An XPS study on the valence states of arsenic in arsenian pyrite: Implications for Au deposition mechanism of the Yang-shan Carlin-type gold deposit, western Qinling belt

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• 作者：Jin-long Liang^a ; ^b ; ^{richardljl04@yahoo.com.cn} ; Wei-dong Sun^c ; ^{weidongsun@gig.ac.cn} ; Yi-liang Li^d ; San-yuan Zhu^b ; ^d ; He Li^c ; Yu-long Liu^c ; Wei Zhai^e
• 关键词：X-ray photoelectron spectroscopy ; Arsenic valence state ; Arsenian pyrite ; Au deposition mechanism
• 刊名：Journal of Asian Earth Sciences
• 出版年：2013
• 出版时间：30 January, 2013
• 年：2013
• 卷：62
• 期：Complete
• 页码：363-372
• 全文大小：1700 K

文摘

The enrichment of gold in arsenian pyrite is usually associated closely with the enrichment of arsenic in the mineral, generally known as As^1?-pyrite [Fe(As, S)₂]. Direct analyses of the valence state of Au in pyrite are, however, difficult due to generally low (¡«ppm level) Au concentrations. By means of X-ray photoelectron spectroscopy (XPS), this study obtained reliable valence states of As in pyrite from the Yang-shan gold deposit, a giant ¡°Carlin-type¡± Au deposit in the western Qinling orogen, central China. The arsenian pyrite specimens were sputtered with Ar⁺ beam in the vacuum chamber of an XPS to obtain pristine surfaces and to avoid As oxidation during sample preparation. Analyses before and after sputtering show that the As³⁺ peak are only present on surface that was once exposed to the air. In contrast, the peak of As^?1 was essentially unchanged during continuous sputtering. The results indicated that As^? is the predominant state on the pristine surface of arsenian pyrite; the peak of As³⁺ previously reported for Au-bearing arsenian pyrite was probably due to oxidation when exposed to air during sample preparation. It is unlikely that the coupled substitution of (Au⁺ + As³⁺) for 2Fe²⁺ takes place in the pyrite lattice. The so-called As³⁺-pyrite proposed by previous studies may occur in some special (oxidizing) geologic settings, but it is not observed in the Yang-shan gold deposit, and is unlikely to be important in typical orogenic or Carlin-type gold deposits, in which arsenian pyrite is a dominant Au carrier. Combining previous studies on Carlin-type Au deposits with our XPS experimental results, we suggest that the most likely state of Au in the Yang-shan Au deposit is lattice-bounded Au with or without nanoparticles (Au⁰).