Exhaustive gold mineralizing processes of the Sanshandao gold deposit, Jiaodong Peninsula, eastern China: Displayed by hydrothermal alteration modeling

Geochemical modeling is applied to examine the hydrothermal alteration and gold precipitation processes in the Sanshandao deposit. Modeling shows that a gold-bearing fluid is potential to form an economic gold deposit via various paths, including fluid cooling, water-rock interaction, and fluid mixing with groundwater. The simulation results indicate that the auriferous quartz veins located in the alteration zones are probably generated by fluid cooling and mixing, whereas gold mineralization in the sulfide-sericite alteration stage is primarily caused by water-rock reaction that also produces the hydrothermal alteration following the potassic alteration. To evaluate the roles of water-rock interaction in gold mineralization at different temperatures, we execute simulations at T = 400 °C and 300 °C at pressure of 2 kbar. Gold precipitation at >400 °C is driven by strong water-rock reaction with low water/rock ratio, during which the gold precipitation is associated with pyrrhotite rather than pyrite, and thus the pyrite at this temperature scale is always gold-absent; at low temperature (∼300 °C), the water-rock interaction is effective to precipitate gold from the fluids, and gold mineralization links to pyrite precipitation. The comparison between these two simulations with different temperatures indicates that water-rock interaction at moderate temperature is prior to precipitate gold from hydrothermal fluid, which can be invoked to interpret the fact that gold mineralization is always intense in shallow level and host majority of gold reserve in this deposit. The modeling suggests that pyrrhotite should be paid more attention in future deep exploration since its ability to host certain gold budget at relatively high temperature.