A STUDY OF SOME PROBLEMS ABOUT THE ORIGIN OF EXHALATIVE-SEDIMENTARY ORES
Qj Sijing Ma Guoliang (Xi'an College of Geology)
Exhalative-sedimentary ores are of the syngenetichydro thermal origin. The underlying stockword zone of the stratiform orebody and the exhalites in ore-bearing zone are the main features of these deposits.The concordant single lens or the vertical array of ore lenses in a definite strata horizon, the massive banded and laminated ore structures and the metal zoning in vertical direction through the ore-bearing sequences are also of the characteristics showing the syngenetic-hydrothermal origin. The hydrothermal-convection model may successfully explain the conditions and processes of the formation of these ore deposits, and the size of the deposits is tested by using a thermal balance model. Exhalative activity happened frequently in a long geological history. The formation of the exhalation sedimentary deposits is related to several definite tectonic setting. The largest exhalation sedimentary deposits are found to be located in the fine clastic sedimentary rocks of trough facies. And the adjacent depression on the carbonate platform is another type of favourable environment for the formation of these deoosits.