| Porphyry copper-molybdenum deposit is an important type in Sanjiang region. Thereare Narigongma, Xiariduo, Hengxingcuo, Yulong, Zhagana, Mangzong, Duoxiasongduo,Malasongduo deposits distributed in Narigongma-Yulong metallogenic belt, northernSanjiang area, where research works remain in a relative low degree compared withmiddle-southern part of Sanjiang, and mostly focused on the macroscopic scale analysisand prediction, not systematic in analysis of the specific deposit geology, explorationmodel and prospecting exploration, especially in Narigongma porphyry copper-molybdenum deposit. According to "on mine prospecting" ideas, summarizing themineralization law and exploration model of the existing deposit, combiningcomprehensive information from geological survey to guide the surface prospecting is aneffective way to make a breakthrough in copper-molybdenum mine prospecting this area.In this paper, the theory and methods of metallogenic system, previous studiescombined with research projects recently have been applied, geological setting, depositgeology, geophysics, and geochemistry charactoristics, ore-forming elements, metallotectshave been summarized, a comprehensive exploration model has been established, andmetallogenic prediction has been carried out base on the comprehensive information ofgeophysical, geochemical, mineralization, etc. to delineate prospecting targets availablefor exploration and evaluation.Studies show that granite porphyry stock is closely related to the porphyry mineralization, with chemical characteristics of high-K calc-alkaline, enrichment of LREE,Rb, Ba and other large LILE, Th, U, etc. depleted in HREE, Nb, Ta, Ti etc.Pb, Sr, Ndisotopic compositions indicate that the main source of ore-bearing porphyry is enrichedmantle, close to the potassic volcanic rocks in northern Tibet, Combined with εNd (t)andεSr (t), magma has the mixing characteristics of the upper mantle and crustal. R1-R2diagram shows the orogenic extensional tectonic setting, consistent with the regionalextensional tectonic background during50-30Ma.The main ore bodies are Ⅲ-molybdenum andⅡ-copper in Narigongma Cu-Modeposit. Ⅲ orebody is located in the upper part of the porphyry, along with the contactzone between the porphyry and the host rock. Ⅱ-Cu body is located the upper side of theporphyry, besides the neighboring basalt. Wall-rock alteration are potassic, phyllic andpropylitic from center to outward, respectively, zonation is obvious. The main oreminerals are pyrite, chalcopyrite and molybdenite with characteristic of upper-Cu andunder-Mo and stratabound, copper mineralization is mainly in basalt.Ore δ34S values ranges in7.16‰-7.50‰, positive values deviation from themeteorite sulfur in uniformity, sulfur source is mainly from magma. the upper crustprovides some minerals. Ore-forming fluid is rich in water, CO2and acidic fluids. Fluidinclusions are mainly two-phase of liquid-gas and three-phase of daughter mineralsbearing. small ratio of F-/Cl-and high contents of Na+and Ca2+in fluid, high Ca2+levelsindicates the added of atmospheric water. Mineralization temperature is mainlyconcentrated in the246-300℃, with salinity of31.3-42.2wt%. Fluid is from theexsolution of shallow hydrothermal felsic magma under environmental stress relaxation,and later mixed of the atmospheric water, mineral precipitation set in fluid boiling of theearly stage and the addition of atmospheric water in late stage. It is determined typeporphyry type deposit, and established metallogenic model. At the regional and belt scaledeposit produced in the gravity gradient zone, aeromagnetic anomalies mutation positiveand negative magnetic anomalies with a close positive side, reflecting the deep fault zonewhich is characterized by regional tectonic and magmatic belt control; On the scale mining, ore-bearing porphyry with positive magnetic anomalies in the background ofnegative magnetic anomaly zone, relatively low gravity anomalies corresponding to thischaracteristic and porphyry with a relatively low density of magnetic and relevant; whileporphyry and rock in the copper-molybdenum mineralization is relatively low resistivitywith a high polarization (amplitude and frequency) characteristics, thus can bedelineated copper-molybdenum mineralization and ore.Different scales reflectgeophysical field or unusual for delineation of prospects, prospecting targets andmineralization provides geophysical basis.Geochemical methods has played a decisive role in the discovery of porphyrycopper-molybdenum deposit. Whether it is1/200000regional geochemical survey, or1/50000mineral prospective investigation, or1/10000sectional geochemical survey,geochemical signs are extremely obvious. Geochemical anomalies are mainly Cu, W, Mo,Ag, associated Au, Pb, Zn, Se, Sn, etc., complex combination of elements, each elementanomalies superimposed on each other, consistent with the deposit type and distributionof minerals, and thus constitutes a key predictive marker in deposit prospecting model.Due to the unique geological and landscape conditions, a single geological orgeophysical, or geochemical method is ineffective in prospecting, a comprehensiveintegrated approach of geological-geophysical-geochemical-remote sensing explorationis need to adopt prospecting. An exploration model is established for porphyry Cu-Modeposit by analysis of various methods previously obtained and understanding of theirimplications for porphyry deposits, which will play an important role in guiding andprospecting of porphyry mine.One the basis of Narigongma exploration model, combined with theconstruction-structures map, the distribution of mine, elements and magnetic anomalymaps, according to the superposition of the distribution of predicted elements, it isdelineated12prospecting target in the periphery area of Narigongma. Among them,Lurige, Zhonggenyong, Dagugongka and Hengsaiqing A-class exploration targets havebeen discovered copper ore and molybdenum mineralization information, and the remaining prospecting targets also has a large exploration prospects, need much attentionin the next step. Therefore, the results of this study has an important role in guidingexploration of porphyry copper-molybdenum deposit in the area. |
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