邯邢地区中生代侵入岩中磷灰石的成因矿物学研究

Genetic Mineralogy of Apatite in Mesozoic Intrusive Rocks in the Handan-Xingtai Region,Hebei Province

氧逸度为有效的氧分压,是实验岩石学中重要的研究课题,岩浆的氧逸度是继温度、压力、浓度等影响成岩成矿过程的关键性物理化学参数。本文利用磷灰石的氧逸度计,对邯邢地区六大主要岩体的岩浆氧逸度进行了计算。研究结果显示,样品中的磷灰石主要为羟-氟磷灰石,磷灰石的形态、成分和结构特征指示其为岩浆成因。磷灰石中的Mn元素在晶格中有两种方式,多以Mn3+和Mn5+的方式进入晶格。磷灰石氧逸度计计算的logfO2为-12.31^-9.75,均值-11.02。参考与磷灰石共生的角闪石的形成温度,认为邯邢地区岩浆岩普遍具有较高的氧逸度。根据磷灰石氧逸度值与矿床规模的填图结果,认为并非氧逸度越高越有利于邯邢式铁矿的形成。结合矿物学填图等值线闭合的趋势,进而推断邯邢地区中部的符山和武安岩体深部可能仍存在较好的找矿远景。

Oxygen fugacity is an effective partial pressure of oxygen,which is an important research topic in experimental petrology.Oxygen fugacity of magma is a key physical and chemical parameter that affects the processes of diagenesis and mineralization following temperature,pressure,concentration and so on.In this paper,the oxygen fugacity of magma in six main rock bodies from the Handan-Xingtai area,Hebei Province is calculated by using the apatite oxygen fugacity meter.The results show that the apatite in the sample is dominated by hydroxyl-fluorapatite.The morphology,composition and structural characteristics of apatite indicate that it is of a magmatic origin.There are two ways for the Mn element in apatite to be present in the lattice,most of which enter the lattice in the forms of Mn3+and Mn5+.The logfO2 calculated by apatite oxygen fugacity meter is-12.31 to 9.75,with a mean value of-11.02.With reference to the formation temperature of hornblende associated with apatite,it is inferred that magmatic rocks in Handan-Xingtai area generally have high oxygen fugacity.According to the mapping results of the oxygen fugacity value of apatite and the scale of the deposit,it is not considered that the higher the oxygen fugacity is,the more favorable the formation of Han-Xing type iron ore is.Combined with the trend of contour closure on the mineralogical map,it is inferred that there may be a good ore-search prospect in the deep subsurface beneath the Fushan and Wu’an intrusion in the central Handan-Xingtai area.