| The Xiaoxilin lead-zinc deposit, which belongs to Wuxing-Guansongzhen uplift andis influenced by both the Mongolia-Okhotsk orogenic belt and the outer edge of thePacific subduction zone, is located40km southeast away from Yichun City, HeilongjiangProvince. Volcanic activities and tectonic movements occur in the area, stratigraphyscattered distributed in the ‘sea’ of granite.Geochronology and geochemistry studies are taken on the intrusive rocks outcropedin the Xiaoxilin deposit. Zircon U-Pb weighted mean age of adamellite is451±5Ma.Geochemical characteristics are similar with that of I-type granite rocks and displayhigh-K calc-alkaline series, which may be associated with the Northward subduction ofthe Paleo-AsianOcean. Zircon U-Pb weighted mean age of porphyritic granite is200±2Ma.Geochemistry characteristics are similar with that of S-type granites and display high-Kcalc-alkaline series, which may be associated with the closure of Paleo-AsianOcean.Combined with previous studies, it can be concluded that Caledonian granites left in lateIndosinian granites.Comparing the geological characteristics of vein I orebody in the Xiaoxilin, theLaodaomiaogou deposit and the newly discovered orebody, the genesis of Xiaoxilindepositis discussed below.Vein I orebody in Xiaoxilin mainly occurs in marble of Qianshan group, controlledby strata, and the newly discovered orebodies are located in the EW trending faults, whilethe Laodaomiaogou deposit is located in nearly NS trending alteration zone in granite ordiorite.Ore minerals in the three deposit are mainly pyrrhotite, galena, sphalerite, pyrite, andmagnetite, and followedby chalcopyrite. Vein I orebody in the Xiaoxilin deposit also has a small amount of arsenopyrite, and the Laodaomiaogou deposit has a small amount ofarsenopyrite and limonite, while in the newly discovered deposit a small amount offerberite and limonite are also found. There also has some differences in gangue minerals.Gangue minerals in vein I orebody in the Xiaoxilin deposit mainly are dolomite, quartzand calcite, followed by biotite, muscovite, actinoliteandtremolite. Gangue minerals in theLaodaomiaogou deposit mainly are quartz, feldspar, muscovite，sericite， feldspar,hornblende, biotite, calcite and so on, and gangue minerals in the newly discovereddeposit are muscovite, calcite, quartz and so on.Vein I orebody in the Xiaoxilin deposit are mainly massive and banded structures,followed by disseminated and vein-like structures. Textures are mainlyanhedralmetacrystal textures, followed by some filling and replacement textures. TheLaodaomiaogoudeposit are mainly disseminated and vein-like structures, and followed bymassive and lumpy structures. Textures are mainly replacement and anhedralmetacrystaltextures. And the newly discovered deposit are mainly massive structures, and textures aremaily replacement and anhedralmetacrystal textures, followed by cataclastic textures.In the vein I orebody in the Xiaoxilin deposit, the Laodaomiaogou deposit and thenewly discovered deposit, main ore-forming elements Pb, Zn are closely associated withCd, Sb, and Hg. Besides, the vein I orebody in the Xiaoxilin deposit is also closelyassociated with Ag and Au, the Laodaomiaogou deposit is also closely associated with As.The alteration rocks on the hanging wall of vein I orebody in the Xiaoxilin depositare mainly tremolite, carbonate and silicified, while on the footwall include silicified，biotite, quartz, sericite, chlorite, actinolite, weak skarn minerals (eg "skarn-like" andtremolite), and so on. Alteration rocks in the Laodaomiaogou deposit include muscovite,silicified，sericite, biotite, carbonate and so on, and the newly discovered deposit havefound hornfels of granite, silicified, and carbonate.It can be shown in the sulfur isotope in the vein I orebody in the Xiaoxilin deposit,the Laodaomiaogou deposit and the newly discovered deposit, that sulfur in the ore bodyare mainly from the deep sources, while vein I orebody in the Xiaoxilin deposit may alsohas an addition of seawater and biological sulfur. Lead isotopes in the vein I orebody inthe Xiaoxilin deposit shows a mixture of upper mantle and crustal sources, while theLead isotopes in the Laodaomiaogou deposit mainly shows the mantle source, and it maybe partially derived from Cambrian strata.Study on the ore-forming fluids inclusions in the vein I orebody in the Xiaoxilindeposit shows that the ore forming fluids is megathermal and middle salinity fluids. Study on the ore-forming fluids inclusions in the Laodaomiaogou deposit and the newlydiscovered deposit shows that the ore forming fluids are mesothermal and low-middlesalinity fluids, and are formed in the same period.The ore forming pattern model in the vein I orebody in the Xiaoxilin deposit ismainly the chemical sedimentary, followed by filling. While the ore forming pattern in theLaodaomiaogou deposit is mainly replacement, followed by filling.supplemented byfilling mineralization. The ore forming pattern in the newly discovered deposit is mainlyfilling, followed by replacement.Pb and Zn are the main ore-forming elements in all the three deposits. Cd, In, Ag, Au,Co, Fe, Cu, As, Ga, Ge, Se and Te are also ore forming elements in the vein I orebody inthe Xiaoxilin deposit, and Cd, In and Ag are comprehensive utilization elements. Ag, S, Fe,Cu and As are also ore forming elements in the Laodaomiaogou deposit, and Ag and Scomprehensive utilization elements. While Fe, Cu and W are also ore forming element inthe newly discovered deposit.In this study, it can be concluded that the Xiaoxilin deposit is formed in theCambrian, while the Laodaomiaogou deposit and newly discovered deposit is formed inthe early Yanshanian.Two ore forming periods can be identified of in the area of Xiaoxilin, the first phaseformed exhalative sedimentary deposit (eg. vein I orebody in the Xiaoxilindeposit), thesecond phase formed middle temperature vein-type deposits (eg. the Laodaomiaogoudeposit and the newly discovered deposit). In summary, the genesis of Pb-Zn deposits inthe area of Xiaoxilin is exhalative sedimentary deposit overlapped with mesothermalvein-type deposits.The detail geophysical and geochemical exploration work focus on the Xiaoxilinmining area and its surrounding9test areas. By studying on geophysical and geochemicaldata，basing on geochemical measurement，combining with electrical measurement，andconsidering with magnetic and mercury vapor measurement and field geological work，the paper suggests that A,D,E test areas have the biggest mineralization potential and aredesignated as the metallogenic target areas; G test area has mineralization potential tosome extent and is divided into metallogenic prospective area.Though analysis of geological characteristics of mining area and geophysical andgeochemical data, we determine that the following prospecting work should foucs oncontacting position of marble and granite, the South-North fracture belt and the secondaryfaults of the rocks or stratum, with special attention on East-West tensional tectonic in the mining area. Although we did not find obvious geophysical and geochemical anomalies inthe marble region, We should pay attention to the prospecting of the stratum in the samelayer with Qianshan Group of marble and in deep part of the deposit. |
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