鄂东北前震旦纪沉积变质磷灰岩矿床地质构造特征

GEOLOGICAL STRUCTURE OF PRE-SINIAN METAMORPHOSED PHOSPHORITE DEPOSITS IN NORTHEASTERN HUBEI

本区前震旦纪沉积变质磷灰岩矿床，呈层状、似层状及透镜状，产于中元占界红安群黄麦岭组下段和上段含磷岩系中。下部含磷岩系分布于大磊山周围，有磷灰岩１一３层，平均厚２～１８ｍ；上部含磷岩系发育在左家湾一双峰尖一带，产磷灰岩１一２层，厚１．５～１３ｍ。本区沉积变质磷灰岩可分为浅粒磷灰岩、变粒磷灰岩、锰质磷灰岩及碳酸质磷灰岩等四种类型，其Ｐ＿２Ｏ＿５含量一般为４．６～２６．１％之间。黄麦岭组属于海湾一浅海相沉积，又可细分为海湾相粉砂岩、磷块岩一粉砂岩、粉砂岩一磷块岩及浅海相白云岩等四种不同相区，其中以第２～３相区磷矿最为富集，形成好多小一大型磷矿床。早一中元古代火山岩喷发活动，是本区磷矿物质的主要来源。此外，扬子期一燕山期的强烈构造变形与变质作用，对本区磷灰岩矿的富集与改造，也具有十分重要的影响。

Pre-Siman metamorphosed phosphorite deposits in northeastern Hubei occur in straitified,stratoid and lenticular forms in Phosphatic sequecces in the upper and lower members of the Huangmailing Formation of the Middle Proterozoic Hongan Group. The lower phosphatic se-quences are distributed in the vicinity of Dalai Mountain ,where there are 1一3 beds of phospho-rite, and 2一18 m thick on the average, The upper phosphatic sequences are developed in the Zuo-jiawan-Shuangrdngjian area ,where there are 1一2 beds of phosohorite,1.5一13 m thick ,Meta-morphosed phosphorite may be classified into four types, such as leucogranulititic , granulititicmanganous and carbonatic phosphorite, The P_2O_5 content generally ranges from 4.6%to 26.1%,The Huangmailing Formation belongs to bay-neritic deposits ,and four different facist areas,i.e,the bay siltstone , phosphorite-siltstone, siltstone-phosphorite and neritic dolomite facies areas,may be distinguished, Phosphorite is more concentrated in the second and third facies areas andmostly makes up small to large phosphate deposits. Phosphatic substances were mainly derivedfrom Early-Middle Proterozoic eruptive deposits. The Yangtze’an and Yanshanian tectonic defor-mation and metamorphism had very important influence on the concentration and reworking of phosphate deposits.