四川雷波地区下寒武统麦地坪含磷地层研究及磷矿资源潜力分析

【研究目的】四川省雷波县至云南省永善县是寒武系麦地坪组磷矿聚集区，含磷地层的研究不仅有助于深入分析磷矿形成的古地理环境及其变化特征，而且结合构造背景的研究，可研究磷矿形成分布规律，为磷矿的开发提供理论依据。【研究方法】以岩心编录及剖面测量为基础，研究了雷波地区麦地坪组含磷层系厚度、岩性、沉积相、沉积模式、构造背景、盆地性质、磷矿成因机制、磷块岩岩石学特征及其变化等。【研究成果】阐明了雷波地区麦地坪组在50km范围内，岩性、岩相的巨大差异以及磷块岩特征，指出雷波地区在麦地坪组沉积时期呈隆、凹相间的格局，缺失浅水陆棚相。白云岩相区属潮坪相，是磷矿聚集的有利地段。硅质岩属深水陆棚相，是火山活动形成的热水作用成因。磷矿的聚集是硅质岩相区火山活动，生物发育，高温洋流由下向上运动，携带生物遗体分解的高P₂O₅浓度海水在凹陷区两侧白云岩相区沉积和改造的结果。从大地构造背景、盆地性质、磷质来源、磷的迁移、沉淀、富集阐述了磷矿成矿作用机制，提出雷波地区磷矿是多种因素作用形成，建立了相应的磷矿成矿模式。【结论】发现揭示了新元古代末期至寒武纪早期，裂谷盆地发育的晚期阶段，一种新的磷成矿作用——隆、凹相间的古地理格局及微弱的火山活动，在空间上有效配置，并由此提出在凹陷两侧白云岩相区寻找磷矿的预测评价新思路，指出针对麦地坪组磷矿找矿的新方向，在找矿空间可由凹陷区向四周拓展。

Phosphorus-bearing strata in Maidiping Formation of the Lower Cambrian in Leibo area of Sichuan Province and its potential of phosphate resources

This paper is the result of mineral exploration engineering. Objective]The phosphate deposit accumulation scope of Maidiping Formation of the Lower Cambrian covers a wide area from Leibo County (Sichuan) to Yongshan County (Yunnan). The study of phosphorus-bearing strata is not only helpful to the reconstruction of the paleogeographic environment and its varied characteristics, but also can obtain the formation and distribution of phosphate deposits in combination with the study of tectonic background, and provide a thedeposittical basis for the development of phosphate deposit. Methods]Based on the cdeposit record and section measurement, this paper studies the thickness, lithology, sedimentary facies, sedimentary model, tectonic background, basin properties, genetic mechanism of phosphate deposit, petrological features of phosphorite, and their changes in Maidiping Formation in Leibo area. Results]The significant difference of lithology and lithofacies of the Maidiping Formation in Leibo area are within 50 kilometers, and the characteristics of phosphorite are well explained. It is pointed out that the Leibo area was an uplift and depression environment during the sedimentary period of Maidiping Formation, and the shallow shelf facies was absent. Dolomite facies area belongs to tidal flat facies, which is a favorable area for the phosphate deposit accumulation. Siliceous rocks belong to deep-water shelf facies and are of hydrothermal origin formed by volcanic activity. The accumulation of phosphorite is the result of volcanic activity in siliceous lithofacies area, biological development, movement of high temperature ocean current from the bottom to the top, sedimentation of the seawater with high P₂O₅ carried by ocean current decomposing biological remains in dolomite facies area on both sides of the sag area and post-sedimentation transformation. Based on the tectonic background, basin nature, source of phosphorus, migration, sedimentation and enrichment of phosphorus, the deposit-forming mechanism of phosphate is described, and the formation of phosphate deposit in Leibo area is suggested by the interaction of many factors, and the corresponding deposit-forming model of phosphate deposit is established. The siliceous rocks in the depression are the result of the hot water activity under volcanism. Conclusions]The study revealed a new phosphorus mineralization style in the late stage of rift basin development from Late Neoproterozoic to Early Cambrian, i.e., the paleogeographic pattern of alternating uplift and depression with the weak volcanic activity. A new idea of predicting and evaluating the phosphate deposit in dolomite facies area on both sides of the depression is put forward. We suggest that the prospecting space of the Maidiping Formation phosphate deposit should be expanded from the depression area to the surrounding areas.