THE PRINCIPLES AND METHODS FOR PREPARING METALLOGENIC-PROGNOSTIC MAPS OF METALLIC ORE DEPOSITS

In this paper the author mainly introduces the following content according to many years of appreciation and practice in the map preparation. Ⅰ. Basic principles for preparing metallogenic-prognostic maps 1. In search for different types of ore deposits, it is necessary to prepare special base maps with different content and use different methods of expression. 2. The scale of maps prepared differs with the usage and detail of the content of the maps. In this paper the scales of maps prepared in China are classified into five scales from large to small. 3. The key link in the preparation of metallogenic maps is to make a metallogenic analysis. Only by making a deep-going and comprehensive analysis and study can one summarize an objective law conforming with reality. 4. The ultimate aim of the map preparation is to elucidate the metallogenic law and predict the direction in ore exploration. Ⅱ. Concrete principles for preparing metallogenic-prognostic maps and main content expressed in maps Taking the preparation of 1:500000-1:1000000 maps for example, this paper indicates that the content of maps should be expressed in nine aspects. The paper places primary emphasis on the following aspects: 1. the important influence of sedimentary formations and source beds on the characteristics of mineralization; 2. the division of fractures into six types according to the relations of different depths at which fracturer are formed to types of. magmatic rocks and mineralization; 3. the division of the phases of formation of magmatic rocks into preorogenic, synorogenic and postorogenic phases and division of magmatic rocks into eight major types according to three different geological settings—oceanic crust, transitional crust and continental crust; 4. the important effects of exogenic water （including groundwater and formational water） on the formation of hydrothermal deposits and division into areas of water-rich, water-poor and water-barren rocks according to the water content in rocks; 5. the important influence of the Moho and Conrad discontinuities and the magnetic boundary on the origin of magmas and mineralization; 6. the importance of the forms of orebodies for industrial and exploration types of ore deposits and division of the forms of orebodies into six types; 7. the character of the superimposition of polygenetic （i. e. "complex origin"） and polyphase mineralizations in many important ore deposits in China. Ⅲ. This paper proposes six basic principles for the division of metallogenic provinces and units and the high-medium-and low-class metallogenic provinces （belts） are distinguished according to the six principles. Ⅳ. With regards to the methods for preparing metallogenic-prognostic maps and criteria for the division of prognostic areas, this paper not only elucidates the methods and content of expression, but also puts forwards five criteria for the division of prognostic areas. Three classes of prognostic provinces are distinguished according to the five criteria and the metallogenic prospects.