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杞落寨稀土矿床位于四川省冕宁县境内,雅砻江西侧。矿体产于英碱正长岩与变质辉绿岩和大理岩接触的构造破碎带中此前,英碱正长岩被认为形成于燕山期,但没有任何同位素年龄资料的报道本文通过~(40)Ar/~(39)Ar 快中子活化分析,得出英碱正长岩微斜长石的~(40)At/~(39)Ar 坪年龄为31.2±0.56Ma,等时线年龄为30.6±2.6Ma。矿石金云母的~(40)Ar/~(39)Ar 坪年龄为35.5±0.5Ma,等时线年龄为35±1Ma。微斜长石的年龄比金云母年龄偏小,是因为两者的 Ar 同位素封闭温度不同,前者约为170℃,而后者为350℃。两者年龄差较大表明在35.5～31.2Ma 之间,矿体和岩体均进入了较慢冷却阶段,冷却速率约为41.9℃/Ma。因此,木落寨矿床的矿石与英碱正长岩的形成年龄接近,均属新生代喜马拉雅期木落寨矿床成岩成矿年龄的确定,对于进一步了解该区域偏碱性火成岩的形成时代及拓宽区域稀土找矿远景,具有很大意义。
Qiluzhai Rare Earth Deposit is located in Mianning County, Sichuan Province, west of Yalong River. Alkali-alkali syenite is thought to have formed in the Yanshanian period but no isotopic age data have been reported. In this paper, ~ (40 ) Ar / ~ (39) Ar fast neutron activation analysis shows that the ~ (40) At / ~ (39) Ar plateau age of the Alkali-alkali syenite is 31.2 ± 0.56Ma and the isochron age is 30.6 ± 2.6Ma. The ~ (40) Ar / ~ (39) Ar plateau age of ore mica is 35.5 ± 0.5Ma, and the isochron age is 35 ± 1Ma. Micro plagioclase is younger than phlogopite due to the different Ar isotopic closure temperatures, which are about 170 ° C for the former and 350 ° C for the latter. The larger age difference between the two shows that between 35.5 and 31.2 Ma, both the ore body and the rock mass enter a slower cooling stage and the cooling rate is about 41.9 ° C / Ma. Therefore, the age of the ore of the Muluzhai deposit is similar to that of the Alkali-alkali syngenetic ores, which are all determined by the age of diagenesis and mineralization of the Muduzhai deposit in the Himalayas of the Cenozoic. It is of great significance to further understand the age and broadening of the over-alkaline igneous rocks in this area Regional prospecting prospect of rare earth, has great significance.