Electrical characteristics and storage rules of groundwater in granite area of Qiongzhong County Hainan Province

Intrusive rocks, mainly granite and granodiorite, are widely distributed in Qiongzhong County of Hainan Province.They were emplaced in Cretaceous, Jurassic, Triassic, and Permian.It is difficult to find groundwater because of the relatively underdeveloped structure, good integrity and dense structure of rocks and various water richness of groundwater.Based on the mutual verification of geological survey, geophysical exploration and hydrologic drilling, this paper systematically analyzes the electrical characteristics and storage rules of three types of groundwater (structural fissure water, weathered crust netted fissure-pore water and contact bedrock fissure water) in granite area.The research results show that structural fissure water mainly exists in the structural fracture zone, especially in NW-trending tensional structural zones with good water richness and large water volume.The weathered crust netted fissure-pore water is widely distributed, mostly in the weathering crust of gully or mountain valley landform with poor water richness and low water volume.The contact type bedrock fissure water is mainly distributed in the contact zone of granite and sedimentary rocks, granite and metamorphic rocks, and sub-granite of different stages, and its water abundance is greatly different.On resistivity isopleth section, the structural fissure water of granite is electrically characterized by "stripe" and "funnel" abnormal curves with steeply decreasing resistance, and the electrical characteristics of granite weathered crust netted fissure-pore water by "lowland" and "groove" shape low resistance electrical characteristics, and contact bedrock fissure water by "layer" and "band" shape with low resistance.