Geologic Feature And Discussion On Genesis Of The Pb-Zn-Fe-Cu-Mo Skarn Deposit In Lietinggang-Leqingla,Tibet

The Lietinggang-Leqingla deposit is the most representative skarn-type deposit develop Pb-Zn-Fe-Cu-Mo five minerals at the same time in this belt of polymetallic mineralization.It is possible to define certain zones and trends of the alteration and mineralization zoning on the space.The Fe-Cu-Mo ore body were mainly developed at contact zones of limestone in two number of Mengla formation and the rock mass related to mineralization,it distribute around the metallogenic rock mass distribution in half ring.Controlled by the contact structure,the ore body is lenticular,cystic and irregular.There mainly developed skarn minerals such as grossularites and a small amount of andradites,ferrosilites,ferroactinolites,epidotes,chlorites and so on.The Pb-Zn-Cu ore body mainly developed exosakrn limestone stratigrapHy far from rock mass,it alternated with Sand and limestone,Influenced by later structure,orebody occurrence forms,mainly developed skarn minerals such as andradites,Mn-hedenbergites,Mn-ferroactinolites,epidotes,chlorites and so on.The rock-forming ages of granite-porpHyry,granodiorite-porpHyry and granodiorite which related to mineralize were 60.69±0.98Ma?62.85±0.58Ma?61.40±1.5Ma.They all had the characteristic of Si-rich,alkalis-rich,belong to high-K,calcium alkalis I-type granite.The primitive mantle standardization distribution curve of trace elements and the chondrite standardization model chart of ree elements are similarity.They had the characteristic of LREE beneficiation,HREE defect,medium exception of Eu,with high LILE including Rb,Ba,Th,U,Pb,severe deletion HFSE including Nb,Ta,Ti,P,Sr severe deletion besides,it has the geochemical characteristics of arc-volcanic rocks.Zircon Hf isotope showed that they were all the conducts of mantle derived magma union dyeing the ancient earth's crust magma.The Re-Os isotope isochron age of molybdenite which symbiosis with chalcopyrite is 59.4±4.5Ma,the Rb-Sr isotope isochron ages of spHalerite is 58±2Ma,both ore-forming age whthin the limit of error,this indicated the Pb-Zn-Fe-Cu-Mo were the same metallogenic system,they were all the product of main collisional early magmatic activity of the India-Asian continent collision orogenic belt.Microthermometry and laser Raman analysis of fluid inclusions show that the fluid inclusions of Lietinggang-Leqingla deposit are L-V two-pHase inclusions and have crystal inclusions,belonging to a Na⁺-Ca²⁺-K⁺-CO₃^2--SO₄^2--Cl^--F^--HS^-brine system.In terms of time,it present temperature drop,higher salinity characteristics from skarn stage to sulfide pHase,In space,it present temperature drop,salinity increases characteristic from near to far mineralization.Ore-forming fluids were mainly from granite magmatic hydrothermal at early stage,there has precipitation join at quarta-sulfide stage from the research of C-H-O isotope.The limestone and marble formation'sd¹⁸O_V-SMOW of two ore body had severe deletion compare with noemal marine sedimentary limestone,it state that the ore-forming fluids miss migration at the whole limestone stratum,so there formate Pb-Zn-Cu ore body at external contact in ore district.the majority of sulfides'?³⁴S in Fe-Cu-Mo ore body concentrated on-1‰^-5‰showed magmatic sulfur source,may be union dyeing sulfur from organic reduction of seawater.The majority of sulfides'?³⁴S in Pb-Zn-Cu concentrated on-7‰^-11‰,it showed the effect of sufur from surrounding rock.Lead isotope of sulfide are similar to those of lead isotope of magmatic rock.So that lead isotope in ore deposit is mainly derived from magma.Comprehensive analysis of deposit and summarize the metallogenic model,India–Asia continental started collision at 65Ma,it caused the Neo-Tethys ocean slab roll-back,this lead to asthenospHere mantle upwelling and intensely transform the hot structure of mantle wedge,and caused the mantle partial melting,formed a large number of mafic magma.The mafic magma intruded upward the lower crust of Lhasa plot and stoped,and evolved magma related to skarn-type Fe-Cu mineralization after MASH process,it intruded upward and miscibile with lower crust magma,and caused the upper and middle crust partial melting,it formed magma relate to skarn-type Pb-Zn-Fe-Cu-Mo mineralization and intruded upward along fault.With the continual crystal fractionation of magma,it formed high temperature,medium salinity ore-forming fluid and that intruded along fault,interlayer fracture zone at the district.It caused bimetasomatism in limestone contact of mengla formation,foemed a series of skarn minerals.With the fluid temperature decrease,hydrolysis reinforced and redox environment changed,PH value increase,the magmatics settling in contact zone.It caused a lot of SO₂,H₂S,HCl,CH₄,N₂ separated from liquid pHase because of precipitation joined and fluid boiling at follow stage,they intruded gaseous pHase and lead to PH value increase,with the temperature and pressure decrease,it formed Fe-Cu-Mo ore body with the characteristic of high temperature at contact zone near the rock mass,and formed Pb-Zn-Cu ore body with the characteristic of medium temperature at external contact zone far away from rock mass.