Formation of Fe-Cu-Au deposit in basin inversion setting in NW China: A perspective from ore-fluid halogen and noble gas geochemistry
Formation of Fe-Cu-Au deposit in basin inversion setting in NW China: A perspective from ore-fluid halogen and noble gas geochemistry
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DOI：
10.1016/j.oregeorev.2021.104011
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发表时间：
2021-01
影响因子：
3.3
通讯作者：
Pei Liang;Richen Zhong;Liandang Zhao;Chao Wu;Yuling Xie
中科院分区：
文献类型：
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作者：
Pei Liang;Richen Zhong;Liandang Zhao;Chao Wu;Yuling Xie
巧夏哈拉矿床是东准噶尔北缘一处重要的古生代铁铜金矿床，已被证实形成于盆地反转环境（弧后盆地消亡）中。对乔夏哈拉各成矿阶段的石英、方解石、绿帘石中流体包裹体中提取的稀有气体（Ar、Kr、Xe）和卤素（Cl、Br、I）进行了成分研究，以追溯矿液来源并探讨成矿成因。乔夏哈拉地区显着的多期矿化被确定为磁铁矿矿化（III 期）、磁铁矿-黄铁矿矿化（IV 期）和黄铜矿矿化（V 期）。同矿流体包裹体显示盐度从 13.2 wt% 到 15.3 wt%（NaCl eq.）不等，与较高的 I/Cl 比率（214 × 10−6 至 3950 × 10−6）、一致的低 Br/Cl 比率（0.78 × 10−3 至 1.30 × 10−3）和低 40 Ar/36 Ar 比率相关（<700）。低 40Ar/36Ar 比值和 Br/Cl 比值排除了岩浆或变质流体（高 40Ar/36Ar）和地下蒸发卤水（高 Br/Cl）的参与。乔夏哈拉各矿化阶段的流体包裹体具有高 I/Cl 比、低 36 Ar 浓度（小于或等于空气饱和水，ASW）以及恒定的 40 ArE/Cl 斜率（10−5 至 10−4），支持了沉积地层水被富含有机物沉积物改造的优势。成矿流体δ18O水值升高（7.2~11.1‰），流体包裹体中普遍存在有机质（如C4H6、C2H2和CH4），进一步表明富含有机物的参与。然而，III期和IV-V期不同的δD水值以及卤素和稀有气体数据之间的显着差距表明，这些阶段涉及不同的沉积地层流体，即III期海水与北塔山组和IV-V期成岩压实形成的地层水之间存在广泛的水墙岩石相互作用。乔夏哈拉的多阶段矿化，即氧化铁和黄铜矿（-金），以及不同来源的不同非岩浆流体的混合，与中部安第斯山脉的许多氧化铁-铜-金矿床（IOCG）相似，表明乔夏哈拉为类IOCG型矿床。这些发现进一步表明，在东准噶尔北缘盆地反转背景下，非岩浆流体主导了IOCG矿床的形成。
The Qiaoxiahala deposit is a significant Paleozoic Fe-Cu-Au deposit in the northern margin of East Junggar, NW China, which has been confirmed to form in a basin inversion setting (dying back-arc basin). The composition of noble gases (Ar, Kr, and Xe) and halogens (Cl, Br, and I) extracted from fluid inclusions, hosted in quartz, calcite, and epidote from various mineralization stages of Qiaoxiahala, are investigated to trace the sources of ore fluids and discuss the ore genesis. Significant multistage mineralization at Qiaoxiahala is identified as magnetite mineralization (stage III), magnetite-pyrite mineralization (stage IV), and chalcopyrite mineralization (stage V). Syn-ore fluid inclusions show salinities varying from 13.2 to 15.3 wt% (NaCl eq.) associated with elevated I/Cl ratios (214 × 10−6to 3950 × 10−6), uniformly low Br/Cl ratios (0.78 × 10−3to 1.30 × 10−3), and low40Ar/36Ar ratios (<700). The low40Ar/36Ar ratios and Br/Cl ratios preclude the involvement of magmatic or metamorphic fluids (high40Ar/36Ar), and sub-aerial evaporation bittern brines (elevated Br/Cl). The predominance of sedimentary formation water modified by organic-rich sediments is supported by the high I/Cl ratios, low36Ar concentrations (less than or equal to that of Air Saturated Water, ASW), and the constant40ArE/Cl slopes (10−5to 10−4) of fluid inclusions from various mineralization stages in Qiaoxiahala. The elevated δ18Owatervalues (7.2–11.1‰) of the ore-forming fluids and the common presence of organic matter (e.g. C4H6, C2H2and CH4) in fluid inclusions further indicated the involvement of organic-rich materials. However, different δDwatervalues and a significant gap between halogen and noble gas data in stages III and IV-V indicate that different sedimentary formation fluids are involved during these stages, i.e., extensive water-wall rock interactions between seawater and Beitashan Formation in stage III and formation waters formed by diagenesis and compaction in stages IV-V. Multistage mineralization, i.e., Fe-oxide and chalcopyrite (-gold), and the mixing of different non-magmatic fluids with variable origins in Qiaoxiahala are similar to many iron oxide-Cu-Au deposits (IOCGs) from the Central Andes, indicating an IOCG-like type deposit for Qiaoxiahala. These finding further suggest that non-magmatic fluids dominate the formation of IOCG deposits in the basin inversion setting at the northern margin of East Junggar.