华北克拉通矽卡岩型富铁矿成矿关键控制因素:来自地层学的制约

Key Ore-controlling Factors of the Skarn Type High-grade Iron Deposits in North China Craton:Constraints from Stratigraphy

华北克拉通矽卡岩型富铁矿床成矿关键控制因素一直是科学研究的热点和难点,也是制约下一步找矿方向和进一步实现找矿突破的关键。本次工作基于对华北克拉通典型矿床矿体分布规律的研究,基于地层学分析,研究了矿体分布的关键控制因素和制约机理。华北克拉通各典型矽卡岩型富铁矿床主矿体与围岩层系、岩溶层、膏岩层等的空间关系密切,主要分布于中奥陶统峰峰组二段、下马家沟组二段和上马家沟组二段,处于主要含膏层的上覆强岩溶层。地层学因素对矽卡岩型富铁矿床成矿的关键控制作用主要表现在四个方面:岩溶层系的垂向分布制约富铁矿体就位的有利空间;不整合面的发育控制岩溶系统发育的程度,影响富铁矿体规模;层序地层对岩溶期次的约束作用,限定了岩溶发育层位以及富铁矿层的分布;膏盐岩层指示阶段性强岩溶作用的底界,限定富铁矿体赋存的有利空间下限。根据研究认识,建立了华北克拉通矽卡岩型富铁矿床地质找矿模型,提出七个潜在成矿空间层段,其中包括三个主力成矿层段,并指出了下一步重点找矿及研究方向。

The key ore-controlling factors of the skarn high-grade iron deposits in North China Craton(NCC)is a challenging topic and largely restrict the ore-prospecting directions in the future and make relevant study breakthroughs impossible.Based on the distribution pattern of typical orebodies in NCC and stratigraphy,we determined the key ore-controlling factors and their restriction mechanism.The large scale of orebodies of typical skarn high-grade iron deposits in NCC are closely related to the surrounding rock series(e.g.,karst layers,gypsum beds)and they are mainly distributed in the middle Carboniferous Fengfeng Formation,the lower Majiagou formation,and the upper Majiagou Formation,which are located in the karst stratum above gypsum.The key controlling factors from stratigraphy on the mineralization of skarn type high-grade iron deposits are mainly manifested in four aspects:the vertical distribution of karst stratum restricts the favorable space for the emplacement of iron-rich orebodies;the unconformity surface controls the development of the karst system,affecting the scale of high-grade iron orebodies;the sequence stratigraphy affects the karst stages,constraining the distribution of karst layers and high-grade iron orebodies;the gypsum salt layer indicates the bottom boundary of the strongly phased karstification,limiting the favorable lower bound for hosting the high-grade iron orebodies.Consequently,the ore-prospecting model for the skarn type high-grade iron deposits in NCC was established,and seven potential mineralization spatial segments,including three major ones,were recommended in the study.The key ore-prospecting and research directions were suggested at end of the study.