| Dasuoerzhugou region is located at the junction of the Xing’an block and the Songnen block in the northern Geat Xing’an Range, the west of the Nenjiang fauit zone and the north of the Nenjiang-heihe suture zone,which is one of the important component areas in the copper and molybdenum polymetallic mineralization belt, Northeast of Mesozoic volcanic-intrusive rock belt in the Geat Xing’an Range. Mesozoic tectonomagmatic activities is strong in the region,which is the ideal location for the study of magmatic evolution and diagenesis dynamics. Research have shown that the polymetallic deposits in the region are mostly related with the Mesozoic magmatic activity,or magmatism,closely related to post-magmatic hydrothermal activity. There is a closely temporal-spital-genetic relationship between mineralization and magmatism. In this study, we focus on the volcanic-intrusive rocks in the Dasuoerzhugou area, the northern Great Xing’an Range. Based on systematic study of field geology, petrographic, geochemical,Zircon U-Pb geochronology and Sr-Nd-Hf isotope geochemistry methods,combined with regional tectonic setting and research results about diagenesis and metallogenesis in the Great Xing’an Range, in-depth study of the diagenetic age, geochemical characteristics, the nature of the source, dynamic process and tectonic setting,to discussion on the relationship between magmatic evolution process and metallogenesis.Furthermore,combined with the geologic, remote sensing, geochemical,and other information, through comparative research of the regional metallogenic, we summary and analysis the temporal-spital-genetic relationship between mineralization, alteration and volcanic-intrusive rocks, to objective evaluation the prospecting potential. The main results and conclusions are summarized as follows:(1) The magmatic rocks of the study area is mainly Xieniqishan granite body, Liujianfang granite body and Manketouebo group middle-acidic volcanic rocks. According to measured geological sections and petrology and mineralogical characteristics, Xieniqishan granite body is divided into three facies, fine-grained biotite plagiogranite of the central phase, fine-grained biotite monzogranite of transition phase(main phase) transition phase, and of fine-grained granite diorite of edge phase (rare); Liujianfang granite body is divided into two facies, coarse-grained monzogranite of the central phase and coarse-grained syenite (alkali feldspar) granite of the edge phase; Manketouebo group volcanic rocks is divided into two zones:the andesitic and dacitic volcanic rocks (mainly lava) and dacitic and rhyolitic volcanic rocks (mainly pyroclastic rocks). (2) Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Liujianfang granite gave a206Pb/238U age of171.9±0.9Ma, the Xieniqishan granite yielded a mean of161.0±1.6Ma,and the Manketouebo group middle-acidic volcanic lave yielded a weighted mean age of160.0±1.7Ma, implying their Middle-Late Jurassic magmatism. These results provide a precise age constraint on Mesozoic magmatism in the Dasuoerzhugou area.(3) Xieniqishan granite and Liujianfang granite central phase rock has a consistent A/CNK values (almost all less than1.10), which are characterized by silicate-rich and alkali-rich, high potassium, and low iron, magnesium, calcium, titanium and phosphorus. The rocks are enriched in LREE and relatively depleted in HREE, significant fractionation between LREE and HREE and relatively flat HREE, and with the medium-weak negative Eu anomaly. Varying degrees of enrichment of Rb, Th, U, K and Pb, the loss of Ba, Sr., Ti, Pi and high field strength elements (HFSE) Nb and Ta and siderophile of Cr and Co., V content lower. Rock major and trace elements geochemical characteristics are similarto the Jurassic highly fractionated I-type granites in Northeast China, and appear as highly fractionated I-type granite. The major and trace element chemical composition in the Manketouebo Fomation volcanic rocks are slightly different in various rock phase, but overall have similar geochemical characteristics to the intrusive rocks, which are characterized by high full-alkali content, sub-alkaline, metaluminous or peraluminum, belonging to K calc-alkaline rock series, relatively rich in silicon, alkali-rich, high potassium, poor in calcium, magnesium, iron. Except rhyolite volcanic rocks,they are different degrees of enrichment in large ion lithophile elements (LILE) Rb, Ba, K and Pb, depleted in high field strength elements (HFSE) of Nb, Ta, P and Ti, at the same time, the basic compatibility components siderophile (Cr, Co and Ni) content is also low, indicating that magma differentiation and evolution of high degree, but relatively lower than the instrusion.(4)Xieniqishan granite, Liujianfang granite and Manketouebo group middle-acidic volcanic rocks zircon and whole rock major and trace elements characteristic and Sr-Nd-Hf isotope composition are similar in the trends of variation and the evolution, showed that they likely originate from the same or similar magmatic source. Agreed with a lower Sr isotope initial ratio ISr(0.70422～0.70843), positive eNd(t) values (-0.3to2.3, the generally positive) and relatively young two-stage Nd model age with T2DM(Nd)(758～982Ma), which were less than1000Ma.εHf(t) values are characterized by small variation range, more concentrated and consistent positive (4.0to9.9) and the young two-stage Hf model age of T2DM(Hf)(574～959Ma). Agreed with zircon Hf isotopes and Sr-Nd isotopes composition, combined with the characteristics of major and trace elements, indicating that the magmatic rocks of the district is derived from Neoproterozoic and Phanerozoic mantle-derived basaltic magma underplating added to the lower crust,and the formation of juvenile crust and pre-existing ancient crust mixed with partial melting in the source region, and experienced varying degrees fractional crystallization of rock-forming minerals and accessory. A simple simulating calculation of Sr-Nd isotope indicates that the juvenile crustal material contribution ratio of60%to80%. (5) The major elements R1-R2cation diagrams and trace elements Rb-Y+Nb and Nb-Y diagram shows most of the magmatic rocks of the district is located in the ransition region between syn-collision and post-orogenic. These magmatic rocks are similar to the same period magmatic rocks in the Geat Xing’an Range with the contemporary tectonic setting,which are formed in the process of transformation from late stage of the continent-continent collision orogeny in the both sides of the Mongolia-Okhotsk ocean to post-orogenic extensional stage.(6) Regional metallogenic Geological Correlation analysis showed that the characteristics of the stratigraphic and magmatic rocks are similar to the Late Jurassic porphyry copper-molybdenum and epithermal Pb-Zn deposit and the mineralization point of adjacent areas., which developed old metamorphic or volcanic-sedimentary strata, Mesozoic Yanshanian, especially Jurassic acidic volcanic-intrusive complex and the subsequent intrusion of acidic porphyry dykes, with good metallogenic geological conditions. And the geological and geochemical characteristics of the magmatic rocks in the area are similar to the mineralization-related instruction in the region, and also have the same or similar diagenetic age and tectonic setting. Furthermore, the magmatic rocks of the area, especially the Manketouebo group volcaniclastic rocks are relatively enriched in ore-forming elements such as Pb, Zn and high the variation coefficient, generally with Mo geochemical anomalies. Agreed that the study area good exploration potential for looking for volcanic-related epithermal Pb and Zn deposits and Mo polymetallic mine closely related to porphyry deposits. The local geology (especially information of alteration and mineralization), Geochemical Exploration information and remote sensing abnormalities information, show a good correlation between alteration, mineralization, geochemical anomalies and remote sensing anomalies. A closely temporal-spital-genetic relationship between the three aspect also show a good exploration potential of this area.(7) Geochemical anomalies, line and loop structure and alteration phenomenon constitutes a major prospecting clues in the study area. The elements of Mo, Pb, Zn constitutes indicator elements of mineralization abnormalities in the region. Combined with the geological background of the study area, this paper preliminary suggest the site of the strong silicification, pyritization, and greisen rock(including mineralized quartz vein and mafic dikes),the site of the strong silicification and pyritization near the contact zone between the biotite monzogranite biotite granite pluton and wall rock Manketouebozu group volcanic J3m, the site development of strong silicification, pyritization in Manketouebo group volcaniclastic rocks, the parts of fracture-intensive activities and near the volcanic edifice are favorable position for mineralization. Pay attention to these favorable alteration and mineralization site will be helpful for finding porphyry copper molybdenum ore related to the Mesozoic intracontinental volcanic-intrusive complex rocks and magmatic epithermal lead and zinc deposit. Based on the above study, the paper finally points out four important favorable areas for mineralization. |
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