(1. 中南大学 有色金属成矿预测教育部重点实验室，长沙 410083；
2. 中南大学 地球科学与信息物理学院，长沙 410083；
3. 金川集团股份有限公司 镍钴研究设计院，金昌 737104)
摘 要: 已发现的金川铜镍硫化物矿床产于两条基性-超基性岩墙中，而金川最大的Ⅱ-1、Ⅱ-2两个矿体均位于南东侧的岩墙内。通过分析Ⅱ-1、Ⅱ-2两个矿体矿石的主量元素、稀土元素以及微量元素的特征，探讨二者的母岩浆在岩浆演化过程中的联系与独立性。Ⅱ-1、Ⅱ-2号矿体矿石均属于具有富MgO(w(MgO)为10.4%~34.5%)、贫Al2O3(w(Al2O3)为0.67%~15.35%)及K2O(w(K2O)为0.01%~1.42%)特征的铁质(m/f=( Mg2++Ni2+)/(Fe2++Fe3++Mn2+)，为1.30~5.16)超基性岩；稀土元素及微量元素配分曲线极为相似，轻重稀土分异明显(Σ(LREE)/Σ(HREE)为 3.27~9.63)，且大离子亲石元素相对富集，显示Ⅱ-1、Ⅱ-2两个矿体的母岩浆具有强烈的亲源关系。通过一系列反映岩浆演化特征的比值及其相互间的关系，如w(Sm)-w(Sm)/w(Yb)、w(La)/w(Sm)-w(Sm)/w(Yb)、w(Th)N/w(Nb)N、w(Th)/w(Yb)-w(Nb)/w(Th)、w(MgO+FeOT)/w(Al2O3)-w(SiO2)/w(Al2O3)(FeOT为全铁含量)等，得出Ⅱ-1、Ⅱ-2两个矿体的母岩浆均为石榴子石二辉橄榄岩经过30%~40%的分离熔融形成，上升过程中混染了5%~20%的地壳物质。同时，岩浆的结晶分异作用由橄榄石控制，均显示了二者的母岩浆在演化过程中密切的联系；但是Ⅱ-2号矿体矿石的各主量元素的质量分数与w(MgO)的线性关系较复杂，这与呈明显单一线性关系的Ⅱ-1号矿体不同，暗示二者在岩浆冷凝过程中演化的独立性。因此，Ⅱ-1、Ⅱ-2号矿体的母岩浆本是在同一岩浆通道中演化，受到地壳混染后，在冷凝过程中发生了分离，而后在横向上并列的两个岩浆通道中分别演化并成矿。
关键字: 金川；铜镍(铂族)硫化物矿床；岩浆作用；源区演化；地壳混染；地球化学
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education,
Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;
3. Nickel Cobalt Research and Design Institute, Jinchuan Group Co., Ltd., Jinchang 737104, China）
Abstract:The discovered Jinchuan Cu-Ni(PGE) sulfide deposit occurs in two ultrabasic dykes, and the two main orebodies in Jinchuan, Ⅱ-1 orebody and Ⅱ-2orebody were outputted in one ultrabasic dyke in Southeastern side. In order to prove the particularity and connection of parental magma of Ⅱ-1 and Ⅱ-2 orebodies during magma evolution, the contents of major elements, REE and trace elements in the two orebodies were measured and compared with each other. The two orebodies belong to iron-ultrabasic rocks (m/f=(Mg2++Ni2+)/(Fe2++Fe3++Mn2+), 1.30-5.16), and have the following features: rich in MgO (w(MgO), 10.4%-33.5%), poor in Al2O3 (w(Al2O3), 0.67%-15.35%) and K2O (w(K2O), 0.01%-1.42%). The two orebodies have similar REE distribution and trace elements distribution and strongly fractionated REE pattern (Σ(LREE)/Σ(HREE), 3.27-9.63), and enriches LILE relative to HFSE, reflecting that the parental magma of Ⅱ-1 and Ⅱ-2 orebodies have a strongly close relationship. Some trace element ratios and relationship characterizing the magma evolution, such as w(Sm)-w(Sm)/w(Yb), w(La)/w(Sm)-w(Sm)/w(Yb), w(Th)N/w(Nb)N, w(Th)/w(Yb)-w(Nb)/ w(Th) and w(MgO+FeOT)/w(Al2O3)-w(SiO2)/w(Al2O3) (FeOT is total iron content), are suggested that the parental magma of Ⅱ-1 and Ⅱ-2 orebodies are generated by 30%-40% fractional melting of the garnet lherzolite, contaminated by 5%-20% crustal materials during digenetic evolution process and experienced olivine crystallization. This indicates that the parental two kinds of magma of Ⅱ-1 and Ⅱ-2 orebodies have close relation during magma evolution. However, there exists an obvious difference that the MgO value of Ⅱ-2 orebody shows a more complicated linear relation with other major elements than that of Ⅱ-1 orebody. It suggests that the two kinds of parental magma have experienced independent evolution in their cooling stage. The two kinds of parental magma of Ⅱ-1 and Ⅱ-2 orebodies are original in the same magma conduit, along with the crustal contamination. The two kinds of parent magma of the orebodies have separated into two coordinate magma conduit systems during the magma crystallizing process, as a consequence, the evolution and metallogenic process of magma of each magma conduit are independent.
Key words: Jinchuan; Cu-Ni(PGE) sulfide deposit; magmatic process; magma sources evolution; crustal contamination; Geochemistry
