Academic literature on the topic 'Metamorphic rocks New South Wales Broken Hill'

AbstractTwo distinct generations of pyrite, with different morphologies, are described from the Proterozoic Broken Hill-type Pinnacles deposit in western NSW. The earlier, py1, forms concentric layers interpreted as colloform banding. Although the textures are somewhat similar to those observed in supergene alteration zones, textural relationships in fresh rocks suggest that these are pre-metamorphic and that the pyrite formed as the result of precipitation from hydrothermal fluids in open veins, vugs and fissures. The second generation, py2, post-dates py1 and forms euhedral overgrowths on it. It is interpreted as being synchronous with the main phase of base metal sulphide mineralisation. The textures reported here are previously unrecorded for Broken Hill-type mineralisation, and have implications for the regional identification of feeder zones to the Broken Hill deposit. The evidence supports a model in which mineralising conditions at the Pinnacles were characterised by slightly higher oxygen and lower sulphur fugacity (further constrained by Fe contents of sphalerite) than at Broken Hill, where pyrrhotite is the major Fe sulphide.The pre-metamorphic textures observed in the pyrite at the Pinnacles deposit are also unusual because they have survived granulite facies metamorphism and five phases of deformation, whereas previously the preservation of such textures has not been recognised at metamorphic grades greater than amphibolite facies.

Abstract. The values and distribution patterns of the strontium (Sr) isotope ratio 87Sr/86Sr in Earth surface materials are of use in the geological, environmental, and social sciences. Ultimately, the 87Sr/86Sr ratios of soils and everything that lives in and on them are inherited from the rocks that are the parent materials of the soil's components. In Australia, there are few large-scale surveys of 87Sr/86Sr available, and here we report on a new, low-density dataset using 112 catchment outlet (floodplain) sediment samples covering 529 000 km2 of inland southeastern Australia (South Australia, New South Wales, Victoria). The coarse (<2 mm) fraction of bottom sediment samples (depth ∼ 0.6–0.8 m) from the National Geochemical Survey of Australia were milled and fully digested before Sr separation by chromatography and 87Sr/86Sr determination by multicollector-inductively coupled plasma mass spectrometry. The results show a wide range of 87Sr/86Sr values from a minimum of 0.7089 to a maximum of 0.7511 (range 0.0422). The median 87Sr/86Sr (± median absolute deviation) is 0.7199 (± 0.0071), and the mean (± standard deviation) is 0.7220 (± 0.0106). The spatial patterns of the Sr isoscape observed are described and attributed to various geological sources and processes. Of note are the elevated (radiogenic) values (≥∼ 0.7270; top quartile) contributed by (1) the Palaeozoic sedimentary country rock and (mostly felsic) igneous intrusions of the Lachlan geological region to the east of the study area; (2) the Palaeoproterozoic metamorphic rocks of the central Broken Hill region; both these sources contribute radiogenic material mainly by fluvial processes; and (3) the Proterozoic to Palaeozoic rocks of the Kanmantoo, Adelaide, Gawler, and Painter geological regions to the west of the area; these sources contribute radiogenic material mainly by aeolian processes. Regions of low 87Sr/86Sr (≤∼ 0.7130; bottom quartile) belong mainly to (1) a few central Murray Basin catchments; (2) some Darling Basin catchments in the northeast; and (3) a few Eromanga geological region-influenced catchments in the northwest of the study area; these sources contribute unradiogenic material mainly by fluvial processes. The new spatial Sr isotope dataset for the DCD (Darling–Curnamona–Delamerian) region is publicly available (de Caritat et al., 2022; https://dx.doi.org/10.26186/146397)​​​​​​​.

AbstractA study of low-grade metamorphism in late Silurian to early Carboniferous rocks in the North Hill End Synclinorium and adjacent anticlinoria has been made by the determination of illite crystallinity and bo values of K-white mica in eighty slates and phyllites. Illite crystallinity values vary from 0.40 Δ°2θ on the Molong Anticlinorium to 0.12 Δ°2θ within the axis of the synclinorium, suggesting anchizonal to epizonal metamorphic conditions. This is in agreement with previous observations on Ca-Al-hydrosilicate assemblages which indicated a change from prehnite-pumpellyite facies in the anticlinoria adjacent to the synclinorium to middle greenschist facies in the axis. Local variations in crystallinity are attributed to variation in ak+ in fluids migrating along cleavage zones.The mean bo value obtained from the pelites is 9.017 Å (σn = 0.008; n = 80) which is in close agreement with that obtained from part of the adjacent Capertee Anticlinorium (x̄ = 9.019 Å; σn = 0.007; n = 52). However, ‘t’ tests indicate that two bo populations are present in the synclinorium (x̄ = 9.019 and 9.022 Å), with the lower values concentrated in the southern portion of this structure. The two populations are considered to be the result of slightly different metamorphic conditions prevailing during the deformation of the rocks in the synclinorium. A higher geothermal gradient affecting rocks giving the lower bo values is attributed to the presence of granitoids at shallower depths than elsewhere in the synclinorium.

The Mount Isa Basin is a new concept to describe the area of Palaeo- to Mesoproterozoic rocks south of the Murphy Inlier (not the Murphy Tectonic Ridge) and inappropriately described as the Mount Isa Inlier. The new basin concept presented in this paper allows the characterisation of basin-wide structural deformation and the recognition of areas with petroleum exploration potential.The northern depositional margin of the Mount Isa Basin is the metamorphic, intrusive and volcanic complex referred to as the Murphy Inlier. The eastern, southern and western boundaries of the basin are obscured by younger basins (Carpentaria, Eromanga and Georgina Basins). The Murphy Inlier rocks comprise the seismic basement to the Mount Isa Basin sequence. Evidence for the continuity of the Mount Isa Basin with the McArthur Basin to the northwest and the Willyama Block (Basin) at Broken Hill to the south is presented. These areas combined with several other areas of similar age are believed to have comprised the Carpentarian Superbasin.The application of seismic exploration within Authority to Prospect (ATP) 423P at the northern margin of the basin was critical to the recognition and definition of the Mount Isa Basin. The northern Mount Isa Basin is structurally analogous to the Palaeozoic Arkoma Basin of Oklahoma and Arkansas in the southern USA but as with all basins it contains unique characteristics, a function of its individual development history. The northern Mount Isa Basin is defined as the basin area northwest of the Mount Gordon Fault.