| The northern section of Helanshan, closed to Alashan metallogenic belt, is located in western margin of Erdos metallogenic (Fe、Pb、Zn) belt, and has experienced multi-tectonic events with widespread igneous rocks and strongly mineralization and alteration. Due to well precious and non-ferrous metal (mainly gold and copper) mineralization geological conditions, it has become one of three significant metallogenic belts of metal ores divided by Ningxia Hui Autonomous Region. Compared to other domestic metallogenic belt, the research level of geological background, metallogenic regularity and metallogenic mechanism of Helanshan metallogenic belt is still lower. Based on field geological survey, this thesis chooses Helanshan metallogenic belt as the research object, to study geological setting and geological conditions of gold and other metals’mineralization, summarize their mineralization law, establish prospecting model, determine the type of mineralization and prospecting indicators, and guide exploration work. The main results and conclusions are as follows:1. Igneous rocks in north section of Helanshan formed in Paleoproterozoic, including granites, diabase and pyroxenite. The granites are peraluminous, with A/CNK> 1.1 (1.16～1.29), low FeOt/MgO ratios (less than 10), high P2O5 (>0.2) and K2O (4.31-5.86), and petrographically riched in biotites, garnets and other minerals, indicating that they are S-type granites. These S-type granites are enriched in light rare earth elements (LREE), depleted in heavy rare earth elements (HREE), with strongly negative Eu/Eu* abnormality. Moreover, they are enriched in Rb, Th, U, K and Pb, depleted in Ba, Sr, P and Ti, with low contents of Nb and Ta. They show similar geochemical characteristics with Helanshan group in both REE and spider diagrams. Furthermore, Hf model ages (2.24-2.44Ga) of inherited zircons and Nd model ages (2.20-2.57Ga) from granite are consistent with Hf model ages (2.1-2.5Ga) of detrital zircons from Khondalite series in study area. All these suggest that these S-type granites could form via decompression partial melting of Helanshan group during the exhumation process after Erdos block collided with Yinshan block. Both diabase and pyroxenite belong to sub-alkaline basalt series, and show similiarity with OIB and primitive mantle respectively in REE and spider diagrams. They should form in extension background after the collision between Erdos block and Yinshan block.2. By comparation of REE characteristic between biotite plagioclase gneiss, leptynite, gold-bearing altered rocks and gold-bearing quartz veins, ore-forming materials of quartz veins were mainly from biotite plagioclase gneiss, and gold-bearing altered rocks were from complex sources. H-O isotopes, from mineralization related quartz fluid inclusions in Niutougou deposit, indicate that its ore-forming fluids were mixed hydrothermal fluids from magmatic and meteoric water. And S isotope suggests the sulfur in sulfides were mainly from deep magma source, or metamorphic fluid. Via the research of fluid inclusion, ore-forming fluids have the characteristics of low temperature and low salinity, and the depth of mineralization was about 5.5-8km, indicating they formed in superficial depth.3. The metallotectonic system in study area has a Trinity mode, Zhengyiguan-F1-bearing quartz veins, and could be divided into three stages. The first stage was rift basin formation stage (Late Carboniferous). With respect to Erdos block, the sinistral movement of Alashan block induced the sinistral strike-slip movement of NNE trending Bayanwulashan-Langshan fault. Then the north section of Helanshan formed a pull-apart basin along sinistral strike-slip Bayanwulashan-Langshan fault, resulted in the formation of basement fault. The second stage was regional squeezing thrust stage (Late Triassic). During this period, the movement of Alashan block changed its direction and started move to SE direction. Subject to Alashan NW-SE trending squeezing, the pull-apart basin reversed, resulted in formation of the current nappe structures, and the damage of early framework of the basin. Influenced by this event, the Zhengyiguan and F1 faults showed sinistral strike-slip movement, and induced a series of secondary structure. However, the secondary structures of F1 fault were not very developed in Beichagou-Liuhulugou and Damailigou regions, only with development of cleavage belt in old metamorphic rocks. The third stage was magmatic hydrothermal activity stage (Late Triassic-Early Jurassic). Regional tectonic regime changed and became into local extension under extrusion background, or conversion from compression to extension. The study area and neighbouring areas experienced strong tectonic thermal event, different levels of gold-bearing hydrothermal activity happened in F1 fault and its secondary structures, and squeezing foliated belt in Beichagou-Liuhulugou and Damailigou regions, resulted in formation of different types of deposit.4. The main mineralization centers in the northern section of Helanshan are distributed along F1 fault, and from the north east to south west were Beichagou-Laoyushugou, Haermuteng, Niutougou-Lianggen, all located in the north of Zhengyiguan fault. Deposits are mainly distributed in interior crystalline basement, and its contact site with sedimentary cover. Mineralization occurred mainly in the north Zhengyiguan fault, F1 fault and its supporting structure system (Shulonggou could be formed in the other structure system), in consistent with ore-controlling fault structure system. Different mineralization types in the study area are related with rock deformation properties within the range of stress, material composition of ore-forming fluid, physical and chemical conditions during fluid migration and precipitation, and wall rock lithology. Beichagou-Laoyushugou, Haermuteng, Niutougou-Lianggen are three big ore-forming fluid activity centers, their center to center spacing is about 5-7km, showing slightly equidistant distribution characteristics, which are related with simultaneous stress release from multiple centers when the block of rock influenced by the same gravitational field.5. Based on field field research, combined with geochemical analysis results and metallogenic regularity summary, this work delineates nine prospecting targets and prospective areas, including 4 gold prospecting targets,2 gold prospecting areas,2 lead and zinc prospecting areas, and 1 copper-nickel mine prospecting area. |
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