Paragenesis and chemical characteristics of the celsian−hyalophane−K-feldspar series and associated Ba-Cr micas in barite-bearing strata of the Mesoarchaean Ghattihosahalli Belt, Western Dharwar Craton, South India
“…Our analytical results for K 2 O and SiO 2 in the Ba-rich K-feldspars, and the correlation between them (Fig. 6 a ), differ from those reported in most previous studies (Jakobsen, 1990; Chabu and Boulègue, 1992; McSwiggen et al , 1994; Moro et al , 2001; Xia et al , 2005; Han et al , 2013; Raith et al , 2014; Henry et al , 2015). As shown in Fig.…”
Section: Resultscontrasting
confidence: 89%
“…Fig. 6.Plots of the contents of main components in Ba-rich K-feldspars in this and previous studies: ( a ) K 2 O and SiO 2 , the Ba-rich K-feldspars in most of the previous studies a strong negative linear correlation between K 2 O and SiO 2 (Jakobsen, 1990; Chabu and Boulègue, 1992; McSwiggen et al , 1994; Moro et al , 2001; Xia et al , 2005; Han et al , 2013; Raith et al , 2014; Henry et al , 2015), whereas the data points from Long et al (1994), Orberger et al (2005), and this study are distributed sparsely in a single area away from the line; ( b ) BaO and SiO 2 , the Ba-rich K-feldspars of this study show a similar negative linear correlation between BaO and SiO 2 , the Ba-rich K-feldspars of Long et al (1994), Orberger et al (2005) and this study show higher SiO 2 contents; ( c ) (K + Na) apfu and Si apfu , similar correlation characteristics to ( a ) are observed, the black solid line represents the theoretical compositional assemblage of hyalophane.…”
Section: Resultssupporting
confidence: 58%
“…Barium is typically a minor constituent of common silicate minerals, but it can be enriched significantly in some contexts, especially in potassic rock-forming minerals such as K-feldspar and muscovite (e.g. Chabu and Boulègue, 1992; Raith et al , 2014; Henry et al , 2015). Ba-rich K-feldspars are typically associated with manganese–ferromanganese deposits (Viswanathan and Kielhorn, 1983; McSwiggen et al , 1994), stratabound Ba-rich sulfide deposits (Fortey and Beddoe–Stephens, 1982; Chabu and Boulègue, 1992), baryte deposits (Moro et al , 2001; Xia et al , 2005; Han et al , 2013), Ba-rich sedimentary or metasedimentary rocks (Reinecke, 1982; Jakobsen et al , 1990; Deer et al , 2001; Essene et al , 2005; Raith et al , 2014), and other Ba-rich rocks such as mafic xenoliths affected by Ba metasomatism (Henry et al , 2015).…”
Barium-rich silicates were recently found in the lower Cambrian black shale sequence of Anhui Province, South China. The Ba silicates can be divided into Ba-poor K-feldspar, Ba-rich K-feldspar and cymrite, on the basis of occurrence and composition. The Ba-poor K-feldspar have low BaO contents (<1.00 wt.%) and occur as sporadic grains in mudstone. In contrast, the Ba-rich K-feldspar have higher BaO contents (1.36–20.51 wt.%) and occur mainly as rims around grains of Ba-poor K-feldspar in mudstone, as void fillings in dolostone, and as grains dispersed in chert. The cymrite is observed only in chert and occurs as dispersed euhedral tabular crystals. Analyses of the Ba-poor K-feldspar and Ba-rich K-feldspar provide compositions that total <100 wt.% and show non-stoichiometry characterized by (Na + K + Ba + Ca)apfu less than 1.00 and (Al + Si)apfu slightly higher than 4.00. Raman and infrared (IR) spectroscopy has revealed the presence of ${\rm NH}_{\rm 4}^{\rm +} $ and H2O in the Ba-rich K-feldspar, which accounts for the unusual composition of these feldspars. We suggest that the formation processes of the Ba-poor K-feldspar, Ba-rich K-feldspar and cymrite were closely associated with multi-stage hydrothermal fluids enriched in Ba and NH4, consistent with an extensional tectonic setting during the early Cambrian. The Ba-poor K-feldspars might have formed through interactions between pre-existing K-feldspars and hydrothermal fluids. The Ba-rich K-feldspars in mudstone and dolostone formed mainly by precipitation from hydrothermal fluids that infiltrated the sediments, and we suggest the Ba-rich K-feldspars and cymrite in the chert are of exhalative hydrothermal origin.
“…Our analytical results for K 2 O and SiO 2 in the Ba-rich K-feldspars, and the correlation between them (Fig. 6 a ), differ from those reported in most previous studies (Jakobsen, 1990; Chabu and Boulègue, 1992; McSwiggen et al , 1994; Moro et al , 2001; Xia et al , 2005; Han et al , 2013; Raith et al , 2014; Henry et al , 2015). As shown in Fig.…”
Section: Resultscontrasting
confidence: 89%
“…Fig. 6.Plots of the contents of main components in Ba-rich K-feldspars in this and previous studies: ( a ) K 2 O and SiO 2 , the Ba-rich K-feldspars in most of the previous studies a strong negative linear correlation between K 2 O and SiO 2 (Jakobsen, 1990; Chabu and Boulègue, 1992; McSwiggen et al , 1994; Moro et al , 2001; Xia et al , 2005; Han et al , 2013; Raith et al , 2014; Henry et al , 2015), whereas the data points from Long et al (1994), Orberger et al (2005), and this study are distributed sparsely in a single area away from the line; ( b ) BaO and SiO 2 , the Ba-rich K-feldspars of this study show a similar negative linear correlation between BaO and SiO 2 , the Ba-rich K-feldspars of Long et al (1994), Orberger et al (2005) and this study show higher SiO 2 contents; ( c ) (K + Na) apfu and Si apfu , similar correlation characteristics to ( a ) are observed, the black solid line represents the theoretical compositional assemblage of hyalophane.…”
Section: Resultssupporting
confidence: 58%
“…Barium is typically a minor constituent of common silicate minerals, but it can be enriched significantly in some contexts, especially in potassic rock-forming minerals such as K-feldspar and muscovite (e.g. Chabu and Boulègue, 1992; Raith et al , 2014; Henry et al , 2015). Ba-rich K-feldspars are typically associated with manganese–ferromanganese deposits (Viswanathan and Kielhorn, 1983; McSwiggen et al , 1994), stratabound Ba-rich sulfide deposits (Fortey and Beddoe–Stephens, 1982; Chabu and Boulègue, 1992), baryte deposits (Moro et al , 2001; Xia et al , 2005; Han et al , 2013), Ba-rich sedimentary or metasedimentary rocks (Reinecke, 1982; Jakobsen et al , 1990; Deer et al , 2001; Essene et al , 2005; Raith et al , 2014), and other Ba-rich rocks such as mafic xenoliths affected by Ba metasomatism (Henry et al , 2015).…”
Barium-rich silicates were recently found in the lower Cambrian black shale sequence of Anhui Province, South China. The Ba silicates can be divided into Ba-poor K-feldspar, Ba-rich K-feldspar and cymrite, on the basis of occurrence and composition. The Ba-poor K-feldspar have low BaO contents (<1.00 wt.%) and occur as sporadic grains in mudstone. In contrast, the Ba-rich K-feldspar have higher BaO contents (1.36–20.51 wt.%) and occur mainly as rims around grains of Ba-poor K-feldspar in mudstone, as void fillings in dolostone, and as grains dispersed in chert. The cymrite is observed only in chert and occurs as dispersed euhedral tabular crystals. Analyses of the Ba-poor K-feldspar and Ba-rich K-feldspar provide compositions that total <100 wt.% and show non-stoichiometry characterized by (Na + K + Ba + Ca)apfu less than 1.00 and (Al + Si)apfu slightly higher than 4.00. Raman and infrared (IR) spectroscopy has revealed the presence of ${\rm NH}_{\rm 4}^{\rm +} $ and H2O in the Ba-rich K-feldspar, which accounts for the unusual composition of these feldspars. We suggest that the formation processes of the Ba-poor K-feldspar, Ba-rich K-feldspar and cymrite were closely associated with multi-stage hydrothermal fluids enriched in Ba and NH4, consistent with an extensional tectonic setting during the early Cambrian. The Ba-poor K-feldspars might have formed through interactions between pre-existing K-feldspars and hydrothermal fluids. The Ba-rich K-feldspars in mudstone and dolostone formed mainly by precipitation from hydrothermal fluids that infiltrated the sediments, and we suggest the Ba-rich K-feldspars and cymrite in the chert are of exhalative hydrothermal origin.
“…Cymrites have been reported to form under diverse pressure-temperature conditions in many geological environments (Runnells 1964;Essene 1967;Reinecke 1982;Moles 1985;Stankova et al 1989;Jacobsen 1990;Hsu 1994;Moro et al 2001;Sorokhtina et al 2008;Raith et al 2014). Reports of cymrite forming from celsian by hydration are documented for barite-bearing siliceous and carbonate rocks (Moro et al 2001).…”
Section: Gittinsite and Strontium Zirconium Silicatementioning
The P-12 Bpara-kimberlite^from Wajrakarur consists of forsteritic olivine, Al-Na-poor diopside, Fe-Tirich, Al-poor phlogopite, K-Ti-richterite, spinel, perovskite, cymrite, apatite, barite, Ba-Sr-bearing calcite, gittinsite, witherite, strontianite, and hydrogrossular (hydrogarnet). The rock also contains small clasts consisting dominantly of calcite, with lesser Ba-Srbearing calcite, cymrite, barite, strontianite, witherite, apatite, and hydrogrossular. Two generations of forsteritic olivine (Fo 80-93 ) crystals are present: common phenocrystalto-microphenocrystal; and rare anhedral macrocrystic olivines. Phlogopite occurs as microphenocrysts and as groundmass poikilitic plates with inclusions of spinel, perovskite, apatite, and chlorite pseudomorphs (after pyroxene). Phlogopites also occur as reaction rims around olivine crystals. The phlogopites have extremely low Al 2 O 3 (2.2-3.8 wt.%) , moderate-to-high FeO (6.9-16 wt.%), TiO 2 (1.9-4.6 wt.%), and Na 2 O (0.4-2.7 wt.%) contents and are enriched in fluorine (up to 6.0 wt.%) and considered to be tetraferriphlogopite. The pyroxenes occur in five parageneses as: (1) phenocrysts and microphenocrysts; (2) small slender crystals(<30 μm) forming part of the groundmass; (3) the cores of richterite crystals; (4) reaction products replacing earlier-formed olivine; (5) acicular crystals mantling carbonate clasts. These pyroxenes do not differ significantly in composition and are all diopsides with minor variation in their TiO 2 , Al 2 O 3 , Na 2 O contents. Titanian-potassium richterite commonly occurs as: (1) groundmass poikilitic plates;(2) small prismatic crystals (<30 μm); (3) reaction rims on olivine and pyroxene crystals. Groundmass poikilitic richterites commonly enclose pyroxene and apatite. Perovskites have a bimodal size distribution. Small (<20 μm) euhedral perovskites are scattered throughout the groundmass, whereas larger (100-300 μm) subhedral-to-euhedral perovskites are patchily-zoned and commonly broken. Micro-clasts consisting of accumulations of perovskite with phlogopite and apatite are also present. Spinels occur as large atoll crystals and small (<20 μm), euhedral-to-subhedral crystals, scattered throughout the groundmass. Some small spinel crystals are also present in the rims of olivine and pyroxene crystals. Atoll spinels are up to 100 μm in size, commonly with single and double cores. Atoll spinels are typically associated with perovskites. The euhedral-tosubhedral small spinels are ulvospinels. The atoll spinels have cores of titanian aluminous magnesiochromite with rims of magnesian titaniferous magnetite. The spinels have compositions which evolve along the lamproite-spinel compositional trend. Zoned calcite crystals occur as residual phases. Late stage residual calcite and carbonate clasts host prismatic cymrite crystals which are interpreted as pseudomorphs after potassium feldspar and/or barite. Subhedral-to-euhedral gittinsite and its Sr-analog are reported for the first time from the groundmass carbonatechlorite mesostasis of a lamproit...
“…The only other reported occurrence of Barich feldspar in India is that from mesoarchaean rocks of Ghattihosahalli schist belt, Dharwar craton, south India (Raith et al, 2014).…”
In melaphonolite of the Sarnu-Dandali, Badmer alkaline complex, high Ba-K-feldspar (sanidine) occurs as phenocrysts. Ba concentration ranges between 2% and 10% by weigth from core to rim. Many BSE images of this Barich sanidine were examined. Large numbers of zoned Ba-rich sanidine phenocrysts were analysed using electron microprobe. BaO shows positive correlation with Al 2 O 3 while there is negative correlation between BaO and K 2 O suggesting substitution of K by Ba. Petrographic evidence is clear that K-feldspar phenocrysts reacted with the melt which was getting richer in Ba during fractionation of melanephelinite to melaphonolite and subsequently this Ba deposited on the rims of K-feldspar. This short note reports results of preliminary investigation of number of Ba-rich sanidine grains from melaphonolite of Badmer and suggests incompatible behaviour Ba and that it was getting enriched in the melt during crystallization of magma.
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