表生钾锰矿物~(40)Ar/~(39)Ar年代学及其古气候意义

红土型风化壳和次生锰矿床形成于温暖和潮湿的古气候条件 ,其中含有丰富的表生钾锰矿物。因此 ,对表生钾锰矿物进行精确的40 Ar/ 3 9Ar年龄测定 ,不仅能查明大陆化学风化和矿床次生富集的时间和过程 ,而且可以为区域古气候的反演提供重要的年代学资料。透射电子显微镜、热重分析、离子交换实验和40 Ar/ 3 9Ar同位素分析表明 ,层状结构的黑锌锰矿、锂锰矿和钠水锰矿以及具有 1× 1隧道结构的软锰矿不适合于40 Ar/ 3 9Ar年龄测定 ;而隐钾锰矿、锰钡矿和锰铅矿因具有致密和稳定的 2× 2隧道结构及很强的保存K Ar体系的能力 ,是40 Ar/ 3 9Ar同位素定年的理想对象。硬锰矿和钙锰矿分别具有 2× 3和 3× 3隧道结构 ,由于隧道孔径过大 ,晶体结构的稳定性较差 ,其作为40Ar/ 3 9Ar测年的适用性有待于进一步证实。采用精细的激光阶段加热技术 ,可以有效克服表生钾锰矿物40 Ar/ 3 9Ar测年过程中3 9ArK 的反冲损失、多世代表生钾锰矿物的共生 ,以及表生钾锰矿物中原生矿物的污染和过量大气氩的存在等问题 ,并获得有意义的风化年龄。已有数据表明 ,表生钾锰矿物的形成主要集中在白垩纪末期、始新世末期—渐新世早期、中新世和上新世中期等 4个时期 ,可能记录了地史时期周期性的化学风化及气候的交替演变     

吐哈盆地硫磺山铜多金属矿床表生黄钾铁矾~(40)Ar/~(39)Ar定年及对风化、地貌演化及古气候的启示

黄钾铁矾是干旱—半干旱地区硫化物矿床氧化带中一种常见表生含钾硫酸盐矿物,对其进行~(40)Ar/~(39)Ar年代学研究,不仅可以直接限定硫化物矿床次生富集的时间,还可以为区域地貌形成演化和古气候演变等重大地质事件提供关键的年代学信息。本文对中国新疆吐哈盆地硫磺山铜多金属矿床氧化带中三个表生黄钾铁矾样品进行了~(40)Ar/~(39)Ar定年,第一次获得了始新世的风化矿物的年龄。结合已发表的年龄数据显示:在吐哈盆地,海拔较高的矿床氧化带剖面(如硫磺山矿床)记录了基岩的持续和较完整的区域风化事件,这些老的风化年龄的存在证明了剥蚀并不是均匀的,即其地貌演化遵循的是斜坡后退模型。对于吐哈盆地的古气候,这些表生硫酸盐的年龄表明:始新世以来吐哈盆地曾多次出现过有利于化学风化和硫化物矿床次生富集的干旱—半干旱气候,且主要集中在以下几个时期:27.7~23.3 Ma、16.4~14.7 Ma、11~7.8 Ma,之后气候开始向极端干旱气候转变,4.1~3.3 Ma之后吐哈盆地可能已经流行大规模的极端干旱气候。     

运用成因矿物学研究冀东长凝风化壳的古气候条件

据国外研究,有一定规模的风化淋滤型富铁矿床的形成和保存条件有四:1.有变质浅的、粒度细的火山-沉积型的厚大的贫矿层作矿源;2.炎热潮湿的古气候条件;3.适合的古构造、古地貌条件;4.富矿形成后,要很快被覆盖保存起来。冀东地区上述矿源层、古地貌等条件是具备的,但能否形成风化淋滤型富铁矿床的关键,首先就在于古气候条件是否有利。不同的古气候决定了不同的风化淋滤作用,从而产生不同的表生矿物类型和矿物的共生组合。本文则利用成因矿物学的方法来研究冀东长凝风化壳的类型,进而推断形成风化壳的古气候条件。     

菲律宾迪纳加特岛红土型镍矿床地质特征及找矿勘查方法

通过对菲律宾迪纳加特岛风化壳氧化镍-硅酸镍矿床的成矿地质条件、矿床地质特征、成矿机制的分析和研究,认为矿床是由于超镁铁岩-橄榄岩在中生代、第三纪、第四纪的热带、亚热带气候条件下,经过风化作用,镍从含镍的硅酸盐矿物中淋滤出来,随地表水向下渗透到风化壳的下部,形成富含镍的次生矿物,具有典型的风化壳型硅酸镍矿床特点。找矿勘探工作要在找矿区域进行地质填图及工程取样扫面来确定矿化区。     

风化矿物黄钾铁矾40Ar/39Ar 测年的基本方法——从样品采集到年龄测试

由于40Ar/39Ar定年方法在技术上极具复杂性,目前,国内在开展干旱区研究中很少使用风化矿物定年研究手段。重点介绍黄钾铁矾矿物40Ar/39Ar定年法的基本流程,并针对该方法的技术问题初步探讨了解决办法。研究表明,科学的野外采集样品、仔细的挑选矿物并综合采用多种测试手段（X衍射、扫描电镜、电子探针）进行监测可以获得纯净的风化矿物,并结合精细的40Ar/39Ar阶段加热技术,能够获得比较可靠的风化矿物40Ar/39Ar年龄。     

风化矿物黄钾铁矾~(40)Ar/~(39)Ar测年的基本方法——从样品采集到年龄测试

由于40Ar/39Ar定年方法在技术上极具复杂性,目前,国内在开展干旱区研究中很少使用风化矿物定年研究手段。重点介绍黄钾铁矾矿物40Ar/39Ar定年法的基本流程,并针对该方法的技术问题初步探讨了解决办法。研究表明,科学的野外采集样品、仔细的挑选矿物并综合采用多种测试手段(X衍射、扫描电镜、电子探针)进行监测可以获得纯净的风化矿物,并结合精细的40Ar/39Ar阶段加热技术,能够获得比较可靠的风化矿物40Ar/39Ar年龄。     

激光显微探针40Ar/39Ar 定年方法研究

实验结果表明，在激光探针40Ar/36Ar年龄和常规40Ar/39Ar年龄之间有较好的吻合性，多次测定BSP-1角闪石国际标样年龄值大部分在2020-20900Ma之间，多次测定周口店花岗岩中ZBH-25国内标样年龄值大部分在130-135.9Ma。分析区域可小到30μm以下（激光束本身可被聚集到10μm以下）。研究表明，激光显微探针技术在下述工作中将是一个极有前途的工具①测定不易大量获取的样品年龄；②研究遭受多期地质历史事件作用因而有复杂Ar状态的岩石年代；③研究在岩石样品中填充在不同结构位置上的矿物年     

激光显微探针39Ar/40Ar测年方法的两个应用研究实例

作者用激光显微探针39Ar/40Ar测年技术测定青藏高原北部东昆仑南韧性剪切带中糜棱岩和粤西云开片麻岩中多期矿物的年龄，从而确定出形成这些多期矿物的地质事件的时代。     

海绿石 K-Ar、40Ar/39Ar 年代学研究

海绿石是与沉积岩同时形成的高钾层状硅酸盐自生矿物，其 K-Ar、40Ar/39Ar 年龄存在失真现象。笔者认为，引起年龄失真的主要原因是由于该矿物结构中含有可膨胀层。通过测量可膨胀层含量及中子活化过程中39Ar的丢失率，使可对海绿石常规 K-Ar、40Ar/39Ar 年龄进行校正，得到其年龄校正公式。     

特殊地质地貌区填图物化探技术应用

基于物化探技术方法在特殊地质地貌区填图中的应用实验,介绍从区域物化探数据提取地质填图信息的方法,指出重磁与氡-汞气测联合应用是覆盖区探测隐伏岩体、断裂的高效低成本物化探技术组合。运用基于地球化学理论方法的元素地球化学判别技术,在强烈风化区定量划分风化等级为:基岩-弱风化-中度风化-强风化-全风化-残积土等;指出风化壳元素地球化学行为对原生矿物分解、次生矿物形成具有示踪效应;不同风化层稀土元素富集分异显著,强烈富集于全风化层（岩土界面或风化岩石顶界）中的稀土元素分布模式,可作为界定风化壳分层的重要地球化学判别指标。      

Growth Rate Estimates of Supergene Manganese Nodule by^40Ar／^39Ar Isotopic Dating

INTRODUCTIONModern4 0 Ar/ 39Arlaserstep heatinganalysishasbeensuccessfullyappliedtodateverysmallmineralgrainsfromdiversegeologicalenvironments .Thefineresolutionofthismethodhasgreatlyhelpovercomeproblemsintrinsicintradi tionalK Armethod ,inducedbyexcessargon ,argonlossbythermalresetting ,39Arrecoilduringirradiation ,andinter growthsand/orcontaminationofdifferentgenerationminer als ,withintheanalyzedmineral (Smithetal.,1998;Vas concelosetal.,1994 ) .Supergenemanganeseoredepositsareeconom…     

Timing and duration of supergene mineralization at the Xinrong manganese deposit,western Guangdong Province,South China: cryptomelane <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating

Supergene Mn-oxide deposits are widely distributed in Guangxi, Guangdong, Yunnan, and Hunan Provinces, South China, accounting for 18% of the total Mn reserves in the country. Direct dating of supergene Mn enrichment, however, is lacking. In this paper, we present high-resolution ⁴⁰Ar/³⁹Ar ages of Mn oxides from the Xinrong Mn deposit, western Guangdong, to place numerical constraints on the timing and duration of supergene Mn enrichment. A total of ten cryptomelane samples, spanning a vertical extent of 67 m, were dated using the ⁴⁰Ar/³⁹Ar laser incremental heating technique, with seven samples yielding well-defined plateau or pseudo-plateau ages ranging from 23.48 ± 0.91 to 2.06 ± 0.05 Ma (2σ). One sample yields a staircase spectrum that does not reach a plateau; the spectrum, however, indicates the presence of two or more generations of Mn oxides in the sample, whose ages are best estimated at 22.34 ± 0.31 and 10.2 ± 0.86 Ma, respectively. The remaining two samples gave meaningless or uninterpretable results due to significant ³⁹Ar recoil and contamination by old phases. The ⁴⁰Ar/³⁹Ar data thus reveal a protracted history of weathering and supergene Mn enrichment that started at least in the end of the Oligocene or beginning of Miocene and extending into the latest Pliocene. Staircase-apparent age spectra, resulting from banded or botryoidal samples, yield an average growth rate of Mn oxides at 0.6–0.7 × 10⁻³ mm kyr⁻¹. The values indicate that a 1-mm grain of Mn oxides may host minerals precipitated during a time span of ca. 1.5 m.y., and accumulation of Mn oxides to form economic deposits under weathering environments may take millions of years. The distribution of weathering ages shows that the oldest Mn oxides occur on the top of the profile, whereas the youngest minerals are found at the bottom, suggesting downward propagation of weathering fronts. However, two samples located at the intermediate depths of the profile yield ages comparable with those occurring at the highest elevations. Such a complexity of age distribution is interpreted in terms of preferential penetration of Mn-rich weathering solutions along more permeable fault zones, or as a result of multi stages of dissolution and re-precipitation of Mn oxides. A synthesis of geochronological and geological data suggests that formation of the Xinrong deposit was a consequence of a combination of favorable lithological, climatic, and structural conditions. Because the climatic and structural conditions are similar among the provinces of South China during the Cenozoic, the geochronological results obtained at Xinrong may also have implications for the timing of supergene Mn enrichment throughout South China.     

Ar/Ar dating of central European K–Mn oxides — a chronological framework of supergene alteration processes during the Neogene

K-bearing Mn oxides may potentially constitute useful objects for isotopic dating of ore-forming events. A comprehensive ⁴⁰Ar/³⁹Ar study performed on supergene K–Mn oxides sampled from different sub-alpine mountain terrains in Germany and France has been undertaken. The objective of these investigations was to provide new insight into how and when these secondary Mn accumulations may have formed. Developed in supergene environments at the expense of Mn²⁺/Mn³⁺-bearing precursor minerals, the Mn⁴⁺ oxides occur either as pseudomorphic ores or as cavity-fillings and linings.

The isotopic ages range from 25 to 1 Ma, indicating intense chemical weathering, especially during the Miocene and Pliocene. It is yet too early to decide whether the age range represents a more or less continuous process or distinct weathering episodes. Formation of supergene Mn oxides may result from combined climatic and tectonic factors: local uplift, exhumation, and associated fracturing of rocks provided fresh mineral surfaces for percolating meteoric fluids that induced subsequent weathering under warm–temperate to subtropical conditions.     

庐山变质核杂岩伸展拆离和岩浆作用的年代学约束

庐山变质核杂岩是华南中生代岩石圈减薄事件的浅层响应。研究伸展拆离和岩浆作用在其形成过程中的相互关系,对于认识地壳浅层的伸展减薄过程和变质核杂岩的形成机制具有重要的意义。在宏观和显微构造研究的基础上,分别对基底拆离断层和玉京山岩体进行了40Ar/39Ar年代学和锆石U-Pb年代学研究,为伸展拆离和岩浆作用提供了年代学约束,主要获得了以下认识:(1)变质核杂岩核部玉京山花岗岩体的锆石LA-ICP-MSU-Pb年龄为(133.0±2.1)Ma,代表了变质核杂岩核部岩浆活动的启动时间。(2)基底拆离断层下盘韧性剪切带内的白云母40Ar/39Ar年龄(140.4±1.7)Ma代表了庐山变质核杂岩的形成时间,也代表了庐山地区岩石圈伸展减薄的时间,即岩石圈伸展减薄始于早白垩世。(3)庐山变质核杂岩是中生代不同尺度的伸展拆离和岩浆活动共同作用的结果,在地壳浅层的具体形成过程中伸展拆离早于岩浆侵位,基底拆离断层的减压效应为深部岩浆的上升侵位创造了条件,岩浆侵位造成山体的隆升,又引发了盖层的重力滑脱。     

激光显微探针~(40)Ar/~(39)Ar同位素定年

已有 5 0年历史的K Ar定年法 ,由于过剩Ar和Ar丢失的普遍发现 ,使其最广泛的应用面临着严重挑战。40 Ar/ 3 9Ar分步加热释氩法是常规K Ar定年法的发展 ,它克服了常规K Ar定年法的一些局限 ,又可以测定岩浆构造热事件。激光显微探针40 Ar/ 3 9Ar定年法是在 2 0世纪末把聚焦激光束应用在40 Ar/ 3 9Ar分步加热释氩法中而发展起来的一种定年方法。它既具有常规K Ar定年法和40Ar/ 3 9Ar分步加热释氩法的所有优越性 ,又把定年引入微观领域。特别是在 2 0世纪的最后几年 ,以激光显微探针40 Ar/ 3 9Ar定年方法的完善和精度的提高为标志 ,把K Ar年代学研究推向了一个新的里程碑。微区微量高精度高分辨定年 ,把定年时限扩展到人类历史范畴 ,精细的分析技术拓宽了年代学的应用范围 ,使之解决的地质问题更广泛和深入 ,并且开始冲击着地球科学中的某些热点和难点课题。     

Precise molybdenite Re–Os and mica Ar–Ar dating of the Mesozoic Yaogangxian tungsten deposit, central Nanling district, South China

The Yaogangxian deposit in the central Nanling region, South China consists of vein-type ore bodies hosted in Cambrian to Jurassic strata and Mesozoic granitic intrusions. Wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz, feldspar, phlogopite, and muscovite. We have carried out molybdenite Re–Os and phlogopite and muscovite ⁴⁰Ar/³⁹Ar dating to better understand the timing and genesis of mineralization. Re–Os dating of eight molybdenite samples yielded model ages ranging from 152.0±3.5 to 161.1±4.5 Ma, with an average of 156.0 Ma. The Re–Os analyses give a well-defined ¹⁸⁷Re/¹⁸⁷Os isochron with an age of 154.9±2.6 Ma (MSWD=2.4). Hydrothermal phlogopite and muscovite display extremely flat ⁴⁰Ar/³⁹Ar age spectra. Phlogopite yields a ⁴⁰Ar/³⁹Ar plateau age of 153.0±1.1 Ma, whereas muscovite yields a plateau age of 155.1±1.1 Ma. Both ⁴⁰Ar/³⁹Ar ages are in good agreement with the Re–Os ages, placing the timing of tungsten mineralization at about 154 Ma. This age is consistent with the field relationships. Our new data, when combined with published geochronological results from other major deposits in this region, suggest that large scale W–Sn mineralization occurred throughout the central Nanling region in the Late Jurassic.     

LASER PROBE ~(40)Ar/ ~(39)Ar DATING OF MICAS ON THE DEFORMED ROCKS FROM ALTYN FAULT AND ITS TECTONIC IMPLICATIONS,WESTERN CHINA

LASER PROBE ~(40)Ar/ ~(39)Ar DATING OF MICAS ON THE DEFORMED ROCKS FROM ALTYN FAULT AND ITS TECTONIC IMPLICATIONS,WESTERN CHINAtheNationalNaturalScienceFundCommittee (NO .4 9772 157)     

Aggregation and Differentiation of Gold and Silver during the Formation of the Gold-Bearing Weathering Crusts (on the Example of Kazakhstan Deposits)

The supergene Au in weathering crusts of both the Suzdal and Raygorodok deposits is characterized by enhanced fineness, grain size, crystallinity, and the appearance of botryoidal aggregates of crystals. In the weathering crust of the Suzdal deposit, the exogenous Au is associated primarily with scorodite and carbonates; for Raygorodok, with chalcocite, bornite, hydrocarbonates and Cu hydrosulfates. The difference in the mineral associations of supergene Au at the deposits is determined by the occurrence of various mineral concentrators of Au in the primary endogenous substrate: arsenopyrite and pyrite at the Suzdal deposit and chalcopyrite with pyrite at the Raygorodok deposit. Due to the much greater mobility of Ag in the supergene zone, the weathering crusts are likely to contain submicron microinclusions of Ag minerals beyond the zones of Au concentration.