Au-Cu mineralization at Palai-Islica occurs as disseminations in massive silicified volcanic rocks and, more abundantly, in sulphide-bearing quartz veins. The major ore minerals in the deposit are pyrite ± chalcopyrite, sphalerite and galena and there is a great variety of accessory minerals, including Au-Ag alloys and native gold. Pyrite, the most abundant sulphide, is closely associated with gold. Seven different types of pyrite have been distinguished with a variable concentration of different trace elements. Among these, the only one free of trace elements (type IV) is related to Au-Ag alloys. Pyrite associated with these Au-Ag alloys has cubic and pentagonal dodecahedral habits, whereas pyrite with pentagonal dodecahedral habit only is from barren zones. In addition, there is no significant invisible gold in the pyrite, but there is a relatively large amount of Ag in collomorphic pyrite (up to 0.20 wt.%) or type III pyrite (up to 1.47 wt.%). Arsenic is the most abundant trace element in pyrite (up to 6.11 wt.%), present as a metastable solid solution or as a non-stoichiometric element. A variety of marcasite related to the gold levels also has a considerable amount of trace elements (As up to 1.15 wt.%, Sb up to 0.40 wt.%).

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