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Conventional diamond exploration seldom searches directly for diamonds in rock and soil samples. Instead, it focuses on the search for indicator minerals like chrome spinel, which can be used to evaluate diamond potential. Chrome spinels are preserved as pristine minerals in the early Paleozoic (∼465 Ma), hydrothermally altered, Group I No. 30 pipe kimberlite that intruded the Neoproterozoic Qingbaikou strata in Wafangdian, North China Craton (NCC). The characteristics of the chrome spinels were investigated by petrographic observation (BSE imaging), quantitative chemical analysis (EPMA), and Raman spectral analysis. The results show that the chrome spinels are mostly sub-rounded with extremely few grains being subhedral, and these spinels are macrocrystic, more than 500 µm in size. The chrome spinels also have compositional zones: the cores are classified as magnesiochromite as they have distinctly chromium-rich (Cr2O3 up to 66.56 wt%) and titanium-poor (TiO2 < 1 wt%) compositions; and the rims are classified as magnetite as they have chromium-poor and iron-rich composition. In the cores of chrome spinels, compositional variations are controlled by Al3+-Cr3+ isomorphism, which results in a strong Raman spectra peak (A1g mode) varying from 690 cm−1 to 702.9 cm−1. In the rims of chrome spinel, compositional variations result in the A1g peak varying from 660 cm−1 to 672 cm−1. The morphology and chemical compositions indicate that the chrome spinels are mantle xenocrysts. The cores of the spinel are remnants of primary mantle xenocrysts that have been resorbed, and the rims were formed during kimberlite magmatism. The compositions of the cores are used to evaluate the diamond potential of this kimberlite through comparison with the compositions of chrome spinels from the Changmazhuang and No. 50 pipe kimberlites in the NCC. In MgO, Al2O3 and TiO2 versus Cr2O3 plots, the chrome spinels from the Changmazhuang and No. 50 pipe kimberlites are mostly located in the diamond stability field. However, only a small proportion of chrome spinels from No. 30 pipe kimberlite have same behavior, which indicates that the diamond potential of the former two kimberlites is greater than that of the No. 30 pipe kimberlite. This is also supported by compositional zones in the spinel grains: there is with an increase in Fe3+ in the rims, which suggests that the chrome spinels experienced highly oxidizing conditions. Oxidizing conditions may have been imparted by fluids/melts that have a great influence on diamond destruction. Here, we suggest that chrome spinel compositions can be a useful tool for identifying the target for diamond potential in the North China Craton. 相似文献
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Simple, rapid, and sensitive spectrophotometric methods have been proposed for the determination of cationic surfactants (CS) as cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium (DTAB), and cetylpyridinium bromide (CPB). The methods are based on the effects of CSs on the complexes of Al3+ and Be2+ with Chrome Azurol S (CAS). The optimum reaction conditions such as CAS concentration, metal ion concentration, and pH have been studied and found to be 2.0 × 10?4 mol L?1 CAS, 0.5 mg L?1 Al3+ or 0.4 mg L?1 Be2+ and pH 5.4. The analytical characteristics of the methods such as limit of detections, limit of quantifications, and linear ranges have been obtained. CTAB, CPB, and DTAB could be determined by the Al–CAS complex in the ranges of 0.50–40.00, 0.20–10.00, and 0.40–10.00 µmol L?1, and for the Be–CAS complex in the ranges of 0.08–5.00, 0.08–3.00, and 0.20–6.00 µmol L?1, respectively. The limit of the detections of the method for the determination of CTAB, CPB, and DTAB for the Be–CAS complex has been found as 0.025, 0.024, and 0.061 µmol L?1, respectively. The interfering effect of some anions and cations was also tested. The method was applied to the determination of CS CTAB in conditioner shampoo and water samples. 相似文献
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铬铁矿贺根山蛇绿岩带地处西伯利亚板块和华北板块的汇聚部位,该带出露中国北方最大的超基性岩体群,大小有超过超过30个超基性岩块,其中自西向东分布的朝根山,贺根山,崇根山,乌兹尼黑为最大的蛇绿岩块。与超基性岩关系最密切的矿产莫过于铬铁矿,数年来很多学者针对贺根山蛇绿岩的含矿性做了大量工作(白文吉等1993,1995; Miao Laicheng et al.,2008;段明,2009,2015;黄竺,2015;王成,2016),该带分布的铬铁矿床（点）众多,有代表性矿床(点)为赫根敖拉、733和3756,然而能达到工业开采的矿床只有3756。近些年在该地区的找矿勘查工作未取得突破,笔者认为很多原因在于该区覆盖面积太大,找矿靶区定位不准以及对隐伏的矿体勘查力度不够。2013-2015年天津地质调查中心在2009~2011年度新飞的航磁资料基础之上对该区进行了航磁异常查证与评价研究工作,对该区的成矿潜力与找矿方向提出了心得认识。 相似文献
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Ccile Quantin Vojt ch Ettler Jrmie Garnier Ond&#x;ej &#x;ebek 《Comptes Rendus Geoscience》2008,340(12):872-882
Soil profiles developed on serpentinites from several localities in the Czech Republic were investigated by a combination of geochemical and mineralogical methods (selective extractions, XRD, SEM/EDS) to determine the partitioning and mobility of chromium (Cr) and nickel (Ni). Whereas Cr is released from pyroxenes, amphiboles and Cr-spinels present in the bedrock, Ni is primarily mobilized from olivines and small Fe-Ni sulphide inclusions. The results of extraction methods indicated significant differences in the availability and mobility of Cr and Ni in soils. Chromium is almost not phytoavailable, as indicated by the DTPA extractions. The selective extractions showed that Cr is tightly bound to well-crystallised Fe-oxides and primary rock-derived phases. In contrast, Ni is substantially more mobile in soil, being mainly controlled by Mn-oxides and amorphous/less crystallised Fe-oxides. The DTPA extraction indicated that up to 10% of total Ni might be phytoavailable. 相似文献
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An on‐line solid phase extraction method for the preconcentration and determination of Cu(II) by flame atomic absorption spectrometry has been described. The procedure is based on the retention of Cu(II) ions at pH 6.0 on a minicolumn packed with Amberlite XAD‐1180 resin impregnated with chrome azurol S. After preconcentration, Cu(II) ions adsorbed on the impregnated resin were eluted by 1 mol L?1 HNO3 solution. Several parameters, such as pH, type of eluent, flow rates of sample and eluent solutions, amount of resin were evaluated. At optimized conditions, for 3.5 min of preconcentration time, the system achieved a detection limit of 1.0 µg L?1, and a relative standard deviation of 1.2% at 0.2 µg mL?1 copper. An enrichment factor of 56‐fold was obtained with respect to the copper determination. The proposed method was successfully validated by the analysis of standard reference material (TMDA 54.4 lake water) and recovery studies. The method was applied to the preconcentration of Cu(II) in natural water samples. 相似文献
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通过柴达木盆地察尔汗地区湖相沉积物的L*、a*和b*值与有关地球化学指标的相关关系分析,对湖相沉积物颜色指标在古气候研究中的意义进行了探讨,并据此分析了130 ka B.P.以来该区的古气候演变过程。结果表明,L*值与沉积物碳酸盐含量正相关,L*值高时,气候冷干,碳酸盐含量较高;反之,气温上升,湿度增加。b*值和a*值与沉积物中Fe、Mg含量相关,高a*值反映气温较高,b*值可用于反映湖水深度变化和有效湿度的变化,b*值高,湖水浅,氧化作用增强。察尔汗地区色度曲线反映的气候变化特征与其他的气候指标曲线相吻合。 相似文献
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首次将金厂金矿床铬绢云母划分为二个矿物为十个矿物种和三个生成世代，并总结出其成因矿物学特征，提出铬绢云母系列的生成与金矿的形成关系密切，铬绢云母系列是该区找金的重要标志。 相似文献
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Serpentinites in the Eastern Desert (ED) of Egypt represent integral components of the ophiolites. Metamorphic textures of the serpentinites preserve the complex mineralogical evolution from primary peridotite through metamorphism, and late-stage hydrothermal alteration. Two textural types are distinguished in the olivines of the present serpentinized peridotites, namely (a) highly-strained olivine grains with kink bands, as in the deformed mantle tectonites from ophiolites, and (b) non-strained grains. The latter may represent recrystallized crystals during later thermal metamorphic events due to the intrusion of granite. On the basis of X-ray diffraction analysis, antigorite is the main serpentine minerals with lesser chrysotile and lizardite which indicates that serpentinites were formed under prograde metamorphism. Relict primary minerals of the serpentinites are Cr-spinel, olivine and pyroxene. Chrome spinel relicts have high Cr# (0.60–0.80), whereas primary olivines are Mg-rich nature (Fo = 89–96). Geochemical compositions of serpentinites indicate that they formed not at mid-ocean ridges but at spreading centers associated with subduction zones and this could have happened in a supra-subduction zone either in the fore-arc or back-arc environments. Mineral compositions of primary chrome spinels and olivines are similar to those of modern fore-arcs. High Cr# in the relict chrome spinels and Fo in the primary olivines of serpentinites indicate that they are residual after extensive partial melting and originated by sea-floor spreading during subduction initiation. 相似文献
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