豫西陆院沟金矿黄铁矿拉曼光谱特征及其对多期成矿的指示意义

豫西陆院沟金矿是熊耳山地区重要的破碎蚀变岩型金矿,黄铁矿是其主要的载金矿物,对黄铁矿主量元素、微量元素、同位素等进行测试能够分析金矿的成矿过程,常规的测试手段主要有电子探针、激光剥蚀电感耦合等离子质谱等方法,但这些方法具有测试时间长、成本高的缺点。不同温压条件下形成的黄铁矿其光谱特征不同,对黄铁矿进行激光拉曼测试,分析其拉曼特征位移峰及半高宽（FWHM）的变化可判断黄铁矿形成的温度和压力,进一步可推测金矿的成矿过程,该方法相比于传统的分析测试方法具有经济、高效的优势。通过对陆院沟金矿不同标高430~670 m的黄铁矿样品进行拉曼光谱分析发现其379 cm-1附近的特征拉曼位移A_g自标高430~500 m呈现不断增大的趋势,自标高500~580 m呈现不断减小的趋势,自标高580~670 m又呈现不断增大的趋势。A_g拉曼位移一般随着成矿压力的增大而增大,推断控矿断裂存在两期构造活动,第一期构造活动破碎带达到标高500 m左右,第二期构造活动是在第一期的基础上继续向上发展,达到标高约670 m的范围。379 cm-1处特征峰半高宽可指示黄铁矿晶体的结晶度和有序度,一般特征峰半高宽越宽其结晶度、有序度越差,黄铁矿结晶沉淀温度越高。从标高430 m至标高500 m,载金黄铁矿在379 cm-1附近峰的半高宽从7.94逐渐增大到12.81,自标高500 m至标高670 m,其半高宽从12.81逐渐减小到8.81。推测与两期构造相对应,存在两期热液活动。通过对标高430 m处的黄铁矿进行电子探针扫面分析,发现确实存在两期热液活动,第一期热液中As元素含量较低,第二期热液As元素含量较高。对标高430 m处第二期热液形成的黄铁矿进行拉曼光谱测试,其A_g为381.86,指示了较低的结晶沉淀压力;半高宽为12.80,指示了较高的黄铁矿结晶沉淀温度。上述事实证实了推测的地质过程。

Raman Spectral Characteristics of Pyrite in Luyuangou Gold Deposit,Western Henan Province and Its Indicative Significance for Multiphase Metallogenesis

Luyuangou gold deposit is an important fractured altered gold deposit in Xiong’er Mountain, and pyrite is its main gold-bearing mineral. Testing the major elements, trace elements and isotope of pyrite can analyze the mineralization process of gold deposits. The conventional testing methods mainly include electron microprobe and laser-ablation inductively coupled plasma mass spectrometry, but these methods have the disadvantages of long test times and high costs. Because of forming under different temperature and pressure conditions, the spectral characteristics of pyrite are different. Conducting laser Raman test to analyze the displacement of Raman characteristic peaks and the change of full width at half maximum (FWHM), we can judge the temperature and pressure of pyrite formation and further infer the mineralization process of gold deposit, which has economic and efficient advantages compared with traditional analysis and test methods. Analyzing Raman spectroscopic of pyrite samples at a different elevation from 430 to 670 m, it found that the characteristic Raman displacement A_g near 379 cm-1 showed an increasing trend from elevation 430 to 500 m, the decreasing trend from elevation 500 to 580 m and a increasing trend from elevation 580 to 670 m. The A_g generally increases with mineralization pressure, and it is inferred that there are two phases of tectonic activity in the ore-controlling structure. The fragmentation zone of the first phase of tectonic activity reaches about elevation of 500 m, and the second phase of structural activity continues to develop upward based on the first phase, reaching an elevation of about 670 m. The FWHM of the characteristic peak at 379 cm-1 can indicate the crystallization and order of pyrite crystals. Generally, the wider FWHM of the characteristic peak, the worse crystallinity and order, and the higher the crystallization and precipitation temperature. The FWHM of gold-bearing pyrite near the peak of 379 cm-1 from elevation 430 to 500 m, increased gradually from 7.94 to 12.81, and from elevation 500 to 670 m, it gradually decreased from 12.81 to 8.81. It is speculated that corresponding to the two-phase structure-activity. There are two-phase hydrothermal activities. Electron microprobe sweeps analysis of pyrite at elevation 430 m revealed -two-phase hydrothermal activity indeed, with low As content in the first phase and higher As content in the second phase. Raman spectroscopy of pyrite formed from the second hydrothermal phase at elevation 430 m with Ag of 381.86 indicating the lower crystallization and precipitation pressure and FWHM of 12.80 indicating the higher crystallization and precipitation temperature, which testify the inferred geology process.