Mineralization And Periphery Metallogenic Prediction Of The Hongling Pb-Zn Polymetallic Deposit In Chifeng, Inner Mongolia

Hongling Pb-Zn polymetallic deposit is a typical skarn type deposit,located inBalin Zuoqi of the city of Chifeng,and is a large typical representative deposit occurred in themetallogenic belt of huanggangliang-Ganzhuermiao. The deposit is occurred in the outercontact zone of the late Yanshanian period Wulanba intrusion and Dashizhai Formation.Skarnization is the most important alteration type for the deposit. Orebody are layered andstratoid occurred in the roof and bottom plate of marble stratum of Dashizhai Formation andinterlaminar fracture. The occurrence of ore bodies are controlled by the marble stratumobviously, concretely which expresses that the thickness of marble stratum is inverse-ly associated with Pb-Zn ore body’s grade and thickness and Fe ore boby mostly enrichtransfer zone of marble stratum’s thickness. As a whole, the Pb-Zn polymetallic ore bobyhas characteristics of Fe-Cu-Zn-Pb vertical zoning from deep to shallow, and from north eastto south west has characteristics of Fe-Cu-Zn-Pb horizontal zoning. Statistics show that richore of hongling mining area is mostly distributed in1-17prospecting line andore body thickness is inversely associated with ore body’s grade. According to the mineralassemblage and vein crosscutting relationships, combing with the result of mineralizationchronology, the mineralization process can be divided into skarn epoch、quartz-Pb-Znpolymetallic sulfide epoch and molybdenum mineralization epoch.Comprehensive studies on fluid inclusions show that the ore-forming fluid in skarnepoch is of high temperature, high salinity and immiscible NaCl-H2O type solutions and theboiling process plays important role in the the precipitation of Pb、Zn、Cu; From morning tillnight, the dropping of homogenization temperatures and salinities of ore-forming fluids inquartz-polymetallic sulfide epoch suggests that meteoric water continuously joining into theore-forming fluid. the ore-forming fluids is of medium-low temperature and low salinity NaCl-H2O type solutions. C, H, O isotope study of fluid inclusions shows that the skarnepoch ore-forming fluids of Hongling Pb-Zn polymetallic deposit mainly came frommagmatic water and that quartz-sulfide epoch ore-forming fluids came from mixedmagmatic water and meteoric water, whereas at the latest stage of mineralization,theore-forming fluids mainly came from meteoric water. The isotopes study of S-Pb andmolybdenite Re-Os implies that the ore-forming materials posed a deep source feature. Wehave carried out chronological research in allusion to Hongling ore district and the mainintrusive rocks of its peripheral region.According to the work of petrography and magmatic Zircon LA-ICP-MS U-Pb dating,The paper divides magmatic rocks of Hongling ore district and the main intrusive rocks ofits peripheral region into five parts. They are flesh-pink medium-coarse granite(144.1±1.5Ma),light brown-gray granite porphyry(141.9±1.2Ma), containing phenocryst light flesh-pink fine-grained granite (139.83±0.82Ma), grayish brown porphyritic granite (139.7±1.1Ma)and light brown granite porphyry(136.70±0.85Ma).The analysis of petrogeochemistry showsthat the granite of this ore district is characterized by riching SiO2、K2O, pooring Al2O3,having Eu negative abnormality, depletion of Ba、Sr, and high field strength elements (likeZr、Hf) and large ion lithophile element (like Rb、U、Th)abundance. It belongs to the typicalA2type,which formed in stretch tectonic system post-tectonic environment.Molybdenite Re-Os chronology study indicates that porphyry molybdenum mineralization with anisochron age of140.3±3.4Ma(MSWD=0.082) shows that its mineralization ages is late Jura-ssic epoch and skarn molybdenum mineralization with Re-Os model age of143.7±3.6Ma represents Pb-Zn forming age of Hongling mining area.Comprehensive studies haveshown that however there is no genesisly relation between Mo (Cu) and multi-metal Pb-Zn inmineralization, the differentiation of Mo(Cu) mineralizing fluid in light brown-graygranite porphyry may overlay and effect Pb-Zn polymetallic mineralization. Both occurred inlate Yanshan period.The author using the basic theory of geotectonics and regional metallogeny, collectedpredecessors’ zircon U-Pb age of main rock in Huangganglian-ganzhuermiao metallogenicbelts ystemly, summed up the metallogenic belt tectonic evolution history to three stages:central Asia orogenic belt (350~280Ma), Mongolia-okhotsk tectonic system (170~120Ma)and Pacific tectonic system (120Ma~today). Combine the rock geochemical analysis, thispaper argues that Hongling Pb-Zn deposit’s metallogenic dynamics background is continentalcrust extension environment, as an result of Mongolia-okhotsk suture zone post-tectonic stretch thinning.Mineralization regularity study shows that Hongling Pb-Zn deposit controled by strata,structure and magmatic rock. In the stratum containing ore and ore-controlling regularity,Permian Dashizhai Formation is favorable mineralization formation in Hongling mining area,obvious enrichment of metallogenic elements such as Cu, Pb, Zn and Sn etc; the formationcontrol the form of orebody, and marble (P1d2) control the output position of Pb and Zn orebody. Structural ore-controlling rules shows that the Haobugao overturned anticline is themain ore-controlling structure in Hongling Pb-Zn deposit, NE strike faults and secondaryfracture structure are the most important ore-controlling and ore-hosting structures in thedeposit. In terms of magmatic rock control function, Pb、Zn mineralization should havegenetic relationships with the red meat gneissic granite, while the porphyry molybdenum(copper) mineralization have genetic relationships with the light brown gray granite porphyry.For the first time in the south west, south of Hongling main metallogenic belt and northwest wing of Haobugao reversal anticline discovered Permian silty slate outcrop, accordingto the Hongling mining area formation, structure, magmatic rock and ore-controllingregularity, the author hold the point that there still has extended on both ends of the mainmetallogenic belt in Hongling, and put forward an original idea that the south side of themain metallogenic belt in Hongling has a “second metallogenic belt” nearly parallel with themain one, widen the Hongling periphery prospecting area. Combined with peripheral regionmineralization alteration, geophysical anomalies, geochemical anomalies and other factors,we can come to an conclusion that on the extension of both ends south west of the Honglingmetallogenic belt (area C) and the north east (area A) have good Pb-Zn mineralizationpotential, light brown gray granite porphyry bodies (area B) has the potential of porphyrycopper and molybdenum mineralization. A, B, C three prospecting work areas in theperipheral region were delineated the A-Ⅰ, B-Ⅰ, B-Ⅱ, C-Ⅰ four prospecting target areas,arranging trough, drilling engineering in the target zone.