The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715...The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715±0.012(MSWD=0.11),showing an S-type affinity.The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh(1590±30 Ma).The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC.Petro-graphic and geochemical studies revealed that the granite is enriched in Rb(271 ppm),Pb(77 ppm),Th(25 ppm),and U(33 ppm)and depleted in Sr(95 ppm),Nb(16 ppm),Ba(399 ppm)and Zr(143 ppm)contents as compared to the normal granite.The Mirgarani granite is a peraluminous(A/CNK=1.23),high potassic(K_(2)O 6.42%),Calc-Alkalic to Alkali-Calcic{(Na_(2)O+K_(2)O)-CaO=6.29}S-Type granite,a feature supported by the presence of modal garnet and normative corundum(2.68%).The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700℃ during the Co-lumbian-Nuna Supercontinent.展开更多
Hydrogeochemical surveys were conducted in parts of the Proterozoic Shillong basin in Meghalaya to locate the unconformity-related uranium deposits,related alteration patterns,and the influence of the rock formations ...Hydrogeochemical surveys were conducted in parts of the Proterozoic Shillong basin in Meghalaya to locate the unconformity-related uranium deposits,related alteration patterns,and the influence of the rock formations on the groundwater solute chemistry.Shillong Basin comprises Proterozoic metasediments and felsic volcanics of Tyrsad Formation,undeformed arenaceous Barapani Formation with intrusive granites,and metabasic sills and dykes.The groundwater quality is determined for drinking,and domestic-agro-industrial utilities using hydrogeochemical tools and physicochemical parameters.The water is acidic to slightly alkaline and has an oxidizing redox environment,Electrical Conductivity(EC),Total Dissolve Solids(TDS),and major ions fell below the World Health Organization(WHO)and Indian Standards Institute(ISI)acceptable limits except for Zn,Fe,and SiO_(2) showing higher concentrations.The sequences of abundance of major cations and trace elements are Fe>Zn>SiO_(2)>Ca^(2+)>Na^(+)>Mg^(2+)>K^(+)>U and anions as HCO_(3)>Cl->SO_(4)^(2-).Groundwater character was assessed by ion exchange,simple dissolution,and unusual dissolution mechanisms.The area has dominant CaHCO_(3),NaHCO_(3),and restricted CaMgHCO_(3) type water.Plagioclase dissolution and high SiO_(2) and cation exchange of Ca for Na were identified.The groundwater indices of Sodium Percent,Kelley’s Index,Sodium Adsorption Ratio,Magnesium Ratio,Electrical Conductivity,TDS,USSL,and Wilcox index were found suitable for agro-industrial uses.Permeability Index is found to be suitable in most areas and the Corrosivity Ratio shows the areas of galvanized pipes and PVC pipes to be used for water supply.AHC analysis shows three distinct groups of water types,as well as the factor analysis,also shows the three prominent factors of water types defining the dimensionality of water types.Magnesium metasomatic alteration zones and Zn anomalous zones are delineated.展开更多
文摘The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715±0.012(MSWD=0.11),showing an S-type affinity.The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh(1590±30 Ma).The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC.Petro-graphic and geochemical studies revealed that the granite is enriched in Rb(271 ppm),Pb(77 ppm),Th(25 ppm),and U(33 ppm)and depleted in Sr(95 ppm),Nb(16 ppm),Ba(399 ppm)and Zr(143 ppm)contents as compared to the normal granite.The Mirgarani granite is a peraluminous(A/CNK=1.23),high potassic(K_(2)O 6.42%),Calc-Alkalic to Alkali-Calcic{(Na_(2)O+K_(2)O)-CaO=6.29}S-Type granite,a feature supported by the presence of modal garnet and normative corundum(2.68%).The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700℃ during the Co-lumbian-Nuna Supercontinent.
文摘Hydrogeochemical surveys were conducted in parts of the Proterozoic Shillong basin in Meghalaya to locate the unconformity-related uranium deposits,related alteration patterns,and the influence of the rock formations on the groundwater solute chemistry.Shillong Basin comprises Proterozoic metasediments and felsic volcanics of Tyrsad Formation,undeformed arenaceous Barapani Formation with intrusive granites,and metabasic sills and dykes.The groundwater quality is determined for drinking,and domestic-agro-industrial utilities using hydrogeochemical tools and physicochemical parameters.The water is acidic to slightly alkaline and has an oxidizing redox environment,Electrical Conductivity(EC),Total Dissolve Solids(TDS),and major ions fell below the World Health Organization(WHO)and Indian Standards Institute(ISI)acceptable limits except for Zn,Fe,and SiO_(2) showing higher concentrations.The sequences of abundance of major cations and trace elements are Fe>Zn>SiO_(2)>Ca^(2+)>Na^(+)>Mg^(2+)>K^(+)>U and anions as HCO_(3)>Cl->SO_(4)^(2-).Groundwater character was assessed by ion exchange,simple dissolution,and unusual dissolution mechanisms.The area has dominant CaHCO_(3),NaHCO_(3),and restricted CaMgHCO_(3) type water.Plagioclase dissolution and high SiO_(2) and cation exchange of Ca for Na were identified.The groundwater indices of Sodium Percent,Kelley’s Index,Sodium Adsorption Ratio,Magnesium Ratio,Electrical Conductivity,TDS,USSL,and Wilcox index were found suitable for agro-industrial uses.Permeability Index is found to be suitable in most areas and the Corrosivity Ratio shows the areas of galvanized pipes and PVC pipes to be used for water supply.AHC analysis shows three distinct groups of water types,as well as the factor analysis,also shows the three prominent factors of water types defining the dimensionality of water types.Magnesium metasomatic alteration zones and Zn anomalous zones are delineated.
