含铜镍岩浆起源及硫饱和机制:以新疆黄山南岩浆铜镍硫化物矿床Sr-Nd-Pb-S同位素和元素地球化学研究为例

Origin of Cu-and Ni-bearing magma and sulfide saturation mechanism: A case study of Sr-Nd-Pb-S isotopic composition and element geochemistry on the Huangshannan magmatic Ni-Cu sulfide deposit,Xinjiang

新疆黄山-镜儿泉一带是天山东段重要岩浆铜镍硫化物成矿带,但对其中含铜镍岩浆起源和硫饱和机制尚存较大争议。黄山南岩体是近年来在该成矿带中发现的另一个含矿性较好的重要岩体。岩体可分为超镁铁质岩相和镁铁质岩相,超镁铁质岩相为主要含铜镍矿岩相,而镁铁质岩相并未发生明显的矿化。超镁铁质岩相岩石类型包括二辉橄榄岩、斜辉橄榄岩、橄榄二辉岩、二辉岩、角闪二辉岩及少量粗粒辉长岩,其中二辉橄榄岩和二辉岩是主要含矿岩石类型。镁铁质岩相由苏长岩、辉长岩、角闪辉长岩、闪长岩及石英闪长岩组成。黄山南岩体的(^(87)Sr/^(86)Sr)i(0.7036~0.7057)、ε_(Nd)(t)(-1.2^+7.4)、(^(206)Pb/^(204)Pb)i(17.152~18.088)、(^(207)Pb/^(204)Pb)i(15.385~15.571)和(^(208)Pb/^(204)Pb)i(37.127~38.252)变化范围均较大,显示了母岩浆遭受了较明显的壳源物质混染。岩浆源区在板片俯冲过程中壳源物质加入明显,而原始岩浆上升过程中壳源物质的混染有限。Sr-Nd-Pb同位素组成指示黄山南含矿岩体的形成与塔里木大火成岩省并无直接联系。虽然黄山南岩浆铜镍硫化物矿石δ^(34)S值介于-1.54‰~2.03‰之间,落在幔源硫的范围内,但是Se(×10~6)/S比值表明壳源硫的加入对成矿母岩浆硫饱和起到重要作用。

The Huangshan-Jingerquan zone is an important Cu-Ni mineralization belt in the eastern part of the Tianshan orogenic belt. However,the origin of the Cu-Ni-bearing magma and sulfide saturation mechanism are still debatable. The Huangshannan mineralized intrusion is a new important discovery from geological prospecting in recent years. This intrusion can be divided into ultramafic and mafic lithofaces,in which ultramafic lithoface contains a large amount of sulfide ores whereas mafic lithoface is without obvious mineralization. The ultramafic unit is composed of lherzolite,olivine websterite,websterite and hornblende websterite and NiCu sulfide orebodies occur mainly within websterite and lherzolite. The mafic unit is composed of norite,gabbro,hornblende gabbro,diorite and quartz diorite. The Huangshannan intrusion is characterized by variable（（87）Sr/（86）Sr）i（ 0. 7036 - 0. 7057）,ε_（Nd）（ t）（- 1. 2- 7. 4）,（（206）Pb/（204）Pb）i（ 17. 152 - 18. 088）,（（207）Pb/（204）Pb）i（ 15. 385 - 15. 571） and（（208）Pb/（204）Pb）i（ 37. 127 - 38. 252） values,indicating significant crustal contamination of the parental magma. We propose that the modification by the subducted slab in mantle source show more important influence on the Huangshannan intrusion than crustal contamination during parental magma ascending up to the shallow magma chamber. The Sr-Nd-Pb isotopic compositions imply that the mineralized Huangshannan intrusion cannot result from the Tarim large igneous province. The δ-（34）S values of the Huangshannan deposit are from- 1. 54‰ to 2. 03‰ within the range of mantle values. However,the Se（ × 10^6）/S ratios show that the addition of crustal sulfur is an important factor for causing the sulfur saturation in the parental magma.