Geochemical Study Of Medium-acid Magmatic Rocks And Skarns In Tayuan Pb-Zn-Cu-Mo Deposit, Heilongjiang

The Tayuan(Cu-Mo)-Pb-Zn deposit is located in the east of the Central Asiann-Mongolia orogenic belt and the northeast of the Deerbugan tectonic-magmati belt.In the Paleozoic,evolution of the Paleo-Asian Ocean led to some micro-contiental blocks to join together Erguna,Xing'an and Songliao from the northwest to the southeast by a series of northeast-trending faults.During the period of the Mesozoic,the area was controlled by Siberian Plate and North China Plate due to collision,then rebuilded by Mongolia-Okhotsk tectonic system,resulting in the accretion of the Jiamusi massif and Nadanhada Terrane in the easternmost part of northeast China.It experiences compressional to extensional tectonics system in the late Mesozoic.Regional tectonic magmatic activity was very strong in Mesozoic.The intrusive rocks in the same period were widely distributed in the region and formed a amount of Pb-Zn-Cu-Mo-Au-Ag polymetallic deposit.It is one of the main metallogenic belt in China.The region has a huge resource potentialSystematic studies on regional geological setting,deposit geology,elemental geochemistry,isotope geochemistry,skarn mineralogy of the Tayuan Pb-Zn-Cu-Mo deposit were conducted.Several conclusions were drawn as below:(1)The SiO2 content of all magmatites changes from 53.55%to 77.46%and K2O+Na2O is from 4.49%to 8.93%.The data of major elements show that the volcanic and intrusive rocks are classified intermediate-acidic magmatic rock.all of samples mostly fall high K field in K2O-SiO2 diagram.Both of Tayuan intrusive and volcanica rock are moderately fractionated with light REEs enrichment and heavy REEs depletion.All of the sample are enriched in large ion lithophile elements(LILE)such as Rb,Ba,K,Pb and are clearly depleted in Nb,Ta,Sm,Ti.The all magmatites have a variable ISr ratios ranging from 0.705127 to 0.706191 with the calculated initial ?Nd(t)values between-1.14 and-0.81,the low Ba/Rb(<50),Nb/La(<1),and positive ?Hf(t)suggesting that the magma is related to subduction zone and some mantle derived magma was contamination by crustal materials or mixing by crustal source magma.(2)The paleo-Pacific Plate subduction to Eurasia influences Mesozoic magmatic activities in the the Great Xing'an Range.Due to the subduction,the continental crust became shorten and thicken gradually during Jurassic Period.Soon afterwards,the subduction direction was turning.The subduction recurvature make a conversion of tectonic regimes from the extrusion to extension in Northeast China.Subsequently it can led to delamination of continental crust and uplift of asthenospher.In this process,the thinning of lithosphere and the uplift of asthenosphere leaded to the intense crust-mantle interaction,the underplating of mantle-derived magma and directly heating on crust of asthenosphere make materials overlying lower crust partial melting and then form Tayuan intermediate-acidic magmas.(3)The mineral assemblage in the Tayuan polymetallic deposit is mainly andradite+grossular+diopside+epidote+wollastonite,and contains a little the spessartine and johannsenite.These characteristics indicate that Tayuan polymetallic deposit mainly belongs to calcareous skarn and a little skam in Tayuan is manganoan skarn.The compositional zone of garnet in the Tayuan deposit also shows that oxygen fugacity is increasing in the process of garnet formation,and ore-forming fluid has been evoluting from acidic to slight alkaline.(4)The geological bodies related to Tayuan deposit are granodiorite porphyry,granite porphyry,monzonite porphyry which diagenetic ages range from 148Ma to 152Ma.And the Chalukou molybdenite Re-Os average age is 148Ma.In conclusion,diagenetic age is similar to metallogenic age which indicates that the diagenetic and mineralization process is a continuous magma-hydrothermal metasomatism process.