Cu-Fe同位素示踪岩浆铜镍硫化物成矿系统中氧逸度变化：以新疆图拉尔根矿床研究为例

Oxygen fugacity is a key parameter in controlling the petrogenesis of mafic-ultramafic rocks and their associate sulfide mineralization. Both Cu and Fe are highly redox-sensitive and, however, whether their isotopes can be applied for tracing oxygen fugacities and mineral exploration in high-temperature magmatic Ni-Cu mineralization system is still not clear. The large-scale Tulaergen Ni-Cu sulfide deposit in Xinjiang Province will be selected for evaluating this possibility. Sulfide ores (including whole rocks and chalcopyrite) and country rocks in different occurrences, positions and mineralization types will be collected for analyzing the Cu-Fe isotopes. Olivine composition and whole-rock element contents will be used for estimating the redox conditions of parental magmas or sulfide melts. The major and trace elements, PGE composition, Re-Os and S isotopes will be applied for constraining the influence of geological factors on the Cu-Fe isotope fractionation. Furthermore, Cu and Fe isotope fractionation during the changes of oxygen fugacities will be discussed. Based on the systemic change of Cu-Fe isotopes, the potential of these isotopes for tracking concealed orebodies will be presented. This study is expected to enrich our knowledge for the application of Cu-Fe isotopes for tracing oxygen fugacities in magmatic Ni-Cu sulfide mineralization system. On the other hand, this study would also widen our eyesight of Cu-Fe isotopic geochemistry in high-temperature conditions.

氧逸度是控制含矿镁铁-超镁铁质岩矿物组合及其矿化类型的重要因素。Cu-Fe元素是氧化还原状态敏感元素，其同位素能否应用于示踪高温岩浆铜镍成矿系统氧逸度变化并应用于找矿评价尚不清楚。本项目拟以新疆图拉尔根大型岩浆铜镍硫化物矿床为对象，分析不同产状、不同空间位置、不同矿化类型、不同品位的岩/矿石（包括全岩和黄铜矿）和围岩样品的Cu-Fe同位素组成；通过橄榄石成分和元素含量，定量计算岩浆/硫化物熔体演化不同阶段氧逸度；通过主微量元素、铂族元素、铼-锇同位素和硫同位素，分析Cu-Fe同位素分馏影响因素；阐明氧逸度变化过程中Cu-Fe同位素分馏行为，并尝试建立Cu-Fe同位素联合用于岩浆铜镍成矿系统找矿预测指标组合。研究将是Cu-Fe非传统同位素联合应用于岩浆成矿系统氧化还原状态示踪与找矿评价的新探索，能为高温自然过程中Cu-Fe同位素地球化学研究提供新参考。

利用Cu-Fe同位素对岩浆型铜镍硫化物成矿系统中关键的成矿过程/成矿机制进行制约具有明显的优越性。然而，控制Cu-Fe同位素在岩浆型铜镍硫化物成矿系统中同位素分馏的关键因素仍不清楚；此外，如何有效示踪隐伏矿体的寻找一直是岩浆型铜镍硫化物矿床研究的难点问题。针对上述科学问题，本项目选择我国东天山图拉尔根大型岩浆型铜镍硫化物矿床为研究对象，系统选取了不同空间位置和矿化类型的矿石开展了黄铜矿的Cu-Fe同位素和全岩的Fe同位素研究，结合其他元素及同位素组成，取得的新认识如下：.1、氧化还原状态的改变是引起图拉尔根岩浆型铜镍硫化物矿床中显著Cu-Fe同位素分馏的关键因素。.2、在硫化物熔离过程中，早期熔离的黄铜矿富集轻Cu和重Fe同位素，而晚期熔离的黄铜矿富集重Cu和轻Fe同位素；在硫化物分异过程中，单硫化物固溶体（MSS）的堆晶导致系统氧逸度升高，剩余硫化物熔体中形成的黄铜矿富集重Cu和轻Fe同位素。.3、镁铁质-超镁铁质岩体中黄铜矿逐渐富集轻Cu和重Fe同位素的方向和全岩Fe同位素变轻的方向可能代表岩浆通道和富镍矿体的位置，而黄铜矿逐渐富集重Cu和轻Fe同位素的方向和全岩Fe同位素变重的方向可能代表富铜矿体的位置。.该研究对完善高温地质环境中Cu-Fe同位素理论体系和促进岩浆型铜镍硫化物矿床的勘查都有一定的参考意义。