铜陵冬瓜山矿床磁黄铁矿的矿物学特征及其指示意义

Mineralogy characteristics of pyrrhotite and its implications for ore genesis of Dongguashan deposit in Tongling area

磁黄铁矿是铜陵冬瓜山矿床中最重要的矿石矿物之一，其标型特征不仅反映其自身形成环境，对矿床成因也具有指示意义。本文选取矿床中不同层位的磁黄铁矿矿石样品，利用矿相学、x射线衍射、电子探针和同位素分析等手段对磁黄铁矿标型形态、成分、结构以及物质来源进行了分析。研究表明：磁黄铁矿主要分布在矿体的中部，根据磁黄铁矿与其共生矿物之间的交代关系，认为金属矿物的生成顺序是黄铁矿→磁黄铁矿→黄铜矿→磁铁矿。x射线衍射显示磁黄铁矿以六方和单斜相为主，近岩体处主要是六方晶系；远岩体处则以单斜晶系为主。且见单斜沿六方磁黄铁矿的边部有交代现象，显示出热液交代作用的特征。电子探针测试显示磁黄铁矿的Fe元素含量为58．435％-60．978％，平均值为59．737％；s元素含量为38．297％～39．891％，平均值为38．696％，分子式为Fe4S5-Fe9S10，也显示磁黄铁矿有六方和单斜两个相，单颗粒成分剖面显示其核部为六方相，边部为单斜相。磁黄铁矿的6’驽组成均为-0．7‰-＋13．5％o之间，δ57Fe的总体分布范围为0．49‰～0．52‰，Fe同位素和s同位素显示它们均来源于岩浆及其热液。说明磁黄铁矿具有岩浆成因和热液交代成因。支持冬瓜山矿床是与燕山期岩浆活动有关的矽卡岩型矿床观点。

Pyrrhotite is one of the important ore mineral in Tongling Dongguashan deposit. The typomorphic characteristics of pyrrhotite not only reflect their own formation environment, also have implications for the genesis of the Dongguashan deposit. In this paper, we select the pyrrhotite ore samples in different layers of the deposit, using mineralography, X ray diffraction, electron probe to analysis the morphology, composition and standard type structure of pyrrhotite, to discuss the mechanism of its formation and using Fe isotope and S isotope analysis to investigate the ore-forming material sources of pyrrhotite. The research shows that： The pyrrhotite is mainly distributed in the middle of the ore body. According to metasomatic relations of pyrrhotite and its paragentic mineral, it was considered that the generated sequence of metal mineral is pyrite→pyrrhotite→chalcopyrite→ magnetite. X ray diffraction indicated that the pyrrhotite include the hexagonal system and the monoclinic system, the hexagonal system is more than monoclinic system. The phenomenon of the monoclinic pyrrhotite along edge of hexagonal metasomatism, shows the characteristics of hydrothermal metasomatism. Electronic probe test displays that the content of Fe element is 58.435%- 60.978%, average value is 59.737%, the content of S element is 38.297% - 39.891%, the average value is 38.696%, the molecular formula is Fe4S5 -FegS10. It also shows that there are the hexagonal system and the monoclinic system, the individual particle component profile of pyrrhotite shows the core part is the hexagonal, the edge is monoclinic. δ34S of the pyrrhotite is distributed between -0.7% to ＋13.5%, the overall distribution of 857Fe is 0.49‰-0.52‰, Fe and S isotopes show that they are all derived from the magmatic hydrothermal fluid in the region. It is indicated that pyrrhotite has magmatic and hydrothermal metasomatic genesis. We support that the Dongguashan deposit is a skarn deposit related to magmatic activity in Yanshan epoch.