Metallogenic Chronology And Its Geological Significance In Nalinggou Sandstone-type Uranium, Ordos Basin

A series of large sandstone type uranium deposit had been found in the northern ordos basin. From east to west is Dongsheng uranium deposit, Hangjinqi (ore body form of V, t he east part of the Nalinggou), and Daying, etc.There are become the largest sandstone ty pe uranium deposits and the most perspective area, and preliminary shows a big uranium m ineralization zone. In prospecting for sandstone-type uranium deposits and study, deposit ti me and space distribution, especially the determination of metallogenic epoch is the key co ntent. Has been limited by theory and test means, sandstone type uranium deposit of traditi onal U-Pb dating might be controversial. Explore new methods is an important task for ge ology workers.In this paper, using the latest femtosecond laser ablation plasma mass spectrometry (fs-LA-ICP-MS) method in the Nalinggou sandstone type uranium deposit exploration for dating in northern ordos basin.fs-LA-ICP-MS uranium situ U-Pb dating have advantages o f high accuracy, short time of denudation,can effectively reduce the matrix effect. In total g et three groups coffinite LA-ICP-MS U-Pb age:3.46±0.2Ma(Pliocene)> 25.1 ± 1.1 Ma (Olig ocene),60.42±0.8Ma(Paleocene).Contact to the background, thought the Nalinggou regio n mainly experiences three periods of metallogenetic:early and late Cretaceous to Paleoce ne ancient interlayer oxidation zone type uranium mineralization period, is the main ore-fo rming period;The late Oligocene, for a mineralization period;The late Pliocene,transformat ion enrichment and protect mine stage.In order to understand the difference of U-Pb dating and new method, we also get th e U-Pb isochron dating,the age is (81±11) Ma. Linked to the predecessors of U-Pb dating in Dongsheng and Hangjinqi (the west part of the ore body), of fs-LA-ICP-MS method age and whole rock U-Pb method of age.Found the common features of age in northern b asin is end of the Jurassic or early cretaceous had begun to mineralization,and mainly creta ceous metallogenic period;And there is little or no Neohene age data.Therefore,the results f rom the data, the traditional U-Pb dating results, can not effectively reveal the young age o f a deposit;And fs-LA-ICP-MS method age is young and can test out the deposit.Contact in the northern ordos basin uplift of geological setting and tectonic evolution, and the characteristics of the sandstone uranium mineralization, Can compare the fs-LA-I CP-MS method and the reliability of the U-Pb dating results. The main body of the sandsto ne uranium metallogenic epoch and the period of the basin or later stage uplift are correspo nding. Ordos basin in late cretaceous and early tertiary period the overall upliftdenudation are appearred the first phase of the planation surface. Late Oligocene and early Miocene ap peared differences uplift, respectively in the second and third phase. Miocene and pliocene basin inversion uplift, Shillong east depression; loess plateau develop about 2.5 Ma. The p eriod of the tectonic events plays an important role in promoting.Based on the coupling rel ationship of tectonic uplift and uranium mineralization period, the age data of the above tw o methods and later stage tectonic events, you can see fs-LA-ICP-MS method more accord s with the practice of geological, thus has higher credibility, is worthy of further developm ent and perfection of sandstone type uranium deposit in the future application of precise da ting.In order to better serve the dating work,Based on the petrography characteristics,micr oscopic observation,electron microprobe analysis,microel-ement analysis.etching analysis t est methods,we detailed study the occurrence of ur-anium of the Nalinggou.There are two occurrences of Uranium state,part is independent uranium mineral (uranium),uramium is fi ne particulate and mainly exists pyrite,carbonate minerals in the form of partical aggregatio n,a small amout of uramium around of cement.The part mainly exists in pyrite and organic matter with dispersed adsorption..