电子探针测年方法应用于晶质铀矿的成因类型探讨

赵慧博; 刘亚非; 阳珊; 叶美芳; 王志海; 王博; 常娜

电子探针测年方法应用于晶质铀矿的成因类型探讨

1.
中国地质调查局西安地质调查中心，陕西西安 710054

2.
安徽省地质实验研究所，安徽合肥 230001

基金项目:
中国地质调查局地质调查工作项目(12120113014500)

详细信息

作者简介: 赵慧博，硕士，助理工程师，岩石矿物学专业。E-mail： zhaohuibo5566@126.com

通讯作者: 刘亚非，工程师，主要从事电子探针方面研究。E-mail： dogwuwu@163.com

收稿日期: 2013-07-11

录用日期: 2013-08-11

The Application of Electron Microprobe Dating Method on a Genetic Type of Uraninite

1.
Xi′an Center of Geological Survey, China Geology Survey, Xi′an 710054, China

2.
Anhui Institute of Geology and Mineral Resources Experiment, Hefei 230001, China

More Information

Corresponding author: yafei Liu, dogwuwu@163.com

Received Date: 11 July 2013

Accepted Date: 11 August 2013

摘要

摘要: 电子探针Th-U-Pb测年因其高分辨率与高精度的优势，在独居石、锆石等定年矿物中得到了推广，但在Th、U、Pb含量高的晶质铀矿、沥青铀矿等矿物中则应用较少。本文在铁矿床变质岩绿泥石、阳起石黑云母蚀变岩首次发现U含量高的晶质铀矿，基于此，结合该铁矿床地区的地质背景，利用偏光显微镜与电子探针等分析测试手段，将镜下蚀变现象、年龄计算与其他相关元素分析相结合，重点对晶质铀矿的成矿年龄及成矿规律进行探讨。研究发现：通过镜下观察判断，晶质铀矿的成因类型与澳大利亚著名的变质型铀矿相似，均为古老的变质型，且周围的脉石矿物均为绿泥石，绿泥石皆由黑云母退变质而成，铀矿的赋存位置显示其与黑云母、绿泥石之间有紧密联系，其成矿年龄与黑云母、绿泥石形成年龄息息相关。继而根据电子探针数据计算成矿年龄，判断成矿期次，得出主要成矿期在(1654±17) Ma~(1805±17) Ma，为中元古代中期，且主要成矿期与热液蚀变作用黑云母化有关，后期活化富集时期在(657±17) Ma~(807±17) Ma，为新元古代南华纪时期，此阶段是热液侵入、绿泥石化广泛发育的时期；选取较大颗粒对晶质铀矿的环带年龄进行计算，从年龄分布上证实后期有强烈的流体活动的发生，且主要与绿泥石化相关。另外，对比变质型与沉积型铀矿中Y2O3与UO2含量发现，两者之间存在负相关关系，此关系对判断铀矿成因即是否为变质型或沉积型可能有指示意义，但缺乏大量的数据佐证，需进一步研究。
- 晶质铀矿 /
- 电子探针 /
- 定年 /
- 环带年龄 /
- 成矿期次
Abstract: Based on the advantages of high resolution and accuracy, Electron Probe Microanalysis (EPMA) method for Th-U-Pb is conducted to date monazite and zircon, is not typically applied in uraninite, pitchblende and other minerals which contain high contents of Th, U and Pb. Uraninite with a high content of U was first found in the iron deposit, whose rock type was chlorite and actinolite biotite altered rock. Based on the region′s geological background, the microscopic alteration, age calculation and other related elements analysis, the uraninite mineralization age and metallogenic regularity have been studied intensely by Microscope and EPMA. The research results indicate that the genetic type of uraninite is similar to the famous metamorphic uraninite in Australia, belonging to the old metamorphic type. The gangue minerals are all chlorite altered by biotite. Occurrence characteristics of the uraninite reveal the close relationship between uraninote and biotite-chlorite. The mineralization age is also intimately related to the formation age of biotite and chlorite. According to the oxide content data of elements (U, Th and Pb) by EPMA, mineralized periods were obtained as the main mineralization stage is (1654±17) Ma-(1805±17) Ma, which is the mid Proterozoic and relate to the hydrothermal alteration of biotite. The later activation and enrichment period is (657±17) Ma-(807±17) Ma, which is the Neoproterozoic Nanhua period when hydrotherm invaded and chloritization was widely developed. Large-sized uraninite grains were selected to calculate their zoning ages. The age distribution shows that the strong fluid activity occurs at the late stage, and is mainly related to the chloritization. In addition, comparing the elements′ content (Y2O3 and UO2) between metamorphic uranium and sedimentary uranium, a negative correlation relationship was found between the two types. This relationship may have significance in determining whether it is metamorphic or sedimentary type, but this conclusion needs further study due to the lack of convincing evidence.
- uraninite /
- Electron Probe Microanalysis /
- age /
- zone age /
- mineralized periods

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图 1 绿泥石化阳起石黑云母岩中矿物特征

Figure 1.

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图 2 四种方法计算年龄结果对比图

Figure 2.

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图 3 晶质铀矿成矿年龄概率统计图

Figure 3.

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图 4 晶质铀矿年龄区间分布图

Figure 4.

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图 5 U9(左)与U18(右)颗粒取点点位

Figure 5.

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图 6 U9和U18颗粒年龄分布图

Figure 6.

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图 7 研究区变质型铀矿与其他地区沉积型铀矿的Y₂O₃与UO₂含量对比图

Figure 7.

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表 1 研究区晶质铀矿与我国其他地区变质型铀矿成分对比

Table 1. Comparison of the uraninite′s component in the study area and other metamorphic regions

研究地区	项目	w/%
研究地区	项目	UO₂	PbO	ThO₂
本研究区变质型晶质铀矿	变化范围	49.44~83.79	6.57~29.37	0.55~14.99
本研究区变质型晶质铀矿	平均值	66.56	17.78	6.90
我国其他地区变质型铀矿^[11]	变化范围	UO₂ 27.16~67.51	6.60~11.24	0.014~0.24
	变化范围	UO₃6.74~48.98	6.60~11.24	0.014~0.24
	平均值	UO₂ 54.49	8.54	0.061
	平均值	UO₃20.97	8.54	0.061

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表 2 晶质铀矿电子探针元素U、Pb、Th含量与年龄计算结果

Table 2. The contents of U,Pb,Th in the uraninite and their ages

编号	w/%			年龄/Ma				编号	w/%			年龄/Ma
编号	UO₂	PbO	ThO₂	Age1	Age2	Age3	Age4	编号	UO₂	PbO	ThO₂	Age1	Age2	Age3	Age4
U1	70.541	22.373	5.147	2457	2278	1938	1894	U14	73.1	21.244	4.465	2261	2115	1831	1770
U2	72.244	21.413	5.044	2299	2151	1825	1796	U15	70.772	20.066	5.378	2194	2071	1719	1730
U3	70.09	18.554	5.333	2049	1952	1604	1635	U16	67.755	19.98	7.553	2254	2142	1640	1772
U4	78.5	6.571	6.008	647	683	506	583	U17	83.797	8.78	0.552	831	844	771	733
U5	66.989	18.436	8.682	2091	2019	1469	1669	U18	67.416	17.615	9.659	1976	1931	1353	1593
U6	68.949	18.864	6.617	2103	2009	1579	1673	U19	66.649	20.231	9.827	2292	2195	1558	1801
U7	49.44	29.367	14.999	4259	3767	2284	2881	U20	70.142	19.972	3.518	2224	2079	1847	1745
U8	57.645	18.909	18.145	2343	2343	1238	1853	U21	74.311	9.239	7.139	955	991	717	838
U9	66.676	19.643	8.328	2242	2140	1589	1766	U22	67.642	20.288	6.678	2303	2173	1719	1802
U10	68.501	22.408	7.874	2498	2338	1805	1925	U23	66.601	18.37	8.182	2100	2023	1495	1674
U11	72.371	20.602	4.637	2213	2078	1779	1740	U24	66.017	21.29	6.952	2471	2311	1820	1907
U12	65.263	17.751	10.103	2049	1999	1374	1643	U25	67.883	19.254	5.131	2196	2072	1721	1730
U13	73.873	17.347	6.815	1807	1759	1367	1473	U26	74.295	11.477	3.46	1208	1210	1012	1034

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表 3 U9晶质铀矿环带数据

Table 3. The band data of uraninite U9

氧化物	w/%
氧化物	U9-1	U9-2	U9-3	U9-4	U9-5	U9-6	U9-7	U9-8	U9-9	U9-10	U9-11	U9-12	U9-13	U9-14	U9-15	U9-16	U9-17	U9-18	U9-19	U9-20
UO₂	59.284	58.777	60.091	60.889	60.201	61.366	61.734	61.141	60.315	61.487	61.88	61.13	61.282	60.199	62.323	61.828	67.684	68.821	63.683	61.426
PbO	18.353	17.312	17.458	17.595	18.069	18.686	15.946	17.709	18.078	17.528	16.873	17.759	18.011	17.833	17.331	17.612	20.294	20.416	19.129	17.744
ThO₂	18.006	20.121	16.939	15.492	16.447	15.213	15.794	15.052	14.766	15.042	14.651	15.111	15.297	16.015	16.3	17.007	8.295	7.928	13.376	16.434
年龄/Ma (Ag4)	1772	1687	1689	1691	1738	1768	1540	1698	1747	1676	1618	1701	1717	1722	1636	1664	1792	1780	1762	1686

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表 4 U18晶质铀矿环带数据

Table 4. The band data of uraninite U18

氧化物	w/%
氧化物	U18-1	U18-2	U18-3	U18-4	U18-5	U18-6	U18-7	U18-8	U18-9	U18-10	U18-11	U18-12	U18-13	U18-14	U18-15	U18-16	U18-17	U18-18	U18-19	U18-20
UO₂	70.475	73.426	74.663	76.972	77.4	79.229	82.957	81.783	82.812	81.881	78.799	77.186	76.769	75.22	75.491	74.086	73.241	73.832	69.946	69.565
PbO	19.763	18.192	18.443	16.443	16.819	9.315	5.54	6.81	5.495	7.355	10.926	10.261	13.434	11.274	12.875	17.164	14.102	13.9	19.197	21.006
ThO₂	2.851	2.095	0.937	2.078	0.962	4.486	4.77	4.378	4.802	3.179	4.591	4.788	3.005	4.861	4.066	2.957	4.71	5.137	3.299	4.938
年龄/Ma (Ag4)	1728	1564	1566	1380	1405	804	473	584	470	629	935	899	1157	1001	1127	1474	1250	1225	1695	1822

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表 5 研究区变质型铀矿与其他地区沉积型铀矿的Y₂O₃与UO₂含量

Table 5. The content of Y₂O₃ and UO₂ in the study area and other sedimentary uranium deposits

氧化物	研究区变质型铀矿 w/%															其他地区沉积型铀矿w/%
氧化物	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	1	2	3	4	5	6	7	8	9	10	11	12	13	14
Y₂O₃	2.68	0.79	2.39	2.69	0.87	3.11	2.27	0.35	0.96	3.58	0.43	0.34	1.30	2.20	0.26	4.97	4.23	9.51	7.57	6.14	6.38	7.45	6.87	4.48	8.44	3.13	7.82	6.29	9.93
UO₂	70.09	78.5	66.99	68.95	77.93	57.65	66.68	68.50	72.37	65.26	73.87	86.77	70.77	67.75	83.8	60.43	54.97	35.62	48.94	32.35	40.89	40.43	43.61	53.42	52.16	55.25	42.48	37.69	36.84

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