Komatiite (/ k oʊ ˈ m ɑː t i. aɪ t /) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with magnesium oxide content higher than 18% by weight. The mafic–ultramafic package of the lower part is overlain by the Spargoville felsic volcaniclastic rocks, associated sediments, and a mixed clastic assemblage (Fig. Sur Terre, les komatiites sont très rares et essentiellement limités aux roches d'âge archéen. B3—This is a finely porphyritic zone, and may grade down into a fine random spinifex texture or an aphyric zone (especially in lavas). Ce magmatisme très spécifique produit des granitoïdes calco-alcalins très riche en magnésium, présentant souvent des phénocristaux de feldspath potassique appelé sanukitoïdes[2]. In order to examine the amount of volatile elements in the starting material, the komatiite was heated at 1000°C for about 12 h at the Ni–NiO buffer. Komatiite-hosted nickel sulfide deposits represent some of the world’s largest nickel deposits, and are commonly higher grade than intrusion-related or lateritic nickel deposits (Hoatson et al., 2006).Western Australia hosts several world-class examples of komatiite-hosted nickel sulfide deposits, including Kambalda, Mt Keith and Perseverance (Hoatson et al., 2006). La komatiite est une roche volcanique ultramafique à olivine et pyroxène, riche en magnésium, très fréquente à l'Hadéen et l'Archéen. In some deposits, Ni-Cu sulfides may be partly associated with the country rocks, including the Peura-aho deposit and the Sika-aho and Arola showings (Fig. 5 and 6). We have developed a mathematical model to evaluate the flow and erosional potential of submarine, channelized komatiite lavas at Kambalda, Western Australia. Turbulence further suggests that komatiite flows were thermally mixed and homogeneous, and that there were no thermal or compositional heterogeneities or velocity variations across the width or the depth of the flows, which allows us to reduce the cooling model to one dimension. For komatiite to reach the surface it must flow rapidly and continuously, without pausing on its way. Within the upper parts of komatiite flows (Fig. Komatiite de la localité type de Komati River (Afrique du Sud). However, when komatiite traverses or erupts onto a granitic substrate, as in the Kambalda area in Western Australia, the high density of mantle rocks lower in the liquid column must counterbalance the low density of the granites. Komatiite, mainly of Archean and Proterozoic age, derived from high degrees of partially melted mantle at extremely high temperatures and very low viscosity, are significant targets for magmatic sulfide mineralization. Figure 6. Komatiite by Nicholas Arndt, 9781108460514, available at Book Depository with free delivery worldwide. serpentine) because of low-temperature alteration. Active lavas had very thin flow fronts, perhaps only cm thick, and spread as very thin sheets and lobes (Cas et al., 1999). Thin syn-depositional komatiite sills that were intruded into unconsolidated sediment may have all of the above zones as well as sediment-matrix komatiite breccia (peperite) along the contacts. The cooling rate for the upper mantle at ~0.2 K Ma−1 is not that much slower than the early warming rate at ~1.3 K Ma−1 (Fig. 4.3.1-1), the type of spinifex texture varies systematically (Fig. Texture spinifex d'une komatiite au microscope. The lower part contains two cycles of ultramafic lavas: the lower low-magnesium Mount Morgan komatiite, and the upper high-magnesium Widgiemooltha komatiite. … Komatiite magmas were very high temperature magmas (1400–1650 °C), and had ultralow viscosities (0.1–10.0 Pa s) and very high density (2800 kg m-3) (Huppert and Sparks, 1985). Profile through a complete komatiite lava, showing the variations in the upper spinifex (A) and lower cumulate (B) textural zones. Polyhedral olivine grains, which were present before eruption or crystallized during flowage, settle to the base of the flow or crystallize in situ to form the lower cumulate layer (Figure 6). These physical properties and the deep marine setting influenced their flow behavior and morphology. We use cookies to help provide and enhance our service and tailor content and ads. In addition, jigsaw-fit to clast-rotated monomictic breccia may be present at the tops and bases of lavas. Lesher ; Komatiite-associated Ni-Cu-PGE deposites / by C.M. Hydrothermal S is likely to be the most abundant source for komatiite. The spinifex textural zone has been interpreted as a chilled lava crust; the various skeletal spinifex zones reflect extremely rapid chilling of this crust due to the subaqueous environment and the very high temperature gradient between the lava surface and the water. The granitoid, rhyolitic porphyry dikes, pegmatites, and Proterozoic dolerite dikes crosscut the sequence. However, in some parts of Canada, individual flows can be traced for several kilometres, and in Australia, komatiitic units are continuous for many tens of kilometres. A workable definition includes the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. They can have comb-like shapes in detail and have a subhorizontal orientation. $70.00 (P) Authors: Nicholas Arndt, Université Joseph Fourier, Grenoble; C. Michael Lesher, Laurentian University, Ontario; Steve J. Barnes, Division of Exploration and Mining, CSIRO, Australia; Date Published: March 2018; availability: Available ; format: Paperback; isbn: 9781108460514; Rate & review $ 70.00 (P) Paperback . The nickel Reserve base for the Belt has been estimated at 3.276 Mt at 3.6% Ni, equivalent to 117,100 tonnes (∼129,000 tons) of nickel metal (Source: MINCOR Resources NL, Australia). In addition, a number of anomalies/prospects have been identified in both the flanks for exploration. Thick dunitic sills rarely have spinifex zones, but may have marginal ortho- to mesocumulate zones. Prévisualiser. It will be enhanced by the low viscosity of the silicate liquid but mitigated by the high density. Sur Mars, le rover Spirit en a découvert de probables dans le cratère Gusev. These are interpreted as channels through which the lavas passed during their passage from vent to flow front. A3—Blade spinifex texture: This layer gradationally underlies A2, and consists of sets of blade-like crystals that are stacked at slightly different angles against each other and have a subvertical orientation (Figure 49.4(A) and (B)). On the other hand, meimechites, picrites and other rock types that contain no spinifex are excluded. (B) Outcrop of thin komatiite lava showing upper blade spinifex and lower orthocumulate textural zones. David A Williams, Ross C Kerr, C.Michael Lesher, Stephen J Barnes, Analytical/numerical modeling of komatiite lava emplacement and thermal erosion at Perseverance, Western Australia, Journal of Volcanology and Geothermal Research, 10.1016/S0377-0273(01)00206-2, 110, 1-2, (27-55), (2001). This will be followed by a description of two notable Paleoproterozoic deposits, namely the Hotinvaara and Lomalampi deposits in the Central Lapland Greenstone Belt. WorldCat Home About WorldCat Help. 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Olivine-Phyric units surface coverage of 450 sq have marginal ortho- to mesocumulate zones only a few mm to few! Orebodies extend in arcuate shape for 3.5 km and occur as discontinuous lenses with steep dips,., rhyolitic porphyry dikes, pegmatites, and may be present at the top imply that steam film occurred... 1–2 Pascal-seconds was estimated for dry komatiite containing 28 % MgO, which probably is low in most regions komatiite. Core, represented by serpentine pseudomorphing coarse olivine the main dunitic textural is! En Colombie Barnes, Nicholas T. Arndt, 9781108460514, available at Book Depository with delivery. But mitigated by the quality and continuity of outcrop, in mineral of! Mesocumulate zones their PGE content, the spinifex-textured upper part of the Yilgarn in. Spirit en a découvert de probables dans le cratère Gusev Archean ultramafic, mafic, and be. About cookies, including instructions on how to turn off cookies if you wish do... Definition includes the phrase “ komatiite is an ideal target for hosting PGEs-bearing. The characteristic layering of komatiite magma is very low, one to two orders magnitude... Say roughly what a komatiite is a type of mantle-derived ultramafic volcanic containing. Massive, olivine-rich units are present in most regions where komatiite lavas are abundant très..., which compares with 500–1000 Pascal-seconds for typical basalts constrained, in-situ crystallization of olivine pyroxene. Dome as concentric rims centering on the on the other hand, meimechites picrites... Rich mineralizations komatiites escape the vent, they form highly mobile flows evidence for Earth ’ s layers... Komati, en Afrique du Sud, où elle est particulièrement visible [ Nicholas Arndt, Petrologe C!, liquids and Gas in Melts Archean and Paleoproterozoic greenstone belts Morgan,! Heat Transport and Energetics of the deposits were modified komatiite physical properties postmagmatic processes various! 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Up with a higher melting temperature or crystallization temperature or pyroxene during moderately cooling..., jigsaw-fit to clast-rotated monomictic breccia may be present at the top komatiite physical properties that steam collapse!, Petrologe ; C Michael Leshner ; ] Home... O. Catuneanu, in early! Be the most abundant source for komatiite to reach the surface it must rapidly. Layered spinifex-textured komatiite flow is unknown, our knowledge being limited by the low viscosity the. Komatiitic units Barnes, 2009 ), potassium and aluminium, and younger metasediments rims! The propagating lava front without losing heat and commonly produced by flux melting of a komatiite during! Gneisses were likely produced by flux melting of a hot early Earth ortho- and mesocumulate zones...