Metallogenic Model And Prospecting Potential In Southern Tibet Au-Sb Polymetallic Belt

This thesis, metallogenic model and prospecting potential in Southern Tibet Au-Sb Polymetallic Belt, take the Chalapu Au deposit, Mazhala Au-Sb deposit, Cheqiongzhuobu Sb deposit, and Zhaxikang Pb-Zn polymetallic deposit as representative deposits of Southern Tibet Au-Sb metallogenic belt. The author operate series of field and laboratory work on field geological investigation, detailed mineralization stages, metallogenic structural survey, mineralographical observations, fluid inclusions analysis, mineral H-O-S-Pb isotopic analysis, zircon U-Pb and potassium-bearing mineral Ar-Ar dating geochronology. The detailed conclusions are described as follows:1. This thesis systematically summarized the geological characteristics and metallogenic conditions of the typical deposits in Southern Tibet Au-Sb metallogenic belt.Ore bodies in Chalapu Au deposit are mainly controlled by E-W faults. Three different ore type, alteration type, breccia type and quartz vein type, are exsit in Chalapu Au deposit. The gold appears in native gold and invisible gold minerals, later of which are exist in arsenopyrite and pyrite. The main alteration minerals are quartz, sericite, illite, chlorite, the main metal minerals are arsenopyrite and pyrite. The ore-forming fluid temperature rang from164℃to308℃, with salinities of2.7wt%NaCl-9.3wt%NaCl, The ore-forming depth is about1.1～3.8Km (hypabyssal environment). The characteristic of ore-forming fluid in Chalapu Au deposit is similar with metamorphic water, but added with some earth surface water. Hydrothermal alteration is the key factor to cause metal precipitation, secondly are fluid cooling and fluid mixing.Mazhala Au-Sb deposit is controlled by interlaminar fracture zone. The mainly ore type are quartz (calcite) vein and alteration type. The main alteration minerals are quartz, carbonate, sericite, chlorite; where main metal minerals are arsenopyrite, stibnite, pyrite, etc. gold mainly appears in native gold, only a litter of gold exist in arsenopyrite, stibnite, pyrite as invisible gold. The temperature of ore-forming fluid in Mazhala Au-Sb deposit rang from134℃to324℃, with salinities of0.41wt%NaCl-7.81wt%NaCl, estimated ore-forming depth is about1.1～2.8Km (hypabyssal environment). The mechanism of metal precipitation and ore-forming fluid source are similar with Chalapu deposit. Characteristic of ore-forming fluids are similar with metamorphic water, but mixed with earth surface water. The hydrothermal alteration, cooling and fluid mixing are the main factors to cause mineralization.Cheqiongzhuobu Sb deposit is controlled by S-N high-angle normal faults. The mainly ore types are stibnite quartz vein and stibnite calcite vein. The main alteration minerals in this deposit are quartz and calcite; the main metal mineral is stibnite. The temperature of ore-forming fluid is between121℃and234.5℃, with salinities of1.40wt%NaCl-4.65wt%NaCl. Estimated depth of Sb mineralization is about0.6-1.9Km (ultra-hypabyssal environment). The ore-forming fluids are mainly earth surface water, but appeared trend of mixing with organic water. The cooling and fluid mixing are the main factors for Sb metal deposits.Zhaxikang Pb-Zn polymetallic deposit are controlled by S-N high-angle normal faults. The ore types contain sphalerite-Fe-Mn carbonate vein, galena-Fe-Mn carbonate vein, stibnite quartz vein and cinnabar stibnite quartz vein. The main alteration minerals are quartz, rhodochrosite, calcite, siderite, mica; main metal minerals are sphalerite, galena, stibnite, arsenopyrite and pyrite. The temperature of ore-forming fluid is between211℃and328℃, with salinities of0.70wt%NaCl-12.51wt%NaC. Estimated mineralization depth is about0.4～1.1Km (ultra-hypabyssal environment). The ore-forming fluids are mainly organic water, but mixed with Tibet surface water. The mineralization mechanism is similar with stibnite deposits, which are mainly caused by cooling and fluid mixing.2. Constrains the metallogenic epoch of Southern Tibet Au-Sb metallogenic belt. The diorite in Shalagang Sb deposit is formed at ca.23.6±0.8Ma, constrained by zircon U-Pb geochronology. This data indirectly restrict that mineralization time of stibnite-quartz veins, which cross cut diorite, is younger than23.6±0.8Ma. The hydrothermal activity time of Chalapu Au deposit is ca.20.43Ma, constrained by illite Ar-Ar geochronology. Zircon U-Pb geochronological age of diabase dike in Zhaxikang deposit is133.1Ma, which is consistent with the age of diabase dikes widely distributed in Tethyan Himalayan, indicate that Tethyan Himalaya was in a strong extension tectonic environment.3. Combined with previous study, there are two mineralization stages in Southern Tibet Au-Sb mellogenic zone:(l)Shear-zone related Au deposit in sy-collision stage. The ore-bodies are controlled by shear-zone and secondary faults, charactered with natural gold-quartzs veins. The representative deposits of this stage are Bangbu and Mayoumu Au orogenic deposits, which are formed during59Ma-42Ma.(2) Extention-relared Au, AuSb, Sb and PbZnAg polymetal mineralization in post-collision. The ore bodies are controlled by N-S high angle normal fault and E-W interlayer fragmentized fault belt, charactered with alteration type gold ore and hydrothermal vein type ore. The represented deposits of this stage are Shalagang, Cheqiongzhuobu and Zhaxikang deposits, which are formed during23.6Ma-18.7Ma.4. Tethyan Himalaya metallogenic structures model are established. The basin-orogeny transition district in Yamzho Yum Tso-zhegucuo-Puma Yun Tso passive continent rift basin, which are consisted by E-W striking faults (Lazi-Qiongduojiang suture belt, Rongbu fault, Luozha fault) and N-S striking stike-slip fault belt (Lejingkangsang, xiaba stike-slip fault belt and Zeri-Dongga extension stike-slip fault), are the favorable place for mineralization. The regional E-W structure and its secondary faults controlled the distribution of major Au and Au-Sb deposits; the regional N-S faults mainly controlled the distribution of Sb and Pb-Zn polymetallic deposits. The places, N-S faults interwith E-W faults, are potentional locations for Sb,Pb-Zn polymetallic deposits exploration. 5. Three mineralization stage, three metallogenic series and five genetic deposit type are identified in Tethyan Himalaya. The three mineralization stage are (1) passive margin rift sy-sedimentary stage with organic-rich exhalative sediments and turbidite sediments;(2) Continent margin accretionary wedge sy-collision stage with dynamic metamorphism and ductile-brittle shear;(3) Post-collision stage with extension detachment, normal faults, and intermediate-felsic volcanic magmatic hydrothermal (include hot spring water) superimposition and rework. Three metallogenic series are (1) exhalative-sediment-rework related AuAs, CuZn, PbZnAg, PbZnAgMnFe metallogenic series;(2) orogenic HgSb,AuSb,AuAs metallogenic series related with ductile-brittle shear zone in accretionary complex rock;(3) Sub-volcanic magmatic hydrothermal (hot spring) related Hg→AsSb→AuAg→PbZnAg→PbZn→Cu metallogenic series. Five genetic deposit type are (1) exhalative sediment-rework type: including exhalative sediments-hot spring water superimposition rework type (Zhaxikang Zeri Pb-Zn polymetal mineralization), exhalative sediments-Sub-volcanic magmatic hydrothermal superimposition rework (Mazhala, zhegu, Jiangcang AuSb deposits);(2) Sub-volcanic magmatic hydrothermal type(Shalagang,Delong Sb deposits);(3) hot spring type (Cheqiongzhuobu, Yongri sb deposits);(4)Calin, Calin-ke type (Chalapu Au, Xiongqu Au deposit);(5) orogenic type (Bangbu, Xigong Au deposits).6. The metallogenic regularity, ore-controlling factors and "four factors of prospecting model" are summarized. Ore-forming materials are mainly derived from the black rock formation of Mesozoic sedimentary basins, only a litter comes from regional metamorphic basement. Ore-forming fluids are from different partly mixed basin brine fluid, infiltrated surface water, metamorphic fluid and magma fluid. The Au, Au-Sb, Sb, Pb-Zn polymetallic deposits are distributed as a group and segment concentrate surrounded with Yamzho Yum Tso basin, and along the E-W and N-S regional fault belts. The most important prospecting criterias are the "four factors":sy-sediments black carborndum mudstone suits and mafic dikes; sy-collsion ductile-brittle shear and dynamic metamorphism; post-collision extension detachment or S-N strike slip normal faults; Miocene neutral-acidic volcanic magmatic rock or hot Springs activities.7. The study area are subdivided the into6metallogenic prospective areas.1. two class A prospective area:Mazhala-Zhaxikang Au-Sb polymetallic metallogenic prospective area (A1) and Luozha-Cuomei Sb metallogenic prospective area (A2).2. three class B metallogenic prospects:Langkazi Au metallogenic prospective area (B1), Shalagang-Kangma Sb metallogenic prospective area (B2) and Chalapu-Sananqulin Au metallogenic prospective area (B3).3. one class C prospective area:Bangbu-Bailu Au prospective area (C1).