Clinopyroxene episyenites in a Proterozoic rapakivi granite,SE Finland — recrystallization textures,mass transfer and implications for the petrology of A-type granite complexes

Mineralogy and Petrology - Na-metasomatic augite and aegirine-augite episyenites are hosted by subalkaline amphibole granites in the 1.644 Ga Suomenniemi rapakivi granite complex,...     

Geology and geochemistry of reworking gold deposits in intrusive rocks of China—I. Features of the intrusive rocks

Most gold deposits in intrusive rocks were formed as a result of reworking processes. The intrusive rocks containing gold deposits and consisting of ultramafic-mafic, intermediateacid and alkaline rocks of the Archean, Proterozoic, Caledonian, Hercynian and Yenshanian periods occur in cratons, activated zones of cratons and fold belts. Among them, ultramaficmafic rocks, diorite, alkaline rocks, and anorthosite are products of remelting in the mantle or mantle-crust or mantle with crustal contamination. However, auriferous intermediate-acid rocks are products of metasomatic-remelting in auriferous volcanic rocks or auriferous volcanosedimentary rocks in the deep crust.     

Radioactive quartz-pebble conglomerates from western margin of Bonai granite pluton,Sundargarh district,Orissa — A new find

Several radioactive quartz-pebble conglomerate (QPC) occurrences at the western margin of Archaean Bonai granite and overlying Iron Ore Group (IOG) rocks have recently been located over a total strike length of 8–10 km intermittently in a NE-SW to E-W trend with steep dips due north-west to north in parts of Sundargarh district of Orissa. The QPC samples have analysed up to 0.039% U₃O₈ and 0.035% ThO₂ with high concentration of Y (74 to 518 ppm), La(<100 to 880 ppm), Cr ( 126 to 633 ppm), Zr (137 to 1250 ppm) and Pb (31 to 581 ppm). Cellulose Nitrate (CN) film studies of few QPC samples indicated adsorbed uranium over goethite and infiltrated ferruginous material (limonite), secondary uranium as encrustation and fracture filling and discrete sub-rounded grains of monazite, zircon, allanite and rare xenotime in the matrix of QPC as radioactive phases. Higher content of Th over U, elevated concentration of Y and La in QPC eliminates the possibility of its low temperature product by epigenetic processes. Poor correlation of U with elements like Pb, Y, Zr, La and Cr can be explained due to surficial leaching of uranium from QPC after its deposition as reflected by adsorbed U over iron-oxides and low U/Th ratio in QPC in the area.     

Development of corona textures around olivine in anorthosites of the Korosten’ pluton, Ukrainian Shield: Mineralogy, geochemistry, and fluid inclusions

New data on the composition of minerals in corona textures around olivine and crystal-fluid inclusions in olivine from anorthosites of the Korosten’ pluton (sampled in the Golovino quarry), Ukrainian Shield were obtained using electron and ion microprobe analyses, Raman spectroscopy, scanning electron microscopy, and cryo- and thermometry. The corona textures developed around olivine grains in contact with plagioclase and consist of inner orthopyroxene rims around olivine and outer rims of orthopyroxene-clinopyroxene-orthoclase-plagioclase symplectites. The symplectites and orthopyroxene rims most probably developed nearly simultaneously and grew in the opposite directions from the original contact of the magmatic olivine and plagioclase and replaced both olivine and plagioclase. The Al₂O₃ and CaO concentrations in the symplectitic orthopyroxene increase toward the contact with magmatic plagioclase, whereas the Al₂O₃ and CaO concentrations in the symplectitic plagioclase simultaneously decrease and its Na₂O and K₂O increase. Optically discernible crystalline and fluid phases of crystal-fluid inclusions in olivine were identified as pyroxenes (orthopyroxene and clinopyroxene), actinolite, Ca-and Fe, Mg-carbonates, and magnetite, along with practically pure highdensity CO₂. The mineral assemblages of corona texture in the Korsten’ anorthosites were produced by autometasomatic processes at a high CO₂ activity, and the local variations in the chemistry of corona minerals were likely controlled by the content and chemistry of the interstitial fluid and primary minerals. The coronas developed under subsolidus conditions, via the reaction interaction of olivine and plagioclase under the effect of an integranular fluid, with the dissolution of olivine and plagioclase at T = 980–860°C and P > 5 kbar. Inasmuch as corona textures do not occur ubiquitously in the rocks, the origin of the former was most probably controlled by the amount of the intergranular fluid.     

Mineralogy,geochemistry, and genesis of high-alumina fenites of the Mont Saint-Hilaire alkaline pluton,Québec,Canada

High-alumina fenites in the Mont Saint-Hilaire alkaline complex, Québec, Canada, form bodies at the contact of peralkaline nepheline syenite. Fenites are subdivided into four types: corundum-spessartine-biotite-feldspar, muscovite-corundum-hercynite-biotite-feldspar, carbonated muscovite-biotite-hercynite-feldspar, and spessartine-hercynite-feldspar. Accessory minerals of the ilmenite-pyrophanite series, columbites, zircon, thorite, pyrrhotite, Fe, Mn, Mg, Ca, Ba, and REE carbonates, uedaite-(Ce), etc. are identified. Three stages are suggested in the formation of these rocks. In mineralogy and geochemistry, the Mont Saint-Hilaire high-alumina fenites are similar to Al-rich fenites replacing xenoliths in the Khibiny alkaline complex, Russia. In both cases, fenites are related to peralkaline rocks and replace high-alumina protoliths: granite at Mont Saint-Hilaire and metapelites in the Khibiny Mountains. These fenites are regarded as a specific type of fenites with rock-forming Mg-depleted hercynite.     

Geology,mineralogy, and geochemistry of fault-controlled hydrothermal Cu–Au mineralization in the Shanmen Volcanic Basin,SE China

The Yukeng–Banling deposit is a typical fault-controlled hydrothermal Cu–Au deposit in the Shanmen Volcanic Basin (SVB), SE China. Ore bodies commonly occur as lodes, lenses and disconnected pods dipping SW with vertical zonation of ore minerals. Ore-related hydrothermal alteration is well developed on both sides of the veins, dominated by silicification, sericitization, chloritization and argillation with a banded alteration zonation. The mineralization can be divided into three stages (stages I, II and III). Native gold is present as veinlets in fractures of fine-grained pyrite from stage II.Zircon U–Pb and Rb–Sr isochron ages indicate that the Cu–Au mineralization is coeval with the Caomen alkaline granite and Xiaokeng quartz-diorite, both emplaced at ca. 102 Ma. Microthermometric measurements of fluid inclusions in quartz and sphalerite from stage II veins indicate that the Yukeng–Banling deposit is an epithermal deposit. Six ore-related quartz grains have δD_H2O values of − 69 to − 43‰, and δ¹⁸O_H2O values calculated using total homogenization temperatures that range from − 2.0 to 0.7‰. All samples plot in an area between the magmatic field and the meteoric line, suggesting that the ore-forming fluids are derived from a mixed source of magmatic and meteoric waters. δ³⁴S values for eight pyrite separates range from − 2.1 to + 4.1‰ with an average of + 1.7‰, and δ³⁴S values for galena and sphalerite are 2.3‰ and 2.2‰, similar to magmatic sulfur. Four alkaline granite samples have Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb)_t = 18.175–18.411, (²⁰⁷Pb/²⁰⁴Pb)_t = 15.652–15.672 and (²⁰⁸Pb/²⁰⁴Pb)_t = 38.343–38.800. Three quartz-diorite samples have ratios (²⁰⁶Pb/²⁰⁴Pb)_t, (²⁰⁷Pb/²⁰⁴Pb)_t and (²⁰⁸Pb/²⁰⁴Pb)_t of 18.277–18.451, 15.654–15.693 and 38.673–38.846, respectively. These age-calculated lead isotopic data for alkaline granite are similar to those for the analyzed sulfides. Co/Ni ratios for stage II pyrites range from 1.42 to 5.10, indicating that the Yukeng–Banling deposit records the past involvement of magmatic hydrothermal fluids. The isotope data, together with geological, mineralogical and geochronological evidence, favor a primary magmatic source for sulfur and metals in the ore fluids. Mixing of the Cu- and Au-rich fluids with meteoric water led to precipitation of the Cu–Au veins along NW-trending faults.The Yukeng–Banling deposit, the contemporaneous Caomen alkaline granite and Xiaokeng quartz-diorite in the SVB formed under an extensional setting, due to high-angle subduction of the paleo-Pacific plate. The extensional setting facilitated the formation of Cu- and Au-rich magmas which was derived from enriched mantle and lower crust.     

Geology,geochemistry and sulphur isotopes of the Hat Han gold–antimony deposit,NE Vietnam

The Song Hien Rift basin is considered as one of the important regions for gold deposits in North East Vietnam. Host rocks of a number gold deposits in the Song Hien Rift basin are mainly in Lower Triassic sedimentary formations. However, there is the Hat Han gold deposit hosted in fined-grained mafic magmatic rocks with similar characteristics as gold deposit hosted in the Triassic sediments. Sulphur isotopic compositions of sulphide are similar to those in carbonaceous shale, suggesting that the sulphur was ‘borrowed’ from sedimentary rocks in filling the rift basin. Gold-bearing sulphides (pyrite and arsenopyrite) are the main form of Au presence in the ore. Gold in pyrite is present as Au^+ 1, and a minor amount of as nanoparticles of native Au (Au⁰); whereas in arsenopyrite, gold is chemically bound as the octahedral complex AuAs₂. Analysis of geology, as well as geochemical and isotopic studies show that the genesis of the Hat Han gold deposit is not related to the Cao Bang mafic magmatism; instead the latter only serves as (ore) host rock. The geochemical results presented above suggest that the gabbro host rock only supplies iron needed for sulphide formation. With regard to ore genesis, the Hat Han gold deposit in the Song Hien rift basin was generated in the similar way as sediment-hosted gold deposit. There are many similar typomorphic features between the Hat Han deposit and Carlin-like deposits in the Nanpanjang sedimentary basin in China.     

Trace metal geochemistry of core sediments between Visakhaptanam and Kakinada, along the eastcoast of India

Six sediment core samples collected from the innershelf of the east coast of India between Visakhapatnam and Kakinada were analyzed for major （Al ＆ Fe） and trace metals （Cu, Co, Ni, Cd, Pb, Zn, Mn ＆ Cr） to study the processes that regulate their concentrations in coastal sediments and to evaluate the metal contamination due to anthropogenic interference. High concentrations of Fe （5%-7%） are attributed mainly to the fine texture and its proximity to the source, maflc rocks. Positive correlation of Fe with Mn in all the cores indicates the influence of early diagenetic process. Positive correlations between Co, Ni, Zn and Cd among themselves and with Fe indicate their adsorption to ferromanganese oxides and involvement in geochemical processes. Further normalization of metals to Al indicates that the sediments are depleted in Mn ＆ Zn and relatively enriched in Cd, Co, Ni, Pb ＆ Cr, which also confirms that the origin of these sediments is of geological rather than biogenic importance. The Geo-accumulation （Igeo） values calculated for Ni, Pb, Co, Cd, Zn ＆ Cr are more or less near to unity （Igeo≥1）, indicating no industrial metal pollution. Pollution Load Index （PLI） values （1-2） calculated for the trace metals confirm the above findings.     

Pb-Nd-Sr isotopic and geochemical constraints on the origin of the 1.54–1.56 Ga Salmi rapakivi granite—Anorthosite batholith (Karelia,Russia)

Summary The Salmi batholith is situated on the eastern edge of the EW-trending anorthositerapakivi granite belt of the Fennoscandian shield, at the contact between Proterozoic and Archean crustal domains. The tectonic setting and high K, Rb, Nb, Y, Zr, REE (except Eu), F, Sn, Be, and Li contents of.the Salmi batholith indicate that it represents typical subalkaline A-type and within plate granites. Gabbro-anorthosites of the batholith demonstrate a concordant U-Pb apatite age of 1563 ± 9 (2) Ma and a Sm-Nd internal isochron age of 1552 ± 69 Ma. Zircons from amphibole-biotite granites have an upper concordia intercept U-Pb age of 1543 ± 8 Ma. An older inherited zircon component with elevated Th/U ratio is found in zircons separated from K-feldspar ovoids. Rb-Sr internal errorchron for the granites yields an age of 1455 ± 17 Ma, probably the time of completion of postmagmatic processes within the batholith. The gabbro-anorthosites and granites show similar initial Nd, Sr, and feldspar Pb isotope compositions ( _Nd = - 6.5 to - 8.2; ₂ = 8.6 to 8.9; ₂ = 3.9 to 4.0; I_Sr = 0.7052 to 0.7057 for the basic rocks, and _Nd = -6.2 to -8.9; ₂ = 8.1 to 9.2; ₂ = 4.0 to 4.4; I_Sr = 0.7050 to 0.7072 for the granites). Two-stage neodymium T_DM model ages for both assemblages range from 2.60 to 2.80 Ga. Old LREE-enriched sources with low time-integrated U/Pb and Rb/Sr and elevated Th/U ratios were involved in the formation of both the gabbroanorthosites and the granites. Bulk contamination with crustal materials cannot explain the data for the basic rocks. Selective incorporation of Pb, Sr, and Nd from Archean lower crust is needed, or else, the gabbro-anorthosites may have been derived from an isotopically anomalous subcontinental mantle source. The ascent of a mantle diapir resulted in anatexis of the lower crust and formation of the parent magma for the rapakivi granites.

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Pb-Nd-Sr Isotope, und geochemische Daten: Bedeutung für die Entstehung des 1,54–1,56 Salmi Rapakivi Granit-ANorthosit-Batholithen (Karelia, Rußland)

Zusammenfassung Der Salmi-Batholith ist am östlichen Rand des Ost-West streichenden Anorthosit Rapakivi-Granitgürtels des fennoskandischen Schildes am Kontakt zwischen proterozoischen und archaischen Krustenbereichen gelegen. Die tektonische Position und hohe K, Rb, Nb, Y, Zr, REE (mit Ausnahme von Eu), F, Sn, Be und Li-Gehalte des Salmi-Batholithen weisen darauf hin, daß es sich hier um einen typischen subalkalischen A-Typ und within plate Granit handelt. Gabbro-Anorthosite des Batholithen zeigen ein konkordantes U-Pb Apatit alter von 1563 ± 9 (2) Ma und ein internes Sm-Nd Isochronenalter von 1552 ± 69 Ma. Zirkone aus den Amphibolit-Biotitgraniten haben ein oberes Concordia U-Pb Alter von 1543 ± Ma. Ein ältere, ererbte Zirkonkom ponente mit erhöhtem Th/U Verhältnis kommt in Zirkonen, die von K-Feldspat Ovoi den abgetrennt wurden, vor. Eine interne Rb-Sr Errorchrone für die Granite ergibtein Alter von 1455 ± 7 Ma. Dies repräsentiert wahrscheinlich die Zeit des Abschlusses postmagmatischer Prozesse innerhalb des Batholithen. Die Gabbro-Anorthosite und Granite zeigen ähnliche Nd, Sr und Feldspat Pb Isotopenzusammensetzungen ( _Nd = –6.5 to 8.2; ₂ = 8.6 to 8.9; K₂ = 3.9 to 4.0; I_Sr = 0.7052 to 0.7057 für die mafischen Gesteine, und _Nd = –6.2 to -8.9; ₂ = 8.1 to 9.2; K₂ = 4.0 to 4.4; I_Sr = 0.7050 to 0.7072 für die Granite). Zweistufige Neodymium T_DM Modellalter für beide Assoziationen liegen zwischen 2.60 und 2.80 Ga. Alte LREE-angereicherte Quellen mit niedrigen, zeitintegrierten U/Pb und Rb/Sr und erhöhten Th/U Verhältnissen waren bei der Bildung der Gabbro-Anorthosite und Granite involviert. Kontamination mit Krus tenmaterial kann die Daten für die basischen Gesteine nicht erklären. Entwederist dazu eine selektive Inkorporation von Pb, Sr und Nd aus der tieferen archaischen Kruste erforderlich oder man muß annehmen, daß die Gabbro-Anorthosite von einer isotopisch anomalen subkontinentalen Mantelquelle stammen. Der Aufstieg eines Mantel-Diapirs führt zu Anatexis der tieferen Kruste und zur Bildung der Ausgangsmagmen für die Rapakivi Granite.

     

Geology,fluid inclusions,and geochemistry of the Zhazixi Sb–W deposit,Hunan, South China

The Zhazixi Sb–W deposit in the Xuefeng uplift, South China, exhibits a unique metal association of W and Sb, where the W orebodies are hosted by interlayer fractures and the Sb orebodies are contained within NW-trending faults. This study proposes that the W and Sb mineralization took place in two separate periods. The mineral paragenesis of the W mineralization reveals a mass of quartz, scheelite and minor calcite. The mineral assemblage of the Sb mineralization developed after W mineralization and consists of predominantly quartz and stibnite, and small amounts of native Sb, berthierite, chalcostibnite, pyrite, and chalcopyrite. Fluid inclusions in quartz and coexisting scheelite are dominated by two-phase, liquid-rich, aqueous inclusions at room temperature. Microthermometric studies suggest that ore-forming fluids for W mineralization are characterized by moderate temperatures (170–270 °C), low salinity (3–7 wt% NaCl equiv.), low density (0.75–0.95 g/cm³), and moderate to high pressure (57.2–99.7 MPa) and these fluids experienced a cooling and dilution evolution during W mineralization. Ore-forming fluids for Sb mineralization are epithermal types with low temperatures (150–230 °C), low salinity (4–6 wt% NaCl equiv.), moderate density (0.82–0.94 g/cm³), and high pressure (42.2–122.5 MPa) and these fluids display an evident decline in homogenization temperature during Sb mineralization. Laser Raman analyses of the vapor phase indicate that the ore-forming fluids for both W and Sb mineralization contain a small amount of CO₂.The ore-forming fluids for Sb mineralization are identified as predominantly originating from the continental crust, as suggested by the low ³He values (0.009 × 10⁻¹² cc.STP/g) and ³He/⁴He ratios (0.002–0.056 Ra) as well as high ³⁶Ar values (1.93 × 10⁻⁹ cc.STP/g) and ⁴⁰Ar/³⁶Ar ratios (909.5–2279.7). The source of S is identified to be the Neoproterozoic Wuqiangxi Formation, as traced by the δ³⁴S_V-CDT values of stibnite (3.1–9.4‰). The ²⁰⁸Pb/²⁰⁴Pb (37.643–40.222), ²⁰⁷Pb/²⁰⁴Pb (15.456–15.681), and ²⁰⁶Pb/²⁰⁴Pb (17.093–20.042) ratios suggest a mixture of lower crustal and supracrustal Pb sources.It is thus concluded that the ore genesis of the Zhazixi Sb–W deposit is related to the intracontinental orogeny during the early Mesozoic. Fluid mixing is considered to be the critical mechanism involved in W mineralization, whereas a fluid cooling process is responsible for Sb mineralization. Furthermore, the absence of Au is attributed to the low Σa_s content in Sb-mineralizing fluids.     

Elemental and organic geochemistry of Gondwana sediments from the Krishna–Godavari Basin,India

Elemental and organic geochemical studies have been carried out on the Gondwana sediments, collected from the outcrops of Permian and Jurassic–Cretaceous rocks in the Krishna–Godavari basin on the eastern coast of India, to understand their paleo and depositional environment and its implications for hydrocarbon generation in the basin. Amongst the studied formations, the Raghavapuram, Gollapalli and Tirupati form a dominant Cretaceous Petroleum System in the west of the basin. Raghavapuram shales and its stratigraphic equivalents are the source rock and Gollapalli and Tirupati sandstones form the reservoirs, along with basaltic Razole formation as the caprock. Major element systematics and X-ray diffraction study of the sandstones indicate them to be variably enriched with SiO₂ relative to Al₂O₃ and CaO, which is associated, inherently with the deposition and diagenesis of the Gondwana sediments. Post-Archean Average Shale normalized rare earth elements in shales show enrichment in most of the samples due to the increasing clay mineral and organic matter assemblage. A negative europium and cerium anomaly is exhibited by the REE's in majority of rocks. Composed primarily of quartz grains and silica cement, the Gollapalli and Tirupati sandstones have characteristics of high quality reservoirs. The shales show a significant increase in the concentration of redox sensitive trace elements, Ni, V, Cr, Ba and Zn. The total organic carbon content of the shales ranges between 0.1 and 0.5 wt%. Programmed pyrolysis of selected samples show the Tmax values to range between 352–497 °C and that of hydrogen index to be between 57–460 mgHC/gTOC. The organic matter is characterized by, mainly, gas prone Type III kerogen. The n-alkane composition is dominated by n-C₁₁–C₁₈ and acyclic isoprenoid, phytane. The aromatic fraction shows the presence of naphthalene, anthracene, phenanthrene, chrysene and their derivatives, resulting largely from the diagenetic alteration of precursor terpenoids. The organic geochemical proxies indicate the input of organic matter from near-shore terrestrial sources and its deposition in strongly reducing, low oxygen conditions. The organic matter richness and maturity derived from a favorable depositional setting has its bearing upon the Gondwana sediments globally, and also provides promising exploration opportunities, particularly in the Raghavapuram sequence of the KG basin.     

Introduction to the Geology of Turkey—A Synthesis

Auriferous quartz veins are known to exist in more than two dozen prospects, encompassing an area of 500 km² northward from Serrita township (state of Pernambuco) in northeastern Brazil. Gold-bearing veins occur either with a strike of 70° to 110°, crosscutting muscovite schists of the Middle Proterozoic Salgueiro Group, or with a strike of 330° in granodiorite intrusions in the same schists. Small amounts of pyrite, galena, arsenopyrite, chalcopyrite, and sphalerite commonly are observed. Sericite, chlorite, and epidote are the most common wall-rock alteration products.

Fluid inclusions were studied in samples of mineralized quartz veins from the Barra Verde III prospect in a small granodiorite body, and from the Ingá, Saburá, and Riacho do Meio prospects in the Salgueiro schists. Some samples of barren quartz veins also were studied for comparison.

Primary and pseudosecondary inclusions in the mineralized veins are triphasic or biphasic aqueous-carbonic at room temperature. The wide range of the CO₂/H₂O volume ratio (between 2:1 and 1:3) in a single group or trail suggests the coexistence of two immiscible fluids during the penecontemporaneous processes of quartz crystallization, deformation, mineralization, and recrystallization. Total homogenization of these inclusions beginning at 290° to 310°C and 1.3 to 1.8 kbar provides the trapping conditions of the heterogeneous, effervescent fluid. CO₂ melting temperatures of ～?57° to °59°C indicate low CH₄ or N₂ contents. Clathrate melting close to 6.3°C indicates a low salinity of ～6.9% NaCl equiv. In addition, the low CH⁴ content of the fluid in equilibrium with sulfides and alteration minerals suggests an oxygen fugacity between 10^?30 and 10^?27, a total sulfur activity of 10^?2 to 10°, and a neutral pH of ～5.     

Geology,geochemistry, and geochronology of Fe-oxide Cu (± Au) mineralization associated with Şamlı pluton,western Turkey

The Şamlı (Balıkesir) Fe-oxide Cu (± Au) deposit, one of several iron (+ Cu ± Au) deposits in western Turkey, is hosted by porphyritic rocks of the multi-phase Şamlı pluton and metapelitic–metadiabasic rocks of Karakaya Complex. Two successive mineralization events are recognized in the area as; i) early magnetite and sulfide and ii) late hematite–goethite-native copper (± Au). Alteration associated with the mineralization in Şamlı is characterized by four distinct mineralogical assemblages. They are, in chronological order of formation, (1) plagioclase–early pyroxene (± scapolite), (2) garnet–late pyroxene, (3) chlorite–epidote, and (4) chalcedony–calcite alteration. Geochemical, isotopic (Sr, Nd, O, S) and geochronological (Ar–Ar) data from alteration and magmatic rocks suggest a temporal and genetic link between the multiphase Şamlı pluton and the hydrothermal system that controls the Fe-oxide-Cu (± Au) mineralization. ⁴⁰Ar/³⁹Ar geochronology on hornblende and biotite separates of the Şamlı pluton yielded an age range between 23.20 ± 0.50 and 22.42 ± 0.11 Ma, overlapping with ⁴⁰Ar/³⁹Ar age of 22.34 ± 0.59 Ma from alteration.The close spatial and temporal associations of Şamlı mineralization with porphyritic intrusions, pervasive Ca-rich alteration (calcic plagioclase, andraditic garnet, diopsidic pyroxene, scapolite, and epidote) are considered as common features akin to calcic assemblages in typical IOCG deposits. Besides abundant low-Ti (≤ 0.5%) magnetite/hematite, high Cu–moderate Au (up to 8.82 ppm) association, structural control and lithologic controls of mineralization, low S-sulfide content (chalcopyrite > pyrite) in the deposit; and the derivation of causative magma from subduction-modified subcontinental lithospheric mantle under a transpressional to transtensional regime, are collectively considered as the features in favor of IOCG-type mineralization for the Şamlı deposit.     

Geology,isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb–Zn deposit,southwest China

The Shanshulin Pb–Zn deposit occurs in Upper Carboniferous Huanglong Formation dolomitic limestone and dolostone, and is located in the western Yangtze Block, about 270 km west of Guiyang city in southwest China. Ore bodies occur along high angle thrust faults affiliated to the Weishui regional fault zone and within the northwestern part of the Guanyinshan anticline. Sulfide ores are composed of sphalerite, pyrite, and galena that are accompanied by calcite and subordinate dolomite. Twenty-two ore bodies have been found in the Shanshulin deposit area, with a combined 2.7 million tonnes of sulfide ores grading 0.54 to 8.94 wt.% Pb and 1.09 to 26.64 wt.% Zn. Calcite samples have δ¹³C_PDB and δ¹⁸O_SMOW values ranging from − 3.1 to + 2.5‰ and + 18.8 to + 26.5‰, respectively. These values are higher than mantle and sedimentary organic matter, but are similar to marine carbonate rocks in a δ¹³C_PDB vs. δ¹⁸O_SMOW diagram, suggesting that carbon in the hydrothermal fluid was most likely derived from the carbonate country rocks. The δ³⁴S_CDT values of sphalerite and galena samples range from + 18.9 to + 20.3‰ and + 15.6 to + 17.1‰, respectively. These values suggest that evaporites are the most probable source of sulfur. The δ³⁴S_CDT values of symbiotic sphalerite–galena mineral pairs indicate that deposition of sulfides took place under chemical equilibrium conditions. Calculated temperatures of S isotope thermodynamic equilibrium fractionation based on sphalerite–galena mineral pairs range from 135 to 292 °C, consistent with previous fluid inclusion studies. Temperatures above 100 °C preclude derivation of sulfur through bacterial sulfate reduction (BSR) and suggest that reduced sulfur in the hydrothermal fluid was most likely supplied through thermo-chemical sulfate reduction (TSR). Twelve sphalerite samples have δ⁶⁶Zn values ranging from 0.00 to + 0.55‰ (mean + 0.25‰) relative to the JMC 3-0749L zinc isotope standard. Stages I to III sphalerite samples have δ⁶⁶Zn values ranging from 0.00 to + 0.07‰, + 0.12 to + 0.23‰, and + 0.29 to + 0.55‰, respectively, showing the relatively heavier Zn isotopic compositions in later versus earlier sphalerite. The variations of Zn isotope values are likely due to kinetic Raleigh fractional crystallization. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of the sulfide samples fall in the range of 18.362 to 18.573, 15.505 to 15.769 and 38.302 to 39.223, respectively. The Pb isotopic ratios of the studied deposit plot in the field that covers the upper crust, orogenic belt and mantle Pb evolution curves and overlaps with the age-corrected Proterozoic folded basement rocks, Devonian to Lower Permian sedimentary rocks and Middle Permian Emeishan flood basalts in a ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagram. This observation points to the derivation of Pb metal from mixed sources. Sphalerite samples have ⁸⁷Sr/⁸⁶Sr_200 Ma ratios ranging from 0.7107 to 0.7115 similar to the age-corrected Devonian to Lower Permian sedimentary rocks (0.7073 to 0.7111), higher than the age-corrected Middle Permian basalts (0.7039 to 0.7078), and lower than the age-corrected Proterozoic folded basement (0.7243 to 0.7288). Therefore, the Sr isotope data support a mixed source. Studies on the geology and isotope geochemistry suggest that the Shanshulin deposit is a carbonate-hosted, thrust fault-controlled, strata-bound, epigenetic, high grade deposit formed by fluids and metals of mixed origin.     

Time relationship between regional deformation and fabric development in the Peralimala pluton,South India — Inferences from magnetic fabric

Anisotropy of magnetic susceptibility (AMS) is investigated in samples of Peralimala (PM) pluton (ca. 550 Ma) and adjacent gneiss, gabbro, mylonite and amphibolite from the Moyar Shear Zone (MSZ), Southern Granulite Terrane (SGT) with an aim to decipher the time-relationship between fabric development in the pluton and regional tectonics. Magnetic foliation recorded in the PM pluton is sub-parallel to the WNW-ESE striking MSZ. Magnetic foliation and lineation trajectories are sigmoidal and curve into the shear zone. A dextral sense of shear is deciphered from the trajectories, which is similar to that reported within the MSZ in some earlier studies. It is inferred that the PM pluton has developed post-emplacement deformation-fabric related to reactivation of the MSZ during Pan-African age. Based on the data and existing information about regional tectonics of the area, the possibility of the (a) PM pluton being a Deformed Alkali Rock and Carbonatite (DARC) and (b) MSZ marking an ancient suture zone, is discussed.     

Tourmaline from quartz lenses of the Urtui granite pluton,Strel’tsovka orefield,Ttansbaikal krai

Quartz-tourmaline lenses, around which host granite is impregnated by uraninite, have been found among porphyritic granite with large phenocrysts of the Urtui pluton in the Ttansbaikal krai framing the Strel’tsovka volcano-tectonic structure. Two generations of tourmaline are distinguished. Most individual crystals belong to the first generation attributed to “fluor-schorl”; tourmaline-II attributed to schorl occurs as thin rims overgrowing tourmaline-I. The major type of cation isomorphic substitution in both tourmalines is Fe²⁺ → Mg. The Fe³⁺/Fe_tot value and Li content in the average sample are 2% and 80 ppm, respectively. The high F content, comparatively high Li, low Fe³⁺/Fe_tot value, and character of cation isomorphic substitution indicate that the tourmaline relates to greisens. The combination of these features allows one to distinguish greisen-type tourmaline-bearing rocks. The impregnated uranium mineralization in granite of the Urtui pluton, one of the probable sources of uranium in economic U ore of the Strel’tsovka deposit, is suggested to be caused by greisenization and the formation of quartz-tourmaline lenses.     

Geology, Geochemistry and Genesis of the Hongshijing Gold Deposit in Ruoqiang,Xinjiang

1IntroductionTheHongshijinggolddepositislocatedinthenorthofLuobupouLakeofRuoqiang ,about 30 0kmsouthwestofHamiCity ,Xinjiang .ItwasdiscoveredbytheSixthGeologicalTeamofXinjiangduringgeo chemicalexploration .TheHongshijinggolddeposit,whichoccursinthegold bearingformationcomposedofMiddleandLateCarboniferousvolcanicandpyroclasticrocks ,isabrittle ductileshearzonetypegolddepositcontrolledbyariftbelt.TheHongshijinggolddepositislocatedinthesouthwestoftheHongshi jing -Maotoushanmineralizationb…     

Geochemistry and Sm–Nd geochronology of the metasomatised mafic rocks in the Khetri complex,Rajasthan, NW India: Evidence of an Early Cryogenian metasomatic event in the northern Aravalli orogen

The mafic magmatic rocks associated with 1720–1700 Ma albitised A-type granites in the northern segment of the Aravalli orogen, NW India show evidence of metasomatism. It is, however, not clear whether the metasomatism of mafic rocks is related to the cooling of these associated granites or whether it took place much later after the emplacement of the granites on a regional scale. For this, we have investigated the mafic magmatic rocks, which occur in close association with these granites. In the Biharipur intrusive, the mafic rocks are intensely commingled with the A-type granites, whereas in the vicinity of the Dosi intrusive, the mafic rocks (clinopyroxenite) do not show any evidence of granite mingling. The commingled and metasomatised Biharipur mafics occur in contact with the albitised granites instead of original granite, indicating that the mafics were metasomatised along with the granites. This is supported by the similarity in REE and spider patterns of the intermixed mafic rocks and the albite granites. On the other hand, the Dosi mafic rocks, free from granite commingling, are scapolitised where the original diopside has been partly transformed to chlorine-rich marialites with a meionite component ranging from Me14.0 to Me16.0. The scapolite, occurring as anastomosing veins, within these rocks is also of similar composition, and the undeformed nature of these veins suggests that the scapolitisation postdates regional metamorphism in the region. Mineralogical, geochemical and Nd isotopic characteristics of the mafic rocks indicate that originally, these were clinopyroxenites, which have been altered to a monomineralic actinolite-bearing rock. The immobile incompatible trace element ratios indicate a continental tholeiite affinity for the mafics, which is in consonance with the A-type nature of the associated granites. During this metasomatic event, the mafic magmatic rocks experienced albitisation and scapolitisation, although the dominance of these processes varied on a local scale depending on the fluid composition.A whole-rock-mineral (clinopyroxene and scapolite) Sm–Nd isochron of the scapolitised clinopyroxenite at Dosi yields an age of 831 ± 15 Ma. Synthesis of this age data along with previously published geochronological data indicate an important Early Cryogenian (850–830 Ma) metasomatic event in the northern Aravalli orogen, which is also synchronous with the Erinpura granite event in the southern Aravalli orogen.     

The Xiaojiao high-grade eclogite-type rutile deposit in Jiangsu, China： Geology, geochemistry and metallogenesis

1INTRODUCTION TITANIUMMETALISPRODUCEDMAINLYFROMNATURAL RUTILEANDSYNTHETICRUTILEOBTAINEDBYENRICHEDILMEN ITE,ANDISWIDELYUSEDASHIGHTECHALLOYS,ESPECIALLY INTHEAIRANDSPACECRAFTINDUSTRYBECAUSEOFITSHIGH STRENGTHATHIGHTEMPERATUREANDRESISTANCETOCORRO SION.THEREISA…