Geology, geochemistry and sulphur isotopes of the Hat Han gold–antimony deposit, NE Vietnam

• First published description of the Hat Han deposit;
• The Hat Han gold deposit hosted in mafic rock.
• There is no genetic link between mafic rock and gold mineralisation;
• Gold-bearing sulphides (pyrite and arsenopyrite) are the main form of presence Au in ore.

The Song Hien Rift basin is considered as one of the important regions for gold deposits in North East Vietnam. Host rocks of a number gold deposits in the Song Hien Rift basin are mainly in Lower Triassic sedimentary formations. However, there is the Hat Han gold deposit hosted in fined-grained mafic magmatic rocks with similar characteristics as gold deposit hosted in the Triassic sediments. Sulphur isotopic compositions of sulphide are similar to those in carbonaceous shale, suggesting that the sulphur was ‘borrowed’ from sedimentary rocks in filling the rift basin. Gold-bearing sulphides (pyrite and arsenopyrite) are the main form of Au presence in the ore. Gold in pyrite is present as Au+ 1, and a minor amount of as nanoparticles of native Au (Au0); whereas in arsenopyrite, gold is chemically bound as the octahedral complex AuAs2. Analysis of geology, as well as geochemical and isotopic studies show that the genesis of the Hat Han gold deposit is not related to the Cao Bang mafic magmatism; instead the latter only serves as (ore) host rock. The geochemical results presented above suggest that the gabbro host rock only supplies iron needed for sulphide formation. With regard to ore genesis, the Hat Han gold deposit in the Song Hien rift basin was generated in the similar way as sediment-hosted gold deposit. There are many similar typomorphic features between the Hat Han deposit and Carlin-like deposits in the Nanpanjang sedimentary basin in China.

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