Tourmaline in Proterozoic Massive Sulfide Deposits from Rajasthan, India

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     

Chemical composition of tourmaline from the Yunlong tin deposit, Yunnan, China: implications for ore genesis and mineral exploration

Summary ?The Yunlong tin deposit is located in the northern part of the Lancangjiang metamorphic zone of the Sanjiang Tethys orogen series in western Yunan province of China. It consists of vein-type cassiterite ores, which are mainly hosted in migmatites of Caledonian age. Abundant tourmaline is associated with the ores, quartz–tourmaline veins and barren migmatized gneiss and migmatites. A detailed electron microprobe study has been carried out to document the chemical compositions of tourmaline from this deposit. The results exhibit a systematic compositional change that might be used as tracer for ore genesis and in prospecting for tin mineralization. Tourmalines from the ore bodies are dravite with Fe/(Fe + Mg) ratios of 0.09 ∼ 0.31 and Ca/(Ca + Na) ratios of 0.03 ∼ 0.40. These tourmalines are also rich in chromium (up to 0.74 wt% Cr₂O₃) and tin (up to 0.42 wt% Sn). In contrast, tourmalines from the barren migmatites are mostly schorl with Fe/(Fe + Mg) ratios of 0.38 ∼ 0.94 and Ca/(Ca + Na) ratios of 0.00 ∼ 0.14. Tourmalines from quartz–tourmaline veins that occur between ore bodies and the migmatites show intermediate compositions, i.e., Fe/(Fe + Mg) = 0.09 ∼ 0.59, Ca/(Ca + Na) = 0.01 ∼ 0.22. It is suggested that the Mg-rich nature of the tourmaline can be used as an exploration tool in this region to target tin mineralization, because the tourmalines show increasing Mg contents and are more dravitic when approaching the ore bodies. It is likely that the formation of the Yunlong tin deposit was related to migmatitic-hydrothermal processes. The high Mg and Cr contents in tourmalines from the ore bodies were probably derived from the local meta-sedimentary and meta-volcanic rocks of the Precambian Chongshan Group rather than from the granites in the region. Received December 28, 2000; revised version accepted January 25, 2002     

广西大厂地区黑云母花岗岩中电气石的化学组成及其对岩浆热液演化的指示

广西大厂地区笼箱盖黑云母花岗岩与区内晚白垩世锡多金属成矿作用在时空上密切相关。岩相学特征表明,笼箱盖黑云母花岗岩中的电气石可以分为三类:1)浸染状电气石; 2)石英-电气石囊; 3)电气石-石英脉。本文利用电子探针和激光剥蚀等离子体质谱系统测定三种不同产状电气石的化学组成。分析结果显示,三种产状的电气石均具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值,主体属于碱基亚类铁电气石。浸染状电气石为岩浆晚期结晶,其Fe/(Fe+Mg)比值变化于0. 85～0. 94,随着岩浆分异,电气石逐渐富集Li、F、Fe和Sn等元素。与浸染状电气石相比,石英-电气石囊中早阶段电气石具有低的Fe/(Fe+Mg)比值,高的V、Co和Sr含量,可能反映了岩浆演化晚期出现的不混溶富硼熔/流体对早期黑云母和长石的交代作用,从而使囊中早阶段电气石继承部分被交代矿物的化学组成特征;石英-电气石囊中晚阶段电气石的化学组成变化较大(如Li、F、Mg、Al、V、Fe和Zn),与热液成因电气石的推论一致。与浸染状和囊状电气石相比,石英脉中的电气石具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值;微量元素组成与囊状电气石相似。就成矿元素锡而言,三种产状的电气石均具有相对高的锡含量,与其他地区锡成矿花岗岩中电气石的成分特征相似。但是,从岩浆晚期到热液阶段,大厂地区电气石的锡含量并没有显著升高,可能反映了早期岩浆热液流体对熔体锡有限的萃取作用。     

Tourmalinization related to Late Proterozoic-Early Palaeozoic lode gold mineralization in the Bin Yauri area, Nigeria

Three types of tourmaline occurrence have been identified in the area of Bin Yauri, Nigeria, mesothermal lode-gold mineralization. These are: (1) stratabound tourmalinites in pelitic metasediments, (2) tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks, (3) tourmaline in auriferous quartz and quartz-carbonate veins. Although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion, geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source. Two stages of tourmalinization are envisaged. The earlier (ca. 1100 Ma) involved syngenetic-diagenetic formation of tourmalinites, while the later (ca. 500 Ma) involved epigenetic (hydrothermal) tourmaline-gold mineralization, possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline-rich rocks or tourmalinites. Electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl-dravite solid solution series. Plots involving FeO, MgO, and/or Al₂O₃ from these analyses are used to constrain the sources and processes of tourmalinization. Two metallogenic implications are derived from this study. One is that, although the tourmalinites are barren of gold and base metal mineralization, their occurrences nevertheless encourages exploration for syngenetic-exhalative massive sulphide deposits in the region. The other implication applies to the potential use of tourmaline in deciphering the physico-chemical conditions of gold-mineralizing fluids in the Bin Yauri area.     

http://www.sciencedirect.com/science/article/pii/S1674987112001478

REE composition of the carbonates of the auriferous quartz carbonate veins (QCVs) of the Neoarchean Ajjanahalli gold deposit, Chitradurga schist belt, Dharwar Craton, is characterized by U-shaped chondrite normalized REE patterns with both LREE and HREE enrichment and a distinct positive Eu anomaly. As positive Eu anomaly is associated with low oxygen fugacity, we propose that the auriferous fluids responsible for gold mineralization at Ajjanahalli could be from an oxygen depleted fluid. The observed positive Eu anomaly is interpreted to suggest the derivation of the auriferous fluids from a mantle reservoir. The location of Ajjanahalli gold deposit in a crustal scale shear zone is consistent with this interpretation.     

Tourmaline from the Archean G.R.Halli gold deposit,Chitradurga greenstone belt,Dharwar craton （India）： Implications for the gold metallogeny

Tourmaline occurs as a minor but important mineral in the alteration zc,ne of the Archean orogenic gold deposit of Guddadarangavanahalli （G.R.Halli） in the Chitradurga greenst~ne belt of the western Dharwar craton, southern India. It occurs in the distal alteration halo of the G.R.Halli golcl deposit as （a） clusters of very fine grained aggregates which form a minor constituent in the natrix of the altered metabasalt （AMB tourmaline） and （b） in quartz-carbonate veins （vein tourmaline）. ~[＇he vein tourmaline, based upon the association of specific carbonate minerals, is further grouped as （i） albite-tourmaline-ankerite-quartz veins （vein-1 tourmaline） and （ii） albite-tourmaline-calcite-quartz veins （vein-2 tourmaline）. Both the AMB tourmaline and the vein tourmalines （vein-I and vein-2） belong to the alkali group and are clas- sified under schorl-dravite series. Tourmalines occurring in the veins are zoned while the AMB tour- malines are unzoned. Mineral chemistry and discrimination diagrams 1eveal that cores and rims of the vein tourmalines are distinctly different. Core composition of the ve：n tourmalines is similar to the composition of the AMB tourmaline. The formation of the AMB tourmaline and cores of the vein tour- malines are proposed to be related to the regional D1 deformational event associated with the emplacement of the adjoining ca. 2.61 Ga Chitradurga granite whilst rims of the vein tourmalines vis-a- vis gold mineralization is spatially linked to the juvenile magmatic accretion （2.56-2.50 Ga） east of the studied area in the western part of the eastern Dharwar craton.     

藏南过铝花岗岩中电气石的矿物化学特征及成因意义

讨论了藏南过铝花岗岩中电气石的地质产状、矿物学和矿物化学特征。结果表明:(1)在以氧原子数为24.5计算的化学式中,电气石的(Fe+Mg)/Mg比值在2.32~5.37之间,指示花岗岩和伟晶岩中的电气石均为黑电气石系列,而且属镁电气石—铁电气石系列中的较富铁电气石的成员;(2)电气石的FeO/(FeO+MgO)值高达0.70~0.89,与贫Li花岗岩接近,Al-Al50Fe50-Al50Mg50图解和Fe-Mg-Ca图解投点均位于贫Li花岗岩区,属于贫Li花岗岩有关的电气石;(3)TiO2-MnO/CaO-MgO/FeO三元图解可判定属于第Ⅰ类,即MgO和FeO含量同步消长,且较贫Mg富Fe,而MnO和TiO2含量为异步消长,这与电气石的FeO/(FeO+MgO)值所反映的性质相同;(4)地质产状、矿物学及矿物化学揭示的成因信息表明藏南过铝花岗岩中的电气石为酸性侵入体岩浆期后热液成因。     

Volcanogenic-related origin of sulfide-rich quartz veins: evidence from O and S isotopes at the Géant Dormant gold mine, Abitibi belt, Canada

The Géant Dormant gold mine is a sulfide-rich quartz vein gold deposit hosted by a volcano-sedimentary sequence and an associated felsic endogenous dome and dikes. The auriferous quartz-sulfide veins were preceded by two synvolcanic gold-bearing mineralizing events: early sulfidic seafloor-related and later disseminated pyrite in the felsic dome. This deposit differs from classical Archean auriferous quartz vein deposits by the low carbonate and high sulfide contents of the veins and by their formation prior to ductile penetrative deformation. The δ¹⁸O values of quartz associated with seafloor-related auriferous sulfides average 11.9 ± 0.6‰ (n = 3). The seafloor hydrothermal fluids had a δ¹⁸O value of 3.2‰ calculated at 250 °C. The oxygen isotope composition of quartz and chlorite from veins average 12.5 ± 0.3‰ (n = 20) and 5.9 ± 1.1‰ (n = 4) respectively. Assuming oxygen isotope equilibrium between quartz and chlorite, the veins formed at a temperature of ∼275 °C, which is consistent with the calculated temperature of 269 ± 10 °C from chlorite chemistry. The gold-bearing fluids had a δ¹⁸O value of 4.7‰ calculated at 275 °C. The δ³⁴S values of sulfides from the three gold events range from 0.6 to 2.8‰ (n = 32) and are close to magmatic values. Sulfur isotope geothermometry constrains the sulfide precipitation in the gold-bearing veins at a temperature of ∼350 °C. The similarity of the isotope data, the calculated δ¹⁸O of the mineralizing fluids and the likely seawater fluid source suggest that the three mineralizing events are genetically related to a volcanogenic hydrothermal system. The high value of the auriferous fluids (δ¹⁸O = 4.7‰) is attributed to a significant magmatic fluid contribution to the evolved seawater-dominated convective hydrothermal system. The two-stage filling of veins at increasing temperature from quartz-chlorite (275 °C) to sulfides (350 °C) may reflect the progressive maturation of volcanogenic hydrothermal systems. These results, together with field and geochemical data, suggest that formation of gold-rich volcanogenic systems require specific conditions that comprise a magmatic fluid contribution and gold from arc-related felsic rocks, coeval with the mineralizing events. This study shows that some auriferous quartz-vein orebodies in Archean terranes are formed in volcanogenic rather than mesothermal systems. Received: 12 December 1998 / Accepted: 5 July 1999     

Geology and Gold Mineralization in the Pan-African Rocks of the Adola Area, Southern Ethiopia

Primary and placer gold deposits are mined from the Pan-African Adola volcano-sedimentary sequence, in southern Ethiopia. Two major mineralized belts can be recognized: the Megado (‘Gold Belt’) and the Kenticha Belts. The Kenticha Belt is also known for its rare metal mineralization. Extensive exploration of the area resulted in two most important primary gold deposits of Lega Dembi and Sakaro. The primary gold deposits are classified into four classes based on their geological setting:

- auriferous veins, lodes, stockworks and silicified zones disseminated in schistose rocks

- gold associated with quartzite

- gold mineralization confined to conglomerates and meta-arkoses

- auriferous quartz veins in high grade gneiss rocks

This classification provides a useful guide for future exploration programme     

REE constraints on fractionation processes of massive-type anorthosites on the Lofoten Islands, Norway

Summary Rare Earth Element (REE) data of 34 samples of magmatic rocks from the Lofoten Islands in Norway lend support to the derivation of anorthosites, ferrodiorites and jotunites by fractionation and cumulus processes from typical basaltic magma. Both REE concentration and Eu anomalies (expressed as Eu/Eu^*) form continuous linear trends from anorthosite towards gabbro, ferrodiorite and jotunite in discrimination diagrams against molar CaO/Al₂O₃ ratios indicating the predominant accumulation of plagioclase. Eu/Eu^* decreases from about 4 in the cumulates (anorthosites) to around 1 in the fine-grained gabbroic dikes and to below 1 in some ferrodiorites and the jotunite. The various types of ferrodiorites and the jotunite are regarded as residual liquids, in some cases with variable amounts of cumulus plagioclase. The whole fractionation series from gabbro towards anorthosites and ferrodiorites can be observed in a single intrusion. With increasing fractionation, the REE patterns generally change from flat, slightly LREE-enriched or LREE-depleted to steep and strongly LREE-enriched. These changes and the REE abundances are mainly controlled by the abundance of apatite. Temporally and spatially related mangerites and charnockites form a trend from low-SiO₂ mangerites with Eu/Eu^* > 1 to intermediate-SiO₂ acidic mangerites with Eu/Eu^* ≈ 1 and charnockites with Eu/Eu^* < 1. Accordingly, the low-SiO₂ mangerites are interpreted as alkali feldspar-rich cumulates and the charnockites as residual liquids derived from the acidic mangerites. The mangerites with Eu/Eu^* around 1 have patterns similar to those of some highly evolved ferrodiorites possibly indicating a genetic link. Received December 12, 1999; revised version accepted November 15, 2000     

Mineral Chemistry and Boron Isotopic Composition of Tourmaline from the Devonian Metallogenic District of Shanyang-Zhashui,Eastern Qinling

Toumaline is widespread in the host strata of strata-bound base metal sulphide deposits in the Devonian metallogenic district around Shanyang-Zhashui in eastern Qinling. As a member of the schorl-dravite series, the tourmaline is characterized by Mg > Fe and Na > Ca, showing apparent chemical zonation which records the geochemistry during its formation and subsequent regional metamorphism and hydrothermal overprint. The close similarity in chemical and isotopic constitutions between the tourmaline of the main metallogenic epoch in this district [FeO/(FeO + MgO)=0.34 − 0.39 and δ¹¹B=−7.6‰ − − 8.8‰] and those related to massive sulphide deposits typical of submarine (exhalative) hydrothermal sedimentation may add further support to a similar mechanism of mineralization for the strata-bound deposits in the district. Supported by the Foundation for Young Scientists under the National Natural Science Foundation of China.     

Grain growth in CaTiO3-perovskite + FeO-wüstite aggregates

Grain growth kinetics in CaTiO₃-perovskite + FeO-wüstite aggregates were studied at the conditions of T = 1223–1623 K, P = 0.1 MPa and P = 200 MPa. Starting samples were fabricated by hot-pressing mechanically mixed powders of CaTiO₃ + FeO with FeO = 0%, 1%, 3%, 6%, 10%, 20% and 100% by weight in a gas-medium apparatus at 1323 K and 300 MPa for 5 h. The increase of grain size (G) of CaTiO₃ with time (t) follows a growth law: G ⁿ −G ⁿ ₀ = κ·t(κ=κ₀exp(−(Q/RT)). Two grain growth regimes are observed at T < 1523 K and T ≥ 1523 K. For T < 1523 K, the best fits of the data to the growth law yield growth exponents of n = 2.2 ± 0.2, 3.0 ± 0.3 and 3.5 ± 0.3 for samples with FeO = 0%, 3% and 10% respectively. Under these conditions the rate constants, κ, obey an Arrhenius relation with Q = 206 ± 35 kJ/mol and 385 ± 65 kJ/mol for samples with FeO = 3% and 10%. Grain growth of CaTiO₃ becomes sluggish when FeO content exceeds 6%. For T ≥ 1523 K, the best fits of the data to the growth law yield n = 2.5 ± 0.2 for both samples with FeO = 3% and 10%. The activation energies (Q ) were determined as 71 ± 30 kJ/mol and 229 ± 45 kJ/mol for samples with FeO = 3% and 10%, respectively. The TEM observations show a remarkable difference in the distribution and geometry of FeO below and above 1523 K: nanometer-sized particles of FeO were observed along CaTiO₃ grain boundaries in samples annealed at T < 1523 K. No FeO particles were detected along CaTiO₃ grain boundaries in samples annealed at T ≥ 1523 K, but large clusters of FeO particles are observed locally indicating a fast separation of FeO from CaTiO₃. Thus we conclude that the slow growth rate of CaTiO₃ at T < 1523 K is due to the pinning by FeO particles at grain boundary, and that the change of grain growth kinetics in CaTiO₃ at T ≥ 1523 K may relate to the separation of FeO from CaTiO₃, which we interpret as due to the phase transformation of CaTiO₃ at around 1523 K. Received: 19 June 1998 / Revised, accepted: 24 March 1999     

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

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

辽东硼矿床中电气石的矿物学特征及成因意义

辽东硼矿床产于早元古代的一套变质岩内，硼矿体赋存于镁质大理岩中。电气石就产在含电气石变（浅）粒岩、电英岩及硼矿体中。电气石的矿物学研究表明：电气石中有Ｍｇ－Ｆｅ和Ｎａ－Ｃａ两个系列；电气石以富镁和钙为特征，ＦｅＯ／（ＦｅＯ＋ＭｇＯ）和Ｎａ２Ｏ／（Ｎａ２Ｏ＋ＣａＯ）比值均小于０．５。不同岩石中的电气石，其矿物学特征明显不同，这些差异反映了它们形成环境的不同，这对成岩成矿有重要的指示意义。经成因分析，电气石是由角闪岩相区域变质作用形成的     

http://www.sciencedirect.com/science/article/pii/S1674987111000806

Zoned tourmaline（schorl-dravite） in the matrix of hydrothermal explosive breccia and ore veins in gold deposits,Chita region.Eastern Transbaikalia.Russia,are associated with Na- and K-rich porphyry-type subvolcanic intrusives.δ¹⁸O values of tourmaline from three gold deposits（Darasun. Talatui,Teremkinskoye） are +8.3‰,+7.6‰,and +6.0‰and calculatedδ¹⁸O values of fluids responsible for the tourmalinization are +7.3‰,+7.7‰,and +4.2‰,respectively.These data imply an igneous fluid source,except at the Teremkin deposit where mixing with meteoric water is indicated.Wide ranges of Fe³⁺/Fe_tot,and the presence of vacancies characterize the Darasun deposit tourmaline indicating wide ranges of f（O₂） and pH of mineralizing fluids.Initial stage tourmalines from the gold deposits of the Darasun ore district are dravite or high mg schorl.Second stage tourmaline is characterized by oscillatory zoning but with Fe generally increasing towards crystal rims indicating decreasing temperature.Third stage tourmaline formed unzoned crystals with x_Mg（mole fraction of Mg） close to that of the hrst stage tourmaline,due to a close association with pyrite and arsenopyrite.From Fe³⁺/Fe_tot values,chemical composition and crystallization temperatures.logf（O₂） of mineralizing fluids ranged from ca.—25 to—20. much higher than for the gold-bearing beresite—listvenite association,indicating that tourmalinization was not related to gold mineralization.     

Högbomite in migmatitic paragneiss in the Betroka shear belt, Vohidava area, Precambrian of southern Madagascar

Summary ?The Betroka sinistral shear belt is a major geotectonic unit in the Precambrian of southern Madagascar. It consists of migmatitic paragneiss commonly interlayered with phlogopite-bearing diopsidite, phlogopite-humite-diopside-spinel marble, sillimanite-garnet quartzite and syn-tectonic S-type leucogranite. H?gbomite occurs sporadically in the migmatitic paragneiss in patches of magnetite with hercynite, and at the border of magnetite where it is in contact with hercynite, rare ilmenite, rutile and cordierite, which contains a network of chlorite, pyrophyllite and rare corundum/diaspore. X_Mg = Mg/(Mg + Fe) decreases as follows: Crd > Bt > Chl > H?g > Hc. The textural relations suggest the following h?gbomite-participating reactions: Ti-bearing hercynite ↠ hercynite + h?gbomite (intergrown/exsolution lamellae) ilmenite + cordierite ↠ hercynite + h?gbomite + rutile + chlorite/pyrophyllite   h?gbomite ↠ hercynite + ilmenite + corundum The chemical composition of h?gbomite varies substantially from grain to grain in individual samples and from sample to sample, this variation being highly dependent on the associated minerals. There is a weak zoning from core to rim in individual grains intergrown with hercynite and also in grains at the margin of hercynite, but this zoning is overprinted by zones formed at grain rims depending on the surrounding phases. In contact with hercynite, h?gbomite has FeO (total Fe as FeO) 27.1–28.5 wt.%, and MgO 4.5–5.8 wt.%, and in contact with magnetite FeO 24.9–26.5 wt.%, and MgO 6.0–8.5 wt.% and the core contents are within these values. TiO₂7.5–4.0 wt.% and Al₂O₃62.0–59.0 wt.% show zonations with increase from core to rim. Estimated P-T conditions are 6.0 ± 1.0 kbar and 700 ± 100 °C reached during a peak metamorphic stage of the Pan-African orogeny. However, the presence of diaspore with exsolved hercynite-magnetite indicates extreme retrograde metamorphism in the decompressional central part of this shear belt of southern Madagascar.

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Zusammenfassung ?H?gbomit in migmatitischem Paragneis von Vohidava in der Betroka Scherzone im südlichen Pr?kambrium von Madagaskar Die sinistrale Betroka Scherzone ist eine ausgepr?gte tektonische Einheit des Pr?kambriums in Süd Madagaskar. Sie besteht aus migmatitischem Paragneis, in dem Phlogopit-führender Diopsidit, Phlogopit-Humit-Diopsid-Spinell-Marmor, Sillimanit-Granat-Quarzit und syntektonischer S-Typ Granit eingelagert sind. Im migmatitischen Paragneis kommen sporadisch H?gbomit/Hercynit Nester im Magnetit vor und am Magnetitrand findet sich H?gbomit im Kontakt mit Hercynit und Cordierit, der mit einem Netzwerk aus Chlorit/Pyrophyllit gefüllt ist, sowie sporadisch mit Korund/Diaspor, Ilmenit und Rutil. X_Mg = Mg/(Mg + Fe) nimmt in folgender Reihung ab: Crd > Bt > Chl > H?g > Hc. Aus den texturellen Beziehungen werden folgende H?gbomit-partizipierende Reaktionen abgeleitet: Ti-führender Hercynit ↠ Hercynit + H?gbomit (verwachsen/Entmischungslamellen)   H?gbomit ↠ Hercynit + Ilmenit + Korund Die chemische Zusammensetzung von H?gbomit variiert betr?chtlich von Korn zu Korn in einer Probe und von Probe zu Probe; wobei die Variation von den Kontaktmineralen abh?ngt. H?gbomit im Hercynit hat eine schwache Zonierung von Kern zum Rand. Im H?gbomit am Hercynitrand ist die Kern-Rand-Zonierung durch die von den Kontaktmineralen abh?ngige Randzusammensetzung überpr?gt. Im Kontakt zum Hercynit hat H?gbomit 27,1–28,5 Gew.% FeO (total Fe als FeO) und 4,5–5,8 Gew.% MgO und im Kontakt zu Magnetit 24,9–26,5 Gew.% FeO und 6,0–8,5 Gew.% MgO, die Kernzusammensetzung liegt zwischen den beiden Randwerten. TiO₂nimmt vom Kern zu den R?ndern von 7,5 bis 4,0 Gew.% ab und Al₂O₃von 62,0 bis 59,0 Gew.%. Die P-T Bedingungen des Metamorphose-Peaks w?hrend der Pan-Afrikanischen Orogenese erreichten 6,0 ± 1,0 Kbar und 700 ± 100 °C. Die sp?te Bildung von Diaspor und die Hercynit-Magnetit-Entmischung weisen auf eine tiefgreifende retrograde Metamorphose im Dekompressions-Zentralbereich der Betroka-Scherzone im südlichen Madagaskar hin.

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Received January 15, 1999;/revised version accepted July 6, 1999     

Complex zoning between super-calcic pigeonite and augite from the Graveyard Point sill, Oregon: a record of the interplay between bulk and interstitial liquid fractionation

The 150 m thick late Miocene Graveyard Point sill (GPS) is situated at the Idaho-Oregon border near the southwestern edge of the western Snake River Plain. It records from bottom to top continuous fractional crystallization of a tholeiitic parent magma (lower chilled border, FeO/(FeO+MgO) = 0.59, Ni = 90 ppm) towards granophyres (late pods and dikes, FeO/(FeO+MgO) = 0.98, 78 wt% SiO₂ 3.5 wt% K₂O, <4 ppm Ni) showing a typical trend of Fe and P enrichment. Fractionating minerals are olivine (Fo₇₉-Fo₂), augite (X _Fe = 0.18−0.95), feldspars (An₈₀Or₁-An₁Or₆₂), Fe-Ti oxides (Ti-rich magnetite and ilmenite), apatite and in two samples super-calcic pigeonite (Wo_18–28 Fs_41–54). The granophyres may bear some quartz. Compositionally zoned minerals record a large interval of the fractionation process in every single sample, but this interval changes with stratigraphic height. In super-calcic pigeonite-bearing samples, olivine is scarce or lacking and because super-calcic pigeonite occurs as characteristic overgrowths on augite, its formation is interpreted to be related to the schematic reaction: augite + olivine (component in melt) + SiO₂ (in melt) = pigeonite, that defines the cotectic between augite and pigeonite in olivine-saturated basaltic systems. Line measurements with the electron microprobe reveal that the transition from augite to super-calcic pigeonite is continuous. However, some crystals show an abrupt “reversal” towards augite after super-calcic pigeonite growth. Two processes compete with each other in the GPS: fractional crystallization of the bulk liquid (the bulk melt separates from solids and interstitial liquids in the solidification front) and fractional crystallization of interstitial melt in the solidification front itself. Interplay between those two processes is proposed to account for the observed variations in mineral chemistry and mineral textures. Received: 25 November 1998 / Accepted: 14 June 1999     

Mineralogy, geochemistry and geological significance of tourmaline-rich rocks from the Paleozoic Cinco Villas massif (western Pyrenees, Spain)

Tourmaline-rich rocks associated with clastic metasedimentary rocks of Carboniferous age occur in the Cinco Villas massif, western Pyrenees. Three types of tourmaline-rich rocks were distinguished: (1) Fine-grained stratiform tourmaline-rich rocks, which are associated with carbonaceous metapelites (TR1); (2) stratabound tourmaline-rich rocks, associated with metapelites in the contact aureole of the Aya granitoid pluton (TR2); (3) stratabound to massive tourmaline-rich rocks, associated with psammopelites in contact with granites and pegmatites (TR3). Tourmalines belong to the schorl–dravite solid solution series and have a wide compositional range, from nearly end-member dravite for TR1 tourmalines to schorl for TR3 tourmalines; TR2 tourmalines have intermediate compositions. The Fe/(Fe+Mg) typically varies between 0.02 and ≈0.55, increasing from TR1 to TR3. The TR1 tourmalines commonly display a discontinuous chemical zoning with Fe-rich green cores (8–8.5% FeO) and Mg-rich colorless rims (10–11% MgO). In contrast, crystals that exhibit fine growth lamellae appear to lack significant chemical zoning. Oxygen and hydrogen isotope compositions also reveal major differences between TR1 and TR3 tourmalines, the former displaying heavier δ¹⁸O values (17.7–19‰) and δD values (−35 to −42‰) than TR3 tourmalines 11 to 13‰ and −47 to −76‰, respectively. The TR2 tourmalines show intermediate values of 11.3 to 14.6‰ for δ¹⁸O and −40 to −55‰ for δD. Linear and continuous chemical variations obtained for major and trace elements of the whole rocks reflect mixing between clay-rich and quartz-rich end-members, indicative that some tourmaline-rich rocks contain a significant detrital component. Chondrite normalized REE (rare earth element) patterns of tourmaline-rich rocks are similar to those of surrounding unaltered clastic metasediments, except for some TR1 rocks which are characterized by low contents of ΣREE. Mass-balance calculations show that tourmaline-forming processes plus metamorphism led to mass and volume changes at mesoscopic scales (≈10% for the TR1 tourmalinites). Silicon, Fe, Mn, and REE elements were partially lost from sedimentary rocks, whereas Mg and particularly B were added to pelitic sediments. Available data, nevertheless, do not allow an assessment of the boron source. Formation of the TR1 tourmaline-rich rocks probably was the net result of several processes, including direct precipitation from B-rich hydrothermal fluids or colloids, early diagenetic reactions of carbonaceous pelitic sediments with these fluids, and subsequent recrystallization during regional metamorphism. The TR2 tourmaline-rich rocks mainly developed by metamorphic recrystallization of TR1. Tourmaline-rich rocks and veins adjacent to pegmatites and granitic rocks (TR3) are the result of boron metasomatism; the primary boron having been recycled from stratiform tourmalinites during regional metamorphism and magmatism. Received: 18 November 1996 / Accepted: 25 April 1997     

山西省中条山铜矿田电气石与电气石岩的研究

本文通过对中条山铜矿田电气石和电气石岩地质产状、岩相学和矿物学、矿物化学等特征的研究，指出本区有三种成因类型的电气石：（１）北峪酸性侵入体岩浆期后热液成因电气石；（２）中条群地层中变质热液形成的电气石；（３）赋矿岩石和近矿围岩中热液蚀变电气石。第（３）类电气石具有特征的产状、矿物化学和矿物共生组合标型，是重要的找矿标志     

Development and Re‐Evaluation of Tourmaline Reference Materials for In Situ Measurement of Boron δ Values by Secondary Ion Mass Spectrometry

Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ¹¹B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ¹¹B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO₂ and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s).