South easterly trade winds have long been thought to transport aeolian dust across northwest Australia, but very little is known about the chemical and particle size characteristics of this material. From July 2008 to May 2009, 36 aeolian dust samples were collected monthly at four sites across Australia's northwest. The results of ion beam analysis indicate that the samples consisted of four major elemental groups, one of which appeared to be transported across the sites during months in winter and summer. This group (characterised by higher ratios of Fe, Ti and Mn/Si than the Earth's Crustal Average) also showed a decrease in particle sizes towards the west. This suggests that the dust may have had a central Australian source, while other groups richer in Si appear to have been locally derived. These results support previous models of seasonal dust transport, and may have relevance in regional climate modelling, the transport of nutrients into the Indian Ocean, mineral exploration and studies of respiratory health. (C) 2013 Elsevier B.V. All rights reserved.

Guest Editors: KEITH M. SCOTT and PETER A. JELL Research School of Earth Sciences, The Australian National University and CSIRO Earth Sciences and Resource Engineering, PO Box 136, North Ryde, NSW 1670, Australia. E-mail: keith.scott@csiro.au Geological Survey of Queensland, Department of Natural Resources and Mines, GPO Box 15216, City East, QLD 4002, Australia. E-mail: peter.jell@deedi.qld.gov.au

Soils from the vicinity of the Endeavor Mine, in the Cobar region of western NSW, have been sieved into the (a) 2-4 mm, (b) 1-2 mm, (c) 0.5-1 mm, (d) 250-500 mu m, (e) 125-250 mu m, (f) 63-125 mu m and (g) <63 mu m fractions, with a magnetic fraction (m) also prepared from the coarser soil fractions. The chemical compositions of these soil fractions show that the coarse (2-4 mm) and magnetic fractions contain the highest As, Fe, and Pb contents whereas the fine (<63 mu m) fraction is enriched in Al, Ca, Cu and Zn. Phosphorus and S have bimodal distributions.Elevated Pb and As contents in the coarse or magnetic fraction of soils in the Endeavor Mine area reflect the underlying weathered Pb-Zn mineralization and may give rise to a larger anomaly than that defined by conventional magnetic lag sampling. Within this area of Pb and As anomalism, the fine fraction of the soils directly above the Northern Pods mineralization (c. 400 m below) exhibit enriched Zn, S and soluble salt contents (the latter measured as electrical conductivity). The association of elevated Zn, S and EC (electrical conductivity) suggests sulphide-derivation and such anomalism appears more prospective than Zn-only anomalism in fine soil fractions from transported material to the SW of the mine.Unfortunately the preparation of the fine soil fraction is time consuming but, because the fine fraction of the Cobar region soils consistently represents 40-50% of the <2 mm soil fraction, the latter can be used as a surrogate for the fine soil fraction. Thus, cost effective exploration for base metal mineralization in the Cobar region could utilize the >2 mm soil fraction for determining Pb and As and the <2 mm soil fraction for S, Zn and EC. Use of the <2 mm soil fraction discriminants should be considered during exploration for Zn-only mineralization in semi-arid regions like that at Cobar.

The terrestrial and oceanic salt (NaCl) components in 39 dust samples from eight sites across south eastern Australia have been calculated from chemical data derived by ion beam analysis (IBA). For samples identified as having a positive terrestrial salt ratio (TSR; i.e., the abundance of terrestrial salt relative to total salt expressed as a percentage), back trajectory analysis (estimation of the path of the wind affecting the site) was used to verify the likelihood of a terrestrial source for such salt. This procedure indicated that the terrestrial salt input to south eastern Australia is non-negligible compared to that of sea salt and the most likely sources of the terrestrial salt deposited in such area are the inland saline regions of the Lake Eyre and Murray Darling Basins. Terrestrial salt ratio values readily screen out the majority of samples for which a terrestrial salt component is unlikely. Thus, calculating the ratios to identify samples which are potentially influenced by terrestrial salt (e.g., prior to conducting a back trajectory analysis on such samples) appears to be useful, especially since such determinations can be done with small sample sets for which statistical analysis is not appropriate. (C) 2011 Elsevier B.V. All rights reserved.

SUMMARY Study of oxidised and supergene Cu-Au mineralisation at New Cobar, provided by integrating results from 164 drill hole samples with data previously obtained from the open pit study (Scott and McQueen, 2000), has revealed the nature of the dispersion of Au and its pathfinder elements. Weathering occurred at two different stages:- initially under acidic sulfate conditions to form secondary sulfides, sulfates, alunite- jarosite minerals and Fe- and Mn- oxides in a mature gossan profile and then under more arid conditions. This latter period, when Cl-rich fluids overprinted pre-existing minerals, is also believed to be largely responsible for the loss of Ag relative to Au up to about 40 m depth and then loss of Au in the top 15 m of the gossanous profile. Some elements, like Zn and Cd, are strongly depleted as soon as the sulfides commenced weathering and others, like Mo and W, appear to be concentrated at about 100-110 m depth in the supergene sulfide zone and Se at 30-40 m depth within the gossanous Fe oxides. Copper contents vary more systematically up the profile but even in this case abundance drop by almost an order of magnitude above 65 m. Examination of the Pb contents in near-surface samples suggests that elevated Pb (>300 ppm) may occur up to 70 m south from the mineralisation. The presence of an extensive Pb anomaly about the economic mineralisation may be useful during surficial regional exploration.

Characterisation of aeolian material in the Girilambone Region of New South Wales (600 km NW of Sydney), using particle size analysis, mineralogy, geochemistry and micromorphological analysis, shows that it consists of spheroidal, highly abraded 70 mu m quartz grains. Although relatively pure aeolian accessions are found on top of Tertiary leucitite flows, the aeolian material is generally admixed with residual and transported soil to a depth of 0.3 m throughout the region. This study has established a set of criteria for identifying the aeolian contribution to soils in the Girilambone region of north western New South Wales where it is difficult to distinguish. These include: a characteristic particle size of 70 pm of the quartz grains; highly abraded and spherical morphology; presence of thin clay coats on wellrounded grains; and gradational patterns in particle size distribution, mineralogy and geochemistry through the soil profile. These types of soils, with a high content of silt and fine sand, do not readily form aggregates, particularly where they have low organic content. To improve the sustainability of cropping and pastoral activities on these soils, their management should aim to maintain or increase structural stability, for example by addition of organic material. Mineral exploration procedures should avoid the diluting aeolian component by sampling the > 150 mu m fraction from surficial soils or material from below 0.3 m. (c) 2006 Elsevier B.V All rights reserved.

In the Parkinson Pit area at Mt Magnet, 560 km NNE of Perth, mafic and felsic rocks occur within a weathering profile that has been stripped to the saprolite. Irrespective of rock type within the pit area, the weathered profile consists of fresh rock, saprock, mottled saprolite and leached saprolite below a thin transported soil cover. The depth of weathering extends to 80 m adjacent to mineralization, although weathering depths appear to be less in mafic volcanic rocks outside the pit. Weathering has led to separation of Ag from the primary Ag-bearing gold and the redistribution of other potential pathfinders elements (As, Co, Cu, Ni, Sb and Zn ) from the original sulphides (mainly pyrite) into Fe and Mn oxides. Gold grades have not been significantly affected by weathering. Both mafic and felsic rocks in the Parkinson Pit area, have been metamorphosed to quartz+chlorite±mica+albite assemblages. However, hydrothermal alteration has destroyed albite and formed additional mica, so that the change: minor muscovite→paragonite±muscovite→muscovite, reflects an approach to mineralization. Because micas are retained when the rocks weather, this characteristic feature is maintained in the regolith, although changes in mica compositions and abundance are more obvious in mafic than in felsic rocks because of the greater initial mica content in the latter. Thus, proximity to mineralization, reflected by mica composition and abundance in mafic volcanic rocks, could be determined by PIMA and radiometric analysis of K content, even from weathered drill cuttings.

The Eastern Highlands of Australia have probably been in existence since the Late Cretaceous or earlier and so there has been ample time for mature gossan profiles to form over outcropping volcanogenic Zn–Pb–Cu mineralisation in the eastern Lachlan Fold Belt. The mature gossan profiles are characterised by the upward progression from supergene sulfides to secondary sulfates, carbonates and phosphates into a Fe-oxide dominated surficial capping which may contain boxwork textures after the original sulfides (as at the Woodlawn massive sulfide deposit). However, the region has locally been subjected to severe erosion and the weathering profile over many deposits is incomplete (immature) with carbonate and phosphate minerals, especially malachite, being found in surficial material. These immature gossans contain more Cu, Pb and Zn but lower As, Sn (and probably Au) than the mature gossans. Although Pb is probably the best single pathfinder for Zn–Pb–Cu VHMS deposits of the eastern Lachlan Fold Belt, Ag, As, Au, Bi, Mo, Sb and Sn are also useful, with most of these elements able to be concentrated in substantial amounts in Fe oxides and alunite–jarosite minerals.

The alunite–jarosite minerals are defined as having the general formula AB 3( X O4)2(OH)6, where A is a large ion in 12-fold coordination ( e.g. , K, Na, Ca, Pb, REE ), B is usually Fe or Al, and the X O4 anions are usually SO4, PO4 or AsO4. Because of the potential for a large number of complex

The Au mineralisation at Goornong South occurs under at least 5 m of transported cover and thus provides a good initial case study for exploration in areas of transported overburden in Central Victoria. The Au mineralisation is associated with As, Sb and W, with the abundances of the Au and As in saprolitic samples (>10 ppb and >100 ppm, respectively) sufficient to define the mineralisation. Dispersion of these elements occurs into the overlying alluvium but their mode of occurrence varies. Gold is concentrated into the clay-rich fine faction (−63 μm) of the surficial soil, whereas As is enriched in the coarse (+2 mm) ferruginous fraction. These elements in these fractions of the soil produce anomalies which may be up to twice the size of those in the weathered bedrock. Because the fine fraction of the soils is subject to possible contamination by aeolian material and it is time-consuming to prepare, use of the coarse fraction is probably the most cost-effective sampling medium for these areas of shallow cover. In this area of Central Victoria, mechanical dispersion is probably more important than hydromorphic dispersion processes. Thus areas with deeper cover, where hydromorphic dispersion is likely to dominate dispersion processes, need to be tested.

Acid insoluble residues of regolith samples after treatment with aqua regia (3HCl:1HNO3) and subsequently with H2SO4 have been tested as a sampling medium for determining geochemical signatures around gold and base metal mineralisation at the McKinnons and Wagga Tank deposits and at the Lower Tank prospect, in the Cobar region, N.S.W., Australia. The residues, composed of quartz, chalcedony and minor mica, retain primary geochemical signatures related to mineralisation/alteration events. Gold and base metal deposits in the Cobar region occur within clastic sediments and volcaniclastics of the Early Devonian Cobar Basin and its equivalents (e.g. Mt Hope Trough). Common alteration styles are silicification and chloritisation with some carbonitisation and sericitisation. Within the regolith, clay mineral alteration is significant. At both the McKinnons and Wagga Tank deposits the weathering profile is about 80–100 m thick. The regolith at McKinnons consists of red-brown soil containing ferruginous pisoliths underlain by saprolite consisting of quartz, clay minerals (mainly illite) and muscovite, pyrite, goethite and haematite. In the Wagga Tank area, the weathering profile consists of soil overlying a residual ferruginous layer underlain by a kaolinite-rich zone which passes into goethitic saprolite containing alunite–jarosite family minerals. Distributions of elements in the acid insoluble residues of rock and regolith (including surface soil) exhibit similar geochemical signatures at the McKinnons and Wagga Tank deposits. There are two main groups of elements of interest. The first group (Cu, Zn, Pb, Ni, As, Mo, Ag, Sb, Ba, Bi and W) are ore-related and are enriched in and around the mineralisation. The second group (K, Fe, Ca, Ti, Mn, Cl, Ga, Rb, Sr, Zr, Y, V, Al, Na, Mg, Tl and F) are generally depleted in acid insoluble residues of the rock and regolith near and around the mineralisation. The depletion of some elements such as K, Al, Ca, Na, Rb and Sr is considered to reflect element loss from the hydrothermal system as a result of feldspar and mica destruction followed by silicification. These signatures are considered to be mainly the result of primary geochemical dispersion and despite the weathering effect are retained within the regolith. The previously defined regolith-hosted base metal anomalies at the Lower Tank prospect are also reflected by anomalous Cu, Zn, Pb, Ni, Mo and As in the acid insoluble residues of both saprolite and drainage sediments. However, K, Fe, Ca, Na, Rb, Sr and Ga are not depleted, which does not support the possibility of wall rock alteration and associated buried mineralisation.

Aeolian soils in the Blayney district are characterised by having approximately 80% of their mass finer than 63 μm, Ti/Zr ratios of approximately 12, radioelement contents of 0.7% K, 2 ppm eU and 11 ppm eTh and a position high in the landscape. Their Ti/Zr ratio and abundant quartz content distinguishes them from soils derived from Tertiary basalts, which share some of the other characteristics. Many soils in the district have a partial aeolian contribution, which can be recognised by a Ti/Zr ratio that differs from that of the underlying rock. Abundance of an aeolian contribution suggests that airborne radiometric surveys should be very carefully interpreted. Ground studies suggest that high Th content in soils contrasted with low Th in adjacent rocks can be indicative of an aeolian contribution in soils. A substantial amount of fine material in a soil can also significantly dilute geochemical signatures if −63 μm (<80 mesh) samples are used for soil surveys during exploration.