Experiments on Topotaxic Reactivation of Sulphides from Natural Ore
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    Abstract:

    Massive sulphide ore from Hongtoushan of Liaoning province comprise pyrite, pyrrhotite, chalcopyrite, sphalerite, quartz and silicate minerals. The ore was cut into cylinders 40 mm in length and 17 mm in diameter, immerged in a solution of 20% NaCl for 260 hours, and then was mounted in a triaxial rock stress machine Changjiang 500. The experiments were performed under various confining and axial pressures for 13 hours at temperatures of 362, 464, 556 and 682℃, respectively, and then the samples were cooled at the room temperature for 24 hours. Strong mechanic deformation was observed in various minerals after the experiment. The pyrite and hornblend are characterized with brittle cracking, while the pyrrhotite, chalcopyrite, sphalerite, quartz and biotite are characterized by plastic deformation, with brittle distortion locally. During the experiment, sulphides were reactivated intensely, and the main products are veinlets and microcrystallites, with the former occurring mostly in fragments of pyrite porphyroclasts but not in chalcopyrite, pyrrhotite, sphalerite and gangue minerals. These veinlets consist mainly of chalcopyrite with lesser pyrrhotite, and minor sphalerite. Pyrrhotite in the veinlets commonly shows optical continuity over a length of 200 μm, implying that it was formed by slow crystallization at relatively higher temperatures. The amount of reactivated veinlets increased with temperature increasing, so did chalcopyrite/pyrrhotite ratio in the veinlets. Reactivated sulphide microcrystallites can be either irregular or rod-like in shape, and were formed during cooling of the runs. Irregular microcrystallites that fill the spaces between fragments of the same mineral include all sulphides in the runs, whereas those rodlike shape and filling fissures of chalcopyrite to form wormlike bodies are almost pure pyrite. In addition, replacement textures of pyrite by chalcopyrite was found in the experimental products at 556℃ and 682℃. Present experimental results indicate that the sulphides can be intensely remobilized in both mechanical and chemical ways in accompany with deformation and metamorphism, and that remobilization will be enhanced at higher temperatures. Mechanical reactivation can take place only in a limited distance and result in minor differentiation between various sulphide minerals. Only chemical remobilization can result in long distance transport of compositions to form new orebodies. In contrast to plastically deformed areas, tensile spaces in the brittle deformation area could provide conduits for fluid transport and space for metal precipitation. Remobilized iron sulphides will precipitate as pyrrhotite at high temperatures and as pyrite when temperature decreases. Chalcopyrite tends to be more remobilized than sphalerite under the conditions in the present experiments. Reactivation of the synsedimentary deposits during deformation and metamorphism would add many epigenetic features to the deposits, which should be paid more attention during research.

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ZHENG Yuanchuan, GU Lianxing, TANG Xiaoqian, WANG Zijiang, WU Changzhi, WU Xueyi, ZHANG Wenlan.2009. Experiments on Topotaxic Reactivation of Sulphides from Natural Ore[J]. Acta Geologica Sinica,83(1):31-42

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History
  • Received:March 06,2008
  • Revised:July 28,2008
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