Academic literature on the topic 'Komatiite Western Australia Norseman'

Forty-two dispersed cuticle taxa are described from late Middle Eocene drill core samples in the Lefroy and Cowan paleodrainages (Kambalda–Norseman region), Western Australia. They are preserved in fluvial-marginal marine sediments of the Pidinga and Werillup Formations. Thirty-four distinct cuticle taxa occur in the richest sample including Cupressaceae, Araucariaceae (Agathis), Podocarpaceae (Dacrycarpus, Acmopyle, Dacrydium), Cunoniaceae, Lauraceae, Myrtaceae, Casuarinaceae (Gymnostoma), Nothofagus subgenus Lophozonia and tribes Embothrieae, Macadamieae and Banksieae of the Proteaceae. The presence of at least 12 taxa of Proteaceae provides further support for palynological evidence of a rich proteaceous component in Eocene Western Australian assemblages.

AbstractStratigraphically and geographically restricted ocellar komatiite flows at Kambalda, Western Australia, appear to represent the products of ground melting of sulphidic sediments by komatiites in lava channels that localized the Fe–Ni–Cu sulphide ores. An immiscible sulphide liquid formed and gravitationally separated from the melted sediment (xenomelt), the resultant buoyant silicate liquid being partly or wholly assimilated by the turbulently convecting komatiite magma. Rarely, the xenomelt gravitationally migrated to the top of flows, and overflowed into the less turbulent lava levees where it collected to form a separate layer overlying a komatiitic layer within a single flow. There was selective preservation of the hybrid felsic layer, as an upper ocellar unit within an ocellar komatiite flow, in lava levees flanking lava channels. The ocellar unit is enriched in elements previously concentrated in the sediments, and shows U–Th–Pb isotopic systematics akin to the underlying sediments. Moreover, the partitioning relationships of U and Pb between the immiscible xenomelt and sulphide liquid enhances the range of U/Pb ratios for components of the ocellar unit, thus allowing sufficient spread of modern uranogenic Pb isotopic ratios to form isochrons, albeit imprecise ones. The range and similarity of model Th/U data from these flows (2.8−3.9) and adjacent sulphidic sediments (2.3−4.4; mostly 2.8−3.9) contrasts with the generally invariable Th/U within Kambalda ultrabasic–basic flows (3.6−3.9), and further supports the ground-melting hypothesis.

AbstractArchaean komatiite volcanics at Kambalda, Western Australia have been metamorphosed to upper greenschist–lower amphibolite grade and have experienced intense though heterogeneously developed polyphase deformation. Despite this, preservation of igneous textural features is often good, particularly in areas which underwent only ‘static style’ metamorphism. Thin lavas from the Tripod Hill Member of the Kambalda Komatiite Formation over the western margin of the Hunt nickel shoot display textural elements and facies variations which are virtually identical to those found in fresher thin komatiite sequences in other Archaean greenstone belts. Four principal flow profile (facies) types are defined, comprising nine subtypes. These represent stages in a facies continuum, ranging from ‘mature’ profiles which comprise thick spinifex textured tops and close packed cumulate bases through to massive, jointed ‘immature’ profiles devoid of mesoscopic spinifex texture. The causes of textural diversity within and between profiles are many and complex. However, facies variations can be attributed mainly to the effects of lava velocity at the time of major heat loss, combined with relative lateral position within any flow. The most mature textural (and geochemical) profiles developed in parts of lavas which had become ponded prior to major heat loss, whereas the least evolved profiles developed along the lateral margins (levees) of moving lavas. The study area komatiites occur as alternating stacks of flows of similar type. This stratigraphy records temporal and spatial shifts in the locus of lava ponding over the western margin of the Hunt nickel shoot. Such shifts may have been caused by irregularities in the underlying volcanic topography and/or by synvolcanic faulting and subsidence.

In December 2005, a wildfire burnt a large area of semi-arid eucalypt woodland along ~10 km of the Norseman- Coolgardie Road north of Norseman in the Great Western Woodlands (GWW), Western Australia. Few birds used the burnt area in the first year after the fire and these were mainly ground and shrub foraging insectivores. There was no influx of seed-eaters or open-country species as reported for post-fire habitats elsewhere in southern Australia. The greatest number of individuals and species of birds occurred in the second year post-fire when ground and shrub vegetation was floristically most diverse. Canopy foragers were attracted to the burnt area in the second year by an outbreak of psyllid insects on seedling eucalypts. At the same time, bark dwelling arthropods associated with the standing stems of fire-killed eucalypts attracted bark-foragers. From the third year, small insectivorous ground, shrub, and canopy foragers dominated the avifauna on the burnt area. These foraged on fire-killed shrubs, as well as living vegetation, including the lignotuberous regrowth of eucalypts. Bark foragers were uncommon after the second year. Throughout the study, the burnt area had fewer species and individuals than adjacent unburnt habitats. Compared with unburnt woodlands there were few differences in how species foraged on the burnt plots, but most species foraged lower reflecting the stature of the vegetation in the burnt woodland. Nectar-feeders, fruit-eaters, large insectivores, raptors, and parrots, although common in the unburnt woodland, were absent or rare in the burnt area. This reflected the limited regrowth of vegetation on the burnt area, which lacked the structural and floristic complexity of nearby unburnt woodlands. Ground foragers probably commenced nesting on the burnt area in the first year, with shrub and canopy foragers nesting from the second year. However, after five years, there was no evidence of large insectivores, nectar-feeders, raptors, seed-eaters, or foliage-eaters (i.e., parrots) nesting despite their abundance in adjacent unburnt woodland. Some of the unburnt woodlands monitored in this study were even-aged regeneration estimated to be 30–50 years post-fire or logging. Regardless of origin, these even-aged plots lacked the diverse avifauna associated with mature woodlands and suggest that post-fire recovery of birds and vegetation in these woodlands is likely to take decades and probably more than 100 years. If so, human activities that increase fire frequency in the GWW, including climate change and fuel-reduction burns, will have long-term adverse impacts on regional biodiversity exceeding those associated with wildfires in less arid forests and woodlands where rates of recovery are more rapid.

AbstractB1 subdivisions are narrow foliated zones of stubby, skeletal olivine blades, situated at the top of the granular olivine cumulates (B2) in ponded komatiite lavas. They developed at a late stage in pond crystallization as a result of compaction-related circulation of intercumulus liquids through and along the top of the cumulates. The total thickness of a B1 and its degree of blade parallelism are related to lateral position within ponded lavas. The deeper, hotter and longer-lived core regions generated a thick B1 with a high degree of blade parallelism (ordered B1), whereas the shallower, peripheral regions produced a narrow B1 with a poor degree of blade parallelism (disordered B1), or failed to develop one at all.

The Kalgoorlie Terrane of the Yilgarn Craton, Western Australia, containing about 60% (~11 Mt) of the world’s known komatiite-hosted nickel sulphide resources, is the world’s best studied and economically most important province for this mineral deposit type. Although increasingly mature in terms of nickel exploration, the Kalgoorlie Terrane is believed to contain significant additional undiscovered nickel endowment. Using the data-rich Kalgoorlie Terrane, this thesis develops a benchmark methodology that combines geological knowledge with spatial analysis and mathematical-statistical methods to estimate undiscovered nickel resources.In the proposed methodology, nickel sulphide deposits are considered realisations of stochastic mineralisation processes and are analysed within the following framework. Komatiites in the Kalgoorlie Terrane constitute the full sample space or the permissive tract. Disjoint, naturally bound individual komatiite bodies that make up the sample space are used as the spatial analysis units. Some komatiite bodies within the sample space contain nickel sulphide deposits (mineralised) and others do not (unmineralised). In this study, the most explored mineralised komatiite bodies constitute local control areas against which nickel resources in the less explored komatiite bodies can be assessed. The concept of local control areas is analogous to the concept of global control areas which are well explored parts of permissive areas for particular deposit types worldwide.Spatial point pattern analyses showed that the spatial distribution of mineralised komatiite bodies within the sample space is clustered. In contrast, nickel sulphide deposits in individual komatiite bodies are either randomly distributed or dispersed, and not clustered. This absence of deposit clustering within individual komatiite bodies indicates that the intensity of the deposit pattern of each komatiite body may be adequately expressed as deposit density (number of deposits per km[superscript]2). In global quantitative resource assessments, regression analysis of the well established power law relationship between deposit density and size of global control areas provides a robust method for estimating the number of deposits.In this study a power law relationship reminiscent of that in global models was found between the sizes of control areas and deposit density. In addition, this study establishes another power law relationship between nickel endowment density (nickel metal per km[superscript]2) and the sizes of control areas. Deposit and endowment density regression models based on the two power laws suggested that, respectively, 59 to 210 (mean 114) nickel sulphide deposits and 3.0 to 10.0 Mt (mean 5.5 Mt) nickel metal remained undiscovered in demonstrably mineralised komatiite bodies within the Kalgoorlie Terrane. More emphasis is placed on endowment density which may be more intrinsic to the Kalgoorlie Terrane than deposit density because deposit counts are confounded by definitional ambiguities emanating from orebody complexities. Thus the spatial pattern of mineral deposits may not coincide with the spatial pattern of mineral endowment as demonstrated by spatial centrographic analyses in this study.To estimate the amount of undiscovered nickel metal in the entire Kalgoorlie Terrane and not just in the demonstrably mineralised komatiite bodies, Zipf’s law was applied. According to Zipf’s law, the size of the largest deposit is twice the size of the second, thrice the size of the third, four times the fourth, and so on. Based on the currently known size of Mt. Keith deposit, the largest nickel sulphide deposit in the Kalgoorlie Terrane, Zipf’s law indicates that the terrane is nearly mature in terms of nickel exploration and contains only about 3.0 Mt nickel metal in undiscovered resources. The collective implication of the regression and Zipf’s law estimates is that in the Kalgoorlie Terrane, no significant nickel resources are likely to be contained in the known komatiites that are presently not demonstrably mineralised. However if, as widely speculated, the actual size of Mt. Keith deposit is about twice the currently known size, Zipf’s law predicts 10.0 Mt nickel metal in undiscovered nickel endowment for the Kalgoorlie Terrane. The additional 7.0 Mt undiscovered nickel metal endowment is attributed to opening up of a new exploration search space through deeper resource delineation, within an otherwise nearly mature terrane.