The Varzaghan district at the northwestern margin of the Urumieh–Dokhtar magmatic arc, is considered a promising area for the exploration of porphyry Cu deposits in Iran. In this study we identified mono-and multi-el...The Varzaghan district at the northwestern margin of the Urumieh–Dokhtar magmatic arc, is considered a promising area for the exploration of porphyry Cu deposits in Iran. In this study we identified mono-and multi-element geochemical anomalies associated with Cu–Au–Mo–Bi mineralization in the central parts of the Varzaghan district by applying the concentration–area fractal method. After mono-element geochemical investigations, principal component analysis was applied to ten selected elements in order to acquire a multi-element geochemical signature based on the mineralization-related component. Quantitative comparisons of the obtained fractal-based populations were carried out in accordance with known Cu occurrences using Student's t-values. Then,significant mono-and multi-element geochemical layers were separately combined with related geologic and structural layers to generate prospectivity models, using the fuzzy GAMMA approach. For quantitative evaluation of the effectiveness of different geochemical signatures in final prospectivity models, a prediction-area plot was adapted. The results show that the multi-element geochemical signature of principal component one(PC1) is more effective than mono-element layers in delimiting exploration targets related to porphyry Cu deposits.展开更多
Hydrochemical facies, groundwater evolution, and physicochemical reactions between soil or rock and water are of considerable importance when evaluating or predicting the nature of anthropogenic impacts on groundwater...Hydrochemical facies, groundwater evolution, and physicochemical reactions between soil or rock and water are of considerable importance when evaluating or predicting the nature of anthropogenic impacts on groundwater quality. In this respect a total of 67 ground water samples were collected randomly in Akure, southwestern, Nigeria from hand pump/dug wells and analyzed for major cations and anions. The domination of cations and anions was in the order of Ca2+ > K+ > Na+ > Mg2+ and ?> Cl- > ?> ?respectively. The pH and Eh of the water samples show an acidic condition, with low salinity hazard (generally less than 250 μS/cm). The Piper classification for hydrogeochemical facies indicates carbonate hardness (secondary alkalinity) exceeds 50% that is by alkaline earths and weak acids, with Ca2+ + Mg2+ + ?water-type. This also suggests a meteoric origin of water quality caused by rock-water interaction. The ratio of ?and Cl- is greater than 1 and implies recharge area or upper water flow course of carbonate rocks (interaction of water with aquifer material). The Na+:Cl- is less than 0.7 signifying loss of Na+ through precipitation of evaporating water;the water is Ca2+ rich and Na+ depleted with Mg2+:Ca2+ less than 0.5 and Na+:K+ less than 15. The Na+:Ca2+ (<1) indicates reverse ionic exchange. The Ca2+:?+ ?for the samples is less than 1.0 suggestive of flow of water through the normal hydrological cycle. The calculated range of values of sodium absorption ratio (1.89 - 26.42), permeability index (42.67 - 170.24), residue sodium carbonate (-1 to 5), magnesium ratio (4 - 53), Kelly ratio (0.04 - 0.84), percent sodium (0.41 - 3.45) suggest good water suitable for irrigation purposes. In addition, the Wilcox plot shows that 98% of the water samples belong to “good to permissible category” for irrigation use.展开更多
Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Mont...Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Montanari et al.,1983;Hildebrand and Boynton,1988,1990）.This evidence,along with ejected terrestrial chromites（Olds et al.,2016）suggest the impact sampled terrestrial mafic and/or ultramafic target rocks which are not known to exist in the Chicxulub target area.Possible resolutions to the paradox are:1)the existence of an unmapped/unknown suture in Yucatan Platform basement,2)an additional small unmapped/unknown impact site on oceanic lithosphere,or 3)an additional large impact on oceanic lithosphere or continental margin transitional to oceanic lithosphere.The third hypothesis is elaborated here since:1)Ophiolites nearest to Chicxulub crater are found in Cuba and apparently were obducted in latest Cretaceous/earliest Danian times（García-Casco,2008）,inconsistent with the documented Eocene collision of Cuba with the Bahamas platform;and 2)Cuba hosts the world’s thickest known KT boundary deposits（Iturralde-Vinent,1992;Kiyokawa et al.,2002;Tada et al.,2003）.These and geometric considerations suggest oceanic crust and upper mantle rock,exposed as ophiolite in the Greater Antilles island chain,marks the rim of a roughly 700 km diameter impact basin deformed and dismembered from an originally circular form by at least 50 million years of left-lateral shear displacement along the North American-Caribbeantransform plate boundary.展开更多
文摘The Varzaghan district at the northwestern margin of the Urumieh–Dokhtar magmatic arc, is considered a promising area for the exploration of porphyry Cu deposits in Iran. In this study we identified mono-and multi-element geochemical anomalies associated with Cu–Au–Mo–Bi mineralization in the central parts of the Varzaghan district by applying the concentration–area fractal method. After mono-element geochemical investigations, principal component analysis was applied to ten selected elements in order to acquire a multi-element geochemical signature based on the mineralization-related component. Quantitative comparisons of the obtained fractal-based populations were carried out in accordance with known Cu occurrences using Student's t-values. Then,significant mono-and multi-element geochemical layers were separately combined with related geologic and structural layers to generate prospectivity models, using the fuzzy GAMMA approach. For quantitative evaluation of the effectiveness of different geochemical signatures in final prospectivity models, a prediction-area plot was adapted. The results show that the multi-element geochemical signature of principal component one(PC1) is more effective than mono-element layers in delimiting exploration targets related to porphyry Cu deposits.
文摘Hydrochemical facies, groundwater evolution, and physicochemical reactions between soil or rock and water are of considerable importance when evaluating or predicting the nature of anthropogenic impacts on groundwater quality. In this respect a total of 67 ground water samples were collected randomly in Akure, southwestern, Nigeria from hand pump/dug wells and analyzed for major cations and anions. The domination of cations and anions was in the order of Ca2+ > K+ > Na+ > Mg2+ and ?> Cl- > ?> ?respectively. The pH and Eh of the water samples show an acidic condition, with low salinity hazard (generally less than 250 μS/cm). The Piper classification for hydrogeochemical facies indicates carbonate hardness (secondary alkalinity) exceeds 50% that is by alkaline earths and weak acids, with Ca2+ + Mg2+ + ?water-type. This also suggests a meteoric origin of water quality caused by rock-water interaction. The ratio of ?and Cl- is greater than 1 and implies recharge area or upper water flow course of carbonate rocks (interaction of water with aquifer material). The Na+:Cl- is less than 0.7 signifying loss of Na+ through precipitation of evaporating water;the water is Ca2+ rich and Na+ depleted with Mg2+:Ca2+ less than 0.5 and Na+:K+ less than 15. The Na+:Ca2+ (<1) indicates reverse ionic exchange. The Ca2+:?+ ?for the samples is less than 1.0 suggestive of flow of water through the normal hydrological cycle. The calculated range of values of sodium absorption ratio (1.89 - 26.42), permeability index (42.67 - 170.24), residue sodium carbonate (-1 to 5), magnesium ratio (4 - 53), Kelly ratio (0.04 - 0.84), percent sodium (0.41 - 3.45) suggest good water suitable for irrigation purposes. In addition, the Wilcox plot shows that 98% of the water samples belong to “good to permissible category” for irrigation use.
文摘Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Montanari et al.,1983;Hildebrand and Boynton,1988,1990）.This evidence,along with ejected terrestrial chromites（Olds et al.,2016）suggest the impact sampled terrestrial mafic and/or ultramafic target rocks which are not known to exist in the Chicxulub target area.Possible resolutions to the paradox are:1)the existence of an unmapped/unknown suture in Yucatan Platform basement,2)an additional small unmapped/unknown impact site on oceanic lithosphere,or 3)an additional large impact on oceanic lithosphere or continental margin transitional to oceanic lithosphere.The third hypothesis is elaborated here since:1)Ophiolites nearest to Chicxulub crater are found in Cuba and apparently were obducted in latest Cretaceous/earliest Danian times（García-Casco,2008）,inconsistent with the documented Eocene collision of Cuba with the Bahamas platform;and 2)Cuba hosts the world’s thickest known KT boundary deposits（Iturralde-Vinent,1992;Kiyokawa et al.,2002;Tada et al.,2003）.These and geometric considerations suggest oceanic crust and upper mantle rock,exposed as ophiolite in the Greater Antilles island chain,marks the rim of a roughly 700 km diameter impact basin deformed and dismembered from an originally circular form by at least 50 million years of left-lateral shear displacement along the North American-Caribbeantransform plate boundary.
