Bias in the analysis of geological materials for gold using current methods

A consistent pattern has been observed in the results obtained for Au in three soil and two porphyry copper ore samples serving as control reference standards in geochemical analyses. The mean reported by wet chemical methods (regardless of the measurement technique) was less than the mean by fire assay-based methods which, in turn, was less than the mean reported by laboratories using direct instrumental neutron activation analysis (INAA). These data have been obtained from 16 laboratories, some employing more than one method. Compared to INAA, values obtained for Au (at the 30–300 ppb level) using aqua regia (AR) dissolution were low by 24–42%, while those reported by fire assay-based methods were low by 14–26%.Studies of these samples and 32 rocks of widely varying composition revealed that the amount of Au remaining in the residue after AR attack ranged from 4% to 59% of the total. Gold dissolved by AR was determined by graphite furnace atomic absorption spectrometry (GFAAS) after extraction into MIBK (methyl isobutyl ketone), whereas Au remaining in the residue was determined by INAA. The slope of the line obtained by plotting Au by INAA vs. the sum of Au by AR/GFAAS and Au in the residue was not significantly different from 1.0.Modifications to the AR procedure such as prior attack by HCl or HF did not improve the recovery of Au in the three reference soils. However, reduction of sample size from 10 g to 1 g while maintaining the volume of AR at about 30 ml did increase results for Au. Furthermore, addition of HF in the attack on 1-g samples yielded results virtually identical to those obtained by INAA. It is thought that the poor extraction efficiency by AR is due to non-wetting of the larger sized sample, a lack of intimate, prolonged contact between the grains of the sample and the acid mixture and the presence of insoluble gangue surrounding Au particles. Constant agitation of the sample during evaporation with AR is desirable.The mean values obtained for Au in the soils by fire assay methods were not significantly different from the results by INAA (low by 14–19%); this was not the case for the two copper ore samples (low by 26%). This probably reflects the difficulties encountered in fire assay by high concentrations of Cu which hinder effective collection and separation of Au into the Pb button. However, the accuracy of the INAA method has not been established and is dependent upon measurement procedures and the degree of certainty associated with the Au values assumed for the reference materials employed for calibration. While estimation of precision does not present a problem, accuracy is difficult to assess in the absence of certified reference materials for Au at concentrations in the 10–300 ppb range. However, it is concluded that methods based upon AR dissolution can lead to low results, the magnitude being dependent upon the sample matrix and the mineralogical association of the Au present.     

地质样品中钴、镍的分析进展

早在20世纪初期, 化学家就开展了比色法分析钴、镍的研究工作。由于比色法灵敏度不高且操作繁琐, 人们开始追求更高效的固体样品消解方法、更简便的操作以及更高灵敏度和高精度的分析技术。在样品分解方面, 逐渐发展出了酸溶和碱熔两套样品分解体系; 在仪器分析方面, 则发展出了原子吸收光谱法、等离子体光谱法、X射线荧光光谱法、等离子体质谱法等更加高效简洁的仪器分析技术。随着地质科学的发展, 电子探针和激光剥蚀电感耦合等离子体质谱微区原位分析技术, 以及多接收等离子体质谱镍同位素分析技术也逐渐发展起来。在元素分析方面, 原子吸收光谱法、等离子体光/质谱法一般需要经过酸或者碱将样品分解为溶液状态, 前处理流程较为繁琐; 而X射线荧光光谱法采用熔片或者压片进行样品制备, 前处理方法简单高效, 更加受到青睐。在同位素分析方面, 镍同位素逐渐应用到钴镍矿床研究中, 近年有望通过典型矿床剖析明确多种成矿过程镍同位素的行为与分馏机制, 如岩浆演化、热液蚀变、风化等。镍同位素的分离技术难度较高, 因此, 创新镍同位素的分离过程和测试方法, 并建立更加简便的分析流程是未来发展的重点方向。在微区分析方面, 激光剥蚀-电感耦合等离子体质谱比电子探针的样品制备简单、分析速度快、成本低, 更有发展潜力。本文总结了近百年来地质样品钴、镍分析方法的演变与突破, 对比了各类方法的优缺点, 展望了地质样品钴、镍分析方法的发展前景。

     

The combined effects of chlorine and fluorine on the viscosity of aluminosilicate melts

The effect of fluorine and fluorine + chlorine on melt viscosities in the system Na₂O-Fe₂O₃-Al₂O₃-SiO₂ has been investigated. Shear viscosities of melts ranging in composition from peraluminous [(Na₂O + FeO) < (Al₂O₃ + Fe₂O₃)] to peralkaline [(Na₂O + FeO) > (Al₂O₃ + Fe₂O₃)] were determined over a temperature range 560-890 °C at room pressure in a nitrogen atmosphere. Viscosities were determined using the micropenetration technique in the range of 10^8.8 to 10^12.0 Pa s. The compositions are based on addition of FeF₃ and FeCl₃ to aluminosilicate melts with a fixed amount of SiO₂ (67 mol%). Although there was a significant loss of F and Cl during glass syntheses, none occurred during the viscometry experiments. The presence of fluorine causes a decrease in the viscosity of all melts investigated. This is in agreement with the structural model that two fluorines replace one oxygen; resulting in a depolymerisation of the melt and thus a decrease in viscosity. The presence of both chlorine and fluorine results in a slight increase in the viscosity of peraluminous melts and a decrease in viscosity of peralkaline melts. The variation in viscosity produced by the addition of both fluorine and chlorine is the opposite to that observed in the same composition melts, with the addition of chlorine alone (Zimova M. and Webb S.L. (2006) The effect of chlorine on the viscosity of Na₂O-Fe₂O₃-Al₂O₃-SiO₂ melts. Am. Mineral.91, 344-352). This suggests that the structural interaction of chlorine and fluorine is not linear and the rheology of magmas containing both volatiles is more complex than previously assumed.     

On the behaviour of fluorine and chlorine during magmatic differentiation

The behaviour of fluorine and chlorine during differentiation is considered in the light of halogen data for granites and separated biotites from the Dartmoor granite pluton of S.W. England, hornblende-bearing ultrabasic and basic rocks from a layered intrusion at Rhiw, N. Wales, and recent literature data on halogens in apatites from the Shonkin Sag laccolith and the Skaergaard intrusion.The data indicate that whereas fluorine concentrations are highest in the late stage differentiates, chlorine concentration is highest in the earlier differentiates. It is suggested that this behaviour of the two halogens is due to their relative affinities for silicate melts. Chlorine having a low solubility in silicate melts and a strong affinity for associated aqueous phases will tend to be concentrated in early formed hydrous minerals, leaving fluorine with its strong affinity for the melt to be enriched in the late-formed hydrous minerals.     

Solar system abundances and condensation temperatures of the halogens fluorine,chlorine, bromine,and iodine

We review a large body of available meteoritic and stellar halogen data in the literature used for solar system abundances (i.e., representative abundances of the solar system at the time of its formation) and associated analytical problems. Claims of lower solar system chlorine, bromine and iodine abundances from recent analyses of CI-chondrites are untenable because of incompatibility of such low values with nuclear abundance systematics and independent measurements of halogens in the Sun and other stars. We suspect analytical problems associated with these peculiar rock types have led to lower analytical results in several studies. We review available analytical procedures and concentrations of halogens in chondrites. Our recommended values are close to previously accepted values. Average concentrations by mass for CI-chondrites are F = 92 ± 20 ppm, Cl = 717 ± 110 ppm, Br = 3.77 ± 0.90 ppm, and I = 0.77 ± 0.31 ppm. The meteoritic abundances on the atomic scale normalized to N(Si) =10⁶ are N(F) = 1270 ± 270, N(Cl) = 5290 ± 810, N(Br) = 12.3 ± 2.9, and N(I) = 1.59 ± 0.64. The meteoritic logarithmic abundances scaled to present-day photospheric abundances with log N(H) = 12 are A(F) = 4.61 ± 0.09, A(Cl) = 5.23 ± 0.06, A(Br) = 2.60 ± 0.09, and A(I) = 1.71 ± 0.15. These are our recommended present-day solar system abundances. These are compared to the present-day solar values derived from sunspots of N(F) = 776 ± 260, A(F) = 4.40 ± 0.25, and N(Cl) = 5500 ± 810, A(Cl) = 5.25 ± 0.12. The recommended solar system abundances based on meteorites are consistent with F and Cl abundance ratios measured independently in other stars and other astronomical environments. The recently determined chlorine abundance of 776 ± 21 ppm by Yokoyama et al. (2022) for the CI-chondrite-like asteroid Ryugu is consistent with the chlorine abundance evaluated for CI-chondrites here. Historically, the halogen abundances have been quite uncertain and unfortunately remain so. We still need reliable measurements from large, representative, and well-homogenized CI-chondrite samples. The analysis of F, Br, and I in Ryugu samples should also help to obtain more reliable halogen abundances. Updated equilibrium 50 % condensation temperatures from our previous work (Lodders, 2003; Fegley and Schaefer, 2010; Fegley and Lodders, 2018) are 713 K (F), 427 K (Cl), 392 K (Br) and 312 K (I) at a total pressure of 10⁻⁴ bar for a solar composition gas. We give condensation temperatures considering solid-solution as well as kinetic inhibition effects. Condensation temperatures computed with lower halogen abundances do not represent the correct condensation temperatures from a solar composition gas.     

Partitioning behavior of chlorine and fluorine in the system apatite-silicate melt-fluid

The partitioning behavior of Cl among apatite, mafic silicate melt, and aqueous fluid and of F between apatite and melt have been determined in experiments conducted at 1066 to 1150 °C and 199-205 MPa. The value of D_Cl^apatite/melt (wt. fraction of Cl in apatite/Cl in melt) ≈0.8 for silicate melt containing less than ∼3.8 wt.% Cl. At higher melt Cl contents, small increases in melt Cl concentration are accompanied by large increases in apatite Cl concentration, forcing D_Cl^apatite/melt to increase as well. Melt containing less than 3.8% Cl coexists with water-rich vapor; that containing more Cl coexists with saline fluid, the salinity of which increases rapidly with small increases in melt Cl content, analogous to the dependency of apatite composition on melt Cl content. This behavior is due to the fact that the solubility of Cl in silicate melt depends strongly on the composition of the melt, particularly its Mg, Ca, Fe, and Si contents. Once the melt becomes “saturated” in Cl, additional Cl must be accommodated by coexisting fluid, apatite, or other phases rather than the melt itself. Because Cl solubility depends on composition, the Cl concentration at which D_Cl^apatite/melt and D_Cl^fluid/melt begin to increase also depends on composition. The experiments reveal that D_F^apatite/melt ≈3.4. In contrast to Cl, the concentration of F in silicate melt is only weakly dependent on composition (mainly on melt Ca contents), so D_F^apatite/melt is constant for a wide range of composition.The experimental data demonstrate that the fluids present in the waning stages of the solidification of the Stillwater and Bushveld complexes were highly saline. The Cl-rich apatite in these bodies crystallized from interstitial melt with high Cl/(F + OH) ratio. The latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated.     

The systematics of chlorine, fluorine, and water in Izu arc front volcanic rocks: Implications for volatile recycling in subduction zones

We studied the systematics of Cl, F and H₂O in Izu arc front volcanic rocks using basaltic through rhyolitic glass shards and melt inclusions (Izu glasses) from Oligocene to Quaternary distal fallout tephra. These glasses are low-K basalts to rhyolites that are equivalent to the Quaternary lavas of the Izu arc front (Izu VF). Most of the Izu glasses have Cl ∼400-4000 ppm and F ∼70-400 ppm (normal-group glasses). Rare andesitic melt inclusions (halogen-rich andesites; HRA) have very high abundances of Cl (∼6600-8600 ppm) and F (∼780-910 ppm), but their contents of incompatible large ion lithophile elements (LILE) are similar to the normal-group glasses. The preeruptive H₂O of basalt to andesite melt inclusions in plagioclase is estimated to range from ∼2 to ∼10 wt% H₂O. The Izu magmas should be undersaturated in H₂O and the halogens at their preferred levels of crystallization in the middle to lower crust (∼3 to ∼11 kbar, ∼820° to ∼1200°C). A substantial portion of the original H₂O is lost due to degassing during the final ascent to surface. By contrast, halogen loss is minor, except for loss of Cl from siliceous dacitic and rhyolitic compositions. The behavior of Cl, F and H₂O in undegassed melts resembles the fluid mobile LILE (e.g.; K, Rb, Cs, Ba, U, Pb, Li). Most of the Cl (>99%), H₂O (>95%) and F (>53%) in the Izu VF melts appear to originate from the subducting slab. At arc front depths, the slab fluid contains Cl = 0.94 ± 0.25 wt%, F = 990 ± 270 ppm and H₂O = 25 ± 7 wt%. If the subducting sediment and the altered basaltic crust were the only slab sources, then the subducted Cl appears to be almost entirely recycled at the Izu arc (∼77-129%). Conversely, H₂O (∼13-22% recycled at arc) and F (∼4-6% recycled) must be either lost during shallow subduction or retained in the slab to greater depths. If a seawater-impregnated serpentinite layer below the basaltic crust were an additional source of Cl and H₂O, the calculated percentage of Cl and H₂O recycled at arc would be lower. Extrapolating the Izu data to the total length of global arcs (∼37,000 km), the global arc outflux of fluid-recycled Cl and H₂O at subduction zones amounts to Cl ∼2.9-3.8 × 10¹² g/yr and H₂O ∼0.7-1.0 × 10¹⁴ g/yr, respectively—comparable to previous estimates. Further, we obtain a first estimate of global arc outflux of fluid-recycled F of ∼0.3-0.4 × 10¹²g/yr. Despite the inherent uncertainties, our results support models suggesting that the slab becomes strongly depleted in Cl and H₂O in subduction zones. In contrast, much of the subducted F appears to be returned to the deep mantle, implying efficient fractionation of Cl and H₂O from F during the subduction process. However, if slab devolatilization produces slab fluids with high Cl/F (∼9.5), slab melting will still produce components with low Cl/F ratios (∼0.9), similar to those characteristic of the upper continental crust (Cl/F ∼0.3-0.9).     

Analysis of fluoride, chloride, nitrate and sulphate in natural waters using ion chromatography

The analysis of anion components of thirty natural water samples using an ion-chromatographic method were compared to analyses for F, Cl, NO₃ and SO₄ obtained by presently used techniques. Of these thirty samples, five were replicates. Precision estimates were also calculated from synthetic solution replicates. In addition, a comparison of results obtained through separator columns of two different lengths (250 mm and 500 mm) was completed. An inter-anion interference test indicated that, at pH 6, analysis of low concentrations of any one of the four anions studied was not affected by large concentrations of the other three anions. Reported detection limits for the ion-chromatographic technique are one to two orders of magnitude below routine methods. Replicate sample analysis indicated that a relative standard deviation below 1 percent was possible for F, Cl, NO₃ and SO₄.     

High-precision EA-IRMS analysis of S and C isotopes in geological materials

The continuous flow elemental analyzer-isotopic ratio mass spectrometer (EA-IRMS) technique provides a significant improvement over conventional extraction methods for the determination of C- and S-isotope ratios in geological materials. It is faster and requires much smaller quantities of material for analysis. Sample preparation is simple, with little or no need for chemical or complete mechanical mineral phase separation, and EA-IRMS sample introduction is rapid. However, because of its simplicity and the fact that data quality depends on the control of a variety of factors, the technique requires rigid adherence to a careful sample analysis protocol.The matching of sample and reference peak heights by sample weight adjustment minimizes non-linearity effects. An accurate calibration should be determined by using standards having a wide range of isotopic compositions, ideally bracketing the samples analysed to both low and high isotopic ratios, and a regular analysis of standards undertaken to maintain the accuracy of the calibration. The calibration equation must be monitored throughout the run by regular analysis of standards, and performance of the Cu-reduction reactor regularly checked to avoid O₂ saturation. With this level of attention to analytical detail, measured precision on replicates of isotopic standards is in the order of ±0.1‰ for both C and S isotopic analyses. For S this is a significant improvement over conventional techniques, with 53% of natural samples analysed replicating to better than ±0.1‰.     

离子色谱法测定土壤中氯、溴

采用扩散技术处理土壤样品,同时用离子色谱测定样品中氯和溴,该方法检出限分别达到4×10-6和0.3×10-6,精密度分别达到9.38%和7.20%。测定快速、操作简单,适合大批量样品分析。     

淮河流域地氟病环境水文地质因素及防病方向的研究

地方性氟中毒病在淮河流域分布较广,部分地区发病率较高,对居民身心健康和区域经济社会发展造成危害。本文以前人工作成果为依据,基于中国地质调查局地质大调查项目多年的数据积累,从整个淮河流域阐述了区内地氟病的分布状况、氟化物在平原区松散层不同层位(埋深小于20m,20～50m,大于50m)地下水中的赋存特征和分布规律。并就本地区水文地质条件及氟化物成因概括了4种氟富集因素,探索性提出了区域地氟病区两种环境地质成病因素。针对不同地区的环境水文地质条件从供水角度提出了防病改水方向。     

The application of radiochemical neutron-activation analysis to the determination of selenium and tellurium in geological materials

A radiochemical neutron-activation technique for the simultaneous determination of traces Se and Te in geological materials is presented. The method is based on an hydrofluoric, nitric and hydrochloric dissolution and a separation by an ion-exchange chromatography on Dowex 1 × 8, 100–200 mesh, in chloride media. Subsequently, these elements are reduced in elemental form by means of a TiCl₃ precipitation. Under the described operating cordebiens, the calculated detection limits are 4 · 10^?3 μg for Se and 9 · 10^?2 μg for Te.Se and Te determinations in some U.S. Geological Survey igneous standard rocks are reported in order to assess the accuracy of the method.     

The use of neutrons and monochromatic X-rays for non-destructive testing in geological materials

In the paper we present our results for element sensitive high-energy X-ray tomography and high-speed thermal neutron tomography applied to geological samples. The tuneable monochromatic X-ray beam was used for element sensitive tomography of geological samples containing heavy elements using the K-edge dichromatic scanning technique. This type of NDT (non-destructive testing) allowed us to reveal the quantity and location of uranium, lead and mercury in Oklo samples (natural nuclear reactor) and Cinnabar stones. Fast 3-D thermal neutron imaging of dynamical processes was successfully tested at the high flux neutron tomography station of the ILL. The qualitative investigation of water repellents and consolidants applied on sandstones of Bray and limestones of Maastricht were the first samples to be studied with the new imaging technique.     

岩土破损力学的系统论基础

天然岩土材料与其它材料的根本不同点在于它的结构性,而形成结构性的根本原因在于胶结的不均匀性.胶结强的部位形成结构体,胶结弱的部位形成结构面.岩土材料是由结构体和破损带组成的二元介质.本文分析了岩土材料的系统特性,对岩土破损力学进行了介绍,从非线性科学的角度阐述了岩土破损力学的系统论基础.     

The use of geological materials in ancient and contemporary art

Mineral‐based pigments have been used for cave paintings and rock art dating as far back as 70–100 ka in Blombos Cave, South Africa. Ancestral indigenous artists used ochre (clay + Fe oxides and hydroxides) for red and yellow pigments in cave art on every inhabited continent for at least 15 000 years, and much longer than that in some localities. Early historic cultures throughout the Middle East, Asia and the Mediterranean basin added other colourful minerals to their palette, including azurite and malachite for blue and green, calcite, gypsum, and diatomaceous earth for white, and charcoal for black. Some of these cultures created additional pigments by roasting or smelting minerals and altering them with vinegar or other organic acids. The use of mineral pigments and pigments of altered minerals using heat and acid continued throughout the Middle Ages and the Renaissance. Similar mineral pigments were used by native peoples in the New World for rock and cave art. Ancestral artists traditionally used water, saliva, oil and fats as binders for their pigments to create their paint.     

国家级矿产实物地质资料的筛选和管理意义

国家级矿产实物地质资料是反映中国矿产资源成矿特点、展现全国矿产勘查与科技工作水平的实物地质资料.国家级矿产实物地质资料由国家实物库永久收藏管理,因此实物地质资料需要筛选.筛选包含2层含义,一是矿床的筛选,即具有典型性、代表性、特殊性的矿床;二是钻孔实物的筛选,即入选矿床最具有代表性的钻孔岩矿心.笔者对2层含义的筛选分别进行了阐述并制定了筛选依据和工作方法,使国家级矿产实物地质资料的筛选有章可循,具可操作性.最后,对全国矿产实物地质资料的管理提出了建议.     

Accounting for spatial patterns of multiple geological data sets in geological thematic mapping using GIS-based spatial analysis

This paper presents a Geographic Information System (GIS)-based spatial analysis scheme to account for spatial patterns and association in geological thematic mapping with multiple geological data sets. The multi-buffer zone analysis, the main part of the present study, was addressed to reveal the spatial pattern around geological source primitives and statistical analysis based on a contingency table was performed to extract information for the assessment of an integrated layer. Mineral potential mapping using multiple geological data sets from Ogdong in Korea was carried out to illustrate application of this methodology. The results obtained from the case study indicated that some geochemical elements and residual magnetic anomaly dominantly affected spatial patterns of the mineral potential map in the study area and the dominant classes of input data layers were also extracted. This information on spatial patterns of multiple geological data sets around mines could be used as effective evidences for the interpretation of the integrated layer within GIS.     

Design,calibration and geological application of the first operational Australian laser ablation sulphur isotope microprobe

This contribution describes the setup and operating procedures of the first operational laser ablation microprobe for stable (sulphur) isotope analysis in Australia as well as some brief geological applications. A significant feature on this laser ablation microprobe is automated gas purification and analysis; operator control is only required to locate and ablate sample targets. As with other laboratories, samples were ablated in an oxygen atmosphere, producing a SO₂/O₂ gas mixture. SO₂ was separated from this mixture by either of two techniques. In the first technique, SO₂ was condensed into a liquid N₂ trap by cryogenic pumping, and O₂ was pumped away. This resulted in the collection of 60–70% of the produced SO₂. In the second technique, SO₂ was condensed into a liquid N₂ trap as the SO₂/O₂ mixture was slowly bled away. This technique collected 90–95% of the SO₂, with a small fractionation of 0.16%. Laser ablation and SO₂ collection via the second technique required a mineral dependent, additive correction of 2.85–5.75% to convert raw δ³⁴S values to δ³⁴S_CDT. These correction factors are mineral and laboratory dependent, and from our data, seem to be dependent on the quality of polish of the ablated sample. Precision (1σ) of laser ablation sulphur isotope analysis is 0.4–0.5%o for 150 μm ablation craters.

Preliminary results of studies on samples from the Broken Hill, Hellyer and active sea floor Pacmanus deposits indicate that laser ablation microprobe analysis can show subtle variations in δ³⁴S not apparent using either conventional or SHRIMP analysis. Laser ablation analysis indicates a larger range, but similar mean values, to conventional analysis on the same samples.