Academic literature on the topic 'Geology, Structural New South Wales Broken Hill'

AbstractEcandrewsite, the zinc analogue of ilmenite, is a new mineral which was first described from the Broken Hill lode in 1970 and discovered subsequently in ores from Little Broken Hill (New South Wales) and the San Valentin Mine, Spain. The name ‘ecandrewsite’ was used in a partial description of the mineral in ‘Minerals of Broken Hill’ (1982), thereby establishing the Little Broken Hill locality, specifically the Melbourne Rockwell Mine, as the type locality. Microprobe analysis of ecandrewsite from the type locality gave ZnO 30.42 (wt.%), FeO (total Fe) 11.37, MnO 7.64, TiO2 50.12, total 99.6%, yielding an empirical formula of (Zn0.59Fe0.24Mn0.17)1.00Ti0.99O3 based on 3 oxygen atoms. All compositions from Little Broken Hill and the San Valentin Mine are ferroan manganoan ecandrewsite. The strongest lines in the X-ray powder diffraction data are (d in Å, (hkil), I/Io):2.746, (104), 100; 2.545, (110), 80; 1.867, (024), 40; 3.734, (012), 30; 1.470, (3030), 30; 1.723, (116), 25. Ecandrewsite is hexagonal, space group RR3¯ assigned from a structural study, with a = 5.090(1), c = 14.036(2)Å, V = 314.6(3)Å3, Z = 6, D(calc.) = 4.99. The mineral is opaque, dark brown to black with a similar streak, and a submetallic lustre. In plane polarized light the reflection colour is greyish white with a pinkish tinge. Reflection pleochroism is weak, but anisotropism is strong with colours from greenish grey to dark brownish grey. Reflectance data in air between 470 and 650 nm are given. At the type locality, ecandrewsite forms disseminated tabular euhedral grains up to 250 × 50 µm, in quartz-rich metasediments. Associated minerals include almandine-spessartine, ferroan gahnite and rutile. The name is for E. C. Andrews, pioneering geologist in the Broken Hill region of New South Wales. Type material consisting of one grain is preserved in the Museum of Victoria (M35700). The mineral and name were approved by the IMA Commission on New Minerals and Mineral Names in 1979.

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 (>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.

"Two independent geochronological techniques specifically targeting post-kinematic or late-stage growth of kyanite, staurolite and late-stage garnet in the southern Curnamona Province has found that these minerals grew during the Delamerian Orogeny (~530-500 Ma). Prograde metamorphism during the Delamerian Orogeny attained kyanite-staurolite-garnet grade (amphibolite-facies). Previous interpretations of an anticlockwise P-T path for the Olarian Orogeny need revising, as these interpretations have been shown in this study to be based on textural relationships spanning ~1100 million years. This highlights the importance of in situ geochronological techniques in defining robust P-T-t paths for a region." --p. 121 of source document.
Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2006.