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Sample records for andradite

  1. Thermodynamic properties of andradite and application to skarn with coexisting andradite and hedenbergite

    Science.gov (United States)

    Zhang, Zheru; Saxena, S. K.

    1991-04-01

    The enthalpy of formation of andradite (Ca3Fe2Si3O12) has been estimated as-5,769.700 (±5) kJ/mol from a consideration of the calorimetric data on entropy (316.4 J/mol K) and of the experimental phaseequilibrium data on the reactions: 1 410_2004_Article_BF00310711_TeX2GIFE1.gif begin{gathered} 9/2 CaFeSi_2 O_6 + O_2 = 3/2 Ca_3 Fe_2 Si_3 O_{12} + 1/2 Fe_3 O_4 + 9/2 SiO_2 (a) \\ Hedenbergite andradite magnetite quartz \\ 1 410_2004_Article_BF00310711_TeX2GIFE2.gif begin{gathered} 4 CaFeSi_2 O_6 + 2 CaSiO_3 + O_2 = 2 Ca_3 Fe_2 Si_3 O_{12} + 4 SiO_2 (b) \\ Hedenbergite wollastonite andradite quartz \\ 1 410_2004_Article_BF00310711_TeX2GIFE3.gif begin{gathered} 18 CaSiO_3 + 4 Fe_3 O_4 + O_2 = 6Ca_3 Fe_2 Si_3 O_{12} (c) \\ Wollastonite magnetite andradite \\ 1 410_2004_Article_BF00310711_TeX2GIFE4.gif begin{gathered} Ca_3 Fe_2 Si_3 O_{12} = 3 CaSiO_3 + Fe_2 O_3 . (d) \\ Andradite pseudowollastonite hematite \\ and 410_2004_Article_BF00310711_TeX2GIFE5.gif log f_{O_2 } = E + A + B/T + D(P - 1)/T + C log f_{O_2 } . Oxygen-barometric scales are presented as follows: 410_2004_Article_BF00310711_TeX2GIFE6.gif begin{gathered} E = 12.51; D = 0.078; \\ A = 3 log X_{Ad} - 4.5 log X_{Hd} ; C = 0; \\ B = - 27,576 - 1,007(1 - X_{Ad} )^2 - 1,476(1 - X_{Hd} )^2 . \\ For the assemblage andradite (Ad)-hedenbergite (Hd)-magnetite-quartz: 410_2004_Article_BF00310711_TeX2GIFE7.gif begin{gathered} E = 13.98; D = 0.0081; \\ A = 4 log(X_{Ad} / X_{Hd} ); C = 0; \\ B = - 29,161 - 1,342.8(1 - X_{Ad} )^2 - 1,312(1 - X_{Hd} )^2 . \\ For the assemblage andradite-hedenbergite-wollastonite-quartz: 1 410_2004_Article_BF00310711_TeX2GIFE8.gif begin{gathered} E = 13.98;{text{ }}D = 0.0081; \\ A = 4log (X_{Ad} /X_{Hd} );{text{ C = 0;}} \\ B = - 29,161 - 1,342.8(1 - X_{Ad} )^2 - 1,312(1 - X_{Hd} )^2 . \\ For the assemblage andradite-hedenbergite-calcitequartz: 1 410_2004_Article_BF00310711_TeX2GIFE9.gif begin{gathered} E = - 1.69;{text{ }}D = - 0.199; \\ A = 4log (X_{Ad} /X_{Hd} );{text{ C = 2;}} \\ B

  2. Heat capacity and thermodynamic properties of andradite garnet, Ca3Fe2Si3O12, between 10 and 1000 K and revised values for ΔfGom (298.15 K) of hedenbergite and wollastonite

    Science.gov (United States)

    Robie, Richard A.; Bin, Zhao; Hemingway, Bruce S.; Barton, Mark D.

    1987-01-01

    The heat capacity of synthetic andradite garnet (Ca3Fe2Si3O12) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 KCop,m and Som are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively.

  3. 钙铁辉石、透辉石和钙铁榴石变化的实验研究

    Institute of Scientific and Technical Information of China (English)

    赵斌; 曹荣龙

    1975-01-01

    Alteration of hedenbergite,diopsite(both natural and synthetie),and andradite bas been experimentally studied at 300-800℃ and 200-2,000 atm.The alteration in various degree has been noted for all these minerals in solutions over a wide range of pH values.It has been shown that,hedenbergite is the most unstable,while andradite the most stable,A preliminary disenssion is given in the light of experimental resalts and pertinent geological environments.

  4. Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates

    International Nuclear Information System (INIS)

    The focus of this thesis is the study of the electronic and magnetic structure of three representatives of the main Fe-bearing rock-forming silicates: Fe2+2Si2O6, almandine Fe2+3Al2(SiO4)3 and andradite Ca3Fe3+2(SiO4)3. For this purpose the quantum mechanical first principles electronic structure calculations are performed by the most efficient DFT method in the local spin-density approximation for calculating spectroscopic data: the spin-polarized self consistent charge X[alpha] method. These minerals have attracted significant attention due to their abundance in the Earth's crust and mantle, and because crystallised silicates are main components of cosmic dust which is the most abundant raw material in the Universe. The specific feature and strength of these investigations consist in the theoretical characterization of these complex systems based on experimental results. This means that, on one hand, experimental spectroscopic and crystallographic data are being used to judge the reliability of the calculations, whereas, on the other hand, experimental data are interpreted and explained by the theoretical results. This work is divided into seven main parts. Chapter 1 is the introduction to the thesis. Chapter 2 describes the theoretical bases, ideas, approximations and advantages of the SCC- X[alpha] method and basics of the art of cluster construction. Chapter 3 considers physical bases of absorption and Moessbauer spectroscopy, crystal field theory, evaluation of the main spectroscopic values within the frames of the SCC- X[alpha] method and magnetic interaction between atoms. In addition, tetragonally, trigonally and angularly distorted octahedral sites with various degrees of the distortions are calculated and analyzed. The electronic and magnetic structures of orthoferrosilite, almandine and andradite are described in Chapters 4, 5 and 6, respectively. In the case of orthoferrosilite the magnetic interactions between the iron spins within the ribbons and

  5. Petrogenesis of skarn related Cu-porphyry intrusion deposit, Ali-Abad- Darreh Zereshk, Yazd

    Directory of Open Access Journals (Sweden)

    Batoul Taghipour

    2011-04-01

    Full Text Available The study area is a part of Cenozoic magmatic belt of Central Iran, which is located in the West of Yazd porovince. Contact metamorphism and skarn occurred in conglomerate part of Sngestan Formation. The Oligocene intrusion bodies of Ali-Abad-Darreh Zereshk are leucocerate and have the chemical composition of granite to granodiorite with calc-alkaline affinity from volcanic arc geological setting. The main mineral assemblage of skarn in order of imprtance is as follow: Garnet + epidote + quartz + calcite + pyrite + iron oxides. Brown garnets are the skarn characteristic mineral. EPMA analysis has shown that the chemical composition with garnet belong to andradite-grossular solid-solution (And 65, Gross 30 with more andradite component. The high permeability and presence of carbonate pebbles in conglomerate are two important factors for fluid flow and genesis of garnets. Distinct oscillatory zoning in garnets is resulted from the change of fO2 in fluids. The evolution of Ali-Abad skarn is took place in the range of 380 to 530 ºC, 0.5 Kbar pressure and high fO2. Also close association of this skarn with Ali-Abad intrusive with Cu-porphyry mineralization shows that this skarn is a Cu-porphyry type skarn.

  6. Origin of Ti-rich garnets in the groundmass of Wajrakarur field kimberlites, southern India: insights from EPMA and Raman spectroscopy

    Science.gov (United States)

    Dongre, Ashish N.; Viljoen, K. S.; Rao, N. V. Chalapathi; Gucsik, A.

    2016-04-01

    Although Ti-rich garnets are commonly encountered in the groundmass of many alkaline igneous rocks, they are comparatively rare in kimberlites. Here we report on the occurrence of Ti-rich garnets in the groundmass of the P-15 and KL-3 kimberlites from the diamondiferous Wajrakarur field in the Eastern Dharwar craton of southern India. These garnets contain considerable Ti (11.7-23.9 wt.% TiO2), Ca (31.3-35.8 wt.% CaO), Fe (6.8-15.5 wt.% FeOT) and Cr (0.04-9.7 wt.% Cr2O3), but have low Al (0.2-5.7 wt.% Al2O3). In the case of the P-15 kimberlite they display a range in compositions from andradite to schorlomite, with a low proportion of grossular (andradite(17.7-49.9)schorlomite(34.6-49.5)-grossular(3.7-22.8)-pyrope(1.9-10.4)). A few grains also contain significant chromium and represent a solid solution between schorlomite and uvarovite. The Ti-rich garnets in the KL-3 kimberlite, in contrast, are mostly schorlomitic (54.9-90.9 mol %) in composition. The Ti-rich garnets in the groundmass of these two kimberlites are intimately associated with chromian spinels, perhaps suggesting that the garnet formed through the replacement of spinel. From the textural evidence, it appears unlikely that the garnets could have originated through secondary alteration, but rather seem to have formed through a process in which early magmatic spinels have reacted with late circulating, residual fluids in the final stages of crystallization of the kimberlite magma. Raman spectroscopy provides evidence for low crystallinity in the spinels which is likely to be a result of their partial transformation into andradite during their reaction with a late-stage magmatic (kimberlitic) fluid. The close chemical association of these Ti-rich garnets in TiO2-FeO-CaO space with those reported from ultramafic lamprophyres (UML) is also consistent with results predicted by experimental studies, and possibly implies a genetic link between kimberlite and UML magmas. The occurrence of Ti-rich garnets of

  7. Kimberlite, lamproite, ultramafic lamprophyre, and carbonatite relationships on the Dharwar Craton, India; an example from the Khaderpet pipe, a diamondiferous ultramafic with associated carbonatite intrusion

    Science.gov (United States)

    Smith, C. B.; Haggerty, S. E.; Chatterjee, B.; Beard, A.; Townend, R.

    2013-12-01

    Are kimberlites, lamproites, ultramafic lamprophyres and carbonatites genetically associated or not? There are strong opinions for and against any relationship. The 20 Ha Khaderpet pipe, discovered by Rio Tinto Exploration, is an unusual diamondiferous carbonatite-kimberlite clan rock (KCR) association in the Anumpalle Cluster of the Wajrakarur Kimberlite Field in the Dharwar Craton of Peninsular Indian. The Khaderpet pipe has a discrete sovite phase intrusive into KCR breccia, not noticed elsewhere in the Wajrakarur kimberlite field. Petrographically, the KCR is a clast-supported lithic breccia and crystal lithic tuff, with occasional pelletal lapilli. Clasts show a weak horizontal imbrication. The overall appearance of the tuffs and breccias is suggestive of terminal-blocked, vent accumulations that formed by under pressure, with spallation of country rock causing an abundance of granitoid debris. The sovite phase has up to 95% calcite, occasionally showing flow textured polycrystalline laths set in a minor saponite matrix. There are mineralogical gradations from an olivine-rich ultramafic to a calcite-dominant rock resembling pure carbonatite. Rare REE mineral phases in the carbonatite include allanite and other REE-rich unidentified mineral phases. Xenocrystic high pressure phases in both ultramafic and carbonatite include mantle-derived diamonds, lherzolitic-, eclogitic- and subcalcic-pyrope, Ti-poor andradite, chrome diopside, picrochromite and picroilmenite. Extensive metasomatism in the form of reddening of country rock feldspars by hematite, introduction of green chlorite, and saponitic alteration of breccia clasts and the ultramafic phase is common. The chemistry of the Khaderpet ultramafic component, suggests that the KCR is transitional between kimberlite and ultramafic lamprophyres, like certain other pipes in the Wajrakarur Kimberlite Field, with strong enrichment in LREE, CaO and CO2. However, low MgO (~ 13%) and high CaO (~ 10%) values are more

  8. Geological, geochronological, and mineralogical constraints on the genesis of the Chengchao skarn Fe deposit, Edong ore district, Middle-Lower Yangtze River Valley metallogenic belt, eastern China

    Science.gov (United States)

    Yao, Lei; Xie, Guiqing; Mao, Jingwen; Lü, Zhicheng; Zhao, Caisheng; Zheng, Xianwei; Ding, Ning

    2015-04-01

    The Edong ore district is located within the westernmost Middle-Lower Yangtze River Valley metallogenic belt (MLYRB), and hosts the largest concentration of skarn Fe deposits in China, although the origin of these deposits remains controversial. The Chengchao deposit is the largest skarn Fe deposit so far discovered within the MLYRB, and provides a good opportunity to address the debate surrounding the origin of these skarn Fe deposits. Here, we present geological, geochronological, and mineralogical data from the Chengchao skarn deposit and associated intrusions, and discuss the relationships between granitoids and mineralization in the Chengchao deposit. The NW-SE-striking orebodies in the study area have porphyritic quartz monzonite and/or granite footwalls, and Triassic marble or diorite hangingwalls, indicating a spatial relationship between these intrusions and Fe mineralization. Zircon U-Pb data from the granite, porphyritic quartz monzonite, diorite, and porphyritic diabase dike within the deposit show ages of 129 ± 1, 128 ± 1, 140 ± 1, and 126 ± 1 Ma, respectively. These ages and the previously reported ages on the timing of mineralization suggest that the porphyritic quartz monzonite and granite are coeval with the formation of the skarn Fe deposit. Our data confirm that the granitic rocks are temporally associated with Fe mineralization. The prograde substage of skarn development is characterized by two stages of andradite (Adr98-38Grs61-2Prp2-0Sps1-0Alm1-0) and diopside (Di95-61Hd37-5Jo3-0), including an early stage of garnet and pyroxene formation that is genetically associated with the mineralization. The early stage garnets are more andradite-rich (Adr98-50Grs49-2Prp1-0Sps1-0Alm0) than the late veinlet garnets characterized by intermediate grandite compositions (Adr67-37Grs61-31Prp2-0Sps1-0Alm1-0). The early stage pyroxenes (Di95-74Hd26-5Jo1-0) are compositionally distinct from the late stage pyroxenes (Di84-61Hd37-16Jo3-0). Compositional

  9. Genetic relationships between skarn ore deposits and magmatic activity in the Ahar region, Western Alborz, NW Iran

    Directory of Open Access Journals (Sweden)

    Mollai Habib

    2014-06-01

    Full Text Available Paleocene to Oligocene tectonic processes in northwest Iran resulted in extensive I-type calc-alkaline and alkaline magmatic activity in the Ahar region. Numerous skarn deposits formed in the contact between Upper Cretaceous impure carbonate rocks and Oligocene-Miocene plutonic rocks. This study presents new field observations of skarns in the western Alborz range and is based on geochemistry of igneous rocks, mineralogy of the important skarn deposits, and electron microprobe analyses of skarn minerals. These data are used to interpret the metasomatism during sequential skarn formation and the geotectonic setting of the skarn ore deposit related igneous rocks. The skarns were classified into exoskarn, endoskarn and ore skarn. Andraditic garnet is the main skarn mineral; the pyroxene belongs to the diopside-hedenbergite series. The skarnification started with pluton emplacement and metamorphism of carbonate rocks followed by prograde metasomatism and the formation of anhydrous minerals like garnet and pyroxene. The next stage resulted in retro gradation of anhydrous minerals along with the formation of oxide minerals (magnetite and hematite followed by the formation of hydrosilicate minerals like epidote, actinolite, chlorite, quartz, sericite and sulfide mineralization. In addition to Fe, Si and Mg, substantial amounts of Cu, along with volatile components such as H2S and CO2 were added to the skarn system. Skarn mineralogy and geochemistry of the igneous rocks indicate an island arc or subduction-related origin of the Fe-Cu skarn deposit.

  10. Hibonite, Ca2/Al, Ti/24O38, from the Leoville and Allende chondritic meteorites.

    Science.gov (United States)

    Keil, K.; Fuchs, L. H.

    1971-01-01

    Hibonite was discovered in light-colored, Ca-Al-Ti-rich and Si-Fe-poor, achondritic inclusions of the Leoville and Allende HL-group chondrites. Two varieties of hibonite occur: one emits a bright red-orange luminescence under electron bombardment and has high amounts of Al2O3 (87.7; 87.9) and low amounts of MgO (0.65; 0.8) and TiO2 (0.68; 0.8). The other emits a bright blue luminescence and is low in Al2O3 (78.7; 79.2) and high in MgO (3.3; 3.7) and TiO2 (6.5; 7.9) (in wt. %). The oxide CaO is about the same in both varieties. It is suggested that the change in the color of the visible luminescence results from changes in composition. The origin of hibonite which occurs in complex mineral assemblages together with anorthite, gelhenite, wollastonite, aluminous diopside, andradite, Ca-pyroxene, perovskite, spinel, taenite, chromite, and pentlandite, and in close proximity to nodules containing calcite, whewellite, forsterite and many of the aforementioned phases, is discussed. The proposition that hibonite and associated phases originated by contact metamorphism and metasomatism of calcite-dolomite bearing assemblages cannot, at this time, be completely ruled out.

  11. Timescales and settings for alteration of chondritic meteorites

    Energy Technology Data Exchange (ETDEWEB)

    Krot, A N; Hutcheon, I D; Brearley, A J; Pravdivtseva, O V; Petaev, M I; Hohenberg, C M

    2005-11-16

    Most groups of chondritic meteorites experienced diverse styles of secondary alteration to various degrees that resulted in formation of hydrous and anhydrous minerals (e.g., phyllosilicates, magnetite, carbonates, ferrous olivine, hedenbergite, wollastonite, grossular, andradite, nepheline, sodalite, Fe,Ni-carbides, pentlandite, pyrrhotite, Ni-rich metal). Mineralogical, petrographic, and isotopic observations suggest that the alteration occurred in the presence of aqueous solutions under variable conditions (temperature, water/rock ratio, redox conditions, and fluid compositions) in an asteroidal setting, and, in many cases, was multistage. Although some alteration predated agglomeration of the final chondrite asteroidal bodies (i.e. was pre-accretionary), it seems highly unlikely that the alteration occurred in the solar nebula, nor in planetesimals of earlier generations. Short-lived isotope chronologies ({sup 26}Al-{sup 26}Mg, {sup 53}Mn-{sup 53}Cr, {sup 129}I-{sup 129}Xe) of the secondary minerals indicate that the alteration started within 1-2 Ma after formation of the Ca,Al-rich inclusions and lasted up to 15 Ma. These observations suggest that chondrite parent bodies must have accreted within the first 1-2 Ma after collapse of the protosolar molecular cloud and provide strong evidence for an early onset of aqueous activity on these bodies.

  12. Mineralogical and geochemical characterization of a rare ultramafic lamprophyre in the Tandilia belt basement, Río de la Plata Craton, Argentina

    Science.gov (United States)

    Dristas, Jorge A.; Martínez, Juan Cruz; Massonne, Hans-Joachim; Pimentel, Marcio M.

    2013-04-01

    A metre-thick ultramafic lamprophyre dyke intrudes the basement of the Tandilia belt at the Sierra Alta de Vela, Argentina. A petrological and geochemical study of this rock and associated small dykes indicates a predominantly calc-alkaline trend. Phlogopite K-Ar dating of the ultramafic lamprophyre gave a minimum age of 1928 ± 54 Ma as a late event of the Transamazonian Orogeny, which is well represented in the basement of the Tandilia belt. An electron microprobe study indicates the presence of phlogopite, albite, chromite and Cr-rich phenocrysts and Cr-free microphenocrysts of diopside as primary minerals. Subsequent to deformation at the contacts with the wall rock, metasomatism generated strongly zoned amphibole (edenite, pargasite, Mg-hastingite and tremolite compositions) and andradite as well as chlorite, sericite, albite, apatite and calcite. The central zone of the lamprophyre is almost undeformed and exhibits some ocellar texture. Geochemical and isotopic signatures of the lamprophyre suggest that its magma source may have previously undergone incompatible element enrichment of the mantle source, representing the original precursor magma for the calc-alkaline dyke series of the Sierra Alta de Vela.

  13. Properties of ceramics prepared using dry discharged waste to energy bottom ash dust.

    Science.gov (United States)

    Bourtsalas, Athanasios; Vandeperre, Luc; Grimes, Sue; Themelis, Nicolas; Koralewska, Ralf; Cheeseman, Chris

    2015-09-01

    The fine dust of incinerator bottom ash generated from dry discharge systems can be transformed into an inert material suitable for the production of hard, dense ceramics. Processing involves the addition of glass, ball milling and calcining to remove volatile components from the incinerator bottom ash. This transforms the major crystalline phases present in fine incinerator bottom ash dust from quartz (SiO(2)), calcite (CaCO(3)), gehlenite (Ca(2)Al(2)SiO(7)) and hematite (Fe(2)O(3)), to the pyroxene group minerals diopside (CaMgSi(2)O(6)), clinoenstatite (MgSi(2)O(6)), wollastonite (CaSiO(3)) together with some albite (NaAlSi(3)O(8)) and andradite (Ca(3)Fe(2)Si(3)O(12)). Processed powders show minimal leaching and can be pressed and sintered to form dense (>2.5 g cm(-3)), hard ceramics that exhibit low firing shrinkage (ceramic tiles that have potential for use in a range of industrial applications.

  14. Production of pyroxene ceramics from the fine fraction of incinerator bottom ash.

    Science.gov (United States)

    Bourtsalas, A; Vandeperre, L J; Grimes, S M; Themelis, N; Cheeseman, C R

    2015-11-01

    Incinerator bottom ash (IBA) is normally processed to extract metals and the coarse mineral fraction is used as secondary aggregate. This leaves significant quantities of fine material, typically less than 4mm, that is problematic as reuse options are limited. This work demonstrates that fine IBA can be mixed with glass and transformed by milling, calcining, pressing and sintering into high density ceramics. The addition of glass aids liquid phase sintering, milling increases sintering reactivity and calcining reduces volatile loss during firing. Calcining also changes the crystalline phases present from quartz (SiO2), calcite (CaCO3), gehlenite (Ca2Al2SiO7) and hematite (Fe2O3) to diopside (CaMgSi2O6), clinoenstatite (MgSiO3) and andradite (Ca3Fe2Si3O12). Calcined powders fired at 1080°C have high green density, low shrinkage (ceramics that have negligible water absorption. The transformation of the problematic fraction of IBA into a raw material suitable for the manufacture of ceramic tiles for use in urban paving and other applications is demonstrated.

  15. Mineral Chemistry of Melanite from Calcitic Ijolite, the Oka Carbonatite Complex, Canada:Implications for Multi-Pulse Magma Mixing

    Institute of Scientific and Technical Information of China (English)

    Wei Chen; Weiqi Zhang; Antonio Simonetti; Shaoyong Jiang

    2016-01-01

    Ti-rich garnet is found within calcitic ijolite from the Oka carbonatite complex in Can-ada, which is characterized by 58%–73% andradite component (2.12 wt.%–4.18 wt.% TiO2) and classi-fied as melanite. The garnet displays complex zoning and contains abundant high field strength ele-ments (HFSEs) and rare earth elements (REEs). Three groups (I, II, III) have been identified based on their petrographic nature. Compared to groups II and III, Group I garnet cores contain higher TiO2, MgO, HFSE, and REE and lower SiO2 abundances. The distinct chemical and petrographic signatures of the investigated garnets cannot be attributed to simple closed system crystallization, but they are consistent with the multi-pulse magma mixing. Combined with previously reported U-Pb ages for apa-tite from the calcitic ijolite, at least three stages of magma evolution and subsequent mixing have been involved in the generation of calcitic ijolite at Oka. The early-formed melt that generated Group I gar-net core was later mixed with at least two small-volume, more evolved melts. The intermediate stage melt formed the remaining garnet along with some pyroxene, calcite, nepheline, and apatite at 127±3.6 Ma. The youngest, most evolved melt generated the majority of pyroxene, calcite, nepheline, and apatite within the calcitic ijolite at 115±3.1 Ma.

  16. Metamorphism, metasomatism and mineralization at Lagoa Real, Bahia, Brazil

    International Nuclear Information System (INIS)

    Uranium deposits cumulatively in the 100,000 tonne U3 O8 range occur within ductile shear zones transecting Archean basement gneisses of the Sao Francisco Craton, at the Lagoa Real region of south-central Bahia, Brasil. The gneisses, dated at 2.6-3.0Ga, are at amphibolite and granulite facies and overlie to the west, the Proterozoic Espinhaco metasedimentary sequence along a thrust fault. Petrography and mineral chemistry show that in the zones of alteration/mineralization, the original K-feldspar + quartz + albite/oligoclase + hastingsite assemblage, is replaced by albite + aegirine - angite + andradite + hematite assemblages, with or without uraninite. This information along with oxygen isotope, whole rock geochemistry and fluid inclusion studies indicate that the alteration process involves removal of Si, K, Rb, Ba and addition of Na under oxidizing conditions. V, Pb and Sr were introduced along with U via interaction with saline SO2 - rich, isotopically light fluids under varying water/rock ratios and at temperatures of 500 - 5500C. 87Sr/86Sr systematics suggest that it is unlikely that Sr, and by extension uranium, were introduced by fluids originating from the basement gneisses. Geological constraints and the general alteration pattern are consistent with the release of the mineralizing fluids in response to the overloading of the basement rocks onto the Sedimentary Espinhaco via a thrust mechanism. (Author)

  17. Raman Spectroscopy of Garnet—group Minerals

    Institute of Scientific and Technical Information of China (English)

    彭明生; H.K.MAO; 等

    1994-01-01

    The Raman spectra of the natural end members of the garnet-group minerals,which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite ,andradite and uvarovite of Ca-Fe garnet series, have been strdied.Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the internal modes, translational and rotatory modes of SiO4 tetrahedra, as well as the translational motion of bivalent cations in the X site.The stretch and rotatory A1g modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series ,owing to the cations residing in the Xsite connected with SiO4 tetrahedra by sharing the two edges.The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series andin the Y site for the Ca-Fe garnet series.

  18. Uraniferous albitites from the Lagoa Real Uranium Province, state of Bahia, Brazil

    International Nuclear Information System (INIS)

    The Uranium Province of Lagoa Real is located in the region of Caetite, throughout the south-central portion of the state of Bahia. The basic chronostratigraphic units are the metamorphic rocks - granitic rocks and gneisses of the Archean basement - and cataclastic metasomatic rocks - albitites and quartzo-feldspathic lithologies of the lower Proterozoic. The albitites, host rocks for the uranium mineralization, occur regionally as numerous lenticular and discontinuos bodies arranged submeridionally according to two main alignments forming an arc, and are therefore called linear albities in allusion to similar features in Kasachstan, Russia, where they were first given this designation. The name albitite was employed to designate the metasomatites in which albitite dominates over the other minerals. The uranium mineralization consists of uraninite and pitchblende and is confined to the ore zones of those albitites containing aegirine, alkali-amphiboles, andradite, biotite and carbonates Furthermore, it displays lithologic-structural control, the morphology being controlled by the location of shear zones. This mineralization usually takes the shape of ore shoots which pitch in the direction and dip of the lineation. The authors describe the various types of albitites (mineralized or unmineralized) and their structural and petrographic characteristics, mode of occurence, geometry, metasomatic alterations, chemistry, uranium mineralization, as well as their genetic aspects. (Author)

  19. Mineralogical characteristics and geologi-cal significance of the Zhuxi Cu-W polymetallic ore deposit, Jiangxi Province%江西朱溪铜钨多金属矿床矽卡岩矿物学特征及其地质意义

    Institute of Scientific and Technical Information of China (English)

    赵苗; 潘小菲; 李岩; 陈国华; 张诚; 康川; 魏锦; 张天福; 刘茜

    2015-01-01

    Abstact:The Zhuxi Cu-W polymetallic ore deposit is located in the northwest of Gandongbei faulted zone. The orebodies mainly occur in the skarn and skarnized marble at the contact zone between Yanshan intrusive rock and carbonate. Typical skarn minerals consist mainly of garnet, diopside, tremolite, wollastonite, serpentine, phlogopite, vesuvianite and chlorite. According to the associa⁃tion and metasomatism relationship of the minerals, the authors infer that the ore-forming fluid might have experienced five evolu⁃tionary stages, i.e., skarn stage, degenerate alteration stage, quartz sulfide stage, quartz carbonate stage, and supergene oxide stage. Elec⁃tron microprobe analyses show that the garnet is mainly composed of grossularite-andradite, the pyroxenes mainly belong to diop⁃side-andradite series, the amphiboles show characteristics of calciferous amphibole, and the chlorites are mainly pycnochlorite and clinochlorite. It is also inferred that after the intrusion ore-forming the fluid was under the medium-acid to acid and weak oxidizing conditions at the skarn stage. At the degeneration alteration stage, the scheelite was separated out after the rise of the oxygen fugacity and the pH. The metal sulfides precipitated along with the drop of the oxygen fugacity. The class of the metal mineralization was also inferred according to its mineral compositions.%朱溪铜钨多金属矿床位于赣东北深大断裂北西侧。矿体主要产于燕山期侵入岩与碳酸盐岩接触带的矽卡岩或矽卡岩化大理岩中,代表性矽卡岩矿物有石榴子石、透辉石、透闪石、硅灰石、蛇纹石、金云母、符山石、绿泥石等。根据矿物共生组合及交代关系推断流体经历了5个阶段,分别为矽卡岩阶段、退化蚀变阶段、石英硫化物阶段、石英碳酸盐阶段和表生氧化阶段。特征矿物的电子探针分析结果表明,石榴子石主要为钙铝榴石—钙铁榴石;辉石以透辉石—

  20. Radiometric, SEM and XRD investigation of black sands at Chituc placer deposit North of the City of Navodari, Romania

    Science.gov (United States)

    Duliu, Octavian G.; Blebea-Apostu, Ana-Maria; Gomoiu, Claudia; Margineanu, Romul M.; Costea, Constantin; Dumitras, Delia; Ion, Adriana

    2014-05-01

    The black sand of the Chituc marine sandbank situated northern of the city of Navodari (Romania), displayed anomalous high ambient dose rates. Field measurements performed during 2013 Summer campaign recorded in some places dose rate up to 200 nSv/h, significantly overpassing the average value of 44 ± 20 nSv/h recorded along the entire Southern sector of Romanian Black Sea shore. Here, the sand presented a black-brownish hue, different by the usual white yellowish colour. Gamma ray spectrometry performed on both Slanic-Prahove Underground Low Background Laboratory and Gological Institute Radiometric Facilities showed with clarity the dominance of 228-Ac radioisotope in the 50 microns fraction together with the 226-Ra and traces of 40-K. No significant amount of anthropogenic 137-Cs were identified. The other granulometric fractions, i.e. 315, 200 as well 100 microns presented a significant lower level of radioactivity. X-ray diffraction (XRD) as well as Scanning Electron Microsopy (SEM) data attested the presence of monazite, zircon, magnetite, ilmenite, andradite, quartz, aragonite and albite in different proportions, the monazite and zircon being preponderant in the 50 microns, the most radioactive fraction. Based on both radiometric and XRD determinations we come to the conclusion that the evidenced radioactivity could be attributed to both uranium and thorium series in the zircon and monazite fractions and to a lesser extent in the garnet fraction. By its position with respect to Danube Delta, the Chituc marine sandbank could be regarded as a placer where heavy minerals discharged in the Black Sea by the Danube River and transported southward by the Great Black Sea Rim are deposited by gravity separation during sedimentary processes. The implications of the Chituc levee radioactive anomaly for any further human activity are analysed and discussed. Acknowledgement: Work done within the BS ERA NET 041 project in the frame of BS-ERA.NET Pilot Joint CAll 2010-2011.

  1. Ca-Fe and Alkali-Halide Alteration of an Allende Type B CAI: Aqueous Alteration in Nebular or Asteroidal Settings

    Science.gov (United States)

    Ross, D. K.; Simon, J. I.; Simon, S. B.; Grossman, L.

    2012-01-01

    Ca-Fe and alkali-halide alteration of CAIs is often attributed to aqueous alteration by fluids circulating on asteroidal parent bodies after the various chondritic components have been assembled, although debate continues about the roles of asteroidal vs. nebular modification processes [1-7]. Here we report de-tailed observations of alteration products in a large Type B2 CAI, TS4 from Allende, one of the oxidized subgroup of CV3s, and propose a speculative model for aqueous alteration of CAIs in a nebular setting. Ca-Fe alteration in this CAI consists predominantly of end-member hedenbergite, end-member andradite, and compositionally variable, magnesian high-Ca pyroxene. These phases are strongly concentrated in an unusual "nodule" enclosed within the interior of the CAI (Fig. 1). The Ca, Fe-rich nodule superficially resembles a clast that pre-dated and was engulfed by the CAI, but closer inspection shows that relic spinel grains are enclosed in the nodule, and corroded CAI primary phases interfinger with the Fe-rich phases at the nodule s margins. This CAI also contains abundant sodalite and nepheline (alkali-halide) alteration that occurs around the rims of the CAI, but also penetrates more deeply into the CAI. The two types of alteration (Ca-Fe and alkali-halide) are adjacent, and very fine-grained Fe-rich phases are associated with sodalite-rich regions. Both types of alteration appear to be replacive; if that is true, it would require substantial introduction of Fe, and transport of elements (Ti, Al and Mg) out of the nodule, and introduction of Na and Cl into alkali-halide rich zones. Parts of the CAI have been extensively metasomatized.

  2. Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

    Science.gov (United States)

    Baudouin, Céline; Parat, Fleurice; Denis, Carole M. M.; Mangasini, Fredrik

    2016-07-01

    North Tanzanian Divergence is the first stage of continental break-up of East African Rift (alkaline lavas with zoned clinopyroxene, nepheline, andradite-schorlomite, titanite, apatite, and pyrrhotite. Lavas are low MgO-nephelinite with low Mg# and high silica content (Mg# = 22.4-35.2, SiO2 = 44.2-46.7 wt%, respectively), high incompatible element concentrations (e.g. REE, Ba, Sr) and display Nb-Ta fractionation (Nb/Ta = 36-61). Major elements of whole rock are consistent with magmatic differentiation by fractional crystallization from a parental melt with melilititic composition. Although fractional crystallization occurred at 9-12 km and can be considered as an important process leading to nephelinite magma, the complex zonation of cpx (e.g. abrupt change of Mg#, Nb/Ta, and H2O) and trace element patterns of nephelinites recorded magmatic differentiation involving open system with carbonate-silicate immiscibility and primary melilititic melt replenishment. The low water content of clinopyroxene (3-25 ppm wt. H2O) indicates that at least 0.3 wt% H2O was present at depth during carbonate-rich nephelinite crystallization at 340-640 MPa and 1050-1100 °C. Mg-poor nephelinites from Hanang represent an early stage of the evolution path towards carbonatitic magmatism as observed in Oldoinyo Lengai. Paragenesis and geochemistry of Hanang nephelinites require the presence of CO2-rich melilititic liquid in the southern part of North Tanzanian Divergence and carbonate-rich melt percolations after deep partial melting of CO2-rich oxidized mantle source.

  3. Geology and Characteristics of Pb-Zn-Cu-Ag Skarn Deposit at Ruwai, Lamandau Regency, Central Kalimantan

    Directory of Open Access Journals (Sweden)

    Arifudin Idrus

    2014-06-01

    Full Text Available DOI: 10.17014/ijog.v6i4.126This study is dealing with geology and characteristics of mineralogy, geochemistry, and physicochemical conditions of hydrothermal fluid responsible for the formation of skarn Pb-Zn-Cu-Ag deposit at Ruwai, Lamandau Regency, Central Kalimantan. The formation of Ruwai skarn is genetically associated with calcareous rocks consisting of limestone and siltstone (derived from marl? controlled by NNE-SSW-trending strike slip faults. It is localized along N 70° E-trending thrust fault, which also acts as the contact zone between sedimentary and volcanic rocks in the area. The Ruwai skarn is mineralogically characterized by prograde alteration comprising garnet (andradite and clino-pyroxene (wollastonite, and retrograde alteration composed of epidote, chlorite, calcite, and sericite. Ore mineralization is typified by sphalerite, galena, and chalcopyrite, formed at early retrograde stage. Galena is typically enriched in silver up to 0.45 wt % and bismuth of about 1 wt %. No Ag-sulphides are identified within the ore body. Geochemically, SiO is enriched and CaO is depleted in limestone, consistent with silicic alteration (quartz and calc-silicate and decarbonatization of the wallrock. The measured resources of the deposit are 2,297,185 tonnes at average grades of 14.98 % Zn, 6.44% Pb, 2.49 % Cu, and 370.87 g/t Ag. Ruwai skarn orebody was originated at moderate temperatures of 250 - 266 °C and low salinity of 0.3 - 0.5 wt.% NaCl eq. The late retrograde stage was formed at low temperature of 190 - 220 °C and low salinity of ~0.35 wt.% NaCl eq., which was influenced by meteoric water incursion at the late stage of the Ruwai Pb-Zn-Cu-Ag skarn formation.

  4. The origin and evolution of skarn-forming fluids from the Phu Lon deposit, northern Loei Fold Belt, Thailand: Evidence from fluid inclusion and sulfur isotope studies

    Science.gov (United States)

    Kamvong, Teera; Zaw, Khin

    2009-05-01

    The Phu Lon skarn Cu-Au deposit is located in the northern Loei Fold Belt (LFB), Thailand. It is hosted by Devonian volcano-sedimentary sequences intercalated with limestone and marble units, intruded by diorite and quartz monzonite porphyries. Phu Lon is a calcic skarn with both endoskarn and exoskarn facies. In both skarn facies, andradite and diopside comprise the main prograde skarn minerals, whereas epidote, chlorite, tremolite, actinolite and calcite are the principal retrograde skarn minerals. Four types of fluid inclusions in garnet were distinguished: (1) liquid-rich inclusions; (2) daughter mineral-bearing inclusions; (3) salt-saturated inclusions; and (4) vapor-rich inclusions. Epidote contains only one type of fluid inclusion: liquid-rich inclusions. Fluid inclusions associated with garnet (prograde skarn stage) display high homogenization temperatures and moderate salinities (421.6-468.5 °C; 17.4-23.1 wt% NaCl equiv.). By contrast, fluid inclusions associated with epidote (retrograde skarn stage) record lower homogenization temperatures and salinities (350.9-399.8 °C; 0.5-8 wt% NaCl equiv.). These data suggest a possible mixing of saline magmatic fluids with external, dilute fluid sources (e.g., meteoric fluids), as the system cooled. Some fluid inclusions in garnet contain hematite daughters, suggesting an oxidizing magmatic environment. Sulfur isotope determinations on sulfide minerals from both the prograde and retrograde stages show a uniform and narrow range of δ34S values (-2.6 to -1.1 ‰ δ34S), suggesting that the ore-forming fluid contained sulfur of orthomagmatic origin. Overall, the Phu Lon deposit is interpreted as an oxidized Cu-Au skarn based on the mineralogy and fluid inclusion characteristics.

  5. Garnetization as a ground preparation process for copper mineralization: evidence from the Mazraeh skarn deposit, Iran

    Science.gov (United States)

    Karimzadeh Somarin, Alireza

    2010-03-01

    The Mazraeh Cu-Fe skarn deposit, NW Iran is the result of the intrusion of an Oligocene-Miocene granitic pluton into Cretaceous calcareous rocks. The pluton ranges in composition from monzonite to quartz monzonite, monzogranite, tonalite and granodiorite with I-type, calc-alkaline, and weakly peraluminous characteristics. The Mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of ~8 km. Pyroxene skarn, garnet skarn, and epidote skarn zones were formed during the intrusive phase. The garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton, respectively, prior to mineralization. Garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies. Mass balance calculation of garnet skarn in the endoskarn zone indicates that hydrothermal fluids originating from the cooling magma introduced Si, Fe, Mn, Ca, Mg, P, Ag, Cu, Zn, La, Pb, Cd, Mo, and Y. The main mass loss in the garnet skarn was due to destruction of feldspars in the Mazraeh plutonic rocks and leaching of K2O and Na2O. Released Ca has been fixed in the andraditic garnet. Garnetization of the Mazraeh pluton was accompanied by mass and volume increase. The magnitude of these changes depends mainly on the degree of alteration and composition of the precursor. The brittle behavior of the endoskarn zone was increased due to formation of massive garnet which subsequently fractured. These fractures not only facilitated movement of hydrothermal fluids but also provided new locations for Cu mineralization. Therefore locating strongly garnetized zones may be a vector to ore in skarn deposits.

  6. Genesis of the Datuanshan stratabound skarn Cu(-Mo) deposit, Middle-Lower Yangtze Valley, Eastern China: constraints from geology, Re-Os geochronology, mineralogy, and sulfur isotopes

    Science.gov (United States)

    Cao, Yi; Gao, Fuping; Du, Yangsong; Du, Yilun; Pang, Zhenshan

    2016-07-01

    Stratabound deposits are the most abundant and economically significant ore type in the Middle-Lower Yangtze River Valley, one of the most important metallogenic belts in China. The Datuanshan deposit is one of the largest and most representative stratabound Cu(-Mo) deposits in the Tongling district of the Middle-Lower Yangtze River metallogenic belt. All the orebodies of the Datuanshan deposit occur around Mesozoic quartz monzodiorite and are tabular or semi-tabular bodies along bedding-parallel faults within upper Permian to Lower Triassic strata. However, discordant and crosscutting relationships (e.g., the host rocks crosscut by skarn- and quartz-sulfide veins, with alteration halos around the veins) have also been found, especially along the skarn-host contact and orebody-host contact, indicating that skarnitization and mineralization postdated the deposition of the host sediments. The skarn consists mainly of prograde garnet and pyroxene and retrograde alteration assemblages of amphibole, epidote, and chlorite, as well as quartz and sulfides. Electron microprobe analyses show that the garnets and pyroxenes are grossular-andradite and hedenbergite-diopside series, respectively, and all samples plot in the field of typical skarn copper deposits worldwide. Molybdenite samples from stratiform copper ores yield Re-Os model ages of 138.2-139.9 Ma with a weighted mean age of 139.2 ± 0.9 Ma. This is reasonably consistent with the ages of the stratiform Mo ores (138.0-140.8 Ma) and genetically related quartz monzodiorite (135.2-139.3 Ma) in the Datuanshan deposit, indicating that the stratiform Cu and Mo mineralization was contemporaneous with emplacement of the quartz monzodiorite magmas in the Early Cretaceous. Fifteen δ34S values for sulfides range from -1.8 to +4.7 ‰, with a mean of 0.5 ‰, indicating that the sulfur was derived mainly from a magmatic source. Moreover, the sulfur isotope values of the ores are consistent with those of Mesozoic intermediate

  7. Matrix Effects in SIMS Analysis of Hydrogen in Nominally Anhydrous Minerals (NAMs)

    Science.gov (United States)

    Mosenfelder, J. L.; Rossman, G. R.

    2014-12-01

    Accurate analysis of trace H in NAMs has become important with recognition that even small amounts of H influence geochemical and geophysical processes. FTIR and SIMS can measure concentrations down to ~1 ppmw H2O. However, a major limitation is that they rely on standards calibrated with other methods. SIMS matrix effects for H in NAMs are poorly constrained, but are likely dominated by differences in mean atomic mass. Here we use volatile-free molar weight (VFMW) normalized to one O/mol as a proxy for this parameter [cf. 1]. Our goal is to constrain SIMS matrix effects by combining our work on olivine [2], pyroxene [3], and feldspar [4] with new data on kyanite, zircon, and 37 garnets (pyropes, grossulars, spessartines, and andradites), while critically evaluating absolute calibrations of IR absorption coefficients (ɛi) for H in NAMs. All of these NAMs taken together span a wider range in VFMW (~32-45) than in previous comparisons [5, 6] concentrating only on olivine, pyroxene, and pyrope-rich garnet (VFMW ~ 34-37). Our results and conclusions include the following: 1) SIMS-FTIR comparisons demonstrate that ɛi is wavenumber dependent for feldspar, zircon, grossular, and clinopyroxene, in accord with theory and empirical calibrations on hydrous materials. On the other hand, a factor of 3 difference in ɛi for H defects in olivine [7] is unsupported by our data [2]. 2) Calibration slopes (for plots of ppmw H2O vs. 16OH/30Si × SiO2) correlate positively with VFMW, an effect not discerned in previous work [6]. This result is also opposite to a study demonstrating a negative correlation for hydrous phases and glasses [1]. This discrepancy may be related to differences in analytical methods (e.g., Cs+ vs. O- primary beam, collection of OH- versus H+). 3) Scatter in the trend of calibration slopes vs. VFMW is likely due to uncertainties in ɛi. Another possible factor is the structure of the matrix, which can affect the kinetic energy of cascade collisions leading to

  8. Evaluation of phase chemistry and petrochemical aspects of Samchampi–Samteran differentiated alkaline complex of Mikir Hills, northeastern India

    Indian Academy of Sciences (India)

    Abhishek Saha; Sohini Ganguly; Jyotisankar Ray; Nilanjan Chaterjee

    2010-10-01

    The Samchampi –Samteran alkaline complex occurs as a plug-like pluton within the Precambrian granite gneisses of Mikir Hills,Assam,northeastern India and it is genetically related to Sylhet Traps.The intrusive complex is marked by dominant development of syenite within which ijolite – melteigite suite of rocks is emplaced with an arcuate outcrop pattern.Inliers of alkali pyroxenite and alkali gabbro occur within this ijolite –melteigite suite of rocks.The pluton is also traversed by younger intrusives of nepheline syenite and carbonatite.Development of sporadic,lumpy magnetite ore bodies is also recorded within the pluton.Petrographic details of the constituent lithomembers of the pluton have been presented following standard nomenclatorial rules.Overall pyroxene compositions range from diopside to aegirine augite while alkali feldspars are typically orthoclase and plagioclase in syenite corresponds to oligoclase species.Phase chemistry of nepheline is suggestive of Na-rich alkaline character of the complex.Biotite compositions are typically restricted to a uniform compositional range and they belong to ‘biotite ’field in the relevant classification scheme.Garnets (developed in syenite and melteigite)typically tend to be Ti-rich andradite,which on a closer scan can be further designated as melanites.Opaque minerals mostly correspond to magnetite.Use of Lindsley ’s pyroxene thermometric method suggests an equilibration temperature from ∼450°–600°C for melteigite/alkali gabbro and ∼400° C for syenite.Critical assessment of other thermometric methods reveals a temperature of equilibration of ∼700°–1350°C for ijolite –melteigite suite of rocks in contrast to a relatively lower equilibration temperature of ∼600° C for syenite. Geobarometric data based on pyroxene chemistry yield an equilibration pressure of 5.32 –7.72 kb for ijolite,melteigite,alkali pyroxenite,alkali gabbro and nepheline syenite.The dominant syenite member of the

  9. Petrogenesis of orbicular ijolites from the Prairie Lake complex, Marathon, Ontario: Textural evidence from rare processes of carbonatitic magmatism

    Science.gov (United States)

    Zurevinski, Shannon E.; Mitchell, Roger H.

    2015-12-01

    A unique occurrence of orbicular ijolite is hosted in a matrix of contemporaneous holocrystalline ijolite at the 1.1 Ga Prairie Lake Carbonatite Complex (Marathon, Ontario, Canada), and is the only known occurrence of this textural type in a rock of ijolitic composition. This mineralogical and petrological study of this orbicular ijolite highlights many of the differences from other rare occurrences of orbicular rocks described from carbonatites, granites, diorites and lamprophyres. The orbicules occur along distinct, densely packed bands in equigranular nepheline-rich ijolite and range up to 6 cm in diameter. Macroscopically, the orbicules show variability in the mineralogy of their cores. Detailed imaging of the cores shows evidence of quench textures. Radial outward zoning is common near the cores with concentric banding occurring toward the margins of the orbicules. The mineralogy of the orbicules consists of: nepheline; diopside; calcite; apatite; andradite-melanite garnet; titanite; Fe-rich phlogopite; titaniferous magnetite; perovskite; with secondary natrolite, calcite and cancrinite. The mineralogy of the host ijolite is similar to that of the orbicules. Mineral compositions from the orbicular ijolite and the host ijolite are similar. Within the orbicules, anhedral minerals are found occurring in a 'matrix' of garnet throughout the distinct concentric bands. The textures within the concentric bands of the orbicules are best described as annealing recrystallization textures. The rims of the orbicules form interlocking crystals with the host ijolite resulting in near-indistinguishable boundaries. The orbicules are interpreted to represent interaction of a partially-crystallized quenched ijolitic melt, which was in contact with a second pulse of consanguineous ijolite magma. Immersion in the latter resulted in sub-solidus diffusion and annealing recrystallization. Orbicular textures were produced from previously formed quenched ijolite, which was

  10. Frictional melting processes and the generation of shock veins in terrestrial impact structures: Evidence from the Steen River impact structure, Alberta, Canada

    Science.gov (United States)

    Walton, Erin L.; Sharp, Thomas G.; Hu, Jinping

    2016-05-01

    Shock-produced melt within crystalline basement rocks of the Steen River impact structure (SRIS) are observed as thin (1-510 μm wide), interlocking networks of dark veins which cut across and displace host rock minerals. Solid-state phase transformations, such as ferro-pargasite to an almandine-andradite-majorite garnet and amorphization of quartz and feldspar, are observed in zones adjacent to comparatively wider (50-500 μm) sections of the shock veins. Shock pressure estimates based on the coupled substitution of Na+, Ti4+ and Si4+ for divalent cations, Al3+ and Cr3+ in garnet (14-19 GPa) and the pressure required for plagioclase (Ab62-83) amorphization at elevated temperature (14-20 GPa) are not appreciably different from those recorded by deformation effects observed in non-veined regions of the bulk rock (14-20 GPa). This spatial distribution is the result of an elevated temperature gradient experienced by host rock minerals in contact with larger volumes of impact-generated melt and large deviatoric stresses experienced by minerals along vein margins. Micrometer-size equant crystals of almandine-pyrope-majorite garnet define the shock vein matrix, consistent with rapid quench (100-200 ms) at 7.5-10 GPa. Crystallization of the vein occurred during a 0.1-0.15 s shock pressure pulse. Majoritic garnet, formed during shock compression by solid state transformation of pargasite along shock vein margins, is observed in TEM bright field images as nanometer-size gouge particles produced at strain rates in the supersonic field (106-108). These crystals are embedded in vesiculated glass, and this texture is interpreted as continued movement and heating along slip planes during pressure release. The deformation of high-pressure minerals formed during shock compression may be the first evidence of oscillatory slip in natural shock veins, which accounts for the production of friction melt via shear when little or no appreciable displacement is observed. Our observations

  11. Process Mineralogy of a Skarn Tungsten-Molybdenum Ore%夕卡岩型钨钼伴生矿工艺矿物学研究

    Institute of Scientific and Technical Information of China (English)

    洪秋阳; 梁冬云; 张莉莉

    2013-01-01

    The researches on a skarn tungsten-molybdenum ore by the internationally advanced MLA testing technology and traditional process mineralogy show that the grade of W and Mo is low with high comprehensive recycling value. The tungsten mainly occurs in the form of scheelite while the molybdenum principally exists as molybdenite, and the molybdenum as isomorphous addition existing in the lattice of scheelite accounts for 16.89%of the total molybdenum. The liberation degree of scheelite is close to 90%while that of molybdenite is less than 80%at the grinding fineness 62%-0.074 mm. The tungsten and molybdenum contained in the magnetic gangue minerals accounts for 2.8 % and 5.8 % respectively. Considering that the magnetic gangue minerals including andradite tremolite, diopside, etc account for about two-thirds of the total and are not closely intergrown with scheelite or molybdenite, pre-discarding these magnetic gangue minerals by high intensity magnetic separation is available so as to simplify the cleaning process of tungsten as well as molybdenum.%采用国际先进的MLA检测技术,结合传统工艺矿物学研究表明,某夕卡岩型钨钼伴生矿虽品位低,但综合回收价值较高。矿石中钨主要以含钼白钨矿矿物形式存在,以类质同象进入白钨矿晶格的钼占原矿总钼的16.89%。钼主要以辉钼矿矿物形式存在。当磨矿细度-0.074 mm占62%左右时,白钨矿单体解离近90%,而辉钼矿解离不到80%。钨、钼与本矿石中约占矿物总量三分之二的钙铁榴石、透辉石、透闪石等电磁性脉石连生关系不密切,分布于其中的钨、钼金属量分别仅2.8%、5.8%。因而可采用强磁选预先丢废而达到简化钨、钼精选。

  12. MINERAL CHARACTERISTIC OF SKARNS IN THE ANQING COPPER DEPOSIT OF ANHUI AND THEIR GEOLOGICAL SIGNIFICANCE%安徽安庆铜铁矿床矽卡岩岩相学和矿物学特征及意义

    Institute of Scientific and Technical Information of China (English)

    滕传耀; 杜杨松; 张智宇; 龙旺生; 董玉翠; 李湘莲

    2012-01-01

    experienced skarn period and hydrothermal alteration period. The skarn period includes the early stage of skarn,magnetite stage and late stage of skarn,and the hydrothermal alteration period includes he early hydrothermal stage,quartz-sulfide stage and quartz-carbonate stage. Massive chalcopyrite mineralization mainly occurred in quartz-sulfide stage. Min-eralogical studies suggest that the garnets are andradite, granular garnet of the early stage of skarn develops rhythm zoning with oscillation of FeO and A12O3 content. Compared with granular garnet,the vein-shape garnet of late stage skarn is higher in andradite end-member. The granular pyroxene in the early skarn stage is diopside with ring structure, its MgO content gradually reduced from the core to the edge, while FeO content gradually increased. Vein-shape pyroxene in the late skarn stage is hedenbergite. In spatial,from exocontact zone to internal contact zone,MgO content of pyroxene and A12O3 content of garnet is reduced, while FeO content of both pyroxene and garnet are increased. Petrography, mineralogy, combined with the existing geochemical research show that skarn of Anqing copper-iron deposit are magmatic-hydrothermal contact meta-somatic origin. Mg came from carbonate rocks,migrated from exocontact zone to internal contact zone. Fe came from magmatic hydrothermal, migrated from internal contact zone to exocontact zone. Due to the change of temperature and pressure conditions in magnetite stage,Fe precipitated and enriched in the exocontact zone in the form of magnetite.

  13. Mesozoic In-situ and External Skarn Magmatic-Hydrothermal Mineralizationin the Anhui Segment of the Lower Yangtze Metallogenic Belt%安徽沿江地区中生代原地和异地矽卡岩岩浆-热液成矿作用

    Institute of Scientific and Technical Information of China (English)

    杜杨松; 曹毅; 张智宇; 庞振山; 李大鹏

    2011-01-01

    , lithologies from the centre to the margin of external skarn body vary from medium-coarse-grained skarn to medium-fine-grained skarn, showing gradual decreasing of crystallization speed with gradual increasing of temperature lowing speed. Mineralogically, in the in-situ skarn, garnet includes andradite, gralmandite and grossular, and pyroxene does diopside and hedenbergite. In contrast, in the external skarn, garnet is almost andradite, and pyroxene is all hedenbergite. Geochemically, compared with the in-situ skarn, the external skarn is evidently rich in W, F, Rb, Be and Fe, but poor in Al, Sr, Ba, Cu, Pb, Zn, Cr, Co and Ni. Petrographically, both of the in-situ and external skarns have automorphic granular texture and mostly contain melt inclusions. However, compared with those in the insitu skarn, garnet and pyroxene in the external skarn are more automorphic and have better zonal structure, and melt inclusions indicate evidently lower homogenization temperature. In ore deposit, the insitu skarn is associated with various deposits such as copper and iron ones, while the external skarn with only iron deposit. A comprehensive analysis is consistent with formation of the in-situ and external skarns by cooling and crystallization of the in situ and external skarn magmas, and supports formation of deposits associated with the in-situ and external skarns by cooling and crystallization of the ore pulp formed through liquation of the skarn magmas and by alteration and replacement of the hydrothermal solution formed through crystalline differentiation of the skarn magmas.%在安徽沿江地区,既分布有大量接触交代成因和叠加复合成因的矽卡岩矿床,也分布有岩浆成因的矽卡岩矿床.本文给出了不同类型岩浆矽卡岩及其矿床的定义,论述了安徽沿江地区中生代岩浆矽卡岩及其矿床的特征,并在此基础上分析了区域中生代矽卡岩岩浆-热液成矿作用.根据矽卡岩岩浆就位位置的不同可将岩浆矽卡

  14. Mineralogy of skarn and magnetite of the Yamansu iron deposit and its geological significance%新疆雅满苏铁矿床矽卡岩和磁铁矿矿物学特征及其地质意义

    Institute of Scientific and Technical Information of China (English)

    曾红; 柴凤梅; 周刚; 耿新霞; 李强; 孟庆鹏; 徐璐璐

    2014-01-01

    雅满苏铁矿床位于东天山中段,矿体赋存于下石炭统雅满苏组安山质火山碎屑岩中,受近EW向断裂及环形断裂构造控制。矿体主要呈层状、似层状、透镜状,近矿围岩蚀变强烈,形成石榴石矽卡岩及复杂矽卡岩。电子探针分析结果表明,石榴石为钙铁榴石-钙铝榴石系列,其化学组成可表示为And45.68~100Gro0.67~57.95(A1m+Sps)11~29.03,与典型的矽卡岩型铁矿中石榴石端员组分相似。在磁铁矿Ca+Al+Mn-Ti+V图解中,大部分样品落入矽卡岩型铁矿区;TiO2-Al2O3-MgO图解中,大多数的样品落入沉积变质接触交代磁铁矿趋势区,部分早期磁铁矿落在岩浆趋势区内。结合矿床地质特征和矿物学研究,认为大多数样品经过了一个热液交代作用过程,表明雅满苏铁矿的形成与岩浆热液交代作用有关。%Located in the middle of Eastern Tianshan Mountains, the large-size Yamansu iron deposit is hosted in Andesitic volcanic clastic rock or andesitic tuff of the Lower Carboniferous Yamansu Formation, with a lenticular marble beneath the main ore body. The ore bodies occur as lamellar stratoids and lenses, controlled by EW-striking faults and circular faults. Wall rock alteration is strong, including garnet skarn and complex skarn. Electeon microprobe analyses show that the end member of garnet is andradite (And) with an average content of 63.59%, grossularite(Gro) with an average content of 34.11%, almandite(Alm) and spessartine (Sps) with an average content of 4.44%. Components of garnet and pyroxene are And45.68~100Gro0.67~57.95(A1m+Sps)11~29.03, which indicates that characteristics of this skarn minerals are quite similar to those in calcic skarn from the major large iron deposits, suggesting that they probably resulted from skarnization; In the Ca+Al+Mn versus Ti+V discriminant diagram showing spot analyses of magnetite and hematite, almost all data from the Yamansu ore

  15. Fluorine-bearing grossular-rich garnet - an indicator for UHP - LT metamorphism of metagranitoids.

    Science.gov (United States)

    Burchard, M.

    2002-12-01

    Melting experiments on biotite-phengite-gneiss at pressures of 1.5 to 4.5 GPa and temperatures of 675°C to 1000°C were performed to clarify the phase assemblages of S-type metagranitoids at high pressures. The starting material used was S-type granitic biotite-phengite-gneiss, which represents the country rock for the pyrope-quarztites from the Dora-Maira-Massif, Western Italy. These pyrope-quarztites contain the silicate ellenbergerite, which, together with the growth of pyrope, indicates P and T of more than 3 GPa and 700°C. Experimental evidence confirms that the presence of ellenbergerite indicates high water activities. For this reason all experiments were performed with a water fraction of 1.9 to 9.9 wt.%. The most important phases in the run products are melt, K-feldspar / K-felspar-hydrate, coesite / quartz, phengite, jadeite-rich clinopyroxene, almandine-grossular garnet, epidote, rutile and sphene. At pressures between 3.5 and 4.5 GPa and T of less than 675°C or 775°C, respectively, small, rare crystals of grossular garnets were observed. These grs-rich garnets form corona structures around the alm-grs garnets of the starting material. EMP-analysis shows that these garnets contain up to 1.2 wt.% F at 700°C, decreasing with temperature to 0.4 wt.% at 750°C. A garnet analysis from a run at 4 GPa and 700°C yields 69% grossular, 8% hydrogrossular, 6% fluorgrossular, 6% almandine, 2% spessartine and 3% andradite. The coexistence of such garnets with sphene and epidote in HP experiments shows that the high-pressure reaction sph + zoi -> grs + coe + H2O suggested by Chopin et al (1991) is not relevant at these conditions. From Chopin et al (1991) and Schertl at al (1991) it is known that there are extremely rare inclusions of grs-rich garnet in plagioclase and alm-grs garnet in the original rock, but these authors unfortunately did not analyze the F content. During a reinvestigation of the biotite-phengite gneiss grs inclusions in sph were found that

  16. Petrology and mineralogy of the La Peña igneous complex, Mendoza, Argentina: An alkaline occurrence in the Miocene magmatism of the Southern Central Andes

    Science.gov (United States)

    Pagano, Diego Sebastián; Galliski, Miguel Ángel; Márquez-Zavalía, María Florencia; Colombo, Fernando

    2016-04-01

    The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32°41‧34″ S - 68°59‧48″ W) of Mendoza province, Argentina, above the southern boundary of the present-day flat-slab segment. It is a 19 km2 and 5 km diameter subcircular massif emplaced during the Miocene (19 Ma) in the Silurian-Devonian Villavicencio Fm. The LPC is composed of several plutonic and subvolcanic intrusions represented by: a cumulate of clinopyroxenite intruded by mafic dikes and pegmatitic gabbroic dikes, isolated bodies of malignite, a central intrusive syenite that develops a wide magmatic breccia in the contact with clinopyroxenite, syenitic and trachytic porphyries, a system of radial and ring dikes of different compositions (trachyte, syenite, phonolite, alkaline lamprophyre, tephrite), and late mafic breccias. The main minerals that form the LPC, ordered according to their abundance, are: pyroxene (diopside, hedenbergite), calcium amphibole (pargasite, ferro-pargasite, potassic-ferro-pargasite, potassic-hastingsite, magnesio-hastingsite, hastingsite, potassic-ferro-ferri-sadanagaite), trioctahedral micas (annite-phlogopite series), plagioclase (bytownite to oligoclase), K-feldspar (sanidine and orthoclase), nepheline, sodalite, apatite group minerals (fluorapatite, hydroxylapatite), andradite, titanite, magnetite, spinel, ilmenite, and several Cu-Fe sulfides. Late hydrothermal minerals are represented by zeolites (scolecite, thomsonite-Ca), epidote, calcite and chlorite. The trace element patterns, coupled with published data on Sr-Nd-Pb isotopes, suggest that the primary magma of the LPC was generated in an initially depleted but later enriched lithospheric mantle formed mainly by a metasomatized spinel lherzolite, and that this magmatism has a subduction-related signature. The trace elements pattern of these alkaline rocks is similar to other Miocene calc-alkaline occurrences from the magmatic arc of the Southern Central Andes. Mineral and whole

  17. Skarn formation and trace elements in garnet and associated minerals from Zhibula copper deposit, Gangdese Belt, southern Tibet

    Science.gov (United States)

    Xu, Jing; Ciobanu, Cristiana L.; Cook, Nigel J.; Zheng, Youye; Sun, Xiang; Wade, Benjamin P.

    2016-10-01

    Trace element concentrations in garnet and associated minerals from the mid-Miocene Zhibula Cu skarn, Gangdese Belt, Tibet reflect a diversity of local environments, evolving fluid parameters and partitioning with coexisting minerals. Exoskarn occurs as massive but narrow intervals within a Lower Jurassic volcano-sedimentary sequence containing limestone, the main skarn protolith. Endoskarn is present at the contact with mid-Miocene granodiorite dikes. Prograde skarn associations are garnet-dominant but also include diopside-dominant pyroxene in variable amounts. Garnet compositions in exoskarn change from andradite (And)- to grossular (Gr)-dominant from the massive intervals to bands/lenses within marble/tuff, but not in endoskarn. In both cases however, associations at the protolith contact include anorthite and wollastonite, both indicative of skarnoid or distal (relative to fluid source) skarn formation. Exoskarns also contain vesuvianite. Retrograde clinozoisite, actinolite and chlorite replace pre-existing skarn minerals. Garnet displays brecciation and replacement by Al-richer garnet. Depending on partitioning among coexisting minerals, chondrite-normalised REY (REE + Y) fractionation trends for garnet depict endo- to exoskarn diversity, the dominance of And- vs. Gr-rich garnet (in turn related to proximal-to-distal relationship to fluid source), as well as prograde-to-retrograde evolution in the same sample. A strong variation in Eu-anomaly, from positive to negative, in And-dominant garnet can be correlated with variation in salinity of ore-forming fluids, concordant with published fluid inclusion data. Trends depicted by And- and Gr-dominant garnets are consistent with published data from skarns elsewhere, in which the dominant substitution mechanism for REY is YAG-type. Zhibula garnets are enriched in a range of trace elements less commonly reported, including W, Sn, and As, but also Mo (as high as 730 ppm), an element seldom analysed for in silicates

  18. Chrysotile asbestos quantification in serpentinite quarries: a case study in Valmalenco, central Alps, northern Italy

    Science.gov (United States)

    Cavallo, Alessandro

    2013-04-01

    fibrous and lamellar polymorphs. A lot of minerals were identified in the mineralized veins: chrysotile, carbonates, talc, forsterite, brucite, chlorite, garnet (andradite), magnetite and sulphides. The quantitative XRPD and SEM-EDS analyses proved chrysotile percentages comprised between 11 and 100% by weight. On the other hand, chrysotile was never detected in the commercial massive rock. Considering the geostructural properties of the rock mass, the total asbestos content of the quarries is comprised between 0.23% and 0.02% by weight, very low percentages of no mining interest, classifiable as naturally occurring asbestos (NOA) occurrence. The SEM-EDS analyses also showed a slight chrysotile contamination close to the salvages of mineralized veins (in the form of chrysotile filled micro-fractures), for a thickness up to 5-6 cm. This study shows that the airborne asbestos exposure risk can be easily reduced by avoiding diamond wire or explosive cutting along the main mineralized veins, and by squaring off the blocks in the quarry (instead of processing plants). However, this study does not consider the possible asbestos occurrence in the form of micro-veins and micro-fractures, outside of the main discontinuities, and cannot be fully applied to highly fractured rock masses.

  19. Mineralogical composition of Oravita calcic skarns as a function of the high-temperature contact

    Science.gov (United States)

    Ghinet, Cristina; Marincea, Stefan; Dumitras, Delia

    2014-05-01

    Insignificant in terms of mineralization, the skarns of Oravita are scientifically interested because of their mineralogical associations. The higher crystallinity and good natural conditions (they are generally barren) are two characteristics of this rocks that can provide the ideally system to understand the behavior of the mineralogical components in certain conditions of temperature and pressure, but also for the hydrated carbonate phases whose forming understanding may be useful in the applied mineralogy. The occurrence of skarns from Oraviţa includes, as representative species, gehlenite, calcic garnet, monticellite, ellestadite-(OH), vesuvianite, that means in the geochemically terms CaO - SiO2 - H2O - Al2O3 system, usually described as C-S-H-A phases by the cement researches, difficult to study because of the small dimensions of the compounds crystals. The inner skarn zone is dominated by the presence of the gehlenite, an aluminum calcium silicate whose formation involves, as conditions, high temperature (~ 750oC) and low pressure (up to 1kbar). Typically, it is associated with monticellite, ellestadite-(OH), wollastonite 2M, diopside and calcic garnets. As it is expected, the intensity of the contact metamorphism decreases from the innermost to the outermost parts of the aureole, reflected in the chemical activity of the cations that participated at the chemical reactions. In this respect, the observed garnets are zoned, being characterized by a peripheral rich in Al, while the centers of the crystals are characterized by a high content of Fe and Ti. The replacement of gehlenite with vesuvianite along the metasomtatic front, a process that was observed at the optical microscope, indicates the existence of late stage metasomatic mineral phases. The presence of the vesuvianite, frequently including partially chloritized clintonite slides, and its main associated minerals as wollastonite 2M and calcium garnet with an andradite composition, points out the

  20. Fluids in distal Zn-Pb-Ag skarns: Evidence from El Mochito, Honduras

    Science.gov (United States)

    Samson, I. M.; Williams-Jones, A. E.; Ault, K.; Gagnon, J. E.; Fryer, B. J.

    2009-05-01

    Zn-Pb-Ag mantos, chimneys, and skarns represent a spectrum of carbonate-hosted sulfide mineral deposits that have been collectively termed carbonate replacement deposits. Most such deposits cannot be related to plutons and, particularly for distal skarns, the role of magmatic versus other fluids (basinal brines and meteoric waters) has been uncertain. The El Mochito Zn-Pb-Ag deposit, Honduras, is an example of a large distal skarn, and comprises mantos and chimneys hosted mainly by limestones of the Early Cretaceous Tepemechin Formation. Previous isotopic studies indicate a magmatic source for the S and Pb and involvement of both magmatic and meteoric fluids in ore formation. The ore is hosted by garnet, magnetite, and pyroxene skarns, which developed sequentially from grandite- to andradite- to magnetite- and hedenbergite- rich skarns. Sphalerite and argentiferous galena occur interstitially to, or replace, the skarn minerals, with Fe- poor sphalerite (S1) principally associated with garnet skarn and Fe-rich (S2) sphalerite associated with pyroxene. Data from primary fluid inclusions show that the salinity of the mineralizing fluids decreased from ˜10-18 wt. % during the formation of garnet skarn and S1 sphalerite to ˜2-13 wt. % during pyroxene skarn formation and S2 sphalerite precipitation. Early, high-salinity fluids (˜33 wt. %) are represented by rare halite-saturated inclusions in garnet. Temperature increased from ˜ 365°C to ˜ 365°C from garnet/S1 sphalerite to pyroxene/S2 sphalerite, assuming a pressure of 500 bars. GC analyses indicate that the total concentrations of COv(2), CH4, and N2 were < 1 mole %. LA-ICPMS analyses were conducted mainly on inclusions in grandite and S1 sphalerite. The principal dissolved elements in the inclusions are Ca and Na, followed by K and Mn. The ore metals, Zn, Pb, and Ag, are present in high concentrations, with median values of 6000, 900, and 50 ppm, respectively. Element concentrations in fluid inclusions hosted

  1. 青海省兴海县赛什塘铜矿床矽卡岩矿物学特征及地质意义%Mineralogical Characteristics and Geological Significance of Skarn in the Saishitang Copper Deposit, Xinghai County, Qinghai Province

    Institute of Scientific and Technical Information of China (English)

    王辉; 丰成友; 李大新; 丁天柱; 王洪庆; 刘建楠; 周建厚

    2015-01-01

    The Saishitang copper deposit is an important skarn deposit located in the Southeast of Ngola Mountain Area, Eastern margin of East Kunlun orogenic belt. The skarn occurs along the contact between Indosinian quartz diorite and middle-lower Triassic Tb21-2 lithologic section. The ore bodies which are stratoid or lenticular mainly occur in exoskarn. The Tb21-2 lithologic section consists of intermediate volcanic rocks, marble and metamorphic siltstone. Cu mineralization is adjacent to the metamorphic andesitic tuff and andesite spatially. Petrography studies of Cu-bearing skarn show four stages of skarn formation and ore development, including skarn stage, retrograde alteration stage, quartz-sulfide stage and quartz-carbonate stage. Skarn stage consists of garnet, pyroxene and wollastonite and retrograde alteration stage dominates by epidote, amphibole and magnetite. In quartz-sulfide stage a large amount of sulfides were precipitated. Electron microprobe analysis shows that components of garnet and pyroxene are Gro0.00~91.00And7.02~100.00(Pyr+Alm+Spe)0.00~4.27 and Di12.80~91.75Hd2.41~79.80(Jo+Jd+Opx)0.00~13.47, respectively. The result indicates that the skarn in Saishitang deposit belongs to typical calcic skarn. High concentrations of grossular and epidote are found in skarns located closer to the contact between quartz diorite and andesite. Andradite is richer near the marble with wollastonite and Mn-bearing hedenbergite. Mineralogical characteristics and compositional variations suggest:from skarn stage to quartz-sulfide stage, the property of fluid changed episodically with two redox fluctuations at least, probably resulting from the influx of meteoric waters in ore-forming fluid. Saishitang copper deposit is a skarn deposit. The quartz diorite-dominated intrusions carrying plenty of heat and fluids intrude into middle-lower Triassic strata. The materials exchange between intrusions and wall rocks may be the mechanism of the development of skarn and ore bodies

  2. 东天山红云滩铁矿床矿物学、矿物化学特征及矿床成因探讨%Mineralogy, mineral chemistry and genesis of the Hongyuntan iron deposit in East Tianshan Mountians, Xinjiang

    Institute of Scientific and Technical Information of China (English)

    张立成; 王义天; 陈雪峰; 马世青; 王志华; 余长发

    2013-01-01

    symmetrical zoning,and the alteration colors change from dark to light from ore bodies outwards.On the basis of observed mineral assemblages and ore fabrics,two periods of ore deposition were recognized,i.e.,skarn period and hydrothermal ore-forming period,which could be further subdivided into four metallogenic stages,namely skarn stage,retrograde alteration stage (main oreforming stage),early hydrothermal stage and quartz-sulfide stage.Electron microprobe analyses show that the end member of garnet is mainly andradite-grossularite.The composition of pyroxene is mainly diopside-asteroite.The amphiboles is composed mainly of actinolite and tremolite with minor magnesiohornblende.The composition of these skarn minerals suggests that skarn in the Hongyuntan iron deposit is calcic skarn,belonging to metasomatic skarn.The characteristics of main and trace elements suggest that the formation of magnetite was closely related to the skarn.In combination with geological characteristics,the authors suggest that the skarn might have resulted from interaction between Ca-rich pyroclastic and Fe-rich magmatic hydrothermal fluid which was transported along the fault system.The formation of magnetite was hence related to the regressive metamorphism of the skarn.

  3. 西藏知不拉矽卡岩型铜矿床矿物学特征及地质意义%Mineralogical Characteristics of Zhibula Skarn-Type Cu Deposit in Tibet and Their Geological Significance

    Institute of Scientific and Technical Information of China (English)

    徐净; 郑有业; 孙祥; 姜军胜; 耿瑞瑞; 申亚辉

    2014-01-01

    西藏冈底斯知不拉矽卡岩型铜矿床位于驱龙超大型斑岩型铜钼矿床以南约2 km,矽卡岩及矿体主要呈层状-似层状赋存于下侏罗统叶巴组凝灰岩和大理岩中,具有凝灰岩-石榴子石化凝灰岩-石榴子石矽卡岩-辉石矽卡岩-(硅灰石化)大理岩的空间分带特征。石榴子石从早期到晚期以及从凝灰岩到大理岩方向均具有暗棕红色-棕红色-绿色(褐色)-淡黄褐色的变化特征,以钙铁榴石和钙铝榴石为主,辉石主要为透辉石,少量为锰钙辉石。靠近凝灰岩的石榴子石 Al、Ti 含量较高,靠近大理岩的石榴子石 Fe、Mn 含量较高。石榴子石环带特征明显,浅色环带富钙铁,暗色环带富钙铝,由核部向边缘整体显示钙铁组分逐渐增加、钙铝组分相对减少的趋势。知不拉层状-似层状矽卡岩型矿体是由深部隐伏岩浆结晶分异的含矿热液在温度与压力的驱动下沿凝灰岩和大理岩的岩性分界面选择性交代形成,属于岩浆热液接触交代型矿床而非层控或喷流成因层矽卡岩型矿床,应与驱龙斑岩铜钼矿床属于同一套斑岩成矿系统。%The Zhibula skarn-type Cu deposit is located about 2 km away from the south of Qulong super-large porphyry Cu-Mo deposit in Gangdese metallogenic belt,Tibet.The skarn and ore body are mainly distributed as layer-stratoid in the tuff and marble of Yeba Group in Lower Jurassic,which show zoning characteristics:tuff-garnert tuff-garnet skarn-pyroxene skarn-(wollastonite)marble.From early to late stages,or from tuff to marble,the colors of garnets change from dark brownish red to brownish red,followed by green(brown),and pale brownish yellow These garnets are mainly grossular and andradite.The end members of pyroxenes are dominated by diopside,with minor johannsenite.Garnets near tuff have higher Al,Ti contents, whereas those nearthe marble have relatively more enriched Fe,Mn contents.Garnets show distinctive light and

  4. 新疆西天山查岗诺尔铁矿床矿物学特征及其地质意义%Mineralogy of the Chagangnuoer iron deposit in Western Tianshan Mountains,Xinjiang, and its geological significance

    Institute of Scientific and Technical Information of China (English)

    洪为; 张作衡; 赵军; 王志华; 李凤鸣; 石福品; 刘兴忠

    2012-01-01

    Located in the eastern Awulale metallogenic belt of Western Tianshan Mountains, the large-size Cha-gangnuoer iron deposit is hosted in andesitic volcaniclastic rocks or andesitic tuff of the Lower Carboniferous Da-halajunshan Formation, with a lenticular marble beneath the main ore body. The ore bodies occur as lamellar, stratoids and lenses, controlled by NW-, NWW- and NEE- striking faults and circular faults. Mineralizations occur along the fissures and fractures in the wall rocks. This ore deposit is composed of two major ore bodies, I. E., FeI and FeII. The FeI ore body strikes NE-SW, about 2 900 m in length, 63 m in average thickness, with Fe average grade of 36.87% and ore reserves of more than 190 million tons. Wall rock alterations includechiefly garnetization, actinolitization, chloritization, epidotization etc. Ore minerals consist mainly of magnetite and subordinated pyrite and chalcopyrite while gangue minerals are composed of garnet, actinolite, chlorite, epidote, tremolite, and calcite. Electron microprobe analyses show that the end member of garnet is andradite (Adr) with an average content of 61.58 %, grossularite (Grs) with an average content of 35.45 %, and alman-dite (Alm) with an average content of 2.48%. The composition of pyroxene is dominated by diopside (Di, 54.22% on average) and hedenbergite (Hd, 44.22% on average), with a small amount of johannsenite (Jo, less than 5.53%). Components of garnet and pyroxene are Adr37.97~97.89Grs0.19~57.21 (Aim + Sps)0.84~4.38, Di28.68~87.46Hd10.46~70.13.Jo0.24~5.53, which indicates that 0 characteristics of these two skam minerals are quite similar to those in calcic skam from the major large iron deposits, suggesting that they probably resulted from skarnization; (2) their wide and different compositions reveal that skarns were not formed under a wholly closed equilibrium condition. Epidote is rich in Al and Ca but poor in Fe and Mg, implying that Fe and Mg were separated from each other at the time when

  5. Metasomatismo en ortoanfibolitas de la Faja máfica-ultramáfica del río de las tunas, Mendoza Metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt, Mendoza

    Directory of Open Access Journals (Sweden)

    M. Florencia Gargiulo

    2012-06-01

    áticos y la secuencia de reemplazo observada en ellos, sugieren que tales asociaciones se generaron a causa de un proceso metasomático, acontecido en condiciones de bajo grado a una presión menor a 4 kbar, durante los estadios finales del ciclo de metamorfismo regional evidenciado en el área.In this contribution, petro-mineralogical and chemical evidences of metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt in Frontal Cordillera of Mendoza province are provided. These orthoamphibolites integrate the metamorphic basement of the Frontal Cordillera and they belong to the Guarguaráz Metamorphic Complex. These rocks show mineral associations and textural relationships indicating disequilibrium conditions between some of the mineral phases. Hornblendic amphibole crystals show a reaction border with development of clinopyroxene (ferroan dioside; meanwhile the calcicplagioclase is mostly replaced by a fine-grained matrix integrated by the mineral association of garnet-epidotes.l -prehnite-pumpellyite- albite. The amphibole and clinopyroxene crystals are also partially replaced by pumpellyite and/or chlorite, meanwhile the matrix is slightly replaced by muscovite and calcite. Garnet compositions belong to the grossular-andradite series and their average composition is: Alm05Adr53Prp01Sps04Grs36Uv01. Some crystals with Cr2O3 content between 11.69-13.17 wt.% and with a subtle chemical zonation (uvarovitic core: Alm03Adr13Prp00Sps02Grs35Uv47 with more grossularic border: Alm03Adr12 Prp00Sps01Grs44Uv40 occur in relationship with magnetite crystals with up to 20% of the chromite component. Pressure estimations based on the compositional zoning of amphibole crystals gave values between 2.5-4.5 kbar. The observed mineral associations together with the textural and chemical characteristics of these rocks show that this kind of orthoamphibolites is completely different from the classical amphibolites of igneous protoliths outcropping in the study area

  6. Petrología de la aureola metamórfica de la granodiorita de Barcelona en la Sierra de Collcerola (Tibidabo

    Directory of Open Access Journals (Sweden)

    Julivert, M.

    1988-12-01

    Full Text Available The Paleozoic materials outcropping in the Sierra de Collcerola área (Tibidabo range from Upper Ordovician up to Carboníferous. These materials approximately define a syncline structure wich minor folds facing to SE or SSE and show the development of a marked slatycleavage. The structures of WNW-ESE direction are cut near Barcelona by a granodioritic intrusion (granodiorite of Barcelona. This intrusion does not show any evidence of regional deformation and presents an oblique contact to the Hercynian structures of the host rocks, affecting, therefore, a great variety of lithologies, the main ones being: 1 metapelites and metapsamites; 2 calcareous and calc-silicate rocks, and 3 metabasites (likely derived from gneous protoliths. The materials affected by the contact metamorphism belong to the Silurian and Upper Ordovician. Previously to the intrusion the Paleozoic materials were affected by a regional metamorphism, syn-kinematic with the development of the main schistosity, which did not surpass conditions of the greenschists facies. As a result of the intrusion of the granodiorite, the host materials underwent a considerable recrystallization which affected rocks situated at even more than two km from the contact. The calcareous and calc-silicate rocks are the first to show the effects of contact metamorphism; metabasites go next, and finally metapelites and metapsamites show those effects too. Calcareous and calc-silicate rocks are the more reactive too during the metamorphic event giving rise to a great variety of minerals through the contact aureole: chlorite, biotite, actinolite, epidote, homblende, clinopyroxene, idocrase, grossular/andradite and scapolite in this order; in the basic rocks a generalized development of homblende and locally of pyroxene took place, while in the pelitic and semipelitic rocks cordierite and andalusite generally formed (the latter only in those levels corresponding to ancient black shales of the Silurian, and

  7. Spurrite, tilleyite and associated minerals in the exoskarn zone from Cornet Hill (Metaliferi Massif, Apuseni Mountains, Romania)

    Science.gov (United States)

    Marincea, S.; Dumitras, D. G.; Calin, N.; Anason, A. M.; Fransolet, A. M.; Hatert, F.

    2012-04-01

    The high-temperature skarn occurrence from Cornet Hill (Apuseni Mountains, Romania) is known as one of the rare occurrences of spurrite and tilleyite worldwide. Both minerals concentrate in the outer skarn zone, corresponding to the exoskarn, at the contact of a monzodiorite - quartz monzonite body, of Upper Cretaceous age, with Tithonic - Kimmeridgian reef limestones. The skarn from Cornet Hill is clearly zoned. The zoning is, from the outer to the inner part of the metasomatic area: calcite (marble) / tilleyite / spurrite / wollastonite + gehlenite + vesuvianite / wollastonite - grossular / quartz monzonite. The mineral assemblage identified so far includes gehlenite, spurrite, tilleyite, diopside, grossular, titanian andradite, magnetite, monticellite, wollastonite, perovskite, vesuvianite, afwillite, fukalite, ellestadite-(OH), calcite, aragonite, pyrrhotite, scawtite, thaumasite, clinochlore, chrysotile, hibschite, xonotlite, thomsonite, gismondine, plombièrite, tobermorite, riversideite, portlandite, allophane. Spurrite composes 90-95 of the rock volume of the inner exoskarn zone, where it forms practically monomineralic masses of grayish blue to pale gray color associated with perovskite, grossular, scarce tilleyite and wollastonite, and secondary afwillite, ellestadite-OH, fukalite and thaumasite. Some of the larger patches of spurrite are, however, cross cut by microveins containing scawtite, plombièrite, tobermorite, calcite and secondary aragonite. The mean unit-cell parameters, obtained as average of seven sets of data refined on the basis of X-ray powder patterns, are a 10.496(15), b 6.719(8), c 14.182(18) Å and ? 101.38(4)°. The average crystal-chemical formula, established on the basis of 23 point analyses is: (Ca5.012Mg0.002Fe2+0.002Na0.011K0.001)(Si1.990Ti0.002)O8(CO3)0.995. Tilleyite represents the main constituent of the outer exoskarn zone. It occurs as monomineralic grey-bluish "orbicules" up to 5 cm2 in size, generally rimmed by scawtite

  8. 青海野马泉矽卡岩铁锌多金属矿区侵入岩、交代岩及矿化蚀变特征%Characteristics of intrusive rock, metasomatites, mineralization and atteration in Yemaquan skarn Fe-Zn polymetallic deposit, Qinghai Province

    Institute of Scientific and Technical Information of China (English)

    刘建楠; 丰成友; 赵一鸣; 李大新; 肖晔; 周建厚; 马永寿

    2013-01-01

    The Yemaquan Fe-Zn polymetallic deposit is located at the junction belt between Chaidamu basin and Qi-mantag area, Qinghai. There are some Hercynian and Indosinian intrusive rocks exposed in the ore dtstrict. The strata in the ore district are mainly Sijiaoyanggou Group. The skarn mainly occurs within the carbonate rocks and igneous conversion boundaries. The skarn minerals are mainly garnet, clinopyroxene, vesuvianite and epi-dote. Metallic minerals mainly include magnetite, chalcopyrite, galena, sphalerite and pyrrhotite. Based on the detailed field geological investigation and the observation of geological sections and drill cores, the authors studied the petrogeochemical characteristics and mineralization of this deposit. The petrochemistry of diorite is characterized by low SiO2 (51.90% ~ 59.03%), high MgO (2.04% ~3.44%) and TFeO (11.39% ~ 11.67%), rich REE (318.57 x 10~6 -327.76 x 10~6), and low LREE/HREE ratios (7.36-7.48). The monzonitic granite is characterized by high SiO2>(77.36% ~77.41%), low MgO (0.04% ~0.10%), low TFeO (0.76% ~1.08%), and high LREE/HREE ratios (9.14-9.37). The diopside-alkali metasomatites show stronger Eu negative anomaly (Eu = 0.07-0.52) and lower LREE/HREE ratios(3.19-7.87)than its original rock. The diopside-sodic metasomatites have low MgO (0.36% ~ 0.92%), high TFeO (3.05% ~ 8.13%) than its original rock. The skarn from Yemaquan deposit can be further divided into two types: calcic skarn and magnesian skarn. The calcic skarn is mainly distributed in the contact zone and consists of garnet and clinopyroxene. The clinopyroxenes distributed near the intrusion have high content of diposide end-member, and the garnet has more andradite end-members at the edge. According to the mineral composition and mineral inter-growth association, the authors have inferred that the diorite possesses remarkable mineralization potentiality, and calcic skarn was formed at an oxidation stage, whereas the magnesian skarn was formed in a reduction state