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1.
We have analyzed the chemical composition and boron isotope composition of tourmaline from tourmalinites, granite and a quartz-tourmaline
vein from the Deri ore zone and from a pegmatitic band in the Rampura-Agucha ore body. These two Proterozoic massive sulfide
deposits occur in the Aravalli-Delhi orogenic belt, Rajasthan, northwest India. Tourmaline from stratiform tourmalinites closely
associated with the massive sulfides in the Deri deposit have preserved their original chemical compositions despite regional
and thermal metamorphism in the area. These tourmalines have low Fe/(Fe + Mg) ratios (0.19–0.30; mean 0.26) that suggest formation
close to the sediment-sea water interface. The δ11B values (−15.5 and −16.4‰) are compatible with boron derived from leaching of argillaceous sediments and/or felsic volcanics
underlying the original massive sulfide deposit during its formation. Boron isotope compositions measured in tourmaline from
a post-ore granite and quartz-tourmaline vein in the Deri deposit indicate that boron in these tourmalines was derived from
the tourmalinites produced during ore formation. The boron isotope systematics of a coarse brown tourmaline crystal from a
pegmatitic band on the hanging wall contact of the Rampura-Agucha deposit indicate that 45 ± 25% of the boron within the original
tourmaline was lost during upper amphibolite facies regional metamorphism.
Received: 3 April 1996 / Accepted: 11 April 1996 相似文献
2.
R. B. Trumbull M.-S. Krienitz B. Gottesmann M. Wiedenbeck 《Contributions to Mineralogy and Petrology》2008,155(1):1-18
Tourmaline is widespread in metapelites and pegmatites from the Neoproterozoic Damara Belt, which form the basement and potential
source rocks of the Cretaceous Erongo granite. This study traces the B-isotope variations in tourmalines from the basement,
from the Erongo granite and from its hydrothermal stage. Tourmalines from the basement are alkali-deficient schorl-dravites,
with B-isotope ratios typical for continental crust (δ11B average −8.4‰ ± 1.4, n = 11; one sample at −13‰, n = 2). Virtually all tourmaline in the Erongo granite occurs in distinctive tourmaline-quartz orbicules. This “main-stage”
tourmaline is alkali-deficient schorl (20–30% X-site vacancy, Fe/(Fe + Mg) 0.8–1), with uniform B-isotope compositions (δ11B −8.7‰ ± 1.5, n = 49) that are indistinguishable from the basement average, suggesting that boron was derived from anatexis of the local
basement rocks with no significant shift in isotopic composition. Secondary, hydrothermal tourmaline in the granite has a
bimodal B-isotope distribution with one peak at about −9‰, like the main-stage tourmaline, and a second at −2‰. We propose
that the tourmaline-rich orbicules formed late in the crystallization history from an immiscible Na–B–Fe-rich hydrous melt.
The massive precipitation of orbicular tourmaline nearly exhausted the melt in boron and the shift of δ11B to −2‰ in secondary tourmaline can be explained by Rayleigh fractionation after about 90% B-depletion in the residual fluid.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
Robert B. Trumbull Marc-Sebastian Krienitz Günter Grundmann Michael Wiedenbeck 《Contributions to Mineralogy and Petrology》2009,157(3):411-427
Tourmalines from the Habachtal emerald deposit in the Eastern Alps formed together with emerald in a ductile shear zone during
blackwall metasomatism between pelitic country rocks and a serpentinite body. Electron microprobe and secondary ion mass spectrometric
(SIMS) analyses provide a record of chemical and B-isotope variations in tourmalines which represent an idealized profile
from metapelites into the blackwall sequence of biotite and chlorite schists. Tourmaline is intermediate schorl-dravite in
the country rock and become increasingly dravitic in the blackwall zones, while F and Cr contents increase and Al drops. Metasomatic
tourmaline from blackwall zones is typically zoned optically and chemically, with rim compositions rich in Mg, Ti, Ca and
F compared with the cores. The total range in δ11B values is −13.8 to −5.1‰ and the within-sample variations are typically 3–5‰. Both of these ranges are beyond the reach
of closed-system fractionation at the estimated 500–550°C conditions of formation, and at least two boron components with
contrasting isotopic composition are indicated. A key observation from tourmaline core analyses is a systematic shift in δ11B from the country rock (−14 to −10‰) to the inner blackwall zones (−9 to −5‰). We suggest that two separate fluids were channeled
and partially mixed in the Habachtal shear zone during blackwall alteration and tourmaline-emerald mineralization. A regional
metamorphic fluid carried isotopically light boron as observed in the metapelite country rocks. The other fluid is derived
from the serpentinite association and has isotopically heavier boron typical for MORB or altered oceanic crust.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
Boron recycling in the continental crust of the central Andes from the Palaeozoic to Mesozoic, NW Argentina 总被引:4,自引:2,他引:2
Simone Kasemann Jörg Erzinger Gerhard Franz 《Contributions to Mineralogy and Petrology》2000,140(3):328-343
Whole-rock chemical composition and 11B/10B isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the Andean
basement from the Palaeozoic to Mesozoic. In the basement (Cambrian to Ordovician high-grade paragneisses, migmatites and
orthogneisses, the Eocambrian Puncoviscana Formation, and Paleozoic-Mesozoic granitoid igneous rocks) whole-rock B contents
are generally below 100 ppm, but B contents of ˜1 wt% are found in cogenetic aplite and pegmatite dikes and in tourmaline–quartz
rocks. In the metasedimentary rocks, no systematic variation in B content because of metamorphic grade and no correlation
of B with other incompatible elements are apparent. Tourmalines from the high-grade metamorphic basement yield δ11B values ranging from −11.2 to −6.8‰ and isotope fractionation during migmatisation was small. Metamorphic tourmalines from
the Puncoviscana Formation have δ11B values between −6.3 and −5.8‰. The calculated (corrected for fractionation) δ11B values of −6 to −2‰ for the sedimentary protolith of the metamorphic basement indicate a continental B source with subordinate
marine input. Tourmalines from Palaeozoic and Mesozoic granitoids display an identical range of δ11B values from −12 to −5.3‰ and indicate a similarly homogeneous B source throughout time. Tourmalines from pegmatites and
tourmaline–quartz rocks record the average δ11B values of the parental granitic magma. We assume that B in the Palaeozoic and Mesozoic granitoids is derived from the local
metamorphic basement supporting the hypothesis that recycling of the lower Palaeozoic crust is the dominant process in granitic
magma formation from Palaeozoic to Mesozoic.
Received: 15 December 1999 / Accepted: 11 July 2000 相似文献
5.
The Houxianyu borate deposit in northeastern China is one of the largest boron sources of China, hosted mainly in the Paleoproterozoic meta-volcanic and sedimentary rocks (known as the Liaohe Group) that are characterized by high boron concentrations. The borate ore-body has intimate spatial relationship with the Mg-rich carbonates/silicates of the Group, with fine-grained gneisses (meta-felsic volcanic rocks) as main country rocks. The presence of abundant tourmalinites and tourmaline-rich quartz veins in the borate orebody provides an opportunity to study the origin of boron, the nature of ore-forming fluids, and possible mineralization mechanism. We report the chemical and boron isotopic compositions of tourmalines from the tourmaline-rich rocks in the borate deposit and from the tourmaline-bearing fine-grained gneisses.Tourmalines from the fine-grained gneisses are chemically homogeneous, showing relatively high Fe and Na and low Mg, with δ11B values in a narrow range from +1.22‰ to +2.63‰. Tourmalines from the tourmaline-rich rocks, however, commonly show compositional zoning, with an irregular detrital core and a euhedral overgrowth, and have significantly higher Mg, REE (and more pronounced positive Eu anomalies), V (229–1852 ppm) and Sr (208–1191 ppm) than those from the fine-grained gneisses. They show varied B isotope values ranging from +4.51‰ to +12.43‰, which plot intermediate between those of the terrigenous sediments and arc rocks with low boron isotope values (as represented by the δ11B = +1.22‰ to +2.63‰ of the fine-grained gneisses of this study) and those of marine carbonates and evaporates with high boron isotope values. In addition, the rim of the zoned tourmaline shows notably higher Mg, Ti, V, Sn, and Pb, and REE (particularly LREEs), but lower Fe, Co, Cr, Ni, Zn, Mn, and lower δ11B values than the core. These data suggest that (1) the sources of boron of the borate ore-body are mainly the Paleoproterozoic meta-volcanic and sedimentary rocks, and (2) the ore-forming fluids should be the high temperature metamorphic fluids related to the amphibolite-facies metamorphism of the Paleoproterozoic foldbelt, which leach boron from the boron-rich meta-volcanic and sedimentary rocks of the Liaohe Group, and the boron-rich metamorphic fluids subsequently interacted with the marine Mg-rich carbonates and evaporates, forming borate deposit, the tourmaline overgrowth in the rim and the tourmaline-rich rocks. 相似文献
6.
Boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites 总被引:8,自引:0,他引:8
Boron isotope ratios (11B/10B) have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings. The coverage of these localities is global (5 continents) and includes the giant ore bodies at Kidd Creek and Sullivan (Canada), Broken Hill (Australia), and Ducktown (USA). Overall, the tourmalines display a wide range in
11B values from –22.8 to +18.3 Possible controls over the boron isotopic composition of the tourmalines include: 1) composition of the boron source, 2) regional metamorphism, 3) water/rock ratios, 4) seawater entrainment, 5) temperature of formation, and 6) secular variations in seawater
11B. The most significant control appears to be the composition of the boron source, particularly the nature of footwall lithologies; variations in water/ rock ratios and seawater entrainment are of secondary importance. The boron isotope values seem especially sensitive to the presence of evaporites (marine and non-marine) and carbonates in source rocks to the massive sulfide deposits and tourmalinites. 相似文献
7.
The strata-bound Cu−Pb−Zn polymetallic sulfide deposits occur in metamorphic rocks of greenschist phase of the middle-upper
Proterozoic Langshan Group in central Inner Mongolia. δ34S values for sulfides range from −3.1‰ to +37.3‰, and an apparent difference is noticed between vein sulfides and those in
bedded rocks. For example, δ34S values for bedded pyrite range from +10.6‰ to +20.0‰, while those for vein pyrite vary from −3.1‰ to +14.1‰. δ34S of bedded pyrrhotite is in the range +7.9‰–+23.5‰ in comparison with +6.5‰–+17.1‰ for vein pyrrhotite. The wide scatter
of δ34S and the enrichment of heavier sulfur indicate that sulfur may have been derived from H2S as a result of bacterial reduction of sulfates in the sea water. Sulfur isotopic composition also differs from deposit to
deposit in this area because of the difference in environment in which they were formed. The mobilization of bedded sulfides
in response to regional metamorphism and magmatic intrusion led to the formation of vein sulfides.
δ18O and δ13C of ore-bearing rocks and wall rocks are within the range typical of ordinary marine facies, with the exception of lower
values for ore-bearing marble at Huogeqi probably due to diopsidization and tremalitization of carbonate rocks.
Pb isotopic composition is relatively stable and characterized by lower radio-genetic lead. The age of basement rocks was
calculated to be about 23.9 Ma and ore-forming age 7.8 Ma.207Pb/204Pb−206Pb/204Pb and208Pb/204Pb−206Pb/204Pb plots indicate that Pb may probably be derived from the lower crust or upper mantle.
It is believed that the deposits in this region are related to submarine volcanic exhalation superimposed by later regional
metamorphism and magmatic intrusion. 相似文献
8.
V. Yu. Prokof’ev N. S. Bortnikov V. A. Kovalenker S. F. Vinokurov L. D. Zorina A. D. Chernova S. G. Kryazhev A. N. Krasnov S. A. Gorbacheva 《Geology of Ore Deposits》2010,52(2):81-113
The chemistry, REE patterns, and carbon and oxygen isotopic compositions of carbonates from ore veins of the Darasun deposit
are discussed. In addition to the earlier described siderite, calcite, and carbonates of the dolomite-ankerite series, kutnahorite
is identified. The total REE content in Fe-Mg carbonates of the dolomite-ankerite series (2.8–73 ppm) is much lower than in
later calcite (18–390 ppm). δ13C of Fe-Mg carbonates and calcite varies from +1.1 to −6.7‰ and from −0.9 to −4.9‰, respectively. δ18O of Fe-Mg carbonates and calcite varies from +17.6 to 3.6‰ and from +15.7 to −0.5‰, respectively. The REE sum and carbon
and oxygen isotopic compositions reveal zonal distribution relative to the central granodiorite porphyry stock. The correlation
between the carbon and oxygen isotopic compositions and REE sum reflects variations in the physicochemical formation conditions
and composition of ore-forming fluid. The isotopic composition of fluid is calculated, and possible sources of its components
are considered. Earlier established evidence for a magmatic source of ore-forming fluid and participation of meteoric water
in ore formation is confirmed. Geochemical evidence for interaction of ore-forming fluid with host rocks is furnished. The
relationships between the REE sum, on the one hand, and carbon and oxygen isotopic compositions of hydrothermal ore-forming
fluid, on the other, are established. 相似文献
9.
辽宁东部古元古界底部地层(南辽河群)中赋存着大型的硼酸盐矿床,含矿层位中广泛分布含电气石的变粒岩和电英岩。空间上这些含电气石的岩石与硼酸盐有着密切的联系,电气石可以作为区域硼矿找矿的标志。已有研究结果表明,该地区的硼酸盐矿床是变质蒸发岩成因。本研究对该区不同产状的电气石和硼酸盐的地质特征,全岩和矿物成分、硼同位素组成进行了分析。本区的电气石包括层状和脉状两大类,而电气石的富集与硼酸盐关系密切,电英岩往往分布在硼酸盐矿体的上盘。而矿体的下盘一般不产出富电气石的岩石。当长英质脉体穿过硼酸盐矿体时,脉体中往往会富集电气石。含电气石岩石的全岩地球化学分析表明,它们的REE及其他微量元素特征以及相关性关系与周围不含电气石的同类岩石十分相似,反映出一种成因上的联系。本区电气石主要属于镁电气石一铁电气石系列,靠近硼矿体的电气石比远离硼矿体的电气石更加富镁,有着更高的Mg/Fe比值。电气石和硼酸盐的硼同位素成分分析显示出二者在同位素组成上的相似性,前者比后者的δ^11B稍低,这可能是由于热液活动过程中同位素分馏的结果。电气石的硼同位素组成在空间上显示出变化规律:远离硼酸盐矿体的电气石的δ^11B值(-5.2‰- 3.6‰)比矿体附近的电气石低(平均 10.5‰)。以上空间和成分上的关系表明硼酸盐可能是形成电气石主要的硼来源,电气石是在热液过程中通过淋滤下伏含硼蒸发岩中的硼形成含硼热液,在与上覆沉积物交代过程中形成含电气石岩石。电气石的条带是热液顺层选择交代的结果。本区电气石与硼酸盐的关系表明,层状电气石可以通过含硼热液交代的方式形成。变质地体中的层状电气石岩石的出现可能与变质蒸发岩有关。这一认识对区域硼矿勘查工作和变质地体的沉积环境分析有借鉴意义。 相似文献
10.
A. I. Grabezhev 《Geology of Ore Deposits》2010,52(2):138-153
The Early Devonian Gumeshevo deposit is one of the largest ore objects pertaining to the dioritic model of the porphyry copper
system paragenetically related to the low-K quartz diorite island-arc complex. The (87Sr/86Sr)t and (ɛNd)t of quartz diorite calculated for t = 390 Ma are 0.7038–0.7045 and 5.0–5.1, respectively, testifying to a large contribution of the mantle component to the composition
of this rock. The contents of typomorphic trace elements (ppm) are as follows: 30–48 REE sum, 5–10 Rb, 9–15 Y, and 1–2 Nb.
The REE pattern is devoid of Eu anomaly. Endoskarn of low-temperature and highly oxidized amphibole-epidote-garnet facies
is surrounded by the outer epidosite zone. Widespread retrograde metasomatism is expressed in replacement of exoskarn and
marble with silicate (chlorite, talc, tremolite)-magnetite-quartz-carbonate mineral assemblage. The 87Sr/86Sr ratios of epidote in endoskarn and carbonate in retrograde metasomatic rocks (0.7054–0.7058 and 0.7053–0.7065, respectively)
are intermediate between the Sr isotope ratios of quartz dioritic rocks and marble (87Sr/86Sr = 0.70784 ± 2). Isotopic parameters of the fluid equilibrated with silicates of skarn and retrograde metasomatic rocks
replacing exoskarn at 400°C are δ18O = +7.4 to +8.5‰ and δD = −49 to −61‰ (relative to SMOW). The δ13C and δ18O of carbonates in retrograde metasomatic rocks after marble are −5.3 to +0.6 (relative to PDB) and +13.0 to +20.2% (relative
to SMOW), respectively. Sulfidation completes metasomatism, nonuniformly superimposed on all metasomatic rocks and marbles
with formation of orebodies, including massive sulfide ore. The δ34S of sulfides is 0 to 2‰ (relative to CDT);87Sr/86Sr of calcite from the late calcite-pyrite assemblage replacing marble is 0.704134 ± 6. The δ13C and 87Sr/86Sr of postore veined carbonates correlate positively (r = 0.98; n = 6). The regression line extends to the marble field. Its opposite end corresponds to magmatic (in terms of Bowman, 1998b)
calcite with minimal δ13C, δ18O, and 87Sr/86Sr values (−6.9 ‰, +6.7‰, and 0.70378 ± 4, respectively). The aforementioned isotopic data show that magmatic fluid was supplied
during all stages of mineral formation and interacted with marble and other rocks, changing its Sr, C, and O isotopic compositions.
This confirms the earlier established redistribution of major elements and REE in the process of metasomatism. A contribution
of meteoric and metamorphic water is often established in quartz from postore veins. 相似文献
11.
I. J. Richards Theodore C. Labotka Robert T. Gregory 《Contributions to Mineralogy and Petrology》1996,123(2):202-221
Late Proterozoic to Cambrian carbonate rocks from Lone Mountain, west central Nevada, record multiple post-depositional events
including: (1) diagenesis, (2) Mesozoic regional metamorphism, (3) Late Cretaceous contact metamorphism, related to the emplacement
of the Lone Mountain granitic pluton and (4) Tertiary hydrothermal alteration associated with extension, uplift and intrusion
of silicic porphyry and lamprophyre dikes. Essentially pure calcite and dolomite marbles have stable isotopic compositions
that can be divided into two groups, one with positive δ13C values from+3.1 to +1.4 ‰ (PDB) and high δ18O values from +21.5 to +15.8 ‰ (SMOW), and the other with negative δ13C values from –3.3 to –3.6‰ and low δ18O values from +16.9 to +11.1‰. Marbles also contain minor amounts of quartz, muscovite and phlogopite. Brown and blue luminescent,
clear, smooth textured quartz grains from orange luminescent calcite marbles have high δ18O values from +23.9 to +18.1‰, while brown luminescent, opaque, rough textured quartz grains from red luminescent dolomite
marbles typically have low δ18O values from +2.0 to +9.3‰. The δ18O values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks, with values between +10.4 and
+14.4‰, whereas mica δD values are very depleted, varying from −102 to −156‰. No significant lowering of the δ18O values of Lone Mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions
because of the essentially pure nature of the marbles. Bright luminescence along the edges of fractures, quartz cements and
quartz overgrowths in dolomite marbles, low δD values of micas, negative δ13C values and low δ18O values of calcite and dolomite, and depleted δ18O values of quartz from dolomite marbles all indicate that meteoric fluids interacted with Lone Mountain marbles during the
Tertiary. Partial oxygen isotopic exchange between calcite and low 18O meteoric fluids lowered the δ18O values of calcite, resulting in uniform quartz-calcite fractionations that define an apparent pseudoisotherm. These quartz-calcite
fractionations significantly underestimate both the temperature of metamorphism and the temperature of post-metamorphic alteration.
Partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in 18O depletion of quartz from dolomite marbles. This partial exchange was facilitated by an increase in the surface area of the
quartz as a result of its dissolution by meteoric fluids. The negative δ13C values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism. Stable isotopic
data from Lone Mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western
Nevada in Tertiary time.
Received: 1 February 1994/Accepted: 12 September 1995 相似文献
12.
Tourmaline mineralization in the Barberton greenstone belt,South Africa: early Archean metasomatism by evaporite-derived boron 总被引:1,自引:0,他引:1
Tourmaline-rich rocks are common in the lowgrade, interior portions of the Barberton greenstone belt of South Africa, where shallow-marine sediments and underlying altered basaltic and komatiitic lavas contain up to 50% tourmaline. The presence of tourmaline-bearing rip-up clasts, intraformational tourmalinite pebbles, and tourmaline-coated grains indicates that boron mineralization was a low-temperature, surficial process. The association of these lithologies with stromatolites, evaporites, and shallow-water sedimentary structures and the virtual absence of tourmaline in correlative deep-water facies rocks in the greenstone bels strengthens this model.Five tourmaline-bearing lithologic groups (basalts, komatiites, evaporite-bearing sediments, stromatolitic sediments, and quartz veins) are distinguished based on field, petrographic, and geochemical criteria. Individual tourmaline crystals within these lithologies show internal chemical and textural variations that reflect continued growth through intervals of change in bulk-rock and fluid composition accompanying one or more metasomatic events. Large single-crystal variations exist in Fe/Mg, Al/Fe, and alkali-site vacancies. A wide range in tourmaline composition exists in rocks altered from similar protoliths, but tourmalines in sediments and lavas have similar compositional variations. Boron-isotope analysis of the tourmalines suggest that the boron enrichment in these rocks has a major marine evaporitic component. Sediments with gypsum pseudomorphs and lavas altered at low temperatures by shallow-level brines have the highest 11B values (+2.2 to-1.9); lower 11B values of late quartz veins (-3.7 to-5.7) reflect intermediate temperature, hydrothermal remobilization of evaporitic boron. The 11B values of tourmaline-rich stromatolitic sediments (-9.8 and-10.5) are consistent with two-stage boron enrichment, in which earlier marine evaporitic boron was hydrothermally remobilized and vented in shallow-marine or subaerial sites, mineralizing algal stromatolites. The stromatolite-forming algae preferentially may have lived near the sites of hydrothermal discharge in Archean times. 相似文献
13.
A rare earth element-rich carbonatite dyke at Bayan Obo, Inner Mongolia, North China 总被引:8,自引:0,他引:8
Summary ?A carbonatite dyke, extremely enriched in rare earth elements (REE), is reported from Bayan Obo, Inner Mongolia, North China.
The REE content in the dyke varies from 1 wt% to up to 20 wt%. The light REEs are enriched and highly fractionated relative
to the heavy REEs, and there is no Eu anomaly. Although carbon isotope δ13C (PDB) values of the carbonatites (−7.3 to −4.7‰) are within the range of normal mantle (−5±2‰), oxygen isotope δ18O (SMOW) (11.9 to 17.7‰) ratios apparently are higher than those of the mantle (5.7±1.0‰), indicating varying degrees of exchange
with hydrothermal fluids during or after magmatic crystallization. The carbonatite is the result of partial melting followed
by fractional crystallization. Primary carbonatite melt was formed by less than 1% partial melting of enriched mantle, leaving
a garnet-bearing residue. The melt then rose to a crustal magma chamber and underwent fractional crystallization, producing
further REE enrichment. The REE and trace element distribution patterns of the carbonatites are similar to those of fine-grained
dolomite marble, the ore-host rock of the Bayan Obo REE–Nb–Fe giant mineral deposit. This fact may indicate a petrogenetic
link between the dykes described here and the Bayan Obo mineral deposit.
Received November 1, 2001; revised version accepted June 16, 2002 相似文献
14.
Mark E. Brandriss Richard J. Nevle Dennis K. Bird James R. O’Neil 《Contributions to Mineralogy and Petrology》1995,121(1):74-86
Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene
Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes
and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes
that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and
chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ18O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ18O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported
for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the
meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic
region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time
of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ18O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ18O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh
basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to
equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ18O partial melts of xenoliths that had been hydrothermally altered and depleted in 18O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country
rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal
fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous
hornblendes from the plutonic rocks have δ18O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The 18O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures,
indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange.
The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic
material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based
partly on the observation that coexisting plagioclase has been extensively depleted in 18O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded
that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus
isotopic equilibration with meteoric–hydrothermal fluids.
Received: 22 March 1994 / Accepted: 26 January 1995 相似文献
15.
The Duolanasayi gold deposit, 60 km NW of Habahe County, Xinjiang Uygur Autonomous Region, is a mid-large-scale gold deposit controlled by brittle-ductile shearing, and superimposed by albitite veins and late-stage magma hydrothermal solutions. There are four types of pyrite, which are contained in the light metamorphosed rocks (limestone, siltstone), altered-mineralized rocks (chlorite-schist, altered albite-granite, mineralized phyllite), quartz veins and carbonatite veinlets. The pyrite is the most common ore mineral. The Au-barren pyrite is present mainly in a simple form and gold-bearing pyrite is present mainly in a composite form. From the top downwards, the pyrite varies in crystal form from {100} and {210} {100} to {210} {100} {111} to {100} {111}. Geochemical studies indicate that the molecular contents of pyrite range from Fe1.057S2 to Fe0.941S2. Gold positively correlates with Mn, Sr, Zn, Te, Pb, Ba and Ag. There are four groups of trace elements: Fe-Cu-Sr-Ag, Au-Te-Co, As-Pb-Zn and Mn-V-Ti-Ba-Ni-Cr in pyrite. The REE characteristics show that the total amount of REE (ΣREE) ranges from 32.35×10 -6 to 132.18×10 -6; LREE/HREE, 4.466-9.142; (La/Yb)N, 3.719-11.133; (Eu/Sm)N, 0.553-1.656; (Sm/Nd)N, 0.602-0.717; La/Yb, 6.26-18.75; δEu, 0.628-2.309; δCe, 0.308-0.816. Sulfur isotopic compositions (δ 34S=-2.46‰--7.02‰) suggest that the sulfur associated with gold mineralization was derived from the upper mantle or lower crust. 相似文献
16.
C. O'Reilly G. R. T. Jenkin M. Feely D. H. M. Alderton A. E. Fallick 《Contributions to Mineralogy and Petrology》1997,129(2-3):120-142
Fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the Caledonian
Galway Granite. These fluids were examined by petrography, microthermometry, chlorite thermometry, fluid chemistry and stable
isotope studies. The earliest fluid was a H2O-CO2-NaCl fluid of moderate salinity (4–10 wt% NaCl eq.) that deposited late-magmatic molybdenite mineralised quartz veins (V1) and formed the earliest secondary inclusions in granite quartz. This fluid is more abundant in the west of the batholith,
corresponding to a decrease in emplacement depth. Within veins, and to the east, this fluid was trapped homogeneously, but
in granite quartz in the west it unmixed at 305–390 °C and 0.7–1.8 kbar. Homogeneous quartz δ18O across the batholith (9.5 ± 0.4‰n = 12) suggests V1 precipitation at high temperatures (perhaps 600 °C) and pressures (1–3 kbar) from magmatic fluids. Microthermometric data
for V1 indicate lower temperatures, suggesting inclusion volumes re-equilibrated during cooling. The second fluid was a H2O-NaCl-KCl, low-moderate salinity (0–10 wt% NaCl eq.), moderate temperature (270–340 °C), high δD (−18 ± 2‰), low δ18O (0.5–2.0‰) fluid of meteoric origin. This fluid penetrated the batholith via quartz veins (V2) which infill faults active during post-consolidation uplift of the batholith. It forms the most common inclusion type in
granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of
biotite and hornblende, sericitization and saussuritization of plagioclase, and reddening of K-feldspar. The salinity was
generated by fluid-rock interactions within the granite. Within granite quartz this fluid was trapped at 0.5–2.3 kbar, having
become overpressured. This fluid probably infiltrated the Granite in a meteoric-convection system during cooling after intrusion,
but a later age cannot be ruled out. The final fluid to enter the Granite and its host rocks was a H2O-NaCl-CaCl2-KCl fluid with variable salinity (8–28 wt% NaCl eq.), temperature (125–205 °C), δD (−17 to −45‰), δ18O (−3 to + 1.2‰), δ13CCO2 (−19 to 0‰) and δ34Ssulphate (13–23‰) that deposited veins containing quartz, fluorite, calcite, barite, galena, chalcopyrite sphalerite and pyrite (V3). Correlations of salinity, temperature, δD and δ18O are interpreted as the result of mixing of two fluid end-members, one a high-δD (−17 to −8‰), moderate-δ18O (1.2–2.5‰), high-δ13CCO2 (> −4‰), low-δ34Ssulphate (13‰), high-temperature (205–230 °C), moderate-salinity (8–12 wt% NaCl eq.) fluid, the other a low-δD (−61 to −45‰), low-δ18O (−5.4 to −3‰), low-δ13C (<−10‰), high-δ34Ssulphate (20–23‰) low-temperature (80–125 °C), high-salinity (21–28 wt% NaCl eq.) fluid. Geochronological evidence suggests V3 veins are late Triassic; the high-δD end-member is interpreted as a contemporaneous surface fluid, probably mixed meteoric
water and evaporated seawater and/or dissolved evaporites, whereas the low-δD end-member is interpreted as a basinal brine
derived from the adjacent Carboniferous sequence. This study demonstrates that the Galway Granite was a locus for repeated
fluid events for a variety of reasons; from expulsion of magmatic fluids during the final stages of crystallisation, through
a meteoric convection system, probably driven by waning magmatic heat, to much later mineralisation, concentrated in its vicinity
due to thermal, tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic
heat has abated.
Received: 3 April 1996 / Accepted: 5 May 1997 相似文献
17.
M. -S. Krienitz R. B. Trumbull A. Hellmann J. Kolb F. M. Meyer M. Wiedenbeck 《Mineralium Deposita》2008,43(4):421-434
We determined the boron isotope and chemical compositions of tourmaline from the Hira Buddini gold deposit within the Archean
Hutti-Maski greenstone belt in southern India to investigate the evolution of the hydrothermal system and to constrain its
fluid sources. Tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and
metadacite host rocks associated with the hydrothermal gold mineralization. The Hira Buddini tourmaline belongs to the dravite–schorl
series with variations in Al, Fe/(Fe+Mg), Ca, Ti, and Cr contents that can be related to their host lithology. The total range
of δ11B values determined is extreme, from −13.3‰ to +9.0‰, but 95% of the values are between −4 and +9‰. The boron isotope compositions
of metabasalt-hosted tourmaline show a bimodal distribution with peak δ11B values at about −2‰ and +6‰. The wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin
from at least two isotopically distinct fluid sources, which entered the hydrothermal system separately and were subsequently
mixed. The estimated δ11B values of the hydrothermal fluids, based on the peak tourmaline compositions and a mineralization temperature of 550°C,
are around +1 and +10‰. The isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization
reactions from the greenstone lithologies, whereas the 11B-rich fluid is attributed to degassing of I-type granitic magmas that intruded the greenstone sequence, providing heat and
fluids to the hydrothermal system.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Hamdy A. El Desouky Philippe Muchez Adrian J. Boyce Jens Schneider Jacques L. H. Cailteux Stijn Dewaele Albrecht von Quadt 《Mineralium Deposita》2010,45(8):735-763
The sediment-hosted stratiform Cu–Co mineralization of the Luiswishi and Kamoto deposits in the Katangan Copperbelt is hosted
by the Neoproterozoic Mines Subgroup. Two main hypogene Cu–Co sulfide mineralization stages and associated gangue minerals
(dolomite and quartz) are distinguished. The first is an early diagenetic, typical stratiform mineralization with fine-grained
minerals, whereas the second is a multistage syn-orogenic stratiform to stratabound mineralization with coarse-grained minerals.
For both stages, the main hypogene Cu–Co sulfide minerals are chalcopyrite, bornite, carrollite, and chalcocite. These minerals
are in many places replaced by supergene sulfides (e.g., digenite and covellite), especially near the surface, and are completely
oxidized in the weathered superficial zone and in surface outcrops, with malachite, heterogenite, chrysocolla, and azurite
as the main oxidation products. The hypogene sulfides of the first Cu–Co stage display δ34S values (−10.3‰ to +3.1‰ Vienna Canyon Diablo Troilite (V-CDT)), which partly overlap with the δ34S signature of framboidal pyrites (−28.7‰ to 4.2‰ V-CDT) and have ∆34SSO4-Sulfides in the range of 14.4‰ to 27.8‰. This fractionation is consistent with bacterial sulfate reduction (BSR). The hypogene sulfides
of the second Cu–Co stage display δ34S signatures that are either similar (−13.1‰ to +5.2‰ V-CDT) to the δ34S values of the sulfides of the first Cu–Co stage or comparable (+18.6‰ to +21.0‰ V-CDT) to the δ34S of Neoproterozoic seawater. This indicates that the sulfides of the second stage obtained their sulfur by both remobilization
from early diagenetic sulfides and from thermochemical sulfate reduction (TSR). The carbon (−9.9‰ to −1.4‰ Vienna Pee Dee
Belemnite (V-PDB)) and oxygen (−14.3‰ to −7.7‰ V-PDB) isotope signatures of dolomites associated with the first Cu–Co stage
are in agreement with the interpretation that these dolomites are by-products of BSR. The carbon (−8.6‰ to +0.3‰ V-PDB) and
oxygen (−24.0‰ to −10.3‰ V-PDB) isotope signatures of dolomites associated with the second Cu–Co stage are mostly similar
to the δ13C (−7.1‰ to +1.3‰ V-PDB) and δ18O (−14.5‰ to −7.2‰ V-PDB) of the host rock and of the dolomites of the first Cu–Co stage. This indicates that the dolomites
of the second Cu–Co stage precipitated from a high-temperature, host rock-buffered fluid, possibly under the influence of
TSR. The dolomites associated with the first Cu–Co stage are characterized by significantly radiogenic Sr isotope signatures
(0.70987 to 0.73576) that show a good correspondence with the Sr isotope signatures of the granitic basement rocks at an age
of ca. 816 Ma. This indicates that the mineralizing fluid of the first Cu–Co stage has most likely leached radiogenic Sr and
Cu–Co metals by interaction with the underlying basement rocks and/or with arenitic sedimentary rocks derived from such a
basement. In contrast, the Sr isotope signatures (0.70883 to 0.71215) of the dolomites associated with the second stage show
a good correspondence with the 87Sr/86Sr ratios (0.70723 to 0.70927) of poorly mineralized/barren host rocks at ca. 590 Ma. This indicates that the fluid of the
second Cu–Co stage was likely a remobilizing fluid that significantly interacted with the country rocks and possibly did not
mobilize additional metals from the basement rocks. 相似文献
19.
The Tuwaishan, Baoban, Erjia, Bumo and other gold deposits in western Hainan occur in Precambrian metamorphic clastic rocks
and are structurally controlled by the Gezhen shear zone. Fluid inclusion studies have been carried out of the gold deposits
mentioned above. The homogenization temperatures of the whole fluid inclusion population range from 140°C to 370°C, indicating
that gold was precipitated mainly at 240–250°C. The salinities are within the range of 2.0–9.2 wt% NaCl equiv. and the pressure
of formation of the deposits was estimated at about 270×105−500×105Pa, corresponding to a depth of about 1.1–2.0 km under lithostatic confinement. Chemical studies show that the ore fluid is
of the Na+(K+)-Ca2+-Cl−(F−) type. Theδ
18O andδD values of the fluid vary from −2.7‰- +4.4‰ and −50‰–−87‰ Evidence developed from fluid inclusions and geological setting
indicates that the ore fluid was a mixture of magmatic and meteoric-hydrothermal waters. Changes in chemical composition andδ
18O andδD of fluid inclusions from one ore field to another seem to be related with regional tectonism, metamorphism and magmatism. 相似文献
20.
In the eastern Sierras Pampeanas, Central Argentina, tourmalinites and coticules are found in close association with stratabound scheelite deposits in metamorphic terranes. In Sierra Grande (Agua de Ramón and Ambul districts) and Sierra de Altautina, tourmalinites are associated with stratabound scheelite deposits related to orthoamphibolites. In the Pampa del Tamboreo area, tourmalinites are located in biotite schists stratigraphically related to acid to intermediate metavolcanic rocks and scheelite-bearing quartzites.The mineral chemistry and boron isotopic compositions of tourmalinite-hosted and vein-hosted tourmalines are investigated. Overall, the tourmalines belong to the dravite-schorl series and are generally aluminous; Fe/(Fe+Mg) ranges from 0.33 to 0.85, Al/(Al+Fe+Mg) from 0.66 to 0.76 and the amount of X-site vacancy (0.12–0.48) indicates significant foitite components. Their boron isotopic compositions (δ11B) are from −24.0‰ to−15.0‰.Similar mineral chemistries and boron isotopic values for tourmaline in tourmalinites related to stratabound scheelite mineralisation and in tungsten-bearing quartz veins suggest a common source for the boron and probably the tungsten. The field, chemical and isotopic relationships are consistent with tungsten and boron in quartz-vein deposits being remobilised from stratabound scheelite and tourmalinite, dominantly by liquid-state transfer associated with regional shear zones. Tungsten and boron in the original sedimentary sequence (now meta-exhalites) are ascribed to volcanogenic exhalations. 相似文献