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1.
In parts of the deeply weathered and semi-arid environments of the Cobar area (NSW, Australia), detection of mineralisation using conventional soil sampling and total metal analysis is impeded. This is due to the intense leaching of trace elements within the weathered profile, discontinuous coverage of transported materials and the existence of diffuse regional geochemical anomalies of ill-defined source. Selective chemical extractions, applied to various regolith components, and biogeochemistry offer a means of isolating localised geochemical patterns related to recent dispersion of trace elements through the overburden. Lag geochemical patterns across the McKinnons deposit (Au) and Mrangelli prospect (Pb–Zn–As) reflect mechanical dispersion processes and minor hydromorphic effects. Concentrations of more mobile elements tend to be higher in the non-magnetic fraction, due to higher proportions of goethite and poorly crystalline hematite than in the magnetic fraction. The subdued soil geochemical responses for metals extractable by cold 40% hydrochloric acid (CHX) and for total element concentration reflect the leached nature of the residual profile, low grade of mineralisation, dilution by aeolian components and disequilibrium of fine fractions with coarser, relict Fe-oxides. The stronger contrast for CHX for most metals, compared with total extraction, indicates surface accumulation of trace elements derived from underlying mineralisation. Enzyme leach element anomalies are intense but generally located directly over bedrock sources or major structural breaks, irrespective of the nature of the overburden. Though mechanisms for the dispersion of trace elements extracted by enzyme leaching are not well established, the lack of lateral transport suggests vertical migration of volatile metal species (atmimorphic dispersion). The strong, multi-element response to mineralisation in cypress pine needles indicates significant metal recycling during the present erosional cycle. However, a comparison of the trace element concentrations in vegetation (cypress pine needles) and selective extractions of soils indicates that recycling by the plants is not the dominant mechanism for transportation of metals through the overburden. The vegetation may be responding to hydromorphic dispersion patterns at depth. The use of selective extractions may be useful in detecting mineralisation through deeply leached profiles, but offers even greater potential when integrated with biogeochemistry to detect targets buried by significant thickness of transported cover.  相似文献   

2.
Effective exploration for polymetallic ore deposits in the Cobar region is hampered by incomplete knowledge of the mineralogical controls on element dispersion in the different regolith-landform settings throughout the area. A detailed mineralogical and geochemical study of regolith profiles over two major mineralised shear zones in a strongly weathered but dominantly erosional setting has delineated the important host minerals for a range of base metal cations. Iron oxides/oxyhydroxides, particularly goethite and to a much lesser extent hematite, are major hosts for Pb, Cu, and Zn as substituted/adsorbed cations and as constituents of associated or intergrown minerals, probably including members of the jarosite–alunite group. Correlations between elements and major regolith minerals suggest that goethite is also a host phase for As, Bi and Sb. Minor manganese minerals, including lithiophorite and cryptomelane group minerals, also host base metals in appreciable amounts. No clear association was found between gold and any particular secondary mineral. It is likely that gold is present largely as elemental gold particles associated with a range of minerals.Sampling strategies for geochemical exploration in variably leached and stripped regolith in the Cobar area should take into account the relative abundance of goethite and manganese oxides/oxyhydroxides within the profiles and overlying lag. Goethite would appear to be the preferred sampling medium for base metals. Highly ferruginous lag has a high proportion of hematite with variable maghemite and very low manganese oxide contents. Most of the base metal content in this surface material is strongly bound to the crystalline oxides/oxyhydroxides. More work is required to understand the effects of surface transformation of goethite to hematite and maghemite on the mobility and distribution of base metal cations in soil and ferruginous lags.  相似文献   

3.
Desert land surfaces are commonly characterized by a veneer or pavement of siliceous and/or ferruginous stony material. This material can be shown in most cases to be predominantly bedrock-derived, despite often severe modification by prolonged weathering, and can therefore be selectively sampled and analyzed as an indicator of bedrock geochemistry in geochemical surveys.Most pavements probably owe their existence to the interaction of several dispersion mechanisms. However, a common factor in all cases is the concentration of coarse particles at the surface as a result of the selective removal by erosion of fine dilutant material. Hence, the preferred name when used in the geochemical context is “lag”.In lag sampling, particles in the range 2.0–6.0 mm are screened on site from the unconsolidated surface material. Material in this size range has been found to be quite uniformly distributed over a wide range of arid region environments, including areas where residual soils are severely diluted by transported alluvial and aeolian materials.Data from exploration programmes for Au, Cu-Pb-Zn-Ba, and Ni allow comparison of results for lag sampling with those for alternative sample media in a variety of arid region environments. Analysis of lag samples for Au, Cu and As clearly indicates the presence of bedrock Au mineralization in the Paterson and Eastern Goldfields Provinces of Western Australia. In these areas both lags and soils exhibit good anomaly contrast, but lags show more extensive lateral dispersion, leading to advantages in reconnaissance exploration.Strong anomalies for Ni and Cu are developed in lags, compared with subdued response in fine-fraction soils over a Ni sulphide occurrence in the Eastern Goldfields which has been subjected to deep lateritic weathering.Lag geochemistry also clearly reflects sub-economic base metal and barite occurrences in the McArthur Basin, N.T., in spite of the dilution of surface soils by sands probably related to a Mesozoic marine incursion. Orientation sampling over a Pb-Zn prospect in the Pine Creek Geosyncline has demonstrated optimum response in lag samples compared with various size fractions of the associated lithosols.Variable dilution of lag samples by coarse quartz sand can be a problem in areas with substantial transported overburden. A simple procedure to ‘correct’ trace-element values using regression analysis based on the Fe content of samples is described as a means of reducing ‘noise’ resulting from such matrix variations.  相似文献   

4.
The problem of using surface geochemical exploration techniques in areas of very thick and electrically conductive weathering residuum is common to much of Australia. At the Elura deposit (New South Wales) a distinct electrogeochemical H+ anomaly can be detected in the top few cm of residual soil above about 100 m of conductive residual overburden. In the present paper the results of an investigation of the much more difficult problem of detecting sulfide mineralization beneath thick conductive transported overburden are described.The objective of the study was to demonstrate that sulfide mineralization beneath thick transported overburden can be detected by geochemical patterns in surface soils in the context of an electrogeochemical model of dispersion.The Thalanga massive sulfide deposit in northeast Queensland has at least 4 million tonnes of 15% combined Zn, Pb and Cu. The mineralized horizon lies at the contact between rhyolitic and dacitic rocks of the Cambro-Ordovician Mt. Windsor Volcanics. The deposit is covered by transported cemented Tertiary terrigenous clayey sandstones and grits; these are electrically conductive and vary in thickness from 0 to 70 m.Near-surface soil samples were collected along five traverses normal to the strike of mineralization. The traverses were located to give 0 m, 1 m, 30 m, 50 m, and 70 m overburden thicknesses; there is no known significant mineralization along the last traverse which is assumed to be background, and there is a small gossan where the overburden is absent.Dispersion patterns influenced by electrogeochemical processes should result in relatively low values for ions over massive sulfides with lateral peaks; this has been termed a “rabbit-ear” anomaly. “Rabbit-ear” anomalies in surface soils for H+, Cu, and Zn occur over the sulfide zone. The H+ pattern is better defined where there is a significant depth of overburden (where the anomaly is about 500 m wide). The Cu anomaly is 300–600 m wide, and the Zn anomaly is 450–675 m wide.Even where the overburden is 50 m thick, anomalous “rabbit-ear” anomalies for H+ and Zn are clearly identifiable, but the anomaly for Cu is a single peak of 20 ppm over the hanging wall. It is suggested that the results of this work convincingly demonstrate that at Thalanga surface soil samples may reliably be used to detect massive sulfide deposits - even where they are effectively blind beneath a considerable thickness of transported and conductive overburden. The processes of dispersion are speculated to be diffusion, and it is argued that the pattern-controlling mechanism is electrochemical.  相似文献   

5.
Thermodynamic calculations and experiments in vitro have pointed to the potential value of carbonyl sulphide (COS) as a gaseous pathfinder for sulphide mineral deposits concealed beneath overburden. Convenient sampling and analytical techniques have, therefore, been developed for the determination of COS in overburden materials. In temperate regions, samples of soil are taken below the normal rooting depth of vegetation; in arid and semi-arid regions the surface microlayer is collected. The analytical procedure involves the selective thermal desorption of COS from the < 150 μm fraction of overburden materials and quantitative determination by a rapid gas chromatographic method.Field studies of surficial dispersion patterns of COS have been carried out in the vicinity of replacement-type Cu (-Zn) and porphyry Cu deposits in the southwestern U.S.A., meta-sedimentary Cu-Zn mineralization in Saudi Arabia, volcano-sedimentary polymetallic sulphides in South Africa and stratabound Pb-Zn mineralization in Ireland, and are described here. These deposits are covered by different types and various thicknesses of overburden material. Anomalous concentrations of COS occur in the overburden above all of these deposits. The anomalies tend to be of modest but satisfactory contrast and are in some instances discontinuous or patchy.Results indicate that COS may be used as a guide to concealed mineral deposits in a variety of geologic and physiographic settings. Significant anomalies can be recognized even where mineralization lies beneath more than 90 m of transported overburden.  相似文献   

6.
A previous study briefly described the occurrence of a new type of Nb(Ta)-Zr(Hf)-REY-Ga (REY: rare earth elements and yttrium) polymetallic mineralization in eastern Yunnan, southwest China. In this paper, the mineralogical and geochemical features have been further advanced through a study of two regionally extensive and relatively flat-lying mineralized layers from No. XW drill core. The layers are clay-altered volcanic ash and tuffaceous clay, and are dominated by clay minerals (mixed layer illite/smectite, kaolinite, berthierine, and chamosite); with lesser amounts of quartz and variable amounts of anatase, siderite and calcite; along with trace pyrite, barite, zircon, ilmenite, galena, chalcopyrite, and REE-bearing minerals. The mineralized samples have higher Al2O3/TiO2 values (13.7–41.4) and abundant rare metal elements (Nb, Ta, Zr, Hf, REE, Ga, Th, and U) whereas less mineralized samples are rich in V, Cr, Co, and Ni and have lower Al2O3/TiO2 values (2.32–7.67). The mineralized samples also have strong negative δEu in chondrite-normalized REE patterns. Two processes are most likely responsible for the geochemical and mineralogical anomalies of the mineralized samples: airborne volcanic ash and multi-stage injection of low-temperature hydrothermal fluids. Based on paragenetic analysis, this polymetallic mineralization is derived from the interaction between alkaline volcanic ashes and subsequent percolation of low-temperature fluids. The intense and extensive alkaline volcanism of the early Late Permian inferred from this study possibly originated from the coeval Emeishan large igneous province (ELIP). This unique Nb(Ta)-Zr(Hf)-REE-Ga mineralization style has significant economic and geological potential for the study of mineralization of the lowest Xuanwei Formation.  相似文献   

7.
Rare earth elements and yttrium geochemistry of dolomite from post-Variscan vein-type Zn–Pb–Cu mineralization was studied in the Nízký Jeseník and Upper Silesian Basins. Combined with crush–leach analyses of fluid inclusions, the study provided important information on fluid–rock interaction, physico-chemical and redox conditions during crystallization of the dolomite. The mineralization is hosted by Carboniferous siliciclastic rocks, representing Variscan flysch and molasse sedimentation. Dolomite samples contain highly variable contents of REE (between 18 and 295 ppm) and Y (between 17 and 95 ppm). REY patterns are divided into four different groups which differ in regional provenance, LREE vs. HREE enrichment/depletion and significance of Eu, Gd and Y anomalies. These patterns can be the result of 1) precipitation of dolomite from near neutral fluids with important concentrations of complexing ligands as a main factor for the REY partitioning, 2) interaction of migrating fluids with host or basement rocks, or, most probably, 3) a combination of both.Regarding the importance of complexing ligands, it is proposed that in all samples fluoride and chloride complexes prevailed over sulphate, bicarbonate and hydroxide complexes. Interaction of fluids with rocks was strongly affected by the fluid temperature. Dolomites which precipitated from fluids with homogenization temperature higher than 110 °C are mostly REY-enriched while fluids colder than 110 °C produced REY-depleted dolomite. The REY-enrichment may indicate higher effectiveness of leaching of REE-bearing minerals (probably monazite, allanite and biotite) at higher temperatures. The preferential loss of LREE can be caused by the recrystallization or remobilization of dolomite. Generally, an increase in salinity and contents of Cl and F in the fluids is mostly accompanied by a higher REY content in dolomite. Positive Eu anomalies and small negative Gd and Y anomalies are typical for most of the chondrite-normalized patterns. Positive EuCN anomalies in dolomites are most probably the result of an increase of Eh in the parent fluid. Distribution of Y is expected to be predominantly controlled by solution complexation.  相似文献   

8.
This paper describes the use of NAnoscale Metals in EarthGas (NAMEG) and MObile forms of MEtals in Overburden (MOMEO) methods in regional scale geochemical exploration for giant deposits in terrains covered by overburden. These methods are based on the premise that gases generated from the earth's interior can not only transport mobile forms of elements from an ore deposit and its geochemical halos to the surface to form a local anomaly, but also transport them from distinct bedrock “geochemical blocks” hosting large and giant ore deposits and give rise to large regional geochemical anomalies and geochemical provinces at the surface.Regional NAMEG and MOMEO surveys for giant gold deposits were carried out in Shandong Province, where the largest gold deposits in China are found, and in the Muruntau region of the Kyzylkum Desert, Uzbekistan, one of the world's largest gold ore provinces.In Shandong Province, where most of the area is covered by complex overburden, large regional anomalies in earthgas and water-extractable Au were delineated over and around the giant gold deposits. For many trace elements, the anomalies are larger in area and have greater contrast than those from other methods. High concentration of water soluble Au extends into the southern area covered by transported overburden, suggesting that this region may have potential for the discovery of new concealed gold deposits. The anomalous provinces of Au in both earthgas and water soluble salts coincide with a deep fault, supporting the idea that the deep fault is the main conduit of Au from the interior.In the central Kyzylkum Desert, nearly all Au-hosting rocks are covered by sedimentary sequences overlain by desert sand. Gold and As anomalies over Muruntau and Kokpatas gold deposits have contrasts ranging from 2 to 400 times background. Strong anomalies were also discovered in the south of the Muruntau region, suggesting a promising area for the discovery of new giant gold deposits.  相似文献   

9.
浙东南火山岩地区的金属矿床与火山构造和隐伏岩体关系密切。笔者近年来在该地区开展了不少磁法工作,在圈定火山构造、隐伏岩体、划分断裂构造等方面取得较好效果,并结合地质资料指出了成矿有利的靶区。后续地质工作在多个靶区发现大量土壤异常,有力推进了区内矿产地质工作。认为在浙东南火山岩地区开展地质勘查时,可通过面积性磁法工作快速缩小找矿靶区,减少勘查风险,提高矿产地质工作效果。  相似文献   

10.
Chromite mineralization in metamorphosed dunites from the southern Klyuchevskoy dunite-harzburgite ultramafic complex (Central Urals) has been investigated using geomagnetic surveys along with laboratory studies of ore-forming and accessory spinels of the same genetic type. Magnetization in the study area is carried mainly by accessory Fe-Cr-spinel of a variable Fe2 +(Cr2 -xFex3 +)O4 composition. Metamorphism caused changes in element contents and in both crystal and magnetic structure of the primary nonmagnetic accessory spinel, unlike the almost fresh ore-forming spinel. Thus, ore bodies stand against their host rocks, which is a prerequisite for the use of geomagnetic surveys for exploration of podiform chromite deposits in dunite-harzburgite complexes. Ground magnetic surveys at a test site composed of faulted rocks bearing disseminated chromite mineralization in metamorphosed dunites resolved a chromite ore zone and a fault block boundary showing up as geomagnetic anomalies. Laboratory studies using high technologies (thermomagnetic analysis at 4 to 1000 K, as well as magnetic resonance and magnetic force spectroscopy) revealed, for the first time, magnetic clusters (superparamagnetic phases) in primary nonmagnetic accessory spinel, which are responsible for the magnetic properties of the host rocks. Microscale variations in Cr-spinel correlate with the geomagnetic anomalies recorded by field surveys at the test site.© 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.  相似文献   

11.
The presence of geochemical anomalies, defining haloes around hydrothermal ore deposits, can be used to vector towards mineralization, or identify ore bodies buried at depth. Several important types of ore deposits, including skarn deposits, are often hosted within carbonate-rich sedimentary rocks. Identifying anomalous trace-element concentrations in carbonate rocks is complicated by variable lithology (i.e. siliciclastic component) and volume loss during hydrothermal alteration. In this study of the world-class Antamina skarn deposit in Peru, we use the ratio of metals:immobile elements (e.g. La, Al2O3) to differentiate genuine and false geochemical anomalies in limestones and marbles surrounding the skarn deposit. Unaltered limestones are used to define threshold values for metal:immobile element ratios (through use of the median value ± 2 median absolute deviations). Genuine anomalies are identified when metal concentrations exceed those predicted using median + 2 median absolute deviations. In addition, comparison of “four acid” and lithium-borate fusion analytical techniques reveals that the lower cost four-acid techniques give reliable results. Our approach can be used to identify geochemical anomalies and halos related to hydrothermal alteration of carbonate-rich rocks, which have direct application to skarn deposits.  相似文献   

12.
Sediment samples were collected from streambeds in an undisturbed watershed in eastern Quebec (Gaspé Peninsula). Two sampling sites were located on a stream draining an area of known mineralization (Cu, Pb, Zn) and two on a control stream. The sediment samples were separated into 8 distinct size classes in the 850 μm to <1 μm size range by wet sieving, gravity sedimentation or centrifugation. Each sediment subsample was then subjected to a sequential extraction procedure designed to partition the particulate heavy metals into five fractions: (1) exchangeable; (2) specifically adsorbed or bound to carbonates; (3) bound to Fe-Mn oxides; (4) bound to organic matter; (5) residual. The following metals were analyzed in each extract: Cu, Pb, Zn; Fe, Mn.Comparison of samples from the mineralized area with control samples revealed the expected increase in total concentrations for Cu, Pb and Zn. Non-detrital metals were mainly associated with Fe oxides (specifically adsorbed; occluded) and with organic matter or resistant sulfides. For a given sample, variation of trace metal levels in fractions 2 and 3 with grain size reflected changes in the available quantities of the inorganic scavenging phase (FeOx/MnOx); normalization with respect to Fe and Mn content in fraction 3 greatly reduced the apparent dependency on grain size.The results of this study suggest that a single reducing extraction (NH2OH.HCl) could be used advantageously to detect anomalies in routine geochemical surveys. A second leaching step with acidified H2O2 could also be included, as the trace metal concentrations in fraction 4, normalized with respect to organic carbon content, also showed high {anomaly/background} ratios.  相似文献   

13.
Geochemical and mineralogical investigations have been carried out on laterite profiles developed in the Lake Sonfon Au district of northern Sierra Leone. The area is underlain by Archean metavolcanics and constitutes part of the Sula Mountains greenstone belt, which is mineralized in Au. Extensive lateritization has affected the rocks of this region, resulting in a profile which from bottom to top consists typically of a decomposed bedrock zone, a pisolitic laterite layer and a duricrust layer. Both the pisolitic and duricrust layers of the laterite are sometimes punctuated by lenses of ironstones containing high amounts of Cu, Zn, Ni, Co and Ce. Gold occurs as small grains within the heavy mineral fraction recovered from the decomposed rock zones and pisolitic layers of the profiles and also in gravels of streams draining the area. The mineralogy of the duricrust and pisolitic layers is dominated by goethite, gibbsite and quartz, with minor amounts (<5% by volume) of ilmenite, magnetite, haematite, rutile and kaolinite. The kaolinite content increases towards the decomposed rock zone, where talc, vermiculite and other layer lattice silicates become abundant. The heavy-mineral fraction of stream sediments is composed essentially of ilmenite, magnetite, haematite, and traces of rutile, zircon, tourmaline and Au. The Au grains are often characterized by a 10–200-μm-wide rim having a much lower content of Ag (0.3 wt.% or lower) than the grain interior (about 5 wt.% on average). Dissolution effects are also observed on the grain surfaces. It is considered that Au derived from the amphibolite parent rock is dissolved, transported, and redeposited during laterization.The duricrust cover of the laterite profiles is characterized by high contents of Fe2O3 (ca. 60 wt.%) and Al2O3 (ca. 32wt.%) and low content of SiO2 (ca. 9 wt.%). In comparison, the pisolitic layer is higher in SiO2 (ca. 18 wt.%) as well as a slightly higher in Al2O3 (ca. 34 wt.%). Lateritic weathering has resulted in the removal of CaO, Na2O, MgO and SiO2, with relative enrichment of Fe2O3 and Al2O3. The geochemical distribution of the trace elements in the laterite profiles can be related to the occurrence of the auriferous mineralization. The significance of these observations is discussed in relation to the origin of the lateritic Au and the role of the associated trace elements as indicators of the mineralization.  相似文献   

14.
郎和都格矿区地表沙土和草原覆盖严重,直接寻找钨多金属矿的信息较少。地质地球化学研究结果表明,与钨多金属矿关系密切的是早白垩世钾长花岗岩,赋矿围岩主要是二叠纪辉石闪长岩。根据围岩与矿体之间的物性差异,完成了矿区1∶1万地质填图、磁法和重力测量,对数据进行重磁联合反演,识别出3条走向北东、长度800～3 000 m、宽度50～100 m的重要的构造蚀变带（分别对应于负磁异常带）,均分布在矿区西北侧的辉石闪长岩中,且平行于辉石闪长岩和钾长花岗岩的接触带。预测了6个综合物探异常区,也位于矿区西北侧的辉石闪长岩分布区,单个异常面积为500 800 m2,异常深度不超过1 000 m。经钻探工程验证,在3个异常部位发现了隐伏的构造破碎带型钨多金属找矿靶区,钨多金属矿体埋藏深度为150～650 m,单个矿体厚度为2～4 m。表明成矿地质条件分析与重磁联合反演相结合的定位预测方法,在覆盖区寻找钨矿效果明显,值得进一步推广。  相似文献   

15.
Vein-type, structurally controlled Cu–Au mineralisation hosted by turbidites of late Silurian to earliest Devonian age, forms an important resource close to the eastern margin of the Cobar Basin. Here we report 103 new sulfur isotope analyses, together with homogenisation temperatures and salinity data for 545 primary two-phase fluid inclusions for the mineralised zones from the central area of the Cobar mining district. A range in δ34S values from 3.8 to 11.2‰ (average 7.9‰) is present. Sulfur is likely to have been derived from rock sulfur/sulfide in basin and basement rocks, but there may be an additional connate-derived component. Homogenisation temperatures (Th) for inclusion fluids trapped in quartz and minor calcite veins range from near 150°C to 397°C. Fluid inclusions are characterised by a low CO2 content and low, but variable salinities (2.1–9.1 wt% NaCl equivalent). Generations of inclusion fluids correspond to six paragenetic stages of vein quartz deposition and recrystallisation at the Chesney mine. Primary fluid inclusions in the first two stages were subjected to re-equilibration resulting from increased confining pressure. Their Th range (151–317°C) is considered a minimum for the temperature of these fluids. Sulfide and gold deposition at Chesney appears to be related to fluids of moderately high Th (range 270–397°C) associated with the final paragenetic stage. Th for the ore-related fluids may be close to the solvus of the H2O–NaCl–CO2 system and hence near trapping temperatures. Late-stage entry of a hot, moderately saline ore-forming fluid is implicated as the origin of the Cu–Au mineralisation. However, comparison with geochemical data for the vein-style Zn–Pb–Ag deposits at Cobar demonstrates that differences in metal content for individual zones cannot be attributed to major differences in fluid temperature or salinity. Rather, these differences are probably due to variations in source-rock reservoirs and structural pathways along which the ore-forming fluids moved.  相似文献   

16.
通过东天山地区地球化学勘查中某些方法的试验,研究了一套适宜于戈壁荒漠景观中地球化学勘查的工作方法.（1）查明了盛行风对岩屑异常特征的影响程度;（2）推荐消除风成沙影响的合理采样粒级;（3）利用水溶态铜、金异常指示被运积物掩盖的铜、金矿体;（4）明确了荒漠区盐磐层不会阻碍在残积物覆盖区发现矿致岩屑异常和在运积物覆盖区发现后生晕.  相似文献   

17.
The basement rocks of the poorly understood Thomson Orogen are concealed by mid-Paleozoic to Upper Cretaceous intra-continental basins and direct information about the orogen is gleaned from sparse geological data. Constrained potential field forward modelling has been undertaken to highlight key features and resolve deeply sourced anomalies within the Thomson Orogen. The Thomson Orogen is characterised by long-wavelength and low-amplitude geophysical anomalies when compared with the northern and western Precambrian terranes of the Australian continent. Prominent NE- and NW-trending gravity anomalies reflect the fault architecture of the region. High-intensity Bouguer gravity anomalies correlate with shallow basement rocks. Bouguer gravity anomalies below –300 µm/s2 define the distribution of the Devonian Adavale Basin and associated troughs. The magnetic grid shows smooth textures, punctuated by short-wavelength, high-intensity anomalies that indicate magnetic contribution at different crustal levels. It is interpreted that meta-sedimentary basement rocks of the Thomson Orogen, intersected in several drill holes, are representative of a seismically non-reflective and non-magnetic upper basement. Short-wavelength, high-intensity magnetic source bodies and colocated negative Bouguer gravity responses are interpreted to represent shallow granitic intrusions. Long-wavelength magnetic anomalies are inferred to reflect the topography of a seismically reflective and magnetic lower basement. Potential field forward modelling indicates that the Thomson Orogen might be a single terrane. We interpret that the lower basement consists of attenuated Precambrian and mafic enriched continental crust, which differs from the oceanic crust of the Lachlan Orogen further south.  相似文献   

18.
从深部矿地球化学勘查实际需求出发,根据近年来20余个矿床研究结果,总结提出了热液成因有色金属矿床矿致异常规律--多维异常体系。多维异常体系是指产出在特定成矿地质时期地质体中,空间有序共存、形成机理各异、成矿指向递进的多属性地球化学异常体系,将在斑岩型、矽卡岩型、热液型以及沉积改造型等与热液作用有关的有色金属矿产深部矿预测和评价中发挥重要作用。以安徽马头斑岩型钼铜矿为例,对该矿床多维异常体系进行了探讨。结果表明: 在该矿床中,存在着以Na2O为代表的负异常体系、以S为代表的矿化剂元素异常体系、矿化剂元素S与Fe和成矿元素间协同平衡体系、成矿及其伴生元素异常体系等,这些异常体系对成矿的指示作用是递进的,从而证实了多维异常体系的存在。对应用多维异常体系思路预测和评价深部矿进行了说明。  相似文献   

19.
Osmium isotopic compositions, abundances of highly siderophile elements (HSE: platinum group elements, Re and Au), the chalcogen elements S, Se and Te and major and minor elements were analysed in physically separated size fractions and components of the ordinary chondrites WSG 95300 (H3.3, meteorite find) and Parnallee (LL3.6, meteorite fall). Fine grained magnetic fractions are 268-65 times enriched in HSE compared to the non-magnetic fractions. A significant deviation of some fractions of WSG 95300 from the 4.568 Ga 187Re-187Os isochron was caused by redistribution of Re due to weathering of metal. HSE abundance patterns show that at least four different types of HSE carriers are present in WSG 95300 and Parnallee. The HSE carriers display (i) CI chondritic HSE ratios, (ii) variable Re/Os ratios, (iii) lower than CI chondritic Pd/Ir and Au/Ir and (iv) higher Pt/Ir and Pt/Ru than in CI chondrites. These differences between components clearly indicate the loss of refractory HSE carrier phases before accretion of the components. Tellurium abundances correlate with Pd and are decoupled from S, suggesting that most Te partitioned into metal during the last high-temperature event. Tellurium is depleted in all fractions compared to CI chondrite normalized Se abundances. The depletion of Te is likely associated with the high temperature history of the metal precursors of H and LL chondrites and occurred independent of the metal loss event that depleted LL chondrites in siderophile elements. Most non-magnetic and slightly magnetic fractions have S/Se close to CI chondrites. In contrast, the decoupling of Te and Se from S in magnetic fractions suggests the influence of volatility and metal-silicate partitioning on the abundances of the chalcogen elements. The influence of terrestrial weathering on chalcogen element systematics of these meteorites appears to be negligible.  相似文献   

20.
There is a growing trend to try to make surface geochemistry effective for exploring areas of transported cover using sensitive techniques such as partial extractions of soil and gas analysis. However, these techniques have had mixed success in delineating buried ore bodies, because the particular mechanisms and their effectiveness in transferring ore-related metals upwards through transported cover are poorly understood. This precludes discriminating null results (a potentially ineffective technique) from negative results (no mineralization). A review of mechanisms capable of transferring metals through barren transported cover to the surface identified those well documented and others not well studied but nonetheless promising. The mechanisms are classified according to two main processes: phreatic process involving groundwater flow, convection, dilatancy, bubbles, diffusion and electromigration; and vadose processes involving capillary migration, gaseous transport and biological transfer. Microbial metabolism affects the kinetics of many hydrochemical processes, especially sulfide oxidation and other redox transfers, and also impacts, negatively and positively, on the generation of gases throughout the entire cover sequence. Phreatic mechanisms require groundwater to transfer solutes and are most effective. These have the most predictive capability where there are shallow water tables. In the Australian landscape, groundwater occurs commonly more than 5 m below surface except in lower, discharge landform sites, and therefore other mechanisms (biological, capillary, gaseous), are necessary to transfer metals up from the water table. Thus, much of the emphasis in this paper is on vadose processes. An integrated approach is necessary, combining different mechanisms with the nature and evolution of the transported cover and climatic settings. Regions and landforms of highly weathered transported cover with current or past water tables residing within the cover and long-standing vegetation will favor combined mechanisms such as electrochemical, plant uptake, capillarity, and bioturbation. Fresh, relatively unweathered and thick (> 30 m) transported cover may prove the most unlikely to develop surface geochemical anomalies. Gas (e.g. CO2, H2S) mechanisms may work, provided that sufficient gases are generated from the oxidation of ore to produce a surface signature.  相似文献   

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