Geochemical characteristics of gold-related granitoids in southwestern New Brunswick, Canada

Two groups of granitoids associated with gold mineralization in the Appalachian orogen of southwestern New Brunswick are recognized: a Late Silurian to Early Devonian (423–396 Ma) granodioritic to monzogranitic series (GMS), and a Late Devonian (370–360 Ma) granitic series (GS). The GMS granitoids are relatively low in silica, calc-alkaline, metaluminous to weakly peraluminous, and show characteristics of normal (oxidized) to reduced I-type granites depending on the properties of country rocks. They may have been derived from partial melting of lower crustal rocks triggered by underplated basaltic magmas; and country rocks bearing reduced organic carbon and/or graphite may have played an important role in the reduction of normal I-type intrusions to reduced I-type, which is essential in the formation of intrusion-related gold systems. In contrast, the GS granites, although calc-alkaline and metaluminous to peraluminous, are relatively rich in silica, incompatible elements, and high field strength elements. They are fractionated I-type granites, and are probably related to the coeval Mount Douglas granite in the Saint George batholith through fractional crystallization. Their parental magmas may have been derived from partial melting of quartzofeldspathic sources at relatively low temperatures. Both GMS and GS intrusions are orogenic, although some of them display the affinity of those emplaced into a within-plate environment. The origin of intrusion-related gold systems in this region appears to be controlled by several factors, including magma sources, magmatic processes, redox conditions (country-rock nature), and local structural regimes.     

Gold contents of sulfide minerals in granitoids from southwestern New Brunswick,Canada

The abundance of gold and selected trace elements in magmatic sulfide and rock-forming minerals from Silurian–Devonian granitoids in southwestern New Brunswick were quantitatively analyzed by laser-ablation inductively coupled plasma mass-spectrometry. Gold is mainly hosted in sulfide minerals (i.e., chalcopyrite, pyrrhotite, and pyrite), in some cases perhaps as submicron inclusions (nanonuggets). Gold is below detection (<0.02 ppm) in major rock-forming minerals (i.e., plagioclase, K-feldspar, biotite, hornblende, and muscovite) and oxides (i.e., magnetite, and ilmenite). Gold distribution coefficients between sulfide and granitoid melt are calculated empirically as: . This result suggests that gold behavior in the granitoid systems is controlled by the conditions of sulfur saturation during magmatic evolution; the threshold of physiochemical conditions for sulfur saturation in the melts is a key factor affecting gold activity. Gold behaves incompatibly prior to the formation of sulfide liquids or minerals, but it becomes compatible at their appearance. Gold would be enriched in sulfur-undersaturated granitoid magmas during fractionation, partitioning into evolved magmatic fluids and favoring the formation of intrusion-related gold deposits. However, gold becomes depleted in residual melts if these melts become sulfur-saturated during differentiation, leading to gold precipitation in the early sulfide phases of a granitoid suite. Late-stage Cl-bearing magmatic–hydrothermal fluids with low pH and relatively high oxidation state derived from either progressively cooling magmas at depth or convective circulation of meteoric water buffered by reduced carbon-bearing sediments, may scavenge gold from early sulfide minerals. If a significant amount of gold produced in this manner is concentrated in a suitable geological environment (e.g., shear zones or fracture systems), intrusion-related gold deposits may also be generated. Exploration for intrusion-related gold systems should focus on the areas around evolved phases of granitoid suites that remained sulfur-undersaturated. For sulfur-saturated granitoid suites, the less differentiated phase and associated structures are the most prospective targets.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Chemical composition of rock-forming minerals and crystallization physicochemical conditions of the Middle Eocene I-type Haji Abad pluton,SW Buin-Zahra,Iran

The Haji Abad intrusion is a well-exposed Middle Eocene I-type granodioritc pluton in the Urumieh–Dokhtar magmatic assemblage (UDMA). The major constituents of the investigated rocks are K-feldspar, quartz, plagioclase, pyroxene, and minor Fe–Ti oxide and hornblende. The plagioclase compositions fall in the labradorite, andesine, and oligoclase fields. The amphiboles range in composition from magnesio-hornblende to tremolite–hornblende of the calcic-amphibole group. Most pyroxenes principally plot in the field of diopside. The calculated average pressure of emplacement is 1.9 kbar for the granodioritic rocks, crystallizing at depths of about 6.7 km. The highest pressure estimated from clinopyroxene geobarometry (5 kbar) reflects initial pyroxene crystallization pressure, indicating initial crystallization depth (17.5 km) in the Haji Abad granodiorite. The estimated temperatures using two-feldspar thermometry give an average 724 °C. The calculated average temperature for clinopyroxene crystallization is 1090 °C. The pyroxene temperatures are higher than the estimated temperature by feldspar thermometry, indicating that the pyroxene and feldspar temperatures represent the first and late stages of magmatic crystallization of Haji Abad granodiorite, respectively. Most pyroxenes plot above the line of Fe³⁺?=?0, indicating they crystallized under relatively high oxygen fugacity or oxidized conditions. Furthermore, the results show that the Middle Eocene granitoids crystallized from magmas with H₂O content about 3.2 wt%. The relatively high water content is consistent with the generation environment of HAG rocks in an active continental margin and has allowed the magma to reach shallower crustal levels. The MMEs with ellipsoidal and spherical shapes show igneous microgranular textures and chilled margins, probably indicating the presence of magma mixing. Besides, core to rim compositional oscillations (An and FeO) for the plagioclase crystals serve as robust evidence to support magma mixing. The studied amphiboles and pyroxenes are grouped in the subalkaline fields that are consistent with crystallization from I-type calc-alkaine magma in the subduction environment related to active continental margin. Mineral chemistry data indicate that Haji Abad granodiorites were generated in an orogenic belt related to the volcanic arc setting consistent with the subduction of Neo-Tethyan oceanic crust beneath the central Iranian microcontinent.     

Sulfur isotopic systematics of granitoids from southwestern New Brunswick, Canada: implications for magmatic-hydrothermal processes, redox conditions, and gold mineralization

Bulk δ ³⁴S_rock values, sulfur contents, and magnetic susceptibility were determined for 12 gold-related granitoid intrusions in southwestern New Brunswick, the Canadian Appalachians. The sulfur isotope compositions of sulfide minerals in some of the granitoid samples were also analyzed. This new dataset was used to characterize two distinctive groups of granitoids: (1) a Late Devonian granitic series (GS) and (2) a Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS). The GS rocks have a large range in δ ³⁴S values of −7.1‰ to +13‰ with an average of 2.2 ± 5.0‰ (1σ), low bulk-S contents (33 to 7,710 ppm) and low magnetic susceptibility values (<10⁻⁴ SI), consistent with reduced ilmenite-series granites. The GMS rocks have a relatively narrower variation in δ ³⁴S values of −4.4‰ to +7.3‰ with an average 1.2 ± 2.9‰ but with larger ranges in bulk-S contents (45 to 11,100 ppm) and high magnetic susceptibility values (>10⁻³ SI), indicative of oxidized magnetite-series granites. The exceptions for the GMS rocks are the Lake George granodiorite and Tower Hill granite that display reduced characteristics, which may have resulted from interaction of the magmas forming these intrusions with graphite- or organic carbon-bearing sedimentary rocks. The bulk δ ³⁴S values and S contents of the GMS rocks are interpreted in terms of selective assimilation–fractional crystallization (SAFC) processes. Degassing processes may account for the δ ³⁴S values and S contents of some GS rocks. The characteristics of our sulfur isotope and abundance data suggest that mineralizing components S and Au in intrusion-related gold systems are dominantly derived from magmatic sources, although minor contaminants derived from country rocks are evident. In addition, the molar sulfate to sulfide ratio in a granitic rock sample can be calculated from the δ ³⁴S_rock value of the whole-rock sample and the δ ³⁴S_sulfide (or δ ³⁴S_sulfate) value of sulfide and/or sulfate mineral in the sample on the basis of S-isotope fractionation and mass balance under the condition of magmatic equilibrium. This may be used to predict the speciation of sulfur in granitic rocks, which can be a potential exploration tool for intrusion-related gold systems.     

甘-新北山地区二叠纪镁铁-超镁铁质岩体造岩矿物化学特征及其岩石学指示

二叠纪镁铁-超镁铁质岩体在北山造山带广泛分布, 其中多发育铜镍硫化物矿化, 并集中在新疆北山坡北和甘肃北山柳园地区。本文对柳园地区二叠纪骆驼山(283Ma)和西南山(277Ma)矿化岩体中早期结晶的造岩矿物开展矿物化学分析, 并对甘-新北山地区矿化岩体的主要造岩矿物进行系统对比研究。骆驼山和西南山岩体主要由单辉橄榄岩、二辉橄榄岩、橄榄辉石岩、橄榄辉长岩和辉长岩组成, 主要造岩矿物为橄榄石、单斜辉石、斜方辉石、斜长石和角闪石, 及少量铬尖晶石和金云母。铬尖晶石Cr^#值范围为52.2~70.4, TiO₂含量为1.1%~4.0%, Al₂O₃含量为8.1%~18.9%。橄榄石Fo值范围为78~86, Ni含量为856×10^-6~2121×10^-6, Ca含量为71.3×10^-6~720×10^-6。斜方辉石主要为顽火辉石和少量古铜辉石; 单斜辉石为透辉石和普通辉石, Mg^#范围为86~88, Al^Ⅳ/Al^Ⅵ比值范围为1.42~3.49。矿物成分计算结果表明岩体的母岩浆为高Mg拉斑玄武质岩浆, 结晶温度范围为1132~1323℃, 结晶压力为0.23~0.25GPa, 氧逸度范围为FMQ +1.0~+1.7, 具有富集LREE以及Nb-Ta-Zr-Hf负异常的特征。富含含水矿物及母岩浆含水量反演结果显示骆驼山和西南山岩体单斜辉石结晶时其岩浆含水量分别为3.4%和3.6%, 表明岩体原始岩浆形成于富水源区, 可能与俯冲交代作用有关。与坡北地区岩体对比, 骆驼山和西南山岩体母岩浆结晶温度略低, 较高的单斜辉石Al^Ⅳ/Al^Ⅵ值以及压力计算表明岩体形成于相对低压环境, 岩浆氧逸度范围略高于坡北地区岩体, 可能与含水的镁铁质岩浆分异演化作用相关。结合区域地质资料认为柳园地区二叠纪岩体形成于碰撞后伸展构造环境, 母岩浆所具有的岛弧岩浆特征来源于地幔源区曾经历的俯冲板片来源熔/流体的改造作用。

     

Compositional diversity among Late Devonian peraluminous granitoid intrusions in the Meguma Zone of Nova Scotia, Canada

Late Devonian (385−370 Ma) granitoid intrusions in the Meguma Zone of southwestern Nova Scotia represent two geographically separate magmatic suites that show subtly different lithological, geochemical and isotopic characteristics. “Central intrusions” crop out with satellite mafic-intermediate intrusions, range in composition from granodiorite to leucogranite, contain two micas, have exclusively peraluminous compositions (molar A/CNK 1.1-1.3), variably high values for FeO_T (0.4–6.0 wt.%), Ba (5–980 ppm), Y (6–50 ppm), Pb (2–50 ppm), Ga (11–53 ppm), ⁸⁷Sr/⁸⁶Sr_i (0.7081-0.7130), δ¹⁸O (9.8–13.0) and δ³⁴S (4.5–11.9), in conjunction with low values for εNd (−1 to −6.5). In contrast, “peripheral plutons” crop out with synplutonic mafic-intermediate intrusions, range in composition from tonalite to leucogranite, may contain minor hornblende, have dominantly peraluminous compositions (molar A/CNK 0.9-1.3), variably high concentrations of TiO₂ (0.1-1.1 wt.%), Al₂O₃ (12.0–19.7 wt.%), CaO (0.2–4.9 wt.%), Sr (7–720 ppm), Cr (3–111 ppm) and V (1–136 ppm), higher εNd values (−2.0 to 3.2), and lower values for ⁸⁷Sr/⁸⁶Sr_i (0.7040-0.7079), δ¹⁸⁸O (7.6–10.5) and δ³⁴S (0–4.6). Such regional diversity is explained by inferring that upper crustal contamination dominated the central granitoid compositions and mixing with mantle-derived mafic-intermediate magmas dominated peripheral granitoid compositions. However, additional contributions from heterogeneous lower crust cannot be excluded.     

Multistage crystallization of tonalitic enclaves in granitoid rocks (Hercynian belt,Spain): implications for magma mixing

The crystallization sequence, nucleation density and crystal index (n = nucleation density/mode) of tonalitic enclaves from different granitoids of the Hercynian orogeny indicate that they are pieces of magma partially crystallized in the interior of synplutonic bodies of basic magma, which was injected into a silicic magma chamber. A rapid cooling stage can be identified from the high nucleation density and high n-values of minerals. A final stage of slow cooling, is identified by a low nucleation density and low n-values. At this stage a residual melt crystallized in thermal equilibrium to the cooling rate of the whole magma chamber. Thermal equilibrium and convection are necessary conditions for mixing. Enclaves can be interpreted as the remaining, non-disaggregated portions of an early injected mafic magma, which in turn underwent hybridization during injection. Their presence indicates the existence of magma mixing processes and the possibility that the host granitoid was a hybrid rock.

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Zusammenfassung Die Kristallisationsabfolge, Keimdichte und der Kristallindex (n = Keimdichte/Modus) von tonalitischen Einschlüssen verschiedener Granitoide des variszischen Orogens zeigen, daß sie Teile eines Magmas sind, das teilweise im Inneren von basischen synplutonischen Magmenkörpern auskristallisierte und in eine silikatische Magmenkammer injiziert wurde. Eine Zeit schnellen Abkühlens kann an Hand der hohen Keimdichte und der niedrigen n-Werte festgestellt werden. Zu diesem Zeitpunkt kristallisierte eine Restschmelze unter thermischen Gleichgewichtsbedingungen und der Abkühlungsgeschwindigkeit der ganzen Magmenkammer aus. Thermisches Gleichgewicht und Konvektion sind für das Mischen notwendig. Einschlüsse können als nichtzerfallene Reste eines früh injizierten mafischen Magmas angesehen werden, welches während der Injizierung eine Hybridisierung erfuhr. Ihre Gegenwart zeigen das Vorhandensein von Magmenmischungsvorgängen und die Möglichkeit, daß der Muttergranitoid ein Hybridgestein war, an.

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Resumen La secuencia de cristalización, densidad de nucleación e índice cristalino (n = densidad de nucleación/moda) de enclaves tonalíticos de diferentes granitoides hercínicos, indican que dichos enclaves representan fragmentas de magma parcialmente cristalizados en el interior de cuerpos simplutónicos de magma básico, que originalmente fue inyectado en una cámara magmática félsica. Se puede identificar una etapa de enfriamiento rápido a partir de los altos valores de n y alta densidad de nucleación de los minerales. Una etapa final de enfriamiento lento es detectada por una baja densidad de nucleación y bajos valores de n de determinados minerales. Un líquido residual cristalizó en esta etapa lenta en equilibrio térmico y a la misma tasa de enfriamiento que toda la cámara magmática en conjunto. Equilibrio térmico y convección son condiciones necesarias para que se produzca mezcla. Los enclaves pueden ser interpretados como porciones no hibridadas de magma que han sido homogéneamente distribuidos dentro del granitoide encajante. Su presencia indicaría la existencia de procesos de mezcla de magmas y la posibilidad de que el granitoide encajante sea una roca híbrida.

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, (n = /) , , , . . . . , , . , , , , .

     

西南天山二叠纪中酸性侵入岩的地质学和地球化学：岩石成因和构造背景

选择3个典型岩体,即位于西南天山东段的拜城县英买来岩体和位于西段阔克萨岭区的川乌鲁岩体、巴雷公岩体（为了对比,也选择了位于塔里木盆地西北缘的麻扎山岩体）,进行了岩石学和地球化学研究。结果表明,这些岩体具有不同的特点。英买来岩体为黑云母花岗岩和二云母花岗岩,具有高的SiO2含量,弱过铝,高的Sr同位素初始值（约0.710）和负的εNd(t)值（-4～-6）,属于S—A型之间的过渡类型。麻扎山岩体由正长岩组成,属于碱性岩,微量元素标准化图解和其他岩体明显不同的是没有明显的Nb和Ta的负异常。川乌鲁岩体是一个由3个不同期次岩石组成的杂岩体,主体为正长岩-二长岩,地球化学特征显示是由基性岩浆和酸性岩浆不同程度混合形成的。位于同一构造区的巴雷公岩体则与川乌鲁岩体中的花岗斑岩的地球化学特征相似。综合岩石学和地球化学特征推测,南天山东段的英买来岩体是地壳熔融的结果,没有任何地幔物质加入的地球化学信息,西段的阔克萨岭地区酸性岩浆的形成则可能是来自于幔源底侵的基性岩浆导致薄的地壳发生熔融的结果。麻扎山岩体则完全是不同构造背景的产物,有可能与发生在塔里木盆地的二叠纪大规模的岩浆活动有关。因此,二叠纪岩浆活动的性质主要受地壳成分和结构的控制。     

Modern observations of floccule ripples: Petitcodiac River estuary,New Brunswick,Canada

Mud floccule ripples, small mud rip‐up clasts, erosional scars and tool marks are reported for the first time from the macrotidal Petitcodiac River estuary, New Brunswick, Canada. The ripples occur on the intertidal flats and are ebb‐oriented. Observations have been conducted during the spring low tide at high‐river and low‐river discharge. Floccule ripples forming during the high‐river flow are characterized by increased silt fraction, low relief and sinuous to lunate form. The ripples forming during the low flow are clay‐dominated, have very low relief and are characterized by narrow straight ridges and patchy distribution. The preserved mud floccule ripples manifest in interbedded silt‐rich and clay‐rich deposits with parallel, wavy, lenticular and current‐ripple lamination. Presented floccule ripples are current‐generated, non‐episodic in nature and are sedimentologically characterized. The ripple origin is constrained by morphometric and grain‐size analyses, and observed hydraulic processes. It is confirmed that mud floccule ripples originate under a similar range of hydraulic parameters as documented in previous flume studies. This study confirms application of work conducted in recent decades on mud‐dominated marginal‐marine environments and helps with understanding of properties and distribution of fine‐grained sediments in tidally influenced settings.     

八达岭花岗杂岩的组成、地球化学特征及其意义

北京地区八达岭花岗杂岩是燕山期岩浆侵入活动的典型代表,按照地球化学特征及成因,本文将其分为3类第1类由辉长-闪长岩组成,富Fe、Ti和P,Th/Ta比值近似等于1(0.7～1.2),ISr和εNd(t)值低(分别为0.705和-8～-11),产于板内环境,推测是大陆岩石圈地幔部分熔融形成的,可能代表了燕山期时底侵到加厚陆壳底部的玄武质岩浆.第2类为八达岭花岗杂岩的主体,由石英闪长岩-花岗闪长岩-二长花岗岩组成,其地球化学特征为SiO2＞57%,K2O＞2.7%,Na2O/K2O=0.9～1.7,Al2O3在16%～14%之间,LREE富集,(La/Yb)N=25～41,HREE亏损(Yb＜1.32μg/g),无或有弱的负铕异常(Eu/Eu*=1.0～0.9),富Sr(354～1191μg/g),贫Y(＜16μg/g),Sr/Y比值高(45～156).上述地球化学特征除了K2O含量偏高和Al2O s含量偏低外,大体类似于埃达克质岩石的性质,表明岩浆的源区很深,与石榴石处于平衡,暗示其来源于燕山期华北加厚的陆壳底部,可能是下地壳中基性麻粒岩部分熔融形成的.第3类由碱长花岗岩和石英二长岩组成,Na2O+K2O＞9%,贫Sr、Ba,富Rb,LREE富集,有明显的负铕异常(Eu/Eu*=0.4～0.5),属于A型花岗岩,是由于第2类埃达克质岩石形成之后,引起了岩石圈拆沉,造成地幔上涌至减薄陆壳的底部,引起壳幔过渡带物质部分熔融的结果.该区燕山期岩浆活动与古太平洋板块的消减作用无关,是板内伸展事件的产物.     

Chemical composition,volatile components,and trace elements in the melts of the Gorely volcanic center,southern Kamchatka: Evidence from inclusions in minerals

Melt inclusions in olivine and plagioclase phenocrysts from rocks (magnesian basalt, basaltic andesite, andesite, ignimbrite, and dacite) of various age from the Gorely volcanic center, southern Kamchatka, were studying by means of their homogenization and by analyzing the glasses in 100 melt inclusions on an electron microprobe and 24 inclusions on an ion probe. The SiO₂ concentrations of the melts vary within a broad range of 45–74 wt %, as also are the concentrations of other major components. According to their SiO₂, Na₂O, K₂O, TiO₂, and P₂O₅ concentrations, the melts are classified into seven groups. The mafic melts (45–53 wt % SiO₂) comprise the following varieties: potassic (on average 4.2 wt % K₂O, 1.7 wt % Na₂O, 1.0 wt % TiO₂, and 0.20 wt % P₂O₅), sodic (3.2% Na₂O, 1.1% K₂O, 1.1% TiO₂, and 0.40% P₂O₅), and titaniferous with high P₂O₅ concentrations (2.2% TiO₂, 1.1% P₂O₅, 3.8% Na₂O, and 3.0% K₂O). The melts of intermediate composition (53–64% SiO₂) also include potassic (5.6% K₂O, 3.4% Na₂O, 1.0% TiO₂, and 0.4% P₂O₅) and sodic (4.3% Na₂O, 2.8% K₂O, 1.3% TiO₂, and 0.4% P₂O₅) varieties. The acid melts (64–74% SiO₂) are either potassic (4.5% K₂O, 3.6% Na₂O, 0.7% TiO₂, and 0.15% P₂O₅) or sodic (4.5% Na₂O, 3.1% K₂O, 0.7% TiO₂, and 0.13% P₂O₅). A distinctive feature of the Gorely volcanic center is the pervasive occurrence of K-rich compositions throughout the whole compositional range (silicity) of the melts. Melt inclusions of various types were sometimes found not only in a single sample but also in the same phenocrysts. The sodic and potassic types of the melts contain different Cl and F concentrations: the sodic melts are richer in Cl, whereas the potassic melts are enriched in F. We are the first to discover potassic melts with very high F concentrations (up to 2.7 wt %, 1.19 wt % on average, 17 analyses) in the Kuriles and Kamchatka. The average F concentration in the sodic melts is 0.16 wt % (37 analyses). The melts are distinguished for their richness in various groups of trace elements: LILE, REE (particularly HREE), and HFSE (except Nb). All of the melts share certain geochemical features. The concentrations of elements systematically increase from the mafic to acid melts (except only for the Sr and Eu concentrations, because of active plagioclase fractionation, and Ti, an element contained in ore minerals). The paper presents a review of literature data on volcanic rocks in the Kurile-Kamchatka area in which melt inclusions with high K₂O concentrations (K₂O/Na₂O > 1) were found. K-rich melts are proved to be extremely widespread in the area and were found on such volcanoes as Avachinskii, Bezymyannyi, Bol’shoi Semyachek, Dikii Greben’, Karymskii, Kekuknaiskii, Kudryavyi, and Shiveluch and in the Valaginskii and Tumrok Ranges.     

Petrology and mass-balance constraints on major-, trace-, and rare-earth-element mobility in porphyry-greisen alteration associated with the epizonal True Hill granite, southwestern New Brunswick, Canada

Endogreisen and exogreisen weakly mineralized with Bi, Sn, and Mo are associated with two of three granite porphyry (granite) cupolas hosted in Silurian metasedimentary rocks at True Hill, southwestern New Brunswick. The epizonal, weakly peraluminous and compositionally evolved True Hill granite is quartz and K-feldspar porphyritic; groundmass textures, such as granophyric patches, miarolitic cavities, and pegmatite pods, are indicative of rapid cooling and vapor saturation.The greisen mineralization in cupolas B and C is overprinted by various types of alteration, reflecting multi-stage devolatilization of the magma. The most intense topaz-bearing greisen is confined mainly to the apical parts of the granite. In places, fluorite is associated with silicification, sericitization, and chloritization, which is common to greisen-type alteration. The alteration types reflect the physical and chemical changes in the hydrothermal fluid that was derived principally by second boiling of the magma. Al-normalized, mass-balanced geochemical data supported by petrographic observations show that in the greisenized True Hill granite, Fe, Mn and Mg enrichment corresponds to chlorite and/or Fe-muscovite alteration and are coincident with leaching of Na and K and deposition of SiO₂. Ca was remobilized in the greisen environment, but erratically deposited as fluorite. Minor P and LREE enrichment are reflected by the presence of monazite in the greisen. The HFSE are mobile to a minor degree, based on correlations with elements known to be hydrothermally mobile. The base metals correlate with S and other ore-forming elements. The distribution of many of the trace elements is related to alteration, including the leaching of alkalis, which leads to the stabilization of aluminosilicates, principally muscovite and topaz. The distribution of trace elements reflects their relative mobility during greisenization, with high-field-strength elements (Zr and Ti) the most immobile and the lithophile and chalcophile elements the most mobile. Breccias and greisen alteration in cupola C at True Hill are similar to those at the base of the W-Mo-Bi porphyry-greisen in the Fire Tower zone above the Mount Pleasant fine-grained granite.     

The distribution of salt marsh foraminifera at Little Dipper Harbour New Brunswick, Canada: implications for development of widely applicable transfer functions in sea-level research

A stepwise linear regression analysis was carried out on both 0–1 and 0–10 cm surface samples from a transect across the marsh at Little Dipper Harbour, New Brunswick. Only the 0–1 cm surface samples produce statistically reliable results (R²=0.705; R′²=0.609). These results are in sharp contrast to those obtained from British Columbia marshes where infaunal habitat and taphonomic biasing result in 0–10 cm samples producing the best results using stepwise linear regression. The fundamental difference in the apparent preferred habitats of marsh foraminifera in these areas pose difficulties for researchers attempting to develop transfer function training sets that can be applied over wide areas in paleo-sea-level research.     

The Omolon pallasite: Chemical composition,mineralogy, and genetic implications

The chemical composition of mineral components of the Omolon pallasite was determined by neutron-activation. Six types of olivines were distinguished. Four types differ in the abundance of Co relative to Ni of CI chondrites. The fifth and sixth types were distinguished on the basis of REE distribution in them. Both last types are variably enriched in LREE relative to CI chondrites. In terms of Ca content relative to CI chondrite, these six types are subdivided into two groups: low-calcium and high-calcium. The difference in Ca contents can be caused by different cooling rate of the precursor of these olivines. The distribution pattern of siderophile elements in the pallasite metal indicates that a metallic phase experienced chemical transformations since the time of its formation. The analysis of chemical composition of accessory minerals showed that: (1) HREE are accumulated in tridymite; (2) troilite and daubreelite were formed under different temperature conditions; (3) magnetite is the mineral of the outer zone of melting crust. Four fragments with anomalous contents of lithophile elements were found in the pallasites and studied. The unusual chemical composition of phases and high degree of HREE fractionation in the fragments suggest their formation at high temperatures at the early stage of the Solar system evolution. It is assumed that the Omolon pallasite was formed as impact-brecciated mixture of the asteroid core (with composition close to IIIAB group of iron meteorites) and mantle olivine from incompletely differentiated parent body of chondrite composition.     

Chemical composition,volatile components,and trace elements in melts of the Karymskii volcanic center,Kamchatka, and Golovnina volcano,Kunashir Island: Evidence from inclusions in minerals

Melt inclusions were examined in phenocrysts in basalt, andesite, dacite, and rhyodacite from the Karymskii volcanic center in Kamchatka and dacite form Golovnina volcano in Kunashir Island, Kuriles. The inclusions were examined by homogenization and by analyzing glasses in more than 80 inclusions on an electron microscope and ion microprobe. The SiO₂ concentrations in the melt inclusions in plagioclase phenocrysts from basalts from the Karymskii volcanic center vary from 47.4 to 57.1 wt %, these values for inclusions in plagioclase phenocrysts from andesites are 55.7–67.1 wt %, in plagioclase phenocrysts from the dacites and rhyodacites are 65.9–73.1 wt %, and those in quartz in the rhyodacites are 72.2–75.7 wt %. The SiO₂ concentrations in melt inclusions in quartz from dacites from Golovnina volcano range from 70.2 to 77.0 wt %. The basaltic melts are characterized by usual concentrations of major components (wt %): TiO₂ = 0.7–1.3, FeO = 6.8–11.4, MgO = 2.3–6.1, CaO = 6.7–10.8, and K₂O = 0.4–1.7; but these rocks are notably enriched in Na₂O (2.9–7.4 wt % at an average of 5.1 wt %, with the highest Na₂O concentration detected in the most basic melts: SiO₂ = 47.4–52.0 wt %. The concentrations of volatiles in the basic melts are 1.6 wt % for H₂O, 0.14 wt % for S, 0.09 wt % for Cl, and 50 ppm for F. The andesite melts are characterized by high concentrations (wt %) of FeO (6.5 on average), CaO (5.2), and Cl (0.26) at usual concentrations of Na₂O (4.5), K₂O (2.1), and S (0.07). High water concentrations were determined in the dacite and rhyodacite melts: from 0.9 to 7.3 wt % (average of 15 analyses equals 4.5 wt %). The Cl concentration in these melts is 0.15 wt %, and those of F and S are 0.06 and 0.01 wt %, respectively. Melt inclusions in quartz from the dacites of Golovnina volcano are also rich in water: they contain from 5.0 to 6.7 wt % (average 5.6 wt %). The comparison of melt compositions from the Karymskii volcanic center and previously studied melts from Bezymyannyi and Shiveluch volcanoes revealed their significant differences. The former are more basic, are enriched in Ti, Fe, Mg, Ca, Na, and P but significantly depleted in K. The melts of the Karymskii volcanic center are most probably less differentiated than the melts of Bezymyannyi and Shiveluch volcanoes. The concentrations of water and 20 trace elements were measured in the glasses of 22 melt inclusions in plagioclase and quartz from our samples. Unusually high values were obtained for Li concentrations (along with high Na concentrations) in the basaltic melts from the Karymskii volcanic center: from 118 to 1750 ppm, whereas the dacite and rhyolite melts contain 25 ppm Li on average. The rhyolite melts of Golovnina volcano are much poorer in Li: 1.4 ppm on average. The melts of the Karymskii volcanic center are characterized by relative minima at Nb and Ti and maxima at B and K, as is typical of arc magmas.     

Physico-chemical conditions of four calc-alkaline granitoid plutons of Chhotanagpur Gneissic Complex,eastern India: Tectonic implications

Petrography and mineralogy of four calc-alkaline granitoid plutons Agarpur, Sindurpur, Raghunathpur and Sarpahari located from west to east of northern Purulia of Chhotanagpur Gneissic Complex, eastern India, are investigated. The plutons, as a whole, are composed of varying proportions of Qtz–Pl–Kfs–Bt–Hbl±Px–Ttn–Mag–Ap–Zrn±Ep. The composition of biotite is consistent with those of calc-alkaline granitoids. Hornblende–plagioclase thermometry, aluminium-in-hornblende barometry and the assemblage sphene–magnetite–quartz were used to determine the P, T and \(f_{\mathrm{O}_2}\) during the crystallisation of the parent magmas in different plutons. The plutons are crystallised under varying pressures (6.2–2.4 kbar) and a wide range of temperatures (896–\(718{^{\circ }}\hbox {C}\)) from highly oxidised magmas (log \(f_{\mathrm{O}_2}\) \(-11.2\) to \(-15.4\) bar). The water content of the magma of different plutons varied from 5.0 to 6.5 wt%, consistent with the calc-alkaline nature of the magma. Calc-alkaline nature, high oxygen fugacity and high \(\hbox {H}_{2}\hbox {O}_{{\mathrm{melt}}}\) suggest that these plutons were emplaced in subduction zone environment. The depths of emplacement of these plutons seem to increase from west to east. Petrologic compositions of these granitoids continuously change from enderbite (opx-tonalite: Sarpahari) in the east to monzogranite (Raghunathpur) to syenogranite (Sindurpur) to alkali feldspar granite (Agarpur) in the west. The water contents of the parental magmas of different plutons also increase systematically from east to west. No substantial increase in the depth of emplacement is found in these plutons lying south and north of the major shear zone passing through the study area suggesting the strike-slip nature of the east–west shear zone.     

Geochemistry of microgranular enclaves in Aligoodarz Jurassic arc pluton, western Iran: implications for enclave generation by rapid crystallization of cogenetic granitoid magma

Microgranular enclaves are common in the Jurassic Aligoodarz granitoids of western Iran. Enclaves Enclosed in Granodiorite (EEG) and Enclaves Enclosed in Tonalite (EET) are different but they overlap their hosts on variation diagrams. The EEG is compositionally intermediate between tonalite and granodiorite. Mixing between tonalitic and granodioritic magmas and fractional crystallization are two models examined as the origin of the EEG. Field, textural, mineralogical and chemical observations suggest that chemical equilibration, common in magma mixing, was not attained between the EEG and its host. This, together with other observations does not support magma mixing as a mechanism for forming the EEG. Alternatively, excessive nucleation of biotite ± Fe-Ti-oxides ± amphibole by rapid cooling at borders of a shallow magma chamber and later fragmentation and dispersal by dynamic arc plutonism best explains the EEG. However, channeling of a new magma into the nearly solid tonalitic host explains formation of the EET.     

An ornamented mudstone cavity, Boss Point Formation, Sackville, New Brunswick, Canada: evidence for mud intrusion and rheoplasis

An ornamented, dome-shaped cavity, partially filled with mudstone, 4 m in diameter at its circular base and 1 m in height occurs in fluvial sandstone of the Carboniferous Boss Point Formation near Sackville, New Brunswick, Canada. The cavity formed by differential weathering and erosion of the mudstone. Its origin is enigmatic though its size, shape and relationship to the underlying mudstone bed on which it rests suggest a diapiric origin for the mudstone that filled it. On the other hand, the ornamentation on the cavity surface includes flute moulds, suggesting an erosional origin for the domal structure. Of the four principal hypotheses for its origin the one preferred by the authors involves formation by diapiric intrusion of semi-fluid mud into liquefied sand, soon after deposition. The ornamentation on the cavity surface would have formed as part of the intrusion process. Structures akin to flute moulds have been produced experimentally in support of this interpretation by differential flow across a cement-mix-mud interface in a flow box and also by diapiric intrusion of mud in a soft cement mix. By analogy the flute moulds on the cavity surface could have been formed in the same way. By this interpretation, primary sedimentary processes need not be invoked to explain their occurrence on either this cavity surface or on the numerous other mudstone cavity surfaces that are ubiquitous in the Permo-Carboniferous of eastern Canada. Results of this study have important implications with respect to the potential diversity of origins of flute moulds in general.