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1.
《International Geology Review》2012,54(9):1097-1121
The Coastal Accretionary Complex of central Chile constitutes the product of early Carboniferous to Late Triassic subduction at the rear of Chilenia, a continental terrane likely derived from Laurentia and accreted to southwestern margin of Gondwana during the Mid to Late Devonian. The complex contains basaltic metavolcanic sequences of the subducted oceanic lithosphere accreted to the active margin. In this paper, we address the tectonic setting of these rocks by means of a geochemical study in the coastal area of Pichilemu region, central Chile. The accreted fragments of oceanic crust occupy different structural levels, exhibit variable metamorphic grade, and have geochemical fingerprints that reveal a compositional heterogeneity of the subducted oceanic crust. The amphibolites have N to E-MORB compositions. Greenschist units include N-MORB and E-MORB transitional to OIB, and blueschists and greenschists interleaved within a single metavolcanosedimentary sequence have OIB signatures. Neodymium isotopic systematics indicate depleted and enriched mantle sources, whereas strontium isotopic systematics indicate seawater/rock interaction. The variety of rocks suggests formation in an oceanic setting characterized by shallow and deep mantle sources, such as plume-influenced ridge. Based on the geological, petrological, geochemical, and isotopic characteristics, we propose that the metavolcanic protoliths of the Pichilemu region formed relatively close to the western margin of the Chilenia terrane during the initial stage (late Cambrian–Early Devonian) of seafloor development and drifting of this continental block. Geochemical similarities with oceanic units accreted to the active margin south of the Pichilemu region indicate a regional pattern of the oceanic crust subducted under the Palaeozoic Chilean margin between, at least, 34°S and 39°S latitude, strongly supporting the activity of a mantle plume. This, in turn, can be correlated with the location of the Pacific plume generation zone in early Palaeozoic era, corroborating a Laurentian origin for the Chilenia terrane. 相似文献
2.
河北省张家口崇礼区北部地球化学特征及其找矿指示 总被引：1，自引：1，他引：0
地球化学测量成果被广泛而成熟地运用在矿产勘查工作中,为明确张家口崇礼区北部成矿、找矿的地球化学指示信息,对该区水系沉积物测量及异常查证成果进行了综合分析。通过计算元素富集系数和变异系数、开展R型聚类分析、统计化探异常区岩石的地质年代、对比该区化探异常及已知矿床与典型矿床的成矿要素,从而推断了该区找矿主攻元素为Ag、Pb、Zn、Mo、Cd,且Ag、Pb、Zn和Mo、W 2组元素分别具有共伴生关系,指出该区化探异常主要受燕山期岩浆热液控制。综合分析认为,本区找矿模型为蔡家营式次火山-热液型多金属矿床,具有寻找次火山-热液型Ag、Pb、Zn、Mo多金属矿床的潜力。 相似文献
3.
James P. Dorian Dr. Allen L. Clark Dr. Yi-Ying Sun Zou-Xia Zhou Ji-Liang Li 《GeoJournal》1988,17(3):373-388
This paper attempts to define apparent mineral distribution patterns of China according to tectono-stratigraphic terrane geology. Associations between specific mineral and hydrocarbon deposits and specific tectono-stratigraphic terranes in China suggest that deposits of certain types are spatially constrained by terrane geology. The definition of specific tectono-stratigraphic terranes of China is a valuable initial step in interpreting the geologic history of the nation, although terrane analysis of China is at a very early stage. The recognition that specific deposit types are associated with specific tectono-stratigraphic terranes may make it possible to select appropriate analogues from elsewhere in the world to evaluate China's mineral and hydrocarbon potential. Additionally, understanding the associations between mineral and hydrocarbon deposits and tectono-stratigraphic terranes in China may serve as an aid to future exploration in the nation. 相似文献
4.
为研究滇黔桂卡林型金矿区水系沉积物和岩石中金的地球化学时空分布及其与金矿规模的对应关系,系统收集了该区1:20万区域化探全国扫面计划水系沉积物和全国地球化学基准计划岩石金的地球化学数据,绘制了水系沉积物和岩石金的地球化学分布图。滇黔桂卡林型金矿区以水系沉积物金地球化学异常面积大于1000 km^2为准,共圈定5处金的地球化学省,这些金的地球化学省同时也是矿床大规模产出的部位。区内右江盆地水系沉积物金背景值(1.94×10^–9)高于扬子克拉通(1.68×10^9),其内以泥岩、页岩、砂岩、灰岩为代表的容矿岩石金背景值(0.51×10^–9)也高于扬子克拉通(0.39×10^–9)。研究区不同构造单元及沉积相中水系沉积物金背景值受岩石金背景值的制约。金的地球化学省是地壳演化过程中不均匀分布的高金背景岩石、金矿化作用及金矿床次生风化作用相互叠加的结果。该研究有助于有效判断异常成因、识别成矿作用存在,对研究金的区域成矿规律和聚焦找矿靶区具有重要意义。 相似文献
5.
《Gondwana Research》2001,4(3):319-328
Examination of Landsat TM images, reconnaissance field traverses and the published geological maps from the Eastern Ghats Mobile Belt (EGMB), India, reveal a network of major ductile shear zones both within and at the margins. These shear zones are characterized by mylonitic foliation, grain size reduction, metamorphic retrogression, stretching lineations and distinct signatures of alkaline, anorthositic and granitic magmatism. These shear zones divide the EGMB into distinct terranes, which are heterogeneously deformed with extensive tracts of foliated mylonitic gneisses and ultramylonites. The main gneissic foliation in all the terranes is refolded in near non-coaxial manner generally about the axis subparallel to the elongation of the terrane.Structural history in each terrane is distinct in the orientation of stretching lineations, attitude of gneissosity and early fold axial planes, lithological assemblages and available geochronological data. It is possible to recognise nine large terranes within the EGMB and the characteristics of each terrane have been described. The terrane distribution in the EGMB could well fit a thrust tectonic, allochthonous model of amalgamation and accretion. Different terranes could be different thrust nappes or allochthonous tectonic sheets representing tectono-stratigraphic terranes. 相似文献
6.
As a result of structural–geological and metallogenic studies and taking into account earlier works, it is established that the Oka ore district formed mainly in the Neoproterozoic–Early Paleozoic under conditions of tectonomagmatic reworking of cratonic terranes and allochtonous oceanic (ophiolitic) terranes over them. The reworking was initiated by island-arc, accretionary–collisional, and plume-related igneous complexes, which arose due to opening and subsequent closure of marginal structures pertaining to the Paleoasian Ocean. Active Middle and Late Paleozoic volcanic and plutonic processes gave rise to the redistribution of ore matter and formation of new mineral deposits. 相似文献
7.
The use of mineral deposit density regression models to estimate the number of undiscovered deposits is gaining acceptance in mineral resources assessments. The deposit density regression models currently in use are based on well-established power law relationships between deposit density (deposits/km2) and the areal extent of the host rocks in well explored regions (control areas) worldwide. Although these generalized or global deposit density models can generate guideline estimates that are useful at the terrane scale, locally-derived terrane-based deposit density regression models may potentially yield more relevant estimates at the terrane scale. Using 12 selected komatiite-defined control areas in the Kalgoorlie Terrane, Western Australia, we found that the size (km2) of the control areas had power law relationships with (i) nickel sulphide deposit density, and (ii) nickel endowment density (nickel metal/km2). Regression analyses showed that both power law relationships are statistically significant at the 5% level. This suggests that nickel sulphide deposit and endowment density models could be used to estimate the number of undiscovered nickel sulphide deposits and amount of nickel metal endowment in less explored komatiites in the Kalgoorlie Terrane. This study shows that global geological relationships can be viably downscaled onto local geological terranes thereby supporting the hypothesis that the processes of mineral deposit formation and preservation are scale-independent and self-similar. 相似文献
8.
杨家杖子钼矿田位于著名的八家子-杨家杖子岩浆热液成矿带的中部,成矿带内由于沉积地层有利、岩浆岩发育、断裂构造复杂等一系列有利条件而形成了一大批大、中型钼矿床.以区域地质特征为基础,重点对矿田内最发育的兰家沟钼矿、杨家杖子钼矿和北松树卯钼矿成矿地质背景、矿床地质特征进行了详尽的研究,并结合成矿物质来源、成矿温度、成矿时代重新确定矿床成因,总结成矿主要过程,从而建立矿田区域成矿模式.在此基础上总结了杨家杖子钼矿田地质、物探、化探找矿标志. 相似文献
9.
《Applied Geochemistry》2005,20(5):1017-1037
Some 434 stream sediment samples were collected in Central Japan for a nationwide geochemical mapping project. The resulting geochemical maps are compared with geological, mineral resource and land use maps. Spatial distribution patterns of elemental concentrations in stream sediments are determined mainly by surface geology. Elevated elemental concentrations of alkali elements, Be, Ga, Y, Cs, Ba, lanthanide (Ln), Tl, Th, and U are consistent with outcrop areas of granite, felsic volcanic rock, and accretionary complexes. High concentrations of MgO, Al2O3, P2O5, CaO, 3d transition metals, Zn, and Sr are present in sediments supplied from mafic volcanic rock, high pressure metamorphic rocks, and mafic-ultramafic rocks in accretionary complexes.A procedure is established and guidelines are set for a statistical test suite for geochemical mapping. Analysis of variance (ANOVA) and multiple comparison tests are effective for comparing means among the data subsets that are classified by parent lithological materials. Among the many procedures that have been proposed for multiple comparison tests, the Holm procedure was selected for this study. Multiple comparison statistically confirmed the correspondence of elemental abundance in stream sediments with surface geologies. However, visual interpretation of some elements is inconsistent with results of multiple comparison. According to the Holm procedure, the U content in stream sediments is affected not by granite, but by felsic volcanic rock. The Holm procedure clarifies that As, Sb, and Bi, that are not explained by the presence of mineral deposits, are enriched significantly in samples derived from accretionary complexes. Hydrothermal activity on the ocean floor might affect their levels of enrichment. Significant enrichment of Cu, Zn, Cd, Sn, Sb, Hg, and Pb observed in urban areas are also supported by the Holm procedure. The authors inferred that these sediment samples had been contaminated. 相似文献
10.
围绕覆盖区矿产综合预测的基本思路和关键方法问题,讨论了非线性矿产预测理论和方法如何在覆盖区矿产综合预测中发挥作用,重点介绍了成矿奇异性理论与非线性矿产预测方法在覆盖区矿产预测“弱信息”提取、“复合叠加信息”分解、“缺失和不完整信息”融合等关键问题中的应用.结合正在实施的中国地质调查局“覆盖区矿产综合预测”计划项目,介绍了三方面的研究进展:(1)覆盖层中地球化学元素迁移机理与覆盖层对地表地球化学异常的屏蔽和衰减作用;(2)如何识别由于覆盖层影响而造成的“弱”且“复杂”的地球化学异常;(3)如何综合具有缺失或不完整的多元勘查信息以达到提高覆盖区矿产综合预测精度、降低预测不确定性的目的.以东天山戈壁沙漠覆盖区海相火山岩型铁矿、大兴安岭南部草原覆盖区铁多金属矿、武夷山层控矽卡岩型铁矿等矿床预测为例,介绍了综合预测方法的应用过程和应用效果.研究结果表明,奇异性理论和分析方法可以有效地用于提取水系沉积物地球化学和地球物理(重、磁)弱异常,合理分解复合叠加异常,在此基础上,采用地球化学和地球物理异常的数据融合技术,分别建立了推断铁镁质火山岩、中酸性侵入岩、矽卡岩和热液蚀变等成矿或控矿地质要素的综合信息模型,以及基于综合预测要素建立的覆盖区矿产预测后验概率证据权模型和模糊逻辑模型.应用结果显示,介绍的预测方法不仅可以在出露区圈定成矿远景区,而且在戈壁沙漠覆盖区及第三、第四系松散沉积物覆盖区等均可圈出具有重要资源潜力的远景区,这些远景区往往会被传统的预测方法所遗漏. 相似文献
11.
The geodynamic nature of the Late Neoproterozoic island-arc dacites (691 ± 8.8 Ma) and rift basalts (572 ± 6.5 Ma) of the Kiselikhinskaya Formation, Kutukasskaya Group, in the Isakovskii terrane is inferred from geochemical data and U–Pb zircon (SHRIMP-II) dates. The volcanic rocks were produced during the late evolutionary history of the Yenisei Range, starting at the origin of oceanic crustal fragments and their accretion to the Siberian craton to the postaccretionary crustal extension and the onset of the Caledonian orogenesis. The reproduced sequence of geological processes marks the early evolution of the Paleo- Asian Ocean in its junction zone with the Siberian craton. The data refine the composition and age of volcanic rocks in the trans-Angara part of the Yenisei Range and specifics of the Neoproterozoic evolution of the Sayan–Yenisei accretionary belt. 相似文献
12.
DUAN Jilin LIU Yanpeng ZHU Lixin MA Shengming GONG Qiuli Alla DOLGOPOLOVA Simone A. LUDWIG 《《地质学报》英文版》2023,97(4):1252-1267
Geochemical maps are of great value in mineral exploration. Integrated geochemical anomaly maps provide comprehensive information about mapping assemblages of element concentrations to possible types of mineralization/ore, but vary depending on expert’s knowledge and experience. This paper aims to test the capability of deep neural networks to delineate integrated anomaly based on a case study of the Zhaojikou Pb-Zn deposit, Southeast China. Three hundred fifty two samples were collected, and ea... 相似文献
13.
J. L. Mair V. J. Ojala B. P. Salier D. I. Groves S. M. Brown 《Australian Journal of Earth Sciences》2013,60(5):895-912
Stress mapping is a numerical modelling technique used to determine the distribution and relative magnitude of stress during deformation in a mineralised terrane. It is based on the general principle that fluid flow in the Earth's crust is primarily related to pressure gradients. It is best applied to epigenetic hydrothermal mineral deposits, where fluid flow and fluid flux are enhanced in dilational sections of structures and in sites of enhanced rock permeability due to high fracture density. These are defined by sites of low minimum principal stress (σ3). Most stress mapping is carried out in two dimensions in plan view using geological maps. This is suitable for terranes with steeply dipping lithostratigraphy and structures in which the distribution of mineral deposits is largely controlled by fault structures portrayed on the maps. However, for terranes with gently dipping sequences and structures, and for situations where deposits are sited in and near the hinges of complex fold structures, stress mapping in cross‐section is preferable. The effectiveness of stress mapping is maximised if mineralisation was late in the evolutionary history of the host terrane, and hence the structural geometry of the terrane and contained deposits were essentially that expressed today. The orientation of syn‐mineralisation far‐field stresses must also be inferred. Two examples of orogenic gold deposits, which meet the above criteria, are used to illustrate the potential of stress mapping in cross‐section. Sunrise Dam, located in the Archaean Yilgarn Craton, is a lode‐gold deposit sited in a thrust‐fold belt. Stress mapping illustrates the heterogeneity of stress distribution in the complex structural geometry of the deposit, and predicts the preferential siting of ore zones around the intersections of more steeply dipping, linking thrusts and banded iron‐formation units, and below the controlling more gently dipping basal thrust, the Sunrise Shear. The Howley Anticline in the Pine Creek block hosts several Palaeoproterozoic gold deposits, sited in complex anticlinal structures in greywacke sequences. Stress mapping indicates that gold ores should develop in the hinge zones of symmetrical anticlines, in the hinge zones and more steeply dipping to overturned limbs of asymmetric anticlines, and in and around thrusts in both anticlines and parasitic synclines. The strong correlation between the predictions of the stress mapping, based on the distribution of low σ3, and the location of gold ores emphasises the potential of stress mapping in cross‐section, not only as an exploration tool for the discovery of additional resources or deposits, but also as a test of geological models. Knowledge of the potential siting of gold ores and their probable orientations also provides a guide to drilling strategies in both mine‐ and regional‐scale exploration. 相似文献
14.
山东半岛的地体构造及金矿成矿的区域地质背景 总被引：5，自引：0，他引：5
本文以不整合面的发现及同位素年龄为依据,重新厘定了本区早前寒武纪的地层,从而搞清了本区的大地构造格架,认为它类似于加拿大地盾的“洋葱构造”。本文将山东半岛划分为４个地体：胶北地体,鲁西地体,胶南地体,胶东南－苏东北－黄海地体。认为胶北地体成矿的大地构造背景与南克拉通成矿背景十分相似。胶南地体,黄海地体对胶北地体的俯冲作用为胶北地体提供了成岩成矿物质。根据胶北群和齐山群的地质及及地球化学特征,认为胶 相似文献
15.
We report quantitative X-ray diffraction, whole-rock geochemical and Sm–Nd isotope data for metabasalts from the Aspiring and Torlesse Terranes in the South Island of New Zealand. These rocks underlie the Mesozoic metasedimentary Otago Schist which is anomalously enriched in gold and host to at least one world-class orogenic gold deposit at Macraes (> 125 t Au). Geochemical and Nd isotopic similarities between the samples point to a common history of the two terranes rather than the amalgamation of one or two allochthonous plate fragments. Furthermore, geochemical and Nd data suggest the metabasalts within both terranes formed in an oceanic but essentially non-subduction-related setting. The origin of the Aspiring and Torlesse basalts can be linked to the formation of an oceanic plateau that had resulted from a (?Permian) mantle plume initiation event proximal to a mid-oceanic rise or triple junction. Given the intrinsically gold-enriched nature of certain oceanic-character mafic rocks, the anomalous gold endowment of the Otago Schist may have been enhanced via the accretion and subduction of a gold-enriched oceanic plateau fragment. The metabasalts are generally enriched in gold (up to 13 ppb) compared to their enclosing metasedimentary rocks (typically ca. 1 ppb), with sulphide-rich metabasaltic rocks having up to 550 ppb Au. However, the relatively small volume of metabasalts in the Otago Schist precludes these rocks as the principal source for Otago Schist orogenic gold, with a primarily metasedimentary source of the gold potentially having a limiting effect on the overall endowment of the Otago Schist. This approach, that employs petrogenetic fingerprinting of potentially fertile source rocks for the assessment of gold endowment, might prove useful in the conceptual exploration targeting of relatively immature and poorly exposed terrains. 相似文献
16.
This study used regional geochemical survey data (1:200,000 scale) from the Manzouli area of China to assess mineral resources. Geochemical survey data was rasterized and a geochemical atlas was generated, with the image pixel size determined according to geochemical exploration sample point spacing. The Wunugetushan, Babayi, and Badaguan porphyry copper deposits were selected as model areas for the assessment of copper mineral resources. Three parameters were considered for the calculation of the mineral resources. An ore-bearing hydrothermal alteration coefficient was determined based on geological characteristics and geochemical characteristics of the model area, in order to determine alteration intensity; a denudation coefficient was calculated to determine denudation extent; and a mineralization intensity coefficient was calculated to determine the intensity of mineralization within each pixel. Resource estimation was conducted through regression analysis of model deposit resources and coefficients. The results can be used to determine prospecting target areas based on frequency classification and can be used to estimate the number of ore deposits. Results show that resource estimation using rasterized geochemical data provides high prediction precision and accurate positioning. 相似文献
17.
The Pacific Border Ranges of the southern Alaskan Cordillera are composed of a number of allochthonous tectonostratigraphic terranes. Within these terranes are widespread volcanogenic, massive sulfide deposits in and adjacent to portions of accreted ophiolite complexes, bands and disseminations of chromite in accreted island-arc ultramafic rocks, and epigenetic, gold-bearing quartz veins in metamorphosed turbidite sequences. A geochemical pilot study was undertaken to determine the most efficient exploration strategy for locating these types of mineral deposits within the Pacific Border Ranges and other typical convergent continental margin environments.High-density sediment sampling was carried out in first- and second-order stream channels surrounding typical gold, chromite and massive sulfide occurrences. At each site, a stream-sediment and a panned-concentrate sample were collected. In the laboratory, the stream sediments were sieved into coarse-sand, fine- to medium-sand, and silt- to clay-size fractions prior to analysis. One split of the panned concentrates was retained for analysis; a second split was further concentrated by gravity separation in heavy liquids and then divided into magnetic, weakly magnetic and nonmagnetic fractions for analysis. A number of different techniques including atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and semi-quantitative emission spectrography were used to analyze the various sample media.Comparison of the various types of sample media shows that in this tectonic environment it is most efficient to include a silt- to clay-size sediment fraction and a panned-concentrate sample. Even with the relatively low detection limits for many elements by plasma spectrometry and atomic absorption spectrometry, anomalies reflecting the presence of gold veins could not be identified in any of the stream-sediment fractions. Unseparated panned-concentrate samples should be analyzed by emission spectroscopy and atomic absorption spectrometry for Ag and Au. If, however, magnetic and nonmagnetic concentrate fractions are used in a reconnaissance program, semiquantitative emission spectrography is adequate for all analytical work. 相似文献
18.
New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin. 相似文献
19.
20.
I. K. Kozakov V. P. Kovach E. V. Bibikova T. I. Kirnozova N. Yu. Zagornaya Yu. V. Plotkina V. N. Podkovyrov 《Petrology》2007,15(2):126-150
The paper reports newly obtained geological, geochronological (U-Pb zircon method), Nd isotopic, and geochemical data on Middle and Late Paleozoic granitoids and metamorphic rocks from the southern slope of the Mongolian Altai and Gobi Altai and on granitoids from the Trans-Altai Gobi. Tectonically, the former rocks are hosted in the margin of a Caledonian paleocontinent, and the latter are localized among island-arc and oceanic complexes related to the development of the Hercynian Southern Mongolian Ocean. According to their geological setting, the intrusive complexes are subdivided into two major groups: (i) related to processes of regional metamorphism and (ii) separated from these processes. Geochemical data suggest that the source of most of the granitoids and metamorphic rocks contained island-arc rocks and their erosion products. Nd isotopic evidence indicates that practically all of the allochthonous granitoids, regardless of their composition, age, and structural setting, have positive ?Nd(T) values [i.e., belong to the ?(+) type] and could not be formed by the melting of metaterrigenous rocks widespread at the modern erosion level. These granitoids in both the Caledonian and the Hercynian structures have practically identical Late Riphean Nd model ages [TNd(DM) = 0.97–0.60 Ga], which become slightly younger in the granitoids of the Hercynides. The exception are ultrametamorphic subautochthonous ?(?) granites of the first group localized in the peripheral part of migmatite fields. The sources of these granitoids could be the host metaterrigenous rocks. The results obtained in the course of this research suggest, with regard for preexisting data on granitoids in the isotopic provinces in Central Asia, that the sources of the Paleozoic granitoids were the rocks of the “juvenile” Caledonian and Hercynian island-arc crust and of the older crust of cratonic blocks with a Early Precambrian and Late Riphean basement, respectively. The Late Riphean crustal material in Caledonian and Hercynian structures related to the development of the corresponding oceanic basins most probably consisted of clastic sediments or relatively small fragments of the Late Riphean crust. The occurrence of this crustal material in the sources of the granitoids can be explained by the involvement of sediments in subduction zones and the participation of these sediments and fragments of Late Riphean complexes in the accretionary-collision processes during the closure of the paleoceanic basins. Simultaneously, the subduction zones received juvenile material that could be later involved in the melting processes together with older rocks. 相似文献