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We present a new lithogeochemical method to target prospective komatiites that may host Ni-Cu-(PGE) deposits. The new methodology is based on the geochemical properties of ruthenium (Ru) and chromium (Cr), elements that are immobile under most conditions; it relies on a restricted number of carefully selected representative samples and is applicable in highly altered terrains. Ruthenium is a platinum-group element (PGE) that exhibits contrasting geochemical behavior in sulfide-saturated and sulfide-undersaturated komatiites. Similarly to other PGEs, Ru shows highly chalcophile behavior in magmas that equilibrate with an immiscible sulfide phase. However, Ru is also compatible in chromite in sulfide-undersaturated systems. If we consider Cr concentration as an index of chromite abundance in chromite-saturated komatiites, we observe that Ru increases or decreases systematically with increasing Cr according to the sulfide saturation state of the magmatic system. In rocks that crystallized from sulfide-saturated melts, Ru contents decrease with increasing Cr. Conversely, in rocks that crystallized from sulfide-undersaturated melts, Ru contents increase with increasing Cr. As a result, on the basis of the Ru-Cr variation it is possible to discriminate whether a komatiite melt equilibrated with a sulfide liquid during crystallization. The strength of this method compared to previous PGE-based lithogeochemical techniques derives from combining the traditional use of the geochemical properties of a highly immobile and chalcophile element that records the ore-forming process (ruthenium) with the occurrence of a mechanically and chemically resistant mineral phase (chromite), which is generally preserved in highly altered komatiites. [ABSTRACT FROM AUTHOR]

Albion Downs is a structural domain within the Agnew-Wiluna Greenstone Belt of Western Australia, which contains one of the most highly Ni-endowed komatiite sequences in the world. Albion Downs comprises adcumulate-textured pods and lenses, which are flanked by thinner meso- and orthocumulate-textured units. Basal massive nickel-sulphide mineralisation (e.g. Jericho) generally occurs in the thinner meso- and orthocumulate-textured units, whereas stratabound disseminated nickel-sulphide mineralisation (e.g. Jordan) is hosted in the largest adcumulate-textured pod. After reaching sulphide-saturation, basal massive sulphides formed in settings where magma flow was less fast and turbulent than in channels. Conversely, in channellike settings sulphide blebs were entrained in the flow, thus forming disseminated sulphides. Platinum-group element lithogeochemistry indicates that the signature associated with the oreforming process is only recorded <100 m-away from nickel-sulphide mineralisation, where samples display a positive relationship between Pd+Pt and MgO and Pd+Pt and S. Conversely, the PGE signature of samples collected farther away is not directly controlled by sulphide segregation. Understanding the scale at which ore-formation processes operate is crucial to the development of any lithogeochemical exploration vector that is dependent on PGE variation. [ABSTRACT FROM AUTHOR]

The Mt Tom Price deposit is a world-class high-grade hematite deposit in the Hamersley Province of Western Australia with an original resource of 900 Mt of almost pure hematite, averaging 63·9 wt-%Fe. Petrological and geochemical studies at both the Southern Ridge and the North deposit at Mt Tom Price have identified three hypogene alteration zones between unmineralised banded iron formation (BIF) and high-grade iron ore. [ABSTRACT FROM AUTHOR]

Situated south of the eastern Himalayan syntaxis at the western margin of the Shan-Thai terrane the high-grade Mogok metamorphic belt (MMB) in Myanmar occupies a key position in the tectonic evolution of Southeast Asia. The first sensitive high-resolution ion microprobe U-Pb in zircon geochronology for the MMB shows that strongly deformed granitic orthogneisses near Mandalay contain Jurassic (∼170 Ma) zircons that have partly recrystallized during ∼43 Ma high-grade metamorphism. A hornblende syenite from Mandalay Hill also contains Jurassic zircons with evidence of Eocene metamorphic recrystallization rimmed by thin zones of 30.9 ± 0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma) I-type granitoids in the MMB, Myeik Archipelago, and Western Myanmar confirm that prior to the collision of India, an up to 200 km wide magmatic belt extended along the Eurasian margin from Pakistan to Sumatra. Metamorphic overgrowths to zircons in the orthogneiss near Mandalay date a period of Eocene (∼43 Ma) high-grade metamorphism possibly during crustal thickening related to the initial collision between India and Eurasia (at 65 to 55 Ma). This was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 Ma. Similar syntectonic syenites and leucogranites intruded the Ailao Shan-Red River shear belt in southern China and Vietnam during the Eocene-Oligocene to Miocene, and the Wang Chao and Three Pagodas faults in northern Thailand (that most likely link with the MMB) were also active at this time. The complex history of Eocene to early Miocene metamorphism, deformation, and magmatism in the MMB provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of India and resulting extrusion or rotation of Indochina. [ABSTRACT FROM AUTHOR]

U–Pb (SHRIMP) detrital zircon age patterns are reported for 12 samples of Permian to Cretaceous turbiditic quartzo-feldspathic sandstone from the Torlesse and Waipapa suspect terranes of New Zealand. Their major Permian to Triassic, and minor Early Palaeozoic and Mesoproterozoic, age components indicate that most sediment was probably derived from the Carboniferous to Triassic New England Orogen in northeastern Australia. Rapid deposition of voluminous Torlesse/Waipapa turbidite fans during the Late Permian to Late Triassic appears to have been directly linked to uplift and exhumation of the magmatically active orogen during the 265–230 Ma Hunter–Bowen event. This period of cordilleran-type orogeny allowed transport of large volumes of quartzo-feldspathic sediment across the convergent Gondwanaland margin. Post-Triassic depocentres also received (recycled?) sediment from the relict orogen as well as from Jurassic and Cretaceous volcanic provinces now offshore from southern Queensland and northern New South Wales. The detailed provenance–age fingerprints provided by the detrital zircon data are also consistent with progressive southward derivation of sediment: from northeastern Queensland during the Permian, southeastern Queensland during the Triassic, and northeastern New South Wales – Lord Howe Rise – Norfolk Ridge during the Jurassic to Cretaceous. Although the dextral sense of displacement is consistent with the tectonic regime during this period, detailed characterisation of source terranes at this scale is hindered by the scarcity of published zircon age data for igneous and sedimentary rocks in Queensland and northern New South Wales. Mesoproterozoic and Neoproterozoic age components cannot be adequately matched with likely source terranes in the Australian–Antarctic Precambrian craton, and it is possible they originated in the Proterozoic cores of the Cathaysia and Yangtze Blocks of southeast China. [ABSTRACT FROM AUTHOR]

Greenstone belts in the northern Murchison Terrane of the Yilgarn Craton contain an extensive suite of 2.9–3.0 Ga, porphyritic komatiites and komatiitic volcaniclastic rocks. These unusual Ti-rich Al-depleted komatiites have been sampled at Gabanintha and are characterised by higher incompatible-element abundances than most suites of Barberton-type Al-depleted komatiites. They form a petrogenetically related group with similar Ti- and incompatible-element-rich, Al-depleted porphyritic komatiites and komatiitic volcaniclastic rocks from Karasjok in Norway, Dachine in French Guiana and Steep Rock – Lumby Lake in Canada (here called Karasjok-type komatiites). Their Al-depletion results from magma generation at depths of >250 km in the presence of residual majorite-garnet. The porphyritic textures and abundance of amygdales and volcaniclastic rocks typical of this type of komatiite are features of hydrous ultramafic magmas. The incompatible-element-rich ultramafic rocks from Dachine contain diamonds that were most likely picked up as parent magmas interacted with mantle lithosphere that had been hydrated and chemically modified. Consequently the interaction of Karasjok-type komatiite magmas with thick, island arc or continental mantle lithosphere may have resulted in their elevated water and incompatible-element contents. The occurrence of Karasjok-type komatiite lavas and volcaniclastic rocks in the northern Murchison Terrane suggests that during the Late Archaean that terrane had a hydrated, metasomatised or subduction-modified mantle lithosphere. [ABSTRACT FROM AUTHOR]

Hemodynamically unstable ventricular arrhythmias are frequently untreatable with radio-frequency ablation due to the difficulty of rapidly and accurately localizing the site of origin of an arrhythmia with current technologies. We demonstrate a new catheter guidance method that will direct the tip of an ablation catheter to the site of origin of an arrhythmia and reduce the time needed to locate the site such that a patient need only be maintained in the arrhythmia for a few beats. The algorithm, based on a single-equivalent moving dipole (SEMD) model, is used to identify the bioelectric dipole corresponding to a site of origin of an arrhythmia. If a current dipole is produced at the ablation catheter tip, the tip position may also be calculated using this algorithm, and the catheter can be guided towards the site of origin of the arrhythmia. We present a method to compensate for the effect of systematic non-idealities, such as boundary effects, on the accuracy of this algorithm. In simulations, this method is able to guide the catheter tip to within 1.5 mm of the arrhythmic site at any location within the model torso with almost 100% success and with a realistic number of movements of the ablation catheter. These results suggest that this method has great potential to direct radio-frequency ablation procedures, especially in the significant patient population that is currently untreatable.