湖北蕲春花岗岩钾长石的结构状态研究

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。640 cm-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540 cm-1吸收谱带则向低波数方向移动。1 010 cm-1吸收谱带随钾长石有序度的增大分裂成1 010和1 046 cm-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。

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

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 131] peak and is locally triclinic ordering. K-feldspar of the late cretaceous granite has lowest ordering index and sharp 131] 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.