Controlling factors on the formation of porphyry-skarn Mo deposits
In this paper,the controlling factors for the formation of porphyry-skarn Mo deposits have been discussed based on investigations of chemical compositions and physicochemical properties of ore-forming magmas and processes of the fluid exsolution and metal precipitation.The results show that Mo was generally depleted in ore-forming magmas of various porphyry-skarn Mo deposits in different tectonic settings.Oxidizing water rich magma is the basis for the formation of porphyry-skarn Mo deposits.The high ore-forming focusing degree along small stocks derived originally from top parts of the deep-sited magma chambers was the critical link for the formation of porphyry-skarn Mo deposits.It is also shown that large to super-large sized porphyry-skarn Mo deposits are commonly characterized with the multi-stage magmatic-hydrothermal superimposed metallogeny and magmas of their ore-forming porphyry stocks were connected with large magma chambers.In addition,their ore-forming magmas resulted in multiple-phases intrusions and metallogenies which are key factors for the formation of large to super-large sized porphyry-skarn Mo deposits.In summary,the porphyry-skarn Mo deposit was the coupling product of various factors including the magmatic volume,magmatic oxygen fugacity,magmatic water content,ore-forming fluid accumulation degree,and the superposition mineralization of multi-stage magmatic-hydrothermal activities.Among them,the magma chamber volume,magmatic oxygen fugacity and magmatic water content are basic factors,the ore-forming fluid focusing degree is a critical factor,and the superposition mineralization of multi-stage magmatic-hydrothermal activities is a key factor mostly required for the formation of large to super-large sized porphyry-skarn Mo deposits.Moreover,it is suggested that in the search for porphyry-skarn Mo deposits,attention should be paid to the geochemical properties and spatial structure properties of porphyry stocks,and the identification of superimposition metallogenic characteristics of multi-stage magmatic-hydrothermal activities.
porphyry-skarn Mo depositmelt Mo concentrationmagma chamber volumefluid focusing degreemultiple-stage of magmatic-hydrothermal activities