The Machangqing Porphyry Cu-Mo-Au Deposit In Yunnan Province: Magmatism And Mineralization

The Machangqing porphyry-type Cu-Mo-(Au) deposit (or deposit cluster) forms in a continental orogeny and it is one of the typical deposits related to alkaline-rich porphyry of Himalaya epoch in the Sanjiang metallogenic belt. This paper reveals that magmatic evolutionary series, the regulation of alteration-mineralizing zonation, fluid evolution and ore-controlling factors, bringing forward some thoughts of ore -exploring further, and achieving anticipated purpose.Magmatic series mainly include following assemblages: porphyritic granite+ lamprophyre, (quartz) orthophyre (syenite)+(quartz)monzonite (ivernite)+granite porphyry and alkaline granite porphyry + lamprophyre. Among them, the assemblage of porphyritic granite+ lamprophyre intrusive age is 50 Ma±, which is the wall-rock of orebody; whereas the assemblage of (quartz) orthophyre (syenite)+ (quartz) monzonite (ivernite)+granite porphyry, its intrusive age is 36Ma±and some dark particulate enclaves of dioritoid with disseminated pyritization and magnetitization have been found in this assemblage, showing that the assemblage is the product of mixture of two kinds magma: crustal magma and mantle magma. Mantle magma provides the magmatic system with mineralizing elements such as Cu,Au,S, fluid and power. The combination of alkaline granite-porphyry+lamprophyre intrusive is at the latest, aged 32Ma.Studying the characteristics of ore-controlling structures, it is confirmed that intrusive-contact structures ascribing to vertical stress due to the force of magma intrusive during the magma intrusive is main rock- and ore-control structures.Porphyry-type Cu-Mo mineralization is controlled by the fissures intra-porphyry rockbody. The contact-metasomatism-type mineralization of Cu-Mo-Au-Fe is controlled by the contact structures. Interlayer decollement near the contact belt controls the compound mineralization of quartz-vein-type, fractured-alteration-type of Au,Ag, and Pb-Zn. Epithermal Au-Pb-Zn-Ag mineralization is controlled by tensile structures of the surrounding rock far from the contact belt, showing the characteristics of intrusion-contact structures. Mineralizing elements is zoned horizontally at the centre of rockbody.In terms of geological characteristics of the deposit, alteration-mineralization types and mineralizing element combination, fluid evolution, isotope geochemical and ore-controlling features, Machangqing Cu-Mo-(Au) deposit and Jinchangqing Au deposit are thought to be the products of the same magmatic-structural-mineralizing system, which is intimated with the mineralization spatially and temporally. By the spatial distribution of alteration-mineralization types, it is clear to image that the mineralizing fluid exsoluted from the crystalling magma and accumulated mineralizing elements in the course of move outward.It demonstrates that diagenetic-mineralization is controlled by the identical dynamic system in Machangqing deposit cluster. With the outwardness of mineralizing fluid exsolution from the crystalling magma and the physicochemical change of mineralizing conditions, it forms different mineralizing types in different boundary conditions. With the processes of ore-forming, mineralization took place from the intra-intrusive→near the contact→far away the contact, mineralizing temperatures, pressures and salinity are from high to low, the tendency of mineralizing depths is from deep to shallow.Alkaline-rich intrusion derives from the transition belt of crust-mantle or thickened lower crustal layer, and it is a kind of potassic adakite belonging to C-type adakite formed in intra-continental collisional belts. The rock combination of (quartz) orthophyre (syenite)+ (quartz) monzonite (ivernite)+granite porphyry is in the form of veins, which is limit to provide mineralizing materials, fluid and dynamic conditions. The superposition of A-,B- and D-veins spatially, unclear zonation, weak mineralization and overlapped Cu-Mo-Au and Pb-Zn mineralizations in north contact are combined to show no large-scale fluid exsolution. These factors may decide the size of deposit.