Platinum\|Group Elements (PGE) along with other highly siderophile elements (HSE) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the earth.However,...Platinum\|Group Elements (PGE) along with other highly siderophile elements (HSE) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the earth.However,the transfer of PGE and other HSE from the mantle may occur by tectonic emplacement of mantle material into the crust or by crystallization of the mantle derived magma in the crust.The formation and emplacement of ophiolites,is therefore,a suitable transfer mechanism in the enrichment of PGE and other metallic mineral deposits.Because of this,in recent years,a great deal of attention is being paid in studying the ophiolites in order to better understand the core\|mantle interaction,chemical evolution of the upper mantle and to explore their noble metal potential.The ophiolites along the Indus Suture Zone (ISZ) in the Himalayas are tectonically related to India\|Eurasia collision.But their detailed geochemical evolution history and economic potentiality (chromite,PGE,gold and Ni\|sulfides) is not evaluated so far.Nidar ophiolite of the eastern Ladakh is one of the ophiolitic suites along the ISZ.The general geology of the area was presented in several research papers.This paper presents the geology,mineralogy and geochemistry of the chromitites and reports on the first platinum\|group elements mineralization to have been discovered.展开更多
Recently,considerable attention is being paid in studying the high\|pressure (rodingites and eclogites etc)crustal segments for understanding the architecture and evolution of collision orogens.This paper presents the...Recently,considerable attention is being paid in studying the high\|pressure (rodingites and eclogites etc)crustal segments for understanding the architecture and evolution of collision orogens.This paper presents the geology,mineralogy and geochemistry of the rodingites,the first reported occurrence in eastern Ladakh,the Himalaya.Nidar ophiolite is one of the well exposed,nearly a complete ophiolite of the Indus Suture Zone present in the eastern Ladakh.Field studies across the Nidar ophiolite in the Nidar—Kyun Tso section unraveled the occurrence of relatively strongly developed rodingites.Rodingites are very hard and dense.They occur as layers and also as boudins within and at the contacts of the serpentinites.The rodingites are fine to medium grained.Grossular is the dominant rodingite mineral and occurs as well developed crystals.At places grossular has coronitic texture.Diopside,clinozosite,rutile and opaques are the other main Ca\|rich minerals present in rodingites.The matrix of the rodingite minerals is highly birefringent.The rodingite mineral assemblage indicates the development of rodingite in the pressure and temperature range of 18～25 kbar and 700 to 800℃,respectively.Rodingites have high abundances (mass fraction) of CaO (10%～12%) and Al\-2O\-3 (12%) contents and generally low in SiO\-2 (46%) and MgO (7%～8%) contents.They have chondrite\|normalized Rare Earth Element (REE) abundances of 25 to 40× on the LREE and 37 to 50× on the MREE and 15 to 24× on the HREE.Overall the REE patterns tend to be concave\|upwards,or relatively light\|REE depleted with almost no Eu\|anomaly.The geologic occurrence,the mineralogy and geochemical (major,trace and REE) data of the rodingites indicate that they were initially gabbros/basalt that have undergone Ca\|metasomatism during serpentinization,followed by high\|pressure recrystallization to rodingites.展开更多
文摘Platinum\|Group Elements (PGE) along with other highly siderophile elements (HSE) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the earth.However,the transfer of PGE and other HSE from the mantle may occur by tectonic emplacement of mantle material into the crust or by crystallization of the mantle derived magma in the crust.The formation and emplacement of ophiolites,is therefore,a suitable transfer mechanism in the enrichment of PGE and other metallic mineral deposits.Because of this,in recent years,a great deal of attention is being paid in studying the ophiolites in order to better understand the core\|mantle interaction,chemical evolution of the upper mantle and to explore their noble metal potential.The ophiolites along the Indus Suture Zone (ISZ) in the Himalayas are tectonically related to India\|Eurasia collision.But their detailed geochemical evolution history and economic potentiality (chromite,PGE,gold and Ni\|sulfides) is not evaluated so far.Nidar ophiolite of the eastern Ladakh is one of the ophiolitic suites along the ISZ.The general geology of the area was presented in several research papers.This paper presents the geology,mineralogy and geochemistry of the chromitites and reports on the first platinum\|group elements mineralization to have been discovered.
文摘Recently,considerable attention is being paid in studying the high\|pressure (rodingites and eclogites etc)crustal segments for understanding the architecture and evolution of collision orogens.This paper presents the geology,mineralogy and geochemistry of the rodingites,the first reported occurrence in eastern Ladakh,the Himalaya.Nidar ophiolite is one of the well exposed,nearly a complete ophiolite of the Indus Suture Zone present in the eastern Ladakh.Field studies across the Nidar ophiolite in the Nidar—Kyun Tso section unraveled the occurrence of relatively strongly developed rodingites.Rodingites are very hard and dense.They occur as layers and also as boudins within and at the contacts of the serpentinites.The rodingites are fine to medium grained.Grossular is the dominant rodingite mineral and occurs as well developed crystals.At places grossular has coronitic texture.Diopside,clinozosite,rutile and opaques are the other main Ca\|rich minerals present in rodingites.The matrix of the rodingite minerals is highly birefringent.The rodingite mineral assemblage indicates the development of rodingite in the pressure and temperature range of 18～25 kbar and 700 to 800℃,respectively.Rodingites have high abundances (mass fraction) of CaO (10%～12%) and Al\-2O\-3 (12%) contents and generally low in SiO\-2 (46%) and MgO (7%～8%) contents.They have chondrite\|normalized Rare Earth Element (REE) abundances of 25 to 40× on the LREE and 37 to 50× on the MREE and 15 to 24× on the HREE.Overall the REE patterns tend to be concave\|upwards,or relatively light\|REE depleted with almost no Eu\|anomaly.The geologic occurrence,the mineralogy and geochemical (major,trace and REE) data of the rodingites indicate that they were initially gabbros/basalt that have undergone Ca\|metasomatism during serpentinization,followed by high\|pressure recrystallization to rodingites.
