Application of fuzzy weights of evidence method in metallogenic prediction for alaskite-type uranium deposits in Namibia
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摘要:
纳米比亚埃龙戈地区位于达马拉构造带中部, 是全球重要的铀成矿带, 但纳米比亚第四系覆盖较重, 严重影响了铀矿找矿效果。为摸清纳米比亚铀资源现状, 开展铀资源潜力评价工作, 充分利用和深度挖掘现有资料, 圈定了预测靶区, 为中国矿业企业在海外投资提供支撑。在对纳米比亚埃龙戈地区白岗岩型铀矿床控矿因素系统总结的基础上, 建立了综合信息找矿模型; 在GeoDAS GIS平台上, 利用非线性理论、奇异性理论及分形滤波技术, 实现了对该区隐伏构造、航放铀异常等弱缓信息的提取; 基于模糊证据权方法开展综合信息矿产预测, 圈定铀找矿远景区7个。通过模型检验, 验证了本次预测工作的有效性。认为Ⅰ级远景区内第四系覆盖区还存在巨大的找矿潜力, Ⅱ级远景区也具有较好的成矿条件, 但工作程度较低, 有望实现找矿突破。
Abstract:The Erongo area of Namibia, located in the central of Damara tectonic belt, is an important uranium metallogenic belt in the world. However, the Quaternary coverage in Namibia is heavy, which seriously affects the prospecting effect of uranium deposits. In order to find out the status of uranium resources in Namibia, we have carried out the uranium resources potential evaluation, which has made full use of and deeply excavate the existing data, delineated the prediction target area, and provided support for Chinese mining enterprises to invest overseas. Based on the systematic summary of the ore-controlling factors of the alaskite-type uranium deposits in the Erongo area of Namibia, a comprehensive information prospecting model is established. On the GeoDAS GIS platform, nonlinear theory, singularity theory and fractal filtering technology are used to extract weak and slow information such as hidden structure and aero-released uranium anomaly in this area. Based on the fuzzy evidence weight method, the comprehensive information mineral prediction is carried out, and 7 uranium prospecting areas are delineated. The validity of this prediction is verified by model test. The paper holds that there is still huge prospecting potential in the Quaternary coverage area of the Grade Ⅰ prospect area, and the grade Ⅱ prospect area also has good ore-forming conditions, which is expected to achieve a breakthrough in prospecting because of the low working degree.
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表 1 纳米比亚埃龙戈地区白岗岩型铀矿找矿模型
Table 1. Table of prospecting model for alaskite-type uranium deposit in the Erongo area, Namibia
找矿要素分类 要素显示特征 区域成矿背景 区域构造 位于达马拉构造带，达马拉构造带为新元古代—早古生代形成的碰撞型造山带，主构造线方向以NE向为主，其次为NNE向断裂，其他方向断裂为从属构造 地球物理场 达马拉构造带南部中央区带为高磁区，其他为中低磁区；达马拉构造带南部中央区带具有高的铀钍背景值 地质找矿要素 地层 斯瓦科普群与诺西布群接触带，以及不同地层、岩性交界部位，如罗辛组/可汗组，或者楚斯组/可汗组接触界线附近。 构造 NE向、NNE向深断裂构造控制着白岗岩的展布，为U元素运移提供了通道，穹隆构造边部控制矿体就位 岩浆岩 D型或E型白岗岩脉 围岩蚀变组合 主要蚀变有高岭石化、伊利石化、硅化、黄铁矿化、绿帘石化和绿泥石化。与成矿关系最密切的是硅化、伊利石化、高岭石化 地球物理找矿要素 航磁 高磁区与穹隆构造吻合度高，航磁解译的NE向、NNE向断裂构造控制白岗岩的分布 航放 铀异常与矿床(点)吻合度高 
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表 2 纳米比亚埃龙戈地区有利预测变量
Table 2. Favorable prediction variable scale in the Erongo area, Namibia
编号 预测变量 有利度 1 断裂构造buffer分析 63%的矿床(点)分布于4 km缓冲区内 2 穹隆构造buffer分析 58%的矿床(点)分布于2 km缓冲区内 3 斯瓦科普群和诺西布群地层接触带buffer分析 68%的矿床(点)分布于2 km缓冲区内，大型矿床均距离接触带2 km以内 4 白岗岩(伟晶岩)脉buffer分析 白岗岩脉为赋矿主岩 5 铝羟基蚀变 伊利石化、高岭石化是非常重要的矿化蚀变标志 6 航放铀异常奇异性指数 异常点与已知矿床(点)吻合度高，矿体与异常吻合度高 7 航放铀增量 异常与已知矿床(点)吻合度高，同时有效去除高铀背景地质体的影响
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表 3 各证据图层隶属度(MSF)与模糊证据权计算
Table 3. Membership of each evidence layer(MSF) and calculation of fuzzy weights of evidence
图层 断裂buffer 穹隆buffer 地层接触带buffer 伟晶岩脉buffer 铝羟基蚀变 U异常奇异性指数 U增量 分类值Value 隶属度MSF 证据权重 隶属度MSF 证据权重 隶属度MSF 证据权重 隶属度MSF 证据权重 隶属度MSF 证据权重 隶属度MSF 证据权重 隶属度MSF 证据权重 1 1 1.36 1 2.19 1 2.44 1 2.87 1 1.72 1 2.44 - - 2 1 1.36 1 2.19 1 2.44 1 2.87 1 1.72 1 2.44 0 -1.43 3 1 1.36 1 2.19 1 2.44 1 2.87 1 1.72 1 2.44 0 -1.43 4 1 1.36 1 2.19 1 2.44 1 2.87 1 1.72 1 2.44 0 -1.43 5 1 1.36 1 2.19 1 2.44 1 2.87 - - 1 2.44 0 -1.43 6 1 1.36 0.83 2.03 0.86 2.23 0.83 2.74 - - 0.83 1.55 0 -1.43 7 1 1.36 0.67 1.85 0.71 1.98 0.67 2.63 - - 0.67 0.95 0 -1.43 8 1 1.36 0.5 1.62 0.57 1.73 0.5 2.51 - - 0.5 0.36 0 -1.43 9 0.6 1.14 0.17 0.98 0.43 1.44 0.17 2.3 - - 0.33 -0.28 0 -1.43 10 0.4 0.95 0 0.4 0.29 1.08 0 2.19 - - 0.17 -1.12 0.17 -0.79 11 0.2 0.62 0 0.4 0.14 0.56 0 2.19 - - 0 -8.9 0.33 -0.29 12 0 -0.16 0 0.4 0 -0.31 0 2.19 - - 0 -8.9 0.5 0.23 13 0 -0.16 0 0.4 0 -0.31 0 2.19 - - 0 -8.9 0.67 0.79 14 0 -0.16 0 0.4 0 -0.31 0 2.19 - - 0 -8.9 0.83 1.5 15 0 -0.16 0 0.4 0 -0.31 0 2.19 - - 0 -8.9 1 3.15 16 - - - - 0 -0.31 - - - - 0 -8.9 1 3.15 17 - - - - 0 -0.31 - - - - - - 1 3.15 18 - - - - 0 -0.31 - - - - - - 1 3.15 19 - - - - 0 -0.31 - - - - - - 1 3.15 20 - - - - 0 -0.31 - - - - - - - - 注：“-”表示无值
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