Microgranitoid Enclaves in Some I—and S—type Granites from Southern China

The three I-type plutons of Guantian(GT),Guidong(GD),Shangbao(SB)and the two S-type plutons of Xucun(XC)and Xiuning(XN) as well as their microgranitoid enclaves in southern China have been studied,Restite in the Motianling(MT) metasomatic granite in this area is described in this paper as well,Microgranitoid enclaves in the I-type granitoids may be divied into autoliths and schlierens which have marked differences both in petrography and geochemistry.In the S-type granitoids,schlierens are the major microgranitoid enclaves,but autoliths are rare.The metasomatic granite contains only restite without other enclaves.The microgranitoid enclaves and their host rocks have close ∈Nd(T)values and the same minerals within them are similar in composition.The microgranitoid enclaves,in general,don‘t represent the products of mixing of the syn-plutonic foreign mafic magma and the host acidic magma.They are the records of the evolution of intermediate-acidic magma itself.The formation of autoliths is related to the interdiffusion of different constituents in magma.Schlierens are the products of immiscible fractionation of the magma.     

Rb—Sr and U—Pb Dating of the Daguzhai and Luobuli Granitic Massifs in South China

Rb-Sr and U-Pb isotopic studies of the two contrasting granite types of the Daguzhai and Luobuli massifs in South China provide new constraints on the interpretation of isotopic age data for plutonic igneous rocks. A Rb-Sr internal isochron age of 146±7Ma for the Luobuli adamellite is interpreted to represent the age of magma crystallization, whereas the whole rock Rb- Sr isochron yields an older apparent age of 161±10Ma which is regarded as resulting from contamination processes affecting the petrogenesis of this adamellite. In the Daguzhai granite the marked scatter of whole- rock Rb-Sr data in isochron diagram is ascribed to the open system behavior of Rb during postmagmatic autometasomatism. Uniformity of initial⁸⁷Sr /⁸⁶Sr ratio in this granite is indicated in a plot of⁸⁷Sr versus⁸⁶Sr. The autometasomatism has also affected zircon U-Pb system, resulting in a spread of data along the concordia curve between 165 and 125Ma. This spread is regarded as indicating the duration of the autometasomatism.     

Subduction—Modified Subcontinental Mantle in South China：Trace Element and Isotope Evidence in Basalts from Hainan Island

Cenozoic lavas from Hainan Island,South China,comprise quartz tholeiite,olivine tholeiite,alkali basalt,and basanite and form a continuous,tholeiite-dominated,compositional spectrum.Highly incompatible elements and their relationships with isotopes in these lavas are shown to be useful in evaluating mantle-source composition,whereas modeling suggests that ratios of elements with bulk partition coefficients significantly larger than those of Nb and Ta may be sensitive to partial melting.Th/Ta and La/Nb ratios of alkali basalts are lower than those of tholeiites,and they are all lower than those of the primitive mantle,These ratios correlate positively with ^207Pb/^204Pb and ^87Sr/^86Sr ratios.Such relationships can be explained by mixing of depleted and enriched source components.A depleted component is indicated by alkali basalt compositions and is similar to some depleted OIB (PREMA).The enriched component,similar to sediment compositions,is indicated by tholeiites with high LILE/HFSE,^207Pb/^204Pb,and ^87Sr/^86Sr ratios.In general,basalts from Hainan and the South China Basin(SCB)share common geochemical characters.e.g.high Rb/Sr,Th/Ta,^207Pb/^206Pb,and low Ba/Th ratios.Such a geochemical trend is comparable to that of EMII-type OIB and best explained as the result of subduction.Occurrence of these characteristics in both continental Hainan basalts and SCB seamout basalts indicates the presence of a South China geochemical domain that exists in the mantle region below the lithosphere.     

Confirmation and Preliminary Study of Aluminous A—Type Granites in the Wuyi Mountain Area,Eastern Jiangxi Province,China

Widespread in the Wuyi Mountain area of eastern Jiangxi are petrochemically peraluminous granites and they are characterized as being high in silica (SiO₂ > 75% ) and highly alkaline (ALK=6.9% -7.5%) with K₂O > Na₂O and rather high ratios of FeO^T/MgO (11.3-17.9). The rocks have low contents of CaO, MgO, TiO₂ and P₂ O₅. The granites are enriched in REE (ΣREE =210.3 - 496. 8 μg/g) with remarkable negative Eu anomalies, but depleted in Eu, Ba, Sr, V, Co, and Ni, with 10000 x Ga/Al ratios, varying from 6. 1 to 9. 8. It is clear that these granites are obviously different from the I- and S-type granites, but are quite similar to those typical A-type granites such as aluminous A-type granites in the coastal areas of Fujian Province. State Geological Survey Project: supported by the Regional Geological Survey Project (No: 20001300002091 ) on the basis of the maps (scale 1: 250000) of Jingdezheng City, Nanchang City and Shangrao City.     

Geochemistry of the Baishitouquan Amazonite—and Topaz—bearing Granite in the Mid—Tianshan Belt,Xinjiang,China

The Baishitouquan amazonite and topaz-bearing granite is one of the typical high-rubidium and high-fluorine granites in the eastern part of the Mid-Tianshan belt. This intrusion is in sharp contact with Mid-Proterozoic schists, gneisses and marbles, and is composed of four zones transitional from the bottom upwards: leucogranite, amazonite granite, topaz-bearing amazonite granite and topaz quartz albitite. The Baishitouquan granite contains highly ordered K-feldspar, Li-rich mica, Mn-rich garnet, α-quartz and low temperature zircon and is chemically high in Si, K, Na, Al, Li, Rb, Cs and F, and low in Ti, Fe, Ca, Mg, P, Co, Ni, Cr, V, Sr and Ba, with Na₂O<K₂O. Amazonite from the amazonite granite zone contains 1867 ppm Rb. The F contents of bulk rocks are 3040 and 4597 for the amazonite granite and topaz-bearing amazonite granite zones, respectively. These two zones have δ¹⁸O values of 8.97–9.85‰ (SMOW) and show flat REE distribution patterns with strong Eu depletion. K-Ar and Rb-Sr ages of this intrusion are 226. 6 Ma and 209. 6 Ma respectively, with an initial⁸⁷Sr/⁸⁶Sr ratio of 0.987±0.213. The Baishitouquan granite is the product of crystallization of a low temperature, and water, rubidium and fluorine-rich magma, which may have been derived from partial melting of muscovite-rich crustal rocks. Consolidation of this granite involved two contrasting and successive stages: melt crystallization and hydrothermal metasomatism and precipitation. Various geological features of this granite were formed during the transition from the magmatic to the hydrothermal stage.     

Mineral Association and Mineralogical Criteria for the Formation Conditions of A B—F—Sn—Bi Skarn in Damoshan,Gejiu Tin Field,Sothwest China

The Damoshan deposit is a small B-F-Sn Bi exoskarn deposit and contains a distinctive mineral assemblage comprising andradite,vesuvianite,calcite,diopside,magnetite,hematite,nordenskioldine,cassiterite,varlamoffite,schenfliesite,native bismuth,eulytite,bismite and bismuthite,in which the occurrence of eulytite is the first reported in China.Textures of the mineral paragenses show that andradite,vesuvianite and diopside were the earliest phases formed during metasomatism,i.e.,the skarn forming stage.Then nordenskioldine,magnetite and native bismuth,perhaps together with eulytite,were precipitated at the stage of retrograde alteration.The minerals varlamoffite,schoenfliesite,hematite ,bismite and bismuthite were probably the product of supergene alteration.The minerals were analyzed by means of electron microprobe.The data on the ,coexisting phases and their compositons show that during the metasomatism reduced F-and Sn-rich primary mineralizing solutions reacted with highly oxidized carbonated of the Gejie Formation,producing a high Fe^2 /Fe^3 skarn(vesuvianite-fluorite skarn)near the contact of granite,and a low Fe^2 /Fe^3 skarn(vesuvianite-fluorite skarn)near the contact of granite,and a low Fe^2 /Fe^3 skarn(andradite skarn)in the outer zone of the skarn body in which andradite is extremely tin-bearing up to 5.14 wt% SnO2),In the retrograde alteration stage ,B-rich,but F-and Si-deficient mineralizing solutions replaced the tin-bearing andradite,forming an association of nordenskioldine and magnetite,No sulphides were deposited at this stage because of the oxidization ambient conditions in the andradite skarn.In the spergene oxidation zone,the nordenskioldine was dissolved into varlmoffite and calcite,the native bismuth was transformed into bismite or bismuthite ,and the magnetite was altered into hematite under the action of the CO2-rich supergene solutions.     

REE Geochemistry of Some Metamorphic Rock Types of the Late Archean Fuping Group and Their Anatectic Derivatives in Pingshan,Hebei Province,China—A Preliminary Study

The Late Archean Fuping Group of the Xiaojiao area in Pingshan Couty,Hebei Province consists mainly of three metamorphic rock types of supracrustal affinity,i.e.,Kfeldspar leucoleptite,biotite leptite-gneiss and hornblendic rocks.Their anatectic derivatives formed in the initial stage of anatexis are petrochemically of K-feldspar granitic trondhjemitic and granodioritic compositions respectively,and in general have inherted the main petrochemical featurews from their parent rock types,Probably due to the fact that they contain less REE rich accessory minerals as compared with their parent rocks,the anatectic derivatives are in general lower in EREE content,But both the derivatives and their parent rocks have similar REE patterns,which serves as an additional indication of the genetic relationship between them.     

华南富氟花岗岩高磷和低磷亚类型对比

根据全岩Ｐ２Ｏ５含量的多寡可将华南富氧花岗岩分为高磷亚类和低磷亚类,它们之间具较大的地球化学差异。高磷亚类以低硅、强过铝和低的ＲＥＥ总量为特征,而低磷亚类则相反。在长石、云母等矿物化学成分上这两亚类花岗岩也有所差异。高磷亚类花岗岩中磷以长石中结构磷和磷铝锂石形式存在,而低磷亚类花夺中的磷则主要存在于磷灰石等磷酸盐矿物中。     

新编华南花岗岩分布图及其说明

展示了新编的《华南花岗岩分布图（1：250万）》,并作了简要说明。该图在前人相关图件的基础上,收集了近15年来华南花岗岩研究的新的主量元素和年代学资料修编而成。此外,该图反映了华南不同时代花岗岩的富铝程度。     

华南某些含钨花岗岩的K-Ar年龄

测定了华南某些与钨矿床有关的花岗岩和钨矿脉样品的K—Ar年龄,共37件。这些花岗岩的表观年龄自183Ma至99.5Ma(年龄值为715Ma的岩体与钨矿无关),其中68％以上样品值域在150Ma左右。~(40)Ar/~(36)Ar—40K/~(36)Ar等时线图解给出的等时年龄为132.1Ma,说明这些花岗岩在形成时代上属中侏罗到早白垩世。我们发现在华南钨矿成矿域内,有一个从中心带向外年龄逐渐变青的趋势。用矿脉中和矿脉侧云英岩中云母类矿物所做的K—Ar定年得到的矿化作用的年龄,与各自相关的花岗岩的年龄非常接近,以至于很难用K—Ar定年法加以区别。即成矿作用和成岩作用有一种准同期性。等时线对应的~(40)Ar/~(36)Ar初始比高于现今大气Ar的比值,表明花岗岩在固结时有继承Ar存在。     

对华南花岗岩研究的若干思考

论述了华南地质历史上四个时期花岗岩特点、成因模式与大地构造框架,从中折射出一些值得进一步思考的问题。晋宁期花岗岩是扬子周边环形岛孤型造山带的组成部分,加里东期、印支期和燕山期花岗岩的形成,分别与早古生代板内压扭性断裂熔融、早中生代板内伸展减压熔融和晚中生代活动陆缘伸展增生造山作用有关。华南四个地质时期的花岗岩的成因各异,模式不同,主导的地球动力学机制也不同。建立能解释多数地质事实的模式,是当前认知的需要。希望在不远的将来,沿着历史长河完整地描述19亿年以来的华南花岗岩地质演变与地壳演化,将华南地质的故事以三维图像形式演示于众。     

Uranium-bearing and barren granites from the Taoshan Complex,Jiangxi Province,South China: Geochemical and petrogenetic discrimination and exploration significance

The Taoshan uranium ore district is one of the most important granite-hosted uranium producers in South China. The Taoshan granitic complex can be petrographically classified into several units of Caijiang, Huangpi, Daguzhai, and Luobuli, but the uranium deposits only occur within the Daguzhai granite unit. LA-ICP-MS zircon U–Pb dating indicates that both the Daguzhai granite and the Huangpi granite were emplaced at 154 ± 2 Ma. U contents (average 19.5 ppm) of the Daguzhai granite are higher than those of the Huangpi granite (average 7.3 ppm). The Daguzhai granite is composed of medium-grained two-mica granite, and the Huangpi granite is composed of medium- to coarse-grained biotite granite. These two granites show obvious differences in major element, trace element and isotopic geochemical characteristics. Compared to the Huangpi granite, the Daguzhai granite has higher A/CNK ratios, higher P₂O₅ contents and lower CaO contents, and is more enriched in Rb, Ba, U, and more depleted in Sr, Eu and Ti. The ε_Nd(t) values of the Daguzhai granite vary from − 12.2 to − 11.0 with two-stage model ages of 1.84 to 1.93 Ga. The ε_Nd(t) values of the Huangpi granite are slightly higher (− 9.7 to − 8.6) and the Nd model ages are younger (1.64 to 1.73 Ga). Comparative studies imply that the Daguzhai granite belongs to typical S-type and might be derived from the partial melting of parametamorphic rocks from metamorphic basement of the Zhoutan Group. In contrast, the Huangpi granite belongs to fractioned I-type, which might be derived from the partial melting of a mixture of ortho- and para-metamorphic rocks of the Zhoutan Group. These different magma sources might explain the different U contents of the two granites. In general, the source factor is an important controlling factor for the genesis of U-bearing granites in South China. U-bearing granites in South China show some common mineralogical and geochemical characteristics, which can be used to guide further exploration of granite-hosted U deposits.     

华南板块北缘东段武功山加里东期花岗岩特征及成因探讨

华南板块北缘东段武功山地区出露大面积的片麻状花岗岩,前人在该区工作时认为属混合成因的“混合岩”,本次工作证实属同熔性花岗岩。采用岩石谱系单位法进行研究,共划分出5个单元,归并为2个超单元。其成岩年龄(U-Pb法)分别为(462.3±3.2)Ma、(409.4±5.1)Ma,属加里东期造山花岗岩。后又经印支—燕山期伸展滑覆构造的叠加、改造,形成片麻状花岗岩。     

Are South China granites special in forming ion-adsorption REE deposits?

Ion-adsorption REE deposits associated with clay minerals are the main global HREE producer. The majority of these deposits are formed by the weathering of granites in South China, but whether there is any fundamental difference between the granites in and outside South China is still unclear. Besides, an effective evaluation system of granite mineralization potential is urgently needed for HREE exploration.To answer this question, we compiled a global granite geochemical dataset from within (n = 1932) and outside (n = 6109) South China, together with a dataset of representative REE deposits in South China (n = 128). The geochemical comparation shows that the South China granites share similar REE contents with those of many granites from places outside South China. Such similarity has also been found between REE ore-related and ore-barren granites in South China. This shows that granites from outside South China could also have ore-forming potential. Warm humid climate and quasi-equalized crustal state promote chemical weathering to continuously leach REEs and store them in the weathering crust. The enrichment ratio (Rx) can be used to quantify the climatic effect between orebodies and parent rocks. The calculated average Enrichment Ratios (Rx) of LREE- and HREE-rich deposits are 2.41 and 2.68, respectively. Sufficient REE content in granite is the prerequisite for mineralization, and we propose that the combination of the minimum REE + Y (172 and 108 ppm in LREE- and HREE-rich parent rocks, respectively) and REE oxide ratio (1.32) can reveal the granite metallogenic potential. Together with the suitable tropical and temperate climate area with ion-adsorption REE deposits, we further identified certain regions with high REE mineralization potential outside South China to assist future exploration.     

华南泥盆系研究中的几个地层问题

简要总结我国泥盆系研究进展的基础上 ,提出华南区泥盆系除滨海相沉积外 ,浅海相沉积可区分出象州型、北流型、南丹型、崇左型 4种基本的相型沉积 ,各自均有特定的岩石组合、生物群特征 ,反映各自特定的沉积环境 ,应分别建立相应的地层柱。如继续保留华南区泥盆系建阶方案 ,泥盆系底部有待重行建阶 ,Emsian阶宜三分 ,与之时限相当的阶 ,自下而上为郁江阶、二塘阶、四排阶     

中国东北地区中新生代花岗岩中氮含量及其同位素特征

通过对中国东北地区花岗岩类样品的分段加热,探讨了岩石氮气同位素组成的测定方法,并测定了释放出的Ｎ２含量及δ＾１５Ｎ值。分析结果表明,中国东北不同地区的花岗岩、流纹岩和花岗斑岩在分段加热过程中,不同温度段释放Ｎ２含量及其同位素组成特征不同,释放Ｎ２含量判别较大。花岗岩释放Ｎ２含量为１．６４～６．２３uＬ／g,最大释放峰温度在６００℃左右,流纹岩、花岗斑岩释放Ｎ２含量为１０８．９８～７５５．９６uＬ／g,     

Petrogenesis of Lingshan highly fractionated granites in the Southeast China: Implication for Nb-Ta mineralization

Whole rock major and trace element and Sr-, Nd- and Hf-isotope data, together with zircon U-Pb, Hf- and O-isotope data, are reported for the Nb-Ta ore bearing granites from the Lingshan pluton in the Southeastern China, in order to trace their petrogenesis and related Nb-Ta mineralization. The Lingshan pluton contains hornblende-bearing biotite granite in the core and biotite granite, albite granite and pegmatite at the rim. In addition, numerous mafic microgranular enclaves occur in the Lingshan granites. Zircon SIMS U-Pb dating gives consistent crystallization ages of ca. 132 Ma for the Lingshan granitoids and enclaves, consistent with the Nb-Ta mineralization age of ∼132 Ma, indicating that mafic and felsic magmatism and Nb-Ta mineralization are coeval. The biotite granites contain hornblende, and are metaluminous to weakly peraluminous, with high initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7071–0.7219, negative ε_Nd(t) value of −5.9 to −0.3, ε_Hf(t) values of −3.63 to −0.32 for whole rocks, high δ¹⁸O values and negative ε_Hf(t) values for zircons, and ancient Hf and Nd model ages of 1.41–0.95 Ga and 1.23–1.04 Ga, indicating that they are I-type granites and were derived from partial melting of ancient lower crustal materials. They have variable mineral components and geochemical features, corresponding extensive fractionation of hornblende, biotite and feldspar, with minor fractionation of apatite. Existence of mafic microgranular enclaves in the biotite granites suggests a magma mixing/mingling process for the origin of the Lingshan granitoids, and mantle-derived mafic magmas provided the heat for felsic magma generation. In contrast, the Nb-Ta mineralized albite granites and pegmatites have distinct mineral components and geochemical features, which show that they are highly-fractionated granites with extensive melt and F-rich fluid interaction in the generation of these rocks. The fluoride-rich fluids induce the enrichment in Nb and Ta in the highly evolved melts. Therefore, we conclude that the Nb-Ta mineralization is the result of hydrothermal process rather than crystal fractionation in the Lingshan pluton, which provides a case to identify magmatic and hydrothermal processes and evaluate their relative importance as ore-forming processes.