusilla, S. rainbowella, and Talentella yassensis. Only the two Canberra species and D. exatripalude occur in Gorstian levels below the Black Bog Shale. All except one species occur in the lower Ludfordian Black Bog Shale, S. rainbowella being restricted to the overlying upper Ludfordian Rainbow Hill Member (basal Rosebank Shale) which also contains very rare S. mediocostata. Both S. pusilla and T. yassensis extend to the lower Prídolí lower Cowridge Siltstone. T. yassensis is the oldest species of that genus so far recorded, and might be derived from S. mediocostata. The Lochkovian species Salopina? herkion (Garra Formation, central NSW) is here referred to Talentella.

Mineral nutrient uptake and removal by canola, Indian mustard, and Linola in two contrasting environments, and implications for carbon cycle effects on soil acidification

Field studies of the oilseed crops canola, Indian mustard, and linseed/Linola were conducted over 2 seasons at 2 contrasting sites in the cropping regions of central and southern NSW to determine the uptake of mineral nutrients and quantities removed in seed. The sites were in the Junee region where production of these oilseeds is common, and at Condobolin, which is regarded as marginal for production of the crops. The 2 rates of nitrogen (N) fertiliser applied were either none or rates that growers in the Condobolin and Junee regions would apply to achieve high seed yields after a cereal crop in the rotation when soil mineral N is low. Concentrations of total N, the major cations (K, Ca, Mg, Na) and major anions (P, S, Cl), and the micronutrients Fe, Mn, Zn, and Cu were determined in shoots harvested at flowering and maturity. Nitrate and sulfate were also measured, and estimates were made of excess cation concentrations in the plant material. The ranges of concentrations of excess cations in shoots of the oilseeds at flowering were 83–206 cmolc/kg and 43–121 cmolc/kg for straw at maturity. Linola had lower concentrations of excess cations in vegetative material (83–108 and 43–82 cmolc/kg at flowering and maturity, respectively) than canola or Indian mustard. Concentrations of excess cations in seed of the crops were lower than for vegetative material, and ranged from 30 to 49 cmolc/kg. Nitrogen fertiliser had relatively little effect on concentrations of mineral nutrients or excess cations in either shoots at flowering and maturity, or in seed. However, N fertiliser increased the growth and seed yields of the crops, and thus the amounts of mineral nutrients and excess cations in shoots and seed. The results are discussed in the context of the depletion of soil nutrients due to their removal in harvested seed of the N-fertilised crops. The contribution of excess cation removal in seed to soil acidification is also discussed. It is estimated that the quantity of lime required to neutralise the acidity resulting from removal of 1 t seed is 22.4 kg for canola, 17.0 for Indian mustard, and 20.8 for linseed/Linola. Estimates of the relative contributions of seed removal and N fertiliser to soil acidification are presented.

Electrical properties of porphyry mineralisation at the Cadia Ridgeway gold-copper deposit, NSW - implications for exploration

The Cadia Ridgeway Au-Cu deposit is a deep (> 500 m) gold-rich porphyry copper system located in central NSW. A chargeability anomaly, recognised within a prospective NW-SE mineralised corridor motivated the drilling program which led to the discovery of the deposit. In-situ and laboratory electrical tests were conducted to characterise the petrophysical properties of the deposit and host sequences. The ore is both chargeable and relatively conductive, although not sufficiently conductive for EM methods. Significant scale variation of apparent resistivity was observed with in-situ measurements using electrode spacing of one metre or more up to two orders of magnitude lower than values determined from laboratory measurements. Forward modelling of measured induced polarisation and apparent resistivity data was conducted using petrophysical properties determined primarily from in-situ testing. The chargeability anomaly identified over the Ridgeway ore body is due largely to disontinuous halos of pyrite alteration above the economic mineralisation, but a highly chargeable source component associated with the economic mineralisation at Ridgeway is also inferred. The contrast in conductivity between ore and host rocks suggests that Ridgeway-style mineralisation may represent a target for magnetometric resistivity (MMR) surveying. Three-dimensional numerical modelling of the expected MMR response indicates that the Ridgeway deposit would be detectable by both surface and down hole MMR surveys.

Geophysics and the discovery of the Cadia gold-copper system

The Cadia Gold Copper system in Central West NSW is a world-class porphyry gold copper system, where geophysics has helped to discover or define some of the resources. Initial drilling at Cadia Hill employed ground magnetic data to help optimise drillhole direction. A ground magnetic target was drilled at Cadia East, and showed increasing copper grades with depth. Follow up drilling discovered the Cadia East mineralisation under Silurian sedimentary cover. Ground magnetic and 200m dipole-dipole IP data led indirectly to the discovery of the Ridgeway mineralisation under Tertiary basalt cover, by detecting the magnetite and pyrite halo above the mineralisation. The IP drillhole intersected anomalous gold and copper. Deeper follow up drilling intersected the Ridgeway orebody. Other data acquired across Cadia include heli-magnetics / radiometrics, gravity, downhole EM at Ridgeway, and physical property measurements. Overall, magnetics and IP have been the most successful methods used to date.

Electrical Properties of Porphyry Mineralisation at the Cadia Ridgeway Gold-Copper Deposit, NSW – Implications for Exploration

The Cadia Ridgeway Au-Cu deposit is a deep (> 500 m) gold-rich porphyry copper system located in central NSW. A chargeability anomaly, recognised within a prospective NW-SE mineralised corridor motivated the drilling program which led to the discovery of the deposit.In-situ and laboratory electrical tests were conducted to characterise the petrophysical properties of the deposit and host sequences. The ore is both chargeable and relatively conductive, although not sufficiently conductive for EM methods.Significant scale variation of apparent resistivity was observed. In-situ measurements, utilising electrode spacings of one to four m, are up to two orders of magnitude lower than values determined from laboratory measurements.Forward modelling of surface induced polarisation and apparent resistivity field data was conducted using petrophysical properties determined primarily from in-situ testing. The chargeability anomaly identified over the Ridgeway ore body is due largely to discontinuous halos of pyrite alteration above the economic mineralisation, but a highly chargeable source component associated with the economic mineralisation at Ridgeway is also inferred.The measured contrast in conductivity between ore and host rocks suggests that Ridgeway-style mineralisation may represent a target for magnetometric resistivity (MMR) surveying. 3D numerical modelling predicts that the MMR response of the Ridgeway deposit would be detectable by both surface and down hole MMR surveys.

Seismic refraction inversion of a palaeochannel system in the Lachlan Fold Belt, Central New South Wales

We assess a method for conducting seismic refraction inversion in a 3-D setting to image the shape and structure of a palaeochannel. The trial survey was conducted over a suspected Tertiary palaeochannel adjacent to the Wyalong goldfields (Lachlan Fold Belt) in central NSW. This work has implications for the control of groundwater migration and dryland salinity studies. The method was conducted using standard multichannel seismic recording equipment and an unconventional 3-D field geometry. Three-dimensional velocity-depth models show a 4-layer sub-horizontal system underlain by high-velocity metasedimentitic basement at a variable depth, ranging from 70 to 170 m. The interpreted palaeochannel is coincident with high magnetic intensity features identified from recent surveys of the region.

Optimal strategies for regional cultivar testing

In undertaking cultivar trials, the variability of the response of the cultivars to the different environments in which they are grown introduces the possibility of release errors and non‐release errors in the decisions made on the basis of the trial results. In this article a model is developed that accounts for the economic costs of those errors as well as the costs of operating the trials, and enables the features of the optimal cultivar testing program to be identified. The model is illustrated by application to wheat cultivar trials in central and southern NSW.

Isozyme Variation in Eucalyptus nitens and E. denticulata

Seed samples from 22 populations across the geographic range ofE. nitens (Deane & Maiden) Maiden s. str. andE. denticulata I.O. Cook & P.Y. Ladiges wereanalysed for isozyme variation and estimation of the genetic distance betweenthe two taxa. Analysis of 12 enzyme systems in 3 buffer systems revealed 12polymorphic and 5 monomorphic loci. The results confirm the distinctiveness ofE. nitens and E. denticulatapreviously reported for morphological characteristics. A single population ofthe related species E. quadrangulata Deane & Maidenwas distinct from, and more heterogeneous than, populations of the other two taxa. The results also show regional genetic variation withinE. nitens that correlates with observed differences inmorphology. Three races were identified: northern and central NSW; southern NSW and Mt Kay in eastern Victoria; Baw Baw Ranges and Central Highlands inVictoria. Geographically isolated populations, particularly from central andnorthern NSW, showed the least genetic variation. Variation was highest in anequivocal population from Mt Gregory, central Victoria, where the distributionof E. nitens overlaps with that ofE. denticulata.

A RE-ASSESSMENT OF THE PETROLEUM POTENTIAL OF THE DARLING BASIN: A DISCOVERY 2000 INITIATIVE

New data, including regional high resolution aeromagnet ic coverage, acquired by the New South Wales Department of Mineral Resources (DMR) as part of its Discovery 2000 Initiative, have provided the first opportunity for a comprehensive review of the regional framework of the Darling Basin. Covering an area of 90,000 km2 in central western NSW, the Darling Basin contains over 8,000 m of mainly Palaeozoic sediments. With only 17 petroleum wells drilled in the basin, mostly during the 1960s and 1970s, and some 1,550 km of modern multifold seismic coverage, the Darling Basin represents one of the major frontier basinal regions of onshore Australia.The initial phase of petroleum exploration was discouraged by the lack of shows, the likelihood of gas-prone source rocks and presence of a thick, red-bed dominated, organically lean, Late Devonian sequence. Renewed interest in the Darling Basin's prospectivity followed from favourable, albeit superficial, comparisons between the Darling Basin and Queensland's Adavale Basin, where commercial gas is produced at the Gilmore Gas Field. Additionally, as part of some $15 million expenditure by the DMR on acquiring new and reassessing old data from the Darling Basin, new geochemical analyses of extracts collected from core holes and out-crop suggest the presence of at least one active Palaeozoic petroleum system. This system has been responsible for generating oil and possibly substantial quantities of gas found dissolved within artesian waters in the overlying shallow Mesozoic sequences.

Different effects of microhabitat fragmentation on patterns of dispersal of an intertidal gastropod in two habitats

Small-scale movements of animals with respect to microhabitat can have important consequences for a species and its interactions with resources and other members of the local assemblage. Patterns of movement of animals in relation to habitat are sometimes predicted using their patterns of distribution with respect to it. Gastropods ( Bembicium auratum (Quoy and Gaimard)) are found in association with fragmented patches of oysters ( Saccostrea commercialis) on sheltered rocky shores and in mangrove forests in central NSW. This paper reports an experimental test of models of movement of Bembicium based on its patterns of distribution with respect to oysters. The experiment was replicated at sites on rocky shores and in mangrove forests. On rocky shores, patterns of dispersal of juvenile Bembicium were as predicted by the models based on patterns of distribution. It was not possible to predict patterns of dispersal of adults using such models. Patterns of dispersal in mangrove forests were very different from those on rocky shores, despite similar patterns of distribution. These results suggest that models predicting patterns of movement of Bembicium auratum must incorporate information about the ages of the animals, the arrangement of microhabitat and the habitat they occupy. It is also clear that models based on patterns of distribution of animals will not always be effective in predicting patterns of movement into and out of patches of habitat and that the extrapolation of models from one habitat to another should be attempted with caution.