The Ospino-Kitoi and Kharanur ultrabasic massifs represent the northern and southern ophiolite branches respectively of the Upper Onot ophiolitic nappe and they are located in the southeastern part of the Eastern Saya...The Ospino-Kitoi and Kharanur ultrabasic massifs represent the northern and southern ophiolite branches respectively of the Upper Onot ophiolitic nappe and they are located in the southeastern part of the Eastern Sayan（SEPES ophiolites）.Podiform chromitites with PGE mineralization occur as lensoid pods within dunites and rarely in harzburgites or serpentinized peridotites.The chromitites are classified into type I and type Ⅱ based on their Cr~#.Type I（Cr~# = 59-85） occurs in both northern and southern branches,whereas type Ⅱ（Cr~# = 76-90） occurs only in the northern branch.PGE contents range from ∑PGE 88-1189 ppb,Pt/Ir0.04-0.42 to ∑PGE 250-1700 ppb,Pt/Ir 0.03-0.25 for type I chromitites of the northern and southern branches respectively.The type Ⅱ chromitites of the northern branch have ∑PGE contents higher than that of type Ⅰ（468-8617 ppb,Pt/Ir 0.1-0.33）.Parental melt compositions,in equilibrium with podiform chromitites,are in the range of boninitic melts and vary in Al_2O_3,TiO_2 and FeO/MgO contents from those of type I and type Ⅱ chromitites.Calculated melt compositions for type Ⅰ chromitites are（Al_2O_3）_（melt） = 10.6—13.5 wt.%,（TiO_2）_（melt） = 0.01-0.44 wt.%,（Fe/Mg）_（melt） = 0.42-1.81;those for type Ⅱ chromitites are：（Al_2O_3）_（melt） = 7.8-10.5 wt.%,（TiO_2）_（melt） = 0.01-0.25 wt.%,（Fe/Mg）_（melt） = 0.5-2.4.Chromitites are further divided into Os-Ir-Ru（Ⅰ） and Pt-Pd（Ⅱ） based on their PGE patterns.The type Ⅰ chromitites show only the Os-Ir-Ru pattern whereas type Ⅱ shows both Os-Ir-Ru and Pt-Pd patterns.PGE mineralization in type Ⅰ chromitites is represented by the Os-Ir-Ru system,whereas in type Ⅱ it is represented by the Os-Ir-Ru-Rh-Pt system.These results indicate that chromitites and PGE mineralization in the northern branch formed in a suprasubduction setting from a fluid-rich boninitic melt during active subduction.However,the chromitites and PGE mineralization of the southern branch could have formed in a spreading zone environment.Mantle peridotites have been exposed in the area with remnants of mantle-derived reduced fluids,as indicated by the occurrence of widespread highly carbonaceous graphitized ultrabasic rocks and serpentinites with up to 9.75 wt.%.Fluid inclusions in highly carbonaceous graphitized ultrabasic rocks contain CO,CO_2,CH4,N_2 and the δ^（13）C isotopic composition（-7.4 to-14.5‰） broadly corresponds to mantle carbon.展开更多
Platinum group element （PGE） mineralization is mostly related to mafc--ultramafic complexes of the dominant magmatic deposit type. Mineralization of this type mainly relies on two conditions： the abundance of PGE i...Platinum group element （PGE） mineralization is mostly related to mafc--ultramafic complexes of the dominant magmatic deposit type. Mineralization of this type mainly relies on two conditions： the abundance of PGE in magma, and the presence of mechanisms favorable to PGE enrich- ment and separation from sulfur-saturated magma during magmatic evolution. Mafic-ultramafic complexes are widely developed in North Xinjiang, including （1） the large-scale copper-nickel deposits of Kelatongke, Huangshan, Huangshan East, and Tulargen, （2） numerous small to medium-sized copper- nickel deposits such as Xiangshan, Tudun, Hulu, Baishiquan, and （3） the Xiangshan West and Weiya medium-sized V--Ti magnetite deposits. However, mafic-ultramafic complexes in North Xinjiang rarely form PGE deposits. Therefore, questions about PGE metallogenesis in North Xinjiang are discussed in this paper from the standpoint of the ore-forming mechanism of PGE deposits and the characteristics of the North Xinjiang magma sources. The rock types of the post-collisional mafic--ultramafic complexes in North Xinjiang are of a ferrous rock series formed by fractional crystallization, a rock type generally favorable for hosting PGE. For the Cu-Ni sulfde deposits of North Xingjiang, the assimilation of crustal material causes sulfide liquation during processes of magmatic evolution and mineralization. This can be shown petrogeochemically, including the characteristics of Sr, Nd, Pb, O, Os, and S isotopes, which indi- cate a magmatic ore-forming mechanism for the Xingjiang PGE deposits. The principal reason for weak PGE mineralization in North Xinjiang may be ascribed to a widely-developed depleted mantle source （with positive end values） that underlies it. The North Xinjiang lithosphere is not of typical Precambrian cratonal type, but has more affinities with modified oceanic lithosphere or immature continental lithosphere that would constitute PGE-poor original magma sources unfavorable to PGE mineralization.展开更多
The Baimazhai Ni-Cu- (PGE) sulphide deposit in southeast Yunnan Province is hosted in mafic-ultramafic intrusions associated with the Permian Emeishan large igneous province. The deposit, one of several in the provinc...The Baimazhai Ni-Cu- (PGE) sulphide deposit in southeast Yunnan Province is hosted in mafic-ultramafic intrusions associated with the Permian Emeishan large igneous province. The deposit, one of several in the province, exhibits field and petrographic features suggestive of post-magmatic modification. The mafic-ultramafic intrusions that host the Baimazhai sulphide ores show near-pervasive to pervasive hydrothermal alteration, with the sulphides be- ing spatially associated with hydrothermal minerals such as biotite, amphibole and chlorite. This intimate association suggests that the sulphide ores were subjected to deformational and hydrothermal redistribution and textural changes resulting in disseminated and brecciated ores. Geochemically the Baimazhai sulphide ores are enriched in Cu, Pd and Au which, according to published studies, reflects the action of hydrothermal fluids. Interestingly, Ar-Ar age data yielded plateau ages of about 160-170 Ma, which also supports the modification features of the sulfide ores.展开更多
基金supported by RFBR grant Nos.16-05-00737 A,1605-00860 A,and 15-05-06950 Ascientific school-7201.2012.5, project SB RAS No.89
文摘The Ospino-Kitoi and Kharanur ultrabasic massifs represent the northern and southern ophiolite branches respectively of the Upper Onot ophiolitic nappe and they are located in the southeastern part of the Eastern Sayan（SEPES ophiolites）.Podiform chromitites with PGE mineralization occur as lensoid pods within dunites and rarely in harzburgites or serpentinized peridotites.The chromitites are classified into type I and type Ⅱ based on their Cr~#.Type I（Cr~# = 59-85） occurs in both northern and southern branches,whereas type Ⅱ（Cr~# = 76-90） occurs only in the northern branch.PGE contents range from ∑PGE 88-1189 ppb,Pt/Ir0.04-0.42 to ∑PGE 250-1700 ppb,Pt/Ir 0.03-0.25 for type I chromitites of the northern and southern branches respectively.The type Ⅱ chromitites of the northern branch have ∑PGE contents higher than that of type Ⅰ（468-8617 ppb,Pt/Ir 0.1-0.33）.Parental melt compositions,in equilibrium with podiform chromitites,are in the range of boninitic melts and vary in Al_2O_3,TiO_2 and FeO/MgO contents from those of type I and type Ⅱ chromitites.Calculated melt compositions for type Ⅰ chromitites are（Al_2O_3）_（melt） = 10.6—13.5 wt.%,（TiO_2）_（melt） = 0.01-0.44 wt.%,（Fe/Mg）_（melt） = 0.42-1.81;those for type Ⅱ chromitites are：（Al_2O_3）_（melt） = 7.8-10.5 wt.%,（TiO_2）_（melt） = 0.01-0.25 wt.%,（Fe/Mg）_（melt） = 0.5-2.4.Chromitites are further divided into Os-Ir-Ru（Ⅰ） and Pt-Pd（Ⅱ） based on their PGE patterns.The type Ⅰ chromitites show only the Os-Ir-Ru pattern whereas type Ⅱ shows both Os-Ir-Ru and Pt-Pd patterns.PGE mineralization in type Ⅰ chromitites is represented by the Os-Ir-Ru system,whereas in type Ⅱ it is represented by the Os-Ir-Ru-Rh-Pt system.These results indicate that chromitites and PGE mineralization in the northern branch formed in a suprasubduction setting from a fluid-rich boninitic melt during active subduction.However,the chromitites and PGE mineralization of the southern branch could have formed in a spreading zone environment.Mantle peridotites have been exposed in the area with remnants of mantle-derived reduced fluids,as indicated by the occurrence of widespread highly carbonaceous graphitized ultrabasic rocks and serpentinites with up to 9.75 wt.%.Fluid inclusions in highly carbonaceous graphitized ultrabasic rocks contain CO,CO_2,CH4,N_2 and the δ^（13）C isotopic composition（-7.4 to-14.5‰） broadly corresponds to mantle carbon.
基金supported by Major State Basic Research Program of the People's Republic of China(Nos.2007CB411304 and 2001CB409806)
文摘Platinum group element （PGE） mineralization is mostly related to mafc--ultramafic complexes of the dominant magmatic deposit type. Mineralization of this type mainly relies on two conditions： the abundance of PGE in magma, and the presence of mechanisms favorable to PGE enrich- ment and separation from sulfur-saturated magma during magmatic evolution. Mafic-ultramafic complexes are widely developed in North Xinjiang, including （1） the large-scale copper-nickel deposits of Kelatongke, Huangshan, Huangshan East, and Tulargen, （2） numerous small to medium-sized copper- nickel deposits such as Xiangshan, Tudun, Hulu, Baishiquan, and （3） the Xiangshan West and Weiya medium-sized V--Ti magnetite deposits. However, mafic-ultramafic complexes in North Xinjiang rarely form PGE deposits. Therefore, questions about PGE metallogenesis in North Xinjiang are discussed in this paper from the standpoint of the ore-forming mechanism of PGE deposits and the characteristics of the North Xinjiang magma sources. The rock types of the post-collisional mafic--ultramafic complexes in North Xinjiang are of a ferrous rock series formed by fractional crystallization, a rock type generally favorable for hosting PGE. For the Cu-Ni sulfde deposits of North Xingjiang, the assimilation of crustal material causes sulfide liquation during processes of magmatic evolution and mineralization. This can be shown petrogeochemically, including the characteristics of Sr, Nd, Pb, O, Os, and S isotopes, which indi- cate a magmatic ore-forming mechanism for the Xingjiang PGE deposits. The principal reason for weak PGE mineralization in North Xinjiang may be ascribed to a widely-developed depleted mantle source （with positive end values） that underlies it. The North Xinjiang lithosphere is not of typical Precambrian cratonal type, but has more affinities with modified oceanic lithosphere or immature continental lithosphere that would constitute PGE-poor original magma sources unfavorable to PGE mineralization.
基金Projects 2002GH11 supported by the International Coorperation Project of Yunnan Province and 2003D0039Q by The Natural Science Fund of Yunnan Province
文摘The Baimazhai Ni-Cu- (PGE) sulphide deposit in southeast Yunnan Province is hosted in mafic-ultramafic intrusions associated with the Permian Emeishan large igneous province. The deposit, one of several in the province, exhibits field and petrographic features suggestive of post-magmatic modification. The mafic-ultramafic intrusions that host the Baimazhai sulphide ores show near-pervasive to pervasive hydrothermal alteration, with the sulphides be- ing spatially associated with hydrothermal minerals such as biotite, amphibole and chlorite. This intimate association suggests that the sulphide ores were subjected to deformational and hydrothermal redistribution and textural changes resulting in disseminated and brecciated ores. Geochemically the Baimazhai sulphide ores are enriched in Cu, Pd and Au which, according to published studies, reflects the action of hydrothermal fluids. Interestingly, Ar-Ar age data yielded plateau ages of about 160-170 Ma, which also supports the modification features of the sulfide ores.
