Precambrian Metamorphic Rocks Research Articles

Magmatic–hydrothermal processes in Sangdong W–Mo deposit, Korea: Study of fluid inclusions and 39Ar–40Ar geochronology

The Sangdong scheelite–molybdenite deposit in northeast South Korea consists of strata-bound orebodies in intercalated carbonate-rich layers in the Cambrian Myobong slate formation. Among them, the M1 layer hosts the main orebody below which lie layers of F1–F4 host footwall orebodies. Each layer was first skarnized with the formation of a wollastonite + garnet + pyroxene assemblage hosting minor disseminated scheelite. The central parts of the layers were subsequently crosscut by two series of quartz veining events hosting minor scheelite and major scheelite–molybdenite ores, respectively. The former veins associate amphibole–magnetite (amphibole) alteration, whereas the latter veins host quartz–biotite–muscovite (mica) alteration. Deep quartz veins with molybdenite mineralization are hosted in the Cambrian Jangsan quartzite formation beneath the Myobong formation. In the Sunbawi area, which is in close proximity to the Sangdong deposit, quartz veins with scheelite mineralization are hosted in Precambrian metamorphic basement. Three muscovite 39Ar–40Ar ages between 86.6 ± 0.2 and 87.2 ± 0.3 Ma were obtained from M1 and F2 orebodies from the Sangdong deposit and Sunbawi quartz veins. The Upper Cretaceous age of the orebodies is concordant with the published ages of the hidden Sangdong granite, 87.5 ± 4.5 Ma. This strongly suggests that the intrusion is causative for the Sangdong W–Mo ores and Sunbawi veins.Fluid inclusions in the quartz veins from the M1 and F2 orebodies, the deep quartz-molybdenite veins, and the Sunbawi veins are commonly liquid-rich aqueous inclusions having bubble sizes of 10–30 vol%, apparent salinities of 2–8 wt% NaCl eqv., and homogenization temperatures of 180–350 °C. The densities of the aqueous inclusions are 0.70–0.94 g/cm3. No indication of fluid phase separation was observed in the vein. To constrain the formation depth in the Sangdong deposit, fluid isochores are combined with Ti–in–quartz geothermometry, which suggests that the M1 and F2 orebodies were formed at depths of 1–3 km and 5–6 km below the paleosurface, respectively. The similarity of the Cs (cesium) concentrations and Rb/Sr ratios in the fluid inclusions of the respective orebodies indicate an origin from source magmas having similar degrees of fractionation and enrichment of incompatible elements such as W and Mo. High S concentrations in the fluids and possibly organic C in the sedimentary source likely promoted molybdenite precipitation in the Sangdong orebodies, whereas the scheelite deposition in the deep quartz–molybdenite veins hosted in the quartzite is limited by a lack of Ca and Fe in the hydrothermal fluids. The molybdenite deposition in the Sunbawi quartz–molybdenite veins hosted in the Precambrian metamorphic basement rocks was possibly limited by a lack of reducing agents such as organic C.

Ore genesis of the Saridala gold deposit, Western Tianshan, NW China: Constraints from fluid inclusion, S-Pb isotopes and 40Ar/39Ar dating

The Saridala gold deposit is located in the Western Tianshan (Xinjiang, NW China), southwestern part of the Central Asian Orogenic belt (CAOB). The deposit is mainly hosted in Precambrian metamorphic rocks and Early Paleozoic granites, and is structurally controlled by the Shenglidaban ductile shear zone. The gold orebodies consist of gold-bearing quartz veins and altered mylonite. The mineralization comprises three stages: quartz-pyrite veins (early stage), sulfide-quartz veins (middle stage), and quartz-carbonate veins/veinlets (late stage). Ore minerals and native gold were mainly formed in the middle stage. Four fluid inclusion types in quartz veins were identified: pure CO2 (PC-type), CO2-H2O (C-type), aqueous (W-type) and daughter mineral-bearing (S-type) inclusions. Hydrothermal fluids related to the mineralization are composed of CO2-H2O-NaCl±N2 fluids (115–307MPa) with Th(total) values of 256–475°C (peak at 320–380°C) and salinities <∼11 wt% NaCl equiv. (mostly 4–7 wt% NaCl equiv.). Ore minerals were likely deposited via fluid immiscibility and the subsequent fluid mixing. Except for the two negative outliners (−4.5 and −4.8‰), δ34S‰ values of the ore pyrite range from 11.0 to 17.9‰, suggesting that the ore-forming fluids contained heavier sulfur from marine sulfate-bearing rocks. Lead isotope compositions of the ore sulfides are characterized by being highly radiogenic and their relatively wide ranges: 18.01–19.62 (206Pb/204Pb), 15.58–15.78 (207Pb/204Pb) and 37.95–39.08 (208Pb/204Pb). These data indicate that the lead in the ores may have been derived from an orogenic reservoir with some crustal input. 40Ar/39Ar age dating on the sericite from the syn-mineralized quartz-sericite-sulfide alteration yielded a plateau age of 337.6±1.7Ma, an age coeval with the subduction–collision tectonic transition related to the closure of the North Tianshan Ocean. We concluded that the Saridala gold deposit shares many similarities with typical orogenic gold deposits, and was likely formed in an orogenic environment.

Thermochronological constraints on the Cambrian to recent geological evolution of the Argentina passive continental margin

Passive continental margins are geo-archives that store information from the interplay of endogenous and exogenous forces related to continental rifting, post-breakup history, and climate changes. The recent South Atlantic passive continental margins (SAPCMs) in Brazil, Namibia, and South Africa are partly high-elevated margins (~2000ma.s.l.), and the recent N-S-trending SAPCM in Argentina and Uruguay is of low elevation. In Argentina, an exception in elevation is arising from the higher topography (>1000ma.s.l.) of the two NW-SE-trending mountain ranges Sierras Septentrionales and Sierras Australes. Precambrian metamorphic and intrusive rocks, and siliciclastic rocks of Ordovician to Permian age represent the geological evolution of both areas. The Sierras Australes have been deformed and metamorphosed (incipient - greenschist) during the Gondwanides Orogeny. The low-temperature thermochronological (LTT) data (<240°C) indicated that the Upper Jurassic to Lower Cretaceous opening of the South Atlantic has not completely thermally reset the surface rocks. The LTT archives apatite and zircon still revealed information on the pre- to post-orogenic history of the Gondwanides and the Mesozoic and Cenozoic South Atlantic geological evolution. Upper Carboniferous zircon (U-Th/He)-ages (ZHe) indicate the earliest cooling below 180°C/1Ma. Most of the ZHe-ages are of Upper Triassic to Jurassic age. The apatite fission-track ages (AFT) of Sierras Septentrionales and the eastern part of Sierras Australes indicate the South Atlantic rifting and, thereafter. AFT-ages of Middle to Upper Triassic on the western side of the Sierras Australes are in contrast, indicating a Triassic exhumation caused by the eastward thrusting along the Sauce Grande wrench. The corresponding t-T models report a complex subsidence and exhumation history with variable rates since the Ordovician. Based on the LTT-data and the numerical modelling we assume that the NW-SE-trending mountain ranges received their geographic NW-SE orientation during the syn- to post-orogenic history of the Gondwanides.

Geology, geochemistry and tectonic settings of molybdenum deposits in Southwest China: A review

Southwest (SW) China hosts more than 26 Mo (Mo-only, Mo-dominated and Mo-bearing) deposits with a total reserve of >2.5Mt Mo metal. The region has become one of the most important Mo mineral provinces in China. These Mo deposits are usually fault-controlled, and are located mainly in: (1) Lhasa Terrane, characterized by widely distributed Yanshanian–Himalayan igneous rocks; (2) Qiangtang Terrane, composed by Proterozoic and Early-Paleozoic crystalline basement and Devonian to Jurassic cover rocks; (3) East Kunlun Terrane, comprising Precambrian metamorphic rocks intruded by Paleozoic and Mesozoic granitoid plutons; (4) West Kunlun Terrane, characterized by Precambrian metamorphic basement, Paleozoic metasedimentary rocks, and Early-Paleozoic and Carboniferous–Triassic arc-type plutons; and (5) Yidun arc, composed by Middle and Upper Triassic volcanic–sedimentary successions. The Mo mineralization styles are dominated by porphyry-type, but also contain porphyry-skarn, skarn and porphyry-quartz vein types. Orebodies are vein-type or lensoidal, and are hosted by a variety of metamorphic, volcanic, granitic and sedimentary rocks of different ages. Fluid-rock interactions are exemplified by alteration zonation, which usually grades from an innermost potassic alteration zone, via a silicic/sericite alteration zone, to an outermost propylitic alteration zone. The initial high-temperature ore-forming fluids are magmatic in origin, and contain CO2-bearing fluid inclusions. The initial ore-forming fluids would have then evolved to low-temperature, low-pressure, low-salinity and CO2-poor (with meteoric water input) at the late alteration/mineralization stage. Causative granitoids for these Mo deposits have relatively high SiO2, K2O and Al2O3, and low TiO2 and MgO, showing a metaluminous to peraluminous high-K calc-alkaline to shoshonitic affinity. These granitoids exhibit significant depletions in Ba, Nb, Ta, P and Ti, and enrichments in Rb, Th, U and K. It is suggested that they were originated from partial melting of a lower rejuvenated crust, as evidenced by their Sr-Nd-Pb isotopic signatures. The Mo deposits in East and West Kunlun were formed in the Triassic (ca. 258–214Ma), related to the Paleo-Tethys Ocean subduction and the subsequent continental collision. Major Mo mineralization in the Qiangtang and Lhasa terranes mainly occurred during the syn-collisional compression to post-collisional extension transition of the Qiangtang–Lhasa (ca. 43–35Ma) and India–Asia (ca. 30–14Ma) collisions, respectively. The Late-Cretaceous Mo mineralization (ca. 88–73Ma) in the Yidun arc was formed during the late- or post- Lhasa–Qiangtang collision setting, or the intraplate extension led by the post-Himalayan escape tectonics. The wide range of molybdenite Re contents in these major SW Chinese Mo deposits indicates remarkable differences in metal, fluid sources and ages.

Detrital zircon ages of the Jiageda and Woduhe formations: Constrains on the tectonic attribute of the Xing’ an terrane in the central Great Xing’ an Range, NE China

To ascertain the late Early Paleozoic tectonic attribute of the Xing’ an terrane, and the distribution and nature of the “Precambrian” basement in NE China, we studied the geochronology, petrology, and geochemistry of the metamorphic rocks of the Jiageda and Woduhe formations in the central Great Xing’ an Range. U–Pb ages of detrital zircons from the Jiageda and Woduhe formations vary from 963 to 374Ma, and can be divided into three groups (963–679, 570–468, and 457–374Ma). The youngest detrital zircons of the three samples from the Jiageda Formation yield weighted mean ages of 413±3, 414±9, and 416±1Ma, respectively, indicating that this formation was formed during the late Silurian–early Devonian. The youngest detrital zircons of the sample from the Woduhe Formation yield a weighted mean age of 429±4Ma, indicating that this formation was formed during the middle–late Silurian. The protoliths of the metamorphic rocks from the Jiageda and Woduhe formations are terrigenous clastic rocks, with some mafic–intermediate volcanic rocks, characterized mainly by volcanic–sedimentary formation. Considering the geochemical characteristics of the rocks and the regional tectonic setting, we suggest that both the Woduhe and Jiageda formations were formed in an island-arc active-continental-margin environment, and that the Xing’an terrane was located in an active continental margin related to the subduction of the Paleo-Asian Ocean during the middle Silurian-early Devonian. A comparison between the Jiageda and Woduhe formations with respect to their protoliths, geochemical properties, sedimentary environment, and geochronological characteristics shows that the Jiageda Formation does not constitute Precambrian crystalline basement, but instead consists of metamorphosed and deformed late Silurian–early Devonian sedimentary strata intercalated with volcanic rocks. By combining these results with the regional geology, we conclude that the Precambrian basement in NE China is not extensively distributed, being limited to Precambrian metamorphic rocks in the northern Erguna massif and Xing’ an terrane, eastern Songliao terrane, and southern Jiamusi massif, and the protolith ages are younger than Neoproterozoic.

Reaction textures and metamorphic evolution of sapphirine–spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India

AbstractThe Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine–spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine–spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd–Opx–Qtz–Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx–Crd–Kfs–Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c. 1000°C and c. 12 kbar were computed by isopleths of XMg in garnet and XAl in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P–T evolution. The P–T path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust.

Hydrodynamic Study of Weathered Zone of Hardrock Aquifers Using Dugwell Data

The present study discusses a technique of locating high-discharging dugwells in Precambrian metamorphic rocks in Balarampur, Purulia district, West Bengal, India and describes the hydrodynamic properties of hardrock aquifers using bedrock joints/fractures, lineaments and weathered zone. Dugwells with higher discharges are mainly concentrated in metapelites, rich in biotite. In groups of dugwells, high-discharging wells exhibit linear spatial distribution, denoted as “well-line,” and consistently show high well discharge along each well-line in every dugwell group. The spatial distributions of high-discharging wells are associated with thick weathered-zones. Well-lines, comprising abruptly high-discharging wells, are spatially correlated to the lithostratigraphic contacts and lower elevation zones.

The petrogenesis and tectonic implications of the granitoid gneisses from Xingxingxia in the eastern segment of Central Tianshan

As part of Central Asian Orogenic Belt (CAOB), the Central Tianshan zone plays a crucial role in the reconstruction of the tectonic evolution of the CAOB. Furthermore, it is bordered by the Tarim Craton to the south, and the comparable evolutionary history between them enables the Central Tianshan zone to provide essential information on the crustal evolution of the Tarim Craton. The eastern segment of the Central Tianshan tectonic zone is characterized by the presence of numerous Precambrian metamorphic rocks, among which the Xingxingxia Group is the most representative one. The granitoids gneisses, intruded into the Xingxingxia Group, consist of two major lithological assemblages: (1) biotite-monzonitic gneisses and (2) biotite-plagioclase gneisses. These metamorphosed granitoid rocks are characterized by enrichment in SiO2, Al2O3 and K2O and depletion in MgO and FeOT. The Rittmann index (σ) spreads between 1.44 and 2.21 and ACNK (Al2O3/(CaO+Na2O+K2O)) ranges from 1.03 to 1.08, indicating that these granitoid gneisses are high-K calc-alkaline and peraluminous. Trace element data indicate that the studied samples are enriched in LREE with moderate REE fractionated patterns ((La/Yb)N=10.5–75.3). The concentrations of HREE of the garnet-bearing gneisses are significantly higher than those of garnet-free gneisses. The former show pronounced negative Eu anomalies (Eu/Eu*=0.32–0.57), while the latter are characterized by negligible negative Eu anomalies to moderate positive Eu anomalies (Eu/Eu*=0.80–1.35). In addition, the enrichment of LILE (Rb, Th, K, Pb) and depletion of HFSE (Ta, Nb, P, Ti) of the examined granitoid gneisses are similar to typical volcanic-arc granites. Zircons U–Pb dating on the biotite monzonitic gneiss yields a weighted mean 206Pb/238U age of 942.4±5.1Ma, suggesting their protoliths were formed in the early Neoproterozoic, which is compatible with the time of the assembly of supercontinent Rodinia. The zircons have a large εHf(t) variation from −5.6 to +3.2, suggesting that both old crust-derived magmas and mantle-derived juvenile materials contributed to the formation of their protoliths. Based on field observation, and petrological, geochemical and geochronological investigations, we infer that the granitoid gneisses from Xingxingxia were probably formed on a continental arc that resulted from the interaction of Australia and the Tarim Craton during the assembly of the Rodinia supercontinent, and that the Central Tianshan zone was a part of the Tarim Craton during that time. Besides, the Grenvillian orogenic events may have developed better in the Tarim Craton than previously expected.

Age and petrogenesis of the Neoproterozoic Chon-Ashu alkaline complex, and a new discovery of chalcopyrite mineralization in the eastern Kyrgyz Tien Shan

Neoproterozoic volcanics and granitoids formed at Rodinia margins within a time span of 880Ma–700Ma, are well-documented in many terranes of the southern Central Asian Orogenic Belt (CAOB). Ages younger than 550Ma corresponding to the opening of the Terskey Ocean are also common. However, so far, there were very few published ages in the range 700Ma–550Ma from the Kyrgyz Tien Shan. In this paper we present new data for the alkaline Chon-Ashu complex emplaced at the end of the Cryogenian Period of the Neoproterozoic (850–635Ma, Gradstein et al., 2012). The alkaline complex intrudes the Precambrian metamorphic rocks north of the Nikolaev Line which separates the Northern and Middle Tien Shan terranes in the eastern Kyrgyzstan. The undeformed shallow level alkaline rocks range from olivine gabbro to nepheline and cancrinite syenites and leucosyenites. The differentiated rock assemblage can be explained by fractional crystallization of high-silica mineral phases which drives nepheline-normative melts away from the silica saturation boundary. The alkaline rocks of Chon-Ashu are enriched in LILE and HFSE indicative of their origin from lithospheric mantle. An age of 678±9Ma (U–Pb, SHRIMP) was obtained for a protolith of country gneiss, and an age of 656±4Ma was obtained for the crosscutting alkaline rocks of the Chon-Ashu complex. Seven zircon grains recovered from gneiss and alkaline rocks had bright overgrown rims which yielded a cumulative age of 400±8Ma. A metamorphic event, followed by uplift and emplacement of shallow level alkaline complex, constrains the geodynamic setting. Alkaline rocks usually form in an extensional setting and originate from lithospheric mantle. The 690Ma xenoliths of mafic granulite from the NW Tarim have been interpreted to originate by mafic underplating. This mafic underplating may have been responsible for metamorphism in the middle crust prior to emplacement of the Chon-Ashu complex. The 670Ma–630Ma period of extension and emplacement of enriched alkaline rocks can be also traced on a regional scale through southern Kazakhstan and the northern Tarim. We tentatively interpret these events as a result of mafic underplating and subsequent rifting related to the break-up of Rodinia. During field work at Chon-Ashu, rich chalcopyrite mineralization has been discovered in carbonate veinlets in leucosyenite alkaline dikes and has also been found in the adjacent Cambrian gabbro and granites shown on the map as undivided Devonian–Silurian. Stockwork mineralization predominates though disseminated mineralization is also present. The Cu content reaches 16,184ppm and is associated with elevated concentrations of Pb, Zn and Ag. The polyphase structural evolution of the area suggests that mineralization could have formed in several genetically unrelated stages. Based on structural and mineralogical evidence we tentatively relate the earliest stage of chalcopyrite mineralization to the late magmatic CO2-rich fluids emanating from the Cryogenian alkaline complex. The Early Devonian thermal event registered by growth of new zircon at 400Ma has important metallogenic implications on a regional scale. However the origin of two zones of alteration in the undivided Silurian–Devonian granites is ambiguous because their age was not determined geochronologically. The 522±4Ma Cambrian gabbro of the Tashtambektor Formation is strongly foliated along the splays of the Nikolaev Line, indicating a Hercynian origin of the fabric. Superimposed mineralized stockwork postdates the foliation and suggests a late-Hercynian age of mineralization in gabbro. The new data enable a reassessment of the metallogenic potential of the Eastern Kyrgyz Tien Shan. Presence of not eroded high-level mineralized Neoproterozoic alkaline intrusions points to a previously underestimated metallogenic potential of pre-Hercynian granitoids which may host preserved porphyry systems, skarns and shear-related mineralization. Finally, the Devonian magmato-metamorphic event which caused formation of a number of ore deposits in central Kyrgyzstan and Kazakhstan could also create potential exploration targets in eastern Kyrgyzstan.

Zircon geochronology constraints on the age and nature of ‘Precambrian metamorphic rocks’ in the Xing’an block of Northeast China

The Great Xing’an Range in Northeast China is located in the eastern part of the Central Asian Orogenic Belt. From north to south, the Great Xing’an Range is divided into the Erguna, Xing’an, and Songliao blocks. Previous U–Pb zircon geochronology results have revealed that some ‘Precambrian metamorphic rocks’ in the Xing’an block have Phanerozoic protolith ages, questioning whether Precambrian basement exists in the Xing’an block. We present laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results for zircons from suspected Precambrian metamorphic rocks in the Xing’an block. Meta-rhyolites of the Xinkailing Group in Nenjiang yield magmatic ages of 355.8 Ma. Detrital zircons from phyllites of the Xinkailing Group in Duobaoshan yield populations of ca. 1505, ca. 810, and ca. 485 Ma, with the youngest peak constraining its depositional age to be <485 Ma. Zircons from amphibolitic gneisses of the Xinkailing Group in Nenjiang have magmatic ages of 308.6 Ma. Mylonitic granites of the Xinkailing Group in Nenjiang have zircon magmatic ages of 164 Ma. Detrital zircons from two-mica quartz schists of the Luomahu Group in the Galashan Forest yield ca. 2419, ca. 1789, ca. 801, ca. 536, ca. 480, and ca. 420 Ma, with the youngest peak indicating its depositional age as <420 Ma. Detrital zircons from mylonitized sericite–chlorite schist of the Ergunhe Formation in Taerqi yield populations of 982–948, ca. 519, and ca. 410 Ma, with the youngest peak demonstrating that its depositional age is <410 Ma. These zircon ages for a range of lithologies show that the Great Xing’an Range metamorphic rocks formed during the Phanerozoic (164–485 Ma) and that this crust is mostly Palaeozoic. Based on these results and published data, we conclude that there is no evidence of Precambrian metamorphic basement in the Xing’an block. In summary, the age data indicate that Precambrian metamorphic basement may not exist in the Xing’an region.

Contrasting Lu–Hf isotopes in zircon from Precambrian metamorphic rocks in the Jiaodong Peninsula: Constraints on the tectonic suture between North China and South China

Zircon Lu–Hf isotopes, together with zircon U–Pb ages, trace elements and O isotopes were analyzed for various types of metamorphic rocks from the Jiaodong and Jiaobei terranes in the Jiaodong Peninsula, east-central China. The results show contrasts in the crustal nature between the two terranes and thus provide constraints on the tectonic suture between the North China Craton and the South China Block in this region. Zircon U–Pb dating for the Jiaodong terrane indicates protolith emplacement mainly in the middle Neoproterozoic and subordinately in the middle Paleoproterozoic. The protolith zircon of Neoproterozoic U–Pb ages exhibits a wide range of ɛHf(t) values from −16.8±1.0 to 5.9±1.0, indicating reworking of both ancient and juvenile crustal rocks during the Neoproterozoic magmatism. Low zircon δ18O values (<5‰) are a diagnostic feature of the Neoproterozoic protolith in the Jiaodong terrane. Growth of the juvenile crust in the middle Paleoproterozoic is also recorded by a few samples. In contrast, zircon U–Pb dating for the Jiaobei terrane yields three episodes of magmatism at ∼2.9, ∼2.7 and ∼2.5Ga, respectively. Zircon Hf isotope compositions suggest growth of the juvenile crust at the two earlier episodes but reworking at the later episode. The crustal reworking is particularly intensive in the middle Paleoproterozoic, resulting in the diagnostic high-pressure granulite-facies metamorphism at 1.90–1.85Ga and migmatization at 1.75Ga. At the same time, remelting of the Archean crust gave rise to the 1.90–1.85Ga S-type granitic rocks. The zircon of Paleoproterozoic U–Pb ages usually exhibits high δ18O values (7–10‰). Taken together, the crustal nature of the Jiaodong and Jiaobei terranes are generally similar to that of the South China Block and the North China Craton, respectively. This lends support to the contention that the suture between the two collided continents is located along the Wulian–Yantai fault marking the boundary between the Jiaodong and Jiaobei terranes.

Influence of Rock Foliation on Fracture Permeability: The Case of Precambrian metamorphics (Purulia, Eastern India)

Influence of Rock Foliation on Fracture Permeability: The Case of Precambrian metamorphics(Purulia, Eastern India) Hydrological influence of foliation in variably fractured Precambrian metamorphic rocks is usually difficult to predict. As an exemplar, the Precambrian metamorphic exposed in and around the Balarampur town of Purulia district, West Bengal (India) were studied to find out the influence of rock foliation on fracture permeability using a hydrostructural domain-based model. These Precambrian metamorphic rocks, characterized by foliated fabric, resulted from the combination of (a) brittle granite gneisses rich in quartz and garnet, (b) an intense brittle-ductile shear zone, and (c) ductile metapelites with micaceous minerals. Pre- and post-monsoon depth-to-groundwater table contour maps, mode, coefficient of variance (Cv) and contour maps of frequencies and apertures of fractures demonstrate inter- and intra-domain variable qualitative fracture permeability’s.

단양지역 지하수중 자연방사성물질 우라늄과 라돈의 산출과 분포특징

Natural radionuclides in groundwater in the Danyang area were investigated to characterize the behaviors of uranium and radon with respect to lithology and physico-chemical components, which can aid our understanding of their occurrence, properties, and origins. To this end, a total of 100 groundwater samples were collected and analyzed, and radionuclide levels were used to construct detailed concentration maps. The water type of the groundwater, assessed using a Piper diagram, is mainly Ca-Na-. The concentrations of uranium range from 0.02 to (average, ) and only 1% exceed USEPA`s MCL (Maximum Contaminant Level). Uranium is enriched in groundwaters of Cretaceous granites and Precambrian metamorphic rocks, whereas it is depleted in groundwaters of sedimentary rocks. The concentrations of radon range from 13 to 28,470 pCi/L (average, 2397 pCi/L). Only 15% of the samples exceed AMCL (Alternative Maximum Contaminant Level) of 4000 pCi/L. The radon concentration is highest in groundwater of Cretaceous granites and lowest in groundwater of sedimentary rocks. In conclusion, the distribution and occurrence of radionuclides are intimately related to the basic geological characteristics of the rocks in which the radiogenic minerals are primarily contained. The behavior of uranium is only weakly related to that of radon (correlation coefficient

Carbonatites and primary carbonates in the Rio Apa and Amambay regions, NE Paraguay

In the Rio Apa and Amambay regions, north-eastern Paraguay (NPAA), potassic, alkaline-carbonatitic rocks (138–139Ma) predate the eruption of tholeiitic flood basalts (133±1Ma). These rocks, mainly outcropping as dykes or ring-like complexes, intrude a Cambro-Ordovician carbonate platform and Precambrian metamorphic rocks along with their Silurian and Permo-Carboniferous sediments. The main rock-types range from basanite to trachyte and trachyphonolite (and intrusive equivalents) to carbonatite, in addition to glimmeritic and pyroxenitic veins. Geological and geophysical evidence indicate that the NPAA magmatism is related to extensional tectonics, like the Early Cretaceous alkaline-carbonatitic complexes from central-eastern Paraguay (127±1Ma) and the eastern magmatic occurrences of the Paraná Basin.Oxygen and carbon isotope compositions (whole rocks and carbonates) vary from values close to the field of continental lithospheric mantle, or that of primary carbonatites, up to values typical of a hydrothermal environment. An isotope exchange model implies that the main isotope variations, ranging from a magmatic (e.g., 1200°C) to a low temperature (<400°C) environment, involved fluids with CO2/H2O ratios between 0.8 and 1.0. In particular, the OC isotopic variations, in combination with the La vs La/Yb ratios, suggest an increasingly higher level of carbonate in the silicate liquids, with increasing evolution, i.e., basanite→phonotephrite→trachyphonolite–phonolite (trachyte)→carbonatite. SrNd isotopes show that the carbonatites are mantle derived without significant crustal contamination and that they can be related to isotopically enriched sources where newly formed veins (enriched component) and peridotite matrix (depleted component) underwent differing isotopic evolution.TDM model ages for NPAA range from 1.2 to 2.3Ga. Considering that in the whole Paraná Basin isotopically distinct K-alkaline and tholeiitic magmas were generated following the enrichment of the subcontinental mantle mainly between 1.0 and 2.3Ga (Paleo-Mesoproterozoic events), the mantle sources preserved the isotopic heterogeneities over long time periods, suggesting a non-convective, i.e., lithospheric, mantle source beneath different cratonic or intercratonic areas.

40Ar/39Ar geochronological constraints on the formation of the Dayingezhuang gold deposit: New implications for timing and duration of hydrothermal activity in the Jiaodong gold province, China

China's largest gold resource is located in the highly endowed northwestern part of the Jiaodong gold province. Most gold deposits in this area are associated with the NE- to NNE-trending shear zones on the margins of the 130–126Ma Guojialing granite. These deposits collectively formed at ca. 120±5Ma during rapid uplift of the granite. The Dayingezhuang deposit is a large (>120t Au) orogenic gold deposit in the same area, but located along the eastern margin of the Late Jurassic Linglong Metamorphic Core Complex. New 40Ar/39Ar geochronology on hydrothermal sericite and muscovite from the Dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130±4Ma and is the earliest important gold event that is well-documented in the province. The Dayingezhuang deposit occurs along the Linglong detachment fault, which defines the eastern edge of the ca. 160–150Ma Linglong granite–granodiorite massif. The anatectic rocks of the massif were rapidly uplifted, at rates of at least 1km/m.y. from depths of 25–30km, to form the metamorphic core complex. The detachment fault, with Precambrian metamorphic basement rocks in the hangingwall and the Linglong granitoids and migmatites in the footwall, is characterized by early mylonitization and a local brittle overprinting in the footwall. Gold is associated with quartz–sericite–pyrite–K-feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault. Our results indicate that there were two successive, yet distinct gold-forming tectonic episodes in northwestern Jiaodong. One event first reactivated the detachment fault along the edge of the Linglong massif between 134 and 126Ma, and then a second reactivated the shears along the margins of the Guojialing granite. Both events may relate to a component of northwest compression after a middle Early Cretaceous shift from regional NW–SE extension to a NE–SW extensional regime.

멕시코 시나올라주의 지질 및 금속광물자원

멕시코 시나올라(Sinaola)주의 지질은 하부로부터 선캠브리아기 변성암(Sonobari Complex), 두 개의 고생대층(하부: 미분화된 변성암, 상부: 석탄기 퇴적암), 변성화산암, 쇄설암, 탄산염암으로 구성된 5개의 중생대층, 화산암으로 구성된 신생대 암석, 제 4기의 쇄설성 퇴적층과 화산류로 구성되어 있다. 시나올라주는 잠재적으로 금속광물자원이 풍부하며 비금속광물은 적은 편이다. 광상들은 다양한 지질환경과 관련되어 있고 지형학상 시에라 마드레 옥시덴탈(Sierra Madre Occidental)에 부존되어 있는 것이 특징적이다. 주로 알려진 광상은 금과 은이며 뒤를 이어 아연, 연, 동과 일부 철이 분포한다. 시나올라주는 가끔 가행하고 있는 몰리브데늄, 텅스텐, 비스무스 광상도 부존되어 있다. 니켈과 코발트도 부존이 알려져 있으나 단지 소규모로 개발되었음이 보고되고 있다. The geology of Sinaola state consists of Precambrian metamorphic rocks(Sonobari Complex), two Paleozoic units(lower non-differentiated metamorphic rocks and upper Carboniferous sedimentary rocks), five Mesozoic units(metavolcanic, clastic, and calcareous rocks), Cenozoic volcanic rocks, and Quaternary clastic sediments and volcanic flows. The Sinaola state is potentially rich in metallic mineral resources with lower degree of non-metallic mineral resources. They are related to a variety of geological environments and are mainly physiographically located on the Sierra Madre Occidental. Mainly known mineral deposits are of gold and silver followed by zinc, lead, copper and some iron. The state also has deposits of molybdenum, tungsten and bismuth that have been occasionally exploited. There is a reference of nickel and cobalt mineralization, but these deposits have been exploited only at a small scale.

A comparative analysis of two Early Palaeozoic marine impact structures in Estonia, Baltic Sea: Neugrund and Kärdla

Kardla and Neugrund are two Early Palaeozoic offshore impact structures located some 50 km apart along the Estonian coast of the Baltic Sea. They share many similarities but differing features are also found. The Kardla impact structure is located at the NE coast of Hiiumaa Island (58°58’N, 22°46’E). The inner crater has a 4 km rim-to-rim diameter and a c. 130 m high central uplift, surrounded by a ring fault, c. 12 km in diameter. The well-preserved buried inner crater is outlined in the landscape by a circular ridge of uplifted bedrock. The perimeter of the outer crater is outlined on the seafloor by a semicircular ridge of narrow shoals. The variable height of the rim wall (50–240 m above the crystalline basement level) and the asymmetric location of the inner crater is obviously a result of an oblique impact in a layered target and partial collapse of the rim wall. Shortly after the impact in a shallow epicontinental sea during Late Ordovician time (c. 455 My), calcareous biodetritic muds were deposited and the crater was buried. The Neugrund impact structure is located in the seabed at the entrance of the Gulf of Finland (59°20’N, 23°31’E). The inner crater has a 7 km rim-to-rim diameter and the outer limit of the structure passes through the Osmussaar Island to the southwest of the impact centre. The crater was buried in a shallow epicontinental sea with siliciclastic deposition shortly after the impact at Early Cambrian time, c. 535 My. It was partially re-exposed by erosion during Pliocene. The target had a three-layered composition: Precambrian metamorphic rocks covered by Ediacaran and Early Cambrian siliciclastic rocks (c. 150 m) and water (c. 100 m). The structure has been studied with seismoacoustic and sidescan sonar profiling, and by diving and sampling of submarine outcrops. Several hundred samples of impact breccias have been collected and investigated from erratic boulders distributed by glacial action in the west Estonian mainland, islands and sea floor.

당두 연-아연 광상의 산출광물과 화학조성

The Dangdu Pb-Zn deposit is located at approximately 10 km south of Jecheon, Korea. Geology of Dangdu deposit area consists of Pre-cambrian metamorphic rocks, Ordovician sedimentary rocks, Jurassic and Cretaceous igneous rocks. The ore deposit is developed along the fracture trending in Ordovician limestone and is considered to be a skarn type ore deposit. The shape of ore bodies developed in the Dangdu ore deposit can be divided into lens-form(two ore bodies of -30 m level adit and one ore body of -63 m level adit) and pocket-form developed in -30 m level adit. Ore minerals observed in the ore deposits are magnetite, pyrrhotite, pyrite, chalcopyrite, sphalerite, galena, cosalite, marcasite, hessite, native Bi and bismuthinite. Chemical composition of sphalerite ranges FeS 14.14~18.08 mole%, CdS 0.44~0.70 mole%, MnS 0.52~1.13, 1.53~2.09 mole%. Galena contains a small amount of silver with an average of 0.54 wt.%. An average composition of cosalite is Ag 2.43 wt.%, Bi 44.36 wt.%, Pb 35.05 wt.% which results the chemical formula of cosalite as . Skarn minerals consist of epidote, garnet, pyroxene, tremolite, quartz and calcite. The zoning pattern of the ore deposit can be subdivided into epidote-clinopyroxene zone, epidote-clinopyroxene-chlorite zone and epidote-garnet-clinopyroxene zone from the central part of the ore body towards the wall rocks. The chemical composition of garnet shows an increasing trend of grossular from epidote-clinopyroxene zone to epidote-garnet-clinopyroxene zone. Clinopyroxene occurs as a solid solution of diopside and hedenbergite, and the ratio of johannsenite increases from epidote-clinopyroxene zone to epidote-clinopyroxene-chlorite and epidote-garnet-clinopyroxene zones. The mineralization of the ore deposit is considered to be one stage event which can be separated into early skarn mineralization stage, middle ore mineralization stage and late low temperature mineralization stage. The temperature estimation from the low temperature mineralization range from which is considered to be representing the temperature of late mineralization.

Selected geotourist attractions of Death Valley, USA

Death Valley National Park located in the U.S. states of California and Nevada is one of many units within the National Park Service established because of their exceptional natural and geological values. Death Valley National Park is renownedworldwide for its perfectly exposed, complex, unique and diverse geological resources. Within the park visitors encounter representatives of many geological epochs, from Precambrian metamorphic rocks exposed in the Black Mountains to recent desert sediments. This paper presents the geology of Death Valley and some of the most interesting geosites: Zabriskie Point, Badwater Basin, Devil’s Golf Course, Harmony Borax Works and Ubehebe Craters.

Hydraulic Significance of Fracture Correlated Lineaments in Precambrian Rocks in Purulia District, West Bengal

Abstract Filter analysis of lineaments in Precambrian metamorphic rocks was used to delineate fracture-correlated lineaments and hydraulically significant fractures. The unfiltered analysis technique fails to show correlation between major lineaments and fractures. Domain-based and discrete filtering techniques successfully identify fracture-correlated lineaments within the brittle-ductile shear zone in conjunction with fractures characterized by high fracture frequencies (&amp;gt;10/m). The locales of hydraulically significant fractures can thus be assessed if the geological controls governing the spatial distribution of fracture frequencies are computed using structural domain approach. The concurrence of fracture-correlated lineaments and hydraulically significant fractures within the brittle-ductile shear zone is evident.