Geochemical characteristics of the platinum-group elements in the Abulangdang ultramafic intrusion,Sichuan Province,China

The contents of the platinum-group elements (PGEs: Os, Ir, Ru, Rh, Pt, Pd) in the Abulangdang ultramafic intrusion have been determined using ICP-MS after nickel sulfide fire assay preconcentration. Different samples show significant differences in absolute PGE abundance. They display a pronounced negative incline in mantle-normalized patterns which are characterized by strong enrichment in IPGEs (Os, Ir, Ru) and depleting to slight enrichment in PPGEs (Rh, Pt, Pd). The characteristics of PGE distribution in the Abulangdang rocks are due to the combined action of sulfide and non-sulfide (spinel/chromite or alloy or micro-granular aggregation of metals). In comparison with the mafic-ultramafic rocks which host Ni-Cu-PGE deposits in the Emeishan Large Igneous Province (ELIP), it is assumed that the Abulangdang ultramafic intrusion may be the product of early-stage magma activity in the ELIP.     

改进的卡洛斯管溶样等离子体质谱法测定地质样品中低含量铂族元素及铼的含量

报道了一个改进的卡洛斯管溶样等离子体质谱法测定地质样品中铂族元素及Re含量的新方法。将封闭的卡洛斯管置于高压釜中,然后在高压釜中加水,密封在高压釜中的水在高温下产生的外压将会抵消卡洛斯管中由酸产生的内压,这样就可以避免传统的卡洛斯管在高温高压下可能发生爆炸的危险。由此可以加大取样量,降低铂族元素测定过程中的块金效应及检出限,使超低含量铂族元素的测定成为可能。12g样品在75mL卡洛斯管中用35mL王水于320℃溶解15h,基本上可以使各种地质样品中的铂族元素矿物完全溶解。一次溶样可以测定全部铂族元素及Re,全流程空白值极低,国际标样测定结果稳定可靠。     

沂水杂岩中超镁铁质岩的岩石地球化学特征

主要以捕虏体形式存在于沂水岩浆杂岩和变质杂岩中的超镁铁质岩石不发育鬣刺结构,岩石化学组成以高MgO和低SiO2、TiO2、K2O含量为主要特征。按岩石中是否含有橄榄石大致可以分为橄榄辉石岩和尖晶角闪二辉石岩两种,前者以强烈发育蛇纹石化为特征,矿物组合以单斜(透)辉石+橄榄石为主(偶见斜方辉石),蚀变矿物组合为蛇纹石±铬铁矿+磁铁矿±角闪石±尖晶石等;后者以局部发育滑石化为特征,矿物组合以斜方(古铜)辉石+单斜(透)辉石+尖晶石为主,其次是角闪石+磁铁矿±滑石等。岩石总体以稀土元素总量(∑REE)相对较低、LREE/HREE=1.64~4.40为特征,稀土元素的球粒陨石标准化配分图解显示所有样品均具Eu和Ce的负异常,除3个橄榄辉石岩样品外,多数样品无明显的轻稀土元素、轻重稀土元素和重稀土元素分异。岩石的微量元素组成以不相容元素Rb、Ba、U、Nb、Sr、Zr等具有明显不同的异常为特征:Ba、Nb呈现负异常,而Rb、U呈现正异常,Sr部分呈正异常,Zr和Ti负异常出现在橄榄辉石岩中,其他样品无Zr异常。样品YS0631的SHRIMP锆石U-Pb定年结果显示其变质锆石年龄值为2 560~2 605 Ma;另有一颗结晶锆石的年龄值为2 719 Ma,εHf(t)值为8.2,亏损地幔模式年龄为2 680 Ma。综上所述,该超镁铁质岩石源于地幔,形成于新太古代早期,随后遭受深熔及岩浆作用影响,经历了变质作用的改造。     

Petrogenesis of garnet-bearing ultramafic rocks and associated eclogites in the Su-Lu ultrahigh-P metamorphic terrane, eastern China

Ultramafic blocks that themselves contain eclogite lenses in the Triassic Su-Lu ultrahigh-P terrane of eastern China range in size from hundreds of metres to kilometres. The ultramafic blocks are enclosed in quartzofeldspathic gneiss of early Proterozoic age. Ultramafic rocks include garnetiferous lherzolite, wehrlite, pyroxenite, and hornblende peridotite. Garnet lherzolites are relatively depleted in Al₂O₃ (<3.8wt%), CaO (<3.2%) and TiO₂ (<0.11 wt%), and are low in total REE contents (several p.p.m.), suggesting that the rocks are residual mantle material that was subjected to low degrees of partial melting. The eclogite lenses or layers within the ultramafic rocks are characterized by higher MgO and CaO, lower Al₂O₃ and TiO₂ contents, and a higher CaO/Al₂O₃ ratio compared to eclogites enclosed in the quartzofeldspathic gneiss. Scatter in the plots of major and trace elements vs. MgO, REE patterns and La, Sm and Lu contents suggest that some eclogites were derived from melts formed by various degrees (0.05–0.20) of partial melting of peridotite, and that other eclogites formed by accumulation of garnet and clinopyroxene ± trapped melt in the upper mantle. Both ultramafic and eclogitic rocks have experienced a complex metamorphic history. At least six stages of recrystallization occurred in the ultramafic rocks based on an analysis of reaction textures and mineral compositions. Stage I is a high temperature protolith assemblage of Ol + Opx + Cpx + Spl. Stage II consists of the ultrahigh-pressure assemblage Ol + Cpx + Opx + Grt. Stage III is manifested by the appearance of fine-grained garnet after coarse-grained garnet. Stage IV is characterized by formation of kelyphitic rims of fibrous Opx and Cpx around garnet, and replacement of garnet by spinel and pargasitic-hornblende. Stage V is represented by the assemblage Ol + Opx + Prg-Hbl + Spl. The mineral assemblages of stages VI_A and VI_B are Ol + Tr-Amp + Chl and Serp + Chl ± talc, respectively. Garnet and orthopyroxene all show a decrease in MgO with retrogressive recrystallization and Na₂O in clinopyroxene also decreases throughout this history. Eclogites enclosed within ultramafic blocks consist of Grt + Omp + Rt ± Qtz ± Phn. A few quartz-bearing eclogites contain rounded and oval inclusion of polycrystalline quartz aggregates after coesite in garnet and omphacite. Minor retrograde features include thin symplectic rims or secondary amphiboles after Cpx, and ilmenite after rutile. P-T estimates indicate that the ultrahigh-metamorphism (stage II) of ultramafic rocks occurred at 820-900d? C and 36-41 kbar and that peak metamorphism of eclogites occurred at 730-900d? C and >28 kbar. Consonant with earlier plate tectonic models, we suggest that these rocks were underplated at the base of the continental crust. The rocks then underwent ultrahigh-pressure metamorphism and were tectonically emplaced into thickened continental crust during the Triassic collision between the Sino-Korean and Yangtze cratons.     

Origin of ultramafic xenoliths in high-Mg diorites from east-central China based on their oxidation state and abundance of platinum group elements

Ultramafic xenoliths are abundant in late Mesozoic high-Mg diorites at Laiwu, western Shandong Province; they are composed of dunite (>80 vol.%) with minor harzburgite (<10 vol.%) and olivine (Ol)-pyroxenite (<10 vol.%). We determined the abundance of siderophile and chalcophile elements of representative samples of xenoliths, and calculated oxidation conditions based on mineral chemistry. Bulk compositions of harzburgite show high Cr (2640–3430 ppm), Co (103–111 ppm), Ni (2210–2400 ppm), and high Ir-type platinum group elements (PGE) (IPGE, 14.0–17.8 ppb), with high ratios of IPGE to Pt-type PGE (PPGE, 3.1–6.3). Spinel contains moderate Cr (Cr# = 0.41–0.61). Our data suggest that the harzburgite is the residue of partial melting. The occurrence of orthopyroxene replacing Ol suggests that harzburgite was metasomatized by a Si-rich melt. Dunite contains high concentrations of Cr (> 3800 ppm), Co (>110 ppm), and Ni (>1680 ppm), and low concentrations of IPGE (<4.8 ppb), with low ratios of IPGE/PPGE (as low as 0.05), suggesting that dunite is the cumulate of a mafic melt. High Cr in chromite (Cr# > 0.7) and high Mg in Ol suggest that the parental melt was boninitic. Some Ol grains show variable, locally high Mg, up to Fo 94.3. We attribute these high values to the interaction of the Ol with abundant chromite in the cumulate. Both dunite and harzburgite indicate high log fO₂ values, ranging from fayalite-magnetite-quartz (FMQ) +1.4 to +2.4. The values contrast with fO₂ below that of the graphite–CO₂ buffer for xenoliths in early Palaeozoic diamondiferous kimberlite pipes in the area. The data indicate a sharp increase in fO₂ during Mesozoic time, likely caused by subduction of the Tethyan oceanic plate before collision with the Yangtze continent below the eastern margin of the North China craton.     

Carius管直接蒸馏快速分离锇方法的改进

蒸馏法是Re-Os同位素测量体系从基质中分离Os的一种快捷方法,但装置繁琐,清洗工作量大,已成为限制其应用的瓶颈。文章对Carius管传统蒸馏装置进行了改进,利用橡胶滴头代替硅胶管和玻璃堵头自制Carius管直接蒸馏接口装置,简化了气体进出口管路,使用电蒸笼代替电热套,对蒸馏时间、样品溶液稀释倍数和吸收液体积等蒸馏条件进行了优化。改进后的装置升温速度、稳定性和简便性得到提高,简化了实验器皿,有利于降低空白,实现在较小操作空间内大批量样品的同时处理。Carius管直接蒸馏实验结果表明,Os的回收率可达86.7%～95.2%。在长时间(2 h)蒸馏条件下,Os回收率比传统蒸馏瓶法高约41%。针对不同样品类型和测试仪器,可选择相应的蒸馏条件,有效压缩了样品处理时间,提高了测量计数。对Re-Os定年标准物质GBW 04436(JDC)测定5次的模式年龄为(139.5±1.9)Ma～(142.0±2.1)Ma,标准物质GBW 04435(HLP)测定2次的模式年龄为(220±3.3)Ma～(223.0±3.2)Ma,分别与标准值(139.6±3.8)Ma和(221.4±5.6)Ma在不确定度范围内一致。改进后的Carius管直接蒸馏装置已应用于日常样品处理。     

苏鲁超高压变质带岗上超镁铁质岩铬尖晶石形成过程——铬成矿新机制

岗上超镁铁质岩主要由纯橄岩和石榴橄榄岩组成,主要组成矿物有橄榄石、铬尖晶石、石榴子石、单斜辉石和斜方辉石等。铬尖晶石的Cr#[Cr/(Cr+Mg)×100]从51到89变化,铬尖晶石矿物表现为4期次演化的特点,反映了从岩浆期向榴辉岩相、角闪岩相和绿片岩相演化特征。随着超镁铁质岩的演化,铬尖晶石中Cr#不断增大(51增大到89),而铬尖晶石Mg#[Mg×100/(Mg+Fe2+)]不断减少,氧逸度不断增加。在绿片岩相—绿片角闪岩相退变质过程中,铬尖晶石中Cr、Mg和Al减少,Fe相对增加,产生富Cr尖晶石变质作用样式。晚期剪切变形等次生变化有利于富铬铬尖晶石矿物的形成和铬尖晶石的富集。同时,角闪岩相和绿片岩相变质作用使铬尖晶石富集呈现容易开采的条带状,降低了铬尖晶石与其他硅酸盐矿物的结合强度,降低了开采强度和成本,使原本不易于开采的铬铁矿矿体变得可以开采。这些意味着铬铁矿矿体展布要结合后期变质作用进行综合分析。     

Revisiting platinum group elements of Late Permian coals from western Guizhou Province, SW China

Twenty five coal samples from the Late Permian coal-bearing strata in Weining, Nayong, and Zhijin, western Guizhou Province, SW, China, were analyzed for platinum group elements (PGEs). The coal ashes were digested by the Carius tube technique and accurately measured by isotope dilution-inductively coupled plasma mass spectrometry (ID-ICP-MS) for all PGEs. The results are much lower than the previous reported values. Our study suggested that the previously reported PGE values are incorrect and may due to the polyatomic interferences in ICP-MS measurements. In our study, samples from the Weining coalfield have the lowest PGE contents (from 0.019 Ir to 0.42 ng/g Pd), which represent the PGE background value in coal in western Guizhou province. Some of the coals have Pt and Pd contents about 20-times higher than the background value, indicating PGEs are concentrated. We also reported new and reliable PGE data and background value of coal in western Guizhou province, SW, China, and suggested to rework the PGE background values of Chinese coals.     

大别造山带毛屋超镁铁岩的铂族元素研究

采用镍锍火试金法结合ICP-MS分析了毛屋斜方辉石岩和石榴二辉岩样品中的Ir、Ru、Rh、Pt和Pd的含量,结果显示其铂族元素(PGE)的含量随岩石类型无规律性的变化,原始地幔标准化后的铂族元素分布模式呈负斜率,Pd、Ir发生了分异。毛屋超镁铁岩铂族元素特征的形成受岩石中铂族元素的存在相制约,PPGE富集在富Cu硫化物,而IPGE以类似残留相、不熔的单硫化物固熔体形式存在,其中地壳混染也起了一定的作用;同时,成岩过程中流体的存在造成了Pt和Pd的活化。因此,单硫化物固熔体和流体的共同作用形成了毛屋超镁铁岩类似残留地幔岩的铂族元素分布特征。     

Geochemistry of Platinum Group Elements in Mafic—Ultramafic Rocks of Xinjie Intrusion

The platinum group elements(PGE)in the mafic-ultramafic suite in the Xinjie layered intrusion and associated basalts and syenites were analyzed using neutron activation techniques after fire-assay preconcentration.On this basis,the geochemistry of the platinum group during the magmatic stage is discussed.With respect to PGE distribution,the Xijie layered intrusion is similar to the Bushveld ferruginous ultramafic series and is distinct from komatiite and Alpine-type peridotite.It is also similar to the Emeishan basalt in PGE characteristics,implying that the original magmas of them may be of the same type.     

Carius管溶样-标准加入电感耦合等离子体质谱法测定土壤中碘

建立了利用Carius管提取与标准加入电感耦合等离子体质谱法测定土壤中碘的方法。样品用φ=10%的NH.H2O溶液于密封的Carius管中150℃提取4 h,溶液适当稀释后离心分离沉淀,取出5等份样品上清液,分别加入不同浓度的碘标准储备液,用电感耦合等离子体质谱法测定溶液中的碘,以126Te作为内标。应用该方法分析了土壤国家一级标准物质GBW07404、GBW 07406、GBW 07407中碘的含量分别为(9.58±0.02)μg/g、(19.83±0.01)μg/g和(18.88±0.03)μg/g。分析结果与标准值相符。碘的检出限为0.02μg/g。     

镁铁—超镁铁质岩浆中铂族元素的富集机理：综述与实例

目前陆地上可利用的铂族元素(PGE)资源主要来自与镁铁—超镁铁质岩浆密切相关的岩浆硫化物矿床。岩浆硫化物矿床成矿理论关注的一个重要问题就是镁铁—超镁铁质岩浆中PGE的富集机理。经典成矿理论认为,由于PGE在平衡的硫化物熔体与硅酸盐熔体之间具有极高的分配系数(105～106),PGE富集成矿主要与成矿体系中硅酸盐熔体与硫化物熔体的质量比有关(R-factor)。但是近些年来,许多新的实验岩石学结果和天然矿石样品纳米尺度PGE赋存状态的观测结果对这一经典理论提出了挑战。本文列举了一些相关的研究实例,显示硅酸盐熔体中的PGE纳米颗粒可以被硫化物或铬铁矿机械捕获、并通过定向附着生长、聚集、粗化和融合,最终形成纳米颗粒集合体和纳米合金。另外,岩浆中半金属元素(TABS,即Te、As、Bi、Sb、Sn)和Se可以与PGE优先形成各种互化物,从而富集于砷化物、铋化物、碲化物或硒化物中,而非硫化物中。因此,镁铁—超镁铁质岩浆体系中PGE的富集可能不仅受其在硫化物熔体中极高的分配系数控制,一些物理过程导致的PGE分配以及半金属元素对PGE的富集作用也不容忽视。由于矿石中的铂族矿物一般为纳—微米级,采用聚...     

地质样品中铂族元素的分析测定方法

文中阐述并归纳了近年地质样品中铂族元素的分离、富集及测试方法方面的最新进展。铂族元素本身的超痕量性,要求实验过程中对空白值的控制,干扰元素的扣除和检测限的降低更为严格,同时要克服块金效应。文中对消解过程中常用的火试金法、酸溶、碱熔方法和卡洛斯管法(Carius tube),分离富集过程中的Te共沉淀和离子交换法,测试手段中的原子光谱法、中子活化法和等离子质谱法等方法的最新进展进行了总结。由于复杂的地质样品中PGE的浓度范围不一、赋存形式多样,要求在具体样品分析过程中灵活地搭配使用各种分离富集和检测方法,结合笔者所在实验室在实验过程中发现的问题,对各种不同类型地质样品中铂族元素的分离富集、样品处理及测定方法也进行了总结。     

西昆仑西北缘柯牙吾齐超镁铁岩的发现及成因

The discovery of ultramafic rocks in the northwestern margin of west Kunlun is of great significance for discussing the tectonic evolution and related mineral resources potential in the western section of west Kunlun. This work conducted microscopic identification, and major and trace element tests on seven ultramafic rock samples. Results show that the ultramafic rocks occur as intermittent veins, and are dominated by serpentinized pyroxene perido-tite. The ultramafic rocks are characterized by relatively low SiO₂ (42.14% ~ 47.43%), low Ti O₂(0.03%-0.24%), high Mg^# (24.69% ~ 31.22%), high FeO^T(7.05% ~ 11.65%)and low alkali(K₂O + Na₂O = 0.55%-0.88%). Mg^# values range from 79. 98 to 86. 70. The m/f ratio of the samples lies in a range of 3. 96 ~ 7. 82. The total amount of REE (£ REE) in the samples is not high (11.41 x 10 6-17. 84 x 10 6), and the LREE/HREE ratio is 2. 81-5. 69. <5Eu shows weakly positive Eu anomaly. The content of compatible elements(Ni, Cr and Co)is high. In the primitive mantle-normalized spider diagram of trace elements, they are enriched in LILE(Rb, Ba, U, Sr and Pb), and relatively depleted in HFSE(Nb, P, Zr, Hf, Ti, etc.), indicating the enrichment of light rare earth elements. Combined with regional tectonic setting, it is suggested that the closure of the Paleotethys ocean resulted in the extension after collision in the Late Triassic, and the magma from the loss mantle was transformed by subduction fluid or melt in the early stage, and intruded along deep fault, which experienced certain crust mixing in the process to finally form the Keyawuqi ultramafic rocks. © 2022 Editorial Board of Geology and Exploration. All rights reserved.     

西藏松多地区超基性岩地球化学特征及对松多古特提斯洋演化的启示

唐加-松多古特提斯缝合带的提出改变了地学界对青藏高原古特提斯演化格局的认识。为进一步约束唐加-松多古特提斯缝合带中蛇绿岩的岩石成因及类型, 以松多地区的超基性岩为研究对象, 对其进行了岩石学和全岩地球化学研究。结果显示, 松多地区超基性岩与原始地幔相比具有较高的MgO和TFe2O3含量, 以及较低的Al2O3和TiO2含量。样品稀土元素总含量介于4.04×10-6~9.31×10-6之间, 大部分低于原始地幔值。稀土元素配分曲线呈较宽缓的"U"型, 轻稀土元素较富集。微量元素分布形式与全球深海橄榄岩的微量元素分布形式基本一致, 具有明显的Th、Nb负异常, 大部分样品具有轻微的Zr、Hf负异常。定量模拟估算表明, 研究区超基性岩主要为尖晶石二辉橄榄岩地幔批式熔融后的难熔残留体, 熔融程度大于25%, 并具一定程度石榴子石相熔融的特征, 未受到后期岩石-熔体反应的改造, 其原岩应为亏损的深海橄榄岩。结合区域研究成果, 松多地区超基性岩可能形成于大洋中脊(MOR)环境, 为典型的大洋中脊玄武岩(MORB)型蛇绿岩端元之一。     

Geochemical characteristics of mafic and ultramafic rocks from the Naga Hills Ophiolite,India:Implications for petrogenesis

The Naga Hills Ophiolite(NHO) represents one of the fragments of Tethyan oceanic crust in the Himalayan Orogenic system which is exposed in the Phek and Kiphire districts of Nagaland, India. The NHO is composed of partially serpentinized dunite, peridotite, gabbro, basalt, minor plagiogranite,diorite dyke and marine sediments. The basalts are mainly composed of fine grained plagioclase feldspar, clinopyroxene and orthopyroxene and show quenching and variolitic textures. The gabbros are characterized by medium to coarse grained plagioclase, orthopyroxene and clinopyroxene with ophitic to sub-ophitic textures. The ultramafic cumulates are represented by olivine, Cpx and Opx.Geochemically, the basalts and gabbros are sub-alkaline to alkaline and show tholeiitic features.The basalts are characterized by 44.1-45.6 wt.% of SiO_2 with 28-38 of Mg#, and the gabbros by38.7-43.7 wt.% of SiO_2, and 26-79 of Mg#. The ultramafic rocks are characterized by 37.4-52.2 wt.% of SiO_2, and 80-88 of Mg#. In multi-element diagrams(spidergrams) both basalts and gabbros show fractionated trends with strong negative anomalies of Zr. Nb. Sr and a gentle negative anomaly of P.However, the rare earth element(REE) plots of the basalts and gabbros show two distinct patterns. The first pattern, represented by light REE(LREE) depletion, suggests N-MORB features and can be interpreted as a signature of Paleo-Tethyan oceanic crust. The second pattern, represented by LREE enrichment with negligible negative Eu anomaly, conforms to E-MORB, and may be related to an arc tectonic setting. In V vs. Ti/1000, Cr vs. Y and AFM diagrams, the basalts and gabbros plot within Island Arc Tholeiite(IAT) and MORB fields suggesting both ridge and arc related settings. The ultramafic rocks exhibit two distinct patterns both in spidergrams and in REE plots. In the spidergram, one group displays highly enriched pattern, whereas the other group shows near flat pattern compared to primordial mantle. In the REE plot, one group displays steeper slopes [(La/Yb)N = 4.340-4.341], whereas the other displays moderate to flat slopes [(La/Yb)N = 0.97-1.67] and negative Eu-anomalies. Our study suggests that the ultramafic rocks represent two possible mantle sources(fertile and refractory).     

利用同一化学流程分析地质样品中的铂族元素含量和铼-锇同位素组成

报道了利用一次溶样和同一化学流程分离富集地质样品中铂族元素(Pt、Pd、Os、Ir和Ru)和Re的方法.该化学流程包括以下几个步骤:(1) Carius管溶样法分解岩石样品中富集铂族元素的矿物;(2)四氯化碳萃取法分离出Os;(3)微蒸馏法进一步纯化Os;(4)阳离子交换树脂法将铂族元素(Pt、Pd、Ir和Ru)以及R...     

The Design of Re‐usable Carius Tubes for the Determination of Rhenium,Osmium and Platinum‐Group Elements in Geological Samples

The traditional Carius tube technique is cumbersome and requires skilful work to seal the Carius tube, which can be used only once. We describe a modification to the technique that does not require the use of a high‐temperature welding torch to melt the Carius tube to seal it. The newly designed Carius tube consists of a main body with a 3 mm‐thick glass wall, a neck and head with walls 4 mm in thickness, and an efficient screw‐thread stopper. These new features allowed the tube to be used repeatedly. We demonstrate relatively low procedural blanks derived for Re and Os, and platinum‐group elements (PGEs), using the redesigned tube. A temperature of 220 °C could be reached for about 5 ml of HNO₃ for a 47 ml tube and for 32 ml of inverse aqua regia for a 200 ml tube. This digestion technique can be used for routine analysis of Re and PGEs in geological samples.