四川马边麦地坪组磷矿沉积特征及其成矿模式

Sedimentary Characteristics and Phosphorite Mineralization Model of Maidiping Formation in Mabian Area, Sichuan

四川马边地区早寒武世麦地坪组是沉积型磷矿的重要产出层位,其磷矿层明显受沉积环境的控制。本文通过沉积特征研究,认为麦地坪组属于局限台地沉积,主要包含潮坪和泻湖两个沉积亚相,并且可进一步划分出多个沉积微相,其沉积演化过程分为三个阶段:麦地坪组一段沉积时期为潮下带—泻湖沉积环境,水体相对较深;麦地坪组二段沉积时期,水体能量相对增强,主要为潮下云坪的间歇高能沉积;三段沉积时海平面相对下降,最初以潮间带沉积为主,后期随着海平面上升,中部变为潮下灰坪,北部和南部地区仍保持潮间带沉积不变。最后,初步建立了马边地区磷矿的成矿模式,其矿床类型属于生物-生物化学聚磷成因的海相磷块岩矿床,潮下间歇高能带为马边地区最有利于磷矿形成的相带。

The Early Cambrian Maidiping Formation is an important stratum for sedimentary phosphate deposit in Mabian area of Sichuan and its ore bed is obviously controlled by sedimentary environment. Based on sedimentary characteristics researches, Maidiping Formation is considered as restricted platform deposits, including tidal flat and lagoon subfacies, and these two subfacies can be divided into several microfacies. The sedimentary evolution can be concluded as three stages: during the early deposition, sedimentary environment is subtidal zone and lagoon and the water is relatively deep. Hydrodynamic force increases at sedimentary period of the second member of Maidiping Formation which consists of intermittently high energy depositions in subtidal dolomite flat. The initial deposition of the third member of Maidiping Formation is intertidal sediments and the sea level falls slightly. When sea level rise later, the middle of Mabian area becomes subtidal limestone flat while the north and south stay the same. At last, this paper establishes the metallogenic model and considering the Mabian phosphorite as marine biological-biochemical phosphate-accumulation deposits. The favorable facies belt is intermittently high energy band in subtidal zone, where the main ore types are psammitic-rudaceous phosphorite.