科研之友
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摘要
Recent investigations found that hydrothermal activity and sulfide mineralization occurs along the Southwest Indian Ridge (SWIR). The Longqi and Duanqiao hydrothermal fields between 49 degrees E and 53 degrees E of the SWIR are two prospective mineralization areas discovered by Chinese scientists. With the aim to determine the mineralogical and chemical characteristics of sulfide minerals, we have conducted detailed studies for samples from the two areas using an optical microscope, X-ray diffractometer, scanning electron microscope, and electron microprobe. The mineralization processes in the Longqi area are divided into three main stages: (1) the low-medium-temperature stage: colloform pyrite (Py I) + marcasite euhedral pyrite (Py II), (2) the high-temperature stage: isocubanite (+/- exsolved chalcopyrite) + pyrrhotite coarse-grained chalcopyrite (Ccp I), and (3) the medium-low-temperature stage: sphalerite + fine-grained chalcopyrite inclusions (Ccp II) aggregates of anhedral pyrite (Py III) +/- marcasite Fe-oxide (-hydroxide) + amorphous silica. The mineralization processes in the Duanqiao area are divided into two main stages: (1) the medium-high-temperature stage: subhedral and euhedral pyrite (Py I) coarse-grained chalcopyrite (Ccp I) and (2) the medium-low-temperature stage: sphalerite fine-grained chalcopyrite (Ccp II) + chalcopyrite inclusions (Ccp II) silica-cemented pyrite (Py II) + marcasite Fe-oxide + amorphous silica. We suggest that the fine-grained chalcopyrite inclusions in sphalerite from Longqi and Duanqiao were formed by co-precipitation and replacement mechanisms, respectively. Primary sphalerites from both fields are enriched in Fe (avg. 5.84 wt% for the Longqi field vs. avg. 3.69 wt% for the Duanqiao field), Co (avg. 185.56 ppm for the Longqi field vs. 160.53 ppm for the Duanqiao field), and Cd (avg. 1950 ppm for the Longqi field vs. avg. 525.26 ppm for the Duanqiao field). Cu contents in pyrite from the Duanqiao field (Py I: avg. 849.23 ppm and Py II: avg. 1191.11 ppm) tend to be higher than those from the Longqi field (Py I: avg. 26.67 ppm, Py II: avg. 445 ppm, and Py III: avg. 179.29 ppm). Chalcopyrite from both fields is enriched in Zn (Ccp I: avg. 3226.67 ppm, Ccp II: avg. 9280 ppm, Ccp I: avg. 848 ppm, Ccp II (inclusions): avg. 1098 ppm, and Ccp II (fine-grained): avg. 1795 ppm). The varying contents of Zn in the different pyrite and chalcopyrite generations may result from the zone refining process. An integrated study of the mineralogy and mineralogical chemistry suggests that the hydrothermal fluids of the Longqi area are likely conditioned with higher temperatures and relatively lower f(O2) and f(S2) than those of the Duanqiao area, but in contrast to the former, the latter is much affected by the compositions of the surrounding rocks.
- 出版日期2018-10
- 单位国家海洋局第二海洋研究所; 中国地质科学院; 中国地质科学院矿产资源研究所; 中国地质大学（北京）
