The geology and petrology of the Adamsfield Ultramafic Complex, Tasmania

Varne, R.; Brown, AV

doi:10.1007/bf01046576

Cited by 32 publications

(4 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Observations of serpentinite characteristics from each locality also support the notion of stichtite reaction-progress ratio. For example, increasing degree of serpentine alteration as recorded in geochemistry and mesh/hourglass textures at specific sites (Rubenach, 1974;Varne and Brown, 1978;Brown et al, 1988;González-Mancera, 2001;Proenza et al, 2004;Bottrill and Graham, 2006;González-Mancera et al, 2009) correlates with our observations of increasing replacement of chromite by stichtite.…”

Section: Mineralogical and Geochemical Interpretationsupporting

confidence: 83%

Conditions of stichtite (Mg6Cr2(OH)16[CO3]·4H2O) formation and its geochemical and isotope record of early phanerozoic serpentinizing environments

Melchiorre

Bottrill

Huss

et al. 2017

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

Stichtite is a magnesium-chromium hydroxycarbonate mineral found in association with early Phanerozoic chromite-rich serpentinite rocks of Tasmania, Australia and Tehuitzingo, Mexico. Elemental analysis of stichtite shows a range of compositions within the Cr-Fe-Al hydrotalcite group, with compositional trends associated with each discrete serpentinite host body. Elemental and textural analysis of stichtite-associated chromite indicates that stichtite forms in fore-arc setting rocks through interaction of chromite and methane-rich serpentinizing fluids. The degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the "stichtite window." Carbon stable-isotope analyses of stichtite suggest carbon sourcing from marine kerogen with a minor marine carbonate component in some samples. The carbon and hydrogen stable isotope profile of stichtite ranges from the field of methane from active serpentinizing zones, to organic thermogenic methane. The association of the stichtite 2H polytype (nee barbertonite) with aragonite ± antigorite suggests this is a higher pressure/temperature polytype of stichtite. Reaction completion textures, isotopic values, and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization of fore-arc setting rocks in a methane/H 2-rich environment within fluid conduits, ranging from near the surface to depths where pressure is up to 1.2 to 0.8 GPa and temperature is up to ~300°C. These unique chemical, isotopic, and textural properties of stichtite from distinct serpentinite bodies likely record the duration of serpentinization at specific thermobarometric conditions, and provide a window into the conditions associated with a potentially habitable environment on early Earth and other bodies of the solar system.

show abstract

Section: Mineralogical and Geochemical Interpretationsupporting

confidence: 83%

Conditions of stichtite (Mg6Cr2(OH)16[CO3]·4H2O) formation and its geochemical and isotope record of early phanerozoic serpentinizing environments

Melchiorre

Bottrill

Huss

et al. 2017

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

show abstract

“…These siliceous magnesian low Ti rocks are found in active island acrs of the southwest Pacific Ocean (e.g., Kuroda and Shiraki, 1975;Dietrich et al, 1978;Cameron et al, 1979;Meijer, 1980;Hickey and Frey, 1982) and are regarded as modern analogues of magnesian low Ti lavas occurring in ophiolites throughout the geologic record (e.g., Sun and Nesbitt, 1978;Varne and Brown, 1978;Coish and Church, 1979;Coish et al, 1982;Cameron, 1985). Their most diagnostic chemical features (Table 1) are high MgO, Cr, and Ni contents, high Mg/(Mg + Fetotal) ratios, SiO2 abundances in the basalt to andesite range, and low TiO2 (•0.5 wt %) and heavy rare earth element contents.…”

Section: Nature Of the Source Of Midocean Ridge Basalt And Second-stamentioning

confidence: 97%

Sulfur saturation and second-stage melts; application to the Bushveld platinum metal deposits

Hamlyn¹,

Keays²

1986

Economic Geology

153

View full text Add to dashboard Cite

A model is presented for the formation of platinum-group element ores by precipitation from sulfur-deficient, platinum-group element-rich, second-stage magmas. Numerous investigations indicate that basaltic magmas originating from undepleted or mildly depleted source regions are sulfur saturated at the time of eruption. Mantle-derived peridotites residual from midocean ridge basalt magma genesis have Pd abundances that are uniformly too high for it to have originated solely from silicate melt retained in the source region at the time of segregation; they imply the presence of an accessory immiscible sulfide melt to host the platinumgroup elements. The very high sulfide melt-silicate melt partition coefficients of the platinumgroup elements would result in strong fractionation of these metals into the accessory sulfide component during the melting event. The extreme platinum-group element enrichment of this accessory sulfide component is evidenced by the discovery ofplatinoid minerals in residual mantle nodules containing Pd (and Pt) abundances at the low ppb level (Keays et al., 1981).Magmas generated by low to moderate degrees of partial melting of undepleted mantle are therefore sulfur saturated at the time of segregation. These (first-stage) magmas become impoverished in platinum-group elements during the early stages of fractional crystallization because of coprecipitation of an immiscible sulfide phase (e.g., midocean ridge basalt glasses average <0. ppb Pd). Further melting of this depleted source leads to complete dissolution of the residual platinum-group element-rich sulfide component and production of secondstage magmas enriched in them but poor in sulfur.Boninitic magmas, generally regarded as second-stage melts generated from strongly depleted mantle sources, have enhanced platinum-group element abundances (mean Pd = 15 ppb) in agreement with the above model. During fractionation of these S-deficient magmas the concentration of platinum-group elements will build up until the onset of sulfur saturation and segregation of sulfides. These sulfides will generally have a higher platinum-group element tenor than those segregating from first-stage melts.A marked similarity in the composition of boninitic magmas and early parental magmas proposed for the Bushveld Complex (Davies et al., 1980;Sharpe, 1981), and possibly other intrusions hosting platinum-group element ores, suggests that their source regions have evolved in a similar manner. This accounts for the timing of deposition of the UG-2 and Merensky cyclic units in the upper partition of the critical zone and the unusual platinum-group elementrich nature of their ores. If this model is relevant to the Bushveld platinum-group element mineralization, then it provides a means of assessing the potential of other stratiform intrusions to host economic platinum-group element deposits.

show abstract

“…There are also green serpentinites, which are lizardite-chrysotile mixtures with localized deformation patterns and brecciation. Finally, there are sheared-contact serpentinites that consist mainly of chrysotile and rare antigorite, and may have formed during tectonic emplacement of the Adamsfield Ultramafic Complex [29]. All three of these serpentinite bodies lie within Middle to Late Cambrian strata.…”

Section: Geology and Mineralogy Of Samples Used In This Studymentioning

confidence: 99%

Insights on Structure and Threshold Detection Limits of Stichtite (Magnesium-Chromium Carbonate-Hydroxide) by Fourier Transform Infrared Analysis

2020

View full text Add to dashboard Cite

Spectral features for natural stichtite at 1042, 1096, 1360, 1638, and 3482 cm−1 provide insights on mineral structure, with peaks consistent with OH− stretching modes bound to Mg or Cr, CO32− antisymmetric stretches and CO32− bound within the sample and molecular water. These Infrared (IR) data suggest natural stichtite forms at a pH of >12 with increased water and decreased carbonate in the interlayer due to a smaller interlayer distance and unit cell. Higher pH favors lower divalent cation purity and may explain observed ranges of non-end member compositions in stichtite from localities around the world, and across geologic time. This constrains stichtite formation to a range of very high pH conditions and is consistent with active serpentinizing fluid vents and some mine wastes. IR has clear application for the detection and quantification of stichtite under field and laboratory conditions within the detection limits of 5% stichtite within a serpentine host. The size and grade of terrestrial stichtite deposits, and resolution of remote sensing instruments, suggest remote IR detection of stichtite is possible, and remote IR detection for Earth and Mars is discussed.

show abstract

The geology and petrology of the Adamsfield Ultramafic Complex, Tasmania

Cited by 32 publications

References 30 publications

Conditions of stichtite (Mg6Cr2(OH)16[CO3]·4H2O) formation and its geochemical and isotope record of early phanerozoic serpentinizing environments

Conditions of stichtite (Mg6Cr2(OH)16[CO3]·4H2O) formation and its geochemical and isotope record of early phanerozoic serpentinizing environments

Sulfur saturation and second-stage melts; application to the Bushveld platinum metal deposits

Insights on Structure and Threshold Detection Limits of Stichtite (Magnesium-Chromium Carbonate-Hydroxide) by Fourier Transform Infrared Analysis

Contact Info

Product

Resources

About