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1.
金属硫化物Re-Os等时线年龄的合理解释是揭示金属矿床成矿时代的关键.通过对新疆东天山梅岭铜矿床开展Re-Os同位素定年研究,结果表明浸染状和脉状矿石中黄铁矿样品在Os浓度和Os同位素比值方面都有很大的变化,这两类样品定义了很好的Re-Os等时线年龄,分别为523±59 Ma和707±99 Ma.由于得到的等时线年龄明显老于它们的实际地质成矿年龄,且187Os/188Os与普通Os的倒数（以1/192Os为例）之间存在着很好的相关性（R2分别为0.997 3和0.994 5）,因此这些样品存在着初始Os同位素组成不均一的现象,这些Re-Os等时线是混合等时线,没有地质意义.理论和数学公式推导显示观测到的Re-Os等时相关性是在形成时期没有达到完全的同位素平衡的二元混合的结果,这种同位素扩散不平衡产生的原因主要是在矿床形成时期Os同位素在金属硫化物与硅酸盐矿物之间的同位素扩散存在限制性.回归得到的Os的初始值更偏向于地壳值,表明矿床形成时期的地壳混染可能造成金属硫化物体系中的这种初始Os同位素不均一.因此,将Re-Os同位素体系应用于金属硫化物样品定年时,187Os/188Os与1/192Os之间是否存在相关关系可以作为Re-Os等时线年龄是否具有地质意义的判断标准. 相似文献
2.
金川铜镍硫化物矿床的Re-Os"年龄"及其意义 总被引：15，自引：0，他引：15
分析了金川铜镍硫化物矿床的一组浸染状矿石和一组块状矿石的Re、Os含量和Os同位素组成.浸染状矿石和块状矿石分别给出Re-Os表观等时线年龄为(1 126±96)Ma和(840±79)Ma,表观初始187Os/188Os比值为0.119±0.018和0.242±0.028.块状矿石的表观年龄与前人报道的同类矿石年龄在误差范围内一致,证明了其分析的可靠性.此结果也与前人报道的锆石和斜锆石的U-Pb年龄在误差范围内一致,说明了金川的新元古代成矿时代.而我们的和前人的工作表明,海绵陨铁状矿石和浸染状矿石给出的Re-Os表观年龄有相当大的变化范围,且都比块状矿石的年龄老.提出了两种模式解释这种现象:在约8亿年前金川矿床形成时地壳混染导致浸染状矿石和海绵陨铁状矿石的Os同位素组成不均一,从而给出偏老的表观年龄;相反,Os同位素在块状矿石中快速扩散而均一化,因此给出成岩成矿年龄.但是,还不能完全排除两期成岩成矿的可能性,即晚期岩浆活动引起了早期岩浆活动中封闭的Re-Os同位素体系的扰动.目前倾向于第一种解释,但后一种可能性还需要检验. 相似文献
3.
力马河镍矿Re-Os同位素研究 总被引：10，自引：0，他引：10
四川力马河镍矿是峨眉山大火成岩省一个重要的岩浆硫化物矿床。本文通过对其主要岩、矿石类型Re、Os及其同位素组成的分析,综合探讨了成矿岩体原始岩浆性质、矿石硫化物成因、成矿机制及Re-Os同位素等时线年龄。结果表明,力马河镍矿不同类型岩矿石样品初始Os同位素组成是不均一的,富硫化物的网脉状矿石及其选纯硫化物Os同位素组成初值差异较小,其等时线年龄为265±35 Ma、与岩体锆石SHRIMP年龄263±3 Ma基本相当;硫化物含量较低的岩、矿石样品间初始Os同位素组成差异较大,其表观等时线年龄大于成矿年龄。分析认为,岩矿样品初始Os同位素组成的不均一是由含较高放射成因187Os丰度的硫化物熔体和含较低放射成因187Os丰度的硅酸盐熔体不同比例混合造成的。混合模型分析表明,硫化物含量超过30％的矿石样品初始187Os/188Os基本接近,硫化物含量低于30％的岩矿石样品初始187Os/188Os随硫化物含量上的不同差异很大,为岩浆硫化物矿床Re-Os等时线年龄可能出现多组年龄解的现象提供了一种可能的解释。成矿岩体中含放射成因187Os丰度最低的岩石样品γOs（t=260Ma）在5左右、Cu/Pd比值在7000左右,表明是基本没有受到地壳混染及硫化物熔离影响的原始岩浆结晶分异产物,估计原始岩浆Os含量在1×10－9左右,为苦橄质岩浆。矿石硫化物Re/Os比值显著高于任何赋矿橄榄岩,γOs（t=260Ma）高达110左右,综合分析揭示了力马河镍矿硫化物为二次熔离成因,模式分析认为,矿石硫化物是由原始岩浆经历R=2000左右的硫化物熔离后、其亏损岩浆再经R=200左右的硫化物熔离形成,与二次熔离相对应,成矿岩浆也经历了两次混染作用,分别为上、下地壳7％左右的混染。 相似文献
4.
四川省会理县青矿山Ni-Cu-PGE矿床成因机制的Re-Os同位素证据 总被引：3，自引：2，他引：1
青矿山Ni-Cu-PGE矿床位于四川会理县小关河地区,是峨眉山大火成岩省中典型含铂岩浆硫化物矿床之一。本文对该矿床开展了Re-Os同位素组成的分析研究。分析结果表明,不同类型岩矿石的初始Os同位素组成具有明显的不均一性,主要区分出三种不同Os同位素组成的岩矿石类型:不含硫化物的橄辉岩具低γOs,变化范围从15.3到40.3;致密块状和浸染状硫化物矿石相近,γOs值在260左右;海绵陨铁状矿石具有最高的放射性Os同位素组成,γOs值在1000左右。分析认为,青矿山Ni-Cu-PGE矿床是多级岩浆房演化的结果,原始岩浆具有苦橄质岩浆的性质,成矿岩体中不含硫化物的橄辉岩具有低的放射性Os同位素组成,其母岩浆不是矿石硫化物的直接母体;致密块状和浸染状硫化物矿石与海绵陨铁状矿石也具有不同的放射性Os同位素组成,是成矿岩浆演化过程中不同期次岩浆硫化物熔离形成的。模式分析认为:(1)原始岩浆在深部岩浆房受到下地壳混染(约1.8%),造成少量Cu、Ni及PGE元素进入熔离硫化物形成PGE适度亏损的成矿母岩浆;(2)海绵陨铁状矿石硫化物是PGE适度亏损的成矿母岩浆受下地壳二次混染形成的具有很高放射性Os同位素组成的岩浆(γOs(t=260Ma)高达1000)经二次硫化物熔离(R≈1000)所形成;(3)PGE适度亏损的成矿母岩浆受上地壳二次混染(约6.7%),形成具有较高放射性Os同位素组成的岩浆(γOs(t=260Ma)在260左右)并发生二次硫化物熔离(R≈5000),部分熔离硫化物积聚成矿浆形成块状硫化物矿石,未得到充分积聚的熔离硫化物形成浸染状硫化物矿石。Os同位素组成的不均一性表明青矿山Ni-Cu-PGE矿床为岩浆通道系统成矿,是多级岩浆房演化过程中不同期次含矿岩浆在岩浆通道系统中复合的结果。 相似文献
5.
杰 《吉林大学学报(地球科学版)》2014,(2):507-517
吉林红旗岭铜镍硫化物矿床主要由1号、2号及7号含矿岩体组成,主要矿石类型为浸染状矿石。其Re-Os等时线年龄研究显示:2号岩体Re-Os等时线年龄((215.0±24.0)Ma)与岩体的锆石SHRIMP U-Pb年龄((212.2±2.6)Ma)一致;而1号岩体Re-Os等时线年龄((237.0±16.0)Ma)则明显老于岩体的锆石SHRIMP U-Pb年龄((216.0±5.0)Ma)。这表明浸染状矿石的Re-Os等时线年龄具有一定的不确定性,应慎重使用。浸染状矿石的Re-Os等时线年龄偏老原因多被解释为地壳混染引起的Os同位素不均一所致,但研究显示:红旗岭1号岩体和2号岩体均有一定量的地壳物质混入,浸染状矿石的187 Os与188 Os初始比值分别为0.215±0.043和0.302±0.089,γOs值分别为67.5~155.8和113.9~206.9;且2号岩体地壳物质混入量略高于1号岩体,混入的壳源Os所占比例为20%~30%。这说明地壳物质混染并非是导致Os同位素不均一的主要原因,其主要原因仍需在今后的工作中深入研究;而地壳物质的混入可能是促进熔离成矿的关键因素。 相似文献
6.
略阳煎茶岭铜镍硫化物矿床Re—Os同位素年龄及其地质意义 总被引：12，自引：0，他引：12
采用矿石Re-Os同位素方法对陕西省煎茶岭硫化镍矿床矿石进行了成矿年代学研究,获得了878士27 Ma(1σ)的等时线年龄,首次厘定了该矿床成矿时代为新元古代,成岩成矿基本同时.通过对878 Ma硫化镍矿石初始Re-Os同位素体系的γOs计算和Re/Os值分析表明,其yOs和Re/Os值变化范围大,深部条带状矿石的Re/Os值仅为0.05,yOs为-6.70;块状矿石的Re/Os值范围为4.24～24.43,γOs为-15.37～+280.65,说明成矿过程中有壳源物质的混染;两件样品的γOs为负值(-15.37,-6.70),可能指示其超镁铁质岩浆来源于Re亏损地幔.煎茶岭超基性岩体年龄及其镍矿石的Re-Os等时线年龄与扬子克拉通北缘火山岩浆活动时间相对应,它们是扬子克拉通西北缘晋宁期构造岩浆成矿作用的产物. 相似文献
7.
东天山天宇铜镍硫化物矿床磁黄铁矿Re-Os同位素物质来源示踪 总被引：4，自引：2，他引：2
天宇岩浆铜镍硫化物矿床的矿体由浸染状矿体和块状矿体组成。采用同位素稀释Triton-plus测定了浸染状矿石和块状矿石的磁黄铁矿Re-Os同位素比值。结果表明:浸染状矿石w(Re)为11.82×10~(-9)~45.28×10~(-9),w(Os)为0.944×10~(-9)~8.528×10~(-9),187Os/188Os初始比值为0.885~2.332,γOs为607~1763;块状矿石w(Re)为49.38×10~(-9)~315.10×10~(-9),w(Os)为0.191×10~(-9)~42.420×10~(-9),187Os/188Os初始比值为0.654~3.322,γOs为423~2555。Re、Os含量、同位素组成和特征值表明,该矿床物质为壳-幔混合来源,块状矿石可能比浸染状矿石经历了更强的地壳物质混染。浸染状矿体发育透闪石化、蛇纹石化、绿泥石化蚀变,表明存在岩浆期后热液活动,但块状矿体热液蚀变不明显,块状矿石的Re-Os同位素特征可能是与地壳岩石直接作用的结果。地壳混染作用发生在深部岩浆房,同时也发生在岩浆侵位及再次迁移过程中,这些过程造成块状矿体与浸染状矿体不同的同位素特征。 相似文献
8.
新疆坡北基性-超基性岩带10号岩体SHRIMP U-Pb和矿石Re-Os同位素定年及其意义 总被引：9，自引：2，他引：7
坡北基性-超基性岩带10号岩体位于塔里木板块东北部北山裂谷带内,岩体侵位于下石炭统红柳园组.前人根据岩体侵位地层的时代,间接推断出该岩体形成年龄为晚石炭世一早二叠世.文章对坡北基性-超基性岩带的10号岩体辉长岩和浸染状矿石分别进行了锆石SHRIMP U-Pb、Re-Os定年和Sr-Nd同位素示踪研究,获得岩体的辉长岩锆石SHRIMP U-Pb年龄信息比较分散,其表面年龄信息从古生代-新元古代-古元古代-新太古代均有显示,揭示了新疆塔里木板块东北部北山裂谷带内的基性-超基性岩体的形成经历了复杂的地质演化历史.所获得的主体锆石的年龄为(289±13)Ma(95%可信度),与岩体侵位于下石炭统红柳园组的地质事实相吻合,可能代表了岩体形成的时间,而年龄信息(2 559～2 589 Ma)暗示了北山地区可能存在古元古代一新太古代的结晶基底.获得浸染状铜镍硫化物矿石的Re-Os等时线年龄为(413±20)Ma(95%可信度),该年龄不仅大于含矿超基性岩体(289 Ma)的形成时代,而且也老于岩体所侵入的下石炭统红柳园组的地层时代,显然与宏观的地质证据相悖.Sr-Nd和Os同位素特征研究表明,坡北岩带在约280 Ma前成岩成矿时,岩浆在从地幔源区侵入到地壳过程中受到了地壳物质混染,致使浸染状矿石的Re-Os同位素体系呈二元混合体系,因此浸染状矿石Re-Os同位素体系确定的等时线疑为假等时线,其年龄不能代表矿床形成时代或不具有确切的地质意义.铜镍矿化无论从时间上还是空间上都与岩体的侵位密切相关,矿床成因类型又为岩浆熔离型矿床,表明坡北10号铜镍硫化物矿床的成岩成矿时间应发生在晚石炭世一早二叠世期间,是后碰撞构造背景下幔源岩浆上侵的产物. 相似文献
9.
10.
新疆哈密月牙湾铜镍矿是近年来在东天山卡拉塔格地区新发现的岩浆型铜镍硫化物矿床.为确定该矿床的成岩、成矿时代及其成矿作用,利用锆石LA-ICP-MS U-Pb定年和硫化物Re-Os同位素等时线定年方法,分别对主含矿岩相橄榄辉长岩和矿石中的磁黄铁矿进行了年龄测定.橄榄辉长岩中锆石的206Pb/238U年龄为255~292 Ma,加权平均值为274±2.4 Ma,代表了橄榄辉长岩的成岩年龄;矿石中磁黄铁矿Re-Os同位素等时线年龄为271.9±9.5 Ma,代表了硫化物熔离成矿的年龄;187Os/188Os初始值为0.279 6±0.008 9,γOs值为117~126,指示在岩浆侵位及硫化物熔离成矿过程中有地壳物质加入.月牙湾镁铁质岩浆的成岩、成矿作用发生于早二叠世,与东天山黄山-图拉尔根一带典型铜镍硫化物矿床为同一时期的产物. 相似文献
11.
Re–Os dating of disseminated ore from the Kalatongke Cu–Ni sulfide mineral deposit, Xinjiang, Northwest (NW) China, yields an apparent isochron age of 433 ± 31 Ma with an apparent initial 187Os/188Os (433 Ma) ratio of 0.197 ± 0.027. This apparent age is older than not only the zircon U–Pb age of the host intrusion (287 ± 5 Ma, Han et al., 2004) but also the stratigraphic age of the intruded country rock. Thus, the regression line is a pseudo-isochron. However, previous Re–Os dating of massive ores of the same deposit yielded an age that is consistent, within analytical uncertainty, with the zircon U–Pb age (Zhang et al., 2008). This relationship is similar to that observed in the Jinchuan deposit, NW China. Therefore, we suggested that the same mechanism, post-segregation diffusion of Os (Yang et al., 2008), is applicable to the Kalatongke deposit.Re–Os isotopic studies of Kalatongke, Jinchuan and representative magmatic Cu–Ni sulfide deposits suggest that the massive ores of mafic–ultramafic-rock-associated Cu–Ni sulfide deposits would yield geologically meaningful Re–Os age, whereas a pseudo-isochron would be obtained for the disseminated ores. Therefore, to obtain a geologically meaningful Re–Os age, the type of the deposit, the type of the ore and the ore-forming process should be taken into account. 相似文献
12.
Shenghong Yang Wenjun Qu Yulong Tian Jiangfeng Chen Gang Yang Andao Du 《Chemical Geology》2008,247(3-4):401-418
Apparent Re–Os ages of some magmatic sulfide ore deposits are older than the zircon and baddeleyite U–Pb ages which are interpreted as the formation age of the host intrusions. The Jinchuan Ni–Cu–PGE deposit of China, the world's third largest, is such a case. We report apparent Re–Os isochron ages of 1117 ± 67 Ma, 1074 ± 120 Ma and 867 ± 75 Ma with initial 187Os/188Os ratios of 0.120 ± 0.012, 0.162 ±0.017 and 0.235 ± 0.027 for disseminated ores, sulfides from the disseminated ores and massive ores from Jinchuan, respectively. Using these data and Re–Os ages from the literature, we find that the oldest apparent Re–Os age and lowest initial Os isotope ratio are from disseminated ores which contain small amounts of sulfide minerals, the highest initial Os isotope ratios and youngest apparent Re–Os ages, consistent with the zircon and baddeleyite U–Pb ages, are from massive ores containing 90–100 modal% sulfide, and net-textured ores with about 25 modal% sulfides yield apparent Re–Os ages and initial Os ratios intermediate between those of the disseminated and massive ores.Because Os diffusion between sulfides is inhibited by the intervening silicates even at high temperatures, re-equilibration did not occur in the disseminated ore and the samples retained the Os ratios of the contaminated magma, leading to geologically meaningless ages that are older than the formation age of the rocks. While Os-bearing sulfide minerals and magnetite show low closure temperatures of Os diffusion and the sulfide minerals in the massive ore are closely connected with each other, facilitating fast diffusion of Os, re-equilibration of Os was achieved during cooling of the ore from about 850 °C after the segregation to about 400 °C. Thus, an age corresponding to the formation time and an elevated initial Os ratio were yielded by the massive ore. Os isotopes in the net-textured ore behave in the way intermediate between the disseminated and massive ores. Pb isotope data support the Os results. Disseminated ores have heterogeneous Pb isotope ratios whereas Pb in the massive ores is more uniform, consistent with Pb isotopic equilibration in the massive ores, but not in the disseminated ores. 相似文献
13.
Re-Os isotopes were used to constrain the source of the ore-forming elements of the Tharsis and Rio Tinto mines of the Iberian
Pyrite Belt, and the timing of mineralization. The pyrite from both mines has simila]r Os and Re concentrations, ranging between
0.05–0.7 and 0.6–66 ppb, respectively. 187Re/188Os ratios range from about 14 to 5161. Pyrite-rich ore samples from the massive ore of Tharsis and two samples of stockwork
ore from Rio Tinto yield an isochron with an age of 346 ± 26 Ma, and an initial 187Os/188Os ratio of about 0.69. Five samples from Tharsis yield an age of 353 ± 44 Ma with an initial 187Os/188Os ratio of about 0.37. A sample of massive sulfide ore from Tharsis and one from Rio Tinto lie well above both isochrons
and could represent Re mobilization after mineralization. The pyrite Re-Os ages agree with the paleontological age of 350 Ma
of the black shales in which the ores are disseminated. Our data do not permit us to determine whether the Re-Os isochron
yields the original age of ore deposition or the age of the Hercynian metamorphism that affected the ores. However, the reasonable
Re-Os age reported here indicates that the complex history of the ores that occurred after the severe metamorphic event that
affected the Iberian Pyrite Belt massive sulfide deposits did not fundamentally disturb the Re-Os geochronologic system. The
highly radiogenic initial Os isotopic ratio agrees with previous Pb isotopic studies. If the initial ratio is recording the
initial and not the metamorphic conditions, then the data indicate that the source of the metals was largely crustal. The
continental margin sediments that underlie the deposits (phyllite-quartzite group) or the volcanic rocks (volcanogenic-sedimentary
complex) in which the ores occur are plausible sources for the ore-forming metals and should constrain the models for the
genesis of these deposits.
Received: 15 March 1999 / Accepted: 26 July 1999 相似文献
14.
Re-Os Age of Cu-Ni Ores from the Huangshandong Cu-Ni Sulfide Deposit in the East Tianshan Mountains and Its Implication for Geodynamic Processes 总被引：4，自引：0，他引：4
MAO Jingwen YANG Jianmin QU Wenjun DU Andao WANG Zhiliang HAN Chunming Faculty of Geosciences Resources China University of Geosciences Beijing E-mail: jingwenmao@.netInstitute of Mineral Resources Chinese Academy of Geological Sciences Beijing National Research Center of Geoanalysis Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》2003,77(2):220-226
An isochron age of 282±20 (95% conf. limit) Ma of the sulfide ores in the Huangshandong Cu-Ni sulfide deposit, the East Tianshan Mountains has been obtained through Re-Os isotopic measurement. The age implies that the Cu-Ni sulfide deposit and other related deposits in the same area occurred in a Permian extensional environment of post-collision instead of Devonian-Early Carboniferous ophiolite-related oceanic or island arc environments inferred before. It shares the same ages with the orogenic and epithermal gold deposit systems in the same area. An initial 187Os/188Os ratio of 0.25±0.04 (1σ) and a γos value of 99 on average display the participation of large quantities of crustal components into the rock-forming and ore-forming system during mineralization and magmatic emplacement. 相似文献
15.
Dating of metallic ore deposits has been one of the problems concerned with by ore geologists for many years.The establishment of the Re-Os Isotope Laboratory at the Institute of Rock and Mineral Analysis,Chinese Academy of Geological Sciences, has provided us with a new technique to carry out geochronological studies of molybdenum ores.As one of the most important Re-bearing minerals, molybdenite contains almost no common osmium, but ^187Os was derived completely from decay of ^187Re, with ^187Os content as the function of Re content in the mineral .An ID-ICP-MS technique has been used in this study,and Re-Os isotopic ages of several large molybdenum deposits of differ-ent types from the East Qinling molybdenum belt have been determined.It is indicated that the Huanglongpu carbonatite vein-type molybdenum-(lead) deposit has a Re-Os age corresponding to Indosinian,while the rest porphyry-type molybdenum deposits and porphyry-skarn-type molybdenum-(tungsten) deposits have Re-Os ages corresponding to Yenshanian. 相似文献
16.
辉钼矿中Re、Os含量高且几乎不含普通Os,通常被认为是开展金属矿床定年的理想对象。然而,在一些矿床中辉钼矿常以浸染状产出,矿物颗粒微小,挑纯难度较大,本文尝试使用含辉钼矿的岩石样品进行测年实验。选择研究程度较高、年龄数据较多的德兴斑岩铜矿田朱砂红矿床的4件含辉钼矿岩石样品进行了Re_Os同位素定年,结果获得等时线年龄为172.6±2.6 Ma,与前人已获得的年龄数据基本一致,说明该年龄数据可靠,样品中的硅酸盐矿物对定年结果没有影响。德兴斑岩铜矿田中3个矿床的辉钼矿Re_Os年龄与花岗闪长斑岩的锆石U_Pb年龄相一致,表明其矿化与斑岩侵入体直接相关。而前人获得的Rb_Sr年龄及K_Ar年龄与近年得到的Re_Os、U_Pb年龄数据存在差别的原因可能是后期热液蚀变及热事件破坏或重置了Rb_Sr和K_Ar同位素体系。 相似文献
17.
Re-Os Dating of Sulfides from the Volcanogenic Massive Sulfide Deposit at Gacun, Southwestern China 总被引：1，自引：0，他引：1
Abstract. The Re-Os isotopic compositions of sulfide ores were analyzed for the Gacun, a volcanogenic massive sulfide deposit in southwestern China, to constrain the timing of mineralization. Sulfide ores from the deposit have a wide range of Re and Os concentrations, varying from 80.2 to 1543.2 ppb and from 0.307 to 8.83 ppb, respectively, and yielded a limited field of high 187 Re/188 Os and high 187 Os/188Os ratios, ranging from 1452 to 3309 and from 5.77 to 13.24, respectively. All sulfide samples yielded an isochron with an age of 217±28 Ma and an initial 187 Os/188 Os ratio of around 0.52±0.73. The Re-Os isochron age agrees with ages previously constrained by the other isotopic dating of the host rocks and fossil strata for the deposit. The rhythmic variation in 187 Os/188 Os and 187 Re/188 Os ratios within massive sulfide zone records a complicated process for ore-forming fluids episodically vented into the brine pool on the Mesozoic seafloor. 相似文献
18.
中条山铜矿峪斑岩铜矿金属硫化物的铼-锇同位素年龄及地质意义 总被引：11，自引：4，他引：7
Re- Os同位素测年法是测定金属矿床成矿年龄较直接、有效的方法。作者对中条山铜矿峪斑岩铜矿中的含辉钼矿硫化物采用 ICP- MS同位素稀释法进行 Re- Os同位素年龄测定。首次获得 2个 Re- Os同位素等时线年龄 ,其值分别为 (2 94 7± 2 8)× 10 6a与 (2 10 8± 32 )× 10 6a。这些年龄数据有力地说明铜矿峪斑岩铜矿的形成不是一个单一的成矿过程 ,而是一个多期的复合成矿过程。它为确定铜矿峪斑岩铜矿的成矿年龄及建立该矿床的成矿演化模式奠定了重要基础 相似文献