Geochemical Features and Formation of the Auriferous Cherts in the Mojiang Gold Deposit,Yunnan

Auriferous cherts in the Middle Carboniferous Jinchang Formation are the dominant host rocks of auriferous quartz veins and mixed orebodies comprised of gold-bearing quartz veins and cherts in the Mojiang gold deposit.The rocks exhibit sedimentary texture and structure and are composed of hot-water deposited minerals.The FeO,Fe2O3,Au and Ag contents of the auriferous cherts are high;the Cr,Ni and Co contents are also high but significantly variable;MnO/TiO2 and TFe/TiO2 ratios are relatively higy.As viewed from a few diagrams that distinguish different chert formations,the auriferous cherts are in or near the range of hot-water deposited cherts.Because the correlation coefficients between Au contents and those of Cr, Ni of the rocks are negative,a great Au amount in the cherts might not be brought about by later hydrothermal alterations.The rare-earth elements,O and Si isotopic compositions of the auriferous cherts demonstrate that the cherts belong to hot-water deposited rocks.The later hydrothermal alterations made the petrochemical compositions of the cherts deviate from the characteristics of hot-water deposition.In general,the geological and geochemical features of the auriferous cherts demonstrate that the rocks were formed by hot water deposition.

Geochemical features and formation of the auriferous cherts in the Mojiang gold deposit, Yunnan

Auriferous cherts in the Middle Carboniferous Jinchang Formation are the dominant host rocks of auriferous quartz veins and mixed orebodies comprised of gold-bearing quartz veins and cherts in the Mojiang gold deposit. The rocks exhibit sedimentary texture and structure and are composed of hot-water deposited minerals. The FeO, Fe₂O₃, Au and Ag contents of the auriferous cherts are high; the Cr, Ni and Co contents are also high but significantly variable; MnO/TiO₂ and TFe/TiO₂ ratios are relatively high. As viewed from a few diagrams that distinguish different chert formations, the auriferous cherts are in or near the range of hot-water deposited cherts. Because the correlation coefficients between Au contents and those of Cr, Ni of the rocks are negative, a great Au amount in the cherts might not be brought about by later hydrothermal alterations. The rare-earth elements, O and Si isotopic compositions of the auriferous cherts demonstrate that the cherts belong to hot-water deposited rocks. The later hydrothermal alterations made the petrochemical compositions of the cherts deviate from the characteristics of hot-water deposition. In general, the geological and geochemical features of the auriferous cherts demonstrate that the rocks were formed by hot water deposition.