STABLE ISOTOPE GEOCHEMISTRY OF ROCKS AND GOLD DEPOSITS IN THE XIONGERSHAN AREA WESTERN HENAN PROVINCE
Fan Hongrui ;Xie Yihan;Zhao Rui; Wang Yinglan(Institute of Geology,the Chinese Academy of Sciences)
The Xiongershan area is located on the southern margin of the north China plateform. Gold deposits in this area can be divided into three types,structral altered rock type,quartz vein type,and blasting-breccia type. Except that blasting-breccia type gold deposit related to granite-porphyry, the other two types can occur in either Archean metamorphic rocks of Taihua group or Proterozoic volcanic rocks of Xionger group.Lead isotope composition and calculated second isochron model-age of gold deposits indicated that material sources for the formation of granitic batholith and gold deposits were mainly from the Archean Taihua group metamorphic rocks. Ranges of δ34S‰ for metamorphic rocks,volcanic rocks and granite are 1.3 to 5.7 , 2.5 to 5.4, 1.8 to 5.4, respectively. Sulfur isotope composition for all types gold deposits are different. δ34S‰ for blasting-breccia gold deposit is near zero ,indicated that the ore-forming hydrothermal fluid derived from magmatism of granite-porphyry. δ34S‰ for other two types are either positive or negative,even that δ34S‰ for different mineralizing stages for a deposit are inconsistent.For example , δ34S‰ for early stage and gold-deposition stage of the Shanggong deposit are 2. 1 to 4. 2 ,-6. 3 to -16. 3 , respectively. The reason causing this difference is physio-chemical condition and variation of hydrothrmal fluids. Respective fluid δ18O‰ and δD‰ for the (1) metamorphic fluids during regional metamorphism-migmatization , (2) magmatic fluids expelled from the granite, (3) gold-bearing hydrothermal fluids of early stage , (4) hydrothermal fluids of gold deposition are :(1) 5. 8 to 6. 8 ,and -24.5 to -27. 6; (2) 6.6 to 8. 5,and -64.7 to -68. 7; (3)5. 2 to 8. 9,and -45.1 to -70. 6;and (4) 1. 5 to 5.0 ,and -55. 2 to -83. 6. These data highlight that ore-forming fluids were related with Yianshanian granitic magmatism ,and mixed with meteoric water during gold mineralization. Combined with the geological background ,formation of gold deposits in this area is related to activity of syn-tectonic granitic magmatism hydrothermal fluid.