| The Queer Mountain granite rock mass lies in in Dege county,the northwest of sichuan province, and the study area is adjacent to the Tibet autonomous region, and its terrain is a typical mountain deep cutting area,showing general topographical features high in the northeast and low in the south west.The Queer Mountain rock intruded into the Permian and the Upper Triassic slate, sandstone within the triangular area of the junction of the Dege-Xiangcheng large fracture and the Ganzi-Litang deep fracture, and was covered by Paleogene System sedimentary rock unconformity, the rock mass output with the form of irregular complex batholith. Although predecessors have made much progress in the regional geological survey and research of the Queer Mountain rock mass, also have published related monographs and articles, through the field geological survey one this papers, lack of actual information, and data support in previous studies for the geology, structure and evolution history of rock intrusion region, and the main regional fractures’ extension, properties, geometry and kinematics characteristics, generation and evolution process,etc. Especially about the problem of the relationship between the Queer Mountain rock and mineralization, it is very weak.Because of that, this thesis selected the topic of the Queer Mountain rock lithology, rock geochemistry and its causes, with in-depth field geological investigation, systematic rock samples collection, test, and the microscopic identification, trying to have an anatomical study of the Queer Mountain rock, and deeply grasp rock types of the Queer Mountain rock mass and its macroscopic microscopic petrology characteristics and intrusion period.Especially through the study of the geochemical characteristics of rocks, analyze and judge the intrusion tectonic attribute of the Queer Mountain rock, and then discuss the mechanism of rock mass in place.Based on the contrast research of the Queer Mountain rock and other acidic rock mass in its adjacent area, intensively focus on the type, size and scale of the acidic pluton’s mineral deposits(spots) which is related to the study area, and do appropriate deposits, ore deposit geochemical studies, seeking the relevance between ore deposit and the rock mass, and then concluding mineralization specificity of rock mass, providing basic data for regional mineral resources related to the acid rock mass.In terms of the tectonic structure, the Queer Mountain rock mass is located in the Ganzi-Litang arc basin system secondary tectonic unit within the Qiangtang- Sanjiang orogenic system first-order tectonic units, affiliated to the Yidun-Shaluli island arc belt tertiary tectonic units. This island arc belt is also called Yidun island arc or Changtai-Xiangcheng island arc belt, with its east boundary in the Judelai-Dingqu, Mulong-Heihuijiang fracture and the Manigange-Labo fracture of the Ganzi-Litang ophiolitic melange belt, including Yidun-Baiyu-Xiangcheng-Daocheng and the Sanjiangkou area.Yidun-Shaluli island arc was conditioned by the Ganzi-Litang ocean subduction to the west on the basis of eastern Zhongzan plot passive continental margin in the early and middle of the late Triassic. Yidun- Shaluli island arc belt has larger scale of plutonic magma activity, constituting a very eye-catching magmatic arc belt, and can be divided into two sub-belts.The intrusive magmatic activity times of the east sub-belt is 237.5-208.0 Ma, emplacing and forming different late Triassic island arc volcanic rock phases in the same period, the main rock types are primary for medium-coarse grain porphyritic monzonitic granite, secondary for granodiorite, and a small amount of diorite, diorite porphyrite, granite porphyry, etc., from early till late the rock is diorite, granodiorite, adamellite granite, granite,granite porphyry, i.e. to the direction of higher acid-alkali quality and increased in sodium, potassium ratio. Especially partial monzonitic diorite porphyrite- granite porphyry small rock mass(ages 208-235 ma)in the southern part of the east sub-belt had controlled the formation of porphyry copper deposits, such as the Prang large porphyry copper mine, the Xuejiping medium-sized porphyry copper deposits, etc.The late collision orogenic period granite age was 208-138 ma, the main rock types are two-mica granite and K-feldspar granite, secondary for monzonitic granite and monzodiorite, superimposed on the subduction granite belt, mainly developed in the northern section of island arc belt,providing geological structure conditions for metallogenic region of non-ferrous and precious metals in southwestern Sanjiang middle north belt.The Queer Mountain rock mass is formed under this tectonic setting.In this paper,strata in the study area belong to Dege- Zhongdian(Shangri-La) Stratigraphic area of Balyanlkalla stratigraphic area within the Qiangtang- Sanjiang stratigraphic region. Exposured strata near the rock mass are basically the late Triassic Tumugou formation(T3t), Lamaya formation(T3lm) and quaternary sediments.The exposed rock types of the Queer Mountain granite rock, basically have porphyaceous biotite monzonitic granite, porphyaceous monzonitic granite, medium grained monzonitic granite, biotite granite, white mica granite, two-mica granite, quartz diorite, K-feldspar granite.With the main, trace and rare earth elements test of the rock mass, it is found that SiO2 content generally ranges from 63.29% to 79.16%, Al2O3 content changes between 10.50%- 15.21%.According to the relational graph between SiO2 and main elements oxide(Al2O3、CaO、Na2O、K2O、TiO2,etc.),diorite samples belong to high potassium calc-alkaline series, other granite samples fall in between high potassium calc-alkaline series and shoshonite series. In the level of trace element,there is a overall distribution patterns of trace elements similar to that of the original mantle standardization, rocks loss large ion lithophile elements Ba, Sr, P, Ti,while relatively enriched in the incompatible element Rb, Th, U, K, Hf. Coupled with Nb*、K*、Sr*、Zr* value,it is infered that the Queer mountain granite is the result of the tectonic background which the Queer mountain granite collided with the arc. The rare earth elements, Σ REE changes between 110.407 and 409.238, with a mean of 236.956; LREE changes between 82.798 and 378.822, with a mean of 211.268; HREE ranges from 13.232 to 39.831,with a mean of 25.688. LREE/HREE ranges from 2.621 to 18.893,with a mean of 8.505.(La/Yb) N ratios are all greater than 1;The δEu are all less than 1,negative anomaly; δCe is approximate to 1, no obvious abnormality, indicating that the Queer mountain rock is acid rock and enriches in alkaline, which should belongs to the typical crust remelting “S” type granite. According to the spider diagram of rare earth, trace elements the tectonic environment discrimination diagram of main elements, it also shows that the Queer Mountain granite batholith emplacement mechanism lies in the volcanic arc- syn-collision tectonic environment.The isotopic age of the rock formation is 102.23±0.91 Ma.The Queer mountain rock mass unit,mainly constituted by monzonitic granite, K-feldspar granite,is associated with rare earth mine.The unit, constituted by K-feldspar granite or by alkali-feldspar granite with K2 O > Na2 O, is associated with tungsten, tin, molybdenum, bismuth, and beryllium. The unit constituted by alkali-feldspar granite with Na2 O > K2 O is associated with Nb and Ta mineralization. The unit mainly constituted by biotite granite is related to rare earths, tungsten, tin. The unit mainly constituted by two mica granite relates to tungsten, tin, molybdenum, bismuth, beryllium. The unit mainly constituted by white mica granite is related to the mineralization of Be, Nb, Li, Ta, Rb etc.The main wall rock alteration types in this thesis are: potassium feldspathization'sodium feldspathization'greisenization' hornfelzation. In the researcher’s opinion, it is possible for us to looking for skarn, hornfels and greisen type deposits of the above mine types in the Queer Mountain granite batholiths and its surrounding rock contact belt. |
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