基于分形信息提取与可解释机器学习的金矿预测:以内蒙古达茂旗为例

    Gold Prospectivity Mapping Based on Fractal Information Extraction and Interpretable Machine Learning: A Case Study in Damaoqi, Inner Mongolia, China

    • 摘要: 内蒙古达茂旗地区成矿地质背景复杂,早期变质型铁矿与晚期热液型金、萤石矿化发生空间叠置,导致地球化学信息混杂,为金矿的专属性找矿预测带来挑战。为解决此问题,本研究提出了一套融合分形信息提取与可解释机器学习的综合预测工作流程。该流程首先对区域地球化学数据进行中心对数比(CLR)变换以消除成分数据的闭合效应。在此基础上,通过主成分分析(PCA)揭示了不同成矿系统在主成分空间的复杂叠加关系,并通过连续二值分解技术(SBP)提取对应元素组合,继而采用能谱—面积(S-A)分形模型对关键地球化学场进行分解,将代表“矿源”的背景场和指示“矿体”的异常场进行定量分离。最后,以已知金矿点为正样本,构建了基于XGBoost算法的预测模型,并通过SHAP方法对“黑箱”模型进行地质可解释性分析。研究结果表明:(1)CLR变换后的主成分分析、连续二值分解技术与S-A分形方法相结合,成功地区分了早期变质型铁矿系统与晚期热液型金-萤石系统的地球化学特征;(2)优化后的XGBoost模型表现出优良的预测性能,其AUC值达到0.92;(3)SHAP分析证实,经过分形分解后的地球化学指标与断裂构造是控制金矿化的最关键因素,其重要性排序与地质成矿规律高度吻合;(4)最终的成矿靶区预测图成功圈定了两处高潜力找矿靶区。

       

      Abstract:   The Damaoqi area in Inner Mongolia is characterized by a complex metallogenic background where early-stage metamorphic iron deposits are spatially superimposed with late-stage hydrothermal gold and fluorite mineralization. This superposition results in mixed geochemical signals, posing significant challenges for target-specific gold prospectivity mapping. To address this issue, this study proposes an integrated predictive workflow that fuses fractal information extraction with interpretable machine learning. The workflow begins with a centered log-ratio (CLR) transformation of the regional geochemical data to mitigate the closure effect of compositional data. On this basis, Principal Component Analysis (PCA) is used to reveal the complex superposition of the different metallogenic systems, and the Sequential Binary Partitioning (SBP) technique is subsequently applied to extract corresponding element assemblages. Following this, the Spectrum-Area (S-A) fractal model is employed to decompose the key geochemical fields, quantitatively separating the background field, which represents the geological "source, " from the anomaly field, which indicates the "orebody" or trap. Finally, using known gold deposits as positive samples, a predictive model was constructed based on the XGBoost algorithm. The geological interpretability of this "black-box" model was then analyzed using the SHAP (SHapley Additive exPlanations) method.
        The results indicate that: (1) The combination of PCA, SBP, and the S-A fractal method, applied after CLR transformation, successfully distinguished the geochemical characteristics of the early metamorphic iron system from the later hydrothermal gold-fluorite system. (2) The optimized XGBoost model demonstrated excellent predictive performance, achieving an Area Under the Curve (AUC) value of 0.92. (3) SHAP analysis confirmed that the fractal-decomposed geochemical indicators and fault structures are the most critical factors controlling gold mineralization, and their importance ranking is highly consistent with geological metallogenic patterns. (4) The final mineral prospectivity map successfully delineated two high-potential exploration targets.

       

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