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1.
The Mombi bauxite deposit is located in 165 km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al2O3, SiO2, Fe2O3 and TiO2 are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE = 162.8–755.28 ppm, ave. ∼399.36 ppm) relative to argillic limestone (ΣREE = 76.26–84.03 ppm, ave. ∼80.145 ppm) and Sarvak Formation (ΣREE = 40.15 ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce3+ to Ce4+), ionic potential, and complexation of Ce4+ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation.  相似文献   

2.
The bauxites in central Guizhou are hosted by the Lower Carboniferous Jiujialu Formation.Geochemistrial characteristics of the Lindai bauxite deposit indicate that the underlying Shilengshui Formation dolomite is the precursor rock of mineral resources.Weathering simulation experiments show that Si is most likely to migrate with groundwater,the migration rate of which is several magnitude higher than Al and Fe under nature conditions （pH=3-9）.The neutral and acid nonreducing condition is the most conducive to the Al rich and Si removal,while the acid reducing conditions is the most conducive to the Al rich and Fe removal.In the process of bauxite formation,coal beds overlying the Al-bearing rock series or other rock formation rich in organic materials can produce acid reducing groundwater,which are important for the bauxite formation.Finally,propose the metallogenic model of the bauxite in central Guizhou Province and put forward three new words which are ＂original bauxite material＂,＂bauxite material＂ and ＂original bauxite＂.  相似文献   

3.
The Taoxihu deposit (eastern Guangdong, SE China) is a newly discovered Sn polymetallic deposit. Zircon U-Pb dating yielded 141.8 ± 1.0 Ma for the Sn-bearing granite porphyry and 145.5 ± 1.6 Ma for the biotite granite batholith it intruded. The age of the granite porphyry is consistent (within error) with the molybdenite Re–Os isochron age (139.0 ± 1.1 Ma) of the Sn mineralization, indicating a temporal link between the two. Geochemical data show that the granite porphyry is weakly peraluminous, contain high Si, Na and K, low Fe, Mg, Ca and P, and relatively high Rb/Sr and low K/Rb values. The rocks are enriched in Rb, Th, U, K, and Pb and depleted in Ba, Sr, Ti and Eu, resembling highly fractionated I-type granites. They contain bulk rock initial 87Sr/87Sr of 0.707371–0.707730 and εNd(t) of −5.17 to −4.67, and zircon εHf(t) values from −6.67 to −2.32, with late Mesoproterozoic TDM2 ages for both Nd and Hf isotopes. This suggests that the granite porphyry was likely formed by the partial melting of the crustal basement of Mesoproterozoic overall residence age with minor mantle input.δ34SCDT values of the Taoxihu chalcopyrite and pyrite range from 0.1 to 2.1‰ (average: 0.9‰), implying a dominantly magmatic sulfur source. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the Taoxihu sulfide ores are 18.497–18.669, 15.642–15.673 and 38.764–38.934, respectively, indicating a mainly upper continental crustal lead source with minor mantle contribution. The highly fractionated and reduced (low calculated zircon Ce4+/Ce3+ and EuN/EuN1 values) nature of the ore-forming granitic magma may have facilitated the Sn enrichment and played a key role in the Sn mineralization. We propose that the ore-forming fluids at Taoxihu were of magmatic-hydrothermal origin derived from the granite porphyry, and that both the granite porphyry and the Sn mineralization were likely formed in an extensional setting, possibly related to the subduction slab rollback of the Paleo-Pacific Plate.  相似文献   

4.
Three vertical sections through the Zagrad deposit of Jurassic karst bauxite in central Montenegro have provided knowledge of the vertical distribution of major and some selected trace elements, including rare earth elements (REE). Variations in the mineralogy, particularly those hosting REE, have been studied. This has revealed the presence of authigenic mineral phases such as xenotime, mottramite and monazite (best proved using Raman microprobe analysis) as well as residual phases such as zircon, titanite and monazite. The mobility of the elements during bauxitization processes has been studied to show that the REE minerals ensure progressive concentration of these elements during removal of major elements through weathering. The similarity of normalized REE in the bauxite to the typical Post-Archean Australian Shales (PAAS) and Upper Continental Crust (UCC) profile, and the preserved Eu anomaly, are evidence that the bauxite was not derived from carbonates and represents alteration of shale, marly limestone and volcanogenic or proximal igneous sourced detritus that accumulated in the original karst landform. Mass change during bauxitization, using Ti as “index” element and compared to PAAS composition, revealed almost 100% depletion of Si and weak enrichment in Al. Deeper parts of the deposit with authigenic minerals exhibit very strong enrichment in all REE. The bauxite ores have high ΣREE contents (693.5–6953.4 ppm), especially ΣLREE contents (582.8–4882.9 ppm), while ΣHREE contents (106.6–2070.5 ppm) are much lower.  相似文献   

5.
Permian karstic bauxite and its Quaternary derivative, in western Guangxi, southwestern, South China Block, possess a total tonnage greater than 0.5 billion tons. The primary late Permian karstic bauxite formed in reduced environment in the background of Tethyan accretionary orogenesis. And as one consequence of Cenozoic convergence of the Indian and Eurasia continents, the primary orebody was uplifted, eroded and re-sedimented within Quaternary laterite. The geochemical variation and its controls during the ore transformation from Permian to Quaternary remain poorly understood. Quaternary ore blocks comprise an inner zone of fresh ore, and then it gradually transited through a middle zone to a margin with extensive weathering. One such bauxite block was selected and further subdivided into twenty-three samples for geochemical and mineralogical analysis. The inner and middle zones contain similar mineralogical compositions, dominated by diaspore and amesite, with minor illite, anatase, goethite, pyrite, zircon, and rutile. The margin is composed of diaspore, with small amounts of amesite, boehmite, illite, goethite, anatase, kaolinite, zircon, rutile, and barite. Bauxite in all three zones is composed of mainly Al, Si, Fe, and Ti, and high contents of Zr, Cr, Li, F, S, Zn, V, Sr, Nb, Ba, and REE. Variations in Fe2+ and Fe3+ between the three zones were observed. The elements Si, Al, Fe2+, Mg, Ba, Cr, F, Li, Ni, Zn, and REE decrease from the core of the ore block outwards, corresponding to an increase in S and Fe3+. Depletions in Si, Al, Fe2+, Mg, Ba, and Cr were caused by the dissolution of amesite. Most of the Al and Si in amesite were lost during the weathering, and minor retained to form kaolinite. Depletions in Li, Ni, and Zn resulted from changes in the depositional environment between the late Permian and Quaternary. Dissolution of REE-bearing fluorocarbonates resulted in depletions of REE and F. The enrichment of Fe3+ and S was related to the precipitation of goethite, hematite, and barite in an oxidizing environment, while local enrichment of Ce resulted from the redox change of Ce3+ → Ce4+ under the same condition. This shows that the chemical composition of laterite enwrapping the bauxite also took part in Quaternary bauxite transformation. This study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes.  相似文献   

6.
The newly discovered Yuanlingzhai porphyry molybdenum (Mo) deposit in southern Jiangxi province belongs to the group of Mo-only deposits in the Nanling region. The mineralization developed at contact zones between the Yuanlingzhai granite porphyry and Neoproterozoic metamorphic rocks of the Xunwu Formation. Precise LA–MC–ICPMS zircon U–Pb dating of the Yuanlingzhai porphyry, as well as the adjacent western Keshubei and eastern Keshubei granites, yielded ages of 165.49 ± 0.59 Ma, 159.68 ± 0.43 Ma, and 185.13 ± 0.52–195.14 ± 0.63 Ma, respectively. Molybdenite Re–Os isochron ages of the ores are 160 ± 1–162.7 ± 1.1 Ma, which is consistent with the age of large-scale W–Sn deposits in South China. The Yuanlingzhai porphyry is characterized by high K2O, P2O5, and A/CNK (1.33–1.59), and low CaO and Na2O. The rock shows relatively enriched LREE without significant Eu anomalies (Eu/Eu* = 0.80–0.90). Geochemical and mineralogical characteristics indicate that the ore-hosting porphyry is a typical S-type granite generated from the partial melting of crustal material with only minor mantle contribution. Both Harker and evolutionary discrimination diagrams indicate that the Yuanlangzhai and western Keshubei granites are not products of co-magmatic evolution. The Keshubei granites and Xunwu Formation were not significant sources for the components in the porphyry mineralization, but the Yuanlangzhai granite may have supplied some ore-forming material. However, the main ore-forming material was carried by fluids from deep sources, as demonstrated by fluid inclusion and stable isotope data from the molybdenum deposit. The Mo porphyry deposit formed in an extensional setting, and was possibly associated with Jurassic subduction of the Izanagi Plate.  相似文献   

7.
This paper contributes to the understanding of the genesis of epigenetic, hypogene BIF-hosted iron deposits situated in the eastern part of Ukrainian Shield. It presents new data from the Krivoy Rog iron mining district (Skelevatske–Magnetitove deposit, Frunze underground mine and Balka Severnaya Krasnaya outcrop) and focuses on the investigation of ore genesis through application of fluid inclusion petrography, microthermometry, Raman spectroscopy and baro-acoustic decrepitation of fluid inclusions. The study investigates inclusions preserved in quartz and magnetite associated with the low-grade iron ores (31–37% Fe) and iron-rich quartzites (38–45% Fe) of the Saksaganskaya Suite, as well as magnetite from the locally named high-grade iron ores (52–56% Fe). These high-grade ores resulted from alteration of iron quartzites in the Saksaganskiy thrust footwall (Saksaganskiy tectonic block) and were a precursor to supergene martite, high-grade ores (60–70% Fe). Based on the new data two stages of iron ore formation (metamorphic and metasomatic) are proposed.The metamorphic stage, resulting in formation of quartz veins within the low-grade iron ore and iron-rich quartzites, involved fluids of four different compositions: CO2-rich, H2O, H2O–CO2(± N2–CH4)–NaCl(± NaHCO3) and H2O–CO2(± N2–CH4)–NaCl. The salinities of these fluids were relatively low (up to 7 mass% NaCl equiv.) as these fluids were derived from dehydration and decarbonation of the BIF rocks, however the origin of the nahcolite (NaHCO3) remains unresolved. The minimum P–T conditions for the formation of these veins, inferred from microthermometry are Tmin = 219–246 °C and Pmin = 130–158 MPa. The baro-acoustic decrepitation analyses of magnetite bands indicated that the low-grade iron ore from the Skelevatske–Magnetitove deposit was metamorphosed at T = ~ 530 °C.The metasomatic stage post-dated and partially overlapped the metamorphic stage and led to the upgrade of iron quartzites to the high-grade iron ores. The genesis of these ores, which are located in the Saksaganskiy tectonic block (Saksaganskiy ore field), and the factors controlling iron ore-forming processes are highly controversial. According to the study of quartz-hosted fluid inclusions from the thrust zone the metasomatic stage involved at least three different episodes of the fluid flow, simultaneous with thrusting and deformation. During the 1st episode three types of fluids were introduced: CO2–CH4–N2(± C), CO2(± N2–CH4) and low salinity H2O–N2–CH4–NaCl (6.38–7.1 mass% NaCl equiv.). The 2nd episode included expulsion of the aqueous fluids H2O–N2–CH4–NaCl(± CO2, ± C) of moderate salinities (15.22–16.76 mass% NaCl equiv.), whereas the 3rd event involved high salinity fluids H2O–NaCl(± C) (20–35 mass% NaCl equiv.). The fluids most probably interacted with country rocks (e.g. schists) supplying them with CH4 and N2. The high salinity fluids were most likely either magmatic–hydrothermal fluids derived from the Saksaganskiy igneous body or heated basinal brines, and they may have caused pervasive leaching of Fe from metavolcanic and/or the BIF rocks. The baro-acoustic decrepitation analyses of magnetite comprising the high-grade iron ore showed formation T = ~ 430–500 °C. The fluid inclusion data suggest that the upgrade to high-grade Fe ores might be a result of the Krivoy Rog BIF alteration by multiple flows of structurally controlled, metamorphic and magmatic–hydrothermal fluids or heated basinal brines.  相似文献   

8.
The Damiao type iron deposit is hosted in a typical Proterozoic anorthosite complex in the northern North China Craton. The types of ores in Damiao mainly comprise massive Fe ores, massive Fe–P ores, and disseminated Fe and Fe–P ores. The disseminated Fe and Fe–P ores formed by fractional crystallization are generally hosted in oxide-apatite gabbronorite and account for 70% of the proven reserve of the Damiao type iron ore. The massive Fe and Fe–P ores account for 30% of the proven reserve of the Damiao type deposit iron ore and generally occur as irregular dykes or veins filling vertical fractures of the previously consolidated anorthosite, showing typical features of hydrothermal mineralization. The contact between the massive orebodies and wall rocks is sharp and straight. The anorthosite comprises white and dark varieties, with the former resulted by the alteration of the latter that occurs as relicts. Petrographic observation and electron microprobe analyses show abundant Fe–Ti oxide inclusions in plagioclase which impart the dark color to the rock. The similar spider diagram patterns between fresh and altered plagioclase and between dark- and white-colored anorthosite imply a genetic relationship between the dark and white types. During the alteration of anorthosite, CaO and MgO were slightly decreased, the SiO2, Al2O3 and Na2O were significantly increased, and the TFe2O3 and TiO2 were significantly decreased. The TFe2O3 and TiO2 in the dark-colored anorthosite have a range of 4.86–12.18 wt.% and 0.37–1.65 wt.%, respectively. However, The TFe2O3 and TiO2 in the white-colored anorthosite have a range of 1.67–3.1 wt.% and 0.14–0.31 wt.%, respectively. These features suggest that the alteration of the anorthosite led the Fe element by leaching from the dark-colored anorthosite at highly oxidized condition, and then precipitated within the fractures of the anorthosite, thus forming the massive Fe and Fe–P orebodies. Because the estimated amount of transported Fe is much more abundant than the proven ore reserve, we infer that there should be huge potential for prospecting Damiao type iron ores.  相似文献   

9.
清镇林歹铝土矿赋矿层位为下石炭统九架炉组,含矿层序具有典型的炭质页岩—铝土矿—铁质岩结构。本研究以铝土矿层顶、底板为主要研究对象,围绕林歹铝土矿顶板炭质页岩、底板喀斯特面及紫红色泥岩开展野外调查、地球化学分析测试、古生物化石鉴定等研究,结果发现在铝土矿顶部的炭质页岩中含大量的黄铁矿、丰富的植物和动物化石,植物化石主要为芦木、裸蕨类,由化石组合确定铝土矿形成时代为早石炭世。在炭质页岩中发现含腕足、腹足化石的白云岩夹层,证明炭质页岩形成于滨岸近海环境,由此推测铝土矿也形成近海湖泊环境。对含大量黄铁矿炭质页岩进行蒸馏水浸泡试验,发现炭质页岩浸泡液体pH值为1.5~2,呈现出强酸性,结合清镇林歹、小山坝等地铝土矿层与炭质页岩叠覆特征,认为铝土矿形成后,上覆炭质页岩在大气淡水淋滤下会对下伏铝土矿层起脱硅除铁作用,使铝土矿品位进一步提高。在铝土矿底板发现强风化白云岩砂、溶蚀裂隙、钙结层、湖泊沉积纹层等,认为寒武系白云岩中紫红色泥岩夹层很可能是铝土矿成矿母岩,且具有一定的找矿指示意义。  相似文献   

10.
Bauxite deposits, traditionally the main source of aluminum, have been recently targeted for their remarkable contents in rare earth elements (REE). With ∑REE (lanthanoids + Sc + Y) concentrations systematically higher than ∼1400 ppm (av. = 1530 ppm), the Las Mercedes karstic bauxites in the Dominican Republic rank as one of the REE-richest deposits of its style.The bauxitic ore in the Las Mercedes deposit is mostly unlithified and has a homogeneous-massive lithostructure, with only local cross-stratification and graded bedding. The dominant arenaceous and round-grained texture is composed of bauxite particles and subordinate ooids, pisoids and carbonate clasts. Mineralogically, the bauxite ore is composed mostly of gibbsite and lesser amounts of kaolinite, hematite, boehmite, anatase, goethite, chromian spinel and zircon. Identified REE-minerals include cerianite and monazite-Ce, whose composition accounts for the steady enrichment in light- relative to medium- and heavy-REE of the studied bauxites.Considering the paleo-geomorphology of the study area, we propose that bauxites in the Las Mercedes deposit are the product of the erosion and deposition of lithified bauxites located at higher elevations in the Bahoruco ranges. Based on the available data, we suggest a mixed lithological source for the bauxite deposits at the district scale: bedrock carbonates and an igneous source of likely mafic composition.  相似文献   

11.
Copper, gold and molybdenum mineralization of the Kalmakyr porphyry deposit in Uzbek Tien Shan occurs as stockworks, veinlets and disseminations in the phyllic and K-silicate alteration zones developed predominantly in a middle to late Carboniferous intrusive complex composed of monzonite and granodiorite porphyry. Zircon U–Pb dating yielded an age of 327.2 ± 5.6 Ma for the ore-hosting monzonite and an age of 313.6 ± 2.8 Ma for the ore-bearing granodiorite porphyry. Re–Os dating of seven molybdenite samples from stockwork and veinlet ores yielded model ages from 313.2 to 306.3 Ma, with two well-constrained isochron ages of 307.6 ± 2.5 Ma (five stockwork ores) and 309.1 ± 2.2 Ma (five stockwork ores and two veinlet ores), respectively. These results indicate that Cu–Au mineralization post-dated the emplacement of the monzonite, started right after the emplacement of the granodiorite porphyry, and lasted for ca. 7 Ma afterward. The geochronological and geochemical data suggest that the Kalmakyr deposit was formed in a late Carboniferous mature magmatic arc setting, probably related to the latest subduction process of the Turkestan Ocean beneath the Middle Tien Shan. The εHf(t) values of zircon grains from the monzonite vary from +11 to +1.7, with an average of +5.1, and those of zircon grains from the granodiorite porphyry range from +5.7 to −1.8, with an average of +2.4. These data indicate that the magma of both monzonite and granodiorite porphyry was derived from partial melting of a thickened lower crust with input of mantle components and variable crustal contamination, and that there was more mantle contribution to the formation of the monzonite than the granodiorite porphyry. The high rhenium concentrations of molybdenite (98–899 ppm) also indicate major mantle contribution of rhenium and by inference ore metals. The relatively high EuN/EuN1 values (average 0.68), Ce4+/Ce3 values (average 890) and Ce/Nd values (average 36.8) for zircon grains from the granodiorite porphyry than those from the monzonite (average EuN/EuN1 = 0.33, average Ce4+/Ce3 = 624, average Ce/Nd = 3.9) suggest that the magma for the syn-mineralization granodiorite porphyry has higher oxygen fugacity than that for the pre-mineralization monzonite. Based on these data, it is proposed that while the monzonite was emplaced, the oxygen fugacity and volatile contents in the magma were relatively low, and ore metals might disperse in the intrusive rock, whereas when the granodiorite porphyry was emplaced, the oxygen fugacity and volatile contents in the magma were increased, favoring copper and gold enrichment in the magmatic fluids. The Kalmakyr deposit formed from a long-lived magmatic-hydrothermal system connected with fertile magmatic sources in relation to the subduction of the Turkestan Ocean beneath the Middle Tien Shan.  相似文献   

12.
The Huangshaping granites in Hunan Province, South China were investigated for their geochemical characteristics. Three types of granites have been petrographically identified: quartz porphyry, granophyre, and granite porphyry. Whole rock geochemistry suggests that the Huangshaping granites, especially the granite porphyry, exhibit typical A-type granite characteristics with their enrichment in Si, Rb, U, Th, and Nb and significant depletion in Ba, Sr, Ti, Eu, and P. Based on the Al, Y and Zr contents as well as the REE patterns of the rocks investigated, the quartz porphyry and the granophyre are classified as A1 type alkaline granites whereas the granite porphyry is considered as A2 type aluminous granite. Whole rock and quartz/feldspar O isotope data yields a wide range of δ18OSMOW values (11.09–26.32‰). The granites are characterized by high radiogenic Pb isotopic composition. The present-day whole rock Pb isotopic ratios are 206Pb/204Pb = 18.706–19.155, 207Pb/204Pb = 15.616–15.711 and 208Pb/204Pb = 38.734–39.296. Combining the O–Pb isotope compositions with major, trace and REE geochemistry and regional geology characteristics, the Huangshaping granites were determined to resemble within-plate granites that were mainly derived from a felsic infracrustal source related to continental extension. The magma source of the quartz porphyry and the granophyre may have been generated from deeper depths, and then ascended rapidly with limited water content and low oxygen fugacity, which contributed to Cu, Pb and Zn mineralization. On the other hand, the magma that generated the granite porphyry may have ascended relatively slower and experienced pronounced crystal fractionation, upper-crustal basement rock contamination (assimilation) and wall–rock interaction, producing the Sn- and W-rich granite porphyry. This study reveals the crustal extension process and associated magmatic–metallogenic activities during 180–150 Ma in South Hunan.  相似文献   

13.
Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong ore district) and Tieshan Fe–(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China.Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe–(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate).Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid–rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and fO2, may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of fO2, but lower fluid–rock interactions and ore-forming temperature than the Longqiao deposit. The TiO2–Al2O3–(MgO + MnO) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe–(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed.  相似文献   

14.
The oolitic ironstones ore deposit of Jebel Ank (central Tunisia), is a simply folded stratiform ore body of about 2.5–8 m thickness located in the upper part of the epicontinental Souar Formation (Late Eocene) and is covered by the continental Segui Formation (Mio-Pliocene). The deposit contains about 20 Mt of ore with an average grade of 50% Fe. Generally, oolitic iron deposition occurs in shallow water lagoonal environments. The Jebel Ank deposit lies between two regional disconformities (Late Eocene and Miocene), and is evidence of a transitional stage at the end of regional regression before renewed transgression. The footwall of the oolitic iron ore-bearing bed consists of a fine-grained sandstone bed (10–20 cm-thick) pinching out laterally westward into green clays. The hanging wall is composed of thin-bedded limestone and clay alternations (2–3.5 m-thick).Iron occurs in the form of cryptocrystalline goethite with limited Al-Fe substitution. The goethite contains around 48% Fe, 5% Al and up to 1.5% P. Jarosite, alunite and manganese minerals (cryptomelane, psilomelane and manjiorite) are supergene secondary minerals, probably related to descending surface fluids. These manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies (local cement, space filling and free centimeter sized nodules). Fe-oolites in the deposit are similar to those documented in many other oolitic ironstone deposits. The dominant Fe-oolite type (>90%) has a concentrically laminated cortex with no nucleus. The nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains.Major elements in high grade samples (Fe2O3 > 65%) vary within a limited range and show higher concentrations of SiO2 (average 7.85%) and Al2O3 (average 5.1%), with minor TiO2, MnO, MgO, Na2O, K2O, and SO3 (less than 1%). PAAS-normalized trace elements of bulk samples and Fe-oolite generally show similar behavior, both are enriched in V, Co, Ni, Mo, As, Zn, and Y and are depleted in Cu, Rb, Zr, Nb, Ba, and Hf. Anomalous V, Cr, Ni, Zn, and REE-Y are correlated with goethite. PAAS-normalized REE-Y patterns of both bulk samples and Fe-oolite show slight HREE enrichment, positive Ce with negative Y anomalies.The mineralogy (goethite and cryptomelane) along with the geochemistry (Si vs. Al; As + Cu + Mo + Pb + V + Zn vs. Ni + Co binary plots; Zn–Ni–Co triangular diagram, REE-Y content and patterns and Ce/Ce1 vs. Nd and Ce/Ce1 vs. YN/HoN binary plots) of the studied oolitic ironstone are congruent with a hydrogenetic type. While two possible sources of iron for Jebel Ank ironstone can be proposed: (i) submarine weathering of glauconite-rich sandstone and (ii) detrital iron from adjacent continental hinterland, the later is the more plausible source of iron, based on paleogeographic setting, the occurrence of fine sandstone underlying the iron level, occurrence of Mn-ores in the lower part of the Fe-ores succession, high phosphorous, zinc, ∑REE-Y concentrations and Y/Ho ratios, and low La/Ce ratios.  相似文献   

15.
The Tieshan Fe–Cu deposit is located in the Edong district, which represents the westernmost and largest region within the Middle–Lower Yangtze River Metallogenic Belt (YRMB), Eastern China. Skarn Fe–Cu mineralization is spatially associated with the Tieshan pluton, which intruded carbonates of the Lower Triassic Daye Formation. Ore bodies are predominantly located along the contact between the diorite or quartz diorite and marbles/dolomitic marbles. This study investigates the mineral chemistry of magnetite in different skarn ore bodies. The contrasting composition of magnetite obtained are used to suggest different mechanisms of formation for magnetite in the western and eastern part of the Tieshan Fe–Cu deposit. A total of 178 grains of magnetite from four magnetite ore samples are analyzed by LA–ICP–MS, indicating a wide range of trace element contents, such as V (13.61–542.36 ppm), Cr (0.003–383.96 ppm), Co (11.12–187.55 ppm) and Ni (0.19–147.41 ppm), etc. The Ti/V ratio of magnetite from the Xiangbishan (western part of the Tieshan deposit) and Jianshan ore body (eastern part of the Tieshan deposit) ranges from 1.32 to 5.24, and 1.31 to 10.34, respectively, indicating a relatively reduced depositional environment in the Xiangbishan ore body. Incorporation of Ti and Al in magnetite are temperature dependent, which hence propose that the temperature of hydrothermal fluid from the Jianshan ore body (Al = 3747–9648 ppm, with 6381 ppm as an average; Ti = 381.7–952.0 ppm, with 628.2 ppm as an average) was higher than the Xiangbishan ore body (Al = 2011–11122 ppm, with 5997 ppm as an average, Ti = 302.5–734.8, with 530.8 ppm as an average), indicating a down–temperature precipitation trend from the Jianshan ore body to the Xiangbishan ore body. In addition, in the Ca + Al + Mn versus Ti + V diagram, magnetite is plotted in the skarn field, consideration with the ternary diagram of TiO2–Al2O3–MgO, proposing that the magnetite ores are formed by replacement, instead of directly crystallized from iron oxide melts, which provide a better understanding regarding the composition of ore fluids and processes responsible for Fe mineralization in the Tieshan Fe–Cu deposit.  相似文献   

16.
The Jidetun deposit is a large porphyry Mo deposit that is located in central Jilin Province, northeast China. The Mo mineralization occurs mainly at the edge of porphyritic granodiorite, as well as the adjacent monzogranite. Field investigations, cross-cutting relationships, and mineral paragenetic associations indicate four stages of hydrothermal activity. To determine the relationships between mineralization and associated magmatism, and better understand the metallogenic processes in ore district, we have undertaken a series of studies incluiding molybdenite Re–Os and zircon U–Pb geochronology, fluid inclusions microthermometry, and C–H–O–S–Pb isotope compositions. The molybdenite Re–Os dating yielded a well-defined isochron age of 168.9 ± 1.9 Ma (MSWD = 0.34) that is similar to the weighted mean 206Pb/238U age of 173.5 ± 1.5 Ma (MSWD = 1.8) obtained from zircons from the porphyritic granodiorite. The results lead to the conclusion that Mo mineralization, occurred in the Middle Jurassic (168.9 ± 1.9 Ma), was spatially, temporally, and genetically related to the porphyritic granodiorite (173.5 ± 1.5 Ma) rather than the older monzogranite (180.1 ± 0.6 Ma). Fluid inclusion and stable (C–H–O) isotope data indicate that the initial H2O–NaCl fluids of mineralization stage I were of high-temperature and high-salinity affinity and exsolved from the granodiorite magma as a result of cooling and fractional crystallization. The fluids then evolved during mineralization stage II into immiscible H2O–CO2–NaCl fluids that facilitated the transport of metals (Mo, Cu, and Fe) and their separation from the ore-bearing magmas due to the influx of abundant external CO2 and heated meteoric water. Subsequently, during mineralization stage III and IV, increase of pH in residual ore-forming fluids on account of CO2 escape, and continuous decrease of ore-forming temperatures caused by the large accession of the meteoric water into the fluid system, reduced solubility and stability of metal clathrates, thus facilitating the deposition of polymetallic sulfides.  相似文献   

17.
The Maozu Pb–Zn deposit, located on the western margin of the Yangtze Block, southwest China, is a typical carbonate-hosted deposit in the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province with Pb + Zn reserves of about 2.0 million tonnes grading 4.15 wt.% Pb and 7.25 wt.% Zn. Its ore bodies are hosted in Sinian (635–541 Ma) Dengying Formation dolostone and show stratiform, vein and irregular textures. Ores are composed of sphalerite, galena, pyrite, calcite, dolomite, quartz and fluorite with massive, banded, disseminated and veined structures. The C–O–Sm–Nd isotopic compositions of hydrothermal calcites and S–Pb isotopic compositions of sulfides were analyzed to constrain the origin of the Maozu deposit. δ13CPDB and δ18OSMOW values of hydrothermal calcites range from −3.7‰ to −2.0‰ and +13.8‰ to +17.5‰, respectively, and plot near the marine carbonate rocks field in a plot of δ13CPDB vs. δ18OSMOW, with a negative correlation. It suggests that CO2 in the hydrothermal fluids was mainly originated from marine carbonate rocks, with limited influence from sedimentary organic matter. δ34SCDT values of sulfides range from +9.9‰ to +19.2‰, similar to that of Cambrian to Triassic seawater sulfate (+15‰ to +35‰) and evaporate (+15‰ to +30‰) in the Cambrian to Triassic sedimentary strata. It suggests that reduced sulfur was derived from evaporate in sedimentary strata by thermo chemical sulfate reduction. Sulfides have low radiogenic Pb isotope compositions (206Pb/204Pb = 18.129–18.375, 207Pb/204Pb = 15.640–15.686 and 208Pb/204Pb = 38.220–38.577) that plot in the field between upper crust and the orogenic belt evolution curve in the plot of 207Pb/204Pb vs. 206Pb/204Pb, and similar to that of age corrected Proterozoic basement rocks (Dongchuan and Kunyang Groups). This indicates that ore-forming metals were mainly derived from basement rocks. Hydrothermal calcite yields a Sm–Nd isotopic age of 196 ± 13 Ma, possibly reflecting the timing of Pb–Zn mineralization in the SYG province, younger than the Permian Emeishan mantle plume (∼260 Ma). All data combined suggests that hydrothermal fluids circulated through basement rocks where they picked up metals and migrated to surface, mixed with reduced sulfur-bearing fluids and precipitated metals. Ore genesis of the Maozu deposit is different from known magmatic–hydrothermal, Sedimentary Exhalative or Mississippi Valley-types, which maybe represent a unique ore deposit type, named as the SYG-type.  相似文献   

18.
The Yinjiagou Mo–Cu–pyrite deposit of Henan Province is located in the Huaxiong block on the southern margin of the North China craton. It differs from other Mo deposits in the East Qingling area because of its large pyrite resource and complex associated elements. The deposit’s mineralization process can be divided into skarn, sulfide, and supergene episodes with five stages, marking formation of magnetite in the skarn episode, quartz–molybdenite, quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite, and calcite–galena–sphalerite in the sulfide episode, and chalcedony–limonite in the supergene episode. Re–Os and 40Ar–39Ar dating indicates that both the skarn-type and porphyry-type orebodies of the Yinjiagou deposit formed approximately 143 Ma ago during the Early Cretaceous. Four types of fluid inclusions (FIs) have been distinguished in quartz phenocryst, various quartz veins, and calcite vein. Based on petrographic observations and microthermometric criteria the FIs include liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions. The homogenization temperature of FIs in quartz phenocrysts of K-feldspar granite porphyry ranges from 341 °C to >550 °C, and the salinity is 0.4–44.0 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite veins is 382–416 °C, and the salinity is 3.6–40.8 wt% NaCl eqv. The homogenization temperature of FIs in quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite ranges from 318 °C to 436 °C, and the salinity is 5.6–42.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite stockworks is in a range of 321–411 °C, and the salinity is 6.3–16.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–sericite–pyrite is in a range of 326–419 °C, and the salinity is 4.7–49.4 wt% NaCl eqv. The ore-forming fluids of the Yinjiagou deposit are mainly high-temperature, high-salinity fluids, generally with affinities to an H2O–NaCl–KCl ± CO2 system. The δ18OH2O values of ore-forming hydrothermal fluids are 4.0–8.6‰, and the δDV-SMOW values are between −64‰ and −52‰, indicating that the ore-forming fluids were primarily magmatic. The δ34SV-CDT values of sulfides range between −0.2‰ and 6.3‰ with a mean of 1.6‰, sharing similar features with deeply sourced sulfur, implying that the sulfur mainly came from the lower crust composed of poorly differentiated igneous materials, but part of the heavy sulfur came from the Guandaokou Group dolostone. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of sulfides are in the range of 17.331–18.043, 15.444–15.575, and 37.783–38.236, respectively, which is generally consistent with the Pb isotopic signature of the Yinjiagou intrusion, suggesting that the Pb chiefly originated from the felsic–intermediate intrusive rocks in the mine area, with a small amount of lead from strata. The Yinjiagou deposit is a porphyry–skarn deposit formed during the Mesozoic transition of a tectonic regime that is EW-trending to NNE-trending, and the multiepisode boiling of ore-forming fluids was the primary mechanism for mineral deposition.  相似文献   

19.
The Hongshan Cu-polymetallic deposit is located in the southern Yidun arc in southwestern China, where both subduction-related (Late Triassic) and post-collisional (Late Cretaceous) porphyry–skarn–epithermal mineralization systems have been previously recognized. In this study, two distinct magmatic events, represented by diorite porphyry and quartz monzonite porphyry, have been revealed in the Hongshan deposit, with zircon SHRIMP U–Pb ages of 214 ± 2 Ma and 73.4 ± 0.7 Ma, respectively. The 73 Ma age is comparable to the Re–Os ages of 77 to 80 Ma of ore minerals from the Hongshan deposit, indicating that the mineralization is related to the Late Cretaceous quartz monzonite porphyries rather than Late Triassic diorite porphyries. The Late Triassic diorite porphyries belong to the high-K calc-alkaline series and show arc magmatic geochemical characteristics such as enrichment in Rb, Ba, Th and U and depletion in HFSEs, indicating that they were formed during the westward subduction of the Garzê–Litang Ocean. In contrast, the Late Cretaceous quartz monzonite porphyries show shoshonitic I-type geochemical characteristics, with high SiO2, K2O, LILE, low HREE, Y and Yb contents, and high LREE/HREE and La/Yb ratios. These geochemical characteristics, together with the Sr–Nd–Pb isotopic compositions (average (87Sr/86Sr)i = 0.7085; εNd(t) = − 6.0; 206Pb/204Pb = 19.064, 207Pb/204Pb = 15.738, 208Pb/204Pb = 39.733) suggest that the quartz monzonite porphyries originated from the partial melting of the ancient lower crust in response to underplating of mafic magma from subduction metasomatized mantle lithosphere, possibly triggered by regional extension in the post-collisional tectonic stage. The S isotopic compositions (δ34SV-CDT = 3.81‰ to 5.80‰) and Pb isotopic compositions (206Pb/204Pb = 18.014 to 18.809, 207Pb/204Pb = 15.550 to 15.785, and 208Pb/204Pb = 38.057 to 39.468) of ore sulfides indicate that the sulfur and metals were derived from mixed mantle and crustal sources. It is proposed that although the Late Triassic magmatic event is not directly related to mineralization, it contributed to the Late Cretaceous mineralization system through the storage of large amounts of sulfur and metals as well as water in the cumulate zone in the mantle lithosphere through subduction metasomatism. Re-melting of the mantle lithosphere including the hydrous cumulate zone and ancient lower crust during the post-collisional stage produced fertile magmas, which ascended to shallow depths to form quartz monzonite porphyries. Hydrothermal fluids released from the intrusions resulted in porphyry-type Mo–Cu ores in and near the intrusions, skarn-type Cu–Mo ores in the country rocks above the intrusions, and hydrothermal Pb–Zn ores in the periphery.  相似文献   

20.
The Xishan deposit, located in the western Guangdong Province in South China, is a quartz-vein type W-Sn deposit with an average Sn grade of 0.1–0.4 wt%. The deposit is temporally and spatially associated with Xishan alkali feldspar granite. The W–Sn mineralization is present mainly as veins that are hosted by the granite. In this paper we present new zircon U–Pb age, whole-rock geochemical data, Sr–Nd–Pb–Hf isotopic data and Re–Os age in order to constrain the nature and timing of magmatism and mineralization in the Xishan mining district with implications on geodynamic settings. LA–ICP–MS zircon U–Pb analyses yielded an age of 79.14 ± 0.31 Ma for the alkali feldspar granite, consistent with the molybdenite Re–Os age of 79.41 ± 1.11 Ma. The alkali feldspar granite shows high contents of SiO2 (71.52–76.25 wt%), high total alkalis (Na2O + K2O = 9.35–13.51 wt%), high field strength elements (e.g. Zr = 95.4–116 ppm, Y = 97.1–138 ppm, Nb = 36.1–55.5 ppm, Ga = 97.1–138 ppm), and rare earth elements (total REE = 171.8–194.0 ppm) as well as high Ga/Al ratios (10,000 × Ga/Al = 3.23–3.82) suggesting that it has the geochemical characteristics of A-type granite and shows an A2 subtype affinity. Sr–Nd isotopes of the alkali feldspar granite show that (87Sr/86Sr)i values range from 0.7111 to 0.7183, and the εNd(t) values and Nd model ages (T2DM) vary from −6.8 to −6.5 and 1414 to 1433 Ma, respectively. The Pb isotopic compositions are variable, with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values ranging from 18.783 to 18.947, 15.709 to 15.722 and 38.969 to 39.244, respectively, indicating that the alkali feldspar granite was derived from a mantle-crust mixed source. In situ Hf isotopic analyses reveal that the alkali feldspar granite has εHf(t) values ranging from −9.69 to −0.04 and two-stage Hf model ages from 1145 Ma to 1755 Ma, indicating that the alkali feldspar granite was formed by the partial melting of Mesoproterozoic crusts of the Cathaysia Block with additions of mantle-derived materials. These results, together with previously presented regional geological relationships, suggest that the formation of the Xishan granite and associated W–Sn mineralization is related to lithospheric extension and asthenospheric upwelling that are attributed to a directional change of Pacific plate motion.  相似文献   

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