Type Classification and Qinghai Example Analysis of Orefield Structure and Magma-thermodynamic Structure

Based on a lot of orogenic belts and basin orefields in the western and middle parts of China,the characteristics of thermal action and thermal structure are extensive and special.Magma-thermodynamic structure is a series of thermal structure formed in magma body or wall rock stratum or the area influenced by remote thermal action,and connected with magmatic intrusions or volcanic eruption by controlling of magma-thermal action.Based on the concepts and type classification of orefield,orefield geology and orefield structure,the scheme for type classification of orefield structure and magma-thermodynamic structure were studied.According to the main controlled action formed by the structure in the epoch of mineralization,orefield structure was divided into stress,thermodynamic,gravity and combined transformed structures.According to the controlling effect of orefield magma-thermodynamic action on the mineralization depth,tectonic environment and metallogenic type,orefield magma-thermodynamic structure was divided into 5categories and 24 sub categories.The 5categories include:1the near-surface sedimentary exhalative-geothermal anomaly cluster type; 2 hydrothermal type; 3 magma intrusion-porphyry-skarn-ductile shear-thermal dome type;4 magma conduit-small rock body deposit-crust mantle mixed metallogenic type;5mantle plume type.These different depths of magma-thermodynamic structure actions form different types of deposits;under the action of crust mantle magma-thermodynamic structure,the important mineralization types and super large-scale ore deposits are usually formed.The magma-thermodynamic structure including salt dome,magma diapers thermal dome,geothermal abnormal,crust mantle plume were analyzed in brief.Jingren-Hutouyapolymetallic orefield of Qimantage metallogenic belt of Qinghai,the western China was taken as an example.According to the theory of orefield geology,based on orefield formation and structure-lithofacies geological mapping,the characteristics of magmahydrothermal structure in the mine are porphyry+skarn+hydrothermal controlled by faults.The results show that Late Triassic magma intrusions are the main internal factors of large-scale polymetallic mineralization;the magmatic intrusion and carbonate rock contact zones in different stages form the skarn deposit;Indosinian magmatic intrusions,porphyry,skarn,multigroup faulted fracture zones and hydrothermal alterations belts develop nearly in the same place with the mineralization enrichment center;the ore-controlling effects of faults in different directions are not the same,and the near-EW and NWW faults are obvious;metallogenetic potentiality in the middle and deep parts of orefield is great.