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1.
In the Salma eclogite of the Belomorian eclogite province, a dumortierite–phengite–corundum–bearing quartz–feldspar rock has been studied: its primary HP mineral paragenesis included garnet, phengite, and quartz. The phengite–quartz rocks were formed during dehydration and/or melting of boroncontaining rocks when they were dipped in the Meso- Neoarchaean subduction zone to a depth of not less than 70 km. As a result of the subsequent superimposed high-temperature metamorphic events under PT conditions of high-pressure granulite facies, the phengite in quartz underwent incongruent dehydration melting with formation of complex polymineral pseudomorphs, consisting of feldspars, biotite, newly formed muscovite, kyanite, corundum, and dumortierite. New estimates of the metamorphic temperature (850–900°C according to the melting reactions of phengite and the dumortierite field of stability; about 1000°C by the reintegrated composition of feldspar–mesoperthite) that affected the HP parageneses of Salma eclogitized rocks are at least 50–100°C (or even more) higher than them estimated earlier.
相似文献2.
A. V. Volkov A. A. Sidorov K. Yu. Murashov N. V. Sidorova 《Russian Journal of Pacific Geology》2016,10(5):386-394
The enrichment of gold–quartz ores from the Rodionovskoe deposit in chalcophile elements (Au, Ag, As, Sb) is established. The ores are characterized by small negative Eu anomalies and low REE contents, which are typical of magmatic fluids. Slight enrichment of ores in Bi is evidence of the possible involvement of magmatic fluid in ore formation, which may have been superimposed on early metamorphic quartz veins and veinlets. The variously oriented REE patterns also indicate the presence of another magmatic fluid source, which could be related to the post-ore granitic intrusion. These results generally confirm the metamorphic–magmatic model of the formation of the gold–quartz deposits of the Yana–Kolyma belt. Our data are of practical interest for regional metallogenic forecasts, search, and evaluation of gold deposits. 相似文献
3.
The southern Tien Shan metallogenic province of Central Asia hosts a number of important gold resources including the Jilau
gold–quartz vein system in western Tajikistan. These deposits were formed at the late stages of continent–continent collision
in association with subduction-related magmatism, metamorphism and continental margin deformation attributed to the Central
Asian Hercynian Orogeny. Jilau is hosted by a Hercynian syntectonic granitoid intrusive that was emplaced into bituminous
dolomite country rocks. Economic mineralisation is associated with a dilational jog within a high-angle, oblique dextral-reverse
slip shear zone that was undergoing brittle–ductile deformation. The orebody takes the form of shear-zone subparallel quartz
veins and lenses that emanate from a steeply plunging ore shoot of veins and stringers within a silicified and sulphidised
granodiorite core. It is thought to have formed by a dynamic process in which fluid flow was governed by a fault-valve mechanism.
Numerous cycles of fluid pressure build-up, fault failure, jog dilation, fluid flow, phase separation of low salinity H2O–CO2–CH4(–N2) fluids, and sealing took place. Gold appears together with scheelite and bismuth minerals predominantly as inclusions in
arsenopyrite in quartz veins and altered wall-rock, and is mainly associated with quartz containing fluid inclusions enriched
in CH4. The correlation between high gold grades and high CH4 concentrations suggests that components of the mineralising fluids were derived from, or passed through, the reducing, carbonaceous
rocks in the contact aureole of the intrusive. The occurrence of Au and W in an adjacent Hercynian skarn deposit and in the
Jilau orebody, infers that the ore metals in both these systems were ultimately derived from a magmatic source.
Received: 15 April 1999 / Accepted: 30 December 1999 相似文献
4.
A. V. Volkov V. Yu. Prokofiev E. E. Tyukova V. A. Sidorov K. Yu. Murashov N. V. Sidorova M. A. Zemskova 《Geology of Ore Deposits》2017,59(2):112-130
This paper is focused on the new data for geology, mineralogy, and geochemistry of stockworks consisting of steep and gentle quartz veins and veinlets forming a complex multilevel structure at the Rodion deposit. These stockworks range from 25 to 150 m in thickness. Average gold grade is 1.8 g/t. Ore minerals pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, and native gold are predominantly concentrated on the vein and veinlet walls. Thermal metamorphism caused by the intrusion of the Ulakhan granodiorite pluton is the important singularity of the deposit. The deposit ore is enriched in chalcophile microelements Au, Ag, As, Sb, Cu, Pb, Zn, and Bi as compared to the average composition of the upper crust and hosting Permian sequences. The enrichment factors range from a few to hundreds of times. Bi, W, Pb, Ag, and Na2O are positively correlated between each other and with Au. The highest correlation coefficient 0.59 is between Au and Bi. Au is negatively correlated with Ba, Li, Co, Ni, Mn, Ti, and Be. The stockwork ores were formed involving homogeneous low-saline (9.4–4.3 wt % NaCl equiv) substantially aqueous bicarbonate-chloride fluid at 275–330°C and 300–1840 bar fluid pressure. Fluid has a high concentration of CO2 (up to 349 g/kg of water) and is reductive (СО2/СН4 = 17–37.3). Na and Ca are the major cations in the fluid, whereas K and Mg are minor. In addition, many microelements were detected in the fluid: As, Li, Rb, Cs, Mo, Ag, Sb, Cu, Zn, Cd, Pb, U, Ga, Ge, Ti, Mn, Fe, Co, Ni, V, Cr, Y, Zr, Sn, Ba, W, Au, Hg, and REE. The results obtained are consistent with the metamorphic–magmatic formation model of orogenic gold–quartz deposits within the Yana–Kolyma belt. 相似文献
5.
Quartz Crystallographic Preferred Orientation (CPO) patterns are most commonly a result of deformation by dislocation creep. We investigated whether Dissolution–Precipitation Creep (DPC), a process that occurs at lower differential stresses and temperatures, may result in CPO in quartz. The Purgatory Conglomerate is part of the SE Narragansett basin where strain intensity increases from west to east and is associated with top-to-the-west transport and folding during the Alleghanian orogeny. Within the Purgatory Conglomerate, DPC led to quartz dissolution along cobble surfaces perpendicular to the shortening direction, and quartz precipitation in overgrowths at the ends of the cobbles (strain shadows), parallel to the maximum extension direction. Quartz c-axis orientations as revealed by Electron Backscatter Diffraction (EBSD) methods were random in all analyzed domains within the cobbles and strain shadows irrespective of the intensity of strain or metamorphic grade of the sample. Quartz dissolution probably occurred exclusively along the cobbles' margins, leaving the remaining grains unaffected by DPC. The fact that quartz precipitated in random orientations may indicate that the strain shadows were regions of little or no differential stress. 相似文献
6.
7.
V. V. Aristov I. I. Babarina A. V. Grigor’eva V. Yu. Alekseev V. Yu. Prokof’ev A. A. Uzyunkoyan O. V. Zabolotskaya S. G. Titov 《Geology of Ore Deposits》2017,59(1):68-101
Gold deposits and occurrences small in reserves and high in Au grade conventionally determine the line of prospecting in terrigenous sequences of the Verkhoyansk–Kolyma region. In this paper, the geological structure of such gold objects is considered with the example of the deposits and prospects making up the Zhdaninsky ore–placer cluster in the Republic of Sakha (Yakuia). From lithological, structural, and mineralogical–geochemical data, the formation conditions of ore-bearing complexes are specified, the geological evolution history of the northern Ol’chan Zone of the Kular–Nera Belt is reconstructed, and the zonal distribution of mineralization within the ore–placer cluster is revealed. The structural–compositional complexes were formed in the following succession: (1) sedimentation at the shelf of the passive margin accompanied by synsedimentation deformations; (2) metagenesis of sediments and the development of bedding-plane intraformational detachments of collision stage D1 under conditions of tangential compression and accompanied by the formation of carbon dioxide–aqueous metamorphic fluid at a temperature of 300°C and under a pressure of 1.4 kbar; (3) folding and faulting of orogenic stage D2 with the formation of synkinematic magmatic bodies, metasomatic alteration, and Au-bearig mineral assemblages. Small Au-bearing objects with veined mineralization and high Au grade are localized in structures of stage D2 transverse to bedding-plane schistosity S1. They form at the collision stage above intraformational detachment surfaces and are controlled by shear structures of the orogenic stage with misalignment of these deformations. The ore zoning is determined by the distribution of Co and Ni minerals and by variations in the anionic composition of ore (S, As, Sb). 相似文献
8.
Thorsten Beitter Thomas Wagner Gregor Markl 《Contributions to Mineralogy and Petrology》2008,156(6):689-707
In this study, we have investigated the formation of quartz–kyanite veins of the Alpe Sponda, Central Alps, Switzerland. We
have integrated field observations, fluid inclusion and stable isotope data and combined this with numerical geochemical modeling
to constrain the chemical processes of aluminum transport and deposition. The estimated P–T conditions of the quartz–kyanite
veins, based on conventional geothermometry (garnet–biotite, white mica solvus and quartz–kyanite oxygen isotope thermometry)
and fluid inclusion data, are 550 ± 30°C at 5.0 ± 0.5 kbar. Geochemical modeling involved construction of aqueous species
predominance diagrams, calculation of kyanite and quartz solubility, and reaction–path simulations. The results of the modeling
demonstrate that (1) for the given chemical composition of the vein-forming fluids mixed Al–Si aqueous species are dominant
in transporting Al, and that (2) fluid cooling along a small temperature gradient coupled with a pH decrease is able to explain
the precipitation of the quartz–kyanite assemblages in the proportions that are observed in the Alpe Sponda veins. We conclude
that sufficient amounts of Al can be transported in typical medium- to high-grade regional metamorphic fluids and that immobile
behavior of Al is not very likely in advection–dominanted fluid–rock systems in the upper and middle crust. 相似文献
9.
A. V. Volkov A. A. Sidorov N. E. Savva E. E. Kolova K. Yu. Murashov N. V. Sidorova 《Doklady Earth Sciences》2016,470(1):933-937
The main task of this study was to reveal geochemical and distinctive features of gold–quartz vein ores of deposits in granitoid intrusive bodies and in terrigenous black-schist masses of the Yana-Kolyma folded belt. The results obtained point to the significant role of metamorphism of the enclosing terrigenous carbonaceous masses in ore formation of both types of deposits. The established facts are not contradictory to the metamorphic–magmagene model of the formation of gold deposits in the Yana–Kolyma belt. The geochemical similarity of both types of deposits shows that these are products of the same orogenic system, which confirms the validity of combining these deposits to form a unified gold–quartz formation. 相似文献
10.
The incorporation of OH defects in quartz from the systems quartz–water, quartz–albite–water and granite–water at pressures between 5 and 25?kbar and temperatures between 800 and 1,000?°C was investigated by IR spectroscopy. The two most important OH absorption features can be assigned to hydrogarnet defects (absorption band at 3,585?cm?1) and coupled substitutions involving Al3+ (Al–H defects, absorption bands at 3,310, 3,378 and 3,430?cm?1). Al incorporation in quartz is controlled by mineral/melt partitioning (D Al Qz/Melt ?=?0.01) and exhibits a negative pressure dependence. This trend is not clearly reflected by the concentration of Al–H defects, which shows positive deviations from the theoretical 1:1 correlation of Al/H for some samples. In contrast to the Al–H defects, formation of hydrogarnet defects appears to be positively correlated to pressure and water activity, and may be used a petrological indicator. The overall water concentration exhibits only minor changes with pressure and temperature, but a clear correlation of water activity (controlled by various amounts of dissolved salts) and hydrogarnet substitution could be established. 相似文献
11.
Werner Schreyer André-Mathieu Fransolet Heinz-Jürgen Bernhardt 《Contributions to Mineralogy and Petrology》2001,141(5):560-571
In a newly found type of quartz vein cross-cutting the famous "viridine"-bearing phyllites at Le Coreux, hollandite, ideally BaMn8O16, was discovered for the first time at this locality and in Belgium. Because the crystals contain up to 60 mol% of the Sr end member, this is also the second occurrence of strontiomelane. The coexisting "viridine" (= kanonaite) contains the highest amount (88 mol%) of the ideal end member MnAlSiO5 ever found worldwide. The hollandite-type minerals are intimately intergrown with braunite containing appreciable Ca and Mg. Ba-bearing muscovite, Fe-poor excess-Al clinochlore (not quite trioctahedral), and albite are the remaining accessory minerals in the dominant quartz matrix. Microprobe analyses of all phases show rather extreme element fractionations: nearly all K is located in muscovite and none in the hollandite phase despite the existence of the end member KMn8O16 (cryptomelane). Similarly, nearly all Na is in albite and not in hollandite (no NaMn8O16=manjiroite component). Nearly all Mn resides in the two oxide phases and in kanonaite. Mg is strongly fractionated into chlorite. The small amounts of Fe and Ti present are predominantly partitioned into the hollandite phase, which also accommodates most of the Ba and Sr. Indeed, the hollandite phase is stabilized by the latter two elements relative to other Mn oxides. Kanonaite is stabilized by Al. Although no requisite sites are available in its crystal structure, braunite always contains small amounts of Ba and Sr. However, the Sr/(Sr+Ba) ratios in braunite are spurious and unrelated to those of the directly adjoining hollandite phases The conditions of formation of these veins may be well below 300 °C at low pressures (1-2 kbar), in agreement with the experimental results that the maximum Mn contents in kanonaite increase with falling temperatures. 相似文献
12.
The Pb–Zn–Ag quartz vein from Terramonte cuts the Neoproterozoic–Cambrian schist–greywacke complex. This orebody was partially exploited. The paragenetic sequence consists of four stages containing quartz accompanied mainly by arsenopyrite and pyrite in the first stage, sphalerite in the second stage, galena showing many inclusions of several sulphosalts in the third stage and carbonates in the fourth remobilization stage. Several sulphide and sulphosalt grains are oscillatory zoned. The chemical distinction between lighter and darker zones in backscattered images of arsenopyrite, pyrite, sphalerite and freibergite is due to substitutions in the mineral lattices. But the distinction between these zones in semseyite is due to a higher Pb content and a lower Sb content in the lighter zone than in the darker zone and the metal and metalloid are the main constituents in the solid solution, but are not correlated. The Sb, Ag and Bi substitute for Pb in galena, but did not cause any zoning. Ore deposition was possible due to mixing of a hypersaline fluid with up to 26 wt.% NaCl equivalent (and occasionally with CaCl2 up to 17 wt.%), which carried the metallic content of the fluid, with an extremely low salinity fluid of presumed meteoric origin that percolated down into the basement. The metals could have been leached from a mixture of mainly metasediments and also previous Sb–Au deposits by fluids that acquire high salinity in one of two probable ways: leaching of salt beds or following seawater evaporation. The entire mineralizing event probably occurred at a relatively low temperature, possibly between 120 and 230 °C. Remobilization of Pb, Zn, Ag, As, Sb and Cu will be due to the tectonic evolution of the opening of the Atlantic Ocean. This vein is probably of Alpine age. 相似文献
13.
14.
V. B. Savelyeva E. P. Bazarova V. V. Sharygin N. S. Karmanov 《Geology of Ore Deposits》2015,57(8):645-656
Fine-grained segregations up to 5 mm in size composed of graphic intergrowths of zircon, quartz, calcite and containing up to 0.8 wt % SrO have been found in albite–riebeckite and dolomite–biotite metasomatic rocks formed after alaskite granite. They contain magnetite, titanomagnetite (25.4 wt % TiO2), cerite-(Ce,Nd), rutile (up to 1.2 wt % Nb2O5), as well as rare micrograins of monazite-(Ce), bastnaesite-(Ce), and barite (up to 5.7 wt % SrO). The fine-grained structure of mineral aggregates suggests a metacolloidal nature. It is assumed that the zircon–quartz–calcite assemblage was formed due to exchange decomposition reaction between the salt phase of hydrothermal solution with predominant Na2CO3, elevated Zr and, to a lesser extent, Fe, Ti, LREE, Nb contents and dissolved calcium and silica compounds of a Na2SiO3 type. 相似文献
15.
《International Geology Review》2012,54(12):1435-1449
Recent research has identified an early to late Carboniferous magmatic arc that extends from Suzuo Qi to Xiwu Qi in Inner Mongolia, China, but the eastern extension of this arc is unknown. Understanding the relationship between this arc and the Hegenshan ophiolite belt and Xilamulun Solonker suture zone is important to our understanding of the tectonic evolution of the late Palaeozoic Palaeo-Asian Ocean. Here, we present new zircon laser ablation–inductively coupled plasma mass spectrometry U–Pb and geochemical data for the Maoliger quartz monzodiorites within the Jalaid Qi area. The Maoliger quartz monzodiorites formed at 329 ± 2 Ma, are low-K and tholeiitic, and have geochemical signatures indicative of formation within a magmatic arc. These rocks are large-ion lithophile element (e.g. Rb, Ba, and Sr)-enriched and high-field-strength element (e.g. Nb and Ta)-depleted. Combined with previously published researches, it is suggested that the quartz monzodiorites within the Jalaid Qi area formed contemporaneously with and are geochemically similar to quartz diorites of the Xiwu Qi area and the Baolidao pluton in the Suzuo Qi area. This indicates that the early to late Carboniferous magmatic arc in this region extends eastward to the Jalaid Qi area. This arc is located in an area parallel to a southerly early Permian magmatic arc, suggesting that the Palaeo-Asian Ocean subduction zone migrated south between the early Carboniferous and early Permian. The new data show that the Palaeo-Asian Ocean closed after the late Carboniferous. 相似文献
16.
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+/Fetot value and Li content in the average sample are 2% and 80 ppm, respectively. The high F content, comparatively high Li, low
Fe3+/Fetot 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. 相似文献
17.
18.
Quartz–amphibole–pyroxene gneiss from the island of Akilia, Southwest Greenland has been claimed to contain the earliest traces
of life on Earth in the form of biogenic carbonaceous matter encapsulated as inclusions in apatite crystals. Various lines
of evidence, including petrography, geochronology, field relations, and geochemistry, have, however, been presented that challenge
this interpretation. Textural relationships and geochemical signatures in this controversial gneiss presented here manifest
a complex, spatially variable metamorphic history that includes granulite- and amphibolite-facies overprints and metasomatism.
A peak metamorphic, granulite-facies, quartz–orthopyroxene–clinopyroxene–amphibole–magnetite assemblage is preserved in only
a few centimeter-scale layers within the 5-m-thick, quartz–amphibole–pyroxene gneiss unit. Calcite veinlets that appear to
postdate the peak metamorphism occur in pyroxene. The quartz–amphibole–pyroxene gneiss unit has subsequently experienced isochemical
(except hydration) amphibolite-facies alteration during which pyroxenes were retrogressed to amphiboles and magnetite, and
calcite was consumed. Parts of the quartz–amphibole–pyroxene gneiss that contain texturally late hornblende have experienced
metasomatic alteration by Al-carrying fluids. These fluids controlled the alteration of pyroxenes and amphiboles to hornblende,
and modified the trace-element composition by remobilizing LREE and Eu. Apatite has variable REE composition and 87Sr/86Sr in the quartz–amphibole–pyroxene gneiss, but on the local scale (cm) is in equilibrium with co-existing silicates. Effective
recrystallization of apatite crystals as well as co-existing silicates during several stages of the metamorphic history makes
the intact preservation of diagenetic apatite with encapsulated primary carbonaceous matter implausible. Hence, it is highly
unlikely that Akilia apatite could serve as repository of the earliest traces of life on Earth. 相似文献
19.
S. D. Velikoslavinskii A. B. Kotov E. B. Sal’nikova A. B. Kuznetsov V. P. Kovach N. V. Popov E. V. Tolmacheva I. V. Anisimova Yu. V. Plotkina 《Doklady Earth Sciences》2018,482(2):1265-1269
New U–Pb zircon (TIMS) results allow dating of protoliths of tonalite–trondhjemite orthogneisses of the Olekma Complex in the central part of the Chara–Olekma Geoblock (Aldan Shield) to 2825 ± 3 Ma and 2994 ± 3 Ma. Together with the results of previous geochronological studies, this proves that the Olekma Complex comprises heterochronous igneous rocks intensively reworked under amphibolite facies conditions and formed during different stages of geological evolution of the Aldan Shield. 相似文献
20.
Prakash Abhishek Piazolo Sandra Saha Lopamudra Bhattacharya Abhijit Pal Durgesh Kumar Sarkar Saheli 《International Journal of Earth Sciences》2018,107(6):2265-2292
International Journal of Earth Sciences - In the present study we investigate the microstructural development in mullite, quartz and garnet in an anatectic migmatite hosted within a Grenvillian-age... 相似文献