Contrast Study On The Hadamengou Gold Deposit And Jinchangouliang Gold Deposit, Inner Mongolia

Northern margin of North China Craton is located at the convergence of North China Craton and central Asian orogenic belt, which is characterized by perfectly developed early precambrian strata, complex geological structures, frequent magmatic activities, rich gold ore resources and lots of gold deposits, has good mineral-forming condition and great prospection potential, thus formd an important gold metallogenic belt in China, In which Hadamengou gold deposit and Jinchanggouliang gold deposit are very typical large gold deposits. Based on the previous results, combining field geological investigation and laboratory study, in this paper, we gave a detailed analysis on the two typical gold deposits, preliminary identified regional ore-forming geological background, geological features of deposits, source and evolution of ore-forming fluid and ore-forming material source, determined metallogenic epoch, illustrated ore-forming mechanism. Further synthetically analyzing regional metallogenic geological setting, ore-control factors and metallogenic law by contrasting study on the two deposits, discussing on the relationship of regional tectonics setting, magmatism evolution and gold metallogeny, deepening cognition on gold mineralization law in the northern margin of North China Craton, enriching metallogenic theory and providing guidance for regional prospecting.Hadamengou large gold deposit in Inner Mongolia is one of the important deposit, located in southern margin of Wulashan anticlinorium of Yinshan uplift(west part of the Inner Mongolian earth axis) on the north margin of North China Craton. The gold orebodies mainly lies in the metamorphic rock of Wulashan Group, Archaeozoic erathem., main ore type include gold-bearing quartz vein type, gold-bearing quartz-potassic feldspar vein type, gold-bearing altered rock type. In the gold mineralization district, zircon SHRIMP U-Pb age of the Dahuabei granite is 353±7Ma, Early Hercynian. Zircon SHRIMP U-Pb weighted average age of the Shadegai granite is 221.6±2.1Ma, zircon LA-ICP MS U-Pb weighted average age of Xishadegai granite is 222.9±0.82Ma, both were formed in the Indosinian. Lithogeochemical characteristics show that those granites are characterized by high silicon, alkali-rich, weakly peraluminous. In the Rb-(Y+Nb)diagram and R1-R2 diagram, the geochemical data of Dahuabei Intrusive rock plotted into syn-collision and post-collision range, the geochemical data of Shadegai Intrusive rock plotted into post-oro genic range, ore-forming fluid is characterized by intermediate-low temperature (160～300℃), mid-low salinity (5%～15% NaCleq).The gas component of fluid inclusions is dominated by H2O and CO2, The main anions in the liquid composition are Cl- and SO42-, and the cations are Na+, K+ and Ca2+.The sulfur isotope composition of the oreδ34S vary from -21.7‰to 5.4‰, the change range is 27.1‰, average value is -10.6‰, depleted 34S, indicated the sources of ore-forming material are complexity, sulfur isotope composition inherited archean strata, mixed with sulfur in deep-sourced ore-bearing Fluid. Lead isotopic compositions of the ore, single-stage model age, Th/U ratios,μvalue vary in a large range, indicated multiple sources characteristics. In plumbotectonic model diagram by Zartman and Doe, the lead isotopic compositions of ore mineral plotted scattered, this demonstrates that the ore lead came from the mixed lead. Hydrogen and oxygen isotopes show that the ore-forming fluid was derived from magmatic and small metamorphic water, Late mixed with meteoric water, molybdenite Re-Os weighted mean age is (386.4±2.7)Ma and isochron age is (386.6±6.1)Ma of the orestone, which show the main metallogenic epoch is early devonian, later multi-phase hydrothermal activity probably superimposed on the early stages. The deposit formed in intracontinental extensional tectonic setting after arc-continental collision.Jinchanggouliang gold deposit in Inner Mongolia is another important deposit, located in Nuluerhushan uplift belt of mid-east part of Yinshan-Yanshan uplift(the Inner Mongolian earth axis) on the northern margin of North China Craton. The ore bodies are mainly hold within the the metamorphic rock of Xiaotazhigou Formation of Neoarchean Jianping group. The main type of ore include sulfide type, sulfide-rich quartz vein type and sulfide-rich altered rock type. In the gold mineralization district, the zircon LA-ICP MS U-Pb weighted mean age of Jinchanggouliang gneissic granite is 258.6±1.6Ma-261.61±0.94Ma, mid-late permian. The zircon LA-ICP MS U-Pb weighted mean age of Xitaizi porphyraceous biotite admellite is 226.8±0.87Ma, middle-late triassic. The zircon LA-ICP MS U-Pb weighted mean age of Duimiangou porphyraceous granodiorite is 140.86±0.71Ma～142.65±0.44Ma and weighted mean age of fine grained granodiorite 138.7±1.2Ma, early cretaceous. The major elements, trace elements, rare earth elements and Neodymium-Strontium-Lead isotope composition of these Intrusive rocks are similar, their zircon U-Pb isotope ages displayed inherited zircon age features, which indicated that these intrusive rocks had some correlations in metarial source. In the Rb-(Y+Nb)diagram and R1-R2 diagram, the geochemical data of Jinchanggouliang gneissic adamellite plotted into syn-collision and post-collision transitional environment, the geochemical data of Xitaizi porphyraceous biotite admellite, Duimiangou porphyraceous granodiorite and fine grained granodiorite plotted into post-orogenic stage extensional environment. Ore-forming fluid is characterized by medium-high temperature (190-380℃), low salinity(0.18～8.81 wt%NaCleq). The gas component of fluid inclusions is dominated by H2O and CO2, The main anions in the liquid composition are Cl-and SO42-, and the cations are Na+, K+ and Ca2+. The sulfur isotope composition of the oreδ34S vary from-2.8‰to-0.6‰, the change range is 2.2‰, average value is-1.61‰, similar to the sulfur isotope composition of ores in the Changgaogou and Erdao gold deposit, the averageδ34S values are all concentrated near 0 value, indicating that the magmatic sulfur source is dominant. A series of parameters such as Lead isotopic compositions of the ore, single-stage model age, Th/U ratios, p. values etc. are similar in Jinchanggouliang gold deposit, Erdaogou gold deposit and Changgaogou gold deposit, parameters variable range are very small. In plumbotectonic model diagram by Zartman and Doe, the lead isotopic compositions of ore mineral plotted between upper mantle curve and lowercrust curve, near the upper mantle curve, this indicated that source of Pb main derived from mantle and lowercrust, simultaneously a little orogenic belt Pb mixed. Hydrogen and oxygen isotopes show that the ore-forming fluid was mainly derived from magmatic water, Late mixed with some meteoric water. The zircon LA-ICP MS U-Pb weighted mean age of the biotite trachyandesite porphyry dyke is 258.6±1.6Ma～261.61±0.94Ma, which is mutual interpenetrated with Jinchanggouliang gold ore veins, thus the age basically constrained Jinchanggouliang gold metallogenic age. Duimiangou copper-molybdenum mineralization area, Molybdenite Re-Os weighted mean age is 131.45±0.93Ma, essentially consistent with Jinchanggouliang gold ore-forming age. molybdenum mineralization quartz veins in the deep position of western mining area of Jinchanggouliang gold deposit, Molybdenite Re-Os weighted mean age is 243.5±1.3Ma and isochron age 244.7±2.5Ma, show that existing triassic molybdenum mineralization in this area. The Early Cretaceous was a period of intensive intracontinental rifting, crustal stretching and lithospheric thinning in Eastern China and adjacent areas. By regional contrast, Jinchanggouliang gold deposit formed in lithosphere extension-thinning tectonic setting.By comparative study, the mineralization of Hadamengou gold deposit is main related to deep-seated faults which undergone multistage activities, in the northern margin of North China Craton. Ore-forming materials partly come from metamorphic rocks of Archean Wulashan group and mainly from deep potassium-bearing magmatic hydrothermal fluid. Jinchanggouliang gold metallogeny main related to the lithosphere thinning in eastern China, metallogenic materials originated from ore-bearing magmatic hydrothermal fluid of Duimiangou intrusive rocks. Both deposits hosted in high grade metamorphic rocks of northern margin of North China Craton, but their mineralization mechanism are different.on the basis of geological setting of ore-forming processes, geological characteristic and ore-controlling factors, deduced that prospecting potential is tremendous in deep and peripheral area of the two typical deposits, In Hadamengou gold deposit area, gold prospecting not limited the deep of exited orebodies, there is a great prospecting potential in the north and east of the Hadamengou gold mineralization area. Potassic alteration, sillcification alteration, pyrite and other alteration, pegmatite veins, intermediate-acid intrusive rocks, geochemical anomalies, sub-regional deep fault rupture is an important prospecting symbols. In the Jinchanggouliang gold mineralization area, gold prospecting should surround the Duimiangou intrusive rocks. At present, there had found a series of gold-molybdenimum deposit(occurences) in the east of Duimiangou intrusive rocks such as Jinchanggouliang, Erdaogou, Changgaogou gold deposits, Duimiangou copper-molybdenum deposit and other gold occurrences, but not found in the west of Duimiangou intrusive rocks. Therefore, the west of Duimiangou plutons is a potential area for gold-molybdenum porospecting. Regional prospecting should pay attention to Archean metamorphic bedrocks outcrop area, regional tectonic uplift belts such as Nuluerhushan uplift belt, Kalaqinqi uplift belt and Mingshan uplift beli etc., intermediate-acid dykes and intermediate-acid intrusive rocks distribution extensively, geochemical anomalies and intense tectonic active area.