Investigating porosity structure effects on hydrothermal mineralization patterns within permeable horizontal layers of fluid-saturated rocks: Semi-analytical approach through generic models

The porosity structures of a permeable rock can have remarkable effects on pore-fluid flow within the rock. According to the modern mineralization theory, the mineralization pattern in a hydrothermal ore-forming system is strongly dependent on the pore-fluid flow velocity, so that different porosity structures of a permeable rock can affect significantly hydrothermal mineralization patterns within the permeable layers consisting of fluid-saturated porous rocks. This paper presents a semi-analytical approach, in which pore-fluid velocity is directly used as fundamental primary variables in the governing equations of the problem and the property matrices of finite elements are analytically evaluated in a purely mathematical manner, to ensure the high accuracy of the obtained pore-fluid velocity, which is involved in controlling mineralization patterns in hydrothermal ore-forming systems. After the proposed semi-analytical approach is verified through comparing the numerical solution with the analytical solution for a benchmark problem, it has been used to investigate how different porosity structures can affect the hydrothermal mineralization patterns within permeable horizontal layers consisting of fluid-saturated porous rocks through using a generic model, which can be viewed as the representation of a generalized and simplified geological model. Main outcomes of this study have demonstrated that: (1) the proposed semi-analytical approach can produce highly-accurate numerical solutions for solving coupled pore-fluid flow and heat transfer problems in fluid-saturated porous rocks with different porosity structures; (2) the different porosity structure within a permeable horizontal layer consisting of fluid-saturated porous rocks can have a significant effect on the hydrothermal mineralization pattern of the permeable horizontal layer; (3) layered pore-fluid vertical velocity focusing may take place within a permeable horizontal layer involving a heterogeneous porosity structure.