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Pyrite and magnetite Re–Os isotope systematics at the Laoshankou Fe–Cu–Au deposit in the northern margin of the East Junggar terrane, NW Xinjiang, China: Constraints on the multistage mineralization and metal sources
Author(s) -
Liang Pei,
Chen Huayong,
Wu Chao,
Xie Yuling
Publication year - 2020
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3687
Subject(s) - isochron , geology , geochemistry , mineralization (soil science) , molybdenite , basalt , breccia , pyrite , magmatism , sulfide , isochron dating , terrane , magnetite , mineralogy , chemistry , paleontology , quartz , fluid inclusions , tectonics , soil science , soil water , organic chemistry
The northern margin of the East Junggar terrane is highly prospective for Fe–Cu–Au mineralization. However, due to the lack of precise mineralization ages, intensive debates regarding ore genesis existed. In this study, pyrite and magnetite Re–Os isotopes are first used to determine the metallogenic ages and possible genetic links with magmatism at the Laoshankou deposit, the most important Fe–Cu–Au deposit in the region. Magnetites from Fe mineralization stage yield an 187 Re/ 188 Os versus 187 Os/ 188 Os isochron age of 391 ± 55 Ma, which is in broad agreement with ages of the Beitashan Formation volcanic rocks (~390 Ma). The low initial 187 Os/ 188 Os ratio of −0.08–0.16, depleted γOs values of −161–27 and low Re/Os (common) indicated a mantle source composition, implying Fe metals are from the Beitashan Formation Fe‐rich basalts and basaltic breccias. Pyrites from sulfide mineralization stage yield a weighted average Re–Os model age of 390 ± 17 Ma with a matched 187 Re versus 187 Os r (radiogenic 187 Os) isochron age of 391 ± 9 Ma, consistent with the symbiotic molybdenite Re–Os model age of 383.2 ± 4.5 Ma, indicating a timing of ~380 Ma for sulfide–Cu–Au mineralization. The high initial 187 Os/ 188 Os ratio of 0.53–3.6, large positive γOs values of 323–2,754 and higher Re/Os (common) indicated the increase of crustal materials, which is further limited to the Beitashan Formation S‐rich marine sedimentary rocks. In summary, based on the significant two‐stage mineralization, that is, Fe (~390 Ma) and sulfide–Cu–Au (~380 Ma), and the different nonmagmatic fluid and metal sources, we prefer considering the Laoshankou Fe–Cu–Au deposit as an IOCG‐type.