湖北蕲春花岗岩钾长石的结构状态研究

Study on the Fine Structure of K-Feldspar of Qichun Granite

为探究湖北蕲春花岗岩岩体的岩浆作用演化与辉钼矿化作用关系,采用X射线粉晶衍射(XRD)、傅里叶红外吸收光谱(FTIR)、以及电感耦合等离子体质谱(ICP-MS)等方法,对岩体不同岩性单元中钾长石的结构状态特征开展深入研究。结果显示,蚀变钾化脉体中钾长石有序度、三斜度均较高,为具有三斜对称的微斜长石。白垩纪早世钾长石有序度相对较低,T1(o)位置中Al占位率也较低,[131]峰发生明显的宽化现象,结构由无序逐渐过渡到局部三斜有序。白垩纪晚世钾长石有序度最低,T1(o)位置中Al占位率最小,[131]峰形敏锐,为均匀、单一的单斜钾长石。640cm-1吸收谱带显示出随钾长石有序度增大而向高波数方向移动的趋势,而540cm-1吸收谱带则向低波数方向移动。1 010cm-1吸收谱带随钾长石有序度的增大分裂成1 010和1 046cm-1两个,形状也从宽缓变为尖锐。白垩纪早世钾长石含较高的成矿元素和稀土元素,有较好的成矿物质背景,蚀变脉体中的钾长石Sr和Ba含量明显偏低,证实蚀变热液流体为岩浆期后的产物,钾化蚀变是辉钼矿的重要找矿标志。

Fine structure of K-feldspar from the Qichun granite was investigated using X-ray diffraction（XRD）,Fourier infrared absorption spectroscopy（FTIR）,and inductively coupled plasma mass spectrometry methods to understand the evolution of the granitic magmatism and its correlation to molybdenite mineralization.The XRD results showed that K-feldspar of the potassic alteration veins has higher ordering index and triclinicity and is namely microcline with triclinic symmetry.K-feldspar of the early cretaceous granite has relatively lower ordering index and has widening peak and is locally triclinic ordering.K-feldspar of the late cretaceous granite has lowest ordering index and sharp peak and is homogeneously monoclinic.The FTIR results showed that the IR spectra of the Qichun K-feldspar are similar to that of orthoclase reported by Farmer（1974）.The 640 cm-1 absorption band increases while the 540 cm-1 absorption band decreases with increase in K-feldspar ordering index,also,the 1 010 cm-1 absorption band separates into 1 010 and 1 046 cm-1 absorption bands,with a change in the band shape from widening to sharp outline.The ICP-MS results suggested that K-feldspar of the early cretaceous granite has relatively higher metal elements and rare earth elements,and the granite exhibits better mineralization background,K-feldspar of the potassic alteration veins has markedly lower Sr and Ba,indicating that the alteration fluid originated from the granitic magmatism,and hence,potassic alteration is a good indicator for molybdenite exploration.