3D Mineral Prospectivity Prediction In Zhonggu Ore Fields, Ningwu Basin

With the depth of exploration increasing, the difficulty of prospecting grows. Traditional exploration based on2d surface data, data dimension restriction makes the deep geological information hard to be expressed clearly, and quantitative targeting of the concealed ore deposit and deep ore deposit is hard to finish. In recent ten years, three-dimensional modeling technology gradually mature, and metallogenic prediction develops from qualitative prediction to quantitative prediction, so the prediction begin from2D to3D. Most of the data accumulated by traditional prospecting exploration work can’t support prediction in three dimension, and the traditional research on ore deposit also stays on concept and qualitative research stage. So, it’s very difficult to predict the concealed deposit and deep deposit in three-dimensional space quantitatively. The problems have always been lying on several aspect:the first one is how to utilize traditional one-dimensional data, such as the text record, and the two-dimension data, such as maps data; the second one is how to realize3d modeling and mapping on different scale; the third one is how to use three-dimensional spatial analysis method to analyse the ideological trend ore-controlling geological factors extraction; the final one is how to choose reasonable and reliable metallogenic prediction model to evaluate the results of3D metallogenic prediction.Ningwu basin, located at Yangtze paraplatform depression belt, is a famous iron district of the Middle-Lower Yangtze River Valley metallogenic belt. Zhonggu ore fields located in the south of the Ninwu basin, is an iron ore mineralization concentration area,. A lot of previous work focus on Zhonggu ore fields and "Porphyrite iron ore" metallogenic model and prospecting model of Zhonggu ore fields bas been built, giving strong theoretical support for prospecting. Limited by exploration technology, known ore deposits in Zhonggu ore field are mostly below600m from the surface, while the deep prospecting at a depth more than600m still need to strengthen. Both of the new large Yang Zhuang iron ore and the middle Zhong Jiu iron ore deposits which have been found in recent years belong to "Baixiangshan type" iron ore deposits, which have been confirmed that Zhonggu ore filed has good prospective at the deep part of ore field(the second space). In the National Twelfth Five-year Plan, the Zhonggu ore field has become a key target of the prospecting work aimed at looking for "Baixiangshan type" iron ore deposits. So, urgent work of comprehensive research and metallogenic forecasting needs to be done for "Baixiangshan type" iron ore deposits in Zhonggu ore field. For the Ningwu basin, its mineral type is simple, theoretical research is mature, exploration data is rich, and deep prospecting potential is tremendous, and all of these factors makes it as a rare natural laboratory and a perfect place for three-dimensional prospecting prediction. The ore deposit geological characteristics, metallogenic age, genesis of mineral deposit, mineralization background and discipline of "Baixiangshan type" iron ore deposits is clear basically, and this also lays a theoretical foundation for looking for this type of ore deposits.Thus, a large number of data of typical ore deposits and ore fields is collected in this paper. Based on comprehensive analysis for the data, the integrated geological-geophysical prospecting sections and geological comprehensive database of Zhonggu ore deposits are built. With the support of these data and three-dimensional modeling technology, stereo mapping for Zhonggu ore deposits has been done. Based on three-dimensional spatial analysis method, quantitative extraction of ore-controlling factors is realized, and the weights of evidence method is chosen as metallogenic prediction model to predict the positionof ore deposits in three dimensional, and then after making comprehensive assessment by comparing with the geophysical anomaly and remote sensing of metallogenic prediction results, the reliable targets have been predicted, and its accuracy is verified by exploration.There are four main developments as follows:(1) Construction of the Stereo mapping workflow on ore field scaleStereo mapping on ore field scale is done based on curve redrawingmethod, combined with geophysical prospecting data, geology data and drilling data. This proves that stereo mapping can not only be used in large scale ore deposits with high data density, but also can be used in middle scale ore field with sparse data density, which promote the promotion of3d modeling method, providing method support for extensiveness stereo mapping.(2) Realization of a variety of three-dimensional spatial analysis methods Three-dimensional spatial analysis method related to three dimensional metallogenic prediction is systematically realized. These methods not only can support prospecting prediction work in Zhonggu ore field, but also can be used to extract the ore-controlling factors in three-dimensional prospecting prediction for other zones. And meanwhile, it can give technical support for looking for concealed deposits and buried ore deposits in three-dimensional space.(3) Using weights of evidence method to prediction in three dimensionOre-controlling factors in Zhonggu ore deposits is extracted by using three-dimensional evidence model. And weights of evidence method is extended from2D to3D to integrate each three-dimensional ore-controlling factors. Finally, some prospecting targets are extracted according to the posteriori probability.(4) Proposing the evaluation methods for metallogenic prediction ResultsThe integration solution of geophysical anomaly, remote sensing abnormal and three dimensional metallogenic prediction is used in this paper, sloving the problem that three dimensional metallogenic prediction target is difficult to verification, and improving the accuracy of the results. Drilling verification shows that the targets predicted in this paper are high reliable and accurate.This paper bulids a systematic solution for three dimensional metallogenic prediction, offering a new thought and feasible method for metallogenic prediction in deep ore prospecting. Intuitive, rapid, operational strong technical support is offered for looking for "Baixiangshan type" iron ore deposits in deep area, Ningwu, providing a good example for the practical application of three dimensional metallogenic prediction, and a practice basis and feasible means for targeted looking for deep deposits and concealed deposits. The paper can be used for the further deep prospecting work for the "Porphyrite iron deposit".