宁镇地区中生代安基山中酸性侵入岩的地球化学：亏损重稀土和钇的岩浆产生的限制

江苏省宁镇地区的中生代安基山中酸性侵入岩以亏损重稀土和钇及富集锶为成分特征，它们与消减过程的板片熔融无关，也不是基性岩浆分离结晶和地壳物质混染的产物，很有可能是相对较厚的地壳下部的镁铁质物质部分熔融产生的。相比，与安基山岩体邻近的同时代的苏州－无锡地区的和江浙地区的中酸性侵入岩和火山岩不具有亏损重稀土和钇特征，它们可能是中上地壳物质部分熔融的产物。研究表明，中生代时宁镇地区可能存在一个相对较厚的地壳（＞40km)。由于宁镇地区现在地壳的厚度仅30km左右，因此该地区中生代域之后可能经历了一个地壳的减薄过程。     

西秦岭北缘与埃达克岩和喜马拉雅型花岗岩有关的斑岩型铜-钼-金成矿作用

埃达克岩是以往20年中特别引起人们兴趣和关注的与成矿有关的中酸性岩浆岩之一,而喜马拉雅型花岗岩是最近提出来的也与地壳加厚有关的花岗岩类。本文的研究表明,在西秦岭北缘存在印支期的埃达克岩和喜马拉雅型花岗岩,而且它们均与金、铜、钼等成矿作用有关。研究表明,本区阿姨山和德乌鲁-黑河地区的埃达克岩和喜马拉雅型花岗岩具有较高的Mg^#数值,可能是加厚地壳底部幔源岩浆和壳源岩浆混合形成的,而温泉和柴家庄地区的埃达克岩和喜马拉雅型花岗岩Mg^#低,应当是加厚的下地壳部分熔融形成的。文中介绍了西秦岭北带斑岩铜-钼-金矿带的地质背景,讨论了埃达克岩和喜马拉雅型花岗岩的特征及其与成矿作用的关系,提出了进一步找矿工作的建议。研究表明,三叠纪时期的西秦岭造山带地壳厚度大,岩浆活动频繁,找矿潜力巨大,是我国新一轮的铜钼金找矿区之一,发展前景很大。     

北天山东段阿奇山组火山岩的地球化学特征及锆石U-Pb年龄

阿奇山组分布于北天山东段觉罗塔格构造带内部的雅满苏岛弧带中,属于原雅满苏组下部的火山岩部分,而上部火山岩则属于土古土布拉克组。在阿奇山地区,阿奇山组由中-酸性火山岩、火山碎屑岩和火山碎屑沉积岩组成。岩石地球化学特征显示为钙碱性岛弧火山岩系列,火山岩主体具有高Sr、Na₂O、Al₂O₃、SiO₂, 低MgO、Y、Yb,及明显亏损HFSE、Nb、Ta等特征,与经典埃达克岩地球化学特征吻合,Nb、Sr、Sr/Y值显示为俯冲型埃达克岩。地球化学相关图解等表明岩浆同化混染作用弱、经历了辉石、斜长石、钛铁氧化物和磷灰石的分离结晶作用、且部分熔融发生在石榴石稳定域。与东部土屋-雅满苏地区阿奇山组火山岩的对比研究表明,东部地区的火山岩不具埃达克岩特征,说明埃达克岩分布的局限性。锆石U-Pb SHRIMP 谐和年龄为341.7±2.7Ma,与首次在该组中采集的化石资料完全一致,代表了火山岩的形成年龄。与其北部大南湖岛弧带中的小热泉子组、企鹅山组形成年龄（325.1±3.2Ma、322.6±2.0Ma）对比研究暗示,准噶尔板块南缘石炭纪存在构造-岩浆活动随时间由南向北迁移。     

Petrogenesis and timing of emplacement of porphyritic monzonite,dolerite, and basalt associated with the Kuoerzhenkuola Au deposit,Western Junggar,NW China: implications for early Carboniferous tectonic setting and Cu–Au mineralization prospectivity

ABSTRACT

The Kuoerzhenkuola epithermal Au deposit is located in the northern part of the West Junggar region of NW China and is underlain by a recently discovered porphyritic monzonite intrusion that contains Cu–Au mineralization. Zircon LA-ICP-MS U–Pb dating of this intrusion yielded an age of 350 ± 4.7 Ma. The porphyritic monzonite is calc-alkaline and is characterized by high concentrations of Sr (583–892 ppm), significant depletions in the heavy rare earth elements (HREE; e.g. Yb = 0.96–2.57 ppm) and Y (10.4–23.3 ppm), and primitive mantle-normalized multi-element variation diagram patterns with positive Sr and Ba and negative Nb and Ti anomalies, all of which indicate that this intrusion is compositionally similar to adakites elsewhere. The composition of the porphyritic monzonite is indicative of the derivation from magmas generated by the melting of young subducted slab material. The area also contains Nb-enriched basalts that are enriched in sodium (Na₂O/K₂O = 1.20–3.90) and have higher Nb, Zr, TiO₂, and P₂O₅ concentrations and Nb/La and Nb/U ratios than typical arc basalts. The juxtaposition of adakitic rocks, Nb-enriched basalts, and dolerites in this region suggests that the oceanic crust of the expansive oceans within the West Junggar underwent early Carboniferous subduction. Magnetite is widespread throughout the Kuoerzhenkuola Au deposit, as evidenced by the volcanic breccias cemented by late hydrothermal magnetite and pyrite. In addition, the zoned potassic, quartz-sericite alteration, and propylitic and kaolin alteration in the deeper parts of the porphyritic monzonite are similar to those found in porphyry Cu–Au deposits. These findings, coupled with the mineralogy and geochemistry of the alteration associated with the Kuoerzhenkuola Au deposit, suggest that the mineralization in this area is not purely epithermal, with the geology and geochemistry of the porphyritic monzonite in this area suggesting that a porphyry Cu–Au deposit is probably located beneath the Kuoerzhenkuola Au deposit.     

Adakite-like signature of porphyry granitoid stocks in the Meiduk and Parkam porphyry copper deposits,NE of Shahr-e-Babak,Kerman, Iran: Constrains on geochemistry

The Middle Miocene porphyry granitoid stocks of Meiduk and Parkam porphyry copper deposits are intruded in the north-western part of the Dehaj-Sarduiyeh volcano-sedimentary belt in the south-eastern extension of the Urumieh-Dukhtar Magmatic Arc (UDMA) in Iran. The porphyritic to microgranular granitoids are mainly consist of quartz diorite, granodiorite and diorite. The whole rock geochemical analyses of these rocks reveals sub-alkaline, calc-alkaline, meta-peraluminous and I-type characteristics. Their geochemical characteristics such as Al₂O₃ content of 13.51–17.05 wt%, high Sr concentration (mostly >400 ppm), low Yb (an average of 0.74 ppm) and Y (an average of 9.02 ppm) contents, strongly differentiated REE patterns (La/Yb ≥ 20), lack of Eu anomaly (Eu/Eu¹ ≥ 1) are indicative of adakitic signature. Their enrichment in low field strength elements (LFSE) and conspicuous negative anomalies for Nb, Ta and Ti are typical of subduction related magmas. Detailed petrological studies and geochemical data indicated that Meiduk and Parkam porphyry granitoids were derived from amphibole fractionation of hydrous melts at a depth of >40 km in a post-collisional tectonic setting.     

Two different types of granitoids in the Suyunhe large porphyry Mo deposit,NW China and their genetic relationships with molybdenum mineralization

The Suyunhe large porphyry Mo deposit (∼0.57 Mt molybdenum), located in the West Junggar, NW China, is the largest known porphyry Mo deposit in Xinjiang. Granitoids in this deposit are mainly characterized by three closely spaced intrusive centers (known as stocks I, II and III respectively). The stocks I and III mainly consist of barren granodiorite porphyry and tonalite porphyry, whereas the stock II is mainly composed of fertile monzonitic granite porphyry and granite porphyry. Based on detailed major and trace element, and Sr–Nd isotopic analyses, two distinct compositional groups can be identified. The first group of high-silica end-members (HSE) is characterized by high SiO₂ (mostly >75 wt%), low MgO (0.07–0.69 wt%) and Mg# (0.19–0.36), significant Eu depletion in the chondrite-normalized diagram, and low Sr/Y and La/Yb, as well as noticeably negative anomalies of Ba, Sr, P and Ti in the primitive mantle-normalized diagram. The second group of low-silica end-members (LSE), however, displays adakite-like features with lower SiO₂ (<75 wt%), higher MgO (0.52–1.32 wt%) and Mg# (0.32–0.52; mostly >0.4), and higher Sr/Y (mostly >20) and La/Yb (>8). The depleted Sr–Nd isotopic characteristics (ε_Nd(T) = 3.5–6.4 and I_sr = 0.7026–0.7055) and young two-stage model ages of HSE and LSE indicate that they were both derived from partial melting of juvenile lower crust that might be triggered by asthenosphere upwelling subsequent to a slab rollback event. However, the depths of initial melting might be different. The current evidence demonstrates that HSE in the Suyunhe deposit formed by partial melting of juvenile crust at depths of less than ∼33 km with a plagioclase residue, whereas that for LSE occurred at depths of >40 km where a garnet residue existed and the crust was thickened. The lower source depth, as well as subsequently strong plagioclase fractionation, results in the absence of adakite-like characteristics in HSE.The Ce⁴⁺/Ce³⁺and Eu_N/Eu_N1 ratios in zircons of HSE are much lower than ore-forming intrusions from porphyry Cu deposits in the Central Asian Orogenic Belt, but noticeably higher than barren intrusions from the Lachlan fold belt and ore-bearing intrusions from small-intermediate porphyry Mo deposits from the East Qinling–Dabie and the Nanling metallogenic belts, China, indicating that neither too high nor too low oxygen fugacities are favorable for large porphyry Mo deposits. Based on previous studies of adakitic rocks in the world, adakite-like LSE in the Suyunhe deposit are believed to have higher oxygen fugacities, and thus be less fertile than HSE. We finally suggest that adakites and adakite-like rocks are unproductive for porphyry Mo deposits.     

滇西剑川始新世富碱岩浆岩锆石U-Pb年代学与Sr-Nd-Hf同位素地球化学及其对岩石成因的制约

滇西剑川富碱岩浆岩位于青藏高原东南缘的三江南段,是金沙江-红河富碱岩浆岩带的重要组成部分。剑川富碱岩浆岩包括花岗岩和正长岩两类岩石,前者主要有花岗斑岩和石英二长斑岩,后者主要是正长斑岩和粗面岩。本文对剑川富碱岩浆岩进行了主微量元素、锆石U-Pb年代学和Sr-Nd-Hf同位素特征研究。锆石U-Pb测年结果显示,剑川花岗岩结晶年龄为35. 1～36. 1Ma,正长岩结晶年龄为35. 7～35. 8Ma,均形成于始新世。花岗斑岩和石英二长斑岩的SiO_2含量为67. 92%～69. 93%,K_2O/Na_2O比值介于0. 86～1. 22,具有高钾钙碱性特征;正长斑岩和粗面岩的SiO_2含量为53. 94%～63. 51%,K_2O/Na_2O比值介于1. 30～2. 68,属于钾玄质岩石系列。两类岩石都富集轻稀土元素(LREE)和大离子亲石元素(LILE),相对亏损高场强元素(HFSE)。其中,花岗斑岩和石英二长斑岩有着较高的Sr、Sr/Y、La/Yb值和低的Y、Yb含量,具有埃达克质岩浆属性。结合Sr-Nd-Hf同位素研究认为,滇西剑川地区花岗岩起源于增厚的镁铁质新生下地壳部分熔融,正长岩是由交代富集的岩石圈地幔熔融产生的基性岩浆演化而来的产物。滇西剑川新生代富碱岩浆活动是对印度与欧亚板块晚碰撞阶段,岩石圈地幔发生对流减薄和软流圈物质上涌过程的响应。     

黑龙江金厂铜金矿床闪长玢岩地球化学及锆石U-Pb年代学

黑龙江省东宁金厂铜金矿床为最新勘查突破的特大型矿床,矿床矿体类型以角砾岩型为主,且角砾岩型矿体与闪长玢岩岩体空间关系密切。岩相特征显示闪长玢岩为多斑-基质隐晶结构,斑晶以斜长石、角闪石为主,并见少量辉石。闪长玢岩SiO2含量为54.62%～67.82%,平均60.33%;Al2O3含量为14.52%～18.25%,平均16.62%,且K2O/Na2O为0.06～0.31,均小于0.5,属于亚碱性岩系并具钙碱性演化趋势,但钾含量较低。稀土元素的LREE/HREE值较高,介于5.06～14.24之间,平均9.16;δEu为0.85～1.46,平均1.21,表现为正Eu异常。微量元素以低Y和Yb,高Sr为特征,其Sr/Y值为35.87～111.4,平均57.57(>40);此外,微量元素富集大离子亲石元素(LILE),亏损高场强元素(HSFE),尤以Nb、Ta和Ti亏损最为显著,且见Pb富集明显。地球化学特征显示闪长玢岩具有埃达克质岩的特征,表明闪长玢岩不仅为重要的含矿母岩,而且指示金厂金矿具备进一步找矿的潜力。同时,闪长玢岩的地球化学特征还显示其岩浆演化以结晶分异为主,而岩浆则可能起源于俯冲流体交代的地幔楔部分熔融,岩浆上涌时受地壳混染。闪长玢岩的锆石U-Pb年龄介于118.1±1.6Ma～115.7±2.0Ma之间,结果表明118.1±1.6Ma可以代表金厂斑岩型铜金矿床尤其是角砾岩型矿体的成矿时代,与区域120～110Ma的大规模岩浆活动时间一致,说明金厂斑岩型铜金矿床的成矿可能与早白垩纪太平洋板块的俯冲作用有关。区域上寻找同时期的斑岩型-浅成低温热液型铜金矿床潜力巨大。     

西天山特克斯北中酸性火成岩地球化学特征及成因意义

新疆西天山特克斯县城北部伊特公路沿线和库勒萨依出露大量中酸性火成岩,伊特公路沿线为石英钠长斑岩,库勒萨依为石英闪长斑岩和花岗闪长斑岩。岩石地球化学和同位素组成研究表明,前者为典型的岛(陆)弧带火成岩,而后者具有埃达克岩的成分特征,两者均为古亚洲洋壳在俯冲过程中岩浆活动的产物。早先俯冲的较冷洋壳板片在深处脱水诱发上覆地幔楔熔融,熔体上升并经历壳幔相互作用等过程引发伊特公路一带弧岩浆活动; 由于洋壳持续俯冲,后来新形成的靠近洋脊的年轻板片由于高热在较浅处直接发生部分熔融形成埃达克岩浆,并上侵至库勒萨依一带。库勒萨依斑岩体SIMS锆石 U-Pb年龄为342.5±2.3Ma,属于早石炭世。两组中酸性火成岩的地球化学特征表明,古亚洲洋(南天山洋)在早石炭世还未完全闭合,洋壳向北的持续俯冲过程造成伊犁-中天山板块南缘广泛的岩浆活动,此时西天山陆壳增生方式主要为侧向增生,增生物质主要为洋壳板片(埃达克岩)和洋壳板片流体交代的地幔楔成分。     

东天山—北山地区埃达克岩与斑岩型铜、金、钼矿床研究现状综述

该文是东天山-北山地区近些年来有关埃达克岩与斑岩型铜、金、钼矿床研究现状的综合归纳与总结。在明确埃达克岩原始定义和其概念扩展的基础上,着重表述了这类岩石在东天山-北山地区的发育状况、空间展布、岩石学特征及其成矿现状等,并对其在区域上的找矿前景作了概略性分析,以期引起找矿者对东天山-北山地区与埃达克岩有关的斑岩型矿床的研究兴趣和广泛关注。