WANG Ye-jian1,2, HAN Xi-qiu2, JIN Xianglong2, QIU Zhong-yan1,2, ZHU Ji-hao2
(1. Department of Earth Sciences,Zhejiang University, Hangzhou 310027, China;
2.Key Laboratory of Submarine Geosciences & Second Institute of Oceanography,State Oceanic Administration, Hangzhou310012, China)
Fig. Micro-morphology characteristics of pyrite from the study area.
Abstract: During 2005’ DY105-17A cruise, abundant hydrothermal sulfides samples were retrieved from Edmond hydrothermal field, Central Indian Ridge at 23°S by using TV guided grab. Based on the detailed study of mineralogy and ore microscopy, in this paper we focused on the typomorphic characteristics and their evolution of pyrite in the massive sulfide to understand the seafloor hydrothermal mineralization. As a result, three types of pyrite were identified from our sulfide samples: (1) Type-Ⅰ occurs as euhedral cubic crystals and its average S/Fe atomic ratio is close to 2.00. This type is characterized by high content of Cu, and low contents of Zn, As, Ni, Pb, and Ag. Its average Cu/Zn ratio is close to 4.26; (2) Type-Ⅱ occurs as subhedral cubic crystals, and its average S/Fe atomic ratio is 2.03. This type is enriched in trace elements Zn and Co, but depleted in Cu, with a low average Cu/Zn ratio (0.04); and (3) Type-Ⅲoccurs as framboids or colloform with a high average S/Fe atomic ratio (2.04). This type is commonly enriched in trace elements such as Pb, Ag, As, and Zn, with the average Cu/Zn ratio (1.09) lies between that of Type-Ⅰ and Type-Ⅱ. According to the mineral assemblages and geochemistry characteristics, it is considered that type-Ⅰ, Ⅱ, and Ⅲ represent for high-, high to medium-, and low-temperature mineralization, respectively, and the combination of typomorphology and chemical composition of pyrite can be used as a good indicator for the environmental condition during the seafloor hydrothermal mineralization.
Key words: pyrite; typomorphic mineral; metallogenic environment; Edmond hydrothermal field; Central Indian Ridge
E-mail: xqhan@sio.org.cn
ACTA MINERALOGICA SINICA Vol. 31, No. 2, 2011, Page 173-179
