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Relationships between Alkaline Ti-Fe-Rich Gabbros and Iron-Oxide Copper-Gold Deposits in the Baixila Ore District, Yunnan
详细信息   
摘要
Low-Ti iron oxide Cu-U-Au-REE deposits commonly consist of low-titanium iron ore containing variable amounts of copper,uranium,gold,and rare earth elements. However,high-Ti iron oxide Cu-Au-Ag-REE deposits were found in Yunnan and Sichuan provinces,southwestern of China. Based on petrography,geochemistry of major and trace elements,and zircon U-Pb dating,we delineated the relationships between the alkaline Ti-Fe-rich gabbros and the IOCG deposit found recently in the Baixila ore district in Yunnan province,China. Firstly,petrofacies-logging for the gabbros were done in detail for the No. 59,179,and 219 exploration profiles at the 2360m-shafts underground in the Baixila ore district in order to study the gabbros hosting the IOCG or otherwise. Secondly,lithofacies analysis and re-mapping were completed in office study based on the new comprehensive study methods,which include geochemical lithofacies for the rocks and ores,trace element concentrations,and mineralogy of the artificial heavy-mineral-concentrates. Thirdly,the zircons were separated from the gabbros in the Baixila ore district,and then,CL images were used to identify the metamict zircons( ZS02,ZS03 and ZS04) and pristine zircons( ZS01) from the gabbros in the Baixila ore district. Finally,SHRIMP zircon U-Pb dating was carried out.Alkaline Ti-Fe-rich gabbros in the Baixila ore district in Yunnan province,which are closely related to the iron-oxide copper-gold( IOCG) deposits,are obviously lithofacies zonated. On the contrary,the barren alkaline Ti-Fe-rich gabbros are lack of petrofacies zonation. In fact,the iron-oxide copper-gold deposit found recently was controlled by the alkaline Ti-Fe-rich gabbros with obvious lithofacies zonation,and particularly the cryptoexplosion breccia of the gabbros.The alkaline Ti-Fe-rich gabbros are characterized by low Si,and high alkaline,P,Ti-Fe,LILE,REE,and HFSE,which are similar to those of the OIBs derived from the Fe-rich mantle source. It may be supposed that the alkaline Ti-Fe-rich gabbros in this study area could be derived from the intra-plate ocean island basalt. Geodynamically,metasomatism of Fe-rich mantle melting fluid might have resulted in the upwelling of the alkaline Ti-Fe-rich gabbros.SHRIPM Zircon U-Pb dating indicated that the alkaline Ti-Fe-rich gabbros and IOCG were formed at 1067±20 Ma～1047±15 Ma,i. e.,the Late Mesoproterozic( Stenian Period). The alkaline Ti-Fe-rich gabbros and IOCG in the Baixila ore district might have been formed in the syn-orogenic magmatic-tectonic event during the Grenville orogeny. They implied that IOCG metallogenic zone from the Baixila Fe-Cu ore district to the Tangdan copper-iron ore district,the east-west-trending magmatic-tectonic zone in the study area,might have attached to the syn-orogenic magmatic-tectonic event in the Grenville orogeny.In summary,this type of Fe-rich mantle source in the Baixila ore district,Yunnan province,China,might supply the abundant metallogenic materials for large-scale accumulations of iron and copper metals. It might have been the excellent metallogenic environments not only for large to superlarge iron-oxide copper-gold( IOCG) deposits,but also for the formation of titanic iron ores and copper-sulfide-PGE deposits.

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