THE ERUPTIVE ORIGINS OF COPPER AND MULTI-METAL DEPOSITS IN THE SKARNS IN JIAMA,TIBET

The skarn with special eruptive deposition and metasomatism is the main ore-bearing rock in Jiama deposits.The main characteristics of the skarn are as follows:(1)occurring as bedded,para-bedded in the contact zone between carbonate and microclastic rock,and its occurrence being accordance to the strata;(2)cut by later vein rock,so having no relation with the magmatic rock on genesis;(3)metasomatic skarn having replacement remnant texture,pseudobreccia structure,while depositional skarn,particulate crystallitic texture and ribbon,stratified structure.These reflect they are eruptive genesis;(4)typical low temperature (300℃) mineral assemblage developing in skarn;(5)the same REE pattern of the skarn and the wall rock.The skarn in Jiama deposits is regarded as the coupled results of contemporaneous fault system,submarine hydrothermal+deep-rooted hydrocarbon and alkali fluids and carbonate rock+microclastic rock.The diagenesis of the skarn has close relationship with the ore forming process.