新疆包古图斑岩铜矿III- 2岩体氧逸度研究：来自矿物成分的指示

包古图斑岩铜矿位于新疆西准噶尔地区,是区内规模最大的斑岩型矿床,成矿作用与晚石炭世中酸性侵入体密切相关。III- 2岩体位于矿区南部,该岩体全岩矿化,但品位较低,是探讨成矿岩浆性质的理想对象。本文结合岩石学和角闪石、锆石等矿物成分分析,通过与典型斑岩铜矿进行对比,探讨了成矿岩浆的氧逸度。研究表明,包古图III- 2岩体以石英闪长（玢）岩和闪长岩为主,少量辉石闪长岩,主要由斜长石、角闪石、黑云母、石英和钾长石组成,含少量钛铁矿、榍石和磷灰石。石英闪长岩中早期结晶的自形角闪石属于钙质闪石,Mg#较高（0. 72~1. 00）,成分分析指示成矿岩浆的氧逸度为：△NNO+1. 4~△NNO+2. 6,位于斑岩铜矿含矿岩体的分布范围。从中分选出的锆石REE含量高（338×10-6~959×10-6）,具有左倾型稀土配分模式,轻稀土亏损,重稀土富集,显示强烈Ce正异常和Eu负异常。Ce4+/Ce3+比值为29. 55~89. 50,Eu/Eu*比值为0. 32~0. 47,分布于斑岩铜矿含矿岩体和未矿化岩体的叠加部位。研究结果显示,包古图斑岩铜矿III- 2岩体成矿岩浆氧逸度较高,有利于成矿元素的溶解和迁移,对斑岩铜矿的形成有促进作用。     

新疆包古图斑岩铜矿床成矿流体及成矿物质来源——来自硫、氢和氧同位素证据

包古图大型斑岩铜矿位于准噶尔盆地西缘。铜矿化主要呈浸染状、细脉浸染状分布于似斑状(石英)闪长岩、闪长玢岩、隐爆角砾岩和少量花岗闪长岩中。依据矿脉的穿插关系和矿物组合,成矿过程经历了黑云母-钾长石-钠长石阶段、石英-硫化物阶段和石英碳酸盐阶段。矿脉中石英的δDSMOW值介于-107‰～-86‰,δ18OSMOW值变化于11.3‰～16.2‰,δ18OH2O值为4.4‰～9.3‰,表明成矿流体来源为深源的岩浆水。硫化物的δ34S值介于-5.1‰～0.7‰,平均为-1.8‰,表明硫来源于深部岩浆或地幔。结合Ⅱ、Ⅲ和Ⅴ号含矿岩体锆石LA-ICP-MSU-Pb年龄及辉钼矿Re-Os年龄,推断包古图铜矿床成矿作用发生在晚石炭世,与中酸性斑岩体的侵入有密切成因关系。     

西准噶尔包古图I号岩体的锆石U-Pb年代学和地球化学特征

西准噶尔包古图地区发育一些小型的闪长质岩体。前人对这些小岩体开展了岩石学、年代学和地球化学等研究,然而,其成因机制和构造背景仍然存在争议,阻碍了区域构造演化和成矿作用的认识。本文在前人研究的基础上,选择包古图I号岩体为研究对象,有望揭示包古图岩体的岩石成因和构造背景。锆石U-Pb年代学研究显示,包古图I号岩体形成于（313.8±1.1）Ma。包古图I号闪长岩体以富SiO₂（58.0%~59.0%）、Al₂O₃（16.6%~17.4%）和Sr（757×10^-6~882×10^-6）,低的Y（14.6×10^-6~15.7×10^-6）和Yb（1.51×0^-6~1.60×0^-6）质量分数为特征,具有高的Sr/Y（50~59）值和弱的Eu异常,类似于俯冲成因的埃达克岩。另外,这些闪长岩具有较高的Mg（w（MgO）=3.46%~3.77%,Mg^#=52.8~53.2）,高的Cr（63.8×10^-6~74.7×10^-6）和Ni（45.2×10^-6~49.8×10^-6）质量分数,亏损HFSE（Nb,Ta和Ti）。该闪长质岩体可能由俯冲的板片熔体与上覆地幔相互作用而成。它的形成可能与西准噶尔地区晚石炭世的洋脊俯冲作用有关。     

Mineralogical evidence for crystallization conditions and petrogenesis of ilmenite-series I-type granitoids at the Baogutu reduced porphyry Cu deposit (Western Junggar,NW China): Mössbauer spectroscopy,EPM and LA-(MC)-ICPMS analyses

Primary ore-forming minerals retain geochemical signatures of magmatic crystallization information and can reveal the petrochemical conditions prevalent at the time of their formation. The Baogutu deposit is a typical reduced porphyry Cu deposit. Amphibole and biotite Fe³⁺/ΣFe ratios, minerals (feldspar, biotite, amphibole, zircon and apatite), in situ elemental and apatite Nd isotopic compositions were determined by Mössbauer spectroscopy, electron probe microanalysis, and laser ablation multiple-collection inductively coupled plasma mass spectrometry, respectively, to investigate the magma oxidation state, petrogenesis, source features, and to constrain the carbon species at magmatic stages for the intrusive phases. The results show that the primary plagioclase and amphibole in the mineralized diorite to granodiorite porphyry and post ore hornblende diorite porphyry are distinct (An_26-55 versus An_60-69; Mg-hornblende versus tschermakite). In particular, the amphibole shows distinct major and trace element compositions with light rare earth element enrichments and negative Eu anomalies in Mg-hornblende and light rare earth element depletions and no Eu anomalies in tschermakite. All the analyzed biotites are primary igneous phases with a biotite phenocryst profile showing significant variations of Zn, Cr, Sc and Sr from core to rim. These results may indicate the occurrence of mixing between two distinct magmas during mineral formation. Titanium in zircon and Si¹ in amphibole thermometries indicate that magma crystallized at >900 °C and continued to ∼650 °C. In situ apatite Nd isotope (εNd(t) = 5.6–7.6, T_DM2 = 620–460 Ma), indicate absence of significant reduced sedimentary contamination and the source of juvenile lower crust. Slightly decreasing Fe³⁺/ΣFe ratios from biotite and amphibole to whole rock indicate decreasing oxygen fugacity during magma crystallization. Recalculated biotite compositions according to Fe³⁺/ΣFe ratios indicate fO₂ values of less than Ni-NiO buffer (NNO) which show slightly lower values than that estimated according to zircon/melt distribution coefficients Ce anomalies (∼ΔNNO + 0.6). These values are consistent with the features of reduced porphyry Cu deposits. Crystallization of other mineral phases significantly affects the reliability of oxybarometer of zircon/melt distribution coefficients Eu anomalies and Mn contents in apatite. This oxidation state suggests that only CO₂ was present at the magmatic stage, and implies that CH₄ formed during CO₂ reduction occurring later hydrothermal alteration. The alteration of primary amphibole to actinolite released Ti, Al, Fe, Mn, Na and K to the fluid with later precipitation of titanite, albite and minor ilmenite and magnetite during actinolite alteration.     

新疆西准包古图地区斑岩铜矿找矿的重大突破及意义

新疆西准托里成矿带过去是以金矿、铬铁矿为主的找矿区，2001-2004年包古图地区铜矿找矿获重大突破。包古图铜矿与花岗闪长斑岩密切相关．金属矿物成分简单，矿石构造为细粒浸染状和细脉浸染状。矿石品位低、矿化均匀，矿床蚀变组合和分带特征明显，属典型斑岩型铜钼矿。包古图斑岩型铜矿的发现，在西准是首次，并且证明了哈萨克斯坦巴尔喀什斑岩铜矿带东延至中国境内。对西准地区今后的找矿工作将起到重要的推动作用。     

新疆包古图地区金矿床地质特征及成矿模型研究

包古图地区是新疆西准噶尔重要的金矿集区之一,根据矿床地质和矿化类型,可将区内金矿化分为2类:以阔个沙也金矿床(包古图金矿Ⅰ~Ⅳ号点)为代表的石英脉型金矿化,产于部分中酸性斑岩体周边地层中,赋矿围岩为下石炭统包古图组凝灰质砂岩、凝灰岩等,围岩蚀变以硅化、绢云母化、黄铁矿化、毒砂化和碳酸盐化为主,矿体为黄铁矿_石英脉型、辉锑矿_石英脉型和自然砷_石英脉型或石英网脉型/蚀变岩型,受NE向断裂控制,与矿区密集分布的中酸性脉岩伴生,主要矿物组合为黄铁矿_毒砂_自然砷_辉锑矿_自然金_银金矿,矿化元素组合为Au_As_Sb,是中酸性斑岩系统热液演化晚期的产物;另一类金矿化产于中酸性斑岩与下石炭统火山_沉积地层的接触带中,以包古图金矿Ⅺ号点为代表,矿体为石英_硫化物脉型,矿物组合为黄铁矿_毒砂_自然铋_辉铋矿_自然金_黄铜矿,是斑岩系统热液演化较早期的产物。结合已有研究资料,可将区内金矿床的成矿模型总结如下:斑岩岩浆系统演化晚期分异出含Au_Cu_Bi_As_Sb的岩浆热液,在岩体内部形成斑岩型铜矿化,岩体与围岩接触带形成高温石英_硫化物脉型Au_As_Bi矿化,部分含矿热液随中酸性岩脉向外围迁移,并逐渐与大气水混合,最终在NE向断裂中形成石英脉型Au_As_Sb矿化。基于此成矿模型,认为包古图地区金矿找矿工作的重点应该放在中酸性斑岩体与围岩接触带和斑岩体外围NE向断裂(中酸性脉岩)密集分布区,尤其是As_Sb、As_Bi化探异常叠加区。矿床地质和地球化学特征对比显示,包古图金矿成矿系统与侵入岩有关的金矿成矿系统非常相似。     

新疆西准噶尔包古图组凝灰岩锆石SHRIMP年龄及其地质意义

西准噶尔地区出露巨厚层的下石炭统火山-沉积岩,包括太勒古拉组、包古图组和希贝库拉斯组,前人主要通过生物化石来确定各组之间的层位关系,并存在争论。本文对包古图金矿区包古图组中3个蚀变凝灰岩样品开展的锆石SHRIMP年代学研究表明,凝灰岩的年龄分别为328.4Ma（MSWD=0.72）、342.6Ma（MSWD=0.76）和336.5Ma（MSWD=1.6）。结合太勒古拉组年代学数据和下石炭统火山-沉积地层的分布关系,确定西准噶尔下石炭统火山-沉积地层从下到上依次为：希贝库拉斯组、包古图组和太勒古拉组。     

新疆包古图斑岩型铜钼矿床容矿岩石及蚀变特征

新疆包古图斑岩型铜钼矿床位于西准噶尔晚古生代达拉布特岛弧南部。根据容矿岩石、热液蚀变和矿化特点,结合成矿元素Cu-Mo-(Au)组合特征,认为该矿床是斑岩型铜钼矿床。 研究识别出含矿岩体是一个岩性和岩相复杂的中性斑岩体,岩性主要为闪长岩、似斑状(石英)闪长岩、(石英)闪长玢岩、隐爆角砾岩和各种脉岩,有少量的花岗闪长岩,岩相从岩体中心向外依次为中心相、主体相和边缘相,稍晚形成的深部隐爆相叠加在上述各岩相上。浸染状和细脉浸染状矿化赋存于岩体各岩相尤其是深部隐爆相中,少量赋存于围岩中。热液蚀变填图和研究显示,蚀变从岩体中心向外依次为由钾硅酸盐化和石英绢云母化组成的叠加带、角岩化带和青磐岩化带,与Hollister的模式类似。矿体主要赋存于叠加带中,部分赋存于角岩化带中。包古图斑岩型铜钼矿床中性岩浆-流体活动控制着岩体的蚀变与矿化。     

Magmatic process recorded in plagioclase at the Baogutu reduced porphyry Cu deposit,western Junggar,NW-China

Despite the fact that porphyry Cu deposits contain large amounts of Cu in one or more small stocks, few studies have discussed evidence for significant magma recharge in porphyry Cu deposits. A systematic elemental and Sr isotopic study of plagioclase crystals from mineralized diorite and granodiorite porphyry constrains the processes of crystallization and magma recharge at the Baogutu reduced porphyry copper deposit, western Junggar, NW-China. Large compositional changes in An (12–24 mol%) are observed along with strong positive correlations between An and FeO. Significant resorption textures are also preserved in plagioclase crystals as well as repeated oscillatory zoning in An and FeO, and complex Sr isotope variations. Three types of crystals with different core-to-rim Sr isotope variations are recognized. Type I crystals have core-to-rim increases in (⁸⁷Sr/⁸⁶Sr)_i that could be explained by diffusion. For example, Sr isotope variations recorded in BCK2-1-2 crystal could be generated by diffusion with simulated maximum crystal residence times of 100–500 years with the proximate value of ∼300 years. Type II crystals with different variation trends in (⁸⁷Sr/⁸⁶Sr)_i on opposite sides of the core could be produced either by multi-stage crystallization or by analytical uncertainty. Whereas, type III crystals with complex core-to-rim variations in (⁸⁷Sr/⁸⁶Sr)_i, may record repeated magma recharge events. All these results suggest repeated recharging of the magma chamber by hotter, more mafic and less radiogenic Sr isotope melts. Therefore, more mafic melt injection recorded in plagioclase profiles may provide significant metal contributions to the magma chamber, which ultimately results in Cu mineralization at the Baogutu reduced porphyry copper deposit.     

ASTER数据在浅覆盖区蚀变遥感异常信息提取中的应用——以新疆西准噶尔包古图斑岩铜矿岩体为例

遥感卫星的多光谱数据应用于找矿已取得显著成效,2004年7月中国卫星地面站开始提供ASTER（Advanced Spaceborne Thermal Emission and Reflection Radiometer,高级星载热发射反照辐射计）数据,因涵盖波长范围宽［VNIR（Visible and Near Infrared）、SWIR（Short wavelength Infrared）、TIR（Thermal Infrared）］、波段多（14个波段）、性价比合理等因素,ASTER数据的研究迅速发展。长久以来,对覆盖区进行蚀变遥感异常信息提取一直是遥感找矿的关注点之一。笔者等利用ASTER数据对浅覆盖区——包古图斑岩铜矿的Ⅱ号、Ⅴ号斑岩体进行蚀变遥感异常提取,提取的蚀变异常与野外地质情况吻合性好。分别提取了光谱特征谱带差异明显的2组蚀变矿物的异常信息：第一组是蒙脱石、埃洛石、伊利石与绢云母;第二组是方解石、黑云母与绿泥石。提出了需要进一步工作的异常靶区。