| Located on the northeastern margin of the Tibetan Plateau,the North Qaidam is adjacent to the Qaidam block and the Qilian orogenic belt,which is a typical composite orogenic belt,including the Caledonian orogenic,the Hercynian-Indosinian collisional orogenic,and the Meso-Cenozoic intracontinental or intraplate evolution,with obvious muti-phase complex metallogenic system assemblage and evolution sequence.The metallogenic belt of the North Qaidam is rich in endogenous metal resources,with a concentrated of iron,copper,gold,lead,zinc and other important metal,such as the famous Tanjianshan gold deposit,Xitieshan lead-zinc deposit.With obvious mineralization bodies,structures and markers,the North Qaidam is provided with excellent metallogenic geological conditions.Although the research on the tectonic evolution of the North Qaidam is relatively deep,there is still a lack of attention on the inner relationship between tectonic evolution and mineralization,and insufficient research on the classification,evolution and superimposition of the metallogenic system,as a result,the theory of metallogenic system to guide regional ore prospecting rarely,without effective prospecting prediction.This thesis takes the Changzhenggou-Hongqigou mineral concentration as the research area,which in Saishiteng Mountain in the western of the North Qaidam,and takes the iron-copper-gold-zinc polymetallic ore to analyze the key issues related to the characteristics of metallogenic system and the typical deposits.Core of magma-tectonic evolution,guided by metallogenic systems,summarize the classification and evolution of the metallogenic system in the North Qaidam,and carry out ore prospecting according to the integrated method of the metallogenic body,structure,and markers.The main achievements and innovations have been gained as follows:(1)According to the regional magmatic-tectonic evolution and mineralization,divided the North Qaidam into three metallogenic systems and six subsystems,with obvious metallogenic evolution sequences.Although the Caledonian-Indosinian basic geology and tectonic evolution of the North Qaidam has been studied in depth,but there was little attention on metallogenic systems.Guided by the theory of metallogenic systems and according to the magmatic and tectonic evolution,the North Qaidam can be divided into three metallogenic systems: the Caledonian subduction and collision metallogenic system related to volcanism and magmatic intrusion,the Hercynian postcollision and extension metallogenic system related to magmatic intrusion,and the Indosinian intraplate orogeny metallogenic system related to magmatic activity.Further,combined with the tectonic,mineralization and deposit assemblage,it is divided into 6 metallogenic subsystems: the early-middle Caledonian oceanic-continental subduction metallogenic subsystem related to marine volcanic eruptive deposition and magmatic intrusion,the late Caledonian continent-continent collision metallogenic subsystem related to magmatism and shear,the early Hercynian deep subduction and collision metallogenic subsystem related to magmatism and shear,the middle Hercynian metallogenic subsystem related to magmatic intrusion,the late Hercynian metallogenic subsystem related to magmatism,and the Indosinian intracontinental orogeny metallogenic subsystem related to magmatic and shear.The metallogenic subsystems can be formed independently,and the late metallogenic subsystems can also be superimposed on the early ones,forming a multi-phase composite superimposed reworked metallogenic system.The skarn iron-copper-gold-zinc deposits in the Changzhenggou-Hongqigou mineral concentration area can be considered as a subsystem of the early-middle Caledonian oceanic-continental subduction metallogenic system related to marine volcanic eruptive deposition and magmatic intrusion,Kuangou-Hongqigou ductile shear zone copper-gold deposit as a superimposed transformation of the late Caledonian and the early Hercynian metallogenic system.(2)The Cambrian-Ordovician Tanjianshan Group volcanic sedimentary rocks related to the Caledonian metallogenic system in the mineral concentration area is an important ore source layer,and is the product of different evolutionary stages of ocean-continent subduction and collision.As an important ore source,the quite different understandings of Tanjianshan Group formation environment were due to the difference in the outcrop location and rock assemblage.The multi-layered carbonate rocks in the Tanjianshan Group are extremely important for the formation of skarn-type iron-polymetallic deposits during the intrusion ofmedium-acid rocks,so we are very concerned about it.The volcanic rocks in our research area are composed of basalt-andesite and dacite-rhyolite series,with high alumina and are calc-alkaline tholeiitic series.The Basalt may be formed by partial melting of the protolith form enriched mantle,contamination of the crust with Nb and Ta negative anomaly.The basalts of the Tanjianshan Group are distributed from mid-ocean ridges,oceanic islands,continents and orogenic belts in the tectonic discrimination diagram,indicating that the tectonic environment is complex,and records the different process of early Paleozoic mid ocean ridge expansion to ocean-continent subduction and collision,in which iron-copper-gold and other metallogenic elements are pre-enriched,are favorable sources for the later reformation copper-gold deposits.(3)The Ordovician Saishitengshan pluton,which is related to the Caledonian metallogenic system in the mineral concentration area,is an important source rock and was formed in the oceanic subduction island arc environment.The formation environment and diagenetic age of the Saishitengshan pluton related to mineralization in the Changzhenggou-Hongqigou mineral concentration area have not been studied before.The pluton is mainly composed of diorite,granodiorite,monzogranite,and a small amount of gabbro and tonalite.Geochemistry shows that the pluton is calc-alkaline meta-aluminous,enriched in large ion lithophile elements(LILE)K,Rb,Ba,Sr,and relatively enriched in high field strength elements(HFSE)Th,Pb,Zr,Hf,depletion in Nb,Ti,with obvious negative anomalies of Nb,Ce,Pr,Ti.The newly obtained Saishitengshan quartz diorite and granodiorite age are 444.0±2.5Ma and 446.3±2.4Ma respectively with zircon U-Pb dating.Combined with previous research,it is believed that the age of the Saishitengshan pluton is 443-470 Ma,in the middle and late Ordovician period,it belongs to the I type granite,and Caledonian island arc.(4)The Changzhenggou-Hongqigou mineral concentration area is divided into two metallogenic subsystems.Due to the harsh physical geography,the geology and minerals research in the Changzhenggou-Hongqigou mineral concentration area is less.The Changzhenggou iron-copper-gold-zinc deposit what we have discovered is mainly related to the magmatic activities with ocean subduction in the middle Caledonian,and the Kuangou-Hongqigou copper-gold deposit related to collision orogeny in the late Caledonian-early Hercynian.Guided by the theory of metallogenic systems,according to the regional tectonic evolution,mineralization buildup and deposit assemblage,the Changzhenggou-Hongqigou mineral concentration area is divided into the middle Caledonian iron-copper-gold-zinc metallogenic subsystem related to intermediate-acidity magma intrusion,and the late Caledonian-early Hercynian copper-gold metallogenic subsystem related to superimposed transformation,with obvious assemble and evolution sequence.(5)The middle Caledonian metallogenic subsystem related to intermediate-acidity magma intrusion in the Changzhenggou-Hongqigou mineral concentration area are mainly skarn-type iron-copper-gold-zinc deposits,and the late Caledonian-early Hercynian superimposed transformation metallogenic subsystem are mainly ductile shear zone copper-gold deposit.The deposits newly discovered in the mineral concentration area include the North Heishanquan iron-copper deposit(K1),the East Zangyanggou iron deposit(K3),the Gobi Desert blind iron deposit(K2),and the Changzhenggou-Zangyanggou copper-zinc deposits(K4),the East Kuangou iron deposit(K5)and so on,The main intrusive related the iron-copper-gold-zinc deposit is medium-acidic rocks interspersed with a small amount of basic rocks.The wall rocks are volcanic sediment assemblage bearing carbonate in Cambrian-Ordovician Tanjianshan Group;the ore-controlling structure are NW trend brittle-ductile faults,the metallogenic markers of skarnization and lenticular ore bodies are distributed near the fault zone.According to the above geological characteristics,it is determined as skarn deposits,and the metallogenic age is close to the age of the related intrusive rocks(444-446 Ma),which was the Middle Caledonian.The Hongdenggou(K6)and Tuanjiegou(K7)copper-gold deposit discovered in the mineral concentration area,copper-gold mineralization are closely related to the North Qaidam subduction-collision orogeny,the gold ore bodies are hosted in quartz veins or alteredrocks in the brittle-ductile shear zone of greenschist facies in the Tanjianshan Group,inheriting the substance formed by the skarn in the Middle Caledonian,and accompanied by strong pyrite sericite.According to the above characteristics,it is determined as ductile shear zone copper-gold deposit.Slightly later than Caledonian peak metamorphism(426-413Ma),and the gold metallogenic age is inferred to be late Caledonian-early Hercynian,and superimposed the products of the Middle Caledonian metallogenic subsystem.(6)Applied the theory of prospecting in the exploration area,metallogenic and geological model for prospecting of typical deposit in the mineral concentration area were constructed,and prospecting predictions.Due to less research on geology,minerals and the metallogenic prospecting prediction model in the mineral concentration area,with the theory of metallogenic system,skarn iron-copper-gold-zinc deposit and ductile shear zone copper-gold deposit superimposed metallogenic and prospecting geological model for prospecting were constructed for the Changzhenggou-Hongqigou mineral concentration area.Integrated with multi-information abnormal,such as geological,geophysical,geochemical,remote sensing,it is delineated the prospecting seven target area,include(1)Heishanquan skarn iron-copper-gold polymetallic target(B1),(2)Changzhenggou skarn iron target(B2),(3)Changzhenggou skarn iron target(A1),(4)Hongdenggou ductile shear zone copper-gold target(B3),(5)Tuanjiegou ductile shear zone copper-gold target(B4),(6)South Hongdenggou iron target(B5),(7)Changzhenggou ductile shear zone gold target(C1),which been proved good by engineering,the theory is significant for prospecting prediction.Innovation:(1)The North Qaidam is divided into 3 metallogenic systems and 6 subsystems.Base on above,highlight on the analysis of the metallogenic subsystems related to the mid-caledonian intermediate-acid magma intrusion and the late Caledonian-early Hercynian superimposed reformation in the Changzhenggou-Hongqigou ore concentration area.(2)Applied metallogenic system and prospecting prediction theory,prospecting prediction geological model for skarn iron-polymetallic and ductile shear zone copper-gold deposits in the Changzhenggou-Hongqigou mineral concentration area were constructed. |
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