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1.
Cihai and Cinan are Permian magnetite deposits related to mafic-ultramafic intrusions in the Beishan region, Xinjiang, NW China. The Cihai mafic intrusion is dominantly composed of dolerite, gabbro and fine-grained massive magnetite ore, while gabbro, pyrrhotite + pyrite-bearing clinopyroxenite and magnetite ore comprise the major units in Cinan. Clinopyroxene occurs in both deposits as 0.1–2 mm in diameter subhedral to anhedral grains in dolerite, gabbro and clinopyroxenite. High FeO contents (11.7–28.9 wt%), low SiO2 (43.6–54.3 wt%) and Al2O3 contents (0.15–6.08 wt%), and low total REE and trace element contents of clinopyroxene in the Cinan clinopyroxenite imply crystallization early, at high pressure. This clinopyroxene is FeO-rich and Si and Ti-poor, consistent with the clinopyroxene component of large-scale Cu-Ni sulfide deposits in the Eastern Tianshan and Panxi ares, as well as Tarim mafic intrusion and basalt, implying the Cinan mafic intrusion and sulfide is related to tectonic activity in the Tarim LIP. The similar mineral chemistry of clinopyroxene, apatite and magnetite in the Cihai and Cinan gabbros (e.g., depleted LREE, negative Zr, Hf, Nb and Ta anomalies in clinopyroxene, lack of Eu anomaly in apatite and similarity of oxygen fugacity as indicated by V in magnetite), indicate similar parental magmatic characteristics. Mineral compositions suggest a crystallization sequence of clinopyroxenite/with a small amount of sulfide – gabbro – magnetite ore in the Cinan deposit, and magnetite ore – gabbro – dolerite in Cihai. The basaltic magma was emplaced at depth, with magnetite segregation (and formation of the Cinan magnetite ores) occurring in relatively low fO2 conditions, after clinopyroxenite and gabbro fractional crystallization. The evolved Fe-rich basaltic magma rapidly rose to intermediate or shallow depths, forming an immiscible Fe-Ti oxide magma as fO2 increased and leaving a Fe-poor residual magma in the chamber. The residual magmas was emplaced at different levels in the crust, forming the Cihai gabbro and dolerite, respectively. Finally, the immiscible Fe-Ti oxide magma was emplaced into the earlier formed dolerite because of late magma pulse uplift, resulting in a distinct boundary between the magnetite ores and dolerite. 相似文献
2.
The Xinjie layered intrusion in the Panxi region,SW China,hosts both Fe-Ti oxide and platinum-group element（PGE） sulfide mineralization.The intrusion can be divided,from the base upward,into UnitsⅠ,ⅡandⅢ,in terms of mineral assemblages.UnitsⅠandⅡare mainly composed of wehrlite and clino-pyroxenite, whereas UnitⅢis mainly composed of gabbro.PGE sulfide-rich layers mainly occur in Unit I, whereas thick Fe-Ti oxide-rich layers mainly occur in UnitⅢ.An ilmenite-rich layer occurs at the top of UnitⅠ.Fe-Ti oxides include magnetite and ilmenite.Small amounts of cumulus and intercumulus magnetite occur in UnitsⅠandⅡ.Cumulus magnetite grains are commonly euhedral and enclosed within olivine and clinopyroxene.They have high Cr2O3 contents ranging from 6.02 to 22.5 wt.%,indicating that they are likely an early crystallized phase from magmas.Intercumulus magnetite that usually displays ilmenite exsolution occupies the interstices between cumulus olivine crystals and coexists with interstitial clinopyroxene and plagioclase.Intercumulus magnetite has Cr2O3 ranging from 1.65 to 6.18 wt.%, lower than cumulus magnetite.The intercumulus magnetite may have crystallized from the trapped liquid.Large amounts of magnetite in UnitⅢcontains Cr2O3（<0.28 wt.%） much lower than magnetite in UnitsⅠandⅡ.The magnetite in UnitⅢis proposed to be accumulated from a Fe-Ti-rich melt.The Fe-Ti-rich melt is estimated to contain 35.9 wt.%of SiO2,26.9 wt.%of FeOt,8.2 wt.%of TiO2,13.2 wt.%of CaO, 8.3 wt.%of MgO,5.5 wt.%of Al2O3 and 1.0 wt.%of P2O5.The composition is comparable with the Fe-rich melts in the Skaergaard and Sept Iles intrusions.Paired non-reactive microstructures,granophyre pockets and ilmenite-rich intergrowths,are representative of Si-rich melt and Fe-Ti-rich melt,and are the direct evidence for the existence of an immiscible Fe-Ti-rich melt that formed from an evolved ferro-basaltic magma. 相似文献
3.
Compositions of immiscible liquids in volcanic rocks 总被引：8，自引：5，他引：8
A. R. Philpotts 《Contributions to Mineralogy and Petrology》1982,80(3):201-218
Immiscible liquids, preserved as chemically distinct, glassy globules, (Si-rich and Fe-rich) occur in many tholeiitic basalts and some alkaline and calcalkaline lavas. The glasses typically form part of a dark mesostasis containing skeletal magnetite crystals. In thick flows, the Si-rich liquid may crystallize to granophyric patches, and the Ferich one to aggregates of hedenbergite, magnetite, and accessory phases. The mesostases containing these immiscible phases constitute from 20% of a primitive olivine tholeiite (MgO=7.5%) to 50% of a highly fractionated quartz tholeiite (MgO=2.8%), but may be less if the rock is oxidized. Abundant ferric iron promotes early crystallization of magnetite and prevents the iron enrichment necessary to reach the immiscibility field; thus, aa flows rarely exhibit immiscibility, whereas the more reduced pahoehoe ones do.Alumina and alkalis are concentrated in the Si-rich liquid, whereas the remainder of the major elements are concentrated in the Fe-rich melt; but the partitioning of Fe, Mg, Ca, and P is less pronounced in alkaline rocks than in tholeiites. Conjugate liquids have compositions of granite and Fe-rich pyroxenite, though the Si-rich melt in alkaline rocks is more syenitic and the Fe-rich one contains considerable normative alkali feldspar. The liquids coexist with plagioclase and augite of, respectively, An50 and Ca34Mg19Fe47 compositions in tholeiites, and An40 and Ca42Mg29Fe29 in alkaline rocks. Immiscibility is not restricted to K-rich residual liquids, but the miscibility gap is narrower for Na-rich compositions. In tholeiitic basalts with 52% SiO2, the Na2O/K2O ratios in conjugate liquids are equal, but at lower silica contents the Si-rich liquid is relatively more sodic, whereas at higher silica contents it is relatively more potassic. This may explain the association of sodic granites with mid ocean ridge basalts.Immiscible liquids are present in sufficient amounts in so many volcanic rocks that magma unmixing should be considered a viable means of differentiation during the late stages of fractionation of common magmas, at least at low pressures. 相似文献
4.
通过龙游晚中生代基性岩岩相学观察、全岩主量、微量元素和Sr-Nd同位素及矿物电子探针分析,对岩石成因、岩浆演化和构造环境进行探讨。龙游基性岩岩性为橄榄辉长岩,Sr-Nd同位素显示为幔源特征;主量、微量元素特征显示其经历了以橄榄石、辉石为主的分离结晶作用,且未发生明显的地壳物质混染。橄榄石颗粒具核-边结构,富Mg贫Fe的核部Fo值为90.1～91.8,指示原始岩浆是软流圈地幔,富Fe贫Mg的边部显示橄榄石Fo值为77.4～85.3,且核-边两部分的Fo值相差较大,显示原始橄榄石形成之后受到地幔熔体/流体的交代作用。辉石斑晶大多属于透辉石,在部分斑晶的边部发育少量霓辉石。透辉石斑晶普遍具有核-幔-边结构,从核部到边部的SiO_2含量降低,TiO_2、Al_2O_3含量升高,结晶温度升高,显示原始辉石形成之后受到温度更高的地幔熔体/流体的交代作用。研究认为,古太平洋板块后撤造成岩石圈地幔拉伸作用并形成赣杭构造带深部断裂后,部分软流圈物质受到地幔流体/熔体的交代作用,并沿这些深部断裂向上侵位,经历了以橄榄石和辉石矿物为主的分离结晶作用和微弱的地壳物质混染,最终形成龙游橄榄辉长岩。 相似文献
5.
The effect of iron on montmorillonite stability. (I) Background and thermodynamic considerations 总被引：1，自引：0，他引：1
It is envisaged that high-level nuclear waste (HLW) will be disposed of in underground repositories. Many proposed repository designs include steel waste canisters and bentonite backfill. Natural analogues and experimental data indicate that the montmorillonite component of the backfill could react with steel corrosion products to produce non-swelling Fe-rich phyllosilicates such as chamosite, berthierine, or Fe-rich smectite. In K-bearing systems, the alteration of montmorillonite to illite/glauconite could also be envisaged. If montmorillonite were altered to non-swelling minerals, the swelling capacity and self-healing properties of the bentonite backfill could be reduced, thereby diminishing backfill performance. The main aim of this paper was to investigate Fe-rich phyllosilicate mineral stability at the canister-backfill interface using thermodynamic modelling. Estimates of thermodynamic properties were made for Fe-rich clay minerals in order to construct approximate phase-relations for end-member/simplified mineral compositions in logarithmic activity space. Logarithmic activity diagrams (for the system Al2O3-FeO-Fe2O3-MgO-Na2O-SiO2-H2O) suggest that if pore waters are supersaturated with respect to magnetite in HLW repositories, Fe(II)-rich saponite is the most likely montmorillonite alteration product (if fO2(g) values are significantly lower than magnetite-hematite equilibrium). Therefore, the alteration of montmorillonite may not be detrimental to nuclear waste repositories that include Fe, as long as the swelling behaviour of the Fe-rich smectite produced is maintained. If fO2(g) exceeds magnetite-hematite equilibrium, and solutions are saturated with respect to magnetite in HLW repositories, berthierine is likely to be more stable than smectite minerals. The alteration of montmorillonite to berthierine could be detrimental to the performance of HLW repositories. 相似文献
6.
Blue Mountain is a central-type alkali ultrabasic-gabbro ringcomplex (lxl7middot;5 km) introducing Upper Jurassic sediments,Marlborough, New Zealand. The ultrabasic-gabbroic rocks containlenses of kaersutite pegmatite and sodic syenite pegmatite andare intruded by ring dykes of titanaugite-ilmenite gabbro andlamprophyre. The margin of the intrusion is defined by a ringdyke of alkali gabbro. The plutonic rocks are cut by a swarmof hornblendebiotite-rich lamprophyre dykes. Thermal metamorphismhas converted the sediments to a hornfels ranging in grade fromthe albite-epidote hornfels facies to the upper limit of thehornblende hornfels facies. The rocks are nepheline normative and consist of olivine (Fo82–74),endiopside (Ca45Mg48Fe7–Ca36Mg55Fe9), titanaugite (Ca40Mg50Fe10–Ca44Mg39Fe17),plagioclase (An73–18), and ilmenitetitaniferous magnetite,with various amounts of titaniferous hornblende and titanbiotite.There is a complete gradation between endiopside and titanaugitewith the coupled substitution Ry+2+Si;;(Ti+4+Fe+3+Al+3 and asympathetic increase in CaAl2SiO6 (0·2–10·2percent) and CaTiAl2O6 (2·1–8·1 per cent)with fractionation. Endiopside shows a small, progressive Mgenrichment along a trend subparallel to the CaMgSi2O6–Mg2Si2O6boundary, and titanaugite is enriched in Ca and Fe+2+Fe+3 withdifferentiation. Oscillatory zoning between endiopside and titanaugiteis common. Exsolved ilmenite needles occur in the most Fe-richtitanaugites. The amphiboles show the trend: titaniferous hornblende(1·0–57middot;7 per cent TiO2) kaersutite (6·4per cent TiO2) Fe-rich hastingsite (18·0–19·1per cent FeO as total Fe). Biotite is high in TiO2 (6·6–7·8per cent). Ilmenite and titaniferous magnetite (3·5–10·6per cent TiO2) are typically homogeneous grains; their compositioncan be expressed in terms of R+2RO3:R+2O:R2+3O4. The intrusion of igneous rocks was probably controlled by subterraneanring fracturing. Subsidence of the country rock within the ringfracture provided space for periodic injections of magma froma lower reservoir up the initial ring fracture to form the BlueMountain rocks at a higher level. Downward movement of the floorof the intrusion during crystallization caused inward slumpingof the cumulates which affected the textural, mineralogical,and chemical evolution of the rocks in different parts of theintrusion. The order of mineral fractionation is reflected by the chemicalvariation in the in situ ultrabasic-gabbroic rocks and the successiveintrusions of titanaugite-ilmenite gabbro and lamprophyre ringdykes, marginal alkali gabbro and lamprophyre dyke swarm. Aninitial decrease, then increase in SiO2; a steady decrease inMgO, CaO, Ni, and Cr: an initial increase, then decrease inFeO+Fe2O3, TiO2, MnO, and V; almost linear increase in A12O3and late stage increase in alkalis and P2O3, implies fractionationof olivine and endiopside, followed by titanaugite and Fe-Tioxides, followed by plagioclase, hornblende, biotite, and apatite.Reversals in the composition of cumulus olivine and endiopsideand Solidification Index, indicate that the ultrabasic-gabbroicsequence is composed of four main injections of magma. The ultrabasic rocks crystallized under conditions of high PH2Oand fairly high, constant 相似文献
7.
A critical study of 311 published WR chemical analyses, isotopic and mineral chemistry of anorthosites and associated rocks
from eight Proterozoic massif anorthosite complexes of India, North America and Norway indicates marked similarities in mineralogy
and chemistry among similar rock types. The anorthosite and mafic-leucomafic rocks (e.g., leuconorite, leucogabbro, leucotroctolite,
anorthositic gabbro, gabbroic anorthosite, etc.) constituting the major part of the massifs are characterized by higher Na2O + K2O, Al2O3, SiO2, Mg# and Sr contents, low in plagioclase incompatible elements and REE with positive Eu anomalies. Their δ
18O‰ (5.7–7.5), initial 87Sr/86Sr (0.7034–0.7066) and ɛ
Nd values (+1.14 to +5.5) suggest a depleted mantle origin. The Fe-rich dioritic rocks occurring at the margin of massifs have
isotopic, chemical and mineral composition more close to anorthosite-mafic-leucomafic rocks. However, there is a gradual decrease
in plagioclase content, An content of plagioclase and XMg of orthopyroxene, and an increase in mafic silicates, oxide minerals content, plagioclase incompatible elements and REE from
anorthosite-mafic-leucomafic rocks to Fe-rich dioritic rocks. The Fe-rich dioritic rocks are interpreted as residual melt
from mantle derived high-Al gabbro melt, which produced the anorthosite and mafic-leucomafic rocks. Mineralogically and chemically,
the K-rich felsic rocks are distinct from anorthosite-mafic-leucomafic-Fe-rich dioritic suite. They have higher δ
18O values (6.8–10.8‰) and initial 87Sr/86Sr (0.7067–0.7104). By contrast, the K-rich felsic suites are products of melting of crustal precursors. 相似文献
8.
攀枝花岩体钛铁矿成分特征及其成因意义 总被引：2，自引：1，他引：1
峨眉大火成岩省是全球最大的钒钛磁铁矿床聚集区,攀枝花岩体是其中的典型代表。根据岩性特点,攀枝花岩体主体可划分为上、中、下三个岩相带,其中中部岩相带和下部岩相带岩性旋回非常发育,每个旋回从下向上铁钛氧化物和暗色硅酸盐矿物逐渐减少,块状铁钛氧化物矿石或磁铁矿辉长岩都出现在每个旋回的底部和下部。然而,尽管钛铁矿固相线以下固溶体出溶远弱于磁铁矿,从而能更好地保留成因信息,但其成分变化的成因意义没有受到足够重视。本次研究发现作为主要金属氧化物之一的钛铁矿的成分不仅在不同岩性中有明显差异,同时,中、下部岩相带的各岩性旋回中钛铁矿成分也具有周期性变化。例如,块状矿石中钛铁矿具有最高的MgO和TiO2及最低的FeO、Fe2O3和MnO,而辉长岩中钛铁矿则具有相反的成分特征。同时,钛铁矿的MgO含量与磁铁矿的MgO含量及橄榄石的Fo牌号具有显著的正相关关系。这种规律性变化说明每个旋回可以代表一次比较明显的岩浆补充,每次新岩浆补充后,钛铁矿和磁铁矿及橄榄石都是结晶较早的矿物。与Skaergaard岩体相比,攀枝花岩体钛铁矿的MgO含量较高,表明攀枝花岩体分离结晶过程中铁钛氧化物结晶较早;与挪威Tellnes斜长岩套铁钛矿床中的钛铁矿相比,攀枝花岩体的钛铁矿不仅具有较高的MgO和FeO,还具有极高的TiO2和MnO,但Fe2O3却很低,说明地幔柱背景下形成的钛铁矿与斜长岩套中钛铁矿的成分有显著的区别。 相似文献
9.
Exsolutions of Diopside and Magnetite in Olivine from Mantle Dunite, Luobusa Ophiolite, Tibet, China 总被引：1，自引：0，他引：1
The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%） ＋ chromite （1%-4%） ＋ diopside （〈1%）. Two types of olivine are found in thin sections： one （Fo = 94） is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other （Fo = 96） is fine-grained and poly-angied. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system （EDS） with unitary analytical method, the average compositions of the inclusions are： Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3, 9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%- 5.27%, which is quite similar to those of amphibole. Diopside is anhedral f＇dling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines, sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and A! and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAI2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na^＋, Al^3＋, Ca^2＋, Fe^3＋, Cr^3＋. With temperature d 相似文献
10.
S. A. Novikova 《Geology of Ore Deposits》2009,51(8):800-811
Fayalite is a common mineral of Fe-rich paralavas related to spontaneous combustion of coal seams. Fayalite has also been
found in parabasalts from burned coal waste piles of the Chelyabinsk coal basin. Among paralavas from different combustion
metamorphic (CM) complexes of the world, fayalite is the most widespread in the fused rocks of the Kuznetsk coal basin (Kuzbass)
and the Ravat area in Tajikistan. The optimal conditions for fayalite formation as products of coal fires in the Kuzbass and
Ravat resulted from a favorable combination of the composition of fused protolith (parental rocks) composed of pelitic and
Fe-rich sediments and the redox conditions of the deep subsurface ($
f_{O_2 }
$
f_{O_2 }
is lower than the QFM buffer). In the Kuzbass, fayalite is commonly hosted in high-silica aluminous Fe-rich paralavas composed
of Fe-cordierite (sekaninaite), tridymite, hercynite-magnetite, cristobalite, aluminous clinoferrosilite, and Al-K silicic
glass. The composition of all Kuzbass fayalites is close to the Fe2SiO4 end member. Kuzbass fayalites are characterized by a negligibly low CaO content and higher MnO and P2O5 contents like fayalites from burned rocks of other CM complexes. In Kuzbass paralavas, Fe-olivine is the late phase that
crystallized after sekaninaite and tridymite, immediately before melt quenching. 相似文献
11.
Titanomagnetite–melt partitioning of Mg, Mn, Al, Ti, Sc, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Hf and Ta was investigated experimentally as a function of oxygen fugacity (fO2) and temperature (T) in an andesitic–dacitic bulk-chemical compositional range. In these bulk systems, at constant T, there are strong increases in the titanomagnetite–melt partitioning of the divalent cations (Mg2+, Mn2+, Co2+, Ni2+, Zn2+) and Cu2+/Cu+ with increasing fO2 between 0.2 and 3.7 log units above the fayalite–magnetite–quartz buffer. This is attributed to a coupling between magnetite crystallisation and melt composition. Although melt structure has been invoked to explain the patterns of mineral–melt partitioning of divalent cations, a more rigorous justification of magnetite–melt partitioning can be derived from thermodynamic principles, which accounts for much of the supposed influence ascribed to melt structure. The presence of magnetite-rich spinel in equilibrium with melt over a range of fO2 implies a reciprocal relationship between a(Fe2+O) and a(Fe3+O1.5) in the melt. We show that this relationship accounts for the observed dependence of titanomagnetite–melt partitioning of divalent cations with fO2 in magnetite-rich spinel. As a result of this, titanomagnetite–melt partitioning of divalent cations is indirectly sensitive to changes in fO2 in silicic, but less so in mafic bulk systems. 相似文献
12.
Textural and mineral–chemical characteristics in the Bangriposi wehrlites (Eastern India) provide insight into metamorphic processes that morphologically and chemically modified magmatic spinel during serpentinization of wehrlite. Aluminous chromite included in unaltered magmatic olivine is chemically homogenous. In sub-cm to 10s-of-micron-wide veins, magnetite associated with antigorite and clinochlore comprising the serpentine matrix is near-stoichiometric. But Al–Cr–Fe3+ spinels in the chlorite–magnetite veins are invariably zoned, e.g., chemically homogenous Al-rich chromite interior successively mantled by ferritchromite/Cr-rich magnetite zone and magnetite continuous with vein magnetite in the serpentine matrix. In aluminous chromite, ferritchromite/Cr-rich magnetite zones are symmetrically disposed adjacent to fracture-controlled magnetite veins that are physically continuous with magnetite rim. The morphology of ferritchromite–Cr-rich magnetite mimics the morphology of aluminous chromite interior but is incongruous with the exterior margin of magnetite mantle. Micropores are abundant in magnetite veins, but are fewer in and do not appear to be integral to the adjacent ferritchromite–Cr-rich magnetite zones. Sandwiched between chemically homogenous aluminous chromite interior and magnetite mantle, ferritchromite–Cr-rich magnetite zones show rim-ward decrease in Cr2O3, Al2O3 and MgO and complementary increase in Fe2O3 at constant FeO. In diffusion profiles, Fe2O3–Cr2O3 crossover coincides with Al2O3 decrease to values <0.5 wt% in ferritchromite zone, with Cr2O3 continuing to decrease within magnetite mantle. Following fluid-mediated (hydrous) dissolution of magmatic olivine and olivine + Al–chromite aggregates, antigorite + magnetite and chlorite + magnetite were transported in 10s-of-microns to sub-cm-wide veins and precipitated along porosity networks during serpentinization (T: 550–600 °C, f(O2): ?19 to ?22 log units). These veins acted as conduits for precipitation of magnetite as mantles and veins apophytic in chemically/morphologically modified magmatic Al-rich chromite. Inter-crystalline diffusion induced by chemical gradient at interfaces separating aluminous chromite interiors and magnetite mantles/veins led to the growth of ferritchromite/Cr-rich magnetite zones, mimicking the morphology of chemically modified Al–Cr–Fe–Mg spinel interiors. Inter-crystalline diffusion outlasted fluid-mediated aluminous chromite dissolution, mass transfer and magnetite precipitation. 相似文献
13.
Relatively strongly magnetic fine components (< 30μm, XS-4J and DS-4J) which are most environmentally sensitive were separated from layer S5-1 in the Xifeng and Duanjiapo loess sections and analyzed by MPV-3 for their morphometric characteristics and reflectance, SEM-ESD for their element contents and XRD for their mineral phases, respectively. The results showed that minerals in both samples are dominated by detrial Fe-Ti oxides of aeolian origin. In sample XS-4J the reflectance and iron contents of magnetic minerals are usually high. In addition to magnetite (Fe3O4), maghemite (γFe2O3) and hematite (Fe2O3), some Fe-high oxide (72.25 wt%–86.67 wt%), ilmenite (FeTiO3), and magnetite-ulvöspinel [Fe(FeCr)O4, Fe (FeNi)O4] were also detected. In sample DS-4J obvious negative linear correlations were found between Ti and Fe, and the contents of Mn, Si, Al and Ca are usually high and the minerals are dominated by magnetite (maghemite), goethite (FeOOH) and limonite (containing Si and OH). In addition, the signs of corrosion of magnetic minerals and newly crystallized magnetite (maghemite) were recognized. Differences in the composition and assemblage characteristics of magnetite minerals between XS and DS reflect significant differences in source rocks and preserving conditions. 相似文献
14.
Pertsev A. N. Bortnikov N. S. Prokofiev V. Yu. Aranovich L. Ya. Ageeva O. A. Beltenev V. E. Zhilicheva O. M. Kovalchuk E. V. 《Doklady Earth Sciences》2018,480(1):661-665
New data on local mineral associations and the microheterogeneity of minerals and fluid inclusions in gabbro were obtained for the gabbro–peridotite oceanic core complex with a long-lived detachment fault controlling the hydrothermal activity. It is assumed that the hydrothermal hydrogen-bearing fluid with a NaCl content of >30 wt % is formed in the seawater/harzburgite (~1/5) reaction of serpentinization. The brine residual after serpentinization interacted with gabbro at the final stages of crystallization of an intrusion and assimilated some components (K, REEs, and Ba) from the residual melt. The interaction was resulted in metamorphic transformations of gabbro at decreasing temperature below 500°C. The reaction of the decomposition of magmatic titanomagnetite with the transition of iron reduced to Fe2+ into newly formed chlorinebearing amphibole at 540–450°C and logf(O2) from–20 to–24 is shown.
相似文献15.
《International Geology Review》2012,54(10):911-924
Mineralogy and petrography of six eelogite xenoliths from the Obnazhennaya kimberlite pipe ar e described. Based upon modal and mineral compositions, these eclogites can be divided into Group A (five samples) and Group B (one sample), as per Coleman et al. (1965) and Shervais et al. (1988). Group-A eclogites are orthopyroxene-bearing, and their constituent minerals have high Mg# and Cr2O3 content. The clinopyroxenes in this type of eelogite have low jadeite component. The geochemical features of Group-A eclogites are similar to garnet pyroxenite, and e believed to be the product of high-pressure fractionates from an alkaline basaltic melt in thear upper mantle. Group-B eelogite (0-82/91) contains higher Al2O3 and FeO and lower MgO and Cr2O3; its composition is similar to a high-aluminum basalt or gabbro. This eelogite could have crystallized under high pressure in the upper mantle from a basaltic melt, without significant fractionation. Alternatively, it also could be the relict of subducted oceanic crust. However, no evidence exists at present that definitively indicates a crustal origin for this Group-B eelogite xenolith. 相似文献
16.
Thomas Frisch 《Contributions to Mineralogy and Petrology》1970,28(1):31-41
A gabbro inclusion typical of the gabbroic xenolith suite in alkalic basalts on Lanzarote is composed of essentially four minerals. Olivine (5 vol.%) and plagioclase An81 (60%) were first to crystallize. The olivine, Fo76 with 0.02% CaO, was subsequently subjected to high-temperature oxidation followed by hydrolysis, resulting in its partial alteration to Fo92 and Fe-oxide-hydroxide plus (free?) silica. Clinopyroxene (30%) Ca43Mg46Fe11 has exsolved orthopyroxene Ca1.6Mg76.0Fe22.4 with 2.10% A12O3 in lamellae ∥ {100}. Orthopyroxene (5%) of the same composition also occurs as discrete crystals and petrographic and chemical criteria suggest that it formed by reaction of olivine with melt. The xenolith probably crystallized from a tholeiitic melt at a depth less than 9 km, i.e. above the Moho discontinuity under Lanzarote. The existence of basalts of olivine-tholeiitic chemistry on Lanzarote suggests a source for the gabbro nodules. Separation of calcic plagioclase from a tholeiitic melt may explain the relatively high alkali contents (Na2O+ K2O= 3.2 to 3.7%) of the Lanzarote olivine-tholeiitic basalts. 相似文献
17.
Implication of Apatite and Anhydrite for Formation of an Iron‐Oxide‐Apatite (IOA) Rare Earth Element Prospect,Benjamin River,Canada 
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下载免费PDF全文 The Benjamin River apatite prospect in northern New Brunswick, Canada, is hosted by the Late Silurian Dickie Brook plutonic complex, which is made up of intrusive units represented by monzogranite, diorite and gabbro. The IOA ores, composed mainly of apatite, augite, and magnetite at Benjamin River form pegmatitic pods and lenses in the host igneous rocks, the largest of which is 100 m long and 10–20 m wide in the diorite and gabbro units. In this study, 28 IOA ore and rock samples were collected from the diorite and gabbro units. Mineralogical observations show that the apatite–augite–magnetite ores are variable in the amounts of apatite, augite, and magnetite and are associated with minor amounts of epidote‐group minerals (allanite, REE‐rich epidote and epidte) and trace amounts of albite, titanite, ilmenite, titanomagnetite, pyrite, chlorite, calcite, and quartz. Apatite and augite grains contain small anhydrite inclusions. This suggests that the magma that crystallized apatite and augite had high oxygen fugacity. In back scattered electron (BSE) images, apatite grains in the ores have two zones of different appearance: (i) primary REE‐rich zone; and (ii) porous REE‐poor zone. The porous REE‐poor zones mainly appear in rims and/or inside of the apatite grains, in addition to the presence of apatite grains which totally consist of a porous REE‐poor apatite. This porous REE‐poor apatite is characterized by low REE (<0.84 wt%), Si (<0.28 wt%), and Cl (<0.17 wt%) contents. Epidote‐group minerals mainly occur in grain boundary between the porous REE‐poor apatite and augite. These indicate that REE leached from primary REE‐rich apatite crystallized as allanite and REE‐rich epidote. Magnetite in the ores often occurs as veinlets that cut apatite grains or as anhedral grains that replace a part of augite. These textures suggest that magnetite crystallized in the late stage. Pyrite veins occur in the ores, including a large amount of quartz and calcite veins. Pyrite veins mainly occur with quartz veins in augite. These textures indicate pyrite veins are the latest phase. Apatite–augite–magnetite ore, gabbro–quartz diorite and feldspar dike collected from the Benjamin River prospect contain dirty pure albite (Ab98Or2–Ab100) under the microscope. The feldspar dikes mainly consist of dirty pure albite. Occurrences of the dirty pure albite suggest remarkable albitization (sodic alteration) of original plagioclase (An25.3–An60 in Pilote et al., 2012) associating with intrusion of monzogranite into gabbro and diorite. SO42? bearing magma crystallized primary REE‐rich apatite, augite and anhydrite reacted with Fe in the sodic fluids, which result in oxidation of Fe2+ and release of S2? into the sodic fluids. REE, Ca and Fe from primary REE‐rich apatite, augite and plagioclase altered by the sodic fluids were released into the fluids. Then Fe3+ in the sodic fluids precipitated as Fe oxides and epidote‐group minerals in apatite–augite–magnetite ores. Finally, residual S2? in sodic fluids crystallized as latest pyrite veins. In conclusion, mineralization in Benjamin River IOA prospect are divided into four stages: (1) oxidized magmatic stage that crystallized apatite, augite and anhydrite; (2) sodic metasomatic stage accompanying alteration of magmatic minerals; (3) oxidized fluid stage (magnetite–epidote group minerals mineralization); and (4) reduced fluid stage (pyrite mineralization). 相似文献
18.
A. Mücke 《Mineralogy and Petrology》2003,77(3-4):215-234
Summary ?Detailed petrographic studies and microchemical analyses of titanomagnetite from igneous and metamorphic rocks and ore deposits
form the basis of this investigation. Its aim is to compare the data obtained and their interpretations with the experimentally
deduced subsolidus oxidation-exsolution model of Buddington and Lindsley (1964). The results are also considered relevant for the interpretation of compositional variations in black sands which
are recovered for titanium production. The arrangement of the samples investigated is in accordance with textural stages C1
to C5 caused by subsolidus exsolution with increasing degrees of oxidation (Haggerty, 1991).
Stage 1 is represented by two types of optically homogeneous TiO2-rich magnetite: a. An isotropic type considered to represent solid solutions of magnetite and ulvite containing between 5.2
to 27.5 wt% TiO2 corresponding to about 14.7 to 77.7 mol% Fe2TiO4 in solid solution with magnetite. The general formula of this type is Fe2+
1+x
Fe3+
2−2x
Ti
x
O4 (x = 0.0–1.0). b. The second type which has not been reported so far is anisotropic and shows complex internal twinning resembling
inversion textures. It is thus attributed to inversion of a high-temperature ilmenite modification (with statistical distribution
of the cations) which forms solid solutions with magnetite. TiO2 varies between 9.3 and 24.5 wt% corresponding to about 17.2 to 43.6 mol% ilmenite in solid solution with magnetite. This
type is interpreted as a cation-deficient spinel with the general formula Fe2+
12/12 + 1/4xFe3+
24/12 − 3/2x
□
0 + 1/4x
Ti
x
O4 (x = 0.0–16/12). Isotropic and anisotropic homogeneous magnetites occur in volcanic rocks only; the homogeneity of the solid
solutions was explained by fast cooling which prevented the development of exsolution textures.
Stages 2 and 3 are represented by magnetite with or without ulvite. The magnetite host contains ilmenite lamellae forming
trellis and sandwich textures. In contrast to the requirement of the oxidation-exsolution model, the ilmenite lamellae are
concentrated exclusively in the cores of the host crystals. The reverse host-guest relationship may also occur. Stages 4 and
5 are identical with thermally generated martite (= martite due to heating). The textures are characterized by very broad
lamellae of ferrian ilmenite or titanohematite dominantly concentrated along the margins of the host crystals. Thermally generated
martite is restricted to subsolidus-oxidation reactions.
The ilmenite lamellae of trellis and sandwich textures contain low Fe2O3-concentrations (average 4.8 mol%; to a maximum of 8.3), whereas the Fe2O3-content of thermally generated martite is between 32 to 71 mol%. With respect to the Fe2O3-concentrations in the ilmenite lamellae, no transition between the two types was observed.
The results of this paper show that the widely accepted oxy-exsolution model of Buddington and Lindsley (1964) which is based on experimental results can – with the exception of thermally generated martite – not explain the tremendous
variety of magnetite–ilmenite–ulvite relationships in natural rocks and ore deposits.
Received October 16, 2001; accepted May 2, 2002 相似文献
19.
《International Geology Review》2012,54(8):671-687
Spinel-lherzolite xenoliths in alkali basalts from eastern China have porphyroclastic to equigranular textures displaying varying degrees of deformation and subsolidus re-equilibration. The proportions of minerals in these xenoliths vary from 52 to 72% homogeneous olivine (Fo88-91); 11 to 26% orthopyroxene (Wo0.9.1.6; En88-90; Fs8.7.10.7), with minor discontinuous variations of Al2O3, FeO, and CaO; 6 to 19% clinopyroxene (Wo43.47; En49.51; Fs3.7.6.7); and 1 to 5% spinel, with similar Mg# (79.6 to 82.6), but wider variations of Al2O3 and Cr2O3 (100Cr/(Cr + Al + Fe3+) = 8.1 to 23.6). Although previous trace-element and isotopic studies have shown that at least two distinctly different mantle sources were sampled by Cenozoic basalts, mineralogical heterogeneities seem to be minor within the spinel-peridotite-facies lithosphere beneath eastern China. These xenoliths experienced limited interaction with the host basaltic magma during eruption. Symplectites of secondary, minute silicates, titanomagnetite, and sulfide have replaced orthopyroxene—and to a lesser extent olivine—at the contact with the basalt. The spinel in the margin of the xenolith is continuously zoned by substitutions of Fe3O4 (magnetite) and Fe2TiO4 (ulvospinel) for MgAl2O3 (spinel), and is rimmed by titanomagnetite with a sharp boundary. However, the compositions of the interior clinopyroxenes were commonly modified by metasomatic partial melting, which resulted in “spongy-textured” rinds on primary clinopyroxene. This secondary assemblage is composed mainly of a refractory, jadeite-poor clinopyroxene, which is largely in optica! continuity with the primary clinopyroxene in addition to interstitial feldspars, with minor titanomagnetite and Fe-Ni sulfides. This assemblage was produced by the introduction of K-rich fluids from the enclosing basaltic magma. The intensity of these secondary reactions appears to have been a function of the residence time of the xenolith in the host basalt. Therefore, all secondary alteration of both external and internal primary minerals in these xenoliths are the result of near-surface metasomatic processes, rather than of mantle phenomena. 相似文献
20.
Yu. V. Bataleva Yu. N. Palyanov Yu. M. Borzdov I. D. Novoselov O. A. Bayukov N. V. Sobolev 《Petrology》2018,26(6):565-574
Of great importance in the problem of redox evolution of mantle rocks is the reconstruction of scenarios of alteration of Fe0- or Fe3C-bearing rocks by oxidizing mantle metasomatic agents and the evaluation of stability of these phases under the influence of fluids and melts of different compositions. Original results of high-temperature high-pressure experiments (P = 6.3 GPa, T = 1300–1500°С) in the carbide–oxide–carbonate systems (Fe3C–SiO2–(Mg,Ca)CO3 and Fe3C–SiO2–Al2O3–(Mg,Ca)CO3) are reported. Conditions of formation of mantle silicates with metallic or metal–carbon melt inclusions are determined and their stability in the presence of CO2-fluid representing the potential mantle oxidizing metasomatic agent are estimated. It is established that garnet or orthopyroxene and CO2-fluid are formed in the carbide–oxide–carbonate system through decarbonation, with subsequent redox interaction between CO2 and iron carbide. This results in the formation of assemblage of Fe-rich silicates and graphite. Garnet and orthopyroxene contain inclusions of a Fe–C melt, as well as graphite, fayalite, and ferrosilite. It is experimentally demonstrated that the presence of CO2-fluid in interstices does not affect on the preservation of metallic inclusions, as well as graphite inclusions in silicates. Selective capture of Fe–C melt inclusions by mantle silicates is one of the potential scenarios for the conservation of metallic iron in mantle domains altered by mantle oxidizing metasomatic agents. 相似文献