| The Zharen copper deposit was located Xulong ,Derong ,Ganzi of Sichuan province, which 12 kilometers away from the Derong county town (linear distance), the center for geographic coordinates is E: 99°10′00″and N:28°45′30″. The deposit is a new-found deposit in Jinshajiang Cu, Pb, Zn ore belt of the Sanjiang region in southwest China, so far there are large-scale Cu deposits (Yangla copper deposit), two medium-scale Cu deposits (Tongjige copper deposit and Tuoding copper deposit), two medium-sized Pb-Zn deposits and more than ten small-scale deposits in the band, the band is one of important Cu, Pb, Zn ore belt in the Sanjiang region.The outcropping strata and the principal lithologic of the Zharen mining area are the different-thickness and alternating-layers combination sedimentation of marble, quartz schist, hornblende schist, mixed rocks and so on in the Proterozoic, the plagioclase amphibolite in the Lower Permian the first sub-segment of the under segment, the gray-green metamorphic basic volcanic rocks (green schist) in the Lower Permian the second sub-segment of the under segment, the slate, sandstone mingled with gray-green metamorphic basic volcanic rocks (vein) in Lower Permian upper segment, the basic volcanic rocks, limestone, slate, quartz sandstone in the upper Triassic under segment of Qugasi group, and the other residual and slope sediments in the Quaternary. There are faults in the mining area, the main faults are Zharen fault (F1), Nizhong falut (F2), F3, F5, F6 and so on. The magmatic rocks are mainly Variscan ultra-basic rocks, Indo-Chinese quartz diorite, the plagioclase granite in the stage of Yanshan and so on.In the mineing area, copper-cobalt mineralized body mainly occurs in the gray-green metamorphic basic volcanic rocks (green schist) in the Lower Permian the second sub-segment of the under segment and the gray-black plagioclase amphibolite in the Lower Permian the first sub-segment of the under segment. The ore bodies are layer, layer-like, vein, lenticular and other forms. The main compositions of ore are chalcopyrite, pyrite, linnaeite, magnetite, malachite, azurite, chlorite, epidote, plagioclase, quartz and so on. The texture of ores are comprised of subhedral grain-like texture, xenomorphic grain-like texture, remnant ballistic texture, erosion texture, skeletal crystal texture, redial texture, crushed texture, interstitial texture; the structure of ores are massive, sparsely disseminated, scattered disseminated, vein, small vein, colloidal structure, earthy, honeycomb structure and so on. Wall rock alterations are silicification, chlorite, epidote petrochemical, sericite, calcitization and so on.There are larger quantities of fluid inclusions in minerals from Zharen copper deposit, the different minerals have different inclusions in distribution, shape, size and type. Most of the inclusions in quartz distribute over cracks of the two groups with orientation. The type of inclusions is gas-liquid two phases, and gas-liquid ratio ranges from 2% to 7%; the inclusions within tremolite occur bamboo-like, which distribute in the tremolite crystal with crossing. The homogenization temperature of inclusions in quartz is varied from 122°C to 153°C, and the average temperature is 135.5°C. According to the temperature, the Zharen copper deposit is supposed to be mesothermal-epithermal deposits.Compared Zharen copper deposit with Tuoding copper deposit in Deqing, they has simiarity in geological features, mineralization characteristics and geological background. Not only the metallogenic temperature is lower , but also the salinity of ore forming fluids is lower, both accur vein in tectonic fracture belt of thrust-nappe zone, the mineral composition reflects the characteristics of low-temperature mineral assemblage, ore structures are in vein-small veins, scattered disseminated, sparsely disseminated and other structures, and the wallrock alterations which are directly related to mineralization are mainly silicification and carbonate, their metallogenesis are filled-accountable manner along the fracture zone.It is circled three obvious polarizability anomalies with geophysical exploration in Zharen copper deposit, two of them correspond with belt of I and II. It is expressed that the synthetical anomaly of Cu, Au, Ag, Co, Sb, As in geochemical exploration, and the anomalies coincide well, they are coincided with the known copper-cobalt mineralized bodies in the mining area, and there are some better anomalies of Cu, Co, Au in the direction of strike and dip in the ore belt.On the basis of analyzing previous data, combining with Southwest Sanjiang regional geological background, this paper focus on geological features and metallogenic conditions of the Derong copper deposit, and summarying metallogenic law, determining the deposit type and indicator, clarifying the prospecting direction.This research obtains the following main achievements and recognition: (1) Zharen copper deposit and Yangla copper deposit located in the Jinshajiang ophiolite belt,but the Zharen copper deposit located in the foreland fold - thrust belt in the eastern edge of Jinshajiang ophiolite belt, and the Yangla copper deposit located in the ophiolite tectonic melange zone of Jinshajiang ophiolite.(2) According to field observation, the texture and structure of ores and mineral association, the metallogenic process of Zharen copper deposit can be divided into two major mineralization phase (hydrothermal and hypergene period), and three ore-forming stages, among which chalcopyrite mineralization of hydrothermal phase is the most important stage.(3) The formation of Zharen copper deposit derived from the product of magmatism, tectonics, hydrothermal system and so on during ocean-continent transformation and basin-mountain transformation since hercynian. Ore-forming in Zharen copper deposit mianly controlled by Zharen fault and secondary faults, which has no close association with magmatism clearly, and the mineralization mostly occurred in continental convergence stage during Yanshan-Himalayan period.(4) By comparing the fluid inclusion characteristics between Zharen copper deposit and Yangla copper deposit, they are very similar for both characteristics, and also have a lower homogenization temperature, which implies that Zharen copper deposit may be a later product during tectonic thermal event.(5) Compared to Tuoding copper deposit, the ore deposit type of Zharen copper deposit belongs to structure-hydrothermal vein-type deposit located in fold-thrust belt. And the metallogenic model is established characterized by continental collision and thrusting-shearing for Zharen copper deposit.(6) The explorative indications have been determined, such as native outcrop, wall rock alteration, stratigraphy, tectonics, geophysics, geochemistry and so on, and they clearly pointed out that the fracture zone is the most important symbol for discovering structure - hydrothermal vein-type Cu deposit.(7) The discovery of Zharen copper deposit is an important breakthrough for structure-hydrothermal vein-type ore deposits in the Jinshajiang metallogenic belt. According to the geological characteristics of deposit, combining the comprehensive information prospecting of geophysics, geochemistry and remote sensing, there are high potential for finding structure-hydrothermal vein-type Cu-Au polymetallic deposit in tectonic fracture belt of thrust-shear zone. |
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