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A metasomatic origin for the iron-oxide Au-Cu Starra orebodies, Eastern Fold Belt, Mount Isa Inlier 总被引:2,自引:0,他引:2
J. F. Rotherham 《Mineralium Deposita》1997,32(3):205-218
The Starra ironstone-hosted Au-Cu deposit in northwest Queensland, Australia, displays evidence of a polyphase history of
late-post metamorphic, structurally controlled metasomatism. The mineralisation is hosted within several massive ironstone
units which occur at a lithological contact of metamorphosed sandstone and siltstone sequences and foliated chlorite-biotite-magnetite
schists. The ironstones strike north-south and occur as discontinuous lenses that cross cut the host rocks in places. Magnetite
ironstone textures are generally massive in appearance, but relict deformed breccia and foliation textures are locally preserved.
Sulphide ore textures are more brittle and consist of fine, pervasive brecciation of the ironstones and host rocks. Petrological
and textural observations support a hydrothermal origin for both ironstone and mineralisation. Three dominant post-peak metamorphic
paragenetic stages of alteration and mineralisation are recognised: (1) early widespread Na-Ca metasomatism consisting of
albite-quartz-actinolite-scapolite, (2) localised K-Fe metasomatism consisting of biotite-magnetite-hematite- quartz-pyrite
and (3) the mineralising stage consisting of anhydrite-calcite-hematisation of magnetite-pyrite-chalcopyrite-gold and extreme
chloritisation of biotite. The Na dominant alteration occurs throughout the Eastern Fold Belt and for at least 50 km to the
east and 150 km to the north of Starra. The ironstones were products of localised Fe-metasomatism associated with shearing
and brecciation of previously Na-metasomatised host rocks. Gold and copper mineralisation resulted from the interaction of
magnetite, a late oxidising fluid and an increase in pH. This produced variable hematisation of magnetite and caused the solubility
of chloride-complexed gold to decrease dramatically. High gold:copper ratios can be explained in terms of the solubility differences
of gold and copper in the thermochemical conditions that existed at Starra.
Received: 15 May 1996 / Accepted: 17 January 1997 相似文献
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de Jong Geoffrey Rotherham Jackie Phillips G. Neil Williams Patrick J. 《Geologie en Mijnbouw》1997,76(4):311-319
In Mid Proterozoic crystalline rocks of the Mount Isa Inlier, around Cloncurry, Australia, 2000 km2 of alteration and brecciation are the product of high-temperature (> 450 °C) concentrated saline solution activity. During retrogression, this fluid was locally responsible for mobility of V, Y, Nb and light rare-earth elements (15 × enrichment). Copper and S were leached during alteration and this may have been a significant source of components in nearby Cu-Au deposits. Similar rare-earth-element behaviour has been observed in the hematite breccias which host Cu-sulfides at the giant Olympic Dam Cu-Au deposit. 相似文献
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Consistency of temporal and habitat-related differences among assemblages of fish in coastal lagoons
The consistency of habitat-related differences in coastal lagoon fish assemblages was assessed across different spatial and temporal scales. Multimesh gillnets were used to sample assemblages of fish on a monthly basis for 1-year in three habitats (shallow seagrass, shallow bare and deep substrata) at two locations (>1 km apart), in each of two coastal lagoons (approximately 500 km apart), in southeastern Australia. A total of 48 species was sampled with 34 species occurring in both lagoons and in all three habitats; species caught in only one lagoon or habitat occurred in low numbers. Ten species dominated assemblages and accounted for more than 83% of all individuals sampled. In both lagoons, assemblages in the deep habitat consistently differed to those in the shallow strata (regardless of habitat). Several species were caught more frequently or in larger numbers in the deep habitat. Assemblages in the two shallow habitats did not differ consistently and were dominated by the same species and sizes of fish, possibly due to habitat heterogeneity and the scale and method of sampling. Within each lagoon, very few between location differences in assemblages within each habitat were observed. Consistent differences in assemblages were detected between lagoons for the shallow bare and deep habitats, indicating there were some intrinsic differences in ichthyofauna between lagoons. Assemblages in spring differed to those in summer, which differed to those in winter for the shallow bare habitat in both lagoons, and the deep habitat in only one lagoon. Fish-habitat relationships are complex and differences in the fish fauna between habitats were often temporally inconsistent. This study highlights the need for greater testing of habitat relationships in space and time to assess the generality of observations and to identify the processes responsible for structuring assemblages. 相似文献
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Douglas Rotherham Charles A. GrayDaniel D. Johnson Paul Lokys 《Estuarine, Coastal and Shelf Science》2008
The effects of diel period and tow duration (5, 10 and 20 min) on samples of estuarine fauna in a beam trawl, were tested over bare sediment in Tuggerah Lake (New South Wales, Australia). Mean catch rates (numbers of fish caught 5 min−1) were significantly larger at night for the total numbers of individuals and abundant, economically important species of fish and invertebrates (e.g. Gerres subfasciatus, Metapenaeus macleayi, Penaeus plebejus). Greater proportions of larger fish were also caught at night for some species (e.g. G. subfasciatus, Acanthopagrus australis, Rhabdosargus sarba), but not across all tow durations. Multivariate analyses detected dissimilarities in the composition and structure of assemblages between diel periods, which were driven by species caught predominately, or in larger proportions, at night. Short tows (5 min) were more efficient than longer tows (10 or 20 min) for sampling the diversity of species (i.e. most species were caught in the first 5 min of a tow). There were, however, no clear or consistent patterns relating to the effect of tow duration on the catch rates of other variables, the size ranges of abundant species, or the structure and composition of assemblages. Our data confirm that at night, bare sediment is an important habitat for a wide size- and species-range of estuarine fish and invertebrates. In future, more cost-effective and reliable information concerning these taxa would be achieved by sampling with the beam trawl at night, using tow durations of 5 min. We also highlight a problem inherent in the design of many studies of diel variation of fauna (i.e. the potential non-independence of data among day and night periods) and discuss its solution. 相似文献
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