The Application of the Microbeam Analysis Technique in Associated Gold and Its Occurrence State

In this paper, the technique of advanced microbeam analysis using a Scanning Electronic Microscope (with back scattered electron photo), characteristic X-ray line scanning, line-by-line scanning and Energy Dispersive Analysis identification were used to observe micro-fine gold hosted in Liwu copper ores. The micro photos, energy dispersive spectrum, chemical compositions of nanometer-grade and micrometer-grade gold provided a clear line and plane distribution pictures of gold and other coexisting elements. Gold in Liwu copper ores was hosted as isomorphism in Ag-bearing kustelite and bismuth minerals, which disseminate in the cracks of chalcopyrite, pyrrhotite and Mn bearing marmatite. The grain size of the gold carrier minerals is more than 20 nm after matrix interferences correction. This method is easy and simple to obtain reliable and visual analytical results, which significantly increase the efficiency of studying the occurrence states of gold. The hydrothermal ore samples from the Liwu Cu deposit were formed at the middle-late stage of Yanshan 104-142.2 Ma by tectonic movement and metallogenic hydrothermal activities, which was later than the peak mineralization at the middle stage of Yanshan. The ratios of Ag/Au are from 1.38 to 4.59, which indicate the metallogenic temperature was no more than 227℃. The Sulfide ore precipitation and occurrence of chlorite and sericite indicate the Liwu Cu deposit has two mineralization stages as early high-middle temperature hydrothermal activities and late middle-low temperature hydrothermal activities.