黑龙江省团结沟浅成低温热液金矿床成因——锆石U-Pb定年、元素地球化学和Hf-S-Pb-He同位素证据

Genesis of Tuanjiegou Epithermal Gold Deposit in Heilongjiang Province:Evidence from Zircon U-Pb Dating,Element Geochemistry and Hf-S-Pb-He Isotopes

团结沟金矿床位于黑龙江省中部嘉荫县境内,是我国东北地区最大的浅成低温热液型金矿床。本文对与成矿有关的花岗闪长斑岩和花岗斑岩进行了系统的岩相学、锆石U-Pb定年、全岩主量和微量元素、LA-ICP-MS锆石原位微量元素、Hf同位素、LA-ICP-MS原位S同位素及矿石的载金矿物黄铁矿Pb-He同位素研究。结果表明:花岗闪长斑岩和花岗斑岩的锆石U-Pb年龄分别为(105.9±1.1)和(102.3±1.2)Ma,属于钙碱性-高钾钙碱性系列岩石;两者呈现富集轻稀土元素和Rb、K等大离子亲石元素,亏损P、Ti、Nb、Ta等高场强元素特征;花岗闪长斑岩中锆石Ce^(4+)/Ce^(3+)值为165~656(均值为322)、Ti饱和温度为605~715℃(均值为658℃),花岗斑岩中锆石Ce^(4+)/Ce^(3+)值为359~868(均值为480)、Ti饱和温度为606~680℃(均值为646℃);两者的锆石ε_(Hf)(t)值分别为6.9~8.1和5.6~8.2;黄铁矿的δ^(34)S值为-7.8‰~-0.2‰,均值为-3.5‰,普通铅同位素比值^(206)Pb/^(204)Pb值为18.160~18.399、^(207)Pb/^(204)Pb值为15.538~15.590、^(208)Pb/^(204)Pb值为38.135~38.340;黄铁矿中流体包裹体R/R_(a)值为0.75~1.23。综合研究表明:与成矿密切相关的岩浆为同源结晶岩浆演化产物,岩浆就位发生在早白垩世,初始岩浆可能来源于古太平洋板片俯冲背景下年轻下地壳物质部分熔融的产物,形成过程中混合部分幔源物质;成矿流体来自深源岩浆,具有壳-幔混源特征(地壳为主,地幔流体占8.23%~13.62%),花岗斑岩更高的氧逸度和更低的岩浆结晶温度为金富集过程和良好的运移提供了基础,有利于大规模金矿化。

The Tuanjiegou deposit,located in Jiayin County,Heilongjiang Province,is the largest epithermal gold deposit in Northeast China.This study systematically investigated the petrography,zircon U-Pb dating,whole-rock major and trace elements,LA-ICP-MS zircon in-situ trace elements and Hf isotopes of granodiorite porphyry and granite porphyry.Additionally,single mineral Pb-He isotope and LA-ICP-MS in-situ S isotope analyses of gold-bearing pyrite were conducted.The zircon U-Pb ages of granodiorite porphyry and granite porphyry are(105.9±1.1)Ma and(102.3±1.2)Ma,respectively,belonging to calc-alkaline to high-K calc-alkaline series.These rocks are enriched in light rare earth elements and large ion lithophile elements such as Rb and K,but depleted in P,Ti,Nb,Ta and other high field strength elements.The Ce^(4+)/Ce^(3+)values of zircons in granodiorite porphyry range from 165 to 656℃(mean 322℃),with Ti saturation temperatures ranging from 605 to 715℃(mean 658℃).On the other hand,the Ce^(4+)/Ce^(3+)values of zircons in granite porphyry range from 359 to 868(mean 480),with Ti saturation temperatures ranging from 606 to 680℃(mean 646℃).Zirconε_(Hf)(t)values of these two rocks are 6.9-8.1 and 5.6-8.2,respectively.The δ^(34)S value of pyrite ranges from -7.8‰ to -0.2‰ with an average of-3.5‰,and the common Pb isotope ratios are ^(206)Pb/^(204)Pb=18.160-18.399,^(207)Pb/^(204)Pb=15.538-15.590,and ^(208)Pb/^(204)Pb=38.135-38.340.The R/R_(a) values of fluid inclusions in pyrite range from 0.75 to 1.23.Comprehensive characteristics suggest that the mineralization-related magma is derived from the evolution of homologous crystalline magma,and the of magma emplacement occurred during the Early Cretaceous.The initial magma may have originated from the partial melting of the young lower crust material during the subduction of the Paleo-Pacific plate,with some mantle-derived materials mixed in during the formation process.The ore-forming fluid comes from deep magma and exhibits the characteristics of a mixed crust-mantle source(with the crust being the main source and mantle fluid accounting for 8.23% to 13.62%).The higher oxygen fugidity and lower magmatic crystallization temperature of granite porphyry provide favorable conditions for gold accumulation and migration,thus facilitating large-scale gold mineralization.