首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Geochemical anomaly separation using the concentration–number (C–N) method at the Haftcheshmeh porphyry system in NW Iran is the aim of this study. We used lithogeochemical data sets to explore Cu, Mo, Au and Re mineralization in gabbroic, dioritic and monzonitic units at the Haftcheshmeh Cu–Mo porphyry system. The obtained results were interpreted using a rather extensive set of information available for each mineralized area, consisting of detailed geological mapping, structural interpretation and alteration data. Threshold values of elemental anomalies for the mineralized zone were computed and compared with the statistical methods based on the data obtained from chemical analyses of samples for the lithological units. Several anomalies at local scale were identified for Cu (40 ppm), Mo (12 ppm), Au (79 ppb), and Re (0.02 ppm), and the results suggest the existence of local Cu anomalies whose magnitude generally is above 500 ppm. The log–log plots show the existence of three stages of Cu and Mo enrichment, and two enrichment stages for Au and Re. The third and most important mineralization event is responsible for presence of Cu at grades above 159 ppm. The identified anomalies in Haftcheshmeh porphyry system, and distribution of the rock types, are mainly gabbrodiorite–monzodiorite, granodiorite and monzodiorite–diorite that have special correlation with Cu–Mo and gabbroic and monzonitic rocks, especially the gabbrodiorite–monzodiorite type, which is of considerable importance. The study shows that these elemental anomalous parts have been concentrated dominantly by potassic and phyllic, argillic and propylitic alterations within the gabbroic, monzonitic and dioritic rocks especially in the gabrodioritic type in certain parts of the area. The results, which were compared with fault distribution patterns, revealed a positive correlation between mineralization in anomalous areas and the faults present in the mineralized system.  相似文献   

2.
Geochemical anomaly separation and identification using the number–size (N–S) model at Bardaskan area, NE Iran is studied in this paper. Lithogeochemical data were used in this study which was conducted for the exploration for Au and Cu mineralization and enrichments in Bardaskan area. There are two major mineralization phases concluded epithermal gold and a disseminated systems. N–S log–log plots for Cu, Au, Sb, and As illustrated multifractal natures. Several anomalies at local scale were identified for Au (32 ppb), Cu (28 ppm), As (11 ppm), and Sb (0.8 ppm) and the obtained results suggest existence of local Au and Cu anomalies whose magnitudes generally are above 158 and 354 ppm, respectively. The most important mineralization events are responsible for presence of Au and Cu at grades above 1,778 and 8,912 ppm. The study reveals threshold values for Au and Cu are a consequence of the occurrence of anomalous accumulations of phyllic and silicification alteration zones and metamorphic rocks especially in tuffaceous sandstones and sericite schist types. The obtained results were correlated with fault distribution patterns, revealing a positive direct correlation between mineralization in anomalous areas and the faults present in the mineralized system.  相似文献   

3.
PGE-rich disseminated zones with discrete platinum-group minerals (Pd, Pt and Rh mineral phases) have been discovered in three thick (80–130 m), differentiated (peridotite-gabbro) mafic-ultramafic flows of the Archean Abitibi greenstone belt, Ontario. Three mineralization zones (whole-rock ∑PGE + Au = up to 1000 ppb) occur along four stratigraphic cross sections through a 2 km strike-length of the Boston Creek Flow ferropicritic basalt. Their occurrence most strikingly correlates with lenticular-podiform concentrations of disseminated chalcopyrite (1 %) and clinopyroxene + interstitial magnetite-ilmenite intergrowths (15–20% oxide), high concentrations of related metals (3000 ppm Cu, 3000 ppm S, 1200 ppb Ag, and 1000 ppm V), strong PGE depletion in adjacent rocks and along strike, and lithological and textural complexity in the margins of the central gabbro-diorite layer. The mineralization zone (whole-rock Ir + Pt + Pd + Au = 110 ppb) within Theo's Flow tholeiitic basalt is somewhat similar in occurrence, style, and composition to those within the Boston Creek Flow. In contrast, the mineralization zone (whole-rock Ir + Pt + Pd + Au = 340 ppb) in Fred's Flow komatiitic basalt most strikingly correlates with vesicle-filling intergrowths of pyrrhotite + pentlandite ± chalcopyrite (2 modal %) and high whole-rock concentrations of Ni (2500 ppm), Cu (700 ppm), and S (1.1%) in the upper chilled margin of the flow.Although apparently uneconomic, these flow-hosted PGE mineralization zones are of interest in exploration, because they are more similar in stratigraphie setting, style, and composition to PGE-rich disseminated Fe-Cu sulfide mineralization zones within thick differentiated intrusions than to mineralization zones in other Archean volcanic rocks. The characteristics of the mineralization zones and their host rocks, especially high degrees of PGE enrichment, vertical and horizontal patterns of PGE depletion, and accumulation of clinopyroxene + magnetite-ilmenite intergrowths, indicate a critical genetic role for variations in the regime of melt flowage. The mineralization zones in the Boston Creek and Theo's Flows are interpreted to have formed by simultaneous in situ formation of PGE-rich Fe-Cu sulfide and Fe-Ti oxide from flowing silicate liquid in the margins of internal lava channels. The mineralization zone in Fred's Flow is interpreted to have formed by ponding and coalescence of PGE-enriched sulfurous vapor bubbles in the upper chilled margin during olivine accumulation on the base of a dynamic lava channel. The relative abundance of PGE mineralization zones and high degree of PGE enrichment in the Boston Creek Flow suggest that the most favorable exploration targets are rocks crystallized from late-stage, highly fractionated derivative liquids in large differentiated terropicritic units.  相似文献   

4.
Peridotite and granite xenoliths, in the early stage of weathering, occur in the Nyos volcanic region (NW Cameroon). Geochemical data shows that peridotites are marked by high concentrations of MgO (42.30 wt.%, with SiO2/MgO ∼ 1), chromium (2100 ppm), nickel (2100 ppm) and cobalt (104 ppm), as well as by low lanthanide contents (ΣREE: 7.41 ppm). Granites display SiO2 contents (70–73 wt.%), and are mostly peraluminous (1.40 > A/CNK < 1.6). They are also characterized by low contents in chromium (<24 ppm), nickel (ranging from 6 to 15 ppm) and cobalt (ranging from 3 to 6 ppm). Granites possess high lanthanide contents (ΣREE varying between 248.00 and 463.00 ppm), particularly in light lanthanides (LREE/HREE ratios ranging from 21 to 32). The chondrite-normalized patterns of the studied xenoliths are characterized by: (i) LREE enrichments in both rock types; (ii) negative Eu anomalies ([Eu/Eu*] ranging from 0.45 to 0.64) and weak positive Ce anomalies ([Ce/Ce*] ranging from 1.06 to 1.46) in granites. The weathering process provokes a remobilization of several trace elements notably light lanthanides.The geochemical survey of Platinum-Group Elements (PGE) done in these rocks in the early stage of weathering shows that PGE contents are less than 7 ppb in the peridotites. The highly concentrated elements are ruthenium (6.26 ppb) and platinum (5.53 ppb). The total PGE content is 14.57 ppb. These concentrations normalized with respect to chondrites display a flat spectrum from iridium to platinum. PGE contents in the granites are below detection limit except for two samples (LNY01 and LNY02) whose platinum content is close to 0.23 ppb.  相似文献   

5.
The Matuu-Masinga study area, located about 70 km north-east of Nairobi, is predominantly underlain by rocks of the Neoproterozoic Mozambique Belt (MB) of Kenya. The rocks vary from medium to high grade gneisses and granulites, that are intruded by granites, anorthosites, diorites and gabbros. Important high-grade tectonothermal events in the belt took place between about 845 and 715 Ma B.P. The subsequent cooling and uplift of the basement has been traced by K-Ar dates on biotites, which range between 438 and 528 Ma. The belt has been inferred to mark the sites for several superimposed Proterozoic subduction zones and collisional sutures (Muhongo, 1998, and references therein).The general structural trend in the survey area varies from NNW-SSE to NW-SE direction, with westerly dips and localized concentric trends around granitoid intrusions. Competent mafic lensoidal layers that have undergone ductile deformation and associated with rotated boudins and displaced micro-faults define a sinistral sense of shear. The several shear zones, cleavage patterns, boudins and thinning suggest severe strains.The mafic and granitic rocks are interpreted to be mainly metaluminous to slightly peraluminous. Geochemical data and field studies suggest that the granites are of calc-alkaline origin. The discriminant diagrams suggest a dominantly island arc-tectonic setting with subordinate within plate environment.Rb-Sr whole-rock age of 558 ± 16 Ma is given on the granite from Mavoloni hills, Matuu area. From the low initial 87Sr/86Sr ratio of 0.70398, the age is interpreted to indicate the time of emplacement for granite magma from a deep crustal or upper mantle material.The gabbroic and granitic rocks in Matuu-Masinga area, with high Ba (av. 1331 ppm) and Zr (av. 370 ppm) contents, are interpreted to have contained hornblende and biotite mineral assemblage phases that had a relatively high distribution coefficients for Ba and Z. The relatively high concentration of Cu (188–5810 ppm, av. 1960 ppm) and Zn (88–264 ppm, av. 155 ppm) in the mafic rocks of the study area invokes further exploration of their ore minerals.  相似文献   

6.
Geochemical anomaly separation using the concentration–area (C–A) method at Kahang (Gor Gor) porphyry system in Central Iran is studied in this work. Lithogeochemical data sets were used in this geochemical survey which was conducted for the exploration for Cu mineralization in dioritic and andesitic units at Kahang Cu–Mo porphyry system. Similar surveys were also carried out for Mo and Au exploration in these rock units. The obtained results have been interpreted using rather extensive set of information available for each mineralized area, consists of detailed geological mapping, structural interpretation and alteration data. Anomalous threshold values for the mineralized zone were computed and compared with the statistical methods based on the data obtained from chemical analysis of samples for the lithological units. Several anomalies at a local scale were identified for Cu (224 ppm), Mo (63 ppm), and Au (31 ppb), and the obtained results suggests existence of local Cu anomalies whose magnitude generally is above 1000 ppm. The correlation between these threshold values and ore grades is clearly interpreted in this investigation. Also, the log–log plots show existence of three stages of Cu enrichment, and two enrichment stages for Mo and Au. The third and most important mineralization event is responsible for the presence of Cu at grades above 1995 ppm. The identified anomalies in Kahang porphyry system, and distribution of the rock types, are mainly monzodiorite and andesitic units, do have special correlation with Cu and monzonitic and dioritic rocks, especially monzodioritic type, which is of considerable emphasis. The threshold values obtained for each element are always lower than their mean content in the rocks. The study shows threshold values for Cu is clearly above the mean rock content, being a consequence of the occurrence of anomalous accumulations of phyllic, argillic and propyllitic alterations within the monzonitic and dioritic rocks especially in monzodioritic type. The obtained results were compared with fault distribution patterns which reveal a positive direct correlation between mineralization in anomalous areas and the faults present in the mineralized system.  相似文献   

7.
《International Geology Review》2012,54(15):1941-1958
The Qiarbahete complex in NW China consists of gabbroic diorite, granodiorite, and late-stage quartz diorite porphyry veins. Zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses show that the gabbroic diorite and granodiorite formed at 368 ± 5.2 Ma and 354 ± 4.1 Ma, respectively, indicating that the complex was emplaced in the Late Devonian–Early Carboniferous. The gabbroic diorites, characteristic of Sanukitoids, exhibit high Mg# (62 average), MgO (6.84% average), Cr (195 ppm average), and Ni (61.4 ppm average) contents. The rocks show moderately fractionated rare earth element (REEs) patterns and weak negative Eu anomalies (δEu: 0.83–0.89), enrichment of large ion lithophile elements (LILEs), and depletion of high field strength elements (HFSEs), with low ?Nd(t) values (1.46–1.73). The gabbroic diorites originated from partial melting of a hydrous mantle wedge followed by assimilation of crust during ascent. The granodiorites show a geochemical affinity with adakitic rocks, e.g. SiO2 (64.95–67.87%) > 56%, Al2O3 (15.88–16.56%) > 15%, MgO (1.79–2.31%) < 3%, Sr (315–375 ppm) > 300 ppm, and Yb (1.84–2.06 ppm). They are enriched in light rare earth elements (LREEs) and LILEs and depleted in HFSEs, with weak negative Eu anomalies (δEu: 0.78–0.87). The granodiorites were mainly derived by the partial melting of a subducted oceanic slab, followed by subsequent melt–mantle interaction and crustal rocks contamination. All these indicate that the Qiarbahete complex was emplaced in a continental arc setting attending the southward subduction of the Junggar Ocean during the Late Devonian–early Carboniferous, generating the lateral accretion of continental crust in NW Tianshan.  相似文献   

8.
Direct correlation have been observed between certain trace element and hydrocarbon anomalies in the near subsurface soils of Vindhyan basin, India. This relationship with hydrocarbon is very useful in hydrocarbon exploration. 52 soil samples from Vindhyan basin were collected from a depth of 2.5m. All the soil samples were analyzed for light hydrocarbon, isotope and trace element concentrations. The adsorbed light gaseous hydrocarbon analyses show the presence of methane (8–328 ppb), ethane (0–27 ppb) and propane (0–11 ppb) respectively and these values indicate the presence of hydrocarbon micro-seepage in the study area. The carbon isotopic values determined for methane and ethane for these soil samples are (?26.41 to ?47.70 ‰ PDB) and (?20.07 to ?35.30 ‰ PDB) respectively and they are thermogenic in nature. The trace element concentrations of nickel (33–220 ppm), vanadium (72–226 ppm), copper (20–131 ppm), chromium (94–205 ppm), zinc (66–561 ppm) and cobalt (9–39 ppm) have higher than the normal concentrations in soils. Trace element concentrations are used to plot with the data obtained from light gaseous hydrocarbon concentrations and carbon isotopic values of soil samples of the Vindhyan basin. Trace element anomalies have been observed around the hydrocarbon anomalies in the study area.  相似文献   

9.
The Bulletin lode-gold deposit is within the northernmost part of the Norseman–Wiluna greenstone belt in the Archaean Yilgarn Block, Western Australia. It is located within a brittle–ductile shear zone and hosted by tholeiitic metavolcanic rocks. Syn-metamorphic wallrock alteration envelops the gold mineralisation and is pervasive throughout the entire shear zone and extends up to 150 m into the undeformed wallrocks. Alteration is characterised by the sequence of distal chlorite–calcite, intermediate calcite–dolomite, outer proximal sericite and inner proximal dolomite–sericite zones. The thickness of the alteration envelope, and the occurrence of dolomite in the alteration sequence, can be used as a rough guide to the width, extent and grade of gold mineralisation, because a positive correlation exists between these variables. Mass transfer evaluations indicate that chemical changes related to the wallrock alteration are similar in all host rocks: in general, Ag, As, Au, Ba, CO2, K, Rb, S, Sb, Te and W are enriched, Na and Y are depleted, and Al, Cr, Cu, Fe, Mg, Mn, Nb, Ni, P, Se, V, Zn and Zr are immobile, while Ca, Si and Sr show only minor or negligible relative changes. The degree of mobility of each component increases with proximity to gold mineralisation. The largest potential exploration targets are possibly defined by regional As (>6 ppm) and Sb (>0.6 ppm) anomalies. These anomalies, if real, extend laterally for >150 m from the mineralised shear zone into areas of apparently unaltered rocks. Anomalies defined by Te (>10 ppb), W (>0.6 ppm), carbonation indices, local enrichment of Sb (>2.0 ppm) and As (>28 ppm), and potassic alteration indices also form significant exploration targets extending beyond the HJB shear zone and the Au anomaly (>6 ppb) and, locally, into apparently unaltered rock. Gold, itself, has a restricted dispersion, with an anomaly extending for 1–35 m from ore, and being restricted to within the shear zone itself. Amongst individual geochemical parameters, only As and Sb define significant, consistent and smooth trends (vectors) when laterally approaching the ore. However, the respective dimensions of individual geochemical anomalies can be used as an extensive, though stepwise, vector towards ore.  相似文献   

10.
Detrital zircon U–Pb ages, whole-rock Nd isotopic, and geochemical data of metasedimentary rocks from the Wutai Complex in the Central Zone, North China Craton, have been determined. Compositionally, these rocks are characterized by a narrow variation in SiO2/Al2O3 (2.78–3.96, except sample 2007-1), variable Eu anomalies, spanning a range from significantly negative Eu anomalies to slightly positive anomalies (Eu/Eu* = 0.58–1.12), and positive ε Nd (t) values (0.1–1.97). The 18 detrital zircons of one sample yielded age populations of 2.53 Ga, 2.60 Ga, and 2.70–2.85 Ga. Geochemical data reveal intermediate source weathering, varying degrees of K-metasomatism in the majority of these metasedimentary rocks, whereas other secondary disturbances seem to be negligible. Detailed analysis in detrital zircon U–Pb geochronology, whole-rock Nd isotope, and geochemistry shows that these metasedimentary rocks are derived from a mixed provenance. The predominant derivation is from the late Archean granitoids and metamorphic volcanics in the Wutai Complex, and there is also input of older continental remnants, except TTG gneisses, from the Hengshan and Fuping Complexes. The sediments were probably deposited in fore-arc or/and intra-arc basins within an arc system.  相似文献   

11.
In this paper, we report new whole-rock geochemical and zircon U–Pb data for monzogranites in the NE Xing’an block. These data constrained the petrogenesis of C type (high Sr/Y) adakitic rocks and showed the spatial extent of the influence of the Mongol-Okhostsk ocean tectonic regime and the collision between the Jiamusi Massif and Songliao Terrane. New zircon laser-ablation inductivity coupled plasma mass spectrometry (LA-ICP-MS) U–Pb data indicated that the monzogranites in the studied area were emplaced in the Early Jurassic (~180 Ma). These rocks were characterized by unusally high SiO2 (≥67.49), and Sr (461–759 ppm), but strikingly low Y (4.63–8.06 ppm) and HREE (∑HREE = 3.83–6.49 ppm, Yb = 0.5–0.77 ppm) contents, with therefore high Sr/Y (67.2–119) and (La/Yb)N (29.7–41.5) ratios, showing the geochemical characteristics of C type adakitic granite. The data displayed negligible Eu anomalies (Eu/Eu* = 0.77–1.08), LREE-enriched and pronounced negative Nb and Ta anomalies. The C-type adakites in the studied area were most likely derived from the partial melting of a thickened lower continental curst. The magma source is most likely dominated by amphibolites and garnet amphibolites. In combination with previously-reported data from igneous rocks from the Mesozoic in NE China, we conclude that the Xing’an block was influenced by the Mongol-Okhotsk subduction tectonic system, and experiences compressive settings from the amalgamation of the Jiamusi block in the east of the CAOB.  相似文献   

12.
M.E.P. Gomes  A.M.R. Neiva 《Lithos》2005,81(1-4):235-254
Deformed Hercynian peraluminous granitoids ranging from tonalite to granite crop out in the Rebordelo–Agrochão area, northern Portugal and some of them contain tonalitic and granodioritic enclaves. Variation diagrams of major and trace elements of the rocks, biotites and sphenes show fractionation trends. The most- and the least-deformed samples of granite and their biotites also define fractionation trends. There is decrease in all rare earth element (REE) contents and increase in the Eu anomaly in REE patterns from the most- to the least-deformed samples of granite. All the granitoids define a whole-rock Rb–Sr errorchron. A whole-rock Rb–Sr isochron for the least-deformed samples of granite yields an age of 357±9 Ma and an initial 87Sr/86Sr ratio of 0.7087±0.0007. Geochemical modelling suggests that the tonalitic magma evolved by AFC (fractional crystallization of magnesiohornblende, plagioclase, quartz, biotite and ilmenite, and assimilation of metasediments) to originate tonalitic and granodioritic enclaves, granodiorite and granite. δ18O values support this mechanism. The tonalite is hybrid and derived by interaction of a mantle-derived magma and crustal materials.  相似文献   

13.
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   

14.
基于数字高程模型因子分析的地球化学异常提取   总被引：1，自引：0，他引：1  
利用R型因子分析方法,对西北某地区1∶5万图幅岩屑样测试数据进行了分析,提取了5个代表性因子,绘制地球化学分区图。结合区域成矿地质背景、研究区地质条件及野外地质调查发现的41个矿化点,确定具有成矿意义的因子F3(Cu-Zn-Ag组合)。利用基于GIS数字高程模型对F3因子进行异常信息提取,结果显示76%的铜矿化点与异常吻合,较铜单元素圈定的异常提高了10%。异常主体位于志留系公婆泉组变质安山岩与石炭纪侵入岩的接触带(岩性偏安山岩),野外异常查证发现这些异常部位多见矿化现象。研究区北部钾长花岗岩区出现的少量弱小异常,为岩浆热液有关的黄铁矿化及黄铜矿化引起。槽探工程进一步验证了该方法在中大比例尺异常提取方面的良好效果。  相似文献   

15.
青海玛沁县友后青地区大地构造位置处于阿尼玛卿缝合带内,在友后清地区发现了与基性-超基性岩体关系密切的钴铜矿化带。本文主要分析了友后青地区钴铜矿化带的成矿地质特征,认为华力西-印支期NW-NWW向的深大断裂控制着钴铜成矿作用。高精度磁测显示,区内有一条近NWW走向的磁异常带,异常强度中等偏高,呈串珠状分布。水系沉积物测量表明,以镍钴铬为主的多金属综合异常规模大,元素组合齐全,镍钴铬元素异常套合好。水系沉积物地球化学异常与高精度磁测异常可以很好的叠合在一起,在空间上与基性-超基性岩关系密切。沿NW-NWW向断裂带,与基性-超基性岩叠合较好的物化探异常区是该地区寻找钴铜矿的有利地段。  相似文献   

16.
Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology （the whole-rock Sm-Nd and Rb-Sr isochron methods）, major elements, trace elements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during the Late Yanshanian Orogenic Movement （the Cretaceous Period）, as indicated by the Sm-Nd isochron ages （t）=（99.6±4.5） （2σ） Ma and by the Rb-Sr isochron ages t=（97±1.6） （2σ） Ma. The gabbroic intrusions are attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formed under an extensional background of the continent. Differentiation of their magmatic crystallization resulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophile elements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftward inclined without anomalies of JCe or JEu, and there are high concentrations of PGE and ratios of Pd/Ir （averaging 4.21）. All of these imply that their source areas may be basaltic magma in the upper mantle with high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishan basalt, which may be related to the upper mantle at low-grade partial melting. Emplacement mechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as an isolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into the continental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensional deformation could take place in the shallow part of the continental crust while vertical amassing and accretion of magmatic materials in the deep part of the continental crust. These special processes could supposed to be a special background of continental dynamics for this large-scale epithermal metallogenic domain, such as Au  相似文献   

17.
Mafic intrusions and dykes are well preserved in the Yinmin and Lanniping districts, located within the western margin of the Yangtze Block, SW China. Although these mafic rocks from the two areas formed during different periods, they share similar ranges of PGE concentration. Most of the Yinmin gabbroic dykes contain relatively high PGE concentrations (PGEs = 13.9–87.0 ppb) and low S contents (0.003 %–0.020 %), higher than the maximum PGE concentrations of mafic magmas melting from the mantle. Two exceptional Yinmin samples are characterized by relatively low PGE (PGEs = 0.31–0.37 ppb) and high S (0.114 %–0.257 %) contents. In contrast, most samples from the Lanniping gabbroic intrusion have low PGE concentrations (PGEs = 0.12–1.02 ppb) and high S contents (0.130 %–0.360 %), except that the three samples exhibit relatively high PGE (PGEs = 16.3–34.8 ppb) and low S concentrations (0.014 %–0.070 %). All the Yinmin and Lanniping samples are characterized by the enrichment of PPGE relative to IPGE in the primitive-mantle normalized diagrams, and the high-PGE samples exhibit obvious Ru anomalies. This study suggests that during the ascent of the parental magma, removal of Os–Ir–Ru alloys and/or chromite/spinel leads to high Pd/Ir ratios and Ru anomalies for the Yinmin high-PGE samples and relatively lower Pd/Ir ratios and Ru anomalies for the Lanniping low-PGE samples. We propose that the magmas parental to the Yinmin gabbroic dykes are initially S-unsaturated, and subsequently, minor evolved magma reached sulfur saturation and led to sulfide segregation. Although the Lanniping parental magmas are originally not saturated in S, the high Cu/Pd ratios (3.8 × 104 to 3.2 × 106) for most of the Lanniping samples indicate the S-saturated state and sulfide segregation. A calculation shows that the PGE-poor magmas might have experienced 0.01 %–0.1 % sulfide segregation in the magma chamber. Therefore, our study provides a possible opportunity to discover PGE-enriched sulfide mineralization somewhere near or within the Lanniping mafic intrusion.  相似文献   

18.
位于长江中下游的宣城水东地区发育一套酸性火山岩,主要由流纹质角砾岩、流纹岩和珍珠岩组成。本文对该套火山岩进行了详细的锆石U-Pb年代学、主量元素、微量元素以及Nd-Hf同位素研究。LA-ICP MS锆石U-Pb定年结果显示3种岩性的火山岩年龄分别为133.2±0.8、133.4±0.8和131.5±0.9 Ma。主量元素组成上,这套酸性火山岩具高硅(72.51%~81.79%)、富钾(K_2O/Na_2O=2.04~14.93,平均6.72)、贫钙镁(Ca O=0.19%~1.57%,Mg O=0.06%~0.29%)的特征,属于弱过铝质(A/CNK=1.02~1.24)的高钾钙碱性-钾玄岩系列岩石。微量元素方面,轻重稀土元素分馏明显[(La/Yb)_N=5.43~9.17],具明显的负铕异常(Eu/Eu~*=0.44~0.60),富集大离子亲石元素(LILE)Rb、Th、K和Pb等,亏损Ba、Sr、Nb、P和Ti等元素,表现出壳源的特征。全岩Sr-Nd和锆石Hf同位素组成变化范围相对较小,(~(87)Sr/~(86)Sr)_i为0.707 3~0.708 8,εNd(t)值为-7.05~-5.56,εHf(t)为-8.6~-1.3。结合区域地质研究成果,认为宣城水东地区酸性火山岩可能是在约135 Ma古太平洋板块俯冲作用之后的伸展-拉伸环境下,由新元古代早期新生地壳重熔而成。  相似文献   

19.
张家口北部是河北省重要的铅锌银多金属矿床富集区.区内多金属矿床成矿作用和控矿因素相似,矿化形成均与燕山期酸性小岩体侵入变质结晶基底有关.区域多金属矿床化探异常具可对比性.化探异常图显示区内多金属矿床与化探异常在地表总体呈现无偏性空间分布特征,化探数据因子分析结果表明成矿元素相关性在水系沉积物中未发生改变.据此可将原生晕...  相似文献   

20.
In the Eastern Desert of Egypt, younger granites host U and Th mineralisations which are concentrated along faults and joints. In particular, the Gebel Felat Pluton is characterised by a high level of radioactivity as shown by an aeroradiometric survey. The U content is 82 ppm and the Th content is 15 ppm in areas of high radioactivity. The rocks are cross-cut by two main sets of fractures trending east-west and northwest-southeast. The contour maps of these two trends can be correlated with the aeroradiometric map of the same area.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号