The Isotope Geochemistry Characters Of Lietingang Iron Copper Poly-metallic Deposit Of Duilongdeqing County In Tibet

Lietingang iron copper poly-metals deposit is located in Mendui Village of Deqing Township in Duilongdeqing County, Tibet. In geotectonics, ths deposit is located in Ladakh-Gangdise-Xiachayu Magmatic Arc Belt of first-class tectonic division of Himalayan Orogenic Zone which is thought has experienced three strong tectonic-magmatic evolution stage in previous study, that is, subduction volcanicmagmatic arc in Jurassic-Cretaceous, paleogene collision-type volcanic-magmatic arc and neogene magmatic events after collision, it has developed lots of plutonic rock and volcanic rock, and provided a favorable geological and tectonic conditions for the generation of a series of porphyry Cu-Mo deposit and skarn iron-copper poly-metals deposit in Gangdise Orogen.The metallogenic province of Lietingang Iron-Copper poly-metals deposit has developed Yanshan grano-diorite(γδ53) in its most area, mainly exposed as batholith and stock in its southeast, southwest, central and northern. The main color of rock is gray, and developed porphyritic structure, graphic texture and massive structure. In terms of structure, it is controlled obviously by Oulang-Yangrelang fault. The ore body is main exist in marble and limestone of Lower-Middle Triassic Chaqupu Formation and skarn belt in late Yanshan granodiorite contact belt. The relationship of ore body and its surrounding rock boundary is gradient. At the macro, the ore body is existed as strata form and quasi strata form along the skarn belt, partially are chambered vein and lenticular.Lietingang iron-copper poly-metals deposit is a newly found in Mts. Gangdise, almost no study have been made about its deposit geology, geo-chemistry, fluid inclusion and ore genesis. Therefore, this paper takes C, O, S, Pb stable isotope geochemistry’s study as its topic, pick out monomineral such as pyrrhotite, molybdenite, sphalerite and calcite sample to do C, O, S, Pb’s isotope assaying to study the source of ore-forming materials, metallogenetic fluid properties, and its tectonic environment, and furthermore analysis mineral precipitation mechanism, provide basic data of isotope geochemistry for establishing metallogenic model and provide technical support for prospecting in the deep and periphery of the deposit.By participating in the preliminary exploration of Lietingang deposit, I have grasped the geological and tectonic background in the formation of the deposit, the attitude, scale, and quantity ore body, the stratum which ore existed, alteration types and the metallogenic factors. Under the foundation of the observation and research of the ore’s macro characteristics, systemic sampling have been made to the rock and ore of the deposit, especially the research of the relationship within exposed veins in the wild, and have grasped its mutual interpenetration relationship(the order of formation).Skarn in Lietingang deposit area is main gray, dark green diopside skarn and garnet skarn, it possesses fine-medium grained crystalloblastic texture, metasomatic relict texture and nematoblastic texture. The skarn rocks generally possess massive structure and banded structure. Skarn minerals are garnet, diopside, tremolite, actinolite, idocrase, augite, as well as quartz, calcite, etc, and a little epidote, chlorite, tourmaline, wollastonite and fluorite.Metal minerals in Lietingang deposit are Magnetite, pyrrhotite, chalcopyrite, pyrite, molybdenite, tetrahedrite, chalcocite, azurite, bornite, covellite, bismuthinite, malachite, hematite and limonite.The isotope assaying result of C and O of 5 pieces calcite monomineral sample in this paper as follows: δ18OPDB(‰) =-2.59‰ ~-1.79‰, δ13CPDB(‰) =-24.08‰ ~-23.66‰, the δ18OPDB(‰) range is δ18OSOMW(‰) = 28.24‰ ~ 29.11‰. The projection in δ18OPDB(‰) diagram are all located in the range of sedimental organic phase, it indicated that the source of carbon in gangue minerals’ calcite is sedimental organic carbon, less likely to come from the deep magma’s carbon source. The Carbonaceous is existed in marine sediment, that is, Chaqupu Formation carbonate rock, in the process of granodiorite emplacement and Chaqupu Formation’s skarn double metasomatism, part of the carbon migrated into the ore-forming fluid.In this paper, 22 monominerals(pyrrhotite, chalcopyrite, molybdenite and sphalerite) have been picked out to do isotope assaying, and resulted into δ34SCDT(‰) =-7.02‰ ~ 1.38‰, meanvalue is about-2.92‰. Among this, 5 pieces molybdenite, δ34SCDT(‰) =-5.77‰ ~-1.14‰, its mean value is-3.06‰; 3 pieces sphalerite, δ34SCDT(‰) =-6.59‰ ~-6.47‰, its mean value is-6.52‰; 8 pieces chalcopyrite, δ34SCDT(‰) =-7.02‰ ~-0.4‰, its mean value is-2.67‰; 6 pieces pyrrhotite, δ34SCDT(‰) =-3.53‰ ~ 1.38‰, its meanvalue is-1.42‰. The sulfur isotope is almost all negative, its δ34S numerial number in histogram have a large range, no obvious tower distribution, but wave type distribution. Inferred from the histogram of the composition of sulfur isotope, thedistribution of sulfur isotope are main concentrated in several intervals: δ34SCDT(‰) =-1.0‰ ~ 0‰, δ34SCDT(‰) =-4‰ ~-2‰, δ34SCDT(‰) =-5‰ ~-7‰, it indicated thatsulfur source in the metallogenic fluid of Lietinggang deposit may have different properties and different sources, obviously tower-effect, and also possess the characteristic of deposited sulfur(biological sulfur) and deep source sulfur(magmatic sulfur), it is similar to δ34S characteristic of many skarn deposit in China, that is, its distribution is concentrated, range are generally ≤10‰, sulfide is the main ore minerals and almost no sulfate.In this paper, 17 pieces metal sulfides monominerals have been picked out from ore samples to do Pb isotope analysing. 4 pieces molybdenite, its 206Pb/204 Pb numerical value is among 18.518~18.531, 207Pb/204 Pb numerical value is among 15.571~15.589, 208Pb/204 Pb numerical value is among 38.526~38.595, and its μ numerical value is among 9.4~9.43; 2 pieces sphalerite, its 206Pb/204 Pb numerical value is 18.542 and 18.538, 207Pb/204 Pb numerical value is 15.614 and 15.617, 208Pb/204 Pb numerical value is 38.735 and 38.723, and its μ numerical value is 9.48; 8 pieces chalcopyrite, its 206Pb/204 Pb numerical value is among 18.472~18.55, 207Pb/204 Pb numerical value is among 15.534~15.613, 208Pb/204 Pb numerical value is among 38.435~38.615, and its μ numerical value is among 9.33~9.48; 5 pieces pyrrhotine, its 206Pb/204 Pb numerical value is among 18.47~18.501, 207Pb/204 Pb numericalvalue is among 15.531~15.558, 208Pb/204 Pb numerical value is among 38.444~38.515, and its μ numerical value is among 9.32~9.37. The test results show that the numerical value of Pb isotope is generally low. The difference among these monominerals sample’s isotope composition is small, it illustrated that Pb in the ore is main normal Pb, and do not possess the characteristic of mixed Pb and abnormal Pb. Through project the assaying results of Pb isotope in Zartman diagram of the structure pattern, it revealed that these data are almost all located in orogenic belt or its nearby where is close to the orogenic belt, indicated that the sources of Pb have the obvious characteristic of orogenic belt’s environmental origin, and it also suggests that formation of the deposit is associated with the collision orogeny, and it accord to the tectonic environment of the Gangdise island arc belt. Its numerical value of μ is relatively low, ranging from 9.4 to 9.43, it also suggested that the origin of Pb is main upper mantle or lower crust(magma source), and the mineralization are related to magmatic hydrothermal fluids.In summary, through studying, this paper’s opinion is that C, O, S, Pb isotope composition of Lietingang iron-copper poly-metals deposit obviously possess the characteristic of skarn deposit’s, as a consequence, Lietinggang iron-copper poly-metals deposit is a skarn deposit.