The Application of Electron Microprobe Dating Method on Uranium Minerals in Changjiang Granite, Northern Guangdong
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摘要:
晶质铀矿被认为是花岗岩型铀矿成矿的主要矿源提供者, 在评价岩体的含矿性和确定成岩成矿年龄方面有重要意义。长江岩体属于诸广山复式岩体的一部分, 是粤北地区重要的产铀花岗岩体, 本文利用电子探针对该岩体中的铀矿物进行研究。结果表明:长江岩体中的铀矿物多以充填或被黄铁矿包围的形式存在, 或者分布于石英、黑云母、绿泥石等矿物中; 铀矿物类型主要有晶质铀矿、沥青铀矿、铀石、铀钍石四种。晶质铀矿/沥青油矿的化学年龄值可分为三组:~155 Ma、~106 Ma和~74 Ma。第一组年龄代表岩体的形成时代, 后两组年龄代表铀矿的多期次成矿作用年龄。铀矿物从成岩后到~106 Ma, 成分没有发生明显变化, 直到~74 Ma后才发生明显的U元素活化、迁移。因此, 可以推测长江岩体地区主要的铀矿成矿期应发生在~74 Ma及之后。
Abstract:Uraninite is considered to be the main ore source provider of granite-hosted uranium deposits, it plays a significant role in mineralization assessment of granite and constraining the age of digenesis and uranium mineralization.Changjiang granite is a part of the Zhuguang Mountains, and is important U-bearing granite in the north of Guangdong.Uranium minerals in this granite are studied by Electron Microprobe.Results show that uranium minerals mainly fill in the spaces between minerals or are surrounded by pyrite.Uranium minerals are also found in quartz, biotite, chlorite and other minerals.The main types of uranium minerals are uraninite, pitchblende, uranothorite and uranophane.The chemical ages of uraninite and pitchblende dated by Electron Microprobe can be divided into three groups, 155 Ma, 106 Ma and 74 Ma.The first group represents the formation age of Changjiang granite mass, and the second and third groups represent multiple stages of uranium mineralization.From rock formation to about 106 Ma, the composition of uraninite has not changed significantly.Obvious U activation and migration did not happen until 74 Ma, so the main uranium mineralization of Changjiang granite may have occurred at about 74 Ma or later.
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图 1 长江岩体分布及采样位置略图(据黄国龙等[13],2014)
Figure 1.
表 1 铀矿物的电子探针分析结果及化学年龄
Table 1. EPMA analytical results of the main elements and their ages
样品编号 含量(%) 含量(%) 年龄(Ma) UO 2 ThO 2 PbO SiO 2 CaO FeO Y 2O 3 Ce 2O 3 Nd 2O 3 总量 U Th Pb CJ304-1-1 84.041 8.659 1.631 0 0 0.43 1.656 0.358 0.316 97.091 74.082 7.610 1.514 148.7 CJ304-1-2 83.705 6.177 1.097 0.008 0 0.457 1.624 0.283 0.236 93.587 73.786 5.428 1.018 101.5 CJ304-2-1 88.096 5.253 1.193 0.018 0 0.042 1.187 0.138 0 95.927 77.657 4.616 1.107 105.4 CJ304-2-2 86.737 5.486 1.252 0.01 0 0.021 1.045 0.214 0.031 94.796 76.459 4.821 1.162 112.2 CJ304-2-3 88.812 6.934 1.802 0 0 0.012 0.941 0.113 0.033 98.647 78.288 6.094 1.673 156.9 CJ304-2-4 88.967 5.719 1.408 0.273 0 0 0.946 0.095 0.042 97.45 78.424 5.026 1.307 123.0 CJ304-2-5 89.483 5.054 1.34 0 0 0.057 0.883 0.16 0.049 97.026 78.879 4.441 1.244 116.7 CJ304-2-6 90.133 6.416 1.819 0 0 0 0.821 0.171 0.016 99.376 79.452 5.638 1.689 156.4 CJ304-2-7 90.276 4.176 1.277 0.014 0 0.016 0.827 0.185 0.004 96.775 79.578 3.670 1.185 110.6 CJ304-2-8 86.99 5.449 1.182 0 0 0.055 1.041 0.146 0.041 94.904 76.682 4.789 1.097 105.6 CJ304-2-9 90.546 4.781 1.531 0 0 0 0.697 0.139 0 97.694 79.816 4.202 1.421 131.9 CJ304-2-10 91.823 3.365 1.257 0 0 0.034 0.624 0.16 0.015 97.278 80.942 2.957 1.167 107.4 CJ304-2-11 91.93 5.191 1.877 0.001 0 0.094 0.649 0.14 0 99.882 81.036 4.562 1.742 159.1 CJ304-2-12 91.689 3.756 1.807 0 0 0.034 0.75 0.198 0 98.234 80.824 3.301 1.677 154.4 CJ304-2-13 88.572 4.737 1.326 0 0 0.009 0.859 0.133 0.016 95.652 78.076 4.163 1.231 116.8 CJ304-2-14 89.52 6.788 1.775 0 0 0 0.937 0.094 0 99.114 78.912 5.965 1.648 153.4 CJ304-2-15 90.563 3.784 1.228 0 0 0.059 0.796 0.215 0 96.645 79.831 3.325 1.140 106.2 CJ304-2-16 91.889 3.268 1.151 0 0 0.041 0.709 0.144 0 97.202 81.000 2.872 1.068 98.3 CJ304-2-17 86.916 5.686 1.235 0 0 0 1.06 0.131 0.071 95.099 76.616 4.997 1.146 110.3 CJ304-2-18 86.49 8.482 1.789 0 0 0.003 1.077 0.204 0.045 98.09 76.241 7.454 1.661 158.8 CJ304-2-19 89.073 4.217 1.149 0.125 0 0.037 0.88 0.081 0.102 95.664 78.518 3.706 1.067 100.8 CJ304-2-20 89.749 3.544 1.178 0.106 0 0.044 1.027 0.208 0 95.856 79.114 3.114 1.094 102.9 CJ304-3-1 88.733 5.847 1.766 0 0 0.411 1.647 0.215 0.161 98.78 78.218 5.138 1.639 154.5 CJ304-3-2 89.576 5.529 1.672 0.086 0 0.635 1.464 0.187 0.016 99.165 78.961 4.859 1.552 145.1 CJ304-3-3 88.355 4.316 1.264 0.011 0 0.594 2.305 0.24 0.222 97.307 77.885 3.793 1.173 111.8 CJ304-3-4 84.002 8.173 1.704 0 0 0.078 2.436 0.305 0.161 96.859 74.048 7.182 1.582 155.8 CJ304-3-5 83.635 5.34 1.263 0.143 0 0.121 2.658 0.19 0.167 93.517 73.724 4.693 1.172 117.3 CJ304-3-6 83.401 7.142 1.386 0 0 0.223 2.346 0.237 0.178 94.913 73.518 6.276 1.287 128.1 CJ304-3-7 83.915 8.565 1.734 0.022 0 0.121 2.361 0.345 0.171 97.234 73.971 7.527 1.610 158.4 CJ304-3-8 83.44 4.537 1.179 0.032 0 0.365 2.026 0.186 0.213 91.978 73.552 3.987 1.094 110.2 CJ304-3-9 82.994 6.705 1.357 0 0 0.095 2.175 0.305 0.179 93.81 73.159 5.892 1.260 126.3 CJ304-3-10 83.315 8.644 1.699 0.07 0 0.013 2.391 0.264 0.187 96.583 73.442 7.596 1.577 156.2 CJ304-3-11 83.519 6.105 1.229 0 0 0.064 2.384 0.218 0.187 93.706 73.622 5.365 1.141 114.0 CJ304-3-12 85.782 4.824 1.207 0 0 0.186 2.686 0.268 0.267 95.22 75.617 4.239 1.120 109.6 CJ304-3-13 90.679 5.632 1.828 0.023 0 0.857 1.842 0.245 0.082 101.188 79.934 4.949 1.697 156.7 CJ211-1-1 82.649 5.178 1.23 0 0 0.185 3.583 0.289 0.293 93.407 72.855 4.550 1.142 115.7 CJ211-1-2 85.194 6.32 1.716 0.223 0 0.027 2.158 0.245 0.192 96.075 75.099 5.554 1.593 155.9 CJ211-1-3 84.384 4.743 1.234 0.28 0 0.186 2.699 0.315 0.305 94.146 74.384 4.168 1.146 113.9 CJ211-1-4 86.194 6.241 1.63 0 0 0.498 2.425 0.212 0.103 97.303 75.980 5.485 1.513 146.5 CJ211-1-5 87.942 4.409 1.169 0.142 0 0.955 2.059 0.206 0.346 97.228 77.521 3.875 1.085 103.8 CJ211-1-6 88.39 4.157 1.058 0 0 0.623 1.88 0.186 0.196 96.49 77.916 3.653 0.982 93.6 CJ211-1-7 83.574 4.586 1.155 0 0 0.145 2.895 0.27 0.295 92.92 73.670 4.030 1.072 107.7 CJ211-1-8 86.02 3.391 1.133 0 0 0.009 2.418 0.23 0.221 93.422 75.827 2.980 1.052 103.2 CJ211-1-9 85.326 3.472 1.149 0 0 0.039 2.866 0.372 0.339 93.563 75.215 3.051 1.067 105.5 CJ211-1-10 85.992 4.109 1.144 0.017 0 0 2.03 0.219 0.265 93.776 75.802 3.611 1.062 104.0 CJ211-1-11 88.482 6.872 1.709 0 0 0.39 1.865 0.283 0.249 99.85 77.997 6.039 1.586 149.3 CJ211-1-12 87.528 4.219 1.108 0 0 0.233 1.976 0.262 0.153 95.479 77.156 3.708 1.029 98.9 CJ211-1-13 87.604 4.619 1.176 0 0 0.082 1.848 0.253 0.206 95.788 77.223 4.059 1.092 104.7 CJ211-1-14 84.254 4.158 1.099 0 0 0.054 2.761 0.426 0.484 93.236 74.269 3.654 1.020 101.9 CJ211-1-15 81.635 4.229 1.099 0.314 0 0.082 3.311 0.261 0.282 91.213 71.961 3.716 1.020 105.1 CJ211-2-1 91.438 6.528 1.849 0 0 0.063 0.573 0.077 0 100.528 80.603 5.737 1.716 156.7 CJ211-2-2 89.747 7.336 1.867 0 0 0.124 0.551 0.138 0 99.763 79.112 6.447 1.733 160.6 CJ211-2-3 88.306 7.615 1.804 0 0 0.091 1.088 0.164 0.062 99.13 77.842 6.692 1.675 157.5 CJ211-2-4 88.187 7.346 1.814 0 0 0.514 0.758 0.144 0.022 98.785 77.737 6.456 1.684 158.7 CJ211-2-5 88.688 6.768 1.899 0 0 0.074 1.033 0.153 0.086 98.701 78.178 5.948 1.763 165.6 CJ211-3-1 91.497 4.863 1.797 0.013 0 0.777 0.83 0.22 0 99.997 80.655 4.274 1.668 153.2 平均值 87.328 5.526 1.436 0.034 0.000 0.185 1.632 0.211 0.130 96.483 76.980 4.856 1.333 - CJ304-4-1 77.497 0 0.803 2.121 9.483 0.292 1.033 0.717 1.253 93.199 68.314 0.000 0.745 82.4 CJ304-4-2 76.751 0 0.712 2.908 7.132 0.281 1.347 0.91 1.448 91.489 67.656 0.000 0.661 73.8 CJ304-4-3 77.795 0 0.656 2.244 8.465 0.296 1.463 0.911 1.34 93.17 68.576 0.000 0.609 67.0 CJ304-4-4 78.114 0 0.895 2.367 8.259 0.178 1.27 0.542 1.123 92.748 68.857 0.000 0.831 91.1 CJ304-4-5 75.843 0 0.706 2.401 8.226 0.247 1.313 1.51 2.467 92.713 66.856 0.000 0.655 74.0 CJ304-4-6 74.79 0 0.736 3.903 6.948 0.332 1.718 0.885 1.511 90.823 65.927 0.000 0.683 78.2 CJ304-4-7 76.277 0 0.706 2.209 8.333 0.278 1.344 0.85 1.407 91.404 67.238 0.000 0.655 73.6 CJ304-4-8 77.393 0 0.719 3.339 5.798 0.359 1.398 0.924 1.258 91.188 68.222 0.000 0.667 73.9 CJ304-4-9 76.874 0 0.897 2.038 9.207 0.249 1.132 0.856 2.067 93.32 67.764 0.000 0.833 92.8 平均值 76.815 0.000 0.759 2.614 7.983 0.279 1.335 0.901 1.542 92.228 67.712 0.000 0.704 - CJ211-4-1 17.208 54.92 0.382 13.394 1.232 0.068 3.57 0.198 0.207 91.179 CJ211-4-2 17.589 54.29 0.248 18.613 2.889 0.799 1.197 0.239 0.124 95.988 平均值 17.399 54.605 0.315 16.004 2.061 0.434 2.384 0.219 0.166 93.584 KC301-1-1 66.816 0 0 17.256 1.661 0.044 2.611 0.452 0.452 89.292 KC301-1-2 60.722 0 0.028 18.633 1.462 0 5.664 0.446 0.446 87.401 KC301-1-3 69.959 0 0.065 17.137 1.771 0.015 1.691 0.384 0.384 91.406 KC301-1-4 60.331 0 0.016 19.425 1.819 0.348 3.639 0.632 0.632 86.842 KC301-2-1 59.725 0 0.01 19.555 1.661 0.122 3.757 0.718 0.718 86.266 KC301-2-2 69.825 0 0 11.327 4.367 1.213 0.02 0.781 0.781 88.314 KC301-2-3 71.152 0 0 11.026 4.37 1.123 0.114 0.816 0.816 89.417 KC301-2-4 68.757 0 0 12.201 4.445 1.304 0.073 0.787 0.787 88.354 KC301-2-5 61.244 0 0 18.162 1.473 0.028 4.532 0.473 0.473 86.385 KC301-2-6 69.607 0 0.005 13.011 2.289 0.22 2.284 0.608 0.608 88.632 平均值 65.814 0.000 0.012 15.773 2.532 0.442 2.439 0.610 0.610 88.231 表 2 各期次铀矿物主要元素含量对比
Table 2. Comparison of the major elements' content in different stages
时代 对比项目 主要元素含量(%) UO 2 ThO 2 PbO SiO 2+CaO+FeO REEs ~155 Ma 平均值 88.111 6.8094 1.777 0.250 1.654 变化范围 83.315~91.930 3.756~8.659 1.631~1.877 0~0.880 0.650~2.902 ~106 Ma 平均值 86.612 4.751 1.2019 0.239 0.673 变化范围 81.635~91.823 3.365~8.659 1.097~1.631 0.009~1.097 0.198~1.649 ~74 Ma 平均值 76.429 0 0.703 10.8547 3.580 变化范围 74.790~77.795 0 0.656~0.736 9.496~11.183 5.290~4.109 矿石矿物 平均值 65.814 0 0.016 18.715 3.726 变化范围 59.725~71.152 0 0~0.065 115.520~21.529 1.582~6.556 -
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