The nature of sulfidic metasediments at Kambalda and their broad relationships with associated ultramafic rocks and nickel ores

Bavinton, Owen Alexander

doi:10.2113/gsecongeo.76.6.1606

Cited by 70 publications

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“…The host-rocks are a 2.71 to 2.68 Ga (Watchorn 1998) sequence of Archaean metakomatiites and metabasalts several km thick, which include minor interflow sediments (Bavinton 1981). The sequence is intruded by a 5 number of differentiated tholeiitic sills, which can be up to 100m thick, and by younger felsic to intermediate rocks (2.65 Ga, Watchorn 1998).…”

Section: Geological Settingmentioning

confidence: 99%

A test of the viability of fluid–wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the Kambalda-St. Ives goldfield, Western Australia

Evans

2009

Miner Deposita

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Section: Geological Settingmentioning

confidence: 99%

A test of the viability of fluid–wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the Kambalda-St. Ives goldfield, Western Australia

Evans

2009

Miner Deposita

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“…6; Gresham & Loftus-Hills 1981). Since the sedimentary facies were fine-grained hemipelagic and turbidity-current pelites (Bavinton 1981, Squire et al 1998, Beresford & Cas 2001, originally there should have been as much sediment in trough positions as in flank positions. Therefore, in many trough positions, sediment has been removed by erosion to produce channels, whereas in flank positions it has not (Fig.…”

Section: Contact Relationships and Texturesmentioning

confidence: 99%

“…Given that the sedimentary units in the Kambalda and nearby greenstone successions originated as pelitic and fine siliceous sediments (Bavinton 1981, Marchiori 1995, Squire et al 1998, very low velocities and low levels of turbulence would be required to erode these. The minimum velocities required to erode unconsolidated clay-to silt-size sediments is only 5 cm s -1 , or 100 cm s -1 for cohesive sediment using the Stokes settling velocities of silt-and clay-size particles, and data from Hjulstrom (Sundborg 1956; Fig.…”

Section: Capacity Of Komatiites For Physical Erosionmentioning

confidence: 99%

Field Characteristics and Erosional Processes Associated With Komatiitic Lavas: Implications for Flow Behavior

Fernand

Beresford

2001

The Canadian Mineralogist

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Although komatiitic lavas have long been depicted as turbulent flows, especially near the vent, field characteristics indicate that many komatiitic lavas did not flow turbulently, or only initially so. The bases of komatiites are commonly conformable with their substrate, including fine pelitic sediments, and the margins of komatiites are overwhelmingly coherent, or marked by local quench-fragmented hyaloclastite breccia. Autobreccias are notably missing. These characteristics are not consistent with turbulent flow, but clearly indicate conditions of laminar flow. If komatiitic flows were turbulent, they should commonly have scoured into substrate sediments through a variety of physical erosion processes, including foundering into underlying seafloor sediments, because of density inversion, and turbulence-induced scouring of sediments. These features are not commonly developed, also indicating that generally komatiites were emplaced under tranquil, laminar-flow conditions. Trough-like structures that commonly host nickel sulfide mineralization have commonly been interpreted to originate by thermal erosion of substrate by the komatiitic lava. The evidence supporting thermal erosion is not strong, and commonly ambiguous. Trough structures at Kambalda, Western Australia, are fault bounded, as noted by several previous investigators. However, there is a common, but not universal, antithetic relationship between trough presence and sediment absence. Removal of sediment from troughs could be explained by physical erosion, with an initial narrow, turbulent flow-head scouring a channel in the underlying sediments. As the lava flows spread laterally, their flow-front velocity decreased, and flow became laminar, so explaining the conformable contacts with substrate and the presence of coherent crusts represented by the random spinifex textural zone. Thermal erosion was rare, and could only have resulted beneath sustained lava tubes, within the flow interior, not from the flow head.Keywords: komatiites, laminar flow, field characteristics, physical erosion. SOMMAIREQuoique les coulées de lave komatiitique ont maintes fois été considérées turbulentes, surtout près de l'évent, les caractéristiques de terrain indiquent que dans la plupart des cas, le mode d'épanchement n'était pas turbulent, ou s'il l'était, seulement au tout début. La base d'une coulée est en général conforme avec le substrat, y inclus les cas où ce sont des sédiments pélitiques à grains fins qui sont en contact, et les marges sont conformes dans la grande majorité de cas, ou bien localement marquées par une brèche d'hyaloclastite due au refroidissement brutal. Le phénomène d'autobréchification est complètement absent. Ces caractéristiques ne concordent pas avec une hypothèse de turbulence, mais elles indiquent plutôt des conditions d'épanchement laminaire. Si l'épanchement avait été turbulent, la lave aurait creusé dans les sédiments sousjacents selon une variété de mécanismes physiques d'érosion, par exemple affaissement dans les sédiments des fond...

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“…Direct contamination of the lava/magma by silica, ferric iron, or sulfide is the most feasible mechanism for inducing rapid, significant sulfide exsolution. The cherty, sulfidic sediments at Kambalda, Windarra, Widgiemooltha, and Nepean, for example, are rich in silica and sulfide (Groves et al 1976, Bavinton 1981. The oxide facies iron-formations at Forrestania are rich in silica and ferric iron oxide.…”

Section: Thermodynamic Constraintsmentioning

confidence: 99%

Controls on the Formation of Komatiite-Associated Nickel-Copper Sulfide Deposits

Lesher

Groves

1986

Special Publication No. 4 of the Society for Geology Applied to Mineral Deposits

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Nickel-copper sulfide deposits associated with rocks of komatiitic affinity may be divided into two associations on the basis of host rock composition and ore distribution: (1) stratiform, massive-matrix-disseminated sulfides hosted by cumulate komatiite lava flows (lava conduits), or strata-bound, coarse disseminated sulfides hosted by cumulate komatiite bodies near volcanic vents, and (2) strata-bound, finely disseminated sulfides and more restricted massive sulfides hosted by subvolcanic komatiitic dunites (high-level magma chambers). These deposits represent a continuum in environments of emplacement from distal volcanic through proximal and central volcanic to subvolcanic.Field relationships and geochemical data suggest that the sulfides in these deposits are magmatic in origin. Previous models for their formation involve derivation of sulfides directly from the mantle or from low-level magma chambers, but there are several field, physical, and thermodynamic constraints which suggest that this may not be feasible: (1) the spatial concentration of mineralization within certain parts of otherwise virtually barren host units suggests that the latter were not uniformly saturated in sulfide at the time of emplacement; (2) there are physical problems in transporting dense sulfides in low viscosity komatiite magmas, although dispersed sulfide droplets may be supported during rapid ascent; and (3) high temperature komatiitic melts generated by high-degree partial melting, or sequential melting, of mantle source rocks are unlikely to be sulfide-saturated in the source region or to remain sulfide-saturated during adiabatic ascent. These deposits are, however, commonly associated with specific country rocks, particularly sulfidic sediments, and the distribution of the ores appears to be related to the distribution of these rocks. It is most likely that the sulfide ores exsolved from the komatiitic magmas in situ, in response to assimilation of the country rocks during emplacement. The distribution and texture of the mineralization was probably influenced by (1) the mode of emplacement (volcanic vs subvolcanic) and amount of assimilation; (2) the relative volume of magma (lava conduit vs magma chamber) and its capacity to dissolve sulfur; and (3) the timing of sulfide separation and opportunity for segregation. A fundamental aspect of this model is the coincidence of cumulate komatiitic host units (representing dynamic lava conduits and magma chambers) and siliceous, sulfidic, or ferric iron oxide-rich sediments, the former representing a source of heat for assimilation and of ore metals, and the latter a source of sulfur or of components to induce sulfide separation. Mineralized greenstones appear to have formed in deeper water under conditions of greater extension than unmineralized greenstones; rifting environments represent the most favorable tectonic environment for voluminous komatiite eruption/irruption and for accumulation of sulfidic sediments. Variations in the degree of extension along or within the r...

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The nature of sulfidic metasediments at Kambalda and their broad relationships with associated ultramafic rocks and nickel ores

Cited by 70 publications

References 0 publications

A test of the viability of fluid–wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the Kambalda-St. Ives goldfield, Western Australia

A test of the viability of fluid–wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the Kambalda-St. Ives goldfield, Western Australia

Field Characteristics and Erosional Processes Associated With Komatiitic Lavas: Implications for Flow Behavior

Controls on the Formation of Komatiite-Associated Nickel-Copper Sulfide Deposits

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