滇西来利山锡矿正长花岗岩LA-ICP-MS锆石U-Pb年龄及地质意义

滇西来利山锡矿位于滇西锡成矿带的腾冲-梁河锡成矿亚带,地处三江构造带南段腾冲地块,怒江缝合带和密支那缝合带之间.锡矿体产于中石炭统丝光坪组断裂破碎带及与来利山复式岩体东南边缘的正长花岗岩接触带,成矿与正长花岗质岩浆活动关系密切.正长花岗岩SiO2含量76.00％～77.10％、Al2O3含量12.62％～13.50％、TFeO/MgO为9.79～72.50,具富硅、铝,铁高镁低的特征;铝饱和度(A/CNK)为1.02～1.32,K2O/Na2O为1.42～～2.26,里特曼指数(δ)1.40～2.29,属高钾钙碱性、过铝质花岗岩系列;岩石∑REE值为98.68×10-6～～191.89×10-6,强烈的负Eu异常(δEu=0.07～～0.10),铈异常不明显(δCe=0.63～0.99),LR/HR为0.19～0.69,(La/Yb)N为0.31～1.24,轻重稀土没有明显的分异性;P、Ti强烈亏损,Ba、K亏损,Zr、Th富集,La弱富集,为壳源S型同碰撞花岗岩;LA-MC-ICP-MS U-Pb法测定其成岩年龄为52.53±0.29 Ma(MSWD=1.8),是中始新世印度-欧亚大陆碰撞造山作用的产物,是在地壳强烈挤压、增厚,由上地壳泥质岩类在不饱和水条件下低程度部分熔融岩浆侵位冷凝形成.来利山锡矿的成矿物质主要来源于围岩及花岗岩,成矿流体以岩浆水为主,成矿时代与正长花岗岩成岩年龄一致,锡矿是该区在喜马拉雅早期印度板块与欧亚大陆碰撞造山运动岩浆活动的成矿响应,表明该区在51.1～54 Ma至少存在一次与来利山正长花岗岩关系密切的锡成矿作用.     

新疆拜城波孜果尔碱性岩中副矿物的特征

在野外地质调查的基础上,结合室内显微镜观察及电子探针分析测试,对新疆拜城波孜果尔碱性岩中的副矿物的矿物学特征和化学成分进行了研究.发现这些副矿物常以共生组合的形式产在碱性岩中,主要分布在石英二长闪长岩和石英二长岩中.烧绿石中U、Th和REE替代Ca、Na.独居石富含LREE,Th和LREE相互替代;根据独居石中w(La+ Ce) ＞40％和La/Nd比值在1.6～4.5,推断独居石为热液成因.磷钇矿中富含REE,且以HREE为主;w(Th)＞w(U).锆石中Zr/Hf比值在60％以上,符合碱性岩特征;其Th/U比值为0.6,属于岩浆锆石.星叶石中w(Rb2O)、w(Cs2O)较高.萤石中Y、Ce替代Ca.锆石中的钍石w(U)明显高于磁铁矿中钍石w(U).在石英二长岩中,烧绿石的w(CaO)、w(TiO2)、w(ZrO2)、w(U3O8),磷钇矿的w(Y2O3),星叶石的w(TiO2),萤石的w(Ca),氟碳铈镧矿的w(CaO)较丰富;而在石英二长闪长岩中,烧绿石的w(Ce2O3),磷钇矿的REE含量,星叶石的w(Nb2O5)、w(Rb2O),萤石w(Ce)、w(Y)和氟碳铈镧矿的w(La2O3)较高.     

氧同位素在岩石成因研究的新进展

通过氧同位素分析可以对岩石的成因进行认识,使之成为岩石学研究的一个强有力工具。根据花岗岩的氧同位素高低可以判断其来源于变沉积岩还是变火成岩;对于一个复式岩体,如果不同期次岩石的氧同位素组成存在明显变化,可以有效地判断该岩浆在演化过程中存在不同来源物质的混染,因为岩浆从镁铁质成分向长英质成分的化学分异过程,不会引起明显的氧同位素分馏,分馏值一般不超过0.3‰。氧同位素分析手段从常规BrF₅法,到激光探针BrF₅法,再到离子探针分析法,对岩石矿物样品从全熔分析到微区分析的发展,显示了它们的发展历程和各自的优势及应用范围。本文介绍了氧同位素的不同分析方法,以花岗岩(流纹岩)和变质岩的研究为例阐述了氧同位素分析技术的发展。苏州花岗岩利用全岩和造岩矿物常规氧同位素分析方法得出其为低δ¹⁸O和正常δ¹⁸O岩浆成因的不同认识,近年通过锆石激光氧同位素分析技术,获得岩浆锆石的δ¹⁸O平均为4.92‰,证实其来源于壳源的低δ¹⁸O岩浆。类似地,利用全岩和造岩矿物常规氧同位素分析方法得出的观点难以解释美国黄石高原低δ¹⁸O流纹岩中矿物颗粒间和颗粒内部的氧同位素变化,该氧同位素变化只能通过离子探针矿物微区原位分析得出。在变质岩研究方面,通过激光探针氧同位素分析,人们普遍认为苏鲁造山带变质岩极负的δ¹⁸O值是在新元古代原岩形成时获得的,但是最新的离子探针锆石原位氧同位素分析表明苏鲁造山带变质岩极负的δ¹⁸O主要是在三叠纪超高压变质作用过程中获得的。今后单颗粒矿物尺度上的氧同位素组成分布规律将是氧同位素研究的发展方向。     

Geochemistry of A-type granites in the Huangshaping polymetallic deposit (South Hunan,China): Implications for granite evolution and associated mineralization

The Huangshaping granites in Hunan Province, South China were investigated for their geochemical characteristics. Three types of granites have been petrographically identified: quartz porphyry, granophyre, and granite porphyry. Whole rock geochemistry suggests that the Huangshaping granites, especially the granite porphyry, exhibit typical A-type granite characteristics with their enrichment in Si, Rb, U, Th, and Nb and significant depletion in Ba, Sr, Ti, Eu, and P. Based on the Al, Y and Zr contents as well as the REE patterns of the rocks investigated, the quartz porphyry and the granophyre are classified as A₁ type alkaline granites whereas the granite porphyry is considered as A₂ type aluminous granite. Whole rock and quartz/feldspar O isotope data yields a wide range of δ¹⁸O_SMOW values (11.09–26.32‰). The granites are characterized by high radiogenic Pb isotopic composition. The present-day whole rock Pb isotopic ratios are ²⁰⁶Pb/²⁰⁴Pb = 18.706–19.155, ²⁰⁷Pb/²⁰⁴Pb = 15.616–15.711 and ²⁰⁸Pb/²⁰⁴Pb = 38.734–39.296. Combining the O–Pb isotope compositions with major, trace and REE geochemistry and regional geology characteristics, the Huangshaping granites were determined to resemble within-plate granites that were mainly derived from a felsic infracrustal source related to continental extension. The magma source of the quartz porphyry and the granophyre may have been generated from deeper depths, and then ascended rapidly with limited water content and low oxygen fugacity, which contributed to Cu, Pb and Zn mineralization. On the other hand, the magma that generated the granite porphyry may have ascended relatively slower and experienced pronounced crystal fractionation, upper-crustal basement rock contamination (assimilation) and wall–rock interaction, producing the Sn- and W-rich granite porphyry. This study reveals the crustal extension process and associated magmatic–metallogenic activities during 180–150 Ma in South Hunan.     

秦祁昆结合部瓦勒根金矿床含矿斑岩体岩石学和LA-ICP-MS锆石U-Pb年龄

秦祁昆结合部广泛发育中三叠世岛弧钙碱性岩浆作用,已发现大量与其相关的斑岩型—夕卡岩型铜金、铜钼和银铅锌多金属矿床。瓦勒根金矿床是近年来在该区新发现的一个斑岩型金矿床,矿区内出露有众多的石英斑岩和花岗斑岩,且均发育有金矿化,其中石英斑岩与金矿化关系更为密切。LA-ICP-MS锆石U-Pb年龄表明,花岗斑岩形成于中三叠世(237Ma),其中包含有丰富的晚古生代及元古宙继承性锆石。这一特征与区域上的斑岩型铜金矿床含矿岩体具有相似性。进一步说明,古特提斯洋在秦祁昆结合部发生向北消减所形成的岩浆捕获了早于三叠纪的壳源和幔源物质,从而形成了岛弧钙碱性岩浆及相关的斑岩型—夕卡岩型矿床组合。     

The Yanshanian Granites and Associated Mo-Polymetallic Mineralization in the Xiangcheng-Luoji Area of the Sanjiang-Yangtze Conjunction Zone in Southwest China

The Xiangcheng-Luoji area is located in the conjunction of the southern part of the "Sanjiang" mineralization belt and the west margin of Yangtze craton. The geological studies were carried out to know the Indosinian large porphyry Cu polymetallic deposits. Recent studies revealed that the area existed in the superposition of Late Yanshanian acidic intrusive rock belt and developed Mo-Cu polymetallic mineralization where promising exploration results have been achieved. Through the systematic study of geochronology, formation age of the Renlin Mo-minieralization monzogranite is 81.7±1.1 Ma. Re-Os dating results concentrate on 82.34±1.2–88.27±1.23 Ma for the model ages of molbdenite of Tongchanggou Mo deposits, average age is 85 ± 2 Ma where seven data points constitute a good isochron which shows that they were the same period products of mineralization. Geochemical features shown that the rocks have a high content of SiO 2(66.59–77.36wt%), alkaline-rich(K2O=2.68–6.08wt%; Na2O=0.50–4.91wt%; K2O/Na2 O ratios are 0.71–5.56, where average ratio of 1.89) and have aluminum–rich features(Al2O3 10.38–15.15wt%) with σ values less than 3.3. Which indicate that they belong to the high-K calc-alkali to shoshonite series. Geochemistry of Yanshanian intrusions shows that rocks are enrich in LREE with obvious negative δEu anomalies, enrichment of trace elements like, LILE elements(Rb, Th, Ba) with a relative loss of Ba, and loss of high field strength elements(Nb, Ta, P, Ti) and HREE elements. The granite genetic classification diagram shows that the granites belong to A-type granite and formatted in syn-collision tectonic environment. Meanwhile, the Yanshanian granites also inherited the characteristics of island arc environment which formed in the process of crustal melting caused by upwelling of asthenospheric substances in the extensional tectonic background. The process of partial melting existed substances from the deep(lower crust or upper mantle) which have been added. In the Xiangcheng-Luoji area, monzogranite and granodiorite porphyry bodies are widely developed Mo polymetallic mineralization, the deep porphyry mineralization have great potential for geological prospecting.     

个旧矿区西部凹陷带花岗岩锡矿床地质特征及控矿规律分析

个旧矿区是一个与花岗岩有关的特大型锡多金属矿集区。近年来在花岗岩体内发现了蚀变花岗岩锡多金属矿体,进一步拓展了找矿的空间。笔者在分析个旧老厂矿田西部凹陷带花岗岩锡多金属矿床地质特征的基础上,着重从花岗岩体表层原生破裂构造对矿床的控矿规律进行了探讨。     

甘肃金塔县晚古生代拐把头花岗岩地球化学特征及构造意义

拐把头花岗岩具有高硅低铝、富钾贫钠、准铝质或I型花岗岩,明显富集Rb、Th、K等大离子不相容元素,亏损Ba、Sr、P、Ti等元素,并具有弱Nb亏损,稀土元素分布曲线呈明显的＂海鸥＂型,形成于挤压的构造背景下,代表了北山晚古生代晚期重要的构造—岩浆事件。     

东天山花岗岩的构造岩浆类型划分

花岗岩是陆壳的重要组成部分,花岗岩的研究对研究大陆岩石圈的结构、组成和演化具有重要意义。本文运用Barbarin花岗岩构造类型划分方案,对有关东天山地区花岗岩进行了有益的文献汇总和讨论的基础上,首次将东天山地区花岗岩划分为含角闪石钙碱性花岗岩类,富钾及钾长石斑状钙碱性花岗岩类,含堇青石及黑云母过铝质花岗岩类,含白云母过铝质花岗岩类。根据它们各自的岩石及地球化学特征认为岩浆来源分别为地幔橄榄岩区混熔了一部分楔形地幔上面的地壳;地壳安山质源岩混有部分幔源;硬砂质岩石以及泥质岩石的局部熔融。     

Petrogenesis of the Yangchang Mo‐bearing granite in the Xilamulun metallogenic belt,NE China: geochemistry,zircon U–Pb ages and Sr–Nd–Pb isotopes

The Yangchang granite‐hosted Mo deposit is typical of the Xilamulun metallogenic belt, which is one of the important Mo–Pb–Zn–Ag producers in China. A combination of major and trace element, Sr, Nd and Pb isotope, and zircon U–Pb age data are reported for the Yangchang batholith to constrain its petrogenesis and Mo mineralization. Zircon LA‐ICPMS U–Pb dating yields mean ages of 138 ± 2 and 132 ± 2 Ma for monzogranite and granite porphyry, respectively. The monzogranites and granite porphyries are calc‐alkaline with K₂O/Na₂O ratios of 0.75–0.92 and 1.75–4.42, respectively. They are all enriched in large‐ion lithophile elements (LILEs) and depleted in high‐field‐strength elements (HFSEs) with negative Nb and Ta anomalies in primitive‐mantle‐normalized trace element diagrams. The monzogranites have relatively high Sr (380–499 ppm) and Y (14–18 ppm) concentrations, and the granite porphyries have lower Sr (31–71 ppm) and Y (5–11 ppm) concentrations than those of monzogranites. The monzogranites and granite porphyries have relatively low initial Sr isotope ratios of 0.704573–0.705627 and 0.704281, respectively, and similar ²⁰⁶Pb/²⁰⁴Pb ratios of 18.75–18.98 and 18.48–18.71, respectively. In contrast, the ε_Nd(t) value (−3.7) of granite porphyry is lower than those of monzogranites (−1.5 to −2.7) with Nd model ages of about 1.0 Ga. These geochemical features suggest that the monzogranite and granite porphyries were derived from juvenile crustal rocks related to subduction of the Paleo‐Pacific plate under east China. Copyright © 2013 John Wiley & Sons, Ltd.