The Preconcentration Process of Metal Mineral in the Deep Mgama Chamber of Jinchuan Ni-Cu Suphide Deposit

The Jinchuan Ni-Cu deposit is one of the three largest magmatic sulfide deposits in the world.Jinchuan deposit have some unusual typical geological characteristics.such as the small size of the host intrusion,mainly consist of ultramafic rocks,high sulfide/silicate ration.,different rocks and ores showed the mutation contact relationship.These typical characteristics implied the the metal had preconcentrated in the deep stage magma chamber.The preconcentration process mainly involved three aspects:The mechanism of sulfide segregation;The relative time of sulfide segregation and the amount of sulfide segregated from the magma;The migration and fractional crystallization process of the sulfide.The Fo of olivine in different rocks have a narrow range(Fo=80.11-85.68),which suggest that the deep magma chamber is an open system,the penetration of fresh magma make the Fe/Mg ration of the magma constant.Followthe olivine-liquid equilibrium principle,the MgO content of Jinchuan intrusion parental magma calculated from 10.8%-12.6%,which indicated that the source have a high degree of partial melting.The Sr-Nd-Os isotope and trace element geochemical features implied that the jinchuan intrusion parental magma suffered apparent crustal materials,the extent fo the contamination is about 5%-10%.The Th-Ta,Th-Nb,(Th/Ta)_PM-(La/Nb)_PM diagram showed that part of the contaminated material is a component of the lower crust.The lower crustal material contamination may be the major pechanism of sulfide segregation in the deep magma chamber.The main ore-bearing rock types are lherzolite and dunite,The "Melts" software simulation calculation show that the sulfide segregation occurred in the early stage of magmatic evolution.After the sulfide segregation,as the gravity,it sink to the bottom or the lower part of the chamber.The massive ores of jinchuan deposit have the relative enrichment IPGE,and the rich copper ore body is relatively enriched in Cu and PPGE.The diffrerntiation of metal elements show that the sulfide had undergone significant fractional crystallization in the deep magma chamber.