Petrogenesis and Metallogeny for the Mujicun Porphyry Copper Deposits

Author:Shen Zhichao

Supervisor:Hou Zengqian


Degree Year:2015





The Mujicun porphyry Cu deposit(PCD),different from the PCDs that found in arc orogeny environment and collision orogeny environment,is located in North China Craton.This paper presents new zircon U-Pb dating for the ultramafic-mafic-intermediate-acid rocks of the Laiyuan complex,molybdenite Re-Os dating,and whole-rock elemental,Sr-Nd isotopic of ore-bearing porphyry and in-situ zircon Hf isotopic geochemistry for hornblendite,gabbrodiorite,andesite,and diorite-porphyry.This study also carried out careful observation on the character of sulfide in hornblendite,gabbrodiorite,andesite,and diorite-porphyry so as to better constrain the petrogenesis and metallogeny.LA-ICP-MS and SHRIMP zircon U-Pb dating shows that the Laiyuan complex were emplaced in the early Crataceous(133-142Ma).The porphyries are mainly high-K calc-alkaline and show some adakitic affinities.They have genetic association with the ultramafic-mafic rocks of Laiyuan complex.Coupled with previous tempreture and pressure result of the ultramafic and mafic rocks,this study gains the recognition that heating from the upwelling asthnosphere and decompression in the extensional regime would further facilitate extensive partial melting of enriched SCLM beneath the Taihang orogen,producing primary basaltic magma,and the basaltic melts underwent lower crustal contamination,deep accumulation,shallower two stages of fractional crystallisation to create adakite-like ore-bearing diorite porphyry in an extensional environment.Through the careful study of sulfide in the hornblendite,gabbrodiorite,andesite,and diorite-porphyry,we found that these hornblendites and their parental magma show no Cu enrichment relative to normal arc magmas,and that the formation of the Mujicun deposit does not require anomalous Cu enrichment in the intra-crustal cumulates or mantle source region,and the Mujicun porphyry Cu deposit is likely formed by normal magmatic-hydrothermal processes.