Mineralogical characteristics of polymetallic sulfides from the Deyin-1 hydrothermal field near 15°S, southern Mid-Atlantic Ridge

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• 作者：Shujie Wang ; Huaiming Li ; Shikui Zhai ; Zenghui Yu ; Zongze Shao…
• 关键词：mineralogical characteristics ; mineral ; forming sequence ; polymetallic sulfides ; Deyin ; 1 hydrothermal field ; southern Mid ; Atlantic Ridge
• 刊名：Acta Oceanologica Sinica
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：36
• 期：2
• 页码：22-34
• 全文大小：
• 刊物主题：Oceanography; Climatology; Ecology; Engineering Fluid Dynamics; Marine & Freshwater Sciences; Environmental Chemistry;
• 出版者：The Chinese Society of Oceanography
• ISSN：1869-1099
• 卷排序：36

文摘

A seafloor hydrothermal field, named Deyin-1 later, near 15°S southern Mid-Atlantic Ridge (SMAR) was newly found during the 22nd cruise carried out by the China Ocean Mineral Resources Research & Development Association (COMRA). Sulfide samples were collected at three stations from the hydrothermal field during the 26th cruise in 2012. In this paper, mineralogical characteristics of the sulfides were analyzed with optical microscope, X-ray diffractometer, scanning electron microscope and electron microprobe to study the crystallization sequence of minerals and the process of hydrothermal mineralization. According to the difference of the ore-forming metal elements, the sulfide samples can be divided into three types: (1) the Ferich sulfide, which contains mainly pyrite and chalcopyrite; (2) the Fe-Cu-rich sulfide consisting predominantly of pyrite, chalcopyrite and isocubanite, with lesser amount of sphalerite, marmatite and pyrrhotine; and (3) the Fe-Zn-rich sulfide dominated by pyrite, sphalerite and marmatite, with variable amounts of chalcopyrite, isocubanite, pyrrhotine, marcasite, galena and gratonite. Mineral precipitations in these sulfides are in the sequence of chalcopyrite (isocubanite and possible coarse pyrite), fine pyrite, sphalerite (marmatite), galena, gratonite and then the minerals out of the dissolution. Two morphologically distinct generations (Py-I and Py-II) of pyrite are identified in each of the samples; inclusions of marmatite tend to exist in the coarse pyrite crystals (Py-I). Sphalerite in the Fe-Zn-rich sulfide is characterized by a “chalcopyrite disease” phenomenon. Mineral paragenetic relationships and a wide range of chemical compositions suggest that the environment of hydrothermal mineralization was largely changing. By comparison, the Fe-rich sulfide was formed in a relatively stable environment with a high temperature, but the conditions for the formation of the Fe-Cu-rich sulfide were variable. The Fe-Zn-rich sulfide was precipitated during the hydrothermal venting at relatively low temperature.