基岩区寻找隐伏矿的地球化学方法:构造地球化学测量

构造地球化学测量是在基岩出露区发现深部矿化信息的一种较为有效的方法。本文介绍了构造地球化学的一些基本概念和构造地球化学测量方法的发展历程。为解决岩石样(构造岩样)的代表性和均匀性,提出了方格采样法,即在每个采样网格内多点采样组合分析采样方法,采集以构造破碎带物质、裂隙充填物、蚀变岩石、矿化岩石等为主的能反映深部矿化信息的样品。利用该方法在甘肃西和地区进行了1∶50 000构造地球化学测量试验,采用500 m×500 m的采样网格,在每个采样单元中采集6~8个子样组合,分析了其中的Au、Ag、Pb、Zn等19种元素,圈定了较好的金地球化学异常,经查证发现了金矿体。在江西岩背锡矿外围开展1∶10 000的构造地球化学测量试验,采用100 m×100 m的网格,采集构造裂隙样品,圈定了Sn等元素的地球化学异常,对圈定的Sn地球化学异常进行钻探验证,发现深部隐伏Sn矿体。不同比例尺的构造地球化学测量试验表明,构造地球化学测量在基岩出露区能有效发现深部矿化信息,在寻找隐伏矿工作中具有较好的应用前景,在中国黔西南地区寻找卡林型金矿和东南沿海地区火山岩覆盖区找矿中能发挥一定的作用。     

便携式X射线荧光光谱仪在岩石样品分析中的应用研究

便携式X射线荧光光谱仪(PXRF)因具有快速、无损检测元素含量的能力,通常被用于野外或实验室地质样品的元素含量检测工作中,对于大多数地质样品,在2 min内就能够获得几十种元素的半定量-定量分析结果。但在实际应用中,被测样品的表面平整度、样品中物质的均一性和施测时间等因素都会影响元素分析结果。为了进一步了解样品类型和分析测试方法等因素对元素分析的具体影响,本文对比了PXRF与实验室分析结果、岩石和粉末样品PXRF分析结果、不同检测时间所得PXRF分析结果的关系,在不损失过多分析精度的前提下提出了通过PXRF降低勘查成本、提高工作效率的方案。结果表明:用PXRF直接分析岩石样品时,大多数元素的分析结果可靠性较差,尤其是成矿预测工作中常用的Cu、Pb、Zn、As和Ni等元素;粉末样品的PXRF分析结果与实验室分析结果具有较好的相关性,表明对岩石样品进行粉碎处理能够明显改善PXRF分析质量;元素种类不同,岩石和粉末样品PXRF测量结果的相关性也不同。因此,在实际工作中可以根据感兴趣的目标元素确定是否需要对岩石样品进行粉碎制样处理;检测时间对元素含量分析结果没有明显影响,对于特定元素,如果能够在较短时间内获得其含量信息,则无需增加检测时间。     

便携式X射线荧光光谱技术在泥河铁矿岩心矿化蚀变信息识别中的应用

便携式X射线荧光光谱(PXRF)是针对野外原位快速分析而发展起来的一项新技术,常被用于岩石露头地球化学研究和土壤重金属污染评价等方面.本研究以安徽省泥河铁矿钻孔为例,在野外对5个钻孔的岩心系统划分岩性段,利用便携式X射线荧光光谱仪原位测量每个岩性段的Fe、Mn、Cr、Co、Ni、Ti、V、Cu、Zn、Pb、Ag、Mo、K、Ca、As、Sb、Bi、Cs、Zr、Nb等元素含量,绘制钻孔各元素含量分布图.研究发现,(1)利用PXRF技术获得的岩心Fe元素高含量部位与根据化学分析得到的铁矿石品位数据而圈定的磁铁矿体范围吻合较好;(2)Fe元素和Fe-V-Mn-Cr-Ni-Ti-Bi组合异常、Zn元素和Zn-Cu-Cd组合异常分别对铁矿化和铜、锌矿化具有较好的指示作用;(3)K、Ca异常分别对钾长石化、硬石膏化等蚀变具有较好的指示作用.由此可见,PXRF技术在野外岩心矿化和蚀变信息识别中具有方便、快捷、实用、可靠、无损、成本低廉等优点.      

Moving faults and building fracture models in a digital world—an example from Glen Coe,Scotland

It is now very easy to create realistic 3D models of rock outcrops from digital photographs. Using images captured on a smartphone or a standard digital camera, a series of overlapping photographs of the outcrop can be merged together and draped over a 3D mesh that accurately represents the topography of the real rock face. The information required to generate the 3D model is all contained within the 2D digital photographs and no other sophisticated surveying equipment is required. There are several freely available software applications that can be used to generate and then interrogate this type of 3D model. This article uses an example from Glen Coe in the SW Highlands of Scotland to demonstrate how best to capture the 3D aspects of an outcrop using a digital camera and then illustrates some of the structural features that can be analysed in more detail.     

A Method to Estimate Length Distributions from Outcrop Data

Dimensions of shales and other geologic bodies that affect fluid flow through reservoirs and aquifers are often estimated from analogous deposits exposed in outcrops. Shale lengths observed in outcrops are biased because the finite length of outcrops truncates longer shales and long shales tend to be overrepresented in the sample. Shale length distributions can be modeled using an Erlangian probability density function based on termination frequency. Termination frequency can be calculated from outcrop observations even if the shales are incompletely exposed. Termination frequency is unbiased regardless of underlying shale length distribution and outcrop size and shape. Complex length distributions can be represented by a weighted sum of Erlangian models, each with a distinct termination frequency. The proportions and termination frequencies of the component models can be estimated using Bayes' theorem. Subsamples of the outcrop area can be analyzed to quantify spatial trends in termination frequency and thus shale length. These methods can be applied to estimate length distributions of any geologic object exposed in outcrops or other spatially limited samples. In many cases estimated termination frequency is normally distributed, and its variance can be estimated using closed-form expressions. Shale length distributions for the Frewens Sandstone were modeled using one- and two-component Erlangian probability density functions. The Frewens Sandstone is a tide-influenced deltaic sandstone body within the Cretaceous-age Frontier Formation, exposed in central Wyoming, USA. Length observations and Erlangian models agree reasonably well. Because the models correct for the effects of shale truncation in limited outcrop exposures, predicted means and proportions of long shales are substantially greater than observed values. There is a vertical trend and pronounced vertical cyclicity in termination frequency, indicating that shales become shorter upward and intervals of longer and shorter shales alternate. Along strike, termination frequency decreases away from the sandstone-body axis, reflecting greater preserved shale lengths toward sandstone-body margins. No correlation was observed between distance along dip and termination frequency. Termination frequencies and histograms of shale length for adjacent, perpendicular walls are similar, indicating that there is no anisotropy in shale length.     

热带雨林有色金属矿产地球化学勘查方法探索

为探索热带雨林条件下有效矿产地球化学勘查方法,在西定金矿开展100km2的采样密度、采样层位(土壤)、采样介质、样品加工粒度、分析方法及土壤地球化学剖面等项试验工作,研究矿体与非矿体上部土壤中地球化学元素的分布特征,为今后在热带雨林地区开展有色金属矿产勘查提供依据。     

Adjusting stream-sediment geochemical maps in the Austrian Bohemian Massif by analysis of variance

The Austrian portion of the Bohemian Massif is a Precambrian terrane composed mostly of highly metamorphosed rocks intruded by a series of granitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the field. A detailed geochemical survey of stream sediments in this region has been conducted and included as part of the Geochemischer Atlas der Republik Österreich,and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, multivariate analysis of variance (MANOVA) was applied to the stream-sediment data in order to minimize unwanted sampling variation and emphasize relationships between stream sediments and rock types in sample catchment areas. The estimated coefficients were used successfully to correct for the sampling effects throughout most of the region, but also introduced an overcorrection in some areas that seems to result from consistent but subtle differences in composition of specific rock types. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overcorrection is removed. This iterative process simultaneously refines both the geochemical map by removing extraneous variation and the geological map by suggesting a more detailed classification of rock types.     

Indications of a major Neolithic trade route? An archaeometric geochemical and Sr,Pb isotope study on amphibolitic raw material from present day Europe

In order to interpret pre-historic cultural interactions, the provenance of amphibolitic raw material used for flat-axes and adzes in lower to middle Neolithic cultures throughout present day Germany were investigated by elemental and Sr, Pb isotopic methods. Within all settlements studied, a homogeneous actinolite-hornblende schist rock type (AHS) was found to be massively dominating, with a distinct petrography of needle-shaped actinolite interwoven with single larger grains of hornblende along with calcic plagioclase and large amounts of ilmenite. Geochemically, the AHS group is very homogeneous and has a signature of an enriched basaltic precursor with high concentrations of particularly the LIL-elements. The geochemical signature is relatively rare and can not be matched in nearby geological outcrops, wherefore the conclusion of “imported material” is quickly reached. Strontium and Pb isotopic analyses of the AHS were compared to the isotopic composition of amphibolitic rocks with similar petrography and trace elemental signatures within possible archaeological trade regions. The isotopic data of the archaeological material point roughly to a Proterozoic age of the stone used; an age which can be reasonable matched to a single outcrop situated at Jistebsko within the Czech Republic. This area further shows archaeological traces of prehistoric mining. Based on petrographic, geochemical and isotopic evidence, this area is here presented as the provenance area of the stone raw material, which later spread throughout prehistoric Europe – establishing contact and trade routes between Neolithic cultures.     

宣城地区龙潭组页岩沉积环境与有机质富集

安徽宣城地区上二叠统龙潭组海陆过渡相页岩不仅是我国下扬子区重要的烃源岩,也是目前我国页岩气勘探的重要层位之一。为研究海陆过渡相页岩沉积环境与有机质富集的关系,以港地1井和两个露头剖面为研究对象,系统开展了有机地球化学测试、有机岩石学研究、氩离子抛光—扫面电镜观察、元素地球化学分析等工作。结果表明:下扬子宣城地区龙潭组页岩沉积时期处于暖湿型气候,沉积水体处于氧化—贫氧状态,具有高的生物生产力和沉积速率。海陆过渡相富有机质页岩的形成,不是由单一因素所决定的,而是由古气候、水体氧化还原性质、古生产力、沉积速率等多个要素相互配置与耦合的结果,这些因素都会直接或者间接地影响有机质的供给或者有机质的埋藏和保存。其中,温湿型气候不仅有利于陆源高等植物的生长,而且会促进生物地球化学作用,使得母岩化学风化程度加大,向水体输入的营养物质增多,有利于菌藻类等低等水生生物勃发,高等植物碎屑和低等水生生物共同为富有机质页岩沉积提供了丰富的有机质来源。宣城地区晚二叠世沉积时期,较高的古生产力为海陆过渡相富有机质页岩的形成提供了良好的物质基础,有机质产生后进一步埋藏和保存,虽然富氧水体环境不利于有机质保存,但高的沉积速率可以缩短有机质在富氧水体中暴露的时间,使得有机质来不及被氧化或分解,也可造成有机质的富集。     

Factor Analysis of Soil and Attic-dust to Separate Mining and Metallurgy Influence, Meza Valley, Slovenia

Based on the factor analysis of chemical elements determined in topsoil (0–5 cm) and attic-dust, two natural and two man-made (anthropogenic) geochemical associations were discovered in the Meza valley, an old mining and metallurgic area. The natural geochemical association (Al-Ce-Co-K-La-Li-Nb-Rb-Sc-Th-Ti-V) is influenced mainly by weathering of metamorphic rocks, while the anthropogenic association (Ca-Mg) was determined in an area of carbonate rock outcrops. The man-made associations are a result of lead production (Ag-As-Cd-Mo-Pb-S-Sb-Sn-Zn) and iron production (Co-Cr-Mo-Ni-W).     

AMS 14C ages and petrological features for solidified fractures with carbonates at coastal outcrops of Yakushima Island, Japan

This paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of Yakushima Island, Japan. Microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings. In addition, AMS ¹⁴C dating was also performed to estimate the ages of them. Microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts. SEM observation showed that the cements exhibit the characteristic textures of beachrocks. The cements were identified as Mg-calcite from XRD analysis. It was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures. In addition, AMS ¹⁴C dating for seventeen samples of fracture fillings showed that the ages range from 2,460 to 5,130 years BP which is found to be younger than that of the uplifted coral at Yakushima Island (approximately 5,300–5,600 years BP). The results suggest that the fractures were solidified after the coral was uplifted.     

平原区中大比例尺土壤地球化学调查采样方法--浙江省平湖市试验研究

文章以浙江省平湖市为典型三角洲平原区,开展了多种尺度、不同采样方法的对比试验。结果表明,田块内土壤元素分布较为均匀,小范围内元素的空间分异性较小,而田块之间土壤元素含量差异性明显增加;Hg,Cd等典型污染元素空间分异性较强,而人为污染扰动较弱的元素的空间分布较为均一;不同采样方法取得的区域性资料,其统计值接近,空间分布模式也相似,但有些元素仍有较明显差异。因此,中大比例尺地球化学调查时,应根据调查研究的目标任务,充分考虑地块分布、土壤类型和土地利用方式,选择合理的采样点。土壤样品可采取多坑点采集、多子样组合的方式,以保证样品的代表性,同时减少分析测试工作量。     

Reproducibility of overbank sediment sampling in Greece and Norway

Reproducibility of overbank sediment sampling was tested in twenty-nine floodplains in Europe, ten in Greece and nineteen in Norway, by the collection of duplicate pairs of samples. Distances between duplicate sites in Greece were 60 to 100 m, and in Norway 100 to 200 m. In Norway the same nineteen floodplains were sampled by a second team for the purpose of investigating differences in sampling variability and technique. Total element contents were determined in all samples. Paired samples were compared by calculating Spearman's rank correlation coefficient on the raw analytical data, and one-way analysis of variance on the log-transformed data. Pairs of overbank sediment samples collected from different floodplains by the Hellenic team and the first Norwegian team showed high rank correlations and low within-basin variability (sampling and analytical variance). Statistical results of the second Norwegian team were comparatively poorer; both Spearman's rank correlation coefficient and one-way analysis of variance, showed very low positive to negative correlations and high within-basin variation, suggesting a non-uniform distribution of elements in the Norwegian overbank sediment sequences and differences in the sampling technique of the two teams. Nevertheless, careful location of sample sites, as has been done by the Hellenic and the first Norwegian teams, reduces considerably the sampling variability, and the overall sampling reproducibility for most elements is very good for distances up to 100 m in Greece and 200 m in Norway, provided correlated overbank sediment sequences are sampled. The implication of this study for multinational regional geochemical mapping is that overbank sediment sampling must be carried out by well-trained professional teams of exploration geochemists, and where possible by one sampling team for the whole country.     

Origin of Mantle-Shaped Carbonatite Bodies in the Khalyuta Deposit, Western Transbaikal Region, Russia

The western Transbaikal region is among the long known and well studied ore districts. Nevertheless, carbonatites were unknown in the region until 1990s. About four decades ago, two small outcrops of endogenic carbonatite rocks were discovered in the western sector of this region. Subsequently, one of these outcrops was identified as an epithermal fluorite mineralization in limestones, while the second outcrop was recognized as skarn lode with the barite–strontianite mineralization. Recently, based on geostructural, mineralogical, geochemical, and isotope data, we could identify these rocks as linear or fault-line carbonatites (Bulnaev and Posokhov, 1995; Bulnaev, 1997). Now these sites are known as the Arshan and Khalyuta deposits spaced 20 km apart and located at 45–47 km to the southwest and west of Ulan-Ude, respectively.     

Striated and pitted pebbles as paleostress markers: an example from the central transect of the Betic Cordillera (SE Spain)

Striated and pitted pebbles provide scarce structures that preserve information on the stresses that their host rocks have undergone. This information can be obtained by the measurement of a large number of microfaults with striae and solution marks within a small rock volume. For non-rotational deformation, the statistical procedures for microfault analysis provide a valid tool for determining the overprinting of successive stress ellipsoids, including their axial ratios and the orientations of the main axes. The trends of compressions obtained from striae can be compared with the determinations from the pole of pebble solution pits. However, in complex tectonics settings, the solution pits of several deformation phases are mixed and only striae analysis allows overprinted paleostresses to be accurately distinguished. The analysis of several pebbles from the same outcrop, including five from moderately complex settings, allows determination of the homogeneity of the paleostresses at outcrop scale, the detection of redeposited pebbles, and supports the results of microtectonic analysis for large areas. Solution mark distributions on pebbles depend on the burial and tectonic stresses. Conglomerates from shallow levels, such as those from Quaternary fluvial terraces, only record horizontal compressional solution marks because the minimum vertical stress needed to develop these structures are not reached by burial.In the central Betic Cordillera, striated and pitted pebbles are composed of carbonate surrounded by a matrix containing siliciclastic elements. The study of several outcrops located across a transect of the Cordillera shows a change in the recent stress field. While conglomerates near the Internal–External zone boundary show extensional stresses that may be related to the uplift of the Cordillera since Tortonian times, the outcrops located in the External Zone and up to the mountain front indicate the existence of horizontal NW–SE and NE–SW compressions related to prolate ellipsoids. These two compression directions, which affect conglomerates up to the Quaternary in the same outcrop, may be produced by a local permutation of stress axes, which in general indicates NW–SE compression related to the Eurasia–Africa plate boundary convergence, but which locally may switch to an orthogonal compression.     

Trace-element patterns in lateritic soils applied to geochemical exploration

Geochemical soil surveys in areas underlain by Precambrian volcano-metasedimentary sequences and around rare-metal-bearing pegmatites of southwestern Nigeria demonstrate that residual geochemical soil patterns reflect a wide range of potential source rocks adequately. The secondary geochemical dispersion processes in these typically tropical weathering environments adjust the trace-element distribution during lateritic soil development to narrow fluctuation ranges in comparison to the differing Clarke values of various source rock units.The sample density in these soil surveys, averaging at one sample per square kilometer, favours geochemical inventories even at regional scale and shows great potentials to predict bedrock composition of tropical terrain where rock outcrops are rather scarce.     

化探在小沟铅锌矿勘查中的应用

小沟铅锌矿位于植被覆盖严重、基岩裸露零星且地形陡峭的大巴山地区。该铅锌矿床是在1：1万土壤测量及其所圈定的化探异常Ⅱ级查证基础上,通过地表追索和槽探工程揭露发现的。化探方法对在地表覆盖厚、基岩裸露稀少的中一高山陡坡地区找矿是行之有效的方法之一。     

An evaluation of structural analyses of discontinuities in carbonate rock

The main goal of the study was to compare two methods of structural analysis, based on different principles: an engineering method and the Eraso method. The first one was developed with the intention of studying geotechnical and hydraulic properties on freshly exposed rock surfaces, while the second one is based on microtectonic analysis and is mainly applied on surface outcrops. Structural analysis of discontinuities in fractured and karstified rock at one experimental field site in Slovenia was performed. Measurements were carried out on surface outcrops and in an underground artificial tunnel, twice in two different seasons (autumn 1999 and summer 1996), but by the same personnel. Both methods were found to be more or less repeatable and applicable both on the surface outcrops (weathered rock) and on freshly excavated rock surfaces (artificial tunnels and quarries), and on a macroscale. The results have shown that we can infer from the macroscale data set to the (regional) mega-scale. Copyright © 1998 John Wiley & Sons, Ltd.     

Tectonic and Topographic Framework of Political Division

Boundaries between the various topographic, geologic, and socio-political entities that span the Earths continental surfaces are determined by a myriad of complexly interrelated natural and/or cultural factors. Areas of large river basins, of lithologic units on geologic maps, and of nations exhibit size frequency distributions that are closely approximated by density functions in which diameters of individual areas are distributed exponentially. As such, size distributions of each type of surface unit are closely modeled as randomly delimited areas. In other words, if one were to walk in a straight line across any particular continent, each step along that transect would embody some random continuous probability of passing out of a major drainage basin, or out of an area of more or less homogeneous rock type, or from one country to another. Moreover, this simple truism gives rise to area frequency distributions for large river basin or outcrop or nation area that are primarily dependent on the number of basins or outcrops or countries that exist across that particular landmass. As a consequence, the size frequencies of these areal units can be closely predicted knowing only the total area under consideration and the number of drainage basins, outcrop areas, or nations that exist within the area. The similarity between area frequencies of large river basins and rock types and nations suggests a nontrivial component of geologic influence on the partitioning of continental surfaces into major political divisions, and implies that cultural and economic factors, which serve to divide and unite political entities, do so within a geological framework.