Iron Isotope Fractionation during Skarn Cu-Fe Mineralization

被引：8

作者：

Xue, Song ^{[1
]}

Niu, Yaoling ^{[1
,2
,3
]}

Chen, Yanhong ^{[1
]}

Shi, Yining ^{[1
]}

Xia, Boyang ^{[1
]}

Wang, Peiyao ^{[3
,4
,5
]}

Gong, Hongmei ^{[3
,4
,5
]}

Wang, Xiaohong ^{[3
,4
,5
]}

Duan, Meng ^{[3
,4
,5
]}

机构：

[1] China Univ Geosci, Sch Earth Sci & Resources, Beijing 100083, Peoples R China

[2] Univ Durham, Dept Earth Sci, Durham DH1 3LE, England

[3] Lab Marine Geol, Qingdao Natl Lab Marine Sci & Technol, Qingdao 266061, Peoples R China

[4] Chinese Acad Sci, Inst Oceanol, Qingdao 266071, Peoples R China

[5] Chinese Acad Sci, Ctr Ocean Megasci, 7 Nanhai Rd, Qingdao 266071, Peoples R China

来源：

MINERALS | 2021年 / 11卷 / 05期

关键词：

porphyry-skarn deposits; Fe isotopes; isotopic fractionation; pathway effects; light-Fe fluid; redox state; GEOLOGICAL REFERENCE MATERIALS; HYDROTHERMAL ORE-DEPOSITS; MAFIC LAYERED INTRUSION; EAST PACIFIC RISE; MAGMATIC DIFFERENTIATION; PYRITE FORMATION; ICP-MS; MANTLE; SYSTEMATICS; MAGNETITE;

D O I：

10.3390/min11050444

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

Fe isotopes have been applied to the petrogenesis of ore deposits. However, the behavior of iron isotopes in the mineralization of porphyry-skarn deposits is still poorly understood. In this study, we report the Fe isotopes of ore mineral separations (magnetite, pyrite, chalcopyrite and pyrrhotite) from two different skarn deposits, i.e., the Tonglvshan Cu-Fe skarn deposit developed in an oxidized hydrothermal system and the Anqing Cu skarn deposit developed in a reduced hydrothermal system. In both deposits, the Fe isotopes of calculated equilibrium fluids are lighter than those of the intrusions responsible for the skarn and porphyry mineralization, corroborating the "light-Fe fluid" hypothesis. Interestingly, chalcopyrite in the oxidized-Tonglvshan skarn deposit has lighter Fe than chalcopyrite in the reduced-Anqing skarn deposit, which is best understood as the result of the prior precipitation of magnetite (heavy Fe) from the ore fluid in the oxidized-Tonglvshan systems and the prior precipitation of pyrrhotite (light Fe) from the ore fluid in the reduced-Anqing system. The delta Fe-56 for pyrite shows an inverse correlation with delta Fe-56 of magnetite in the Tonglvshan. In both deposits, the Fe isotope fractionation between chalcopyrite and pyrite is offset from the equilibrium line at 350 degrees C and lies between the FeS-chalcopyrite equilibrium line and pyrite-chalcopyrite equilibrium line at 350 degrees C. These observations are consistent with the FeS pathway towards pyrite formation. That is, Fe isotopes fractionation during pyrite formation depends on a path from the initial FeS-fluid equilibrium towards the pyrite-fluid equilibrium due to the increasing extent of Fe isotopic exchange with fluids. This finding, together with the data from other deposits, allows us to propose that the pathway effect of pyrite formation in the Porphyry-skarn deposit mineralization is the dominant mechanism that controls Fe isotope characteristics.

引用

页数：18

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