The newly discovered Chagele skarn‐porphyry deposit is located in the Middle‐Gangdese metallogenic belt . This study focuses on the zircon U Pb age of the ore‐bearing porphyry and molybdenite Re Os ,the whole rock major elements ,trace elements ,and the Sr Nd Hf isotopic data of the ore‐bearing rocks in Chagele deposit .The zircon U Pb age of the ore‐bearing porphyry changes from 64 .6 to 62 .9 Ma ,which represents the magmatic crystallization age .The Re Os isotopic age shows that the deposit was formed at (62 .3 ± 1 .4) Ma ,which is consistent with the magmatic age in the study area .Combing with the extensive volcanic event of Linzizong Group ,these new data suggests that the different scales of mineralization were formed at different stages in the entire collision between India and Eurasia continent .The ore‐bearing porphyry of Chagele deposit has high contents of SiO 2 ,K2 O , Rb ,Th ,and U ,coupled with low contents of TiO 2 , P2 O5 ,negative anomalies of Nb ,Zr ,variableεHf (t) ( - 7 .02 ~ - 1 .27) ,and ancient TCDM (1 093 ~ 1 419 Ma) .In comparison with the Gangdese continental crust composition ,the ore‐bearing porphyry is high in εNd (t) ( - 6 .64 ~ - 5 .79) and low in (87 Sr/86 Sr)i (0 .711 813 ~ 0 .717 307) .These geochemical features indicate that the porphyry of Chagele deposit is similar to the peraluminous feature of S‐type granite .The above discussion suggests that the Paleocene magmatism and mineralization in the middle section of the Middle‐Gangdese metallogenic belt could be formed through partial melting of the ancient crust materials of Gangdese micro‐continent accompanying with fractional crystallization ,which was probably induced by upwelling of mantle‐derived magma in the main collision between Indian and Eurasia continent .

龙根铅锌矿床是在西藏中冈底斯成矿带中段发现的一个矽卡岩型矿床.对该矿床含矿斑岩进行了LA-ICP-MS锆石U-Pb定年,主量、微量元素分析和Sr-Nd-Hf同位素组成研究,首次获得中冈底斯成矿带中段铅锌银矿床的矿化时代.含矿斑岩锆石U-Pb年龄明显可分为2组,206pb/23sU加权平均年龄分别为(70.5±2.0) Ma和(61.4±1.2) Ma,前者记录了印-亚板块俯冲大陆边缘弧后伸展过程中的早期岩浆-流体成矿事件,后者代表了印-亚板块主碰撞聚合中的主成矿期岩浆-流体成矿作用时代.斑岩具富硅、富钾,贫钛、贫磷等特征,铝饱和指数(A/CNK)为1.11～1.16,富集大离子亲石元素Rb、Th、U,亏损高场强元素Zr、Nd、Sm等,与冈底斯成熟大陆地壳物质相比具相对高的εNd(t)值(-6.42～-6.05)和相对低的(87Sr/86Sr)i值(0.708 026～0.709 071),并具不均一的锆石εNf(t)值(-3.34～-1.12)以及古老的锆石Hf同位素地壳模式年龄(Tc=1.06～1.19 Ca),属于过铝质“S”型花岗岩类.笔者认为中冈底斯成矿带中段晚白垩世一古新世岩浆活动和成矿作用很可能是与雅鲁藏布江洋盆闭合之后的印-亚板块俯冲大陆边缘弧后伸展和主碰撞聚合诱发幔源岩浆底侵导致的冈底斯地体古老地壳物质部分熔融有关,岩浆在上升过程中有不同程度的分离结晶.

A number of large-very large porphyry Cu-Mo-Au deposits have been discovered in the Tibetan plateau,which has caused widespread concern in recent years.Existing research results show that the formation ages of thse ore-bearing porphyries and porphyry deposits in the Tibetan Pleteau concentrate mainly on four stages:120~110 Ma,~90 Ma,54~45 Ma and 18~12 Ma,but the ore-forming geological background of porphyry deposits forming at the second stage(90Ma) is still controversial.This study reports the zircon LA-ICPMS U-Pb and molybdenites Re-Os ages of the porphyry Cu-Mo-Au deposits in the northern Lhasa terrane,along with analysis of ore-forming background.Two weighted average 206Pb/238U ages for two granodioritic porphyry samples are 92.1±1.2 Ma and 93.8±1.2 Ma,which probably record the age of magma crystallization,while the molybdenites Re-Os isotopic age of 88.2~89.6 Ma probably represents the age of mineralization of the Balazha porphyry deposits.Based on the regional geochemical data,this study suggests that the magmatism and mineralizaion at ~90 Ma in the northern Lhasa terrane was neither the prodcut of subduction of the Neo-Tethys ocean and oceanic ridge,which are represented by the Yarlung-zangbo suture,nor the direct result of subduction of the Bangongco-Nujiang Ocean,but likely the product of collision process after the subduction and closure of the Bangongco-Nujiang Ocean.

Chagele skarn-porphyry deposit have been recently discovered in Tibet, which is located in middle of the Gangdese ( or central Lhasa Terrane) metallogenic belt. However, it is absence of the high-precision chronology of porphyritic intrusion and deposit so far. The zircon U-Pb and Molybdenites Re-Os ages are reported in this study, with the bulk-rock major element, trace element and zircon Hf isotopic data on the ore-bearing rocks in Chagele deposit. Zircon U-Pb age of granitic porphyry is divided into two groups, 72. 2 similar to 70. 1Ma and 65. 2 similar to 64. 4Ma, which probably record the early tectonic-magmatic event and the latter magmatic crystallization, respectively. Molybdenites Re-Os isotopic dating shows that the molybdenite is formed at 71. 5 +/- 1. 3Ma, which is consistent with the early magmatism in the studying area. These new data in this studying, combing with the extensive volcanism of Linzizong Group, suggest that different sizes of mineralization were formed at different stages of the entire collision process between India and Eurasia. The ore-bearing porphyry of Chagele deposit have high SiO2, K2O, Rh, Th, and U contents, coupled with low TiO2, P2O5 contents and strong negative anomalies of Ba, Nb, Ta, Sr, P and Eu, variable epsilon(Hf)(t) (-7. 9 similar to -2. 2) and ancient t(DM)(c)(1. 3 similar to 1. 6Ga). These geochemical features suggest that the samples of Chagele deposit are similar to the peraluminous of S-type granites. This paper suggests that the Late Cretaceous magmatism and mineralization in middle of the Gangdese metallogenic belt could be produced by partial melting of ancient crust materials of the Lhasa microcontinent accompanying with fractional crystallization, which are probably induced by underplating of mantle-derived magmas in the main collision setting of the collision between Indian and Eurasia. We also believe that the zonation of the ore-forming element in the Gangdese metallogenic belt is associated with source material of magma during subduction or collision process of the Neo-Tethyan oceanic.

Chagele skarn-porphyry deposit have been recently discovered in Tibet, which is located in middle of the Gangdese (or central Lhasa Terrane) metallogenic belt. However, it is absence of the high-precision chronology of porphyritic intrusion and deposit so far. The zircon U-Pb and Molybdenites Re-Os ages are reported in this study, with the bulk-rock major element, trace element and zircon Hf isotopic data on the ore-bearing rocks in Chagele deposit. Zircon U-Pb age of granitic porphyry is divided into two groups, 72. 2 ∼70. 1 Ma and 65. 2 ∼64. 4Ma, which probably record the early tectonic-magmatic event and the latter magmatic crystallization, respectively. Molybdenites Re-Os isotopic dating shows that the molybdenite is formed at 71. 5 ± 1. 3Ma, which is consistent with the early magmatism in the studying area. These new data in this studying, combing with the extensive volcanism of Linzizong Group, suggest that different sizes of mineralization were formed at different stages of the entire collision process between India and Eurasia. The ore-bearing porphyry of Chagele deposit have high SiO 2, K 2O, Rb, Th, and U contents, coupled with low Ti0 2, P 20 5 contents and strong negative anomalies of Ba, Nb, Ta, Sr, P and Eu, variable ε Hf(t) (- 7. 9 ∼ - 2. 2) and ancient t BM (1.3-1. 6Ga). These geochemical features suggest that the samples of Chagele deposit are similar to the peraluminous of S-type granites. This paper suggests that the Late Cretaceous magmatism and mineralization in middle of the Gangdese metallogenic belt could be produced by partial melting of ancient crust materials of the Lhasa microcontinent accompanying with fractional crystallization, which are probably induced by underplating of mantle-derived magmas in the main collision setting of the collision between Indian and Eurasia. We also believe that the zonation of the ore-forming element in the Gangdese metallogenic belt is associated with source material of magma during subduction or collision process of the Neo-Tethyan oceanic.