Experimental simulation of element mass transfer and primary halo zone on water-rock interaction

•Water-rock interaction to simulate hydrothermal primary halo zone in granite.•The mobility index (MI) is used to describe the transfer sequence of trace elements.•A denudation coefficient of primary halo zone is proposed to assess the degree of approaching to ore body.•A field case study in the Linglong gold deposit in China to test the experimental simulation results.

Primary halo zone is an important theory for prospecting the deep blind ore body and predicting resource potential. The common description of primary halo zone of multiple elements is based on their behaviors during hydrothermal alteration or mineralization. A geofluid with multiple elements, which are Bi, Cu, Pb, Zn, Cd, Ag, and As (bearing Ni and Mo), is prepared to simulate the dispersive transfer of elements in a hydrothermal fluid–granite reaction at 15 MPa, 100 °C using a new-constructed core flow-through pressure vessel reactor. Core granite samples with 5 cm long after water-rock reaction are cut into ten sections to analyze their major oxides and trace elements. According to experiment results and the method of immobile plateau, we determine that Al and Ti are immobile elements during the water-rock reaction and the hydrothermal alteration of granite is a mass gained process. The mobility index (MI) of each of experimental elements is calculated based on the immobile component Al2O3. The sequence of experimental elements is from As to Ag, Pb, Zn, Cu, Bi, Ni, Cd, and Mo, which are sorted on their values of MI in these reacted granite cores from near to far end respecting to the reaction fluid. This result is consistent with the empirical sequence of zonation of primary halo elements which is derived from the statistical results from 58 gold deposits in China. The denudation coefficient of primary halo zone (Zf or Zfe) is proposed to assess the degree of approaching to ore body on these experiments, which is the averaged MI ratio of front halo elements to ore-body halo elements. The denudation coefficient of primary halo zone is applied on the cross section of gold ore-body hosted in the granite of the Linglong gold deposit located in the Jiaodong peninsula of eastern China. The degree of approaching to the gold ore body is clearly illustrated by the denudation coefficient of primary halo zone.