冀南邯邢地区白涧矽卡岩型铁矿磁铁矿成分特征与地质意义

Compositional characteristics and geological significances of magnetite from the Baijian skarn iron deposit in the Handan-Xingtai Area,Hebei Province,China

对邯邢地区白涧铁矿矿体和岩体中磁铁矿的成分特征进行详细的成分分析,通过成因矿物学研究认为白涧铁矿矿床主要为接触交代成因,而非矿浆贯入成矿。富铁的岩浆热液在有利的断裂构造条件下充填到接触带和围岩裂隙当中,与碳酸盐围岩发生接触交代作用,形成矽卡岩型矿床。研究发现,矿区内磁铁矿以自形-半自形为主,部分有被赤铁矿、黄铁矿、黄铜矿等矿物交代的现象.围岩蚀变以矽卡岩化和钠长石化为主,具有分带性。矿体磁铁矿与岩体磁铁矿相比表现出富Mg、Mn、Si、Ca贫Fe2+、V、Cr的特征,且与典型的矿浆型磁铁矿成分差别明显。根据成因投图及单位分子中各阳离子数之间的协变图解发现,Mg、Mn与Fe2+、Si与Fe3+呈现明显的负相关,Ca与Si呈现正相关。此外,成矿过程中发生的非氧化还原反应亦可以解释矿区上方出现气孔状矿石的现象,这些成分之间的差异、相关性及发生的非氧化还原反应具有典型矽卡岩型矿床的特征。

This paper has carried out detailed analyses of compositions of magnetites from ores and intrusive rocks in the Baijian Iron Deposit in the Handan-Xingtai Area. Based on the genetic mineralogy study, it is believed that the Baijian Iron Deposit was mainly formed by the contact metasomatism, rather than the ‘ore magma’ injection. Under favorable fault tectonic conditions, the iron-rich magmatic hydrothermal fluid filled into the contact zones and fractures of wallrocks, resulting to the contact metasomatism of the carbonate wallrocks and the formation of skarn Fe deposit. The study shows that the magnetite in the deposit is mainly euhedral to subhedral crystals, with part of them are replaced by hematite, pyrite and chalcopyrite. The alterations of the wall rocks are dominated by skarnization and albitization, with the zonation of alteration. Compared with magnetite in intrusions, the magnetites in ore bodies are rich in Mg, Mn, Si, Al, and Ca, but poor in Fe2+, V, and Cr, and obviously different to compositions of the typical ‘ore magma’ magnetite;Based on genetic diagram and covariant diagrams of the cation numbers in a unit molecule of the magnetite obtained by calculation, it is found that there are significant negative correlations between Mg, Mn and. Fe2+, and between Si and. Fe3+ contents, but positive correlation between Ca and Si contents. In addition, the non-redox reaction occurred in process of mineralization could also explain the occurrence of stomatal ores in the upper part of orebodies in the deposit. The differences and correlations between two elements of them in compositions of magnetites and the occurrence of non-redox reaction display the characteristics of typical skarn iron deposit.