Nano- to atomic-level analysis of heavy metals in pyrite

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Arsenian pyrite is an important host of Au in the Carlin-type deposit, whereas it always contains significant amount of heavy metals. In order to understand the formation process and the impact to the ambient environment, a detailed examination utilizing a variety of electron microscopy techniques was carried out on the arsenian pyrite collected from various epithermal deposits. New type of arsenian pyrite that contains As^<3+> was characterized in the sample from the Yanacocha deposit. The amounts of defect and the content of other toxic metals increases as the particle size decreases to nanometer size <10 nm. The other finding is a decoupled formation of As and Cu rich pyrite, indicating mixing of two distinct fluid conditions during its formation. In addition, an experimental study revealed the specific As-bearing minerals in the interaction between mackinawite and aqueous As under anoxic condition. Consequently, this project successfully covered a wide range of crystallochemical characteristics of pyrite in the ore deposit.