Bayan Obo Controversy: Carbonatites versus Iron Oxide‐Cu‐Au‐(REE‐U)

The Bayan Obo Fe‐REE‐Nb deposit is the world’s largest rare earth element (REE) resource and its genesis has been the subject of much debate for many years. The most popular are the carbonatite‐related and hydrothermal Fe oxide‐Cu‐Au‐(REE‐U) genetic models. Comparisons of geologic setting, lithology, mineral assemblages, metal associations, geochemistry (particularly REE and light REE/heavy REE ratios), fluid chemistry and isotopics indicate that the Bayan Obo deposit shares features of both types, which are classified differently; that is, the carbonatites model is host‐rock based, while the Fe oxide‐Cu‐Au‐(REE‐U) model is essentially mineral assemblage and metal association based. A speculative classification scheme is tentatively put forward to link the two models, but many questions remain for further studies.     

X射线荧光滤纸片法测定纯氧化铥中主量氧化铥及相邻稀土氧化物杂质

本文拟定了一种采用滤纸片法制样,X射线荧光直接测定纯氧化铥中氧化铥主量以及氧化钬、氧化铒、氧化镱、氧化镥和氧化钇等稀土杂质含量的分析方法。其测定下限为:Tm_2O_30.11％、Ho_2O_30.20％、Er_2O_3 0.05％、Yb_2O_3 0.20％、Lu_2O_3 0.07％、Y_2O_3 0.40％。方法精度为0.2％～8.0％,对人工合成样品及试样分析结果表明方法准确度良好。方法操作简便快速、试剂耗费少、可用于稀土生产中低纯氧化铥产品的分析。     

Gold Mineralization in Banded Iron Formation in the Amalia Greenstone Belt,South Africa: A Mineralogical and Sulfur Isotope Study

The Blue Dot gold deposit, located in the Archean Amalia greenstone belt of South Africa, is hosted in an oxide (± carbonate) facies banded iron formation (BIF). It consists of three stratabound orebodies; Goudplaats, Abelskop, and Bothmasrust. The orebodies are flanked by quartz‐chlorite‐ferroan dolomite‐albite schist in the hanging wall and mafic (volcanic) schists in the footwall. Alteration minerals associated with the main hydrothermal stage in the BIF are dominated by quartz, ankerite‐dolomite series, siderite, chlorite, muscovite, sericite, hematite, pyrite, and minor amounts of chalcopyrite and arsenopyrite. This study investigates the characteristics of gold mineralization in the Amalia BIF based on ore textures, mineral‐chemical data and sulfur isotope analysis. Gold mineralization of the Blue Dot deposit is associated with quartz‐carbonate veins that crosscut the BIF layering. In contrast to previous works, petrographic evidence suggests that the gold mineralization is not solely attributed to replacement reactions between ore fluid and the magnetite or hematite in the host BIF because coarse hydrothermal pyrite grains do not show mutual replacement textures of the oxide minerals. Rather, the parallel‐bedded and generally chert‐hosted pyrites are in sharp contact with re‐crystallized euhedral to subhedral magnetite ± hematite grains, and the nature of their coexistence suggests that pyrite (and gold) precipitation was contemporaneous with magnetite–hematite re‐crystallization. The Fe/(Fe+Mg) ratio of the dolomite–ankerite series and chlorite decreased from veins through mineralized BIF and non‐mineralized BIF, in contrast to most Archean BIF‐hosted gold deposits. This is interpreted to be due to the effect of a high sulfur activity and increase in fO₂ in a H₂S‐dominant fluid during progressive fluid‐rock interaction. High sulfur activity of the hydrothermal fluid fixed pyrite in the BIF by consuming Fe²⁺ released into the chert layers and leaving the co‐precipitating carbonates and chlorites with less available ferrous iron content. Alternatively, the occurrence of hematite in the alteration assemblage of the host BIF caused a structural limitation in the assignment of Fe³⁺ in chlorite which favored the incorporation of magnesium (rather than ferric iron) in chlorite under increasing fO₂ conditions, and is consistent with deposits hosted in hematite‐bearing rocks. The combined effects of reduction in sulfur contents due to sulfide precipitation and increasing fO₂ during progressive fluid‐rock interactions are likely to be the principal factors to have caused gold deposition. Arsenopyrite–pyrite geothermometry indicated a temperature range of 300–350°C for the associated gold mineralization. The estimated δ³⁴S_ΣS (= +1.8 to +2.5‰) and low base metal contents of the sulfide ore mineralogy are consistent with sulfides that have been sourced from magma or derived by the dissolution of magmatic sulfides from volcanic rocks during fluid migration.     

用软锰矿直接制备高纯高比表面四氧化三锰

软锰矿经中性浸出,通过除杂净化,制备出高纯硫酸锰溶液;碱化沉淀,采用微波加热进行控制氧化合成四氧化三锰,确定了该方法的最佳工艺参数.分别用扫描电镜、透射电镜、X射线衍射仪和全自动氮吸附比表面仪对样品进行了检测,结果表明:该方法成功制备了高纯四氧化三锰,比表面积高达28.27 m2/g.     

电感耦合等离子体发射光谱法同时测定地质样品中的钍和氧化钾

同时测定地质样品中的钍和钾,可为放射性矿产资源勘探、天然放射性生态环境评价提供重要依据。对于钍,传统方法使用碱熔法分解试样分光光度法测定,此方法前处理冗长、复杂且不利于多元素的同时测定。而氧化钾一般采用酸溶法消解样品火焰原子吸收分光光度法测定,此方法测定浓度高的溶液需要稀释,检测效率较低。钍和氧化钾的分析涉及了两种配套方法。本文根据地质样品的化学成分特征,筛选出了用硝酸、氢氟酸和高氯酸为溶剂溶解样品,硝酸提取定容后,用电感耦合等离子体发射光谱法(ICP-OES)分别在波长401.913nm和766.490nm处,采用径向观测方式同时测定了钍、氧化钾的含量。钍、氧化钾的标准曲线相关系数均大于0.999,方法检出限分别为0.69μg/g、0.008%,标准物质的测定值与认定值基本一致,二者的对数误差绝对值小于0.1,相对标准偏差(RSD,n=6)小于6.0%,加标回收率在96.0%～104.0%之间,符合《地质矿产实验室测试质量管理规范》的要求。     

聚类方法在电气石颜色成因研究中的应用

天然电气石颜色多种多样,颜色成因非常复杂。为了更好了解它的颜色成因,采用统计学中的聚类方法对其颜色成因进行了分类。该分类方法以Matlab软件为工作平台,从测试数据(电子探针分析结果)中选出对电气石颜色形成起重要作用的氧化物,如TiO2,FeO,Fe2O3,MnO作为聚类分析的特征变量。以这些变量作为距离聚类分析的基础,对所研究各种颜色的电气石进行聚类。通过聚类分析研究,把电气石颜色成因的结果与其它测试方法的结果进行对比,证实本聚类方法真实可靠。     

感耦等离子体质谱法测定高纯氧化钪中15个痕量稀土杂质的研究

文章报道了用感耦等离子体质谱法测定高纯氧化钪中１５个痕量稀土杂质的研究，考察了测定中的各种干扰和影响因素，选择Ｃｓ为内标元素补颈体抑制效应和灵敏度漂移。各稀土元素的检出限在０．００５－０．０２７ｎｇ／ｍｌ范围，标准加入回收率为９４．５％－１０３．７％，精密度为０．８５％－１．９５％，称取１０ｍｇ样品，酸溶解后可直接测定高纯氧化钪中总量低于２μｇ／ｇ的１５个稀土杂质。     

河北阳原盆地井儿洼钻孔岩心氧化铁变化的古环境记录

系统分析了阳原盆地西部井儿洼钻孔剖面的Fe2O3、FeO、TFe(全铁)、Fe3 /Fe2 的变化特点,探讨了阳原古湖氧化铁地球化学特征及其所记录的气候变迁规律。结果表明,阳原盆地的沉积环境相对富集铁,气候总体较温和,垂向上的变化记录了气候的变化过程分为7个明显的阶段。0.2Ma以前以还原环境为主,以后以氧化环境为主。井儿洼岩心沉积物中全铁谱分析表明,0.78Ma之后,具有显著的21.7ka岁差周期,证明了天文因素对气候的影响,而100ka的周期不明显,这与黄土、深海沉积物的记录存在差别。另外还存在390ka、156ka、52ka、33.9ka及14.4ka等周期,表现了湖泊记录的古气候周期的复杂性。     

合成铁氧化物矿物对苯酚的吸附实验研究

采用TEM、X射线衍射分析及BET比表面积测定等手段对合成的针铁矿、赤铁矿两种矿物进行表征,对此两种矿物对苯酚的吸附特性并批处理吸附实验研究结果表明,针铁矿对苯酚的吸附量大于赤铁矿的吸附量;针铁矿吸附苯酚的pH吸收边为峰型曲线,且峰值在pH 7～8。Langmuir方程拟合结果的吻合程度较之Henry线性方程与Freundlich方程高。实验中氧化铁矿物表面对苯酚的吸附则主要表现为表面分子吸附,可能存在表面疏水性作用,而静电离子交换和表面配合吸附模式不明显。     

高分辨电感耦合等离子体质谱法测定地质样品中稀土元素的氧化物干扰研究

电感耦合等离子体质谱(ICP-MS)用于测定稀土元素经常会引起M+、MO+、MOH+离子的质谱重叠干扰,其中制约分析准确度和精密度的主要因素是多原子离子干扰,尤其是轻稀土元素的氧化物和氢氧化物对重稀土元素的干扰,以及钡的7个天然同位素形成的氧化物和氢氧化物对轻稀土元素的干扰.本文采用高温高压密闭消解地质样品,高分辨电感耦合等离子体质谱法(ICP-MS)测定其中的痕量稀土元素,研究了低、中、高三种分辨率模式下氧化物的干扰情况,确定了最佳的测定同位素和合适的分辨率.分析结果表明,在低、中分辨率模式下,轻稀土元素Ce、Pr、Nd、Sm的氧化物和Ba的氧化物干扰明显,Gd元素的测定值严重偏离;在高分辨模式下,Ba氧化物对Eu的干扰以及大部分轻稀土元素氧化物对重稀土元素的干扰基本可以消除,无需进行校正,而只有157Gd受到141pr16O的干扰突出,当样品中Pr/Gd的浓度比值大于100时,Gd的测量值必须进行数学校正.