The Concept of Hydrothermal Sedimentation and Its Petrological Criteria
Chen Xianpei Gao Jiyuan Chen Duofu Dong Weiquan (Guangzhou Branch of institute of Geochemistry, Chinese Academy of Sciences)
Hydrothermal sedimentation is referred to the sedimentation that occurring in the water bodies under the rock-water interface resulting from the hot water upmigration and extrusion under the sedimentary interface, including the contemporaneous (pene-contemporaneous) replacement and infilling happening near the interface. Several petroloical criteria to identify the hydrothermal dimentation are as follows: 1.Contemporaneous (pene-contemporaneous) replacement and infilling with sediments mainly occur in the surrounding rock near the sedimentary interface before the hot water extrusion, usually appearing in the form of veins and altered mass, distributing under the hydrothermal sediments. 2. Erupted bandings and laminae are the results of the hot water extrution from weak to strong and to weak again. In the profile, the block is in the center and bandings and laminae distribute symmetrilly in both sides. The bandings and laminae are usually formed by the hydrothermal sediments themselves or their alternation with the backgroud sediments. 3. Reef-siliceous rock suite is composed of basin-typed reef-beach-phased carbonate and its overlying siliceous rock (including silicified rocks) accompanied by unstable volcanic (and / or subvolcanic) rocks. Important ore- bearing geologic bodies are often found in the transitional position of the reeflimestone-siliceous rock. The shape of ore-body and quility and fabric of ores are related to its occurrence position in reef-siliceous rock suite. More than 10 ore-bearing eef-siliceous rock suites have been found in China and abroad.