Granite-hosted gold mineralization at Timbarra, northern New South Wales, Australia

The Timbarra gold deposits, located in the southern New England Fold Belt of New South Wales, Australia, represent an economically significant and distinctive member of the intrusion-related class of gold deposits. The five known deposits possess a total identified mineral resource of 16.8 Mt at 0.73 g/t gold, for a total of 396,800 contained ounces. The granites in the Timbarra region form a texturally complex, zoned pluton. The gold deposits are found within the Stanthorpe leucomonzogranite (242 to 238 Ma), which intrudes and forms a core to the more mafic, barren, Bungulla monzogranite (248 to 243 Ma). Gold is disseminated in the roof zone (upper 240 m) of a fractionated, magnetite- and ilmenite-bearing, I-type leucomonzogranite phase of the Stanthorpe body. The entire gold resource occurs in the areally extensive main leucomonzogranite pluton and is hosted by a medium- to coarse-grained granite. Disseminated ore is present in all five deposits, comprises >95% of the overall resource at Timbarra, and occurs predominantly as gently dipping, tabular to lenticular bodies that are conformably constrained beneath a fine-grained aplite carapace and internal aplite layers. The disseminated ore consists of gold-bearing muscovite-chlorite-carbonate alteration and infill of primary miarolitic cavities within massive leucomonzogranite or microgranite, and contains no discernable vein, joint, or fracture control at the outcrop or hand specimen scale. Structurally controlled mineralization forms the remaining 5% of the Timbarra resource, and comprises minor, low-density (0.02 to 0.25 per meter), vein-dikes and quartz-molybdenite veins emplaced along steeply dipping east-southeast, east-northeast, and north-northeast striking cooling joints. Both mineralization styles and alteration share a common paragenetic sequence of mineral precipitation. Quartz, perthitic K-feldspar, minor biotite, and albite are the earliest and most abundant infill minerals and commonly line primary cavities and vein-dikes. Subsequent minerals include coeval arsenopyrite, pyrite, fluorite, and molybdenite. The latest minerals include muscovite, chlorite, gold, calcite, silver-bismuth telluride, lead-bismuth telluride, and rare galena and chalcopyrite. The gold ore has a low total sulfide mineral concentration (Б%). Ore contains elevated concentrations of Bi, Ag, Te, As, Mo, and Sb; gold is strongly correlated with Bi, Ag, and Te, but only weakly with Mo, As, and Sb. Gold grains are generally <1 to 50 µm in size, but rarer grains as large as 1 mm in diameter have been observed. Gold fineness ranges from 950 to 600, and varies both within and between individual grains for a given deposit. The moderately oxidized I-type host granite, low-sulfide (Б%) ores, Au-Bi-Ag-Te geochemical signature, muscovite-chlorite-carbonate alteration assemblage, and low-salinity aqueous and carbonic fluids suggest that Timbarra is part of the newly recognized intrusion-related gold deposit class. Timbarra is distinguished from other intrusion-related gold deposits by the disseminated mineralization style within pervasively altered granite, forming gently dipping, tabular to lenticular ore zones.     

Zinc-lead skarn deposits at Leadville, New South Wales, Australia, and their distinction from volcanic-hosted massive sulphides

Exploration of Zn-rich sulphide deposits at Leadville, northern Lachlan Fold Belt, New South Wales, for over two decades has been largely on the premise that the mineralisation represents felsic volcanic-hosted massive sulphides (VHMS). Deposits are hosted by ?Silurian felsic metavolcanic, psammopelitic and calcareous metasedimentary rocks which have been intruded by the late Carboniferous I-type Gulgong Granite. Evidence for an epigenetic replacement (skarn) origin of the deposits, rather than representing metamorphosed volcanogenic massive sulphides, includes the proximity of evolved granitic intrusives and reactive carbonate rocks, a skarn mineral assemblage (with characteristic prograde and retrograde stages), lack of textural or lithological indications of an exhalative origin, and gossan and sulphide compositions consistent with Zn-Pb skarns and atypical of Lachlan Fold Belt VHMS deposits. Furthermore, sulphide lead isotope ratios are significantly more radiogenic than signatures for VHMS deposits in the Lachlan Fold Belt. Carbonate δ¹³C and δ¹⁸O and sulphide δ³⁴S values are consistent with the interaction of magmatic hydrothermal fluids with Palaeozoic carbonate rocks and a largely magmatic source of sulphur. It is concluded that the Leadville deposits are of skarn type, genetically related to the Gulgong Granite.     

Geochemistry of lamprophyre dykes,Wadi Sikait area,South Eastern Desert,Egypt

The Wadi Sikait area lies at about 95 km southwest of Marsa Alam City along the Red Sea Coast, Eastern Desert, Egypt. It is occupied by Precambrian rocks of ophiolitic mélange, metamorphosed sandstones (MSS), gab-bros and monzogranites which were later intruded by lamprophyre dykes and quartz veins. The lamprophyre dykes were extruded in NW-SE and NE-SW trends cutting monzogranites and metamor-phosed sandstones. The lamprophyres are porphyritic and composed of clinopyroxene, olivine and amphibole phenocrysts enclosed in a fine-grained groundmass of clinopyroxene, amphibole, opaque and lithium mica. The al-teration products are represented by amphibole (tremolite-actinolite and hornblende), carbonate, epidote, chlorite, iddingsite, clay minerals, limonite and serpentine. The Sikait lamprophyre dykes can be classified as alkaline lamprophyres characterized by silica contents rang-ing from 41.65 wt% to 50.88 wt% and Na2O>K2O. They are enriched in LILE, LREE and HFSE, but strongly de-pleted in compatible elements such as Cr and Ni relative to the primitive mantle. Sikait lamprophyres have moderate Zr/Hf (35.6-52.8) and Nb/Ta (20.5-22.5) ratios. Most of these features are attributed to the origin of these dykes from the metasomatized mantle affected by subduction-related fluid. These lamprophyres are compositionally similar to Salu lamprophyres in eastern China. The Sikait lamprophyre samples have high LREE (320×10-6-419×10-6) relative to HREE (20×10-6-33×10-6) with ratios (LREE/HREE=11.6-18.7) and no negative Eu anomaly (Eu/Eu*=0.9-1.04). The relative presence of posi-tive Ce anomaly (Ce/Ce*=1.04) in lamprophyre samples suggests the oxidizing condition under which the REEs were precipitated due to the common occurrence of fluorite and apatite.     

The present-day stress field of New South Wales,Australia

The Australian continent displays the most complex pattern of present-day tectonic stress observed in any major continental area. Although plate boundary forces provide a well-established control on the large-scale (>500 km) orientation of maximum horizontal stress (S_Hmax), smaller-scale variations, caused by local forces, are poorly understood in Australia. Prior to this study, the World Stress Map database contained 101 S_Hmax orientation measurements for New South Wales (NSW), Australia, with the bulk of the data coming from shallow engineering tests in the Sydney Basin. In this study we interpret present-day stress indicators analysed from 58.6 km of borehole image logs in 135 coal-seam gas and petroleum wells in different sedimentary basins of NSW, including the Gunnedah, Clarence-Moreton, Sydney, Gloucester, Darling and Bowen–Surat basins. This study provides a refined stress map of NSW, with a total of 340 (A–E quality) S_Hmax orientations consisting of 186 stress indicators from borehole breakouts, 69 stress measurements from shallow engineering methods, 48 stress indicators from drilling-induced fractures, and 37 stress indicators from earthquake focal mechanism solutions. We define seven stress provinces throughout NSW and determine the mean orientation of the S_Hmax for each stress province. The results show that the S_Hmax is variable across the state, but broadly ranges from NE–SW to ESE–WNW. The S_Hmax is approximately E–W to ESE–WNW in the Darling Basin and Southeastern Seismogenic Zone that covers the west and south of NSW, respectively. However, the present-day S_Hmax rotates across the northeastern part of NSW, from approximately NE–SW in the South Sydney and Gloucester basins to ENE–WSW in the North Sydney, Clarence-Moreton and Gunnedah basins. Comparisons between the observed S_Hmax orientations and Australian stress models in the available literature reveal that previous numerical models were unable to satisfactorily predict the state of stress in NSW. Although clear regional present-day stress trends exist in NSW, there are also large perturbations observed locally within most stress provinces that demonstrate the significant control on local intraplate sources of stress. Local S_Hmax perturbations are interpreted to be due to basement topography, basin geometry, lithological contrasts, igneous intrusions, faults and fractures. Understanding and predicting local stress perturbations has major implications for determining the most productive fractures in petroleum systems, and for modelling the propagation direction and vertical height growth of induced hydraulic fractures in simulation of unconventional reservoirs.     

The Prospect Alkaline Diabase-Picrite Intrusion New South Wales, Australia

The Prospect intrusion is a dish-shaped alkaline diabase-picritemass 315–400 ft thick intruded into shale at a depth ofabout 600 ft. Picrite, containing more than 25 per cent olivine,occupies the lower half of the intrusion. In the upper half,alkaline diabase, averaging less than 5 per cent olivine, isconcentrated under structural highs of the contact, and alkalineolivine diabase, containing 10 to 25 per cent olivine, is concentratedunder structural lows. These rocks are separated from the shaleby a fine-grained chilled margin. Vertical sections through the picrite zone show a regular antipatheticvariation of modal olivine and plagioclase with a zone of maximumolivine concentration near the bottom; bulk rock compositionsshow an antipathetic relation between MgO plus total iron andall other constituents. Modal and bulk composition variationsare more erratic in the upper half of the intrusion, but analcite,alkali feldspar, and opaque minerals reach maximum concentrationsin this part of the intrusion. The pyroxene content remainsnearly constant in the major rock types. Trends of olivine andplagioclase composition and grain size vary regularly with heightin the intrusion and cross boundaries between major rock typeswithout deflexion. Olivine becomes progressively more fayaliticfrom the base of the picrite zone to the upper chilled margin,but the plagioclase curve has a trend toward more calcic compositionsin the picrite zone. Mean sizes of plagioclase, pyroxene, andolivine increase upwards between the chilled margins. The lower chilled margin is slightly less mafic than the bulkcomposition of the intrusion and may represent a pre-emplacementdifferentiate, but the major part of the differentiation occurredduring emplacement at the present site. Grain size and otherdata indicate that crystallization took place more rapidly fromthe base than from the top of the intrusion, and a variety ofinternal structures indicate that crystallization and differentiationtook place as the magma was intruded over a considerable periodof time. As consolidation of the intrusion proceeded, the liquid becameenriched in all constituents except magnesium and ferrous ironuntil consolidation of alkaline diabase began (when about 70per cent of the whole intrusion had solidified); at that stagethe proportion of calcium, titanium, and ferric iron in theliquid was reduced and the proportion of silica, alumina, andalkalis increased. Processes of differentiation that contributed most to the originof the main rock types are: diffusion, independently of crystallization,of volatiles, alkalis, and possibly calcium into the structurallyhigh parts of the intrusion; gravity accumulation of olivinethat crystallized a short distance above the main front of consolidationas it moved upwards from the base of the intrusion; and upwarddiffusion of salic constituents and downward diffusion of maficones over concentration gradients produced by crystallization. Removal of volatiles from the lower part of the intrusion beforecrystallization reduced the oxidation ratio in the liquid andresulted in a low proportion of ferric iron minerals; crystallizationof abundant olivine (average composition about Fo₇₀), however,prevented enrichment of the liquid in iron. Addition of volatilesto the upper part of the intrusion retarded crystallizationand raised the oxidation ratio to a level at which a relativelyhigh proportion of ferric iron minerals crystallized. Subordinate processes that contributed to the formation of themain rock types as well as to less abundant ones include gravityaccumulation of heavy minerals that were dispersed in the magmaat the time of emplacement, filter pressing caused by localbuttressing around irregularities of the contact, crystal sortingby viscous flow, and gas transfer. Pegmatitic differentiates are ascribed to a complex diffusionprocess along pressure and concentration gradients caused byshear on laminar flow planes. Syenite may have originated byreplacement of pegmatite, but aplites occupy true dilationaistructures and apparently represent liquid remaining after crystallizationof the adjacent rock.     

Petrogenesis of lamprophyre and associated diabase dykes in Wadi Mandar-Um Adawi area,South Sinai,Egypt

The mafic dykes in Wadi Mandar-Wadi Um Adawi area are as follows: (1) calc-alkaline lamprophyre (i.e., kersantite and spessartite), (2) diabase, and (3) alkaline lamprophyre (i.e., camptonite). The field relations reveal that the emplacement of calc-alkaline lamprophyres preceded the diabase dykes, while alkaline lamprophyres emplaced later than the diabase dykes. Calc-alkaline are basaltic andesite, basaltic trachyandesite to basalt, while the diabase dykes and alkaline lamprophyres are basaltic in composition. These dykes are characterized by metaluminous character. Calc-alkaline lamprophyres and diabase dykes show transitional affinity from calc-alkaline to alkaline, while the alkaline lamprophyres exhibit more strong alkaline character. The mafic dykes were crystallized under temperature 1100–1150 °C and pressure 3–5 kbars in a high oxygen fugacity conditions. Fe-Ti oxides in the dykes are represented by ilmenite and Ti-magnetite. The chemistry of the sulfides hosted in those mafic dykes suggests a magmatic-hydrothermal origin for these minerals. The geochemical behavior of high field strength elements and large ion lithophile elements in these dykes excludes the derivation of diabase or alkaline lamprophyre either by partial melting or fractional crystallization from calc-alkaline lamprophyre. The parental magmatic sources of the studied dykes were generated from crustal material with addition of mantle-derived melt during the post-collisional stage. The mafic dykes in Wadi Mandar-Wadi Um Adawi area were generated from different magmatic sources by partial melting and subsequent fractional crystallization. In addition, the crustal contamination/assimilation process has a prominent role in the magmatic evolution of diabase and alkaline lamprophyre dykes.     

Ordovician Intrusive-related Gold-Copper Mineralization in West-Central New South Wales, Australia

Three major types of Ordovician intrusive-related gold-copper deposits are recognized in central-west New South Wales, Australia: porphyry, skarn and high sulphidation epithermal deposits. These deposits are mainly distributed within two Ordovician volcano-intrusive belts of the Lachlan Fold Belt: the Orange-Wellington Belt and the Parkes-Narromine Belt. Available isotopic age data suggest that mineralization of the three types of deposits is essentially coeval with the Ordovician intrusive rocks (480-430 Ma).Porphyry gold-copper deposits can be further divided into two groups. The first group is associated with monzonite showing shoshonitic features, represented by Cadia and Goonumbla. The second group is associated with diorite and dacite, including the Copper Hill and Cargo gold-copper deposits. Gold skarn is associated with Late Ordovician (430-439 Ma) monzonitic intrusive complexes in the Junction Reefs area (Sheahan-Grants, Frenchmans, and Cor-nishmens), Endeavour 6, 7 and 44, Big and Little Cadia     

Notes on framboidal pyrite from Allandale New South Wales,Australia

Pyrite masses composed of compacted pyrite framboids in chalcedony in weathered andesites at Allandale, New South Wales, Australia, show evidence of colloidal origin and contemporaneous deposition of pyrite and silica. Free framboids and framboidal clusters in the chalcedony show indications of crystallization into pyrite polyhedra and pyrite octahedra.     

Differentiation trends in the Warrumbungle Volcano,New South Wales,Australia

The volcanic rocks of the Warrumbungle Shield volcano in central western New South Wales, Australia show two distinct differentiation trends. One trend of differentiation extends from alkali basalts to phonolitic trachytes becoming increasingly undersaturated with silica and a second differentiation trend extends from trachybasalts to quartzbearing trachyte that becomes progressively more oversaturated. The differentiation trends are the product of low pressure fractional crystallisation of an alkali basalt in a high level magma chamber.Differentiated rocks of the Nandewar Volcano in New South Wales differs from that of the Warrumbungle Volcano in several significant respects. In the Nandewar Volcano, for example, the parental magma is an olivine basalt, the differentiation trend is towards silica rich trachytes and very siliceous alkali rhyolites.The differentiated alkaline rocks from the large shield volcanoes of the Pacific display many affinities to the differentiated alkaline rocks from the shield volcanoes of the Australian continent. On Tahiti a moderately undersaturated alkaline magma has produced contrasting differentiates, silica saturated trachytes; and phonolites. In Hawaii the alkaline volcanic rocks have differentiated to produce oversaturated trachytes. By contrast, in the Galápagos Islands where the parental magma is a tholeiitic basalt the differentiation trend is towards very siliceous trachytes and quartz syentites.The divergent trends of differentiation in the Warrumbungle Shield can be traced via the intermediate lineage members to compositional differences between the basic lineage members. The temperature, pressure and fugacity of oxygen and water have controlled the path and extent of differentiation in high level magma chambers at 8–9 kb or less. Differing degrees of saturation of the basic lineage members are attributed to differing degrees of pyroxene or eclogite fractionation at high pressures. Progressively more undersaturated rocks have been derived at increasing depths or origin.

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Zusammenfassung Die Vulkangesteine des Warrumbungle-Vulkans im mittelwestlichen Neusüdwales, Australien, zeigen zwei verschiedene Differentiationstendenzen. Die eine erstreckt sich von alkalischen Basalten bis zu phonolitischen Trachyten, die immer stärker kieselsäure-untersättigt werden. Die andere erstreckt sich von Trachytbasalten bis quarzhaltigem Trachyt, der immer stärker übersättigt wird. Die Differentiationstendenzen ergeben sich aus der fraktionierten Kristallisation bei niederem Druck von einem alkalischen Basalt in einer nahe der Oberfläche liegenden Magmakammer.Differenziertes Gestein des Nandewar-Vulkans in Neusüdwales unterscheidet sich in einigen wesentlichen Punkten von dem des Warrumbungle-Vulkans. In dem Nandewar-Vulkan ist z. B. das Stammagma ein olivinhaltiger Basalt. Dazu tendiert es zu siliziumhaltigen Trachyten und sehr siliziumhaltigen alkalischen Rhyoliten.Das differenzierte alkalische Gestein von den großen Vulkanen des Pazifiks zeigt viele Ähnlichkeiten mit dem differenzierten alkalischen Gestein von den Vulkanen auf dem australischen Festland. Auf Tahiti hat ein mäßig untersättigtes alkalisches Magma kontrastierende Varianten, Phonolite und siliziumgesättigte Trachyte hervorgebracht. Auf Hawaii hat sich das alkalische Vulkangestein differenziert, wobei übersättigte Trachyte entstanden sind. Dagegen tendiert es auf den Galapagos-Inseln, wo das Stammagma ein tholeiitischer Basalt ist, zu sehr siliziumhaltigen Trachyten und Quarzsyeniten.Die divergierenden Differationstendenzen in dem Warrumbungle-Vulkan lassen sich durch die intermediären Stammglieder auf Zusammensetzungsunterschiede zwischen den früheren Stammgliedern zurückführen. Die Temperatur, der Druck und die Flüchtigkeit des Sauerstoffs und des Wassers haben den Vorgang und das Maß der Differentiation in nahe der Oberfläche begrabenen Magmakammern bei 8–9 kb. oder weniger kontrolliert. Verschiedene Sättigungsgrade der früheren Stammglieder werden verschiedenen Graden von Pyroxenoder Eklogit-Fraktionierung bei hohem Druck zugeschrieben. Zunehmend stärker untersättigtes Gestein ist bei wachsender Entstehungstiefe hervorgebracht worden.

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Résumé Les roches volcaniques du Volcan Warrumbungle, dans la partie centrale de la Nouvelle-Galles du Sud (Australie), montrent deux tendances distinctes de différenciation. L'une de ces tendances s'étend des basaltes alcalins aux trachytes phonolitiques qui deviennent de plus en plus sous-saturés en silice. L'autre tendance de différenciation s'étend des trachy-basaltes aux trachytes quartzifères, qui deviencent de plus en plus sursaturés. Ces tendances de différenciation sont le résultat de la cristallisation fractionnée, sous faible pression, d'un basalte alcalin dans une chambre magmatique proche de la surface.Les roches différenciées du volcan Nandewar en Nouvelle-Galles du Sud différent sous plusieurs aspects importants de celles du volcan Warrumbungle. Dans le volcan Nandewar, par exemple, le magma originel est un basalte à olivine; la différenciation tend vers des trachytes contenant de la silice et des rhyolites alcalines très siliceuses.La roche alcaline différenciée des grands volcans du Pacifique montre beaucoup d'affinités avec celle des volcans du continent australien. A Tahiti un magma alcalin moyennement sous-saturé a produit des roches différenciées très diverses: des trachytes saturés en silice et des phonolites. A Hawaii les roches volcaniques alcalines se sont différenciées pour produire enfin des trachytes sursaturés. Par contre aux Iles Galapagos, où le magma originel est un basalte tholéiitique, la tendance de la différenciation va vers des trachytes très siliceux et des syénites quartzifères.Les tendances divergentes de la différenciation dans le Warrumbungle remontent par des termes intermédiaires à des différences de composition entre les premiers membres dérivés du magma originel.La température, la pression et la fugacité de l'oxygène et de l'eau ont réglé le processus et l'étendue de la différenciation dans les chambres magmatiques enfouies à proximité de la surface, sous une pression de 8–9 kb ou moins. C'est à différents degrés de saturation des premiers membres du magma originel que sont attribués les différents degrés de fractionnement du pyroxène ou de l'éclogite à haute pression. C'est toujours une roche de plus en plus sous-saturée qui est engendrée par augmentation de sa profondeur d'origine.

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Late Quaternary evolution of Lake Urana,New South Wales,Australia

Lake Urana is a well-preserved relict lake in the semi-arid Riverine Plain of southeastern Australia. A compound lunette at its eastern shoreline consists of a quartz-sand-dominated unit (Bimbadeen Formation), thermoluminescence (TL) dated at 30 ka to 12 ka, and a clay and sand facies unit (Coonong Formation), dated at 55 ka to 35 ka. The intervening period indicates a phase of periodically exposed lake floor and soil formation. The older wet phase conforms well with similar environments recorded from the same period at Lake Mungo. However, the return to high water levels from 30 ka to 12 ka departs sharply from the generally accepted palaeoclimatic model from Australia, which demands severe glacial maximum desiccation and widespread construction of clay lunettes. Although hydrological budgets calculated for Lake Urana and nearby Lake Cullivel require high glacial maximum water levels they do not support higher precipitation.     

Exploration rock geochemistry for gold, Parkes, New South Wales, Australia

The London-Victoria lode-type Au deposit near Parkes, New South Wales, was discovered in 1863 and became the subject of modern exploration in 1980 after about 75 years of little or no activity. The deposit lies within Palaeozoic tuffaceous, andesitic rocks. Soil geochemistry was the main technique used to define drill targets, and the deposit is now at an advanced state of assessment for probable development.Rock geochemistry is being investigated as an aid in drill-core interpretation in the search for extensions to the London-Victoria deposit and other similar deposits in the district.At an early stage of the rock-geochemical work it became clear that minor basemetal mineralization was also present in the structural hanging wall at between 30 and 70 m from the lode Au deposit. Interpretation of the geochemical signatures for major elements (Ca, Mg, Na, K, Fe) and trace elements (Cu, Pb, Zn, Mn) is confused by an overlap and merging of responses from the Au and base-metal mineralization. The measurement of bromine-soluble Sb, As, Bi, and Te, together with the more conventional major and trace elements, permits discrimination between geochemical halos related to the Au and those resulting from minor base metal mineralization.The results demonstrate the use of rock geochemistry for Au exploration, its usefulness in drawing attention to geological features, and the utility of bromine-soluble trace elements commonly associated with gold mineralization.     

Wallrock alteration at the western system of the CSA mine,cobar, New South Wales,Australia

Petrological and geochemical characteristics of the sequence from chloritic siltstone through “siliceous siltstone” to “elvan”, which occurs approaching ore on the hanging wall of the Western System in the CSA Mine, Cobar, indicate its formation by extensive dilational silicification together with minor addition of S and K very close to the ore. The manner whereby more chloritic members of this sequence developed from ‘background’ muscovite-rich siltstones remote from mineralization is less clear. “Elvan” is not an exhalative chert. The distribution of wallrock alteration products and characteristics of the ores do not support suggestions that Cobar orebodies are remobilized stratiform deposits. Alteration preceded epigenetic ore emplacement in the early stages of a regional metamorphic episode which took place soon after Early Devonian turbidite sedimentation without associated igneous activity. Mineralization is attributed to diagenetic dewatering or metamorphic dehydration of the sediment pile.     

Shoshonitic and ultrapotassic post-collisional dykes from northern Karakorum (Sinkiang, China)

High-K calc-alkaline, shoshonitic and ultrapotassic post-collisional dykes of Neogene age have been found in the remote and little known region of northern Karakorum located around the Shaksgam valley, north of the K2-Gasherbrum range (China). The dykes derive from more or less comparable basic magma(s) and display rather unusual petrographic and geochemical characters with respect to the other K-rich rocks. The geochemical data are consistent with derivation of the basic magma(s) from small degrees of partial melting of garnet-lherzolites previously enriched in incompatible elements of crustal origin possibly during the subduction of the Indian plate beneath Karakorum. The spectrum of compositions reflects fractional crystallization governed by an early removal of clinopyroxene, phlogopite, plagioclase, garnet±amphibole followed by the precipitation of abundant alkali feldspar, amphibole±apatite±quartz. Additionally, assimilation of crustal rocks during magma ascent contributed to the unusual compositional characteristics and is suggested by the abundance of corroded quartz ( ± plagioclase) xenocrysts and by the occasional presence of granitic xenoliths.

An apparent connection exists between magmatism and tectonism in the complex Karakorum Fault Zone (KFZ). It is suggested that, during the Neogene, the strike-slip KFZ and some adjacent post-metamorphic faults transiently behaved as extensional fault systems down to deep levels, triggering ascent and emplacement of the K-rich magma. The subsequent (re)activation of a compressive and transcurrent regime determined the rapid and recent uplift of the more primitive lamprophyres occurring in the plutonites and metamorphites of the upper Baltoro Glacier and K2-Gasherbrum range, relative to the more fractionated and contaminated lamprophyres injecting the shallower rocks of the Shaksgam valley area.     

Scaling property of regional floods in New South Wales Australia

Regional flood frequency analysis (RFFA) is often used in hydrology to estimate flood quantiles when there is a limitation of at-site recorded flood data. One of the commonly used RFFA methods is the index flood method, which is based on the assumptions that a region satisfies criterion of simple scaling and it can be treated homogeneous. Another RFFA method is quantile regression technique where prediction equations are developed for flood quantiles of interest as function of catchment characteristics. In this paper, the scaling property of regional floods in New South Wales (NSW) State in Australia is investigated. The results indicate that the annual maximum floods in NSW satisfy a simple scaling assumption. The application of a heterogeneity test, however, reveals that NSW flood data set does not satisfy the criteria for a homogeneous region. Finally, a set of prediction equations are developed for NSW using quantile regression technique; an independent test shows that these equations can provide reasonably accurate design flood estimates with a median relative error of about 27%.     

Environmental geochemistry of the derelict Webbs Consols mine,New South Wales,Australia

Small-scale mining and mineral processing at the Webbs Consols polymetallic PbZnAg deposit in northern New South Wales, Australia has caused a significant environmental impact on streams, soils and vegetation. Unconfined waste rock dumps and tailings dams are the source of the problems. The partly oxidised sulphidic mine wastes contain abundant sulphides (arsenopyrite, sphalerite, galena) and oxidation products (scorodite, anglesite, smectite, Fe-oxyhydroxides), and possess extreme As and Pb (wt% levels) and elevated Ag, Cd, Cu, Sb and Zn values. Contemporary sulphide oxidation, hardpan formation, crystallisation of mineral efflorescences and acid mine drainage generation occur within the waste repositories. Acid seepages (pH 1.9–6.0) from waste dumps, tailings dams and mine workings display extreme As, Pb and Zn and elevated Cd, Cu and Sb contents. Drainage from the area is by the strongly contaminated Webbs Consols Creek and although this stream joins and is diluted by the much larger Severn River, contamination of water and stream sediments in the latter is evident for 1–5 km, and 12 km respectively, downstream of the mine site. The pronounced contamination of local and regional soils and sediments, despite the relatively small scale of the former operation, is due to the high metal tenor of abandoned waste material and the scarcity of neutralising minerals. Any rehabilitation plan of the site should include the relocation of waste materials to higher ground and capping, with only partial neutralisation of the waste to pH 4–5 in order to limit potential dissolution of scorodite and mobilisation of As into seepages and stream waters.     

Drainage sampling for uranium in the Torrington district, New South Wales, Australia

A brief orientation study has been conducted to evaluate the use of drainage geochemical sampling for U in the granitic and forested terrain of the Torrington district of northeastern New South Wales. Anomalous U levels are present in both stream sediments and waters draining a known W prospect containing accessory U. The U dispersion is affected by interrelated environmental factors such as catchment physiography and the organic content of the stream sediments. The influence of organic content on U level in stream sediments is most significant. Variation in sediment organic content is related to accumulation of vegetal organic debris and charcoal in stream channels by sheetwashing of sparsely covered forest floors particularly in catchments of high topographic relief. The U is apparently absorbed onto the organic material from ephemerally flowing stream waters. Temporal variations in U content of stream sediment are indicated which necessitate careful consideration in planning and interpreting the results of a survey in this environment.     

Sedimentology of the Middle Devonian Timor Limestone,northeastern New South Wales,Australia

The microfacies assemblages and their distribution within the Middle Devonian Timor Limestone, exposed in the Timor Valley of northeastern New South Wales, Australia are described, and a depositional model for the carbonate buildup presented.Two broad lithological divisions are clearly recognizable within this thick (345 m) but lensoidal mass. Lime wackestones/packstones dominate the lower 200–215 m of the buildup while lime grainstones characterize the upper 130 m. Using cluster-sorting techniques on 697 modally analysed limestone samples, five microfacies and several subgroups each characterized by a unique combination of allochems have been recognized within this gross subdivision.The microfacies data and field observations suggest that carbonate sedimentation was initiated in an open marine shelf environment. It began simply because local conditions were favourable for calcareous organisms to become established. The benthos flourished ultimately spreading out over an area of 25 km². Although reefal in outline, the limestone is a bedded deposit containing chiefly comminuted skeletal debris and never had the ecologic potential to form a wave-resistant mass.Lime mud sedimentation began in a sublittoral environment. Abundant calcareous algae throughout most of the lower two-thirds of the buildup suggest that deposition occurred within the photic zone. In succeeding horizons, pellet and intraclast lime grainstones gradually replace the lime mud dominated microfacies, indicating that carbonate deposition slowly outpaced basin subsidence and shoal-water conditions developed over the buildup. During the buildup's final stage, a transgression occurred resulting in quieter marine conditions and the deposition of coral lime wackestones in the former shoal area.Carbonate sedimentation was terminated by an extensive marine tuff killing the calcareous benthos. No further extensive carbonate sedimentation during the Middle Devonian is recorded in the Timor Valley.     

Skarn development from limestone adjacent to the Glenrock Granodiorite,Marulan Batholith,New South Wales,Australia

Skarns are developed over two temperature‐time intervals in calcite limestone adjacent to the southern extension of the Glenrock Granodiorite, a pluton of the Marulan Batholith, Southern Highlands, New South Wales. The initial volumetrically‐dominant prograde phase of skarn formation produced a suite comprising bimetasomatic skarn, including pyroxene endoskarn, potassic endoskarn and wollastonite‐bearing exoskarn, together with mineralogically‐zoned vein skarn, massive garnet‐pyroxene skarn and calcite‐vesuvianite skarn. Retrograde replacement is manifested by the development of hydrous silicate minerals, carbonate and cross‐cutting sulphide veinlets.

A genetic model is proposed to account for the development of bimetasomatic skarn in the deposit. Exoskarn geochemistry indicates addition of many components relative to an essentially pure limestone precursor, including Si, Al, Fe, Zr, Zn, S, Mn and Cu, negligible transfer of K, Na and Rb and loss of CO₂. Strontium and Ca loss from the parent limestone is indicated by mass balance calculations at constant volume.

Garnet and pyroxene compositions in the massive garnet‐pyroxene skarn range from Gr₃₀ to Gr₆₆ and Hd₆₁ to Hd₈₇, respectively. Compositions from Gr₆₇ to Gr₉₅ are typical of the vein skarn garnets. Chemical zonation patterns in garnet, pyroxene and vesuvianite are generally characterized by rim Fe depletion relative to cores of grains.

Prograde skarn probably formed at T = 500–580°C; P < 220 MPa. The massive garnet‐pyroxene skarn evolved under conditions of log fO₂ = ‐18.9 to ‐22.9 (assuming a constant fCO₂ of 20 MPa) within the fS₂ stability field of pyrrhotite. Retrograde skarn formed at T < 400°C, possibly under conditions of X_H2O < 0.01.

Vesuvianite plus wollastonite assemblages, present in exoskarn, probably attest to very water‐rich conditions. The marble wall rocks, isolated from the source of skarn‐forming fluids, probably evolved under conditions of minimum X_co2 >0.2. Low temperature CO₂ ‐rich fluid inclusions and prehnite (stable at X_co2 <0.01), present in the marble and skarn, respectively, suggest that substantial differences in X_co2: X_H2O were maintained during cooling.

Observed mineralogical and chemical zonation within the skarn reflects the complex interaction of T, P, fO₂, Xco₂ and other chemical variables such as a_SiO2 and a_Al2O3 throughout the skarn system. No single variable can account adequately for the mineralogical diversity observed in the skarn deposit.