Application of EPMA to Study the Characteristics of Gold-bearing Minerals in the Zhaojiazhuang Gold Deposit in Longnan, Gansu Province

Abstract

BACKGROUND Microscopy and Electron Microprobe are the main methods for the study of gold-bearing minerals. Using these methods, the content and morphology of gold-bearing minerals and their spatial relationship with other minerals were studied in the Zhaojiazhuang gold deposit. The gold-bearing minerals were qualitatively and quantitatively analyzed. OBJECTIVES To summarize the gold-bearing minerals with the significance of prospecting and the features of indicator minerals. METHODS Microscopy and Electron Microprobe. RESULTS The main gold-bearing mineral is pyrite, then chalcopyrite and sphalerite. The contents of Au in the main gold-bearing minerals follow the sequence of fine-grained pyrite > coarse-grained pyrite > strawberry pyrite > chalcopyrite. The distribution of Au in different stages of pyrite (coarse pyrite, fine pyrite, strawberry pyrite) is uniform. Fine-grained and strawberry pyrite have higher gold content (average 0.14%-0.18%), indicating that these types of pyrite formed by tectonic hydrothermal fluids where Au concentrates more easily. There are two occurrences of gold in the Zhaojiazhuang Au deposit. Visible gold is wrapped in gangue minerals, or embedded in mineral crystal gaps and cracks in the form of fissure gold. Invisible gold exists in the gold-bearing minerals in the form of nano-scale gold particles. Invisible gold is the main existence form of Au. CONCLUSIONS This study provides evidence for the study of the genesis, metallogenic process and mechanism of the same deposits and it is easy to select suitable methods for ore selection and smelting based on the characteristics of gold-bearing minerals.

Keywords

• electron microprobe
• gold
• occurrence state
• gold-bearing minerals
• pyrite