Criteria for locating Tin Ore
deposites by Remote Sensing detection Feng Junbi Yunnan Institute of Geological Sciences, China In the application of Remote Sensing techniques for locating tin ore deposites, geologic characteristics of tin deposites are studies together with the Remote Sensing images and data obtained through Remote Sensing measurements so as to work out through analysis the Remote Sensing criteria for locating tin ore deposites. Geologic Characteristics of Tin Pre Deposites The geologic characteristics of tin ore deposites are illustrated through the following 3 aspects, geochemistry, types of ore deposites and patterns of ore formation. Geochemistry shows the distribution of tin in the cosmic space by that the iron-nickel meteorite ahs tin concentration of 100 ppm. The average tin concentration in the crust is approximately 2.5 ppm, where as 780 – 7800 ppm in greisen and 0.4 ppm in sandstone. Therefore, in the long process of evolution of the earth and affected by a number of geologic factors, tin enrichment is not uniform and distribution of tin ore deposites in the mantle and crust is also uneven. The primitive tin-rich zones thus emerge. There is not much tin enrichment during the crystallization and differentiation process of the moten magma. During the alteration period, tin is enriched into ore deposites under regional metamorphism. The cassiterite is chemically stable under exagenetic conditions. It deposits into sbauylous ore beds. Tin deposties can be classified into 5 types: a) Tin-rich pematite; b) Classiterite – quars vein; c) Cassiterite – sulfide, including skarns, classiterite-tourmaline sulfide, classiterite-chlorite-sulfide deposites, d) Porphyry, and e) Sabulous tin ores. According to the general law governing the mineralization and the associated types of condition of magma emplacement, the minerogenetic models can be classified models can be classified into 3 types: a) Minerogenetic model which is associated with hypogene-hypabyssal granite intrusive masses; b) Porphyry-tin ore mineroregenetic model and c) Polycycle mineralization model. Criteria for Remote Sensing Detection 1. Mineralization under conditions of continental plates: Tin-mineralized granite is closely related to the plate tectonic margins. Tin mineralization is found existing along the Lanchang River Plate tectonic intersections zone. Plate tectonic margins usually run along gigantic fault zones and appear as linear patterns at the Remote Sensing, and those patterns are characterized by their immense magnitude. 2. Mineralization of the granite intrusive masses; Gejiu Tin Mine is formed at the apical granite extrusive. Hidden granite bodies appear a ring-shape patterns characterized by their synthetic features as the Remote Sensing imageries, and can thus be effectively located at such Remote Sensing image. 3. Tin ores and rocks controlled by linear masses : The acidic magmatic rocks related to the mineralization of tin ores are controlled in their spatial distribution by fault tectonics. Site such faults controlling rocks and ores can be located by studying the linear patterns at the satellite images and aero photographs. 4. Structural regional ring-shape patterns, when a quarts vein extends into the intersection of two groups of faulting, alteration occurs in the wall rocks which results in the enrichment of a tin controlling elements. Owing to the variations of the regional reflective spectrum, due anomalies emerge in Remote Sensing imageries with respect to the Remote Sensing criteria such as changes in tone, patteres, drainage systems, vegetation etc. 5. Detection of ore-controlling stratigaphic units: when tin mineralization is caused by metamorphism, ore deposits will be formed within certain beds whose distribution can be traced by Remote Sensing techniques to locate the tin ore deposits. 6. Cassiterite per-infrared spectrum, As determined by G.R. Hunt, Spectrum lines generated by cassiterite fall into the peri-infrared region. This can be used to differentiate tin ores from the other ore bodies and thus to locate the site of tin mineralization. An Example of Tin Ore Deposits Classiterite-skarns beds a Gejiu Yunnani China. In the comparison pattern of the satellite images, the north-south linear structure is the Geijiu fautla. Dark colors in the northwest represent Gejiu granite. The comparison images show east-west striking linear structures, i.e. ore-controlling structures, thus telling us where to look for the tin ore depsoits. |