Academic literature on the topic 'Veins (Geology) Victoria'

The poly-deformed Priestley schist (Wilson Terrane) of north Victoria Land, Antarctica ranges in metamorphic grade from lower greenschist facies to upper amphibolite facies. All grades of schist have been affected by structurally controlled retrogressive H2O-CO2 fluids with 45–70 mole % CO2. The fluids have deposited quartz-carbonate veins with pyrite and chlorite or biotite in late stage structures. Veins typically constitute < 1% of the rock mass, but in one greenschist facies area > 10% of the rock is vein. Veins in higher grade schists have been boudinaged after formation, and many have been annealed. Primary fluid inclusions are preserved in veins in biotite zone schists in two localities. At one locality, entrapment of immiscible fluids (water with c. 8 and 45 mole % CO2) occurred during vein formation, at about 280–300°C and 700 ± 200 bars fluid pressure. The aqueous fluid is slightly saline (4 wt % NaCl equivalent). At the other primary fluid inclusion locality, veins were formed from a single phase fluid (c. 70 mole % CO2) at 200–350°C and 1600 ± 500 bars fluid pressure. Both these vein systems are inferred to have formed between 2 and 8 km depth, near the brittle-ductile transition. Retrogressive fluid mobility and vein formation occurred throughout schist in the Priestly metamorphic complex during uplift in the latter part of the Ross Orogeny (c. 490 Ma), following near-isobaric cooling at metamorphic depths.

Abstract The Reward mine at Hill End hosts structurally controlled orogenic gold mineralization in moderately S plunging, high-grade gold shoots located at the intersection between a late, steeply W dipping reverse fault zone and E-dipping, bedding-parallel, laminated quartz veins (the Paxton’s vein system). The mineralized bedding-parallel veins are contained within the middle Silurian to Middle Devonian age, turbidite-dominated Hill End trough forming part of the Lachlan orogen in New South Wales. The Hill End trough was deformed in the Middle Devonian (Tabberabberan orogeny), forming tight, N-S–trending, macroscopic D2 folds (Hill End anticline) with S2 slaty cleavage and associated bedding-parallel veins. Structural analysis indicates that the D2 flexural-slip folding mechanism formed bedding-parallel movement zones that contained flexural-slip duplexes, bedding-parallel veins, and saddle reefs in the fold hinges. Bedding-parallel veins are concentrated in weak, narrow shale beds between competent sandstones with dip angles up to 70° indicating that the flexural slip along bedding occurred on unfavorably oriented planes until fold lockup. Gold was precipitated during folding, with fluid-flow concentrated along bedding, as fold limbs rotated, and hosted by bedding-parallel veins and associated structures. However, the gold is sporadically developed, often with subeconomic grades, and is associated with quartz, muscovite, chlorite, carbonates, pyrrhotite, and pyrite. East-west shortening of the Hill End trough resumed during the Late Devonian to early Carboniferous (Kanimblan orogeny), producing a series of steeply W dipping reverse faults that crosscut the eastern limb of the Hill End anticline. Where W-dipping reverse faults intersected major E-dipping bedding-parallel veins, gold (now associated with galena and sphalerite) was precipitated in a network of brittle fractures contained within the veins, forming moderately S plunging, high-grade gold shoots. Only where major bedding-parallel veins were intersected, displaced, and fractured by late W-dipping reverse faults is there a potential for localization of high-grade gold shoots (&gt;10 g/t). A revised structural history for the Hill End area not only explains the location of gold shoots in the Reward mine but allows previous geochemical, dating, and isotope studies to be better understood, with the discordant W-dipping reverse faults likely acting as feeder structures introducing gold-bearing fluids sourced within deeply buried Ordovician volcanic units below the Hill End trough. A comparison is made between gold mineralization, structural style, and timing at Hill End in the eastern Lachlan orogen with the gold deposits of Victoria, in the western Lachlan orogen. Structural styles are similar where gold mineralization is formed during folding and reverse faulting during periods of regional east-west shortening. However, at Hill End, flexural-slip folding-related weakly mineralized bedding-parallel veins are reactivated to a lesser degree once folds lock up (cf. the Bendigo zone deposits in Victoria) due to the earlier effects of fold-related flattening and boudinage. The second stage of gold mineralization was formed by an array of crosscutting, steeply W dipping reverse faults fracturing preexisting bedding-parallel veins that developed high-grade gold shoots. Deformation and gold mineralization in the western Lachlan orogen started in the Late Ordovician to middle Silurian Benambran orogeny and continued with more deposits forming in the Bindian (Early Devonian) and Tabberabberan (late Early-Middle Devonian) orogenies. This differs from the Hill End trough in the eastern Lachlan orogen, where deformation and mineralization started in the Tabberabberan orogeny and culminated with the formation of high-grade gold shoots at Hill End during renewed compression in the early Carboniferous Kanimblan orogeny.

Abstract In many orogenic gold deposits, gold is located in quartz veins. Understanding vein development at the microstructural scale may therefore provide insights into processes influencing the distribution of gold, its morphology, and its relationship to faulting. We present evidence that deformation processes during aseismic periods produce characteristic quartz microstructures and crystallographic preferred orientations, which are observed across multiple deposits and orogenic events. Quartz veins comprise a matrix of coarse, subidiomorphic, and columnar grains overprinted by finer-grained quartz seams subparallel to the fault trace, which suggests an initial stage of cataclastic deformation. The fine-grained quartz domains are characterized by well-oriented quartz c-axis clusters and girdles oriented parallel to the maximum extension direction, which reveals that fluid-enhanced pressure solution occurred subsequent to grain refinement. Coarser anhedral gold is associated with primary quartz, whereas fine-grained, “dusty” gold trails are found within the fine-grained quartz seams, revealing a link between aseismic deformation and gold morphology. These distinct quartz and gold morphologies, observed at both micro- and macroscale, suggest that both seismic fault-valving and aseismic deformation processes are both important controls on gold distribution.

AbstractMantle xenoliths from southern Victoria Land have been collected and extensively studied for over a century. In this chapter, chemical and petrological data are, for the first time, comprehensively collated, and petrogenetic models for the regional mantle are reviewed and assessed. The most common lithologies are spinel lherzolite and harzburgite; plagioclase lherzolite also occurs, and pyroxenite xenoliths found across the province comprise <20% of all mantle xenoliths. The lithospheric mantle in the region has Paleoproterozoic stabilization ages, although pockets of younger mantle may exist. This peridotite mantle comprises a HIMU (high 238U/204Pb = high μ)-component sensu stricto, has been variably carbonated and has undergone multiple melt-depletion events. Regional variations in a sedimentary (EMI: Enriched Mantle I) component to the west, and iron-rich components to the east, reflect a complex history of refertilization and metasomatism. The sources of these fluids are likely to have been oceanic crust subducted during c. 0.5 Ga and older events. Peridotites have been cross-cut by pyroxenite veins, probably in multiple episodes, with the geochemistry of some samples reflecting the involvement of an upper continental crust (EMII: Enriched Mantle II) component. Future research directions should apply advanced isotopic, noble gas and volatile techniques to better understand the upper mantle below this dynamic rifting environment.

Abstract Myanmar is occupied by the N-wards continuation of the Sunda arc and by the Shan Plateau and its continuation through Yunnan into Tibet. Our new tectonic interpretation of the ophiolite–flysch belts, world-famous jadeite and tin deposits in Myanmar west of the Salween adopts previous proposals that, before 450-km post-early Oligocene dextral displacement along the Sagaing Fault, the ophiolite belt in NE Myanmar continued through the topography that is now located west of the fault in the Indo-Burman Ranges. Differences in cross-section through Mogok and the Shan Scarps are reconciled by the recently proposed emplacement, in our view during Permian time, of the Mogok Metamorphic Group onto the Slate Belt to form Sibumasu. We argue that during Early Jurassic time a Neo-Tethys ophiolite nappe was obducted over turbidites on Sibumasu’s passive western margin. Following reversal in tectonic polarity, the remaining Neo-Tethys subducted E-wards generating the 113–128 Ma Mondaung Arc. During ocean closure the Victoria–Katha Block and its Triassic flysch subducted beneath Sibumasu, resulting in jadeite veins in overlying serpentinite that ascended in the subduction zone and were exhumed at Hpakant and Nat Hmaw, bordering the Jade Mines Uplift. Subduction of the Indian Ocean since Albian time generated the Popa–Loimye arc, while extensional faulting led to uplift of the Indo-Burman Ranges and to the formation of the Western Tin Belt granites. Tectonic effects in Myanmar of the India–Asia collision may be confined to the Disang thrust belt in the Naga Hills.