Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these ...Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these dykes have almost similar sequence of mineral-textural patterns indicative of:(1) an early cumulate forming event in a deeper magma chamber where megacrystic/large size phenocrysts of phlogopites have crystallized along with subordinate amount of olivine and clinopyroxene;(2) crystallization at shallow crustal levels promoted fine-grained phlogopite, K-feldspar, calcite and Fe-Ti oxides in the groundmass;(3) dyke emplacement related quench texture(plumose K-feldspar, acicular phlogopites) and finally(4) post emplacement autometasomatism by hydrothermal fluids which percolated as micro-veins and altered the mafic phases. Phlogopite phenocrysts often display resorption textures together with growth zoning indicating that during their crystallization equilibrium at the crystal-melt interface fluctuated multiple times probably due to incremental addition or chaotic dynamic self mixing of the lamproitic magma. Carbonate aggregates as late stage melt segregation are common in both these dykes, however their micro-xenolithic forms suggest that assimilation with a plutonic carbonatite body also played a key role in enhancing the carbonatitic nature of these dykes. Geochemically both dykes are ultrapotassic(K_2 O/Na_2 O: 3.0-9.4) with low CaO, Al_2 O_3 and Na_2 O content and high SiO_2(53.3-55.6 wt.%)and K_2 O/Al_2 O_3 ratio(0.51-0.89) characterizing them as high-silica lamproites. Inspite of these similarities, many other features indicate that both these dykes have evolved independently from two distinct magmas. In dyke 1, phlogopite composition has evolved towards the minette trend(Al-enrichment) from a differentiated parental magma having low MgO, Ni and Cr content; whereas in dyke 2, phlogopite composition shows an evolutionary affinity towards the lamproite trend(Al-depletion) and crystallized from a more primitive magma having high MgO, Ni and Cr content. Whole-rock trace-elements signatures like enriched LREE, LILE, negative Nb-Ta and positive Pb anomalies; high Rb/Sr, Th/La, Ba/Nb, and low Ba/Rb, Sm/La, Nb/U ratios in both dykes indicate that their pareintal magmas were sourced from a subduction modified garnet facies mantle containing phlogopite. From various evidences it is proposed that the petrogenesis of studied lamproitic dykes stand out to be an example for the lamproite magma which attained a carbonatitic character and undergone diverse chemical evolution in response to parental melt composition, storage at deep crustal level and autometasomatism.展开更多
The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotop...The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO_2 gneisses(LSG) and high-SiO_2 gneisses(HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible(K, Sr, Ba, large ion lithophile elements) and compatible elements(MgO, Cr, and Ni). They display fractionated rare earth element patterns(avg.La_N/Yb_N=12.1)with small Eu-anomaly(δEu=0.9), and exhibit negative anomalies of Nb and Ti in primitive mantlenormalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by_(εNd)(t)=4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG:(1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge;(2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and(3)upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantlewedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg#(avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements(MgO=avg. 1.1 wt.%; Cr=avg. 8 ppm; Ni=avg. 6 ppm) but enriched in incompatible elements(Sr=avg. 239 ppm, Ba=avg. 469 ppm). Its_(εNd)(t) values vary from-9.5 to-5.4.These chemical features of the HSG are akin to potassic granitoids found elsewhere. In this backdrop, we propose that the HSG suite of the Mangalwar Complex was derived from re-melting(partial) of an older crust(TTG?) occurring within the BGC-Ⅱ.展开更多
The energy transition challenges faced by modern civilization have significantly enhanced the demand for critical metals like lithium resulting in improved methods to explore,extract,and utilize these metals.In this c...The energy transition challenges faced by modern civilization have significantly enhanced the demand for critical metals like lithium resulting in improved methods to explore,extract,and utilize these metals.In this comprehensive review,we discuss the different types of lithium resources,factors,and mechanisms controlling lithium enrichment in various geological settings including terrestrial and marine environments.Diverse exploration strategies including geological,geophysical,mineralogical,geochemical,and remote sensing techniques including drone-based techniques for lithium exploration studies in different terranes are summarized.An overview of the mining techniques,including beneficiation and extraction,and their principles,mechanisms,operations,and comparison of the various approaches and compatibility with different types of lithium deposits for obtaining maximum yield are evaluated.Lithium isotopic studies are useful in understanding geological processes such as past weathering events and riverine input into the oceans,as well as in understanding the source of lithium in diverse types of deposits.We also highlight the recent developments in other areas such as recycling,environmental impact,and state-of-the-art analytical techniques for determining lithium in different lithium ore deposits and other geological materials.Our overview provides the latest developments and insights in the various sectors related to lithium and prompt further developments to meet the growing demand for this valuable metal as the world transforms to clean energy.展开更多
基金the DST sponsored project vide SERB Grant No.SR/S4/ES-643/2012the CSIR-NGRI funded project(SHORE PSC0205 WP4.2)
文摘Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these dykes have almost similar sequence of mineral-textural patterns indicative of:(1) an early cumulate forming event in a deeper magma chamber where megacrystic/large size phenocrysts of phlogopites have crystallized along with subordinate amount of olivine and clinopyroxene;(2) crystallization at shallow crustal levels promoted fine-grained phlogopite, K-feldspar, calcite and Fe-Ti oxides in the groundmass;(3) dyke emplacement related quench texture(plumose K-feldspar, acicular phlogopites) and finally(4) post emplacement autometasomatism by hydrothermal fluids which percolated as micro-veins and altered the mafic phases. Phlogopite phenocrysts often display resorption textures together with growth zoning indicating that during their crystallization equilibrium at the crystal-melt interface fluctuated multiple times probably due to incremental addition or chaotic dynamic self mixing of the lamproitic magma. Carbonate aggregates as late stage melt segregation are common in both these dykes, however their micro-xenolithic forms suggest that assimilation with a plutonic carbonatite body also played a key role in enhancing the carbonatitic nature of these dykes. Geochemically both dykes are ultrapotassic(K_2 O/Na_2 O: 3.0-9.4) with low CaO, Al_2 O_3 and Na_2 O content and high SiO_2(53.3-55.6 wt.%)and K_2 O/Al_2 O_3 ratio(0.51-0.89) characterizing them as high-silica lamproites. Inspite of these similarities, many other features indicate that both these dykes have evolved independently from two distinct magmas. In dyke 1, phlogopite composition has evolved towards the minette trend(Al-enrichment) from a differentiated parental magma having low MgO, Ni and Cr content; whereas in dyke 2, phlogopite composition shows an evolutionary affinity towards the lamproite trend(Al-depletion) and crystallized from a more primitive magma having high MgO, Ni and Cr content. Whole-rock trace-elements signatures like enriched LREE, LILE, negative Nb-Ta and positive Pb anomalies; high Rb/Sr, Th/La, Ba/Nb, and low Ba/Rb, Sm/La, Nb/U ratios in both dykes indicate that their pareintal magmas were sourced from a subduction modified garnet facies mantle containing phlogopite. From various evidences it is proposed that the petrogenesis of studied lamproitic dykes stand out to be an example for the lamproite magma which attained a carbonatitic character and undergone diverse chemical evolution in response to parental melt composition, storage at deep crustal level and autometasomatism.
文摘The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO_2 gneisses(LSG) and high-SiO_2 gneisses(HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible(K, Sr, Ba, large ion lithophile elements) and compatible elements(MgO, Cr, and Ni). They display fractionated rare earth element patterns(avg.La_N/Yb_N=12.1)with small Eu-anomaly(δEu=0.9), and exhibit negative anomalies of Nb and Ti in primitive mantlenormalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by_(εNd)(t)=4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG:(1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge;(2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and(3)upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantlewedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg#(avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements(MgO=avg. 1.1 wt.%; Cr=avg. 8 ppm; Ni=avg. 6 ppm) but enriched in incompatible elements(Sr=avg. 239 ppm, Ba=avg. 469 ppm). Its_(εNd)(t) values vary from-9.5 to-5.4.These chemical features of the HSG are akin to potassic granitoids found elsewhere. In this backdrop, we propose that the HSG suite of the Mangalwar Complex was derived from re-melting(partial) of an older crust(TTG?) occurring within the BGC-Ⅱ.
文摘The energy transition challenges faced by modern civilization have significantly enhanced the demand for critical metals like lithium resulting in improved methods to explore,extract,and utilize these metals.In this comprehensive review,we discuss the different types of lithium resources,factors,and mechanisms controlling lithium enrichment in various geological settings including terrestrial and marine environments.Diverse exploration strategies including geological,geophysical,mineralogical,geochemical,and remote sensing techniques including drone-based techniques for lithium exploration studies in different terranes are summarized.An overview of the mining techniques,including beneficiation and extraction,and their principles,mechanisms,operations,and comparison of the various approaches and compatibility with different types of lithium deposits for obtaining maximum yield are evaluated.Lithium isotopic studies are useful in understanding geological processes such as past weathering events and riverine input into the oceans,as well as in understanding the source of lithium in diverse types of deposits.We also highlight the recent developments in other areas such as recycling,environmental impact,and state-of-the-art analytical techniques for determining lithium in different lithium ore deposits and other geological materials.Our overview provides the latest developments and insights in the various sectors related to lithium and prompt further developments to meet the growing demand for this valuable metal as the world transforms to clean energy.
