Formation Age and Magmatic Source of the Wulantaolegai Cu-Ni Deposit in Central Inner Mongolia
The newly discovered medium-scale Wulantaolegai copper-nickel sulfide deposit marks a significant breakthrough in nickel prospecting in central Inner Mongolia.Central Inner Mongolia hosts several important mafic and ultramafic metallogenic belts.The Wulantaolegai Cu-Ni deposit formed within the Huanghuatan and Xiaonanshan mineralization belt.To understand the formation age and tectonic setting of the deposit and its cor-relations with the metallogenic zone,we conducted LA-ICP-MS zircon U-Pb dating and Hf isotope analysis,whole-rock major and trace element geochemistry,and Sr-Nd isotope analyses of gabbro and lamprophyre in the mining area.The results show that the U-Pb age of the gabbro is 270.8±3.2 Ma,and U-Pb ages of the lam-prophyre are approximately 251.5-250.9 Ma.They recorded two stages of magmatic activity during the exten-sion following the collision between the Siberian Craton and the North China Craton.The gabbro shows a sub-alkaline tholeiite series with a SiO2 content of approximately 47.3％-51.5％and a Na2O+K2O content of ap-proximately 1.0％-3.1％.The high(87Sr/86Sr)i value of approximately 0.7199-0.7239 and low εNd(t)value of approximately-12.18 to-9.55 suggest that the source of the magma may be EM Ⅱ-type enriched lithospheric mantle.A low SiO2 content of approximately 47.72％-52.15％and Na2O+K2O content of ap-proximately 4.47％-9.43％indicates that the lamprophyre belongs to the calc-alkaline potassium series.The peralkalic lamprophyre,enriched in LILE and LREE but depleted in HFSE(such as Nb,Ta and Ti),as well as its negative εHf(t)of approximately-20.0--2.9,indicates an enriched lithospheric mantle metasoma-tized by subduction fluids.These research achievements provide valuable insights for ore prospecting in the regional mafic and ultramafic rock bodies.
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