Geology and Genesis of Xianglushan Fe-Cu Orefield in Sichuan (SW China): Evidence from C-O-S-Pb Isotopes

Minerals

Chunkit Lai¹  Huan Li²  Tianguo Wang² 

[1] Faculty of Science, Universiti Brunei Darussalam, Gadong BE1410, Brunei;Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;

关键词: IOCG-like deposit;    Sichuan (SW China);    submarine volcanics;    calcite C-O isotopes;    sulfide Pb-S isotopes;    fluid inclusions;    Proterozoic;    Yangtze Block;   

DOI  :  10.3390/min9060338

来源: DOAJ

【 摘 要 】

The Proterozoic Xianglushan Fe-Cu orefield (western Sichuan) is located in the Huili−Dongchuan ore belt on the southwestern margin of the Yangtze Block in SW China. The orefield has experienced complex magmatotectonic activities, and hosts a wide variety of Fe oxide-(Cu-Au) deposits. At Xianglushan, the orebodies are made of stratabound magnetite−hematite orebodies superimposed by vein-type chalcopyrite mineralization. The stratabound Fe orebodies are hosted mainly in the Proterozoic volcanic-sedimentary rocks of the lower Yinmin Formation, whilst the Cu vein or stockwork ores were mainly emplaced into the upper part of the footwall volcanic rocks and the lower part of the Fe orebodies. We divided the alteration/mineralization and their fluid inclusions (FIs) into the (I) sodic-calcic alteration, (II) potassic-silicic-sericite alteration and Fe-(Cu) mineralization, and (III) carbonate alteration and Cu mineralization stages. Stage II FIs are mainly two-phase (vapor-liquid), and are featured by medium temperature (348 to 379 °C) and high salinity (21.8 to 22.9 wt % NaCl eqv). Their generally negative calcite δ¹³C (−4.1‰ to −3.1‰) and δ¹⁸O_H2O (12.2‰ to 15.3‰) values reveal that the Stage II ore fluids have had a seawater-magmatic fluid mixed source. Late Stage II pyrite has δ³⁴S (−3.3‰ to 13.7‰), ²⁰⁶Pb/²⁰⁴Pb (17.663 to 18.982), ²⁰⁷Pb/²⁰⁴Pb (15.498 to 15.824) and ²⁰⁸Pb/²⁰⁴Pb (37.784 to 38.985), suggesting that the ore-forming materials were derived from dominantly upper crustal source. Stage III FIs are also mainly two-phase (vapor-liquid), and are featured by lower temperature (206 to 267 °C) and salinity (19.0 to 22.5 wt % NaCl eqv) than their Stage II counterparts. The Stage III ore fluids were also likely derived from a meteoric−magmatic mixed source with greater magmatic influence, as indicated by the generally negative calcite δ¹³C (−6.9‰ to −4.6‰) and δ¹⁸O_H2O (6.3‰ to 9.2‰) values. Similar to the late Stage II pyrite, the Stage III chalcopyrite δ³⁴S (−4.6‰ to 5.2‰) and Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 18.198 to 18.987; ²⁰⁷Pb/²⁰⁴Pb = 15.534 to 15.876; and ²⁰⁸Pb/²⁰⁴Pb = 37.685 to 39.476) also suggest a crustal ore-forming material source. Therefore, we suggest that the Fe-(Cu) and Cu mineralization at Xianglushan had similar ore fluid and material sources, although the magmatic influence increased in the later stage. This resembles many Fe-(Cu) deposits in the Huili−Dongchuan ore belt. We conclude that the Xianglushan Fe-Cu deposits are both similar to and different from typical iron-oxide copper gold (IOCG) deposits in terms of alteration styles and hydrothermal mineral assemblages, and are thus best classified as IOCG-like deposits hosted in submarine volcanic-sedimentary rocks. Considering the Mesoproterozoic regional tectonics in the southwestern Yangtze Block, we propose that the Xianglushan ore formation occurred in an intra-/back-arc inversion setting, possibly related to the closure of the Anning ocean basin.

【 授权许可】

Unknown