文献类型：期刊文献

英文题名：Experimental study of the formation of chalcopyrite and bornite via the sulfidation of hematite: Mineral replacements with a large volume increase

作者：Zhao, Jing[1,2];Brugger, Joel[1];Chen, Guorong[3];Ngothai, Yung[2];Pring, Allan[1,4]

机构：[1]S Australian Museum, Dept Mineral, Adelaide, SA 5000, Australia;[2]Univ Adelaide, Sch Chem Engn, Adelaide, SA 5005, Australia;[3]E China Univ Sci & Technol, Sch Mat Sci & Engn, Key Lab Ultrafine Mat, Minist Educ, Shanghai 200237, Peoples R China;[4]Univ Adelaide, Sch Chem & Phys, Adelaide, SA 5005, Australia

年份：2014

卷号：99

期号：2-3

起止页码：343

外文期刊名：AMERICAN MINERALOGIST

收录：;WOS:【SCI-EXPANDED(收录号:WOS:000331676800011)】；

基金：We thank Len Green, Aoife McFadden, and Benjamin Wade from Adelaide Microscopy Center for their assistance in using the FESEM, EBSD, ICP-MS, and electron microprobe. The constructive comments of David Vaughan, an anonymous referee and associate editor Daniel Harlov greatly improved the clarity of the text of this paper. This work has been made possible by the financial support of the Australian Research Council (Grant DP1095069). Jing Zhao acknowledges the Australian Department of Education, Science and Training, for an International Postgraduate Research Scholarship, and the University of Adelaide for living allowance.

语种：英文

外文关键词：Hematite; chalcopyrite; bornite; mineral replacement; hydrothermal experiment

摘要：Chalcopyrite (CuFeS2) and bornite (Cu5FeS4) are the most abundant Cu-bearing minerals in hydrothermal Cu deposits, forming under a wide range of conditions from moderate-temperature sedimentary exhalative deposits to high-temperature porphyry Cu and skarn deposits. We report the hydrothermal synthesis of both chalcopyrite and bornite at 200-300 degrees C under hydrothermal conditions. Both minerals formed via the sulfidation of hematite in solutions containing Cu(I) (as a chloride complex) and hydrosulfide, at pH near the pK(a) of H2S(aq) over the whole temperature range. Polycrystalline chalcopyrite formed first, followed by bornite. Assuming that Fe behaves conservatively, the transformation of hematite to chalcopyrite involves a large increase in volume (similar to 290%). The reaction proceeds both via direct replacement of the existing hematite and via overgrowth around the grain. Chemical exchanges between bulk solution and hematite are enabled by a network of micrometer-size pores. However, in some cases the chalcopyrite overgrowth develops large grain sizes with few apparent pores and in these cases fluid transport may have been via a network of fractures. Similarly to the replacement of hematite by chalcopyrite, bornite forms via the replacement of chalcopyrite. The reaction has a large positive volume (similar to 230%), and proceeds both via chalcopyrite replacement and via overgrowth. This study shows that replacement reactions can proceed via coupled dissolution-reprecipitation even where there is a large volume increase between parent and product mineral. This study also provides further evidence about the controls of reaction pathways onto the final mineral assemblage. In this case, the host initial fluid was undersaturated with respect to Fe-bearing minerals. Upon slow release of Fe at the surface of hematite, a mineral assemblage of chalcocite, bornite, and finally chalcopyrite is expected. However, in practice chalcocite did not nucleate on the surface of hematite. Rather relatively slow nucleation of bornite enabled high concentrations of Fe to build up near the dissolving hematite, so that chalcopyrite (high-sulfidation experiments) or chalcopyrite+pyrite (low sulfidation) crystallized first.