世界上超過50%的Cu、幾乎所有的Mo和大量的Au、Ag等金屬均來源於斑巖型礦床，因此斑巖型礦床研究受到廣泛關注。近年來，有關斑巖型礦床的成巖成礦機理進展包括俯衝板片之上地幔楔形區部分熔融、巖漿與巖石圈相互作用以及MASH（熔融-混染-存儲-均化）過程、巖漿在上地殼巖漿房的侵位以及流體出溶機理等。基於此，Richards（2003，2005）建立了經典的巖漿弧斑巖型礦床成礦模式，這一模式得到了普遍的認可。然而，巖漿侵位之後斑巖可能發生的成巖成礦過程仍有許多值得研究的問題。
大多數斑巖銅礦為氧化性斑巖銅礦（含石膏、CO2），含礦巖漿為高氧逸度巖漿，這種巖漿有利於金屬隨巖漿遷移並有效地出溶。然而，還有一些礦床具有還原性特點（含磁黃鐵礦、CH4），其含礦巖漿是否為高氧逸度巖漿，又如何形成了還原性斑巖銅礦，這仍然是一個未解之謎。
中科院地質與地球物理研究所固體礦產資源研究室申萍副研究員等人對新疆西準噶爾地區的包古圖斑巖銅礦進行了研究，認為該礦床具有還原性斑巖銅礦的特點。進一步對含礦巖體研究發現，含礦巖漿侵位之後發生了圍巖的混染作用，其主要依據包括：（1）巖相學研究發現，含礦巖體主階段巖株組成複雜、變化大、界線不清；巖石中包含長英質圍巖捕擄體；斑晶在結構及組成上都不均一（圖1）；（2）區域剖面測量發現，巖體圍巖發育含碳質巖石，如含碳質泥質凝灰巖和含海綿骨針的碳質泥質矽質巖等，表明圍巖混染可導致還原物質加入巖漿；（3）電子探針研究表明，輝長巖和閃長巖礦物化學組成穩定，而強烈混染形成的英雲閃長斑巖礦物化學組成很不穩定，變化大；（4）巖石地球化學和Sr-Nd同位素分析結果表明，混染成因英雲閃長斑巖的巖石地球化學特徵介於閃長巖和圍巖之間。此外，對含礦巖體氧逸度研究表明，包古圖含礦原始巖漿為高氧逸度巖漿，這與經典的斑巖銅礦含礦巖漿特點一致。這種氧化性巖漿侵位之後與圍巖發生了混染作用，而含碳質圍巖等還原物質加入，可導致巖漿氧逸度降低及還原性成礦作用的發生。上述研究表明，巖漿與圍巖的混染作用，對包古圖斑巖銅礦的形成具有重要意義，據此，申萍等人提出了包古圖斑巖銅礦含礦巖漿混染成巖成礦模式（圖2），他們認為這一認識是對經典的巖漿弧斑巖銅礦成礦模式的有益補充。
該研究成果近期發表在國際巖石學研究期刊Lithos上。（生物谷Bioon.com）
生物谷推薦的英文摘要
Lithos doi.org/10.1016/j.lithos.2013.07.019
Country-rock contamination of magmas associated with the Baogutu porphyry Cu deposit， Xinjiang， China
Ping Shena，HongDi Panb
The Baogutu porphyry Cu deposit， located in the West Junggar Region， Xinjiang， China， has the reduced mineralization features. Baogutu is associated with a Late Carboniferous intrusive complex that was emplaced into Lower Carboniferous volcano-sedimentary sequences. The complex consists of a main-stage diorite stock and late-stage diorite porphyry dikes. The former hosts the most of the Cu mineralization. The main-stage stock has a wide range of composition， from minor gabbro through dominant diorite to tonalite porphyry. These are all inhomogeneous over a few meters， with no distinct boundary between the gabbro， diorite and tonalite porphyry. Some felsic microgranular enclaves and heterogeneous phenocrysts occur in these rocks： the latter is a single mineral with a range of compositions. The elemental and Sr–Nd compositions of the tonalite porphyry have a transitional character from the gabbro and diorite to the country rocks. These findings suggest possible country-rock contamination. Mineral composition data suggest that the primary magma at Baogutu is oxidized I-type magma. The gabbro and diorite have high positive εNd(t) (+ 3.3 to + 6.0) and low initial 87Sr/87Sr ratios (0.7035–0.7038)， and are characterized by moderately fractionated rare earth element (REE) patterns， pronounced Nb depletion and weak negative Eu anomalies. These observations suggest that the Baogutu magmas were derived from partial melting of a metasomatized mantle wedge and underwent significant country-rock contamination after emplacement. The contamination process involved the felsic components and reduced materials (e.g. Carbonaceous sediment)， which caused the chemical variation of the Baogutu rocks and the reduced mineralization features in the Baogutu deposit. Thus， contamination played an important role in the formation of the host rocks and associated mineralization at Baogutu.