(1. 中南大學(xué) 有色金屬成礦預(yù)測(cè)教育部重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)沙 410083；
2. 中南大學(xué) 地球科學(xué)與信息物理學(xué)院，長(zhǎng)沙 410083；
3. 金川集團(tuán)股份有限公司 鎳鈷研究設(shè)計(jì)院，金昌 737104)
摘 要: 已發(fā)現(xiàn)的金川銅鎳硫化物礦床產(chǎn)于兩條基性-超基性巖墻中，而金川最大的Ⅱ-1、Ⅱ-2兩個(gè)礦體均位于南東側(cè)的巖墻內(nèi)。通過分析Ⅱ-1、Ⅱ-2兩個(gè)礦體礦石的主量元素、稀土元素以及微量元素的特征，探討二者的母巖漿在巖漿演化過程中的聯(lián)系與獨(dú)立性。Ⅱ-1、Ⅱ-2號(hào)礦體礦石均屬于具有富MgO(w(MgO)為10.4%~34.5%)、貧Al2O3(w(Al2O3)為0.67%~15.35%)及K2O(w(K2O)為0.01%~1.42%)特征的鐵質(zhì)(m/f=( Mg2++Ni2+)/(Fe2++Fe3++Mn2+)，為1.30~5.16)超基性巖；稀土元素及微量元素配分曲線極為相似，輕重稀土分異明顯(Σ(LREE)/Σ(HREE)為 3.27~9.63)，且大離子親石元素相對(duì)富集，顯示Ⅱ-1、Ⅱ-2兩個(gè)礦體的母巖漿具有強(qiáng)烈的親源關(guān)系。通過一系列反映巖漿演化特征的比值及其相互間的關(guān)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為全鐵含量)等，得出Ⅱ-1、Ⅱ-2兩個(gè)礦體的母巖漿均為石榴子石二輝橄欖巖經(jīng)過30%~40%的分離熔融形成，上升過程中混染了5%~20%的地殼物質(zhì)。同時(shí)，巖漿的結(jié)晶分異作用由橄欖石控制，均顯示了二者的母巖漿在演化過程中密切的聯(lián)系；但是Ⅱ-2號(hào)礦體礦石的各主量元素的質(zhì)量分?jǐn)?shù)與w(MgO)的線性關(guān)系較復(fù)雜，這與呈明顯單一線性關(guān)系的Ⅱ-1號(hào)礦體不同，暗示二者在巖漿冷凝過程中演化的獨(dú)立性。因此，Ⅱ-1、Ⅱ-2號(hào)礦體的母巖漿本是在同一巖漿通道中演化，受到地殼混染后，在冷凝過程中發(fā)生了分離，而后在橫向上并列的兩個(gè)巖漿通道中分別演化并成礦。
關(guān)鍵字: 金川；銅鎳(鉑族)硫化物礦床；巖漿作用；源區(qū)演化；地殼混染；地球化學(xué)
（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
