黔中开阳磷矿沉积区震旦纪陡山沱期定量岩相古地理重建

Reconstruction of quantitative lithofacies palaeogeography of the Sinian Doushantuo Age of phosphorite depositional zone in Kaiyang area,central Guizhou Province

磷矿的沉积和成矿与成磷期的古地理环境密切相关。本文首次将＂单因素分析多因素综合作图法＂运用于开阳地区震旦纪陡山沱期沉积型磷矿床的成矿分析和找矿预测上。通过选取陡山沱组及其各岩性段的地层厚度及磷矿层品位作为单因素,确定开阳地区古地理格局;结合地层岩性组合、沉积特征等多因素综合分析,恢复开阳地区成矿期沉积环境,编制陡山沱早期、中期和晚期岩相古地理图。根据定量岩相古地理重建结果,认为开阳地区陡山沱期整体处于南靠黔中古陆、地势南高北低、局部地形复杂的滨岸海滩沉积环境,其中临滨带为最有利成矿带,局部地形变化也会造成矿层厚度、品位的差异;矿层受到的水流冲蚀、暴露、淋滤及再沉积作用是导致矿石品位显著提升的关键因素。通过定量岩相古地理学精确还原成矿期古地理环境、解析多期次沉积成矿过程,对于确定磷矿控矿因素、构建找矿预测模型和预测矿体空间位置具有重要意义。

The deposition and mineralization of phosphorite had intimate relationship with the paleogeographic environment of phosphogenesis.This paper first used the single factor analysis and multifactor comprehensive mapping method to analyze and predict the phosphorite deposits in Kaiyang area during Sinian Doushantuo Age.This paper selected the stratum thickness of the Doushantuo Formation and its each lithologic section and the ore grade of phosphorite bed as the single factors to reflect the palaeogeographical pattern of Kaiyang area.Based on these isoline maps of single factors and other factors like lithologic combinations and sedimentary characteristics,the sedimentary environments of metallogenic epoch were clearly recovered and at last the quantitative lithofacies palaeogeographical maps of the Early,Middle and Late Doushantuo Age were compiled.According to the result of reconstruction of quantitative lithofacies palaeogeography,we proposed that Kaiyang area was in seashore environment which was located in north margin of Central Guizhou Old Land,and the topography became higher from north to south and local terrain was rugged.The nearshore areas were targeted as the most advantageous metallogenic belt and the changeful local terrain affected the thickenss and ore grade of phosphorite,and the phosphorite which experienced multi-stages erosion,exposure,leaching and reworking would had higher ore grade.Using quantitative lithofacies palaeogeography can accurately recover the palaeogeographical environment of metallogenic epoch and analyze the sedimentation and mineralization processes,and it has important significance for confirming the controlling factors of phosphorite,constructing mineral prediction model and predicting the spatial location of orebody.