Listwanite from the Luobusa ophiolite,Xizang,forms a narrow,discontinuous band along the eastern part of the southern boundary fault.We undertook a detailed petrographic and geochemical study to understand the mineral...Listwanite from the Luobusa ophiolite,Xizang,forms a narrow,discontinuous band along the eastern part of the southern boundary fault.We undertook a detailed petrographic and geochemical study to understand the mineral transformation processes and the behaviour of major and trace elements during listwanite formation.Three alteration zones characterized by distinct mineral components and texture are recognized and,in order of increasing degree of alteration,these are:zonem is rich in serpentine minerals;zonen is rich in talc and carbonates;and zone_Ⅰis mainly composed of carbonates and quartz.Geochemical data for the three alteration zones show significant modification of some major and trace elements in the protolith,although some oxides show linear correlations with MgO.Gold mineralization is recognized in the Luobusa listwanite and may signify an important target for future mineral exploration.Gold enrichment occurs in both zone_Ⅰand zone_Ⅱand is up to 0.91 g/t in one sample from zonei.We show that CO_2-rich hydrothermal fluids can modify both the occurrence and composition of chromite grains,indicating some degree of chromite mobility.Low-Cr anhedral grains are more easily altered than high-Cr varieties.The compositions of chromite and olivine grains in the listwanite suggest a dunite protolith.展开更多
基金funded by National Natural Science Foundation of China(Grant No.40930313)the China Geological Survey(Grants No.12120114061801,No.12120114057701,and No.12120114061501)
文摘Listwanite from the Luobusa ophiolite,Xizang,forms a narrow,discontinuous band along the eastern part of the southern boundary fault.We undertook a detailed petrographic and geochemical study to understand the mineral transformation processes and the behaviour of major and trace elements during listwanite formation.Three alteration zones characterized by distinct mineral components and texture are recognized and,in order of increasing degree of alteration,these are:zonem is rich in serpentine minerals;zonen is rich in talc and carbonates;and zone_Ⅰis mainly composed of carbonates and quartz.Geochemical data for the three alteration zones show significant modification of some major and trace elements in the protolith,although some oxides show linear correlations with MgO.Gold mineralization is recognized in the Luobusa listwanite and may signify an important target for future mineral exploration.Gold enrichment occurs in both zone_Ⅰand zone_Ⅱand is up to 0.91 g/t in one sample from zonei.We show that CO_2-rich hydrothermal fluids can modify both the occurrence and composition of chromite grains,indicating some degree of chromite mobility.Low-Cr anhedral grains are more easily altered than high-Cr varieties.The compositions of chromite and olivine grains in the listwanite suggest a dunite protolith.
