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澜沧老厂矿山继上世纪80年代末在钻孔中揭露到花岗斑岩细脉以来,2007年又在ZK153101、ZK14827中揭露到厚大的斑岩脉及主岩体。为了查明隐伏花岗斑岩体的年代,本文应用锆石SHRIMP U-Pb同位素法对老厂花岗斑岩进行了精确的定年,获得的加全平均年龄为44.6±1.1Ma,代表花岗斑岩的结晶年龄。继承锆石的年龄为529.3±13Ma,可能反映了岩浆的源岩年龄。年代学研究表明,花岗斑岩形成于始新世,为老厂斑岩型钼矿的成矿母岩。澜沧老厂斑岩钼矿的成岩成矿作用发生在新生代陆内碰撞造山的主碰撞阶段,与三江地区新生代斑岩型矿床成矿高峰期吻合。澜沧老厂的成岩成矿表明“三江”地区在澜沧江断裂以西也存在新生代斑岩成矿作用。
Lancang old factory mine since the late 80s of the last century exposed in the drill to the granite porphyry vein since 2007, and in ZK153101, ZK14827 revealed thick porphyry veins and the main rock. In order to find out the age of the concealed granite porphyry body, the zircon dating SHRIMP U-Pb isotope method was used to accurately determine the granite porphyry in Laochang. The average age of the granite porphyry was 44.6 ± 1.1Ma, Porphyry crystallization age. The inheritance of zircon is 529.3 ± 13Ma, which may reflect the source rock age of magma. Geochronological studies show that the granite porphyry was formed in the Eocene, which is the metallogenic parent rock of the porphyry molybdenum deposit in Laochang. The diagenesis and mineralization of porphyry molybdenum in Lanchang old factory occurred in the main collision stage of Cenozoic intracontinental collision orogeny and coincided with the peak of the mineralization of Cenozoic porphyry deposits in Sanjiang area. The diagenesis and mineralization of the old Lancang factory indicate that there is also the Cenozoic porphyry mineralization in the “Sanjiang” area west of the Lancangjiang fault.