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Abstract
The low-grade Aitik Cu–Au–Ag deposit is a deformed and metamorphosed porphyry-type deposit, and as such it belongs to the group of ores that require detailed mineralogical investigations of precious metal occurrences to assist in determining the recovery processes. The character of gold in the Aitik deposit varies substantially. Gold alloys display highly variable Au/(Au+Ag) ratios, and Hg is commonly a constituent. A change from dominantly sulphide-associated to groundmass-associated gold as mining progresses towards depth is accompanied by a change in the chemical composition of gold. Towards depth, the gold content in electrum and amalgam decreases (from c. 66 to 22% in electrum and c. 23 to 4% in amalgam), and the amount of native gold grains increases. The most common mineral assemblage associated with gold at deep levels (600 m and below) is K-feldspar, biotite, plagioclase, quartz, chalcopyrite and pyrite. This study demonstrates that magmatic–hydrothermal and metamorphic processes responsible for the diversity in copper mineralisation styles within the Aitik ore body probably have also played a role in the variable character of gold observed at Aitik today.
Acknowledgements
New Boliden is acknowledged for financing the analytical work in this study and for permission to publish this paper. We thank Jan Rutqvist and Riikka Aaltonen and the rest of the Aitik mine personnel who in different ways have been involved in this work. We appreciate comments on the paper by Bertil Pålsson. The authors also thank the two anonymous reviewers for valuable comments.