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Some Microstructures of Copper Sulfides in Dongxiang Copper Mine, Jiangxi Province, and Their Geological Implications

XUE Ji-yue-1, SUN Tao-1, ZHANG Wen-lan-2, CHEN Wu-1 (1.Department of Earth Sciences, Nanjing University, Nanjing 210093; 2. State Key Laboratory for Mineral Deposits Research, Nanjing University, N anjing 210093)  
Based on the optical microscopy, electron microprobe studie s and X-ray powder diffraction analysis it is revealed that the djurleite and dig enite are freguently found in copper ores of Dongxiang Copper Mine, Jiangxi Prov ince. The digenite occurs as the lamellae or lens in the djurleite. These two minerals also appear together with a mutual boundary texture. Their average chemical formulas can be expressed as Cu 1.827Zn 0.004Ag 0. 001S and Cu 1.929Fe 0.002Zn 0.003Ag 0.001S, respectively . Near the area of the metasomatic relicts of pyrites the bornite-digenite z oning is commonly seen. The core is composed of bornite, whereas the digenite oc curs at the rim. The optical property and chemical composition of the digenites in these two different textures are different. These two kinds of digenite are b oth blue gray in reflection color, but the reflection color in digenite intergro wn with djurleite is lighter than that in the zoning one. As for the composition s the digenite intergrown with djurleite does not contain iron, whereas in the z oned digenite the iron contents range from 2.8%(wt.) to 9.1%(wt.). The iron cont ents also decrease toward the rim of the zoning, and the color is getting lighte r under reflected microscope with the iron contents decreasing. The two texture s mentioned above represent two kinds of cooling texture of Cu-S and Cu-Fe- S systems respectively. The intergrowth between the iron-free digenite and the dj urleite was produced by exsolution of high digenite solid solution upon coo ling. The zoning texture of bornite and Fe-bearing digenite is produced by the segregation of the Cu 1.8S-CuFeS 4 solid solution in the disequilibrium c ondition. It is believed that it represents a kind of texture that forms with ra pid cooling.
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