| Erligou gold deposit lies in the Daduhe gold metallogenic belt. On the tectonic location, Erligou gold deposit is located in the west of Yangtze ancient continental plate and in the north west of the Yangtze Block. Meanwhile, it is located in the north of kangding complex which is in the north of NS direction kangdian fault block. On the northwest of it, there is Songpan-Garze tectonic belt. On the south of it, there are Shimian rock mass and Mianning rock mass in the middle of Kangdian fault block. The host rocks are carbonaceous slate and siliceous slate in the Lower Devonian Weiguan Group the First rock group(Dwg1),which color is between black and dark grey.The main metallogenic types of Erligou gold deposit is sulphide-quartz vein type and a few of metallogenic types are altered rock type. Gold-bearing sulphide-quartz vein, with nearly NS-trending output and tendency of 263° ~310°and 52° ~73°angle, are mainly originated from black and dark grey carbonaceous slate and sericite phyllite The ore-controlling condition is simple. Generally, the main ore-controlling geological factors are joint fissures and the prime structures are F1 compressional fracture zone and the “X” conjugate joints.According to the analysis of the quartz-vein type gold mineral elements, the gangue minerals account for more than 95 percent of all minerals with quartz > 80%, mica 5~10%, and less of the content of minerals like calcite, chlorite, zoisite and sphene, while the metal minerals content is about 1 percent to 5 percent. Primary minerals are given priority to pyrites, and contents of galena, sphalerite, chalcopyrite, magnetite,siderite, natural gold, electrum and telluride are small, while the secondary minerals are goethite, lepidocrocite and Limonite. The partical sizes of the pyrite are between 0.03~0.5mm, and the numbers of cubic and pyritohedral pyrites are large. These granular, disseminated and veinlet pyrites distribute in the orebody. The gold content of ore are mainly natural gold. The conditions of gold-bearing are microscopic gold, and a few conditions are obvious gold and extra-micro gold. Irregular granular natural gold is closely related to pyrites and is often setting in the cracks. The main textures of orebody are xenomorphic-automorphic granular texture, pressure texture and metasomatic relict texture, and the minority textures are pseudoeutectic texture, filling texture, mosaic texture and metasomatic dissolution texture. The main structure of orebody are massive structure, and the minority structures are reticular structure, brecciated structure and disseminated structure, and very tiny star-like structure, spotted structure, nodular structure and miarolitic structure partly. The prime wall rock alterations are pyritization and silicification, and the minority wall rock alterations are sericitization, chloritization and carbonatation.Results testing pyrites’ S-isotope contents in Erligou gold deposit show that the composition of S-isotope is uniform and the range of variation is narrow which δ34S value is between-5‰~4.6‰ and the average mean is about 2.36‰. In addition to individual S-isotope value of pyrites in carbonaceous slate, the rest are positive and change range is very small, between 3.3‰~4.6‰, which indicate that the source of sulfur is uniform and has the feature of mantle source of sulfur in Erligou gold deposit. Pyrites which lie in black carbonaceous slates are relatively lack of heavy S-isotope δ34S value. The rest of pyrites accompanying quartz, compared with the standard of meteorite pyrites, are relatively rich of heavy S-isotope δ34S value. Because the main sulfur-bearing minerals are pyrites, therefore, sulfide S-isotope composition range and average can basically represent the S-isotopic composition of ore-forming fluid.Chemical analysis of rock dikes close companion in the ditch mining and ore bodies shows that the mining area exposed magmatic there are two types, one for the ultrabasic rocks, one for basic rocks. Which ultrabasic dikes test sample based on microscopic features combine named pyroxene peridotite, according to the sample Rittmann A δ = 0.38, it is a typical rock-based calcium. Mafic rocks show the results of chemical analysis, ω(SiO2) = 48.27%~48.41%, average 48.34% belong to mafic, lower than 49.88% of the control value diabase, diabase in the ditch K2O+Na2O mean 2.68%, total alkali content is not high, the TAS diagram fall mafic diabase, basalt in the projected points. Full base(K2O+Na2O) ranging from 1.587%~3.78%, CaO content of 8.69%-9.41%, with an average 9.05%, the SiO2 and alkali content(K2O+Na2O) calculated Rittmann index σ=0.47~2.65, with an average of 1.56, typical calc-alkaline rock.NS-trending structure is the basic tectonic framework in this district overlapping NW- direction arcuate structure later. According to mechanical properties, in addition to NS-trending main structure, there are some cross fractures and NE-trending and NW-trending torsion fracture surfaces. The distribution of vein materials is mainly NS-trending and a few of NW-trending and NE-trending. Orebodies is mainly located in NW-trending and a few in NE-trending, and only a little lean mineralized orebodies lie in NS-trending. The directions of best mineralizaion is NW-trending and the NE-trending mineralizaion is also good. It indicates that structure is the prime ore-controlling factor for ore-forming. The NS-trending main structure surface is the ore-guided structure, and NW-trending and NE-trending structures are ore-storage structure. Particularly, NW-trending structure suffer arcuate structure later, so it’s the most favorable metallogenic tectonic space.Magmation, regional metamorphism, and tectonic movement provide source of heat and ore-forming materials to the formation of gold ore. Especially, the magmatic activity plays an important role for the gold deposit formation. On regional scale, mafic dike is closely related with gold mineralization. Aiming at mining area, gold ore is born in mafic-basic dikes and the cracks. According zircon dating results, mafic dikes within the mining area has two phases, the first phase gabbro was formed in 425.2±2.6Ma, another of dating results for 221±16Ma, and the ESR dating of quartz shows gold mineralization is approximately 13.2Ma, gold mineralization was significantly later than the mafic dikes. Such strong magma movement implies that there are rising emplacement channels of mafic magma which are from deep crust or mantle. These channels are not only conducive to deep magma emplacement, but also provide migration path to gold-bearing hydrothermal fluid activity after magma movement. |
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