Molybdenum Isotope Fractionation And Its Genetic Significance In High-temperature Magmatic-hydrothermal System

In recent decades,with the development of analytical instrumentation such as thermal ionization mass spectrometer(TIMS)and multi-collector inductively coupled plasma mass spectrometry(MC-ICP-MS),a new isotopic system(non-traditional stable isotopes)has an explosive advances(e.g.,Cu?Zn?Fe?Se?Mo?Cd?Cr?Hg,and so on).Meanwhile,these new isotopic systems are widely applied to mineral deposits,environmental science and etc.,and become an important geochemical proxy for scientists.Mo has received increasing attention for its specific application,geochemistry and isotopic fractionation.Prior works showed that Mo isotopic fractionation not only controlled by redox condition,but also controlled by evaporation or condensation.As a result,figuring out the Mo isotopic fractionation mechanisms will provide a new insight into the formation and origin of high-temperature ore deposits.Two condition experiments have been done in this study,which target at the Mo isotopic fractionation in open and closed systems,aiming to resolve the problems of Mo isotopic fractionation in a high-temperature magmatic hydrothermal system.Meanwhile,the characteristics of Mo isotopic compositions in the Laba porphyry molybdenum deposit also have been studied to trace the ore-forming fluids of the target deposit.In addition,comparing the Mo isotopic fractionation in the Laba porphyry molybdenum deposit and our condition experiments provide more important information about Mo isotopic fractionation mechanisms,which gives us new insights of Mo isotopic fractionation mechanisms in the Earth.This thesis's main results are as follows:1.Our condition experiments showed that Mo can migrate as gas state in a high-temperature condition,which is consisting with previous studies.2.There is a large Mo isotopic fractionation in open or closed system.In open system,the total range of Mo isotopic fractionation is 0.32‰,which is consisting with Mo isotopic fractionation in ore deposits.In closed system,diffusion effect can result in large Mo isotopic fractionation,with a total range of 2.12‰.3.The Mo isotopic composition in molybdenites and whole rocks have been measured,we found that different rocks have very different Mo isotopic compositions.From the early to final mineralization stages,heavy isotopes of Mo pretend to enrich in final stage minerals,indicating that Mo isotopes have been fractionated during the process of crystal fractionation and the evolution of magma hydrothermal fluids.Finally,this study provides a good example to use the Mo isotopes to explain the formation of ore deposits.