Inferred fluid flow through fault damage zones based on the observation of stalactites in carbonate caves

Abstract

Faults and fractures are important factors that control fluid flow in rock masses in hydrothermal, groundwater, and hydrocarbon systems. In this paper we examine local variations in fluid flow as evidenced by the distribution patterns and sizes of stalactites in fractured limestone. We observe that the size and distribution of stalactites relate to fluid flow and is strongly controlled by the fracture apertures, intersection of fractures, and development of damage zones around a fault. Fault damage zones are the volumes of deformed wall rocks around a fault surface that result from the initiation, propagation, interaction, termination, and build-up of slip along the fault. They are divided into tip-, wall-, and linkage damage zones depending on their location along the fault. The pattern of deformation within a damage zone mainly depends on fault tip modes (mode II or III), the 3-D locations around a fault surface, and the evolutionary stage of the fault. The development of different structures within damage zones gives valuable information about fault initiation and termination, fault propagation and growth, and fluid flow. Stalactites indicate fluid flow variation within a fault in that fluid flow is high in dilational jogs, variable along the main fault traces, and low in contractional jogs. Variation in ore fluid flow within faults is also important in controlling the position of ore shoots in structurally-controlled hydrothermal mineral deposits. Thus, the characteristics of fluid flow in fractured carbonate rocks can be related to patterns of damage around faults. Hence, the mapping of damage zones can be applied to the study of fracture-controlled fluid flow in the fields of petroleum geology, hydrogeology, and ore deposits.