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Elemental concentrations and stable isotopic compositions of 41 sweeteners (syrups, honeys, and sugars) and 43 edible oils were determined to evaluate their potential as parameters for food authentication. The addition of as little as 10% of corn syrup to pure maple syrup can be detected using molar ratios of Na/(Na + K) and Na/(Na + Ca) for maple syrups. The detection of more than 15% adulterant in maple syrup and honey is also possible due to the 13‰ difference in carbon isotopic composition of C3 plants for authentic honeys and maple syrups (25.1 ± 1.1‰) relative to the carbon isotopic composition of C4 plants for corn syrups and cane sugars (−11.4 ± 0.8‰) as major adulterant agents. Nearly constant net oxygen (1.028 ± 0.002) as well as hydrogen (0.974 ± 0.005) isotope fractionation factors between honeys and average local meteoric waters from two areas, Kingston and Costa Rica, suggests that these isotope ratios of honeys are good candidates to authenticate their geographic locations. The net oxygen (1.03 ± 0.001) as well as hydrogen (0.894 ± 0.003) isotope fractionation factors between olive oils and local meteoric waters from different parts of Italy suggests that these isotope ratios are independent of the oil processing method and therefore can be used to trace geographic locations.

Nitrogen isotopic compositions and concentrations in micas from kimberlite-hosted MARID (mica-amphibole-rutile-ilmenite-diopside) suite of xenoliths from the Kimberley area of the Kaapvaal Craton, South Africa, were measured using continuous-flow isotope-ratio mass spectrometry and Fourier transform infrared spectroscopy. Fourier transform infrared spectroscopy data suggest that the nitrogen in MARID phlogopite is from ammonium in the mica structure. The replacement of potassium by ammonium is the major mechanism for the storage of nitrogen within these phlogopites. The δ15N values of micas from MARID xenoliths range from − 11 to + 9‰, and nitrogen contents range between 113 and 272 ppm. The 15N enrichment of most samples relative to the average upper mantle δ15N value of − 5‰ suggests that the nitrogen reflects a recycled reservoir from subducted material within their source region. The presence of nitrogen from a recycled reservoir indicates that sedimentary organic nitrogen in the sub-continental lithosphere is not effectively cycled to the surface resulting in a geochemically heterogeneous upper mantle.

The Kola Superdeep Borehole, the deepest ever drilled into the Earth's crust with a depth of 12.2 km, is located in the Kola Peninsula, Russia, and consists of high-grade metasedimentary and metaigneous lithologies ranging in age from Archean to Proterozoic. Metabasic rocks and amphibolites from the borehole have δ18O values in the range from +4.4‰ to +9.2‰ and δD values in the range from −73‰ to −40‰, gneisses and a migmatite have δ18O values in the range from +7.8‰ to +9.4‰ and δD values in the range from −63‰ to −44‰, and metasedimentary rocks show large variations in δ18O values from +6.3‰ to +15‰, and have δD values in the range from −57‰ to −33‰. The isotopic compositions of the deep borehole samples are identical with their surface equivalents, indicating that the processes of emplacement and exposure of deep crustal rocks have not affected their H and O isotopic compositions in marked contrast to what has been observed for crust in tectonically active areas. Fluid compositions calculated from the δ18O and δD values of coexisting amphibole, feldspar, biotite and garnet indicate that two isotopically distinct fluids have interacted with the Kola Superdeep Borehole rocks. One fluid has isotopic compositions consistent with locally rock-buffered regional metamorphic fluids, and the other fluid has compositions expected for Paleoproterozoic seawater. The δ18O values of co-existing amphibole–feldspar and biotite–garnet pairs in amphibolites and quartzite have apparent equilibration temperatures from ca. 500 °C to 800 °C, which are in good agreement with temperatures determined by cation exchange geothermometry and co-existing assemblages. Only rocks associated with two major faults and the thrust zone that marks the Proterozoic–Archean boundary indicate isotopic exchange with regional metamorphic fluids circulating along these structures. The stable isotopic compositions of the Kola Superdeep Borehole rocks indicate that there was interaction of the rocks with channelized fluids moving along major faults, but there was no pervasive fluid flow during metamorphism.

Marcona, the preeminent Andean magnetite deposit (1.9 Gt @ 55.4% Fe and 0.12% Cu), is located in the iron oxide copper-gold (IOCG) subprovince of littoral south-central Peru. Fe oxide and Cu (-Zn-Pb) sulfide mineralization was controlled by northeast-striking faults transecting a Middle Jurassic (Aalenian-to-Oxfordian) andesitic, shallow-marine arc and a succession of contiguous, plate boundary-parallel, Late Jurassic to mid-Cretaceous volcanosedimentary basins. At Marcona, hydrothermal activity was initiated in the earliest Middle Jurassic (161–177 Ma) by high-temperature Mg-Fe metasomatism represented by cummingtonite and phlogopite-magnetite assemblages. Subsequently, during the terminal eruptions (156–162 Ma) of the arc, widespread albite-marialite alteration (Na-Cl metasomatism) was followed by the emplacement of an en echelon swarm of massive magnetite ore-bodies with subordinate, overprinted magnetite-sulfide assemblages, hosted largely by Paleozoic metasilici-clastics. The magnetite orebodies exhibit abrupt, smoothly curving contacts, dike-like to tubular apophyses, and intricate, amoeboid interfingering with dacite porphyry intrusions. There is no convincing megascopic or microscopic evidence for large-scale Fe metasomatism associated with the main, sulfide-poor mineralization. The largest, 400 Mt Minas 2-3-4 orebody is interpreted as a bimodal magnetite-dacite intrusion comprising commingled immiscible melts generated through the dissolution of metasedimentary quartz in parental andesitic magma. Oxygen and sulfur stable-isotope geothermometry indicates that the evolution at ca. 159 Ma from magnetite-biotite-calcic amphibole ± phlogopite ± fluorapatite to magnetite-phlogopite-calcic amphi-bole-pyrrhotite-pyrite assemblages coincided with quenching from above 800° C to below 450°C and the concomitant exsolution of dilute aqueous brines. Subsequently, chalcopyrite-pyrite-calcite ± pyrrhotite ± sphalerite ± galena assemblages, in part metasomatic, were deposited from lower temperature (≤360°C) brines. The Cu-poor Marcona (“Kiruna-type”) magnetite and Cu-rich IOCG deposits in the district, therefore, although spatially contiguous, represent contrasting ore deposit types. The former are interpreted as the product of Fe oxide melt coexisting with dacite magma within an andesitic arc which failed during the closure of a back-arc basin. The weak associated magmatic-hydrothermal Cu sulfide mineralization at Marcona was generated through melt vesiculation and contrasts with the considerably higher grade Cu- and Ag-rich orebodies of the major Cu-rich IOCG deposits in the Central Andes, e.g., La Candelaria-Punta del Cobre, Mantoverde, Raul-Condestable, and Mina Justa, which were the products of cool, oxidized, hydrothermal fluids plausibly expelled from the adjacent basins during tectonic inversion.

The Camaguey district, Cuba, is known for its epithermal precious metal deposits in a Cretaceous volcanic arc setting. Recently, the La Union prospect was discovered in the southern part of the district, containing gold and minor copper mineralization interpreted as porphyry type. Mineralization is hosted in a 73.0 ± 1.5 Ma calc–alkaline I-type oxidized porphyry quartz diorite intrusive within volcanic and volcaniclastic rocks of the early Cretaceous Guaimaro Formation. The porphyry is affected by propylitic alteration and crosscut by a network of quartz and carbonate veinlets and veins. Chlorite, epidote, sericite, quartz, and pyrite are the main minerals in the early veins which are cut by late carbonate and zeolite veins. Late barite pseudomorphously replaces pyrite. Gold is associated with pyrite as disseminations in the altered quartz diorite and in the veins, occurring as inclusions or filling fractures in pyrite with 4 g/t Au in bulk samples, and up to 900 ppm Au in in pyrite. Fluid inclusion and oxygen isotope data are consistent with a H2O–NaCl–(KCl) mineralizing fluid, derived from the quartz diorite magma, and trapped at least at 425°C and 1.2 kbar. This primary fluid unmixed into two fluid phases, a hypersaline aqueous fluid and a low-salinity vapor-rich fluid. Boiling during cooling may have played an important role in metal precipitation. Pyrite δ34S values for the La Union prospect range between 0.71‰ and 1.31‰, consistent with a homogeneous magmatic sulfur source. The fluids in equilibrium with the mineralized rocks have estimated δ18O values from 8‰ to 11.8‰, calculated for a temperature range of 480–505°C. The tectonic environment of the La Union prospect, its high gold and low copper contents, the physical–chemical characteristics of the mineralizing fluids and the isotopic signature of the alteration minerals and fluids indicate that the La Union gold mineralization is similar to the porphyry gold type, even though the ore-related epidote–chlorite alteration can be classified as propylitic and not the classic potassic and/or phyllic alteration. The low copper contents in the prospect could be due to a mineralizing fluid previously saturated in copper, which is indicated by trapped chalcopyrite crystals in high-temperature fluid inclusions. The low-temperature paragenesis, represented by carbonate, zeolite and barite, indicates epithermal overprint. The study shows the potential for other gold porphyry-type deposits in the Cretaceous volcanoplutonic arc of Cuba.

Hydrothermally altered basaltic lava-units in the northern Kerguelen Archipelago contain a wide variety of secondary silicate and carbonate minerals, including zeolites, hydrothermal calcite, dolomite and magnesite, as well as celadonite, orthoclase (adularia) and quartz. Petrography, fluid-inclusion microthermometry, trace-elements geochemistry, Sr isotopes and stable-isotope compositions indicate hydrothermal fluid cells derived from meteoric water interacting with basalts and Rb-rich subvolcanic peralkaline rocks at temperatures ranging from 50 to 200 °C associated with the cooling of the lava pile. The calculated δ 18 O values of meteoric-hydrothermal waters in fossil hydrothermal systems are identical to those in present-day hot springs, suggesting that meteoric recharge was continuous throughout the igneous cooling cycles of the 28–23 Ma older host basalts and the younger 15–5 Ma old peralkaline intrusions. The Kerguelen northern coastline hydrothermal system in the basaltic pile demonstrates that much of the silicate mineralogy and almost all carbonate secondary minerals in altered basalts were derived from meteoric-hydrothermal fluids, rather than products of seawater interaction, or even magmatic-hydrothermal fluids associated with peralkaline intrusions.

The Bahamian Archipelago is one of the few locations in the world where ooid formation is actively occurring. Ooid cortices from six locations in the region were incrementally dissolved and analyzed for 14C, δ18O, δ13C, Mg/Ca, and Sr/Ca ratios. Ooids were examined under SEM after each step in the incremental analyses to characterize the nature of dissolution. Radiocarbon dating indicates that ooids presently at the sediment–water interface began forming across the Archipelago between 1000 and 2800 yr BP and continue to form today. The ooids have the same pattern of microboring alteration across the region. The surface and outer cortex of the ooids are punctuated with unfilled microborings, whereas the inner cortex contains two morphologies of aragonite cement filling the microborings. The two morphologies of cement form in association with two different species of cyanobacteria, one is Solentia sp. the other is interpreted to be Hyella sp. The chemistry of ooids from across the region is remarkably similar. δ18O and δ13C values for all samples vary directly, having a slope of approximately 1. The outer cortex has low δ18O and δ13C values of −3.4‰ and 0.2‰ respectively, whereas the δ18O and δ13C values of the inner cortex are high with values of 1.9‰ and 6.8‰ respectively. The presence of aragonite cement in microborings in the inner cortex increases the overall isotopic composition of both oxygen and carbon in the ooid, causing it to appear close to equilibrium with seawater. The isotopic variation in δ18O and δ13C within the cortex can be characterized as a mixing line between the low values in the unaltered ooid laminae and the aragonite cement in the microborings. The most exterior portion of the ooid has very high Mg/Ca values and is interpreted as an amorphous calcium carbonate (ACC) coating. There are two other phases in the cortex, both being aragonite. The outer cortex has a higher Mg/Ca ratio and lower Sr/Ca ratio than the inner cortex. This difference in chemistry is a result of the presence of aragonite cement in the inner cortex. Stable isotopic and trace element results coupled with SEM investigations indicate that microbes do not play a role in ooid formation, but instead alter the texture and chemistry of ooids after they have formed. A new model of ooid formation is proposed whereby a veneer of ACC precipitates on an ooid while it is at the sediment–water interface (the active phase). This veneer of ACC later recrystallizes to aragonite needles and a new cortex layer is formed (the stationary phase). Observations from this study lead to a deeper understanding of the chemical processes involved in ooid genesis, which allow a better understanding of paleoenvironments hosting ooid formation.

The 395 Ma Brazil Lake granitic pegmatite, a rare occurrence of an LCT-type (Li–Cs–Ta) pegmatite in the Meguma Terrane of Nova Scotia, Canada, is hosted by metasedimentary and metavolcanic rocks of the Silurian White Rock Group. Previous mineralogical studies showed the pegmatite formed in two distinct stages, an early spodumene – K-feldspar – quartz ± muscovite stage that was followed by a pervasive metasomatic stage in which albite and secondary muscovite grew at the expense of earlier K-feldspar. The economically important oxide phases (Ta–Nb) are intimately associated with secondary albite. Determination of the stable isotopic (δ18O, D) values for silicate phases (quartz, K-feldspar, spodumene, albite, muscovite, garnet, tourmaline) provide insight into the origin of the pegmatite-forming melt and its subsequent internal evolution. A primary δ18O signature for the melt of +8‰ is calculated using the δ18Ovalues of quartz and Δquartz – whole-rock values from studies on other granitic suites. Interpreted in the context of the geological setting, the δ18O data preclude a dominantly metasedimentary source and suggest, instead, that the pegmatite-forming melt originated via partial melting of a mixed igneous ( i.e., volcanic)- sedimentary source. The calculated δ18OH2O–δDH2O values, at 500°C, correspond to the field for magmatic waters, but some isotopic data, including δD for fluid-inclusion extracts, suggest late-stage incursion of metamorphic water that had equilibrated with the surrounding metasedimentary rocks. Mineral–mineral fractionation ( e.g., ΔQtz–Ms) does not reflect equilibrium within the pegmatite, which may have resulted from several processes, including non-equilibrium crystallization, variable degrees of isotopic exchange during protracted cooling, or interaction with an external reservoir(s). The data for albite (δ18O = +9.1‰, n = 6) are consistent with a magmatic origin, albeit late in the evolution of the pegmatite, on the basis of textural arguments. A model is proposed for the origin of the extensive albite-enriched zones, which involves introduction of a sodic melt derived at depth after protracted fractionation of the same parental melt from which the Li-rich parts of the pegmatite originated.

Quartz cement microstratigraphy and high precision in situ δ 18 O values obtained by secondary ion mass spectrometry (SIMS) from μm-size quartz cement zones have been used here to determine the timing of cementation and to evaluate precipitation mechanisms within the basal sandstones of three economically significant Paleoproterozoic basins, the Athabasca and Thelon basins, Canada, and the McArthur Basin, Australia. In these examples, the earliest quartz cements have the highest δ 18 O values (up to 33‰; mean=26.0‰, V-SMOW) indicative of low temperature precipitation at depths of 0 to 1.1 km. Some paragenetically early cement phases, however, have lighter isotopic values that suggest either precipitation from isotopically depleted water or precipitation at higher temperatures. Subsequent generations of quartz cements have progressively lower δ 18 O values (mean=+16.1±3‰) consistent with precipitation at higher temperatures. These data combined with petrographic observations indicate quartz cementation began in near-surface vadose and phreatic zones; the next stage of cementation is characterized by syntaxial burial cement overgrowths. Regionally and stratigraphically, well-sorted sandstone facies that were initially aquifers preferentially experienced early quartz cementation, which resulted in cement-bridged pore throats at relatively shallow depths of 0–2 km and very early in their burial history transforming these units into diagenetic aquitards. As a result, these units did not experience mineralization. Compositionally and texturally immature braided fluvial facies did not experience early addition of quartz cement, but are instead marked by minor syntaxial overgrowth cement that make upb5% of the intergranular volume, formed at depths of 3–5 km, and were variably replaced by illite and chlorite during burial. These lithologies were still open to fluid movement at critical times in the basin when U and

The Paleo- to Mesoproterozoic McArthur basin in the Northern Territory, Australia, is filled with mixed carbonate-siliciclastic successions and felsic and mafic volcanic units that contain authigenic minerals that formed during burial diagenesis. Petrographic investigations indicate that some of these lithologic units were cemented early by quartz overgrowths and became diagenetic aquitards, whereas secondary porosity was developed in others that became diagenetic aquifers for basinal brines. The authigenic minerals in both lithology types preserve geochemical information about the types of fluids that occurred in the basin, with those that resided in the diagenetic aquifers having similar geochemical composition to those indicated by alteration minerals in the McArthur River Pb-Zn deposit and the Westmoreland U deposits. Quartz overgrowths formed early during shallow burial in all clastic lithologic units and are particularly common in the well-sorted, marine sediments; these became diagenetic aquitards due to the porosity-occluding cement. In the calcareous units, early dolomite replaced calcite and aragonite at shallow burial depths. Fluid inclusion microthermometry indicates that most quartz overgrowths formed between 80° and 125°C from a fluid with a salinity between 0 and 13.1 wt percent NaCl equiv. The isotopic composition of dolomite indicates δ18Ofluid of −4.5 ± 1.5 per mil and δ13Cfluid of −6.9 ± 1.0 per mil, suggesting formation from a mixed marine and meteoric fluid. Illite cemented by early quartz has a 40Ar/39Ar age of 1738 ± 10 Ma in one diagenetic aquitard, which reflects the age when the host sediment was deposited and confirms that quartz cementation occurred early during burial. With increased burial, the poorly sorted sandstones and conglomerates that were initially poor aquifers at or near the surface experienced framework grain dissolution and the creation of secondary porosity at depth. As a result, the sediments of the Westmoreland Conglomerate, the lower Yiyintyi Sandstone, significant proportions of the Warramana Sandstone, and most of the sandstone interbeds of the Gold Creek Volcanics became diagenetic aquifers and conduits for basinal brines. Illite, dolomite, and chlorite formed late in the paragenesis and filled the secondary porosity. Quartz veins formed last and primarily in faults and fractures. The dolomite and quartz veins contain fluid inclusions that have low eutectic temperatures indicative of Ca2+- and Na+-dominated brines and salinities between 18.5 and 30.9 wt percent NaCl equiv. Illite crystallinity data and chlorite chemical compositions indicate formation between 150° and 250°C. The isotopic compositions of illite and chlorite indicate δ18Ofluid values between 2.9 and 9.1 per mil and δDfluid values between −61 and −25 per mil, which suggest formation from a mixed meteoric and marine fluid. These δ18Ofluid values are indistinguishable from those determined from the isotopic composition of alteration minerals at the McArthur River Pb-Zn deposit (5 ± 5‰) or synore illite at the Westmoreland uranium deposit (4 ± 2‰), suggesting that the diagenetic aquifers and the deposits may be linked. Argon ages of illite from the diagenetic aquifers indicate that fluid migration began as early as 1680 Ma and continued to approximately 1541 Ma, coinciding with and extending past the time when the McArthur River Pb-Zn deposit (1640 Ma) and the Westmoreland U deposits (1655–1606 Ma) formed. The results presented in this study show that clastic sediments dominated by poorly sorted sandstone and conglomerate facies evolved through burial diagenesis to become aquifer lithologic units that hosted basinal brines with chemical characteristics and ages similar to those that are reported from the Pb-Zn and U deposits of the southern McArthur basin.

The western succession of the Mount Isa basin in northwest Queensland hosts four supergiant Zn-Pb ± Cu deposits and numerous smaller Cu and Zn-Pb deposits. Mineralization is primarily hosted in carbonaceous and calcareous shales and siltstones belonging to the 1670 to 1575 Ma Isa superbasin, but little is known about the source of metals that formed these deposits. The underlying clastic and volcanic successions belonging to the 1800 to 1750 Ma Leichhardt superbasin and the 1735 to 1690 Ma Calvert superbasin are potential metal source rocks and host a variety of diagenetic minerals that preserve geochemical information about the evolution of brines in the basin. Quartz overgrowths and pressure solution features formed during shallow burial in all clastic lithologic units but are particularly common in the well-sorted, marine-dominated units that became aquitards due to the porosity-occluding diagenetic cement. Microthermometry on fluid inclusions in the quartz overgrowths indicates formation between 100° and 174°C from a low-salinity, 2.7 to 9.1 wt percent NaCl equiv fluid (fluid 1). These data together with sequence stratigraphic mapping, basin reconstruction, and stable isotope values from the quartz overgrowths show that the diagenetic aquitards formed at 18 O fluid and δ D fluid values of 4.5 ± 4.2 and −34 ± 14 per mil, respectively, indicating evolution from a seawater-dominated source. Silicate dissolution and the widespread formation of diagenetic illite and chlorite occurred late, during deep burial diagenesis and primarily in the proximal fluvial lithologic units. These units are recognized as diagenetic aquifers and they occur adjacent to and within the Eastern Creek and Fiery Creek Volcanics where metals could have been sourced. Basin reconstruction shows that the diagenetic aquifers formed at depths between 5 and 10 km. Illite and chlorite extracted from the diagenetic aquifers have distinct δ 18 O fluid and δ D fluid values of 4.5 ± 2.8 and −63 ± 11 per mil, respectively, indicating evolution from a meteoric fluid with a variable marine contribution. These isotopic values cannot be differentiated from published isotopic values of fluid inclusion water in quartz-dolomite-chalcopyrite veins at Mount Isa or sphalerite and illite from the Century Zn deposit and the Zn lodes from the Burketown mineral field. This suggests that the diagenetic aquifers were likely source rocks for metals in the deposits in the Mount Isa basin. In contrast to the phyllosilicates in the diagenetic aquifers, regional dolomitic grainstones and dolomudstones in the Lawn Hill platform precipitated from fluids with δ 18 O fluid between −2.6 and 1.1 per mil and δ 13 C fluid between −8.6 and −3.9 per mil. This suggests that these units did not contribute to the ore-forming brines. Quartz veins formed during the later diagenetic history in the Mount Isa basin from a low-salinity brine, between 2.7 and 10.4 wt percent NaCl equiv (fluid 2). Oxygen isotope geothermometry on quartz-hematite pairs indicates that these veins formed at approximately 230°C. Crosscutting relationships reveal that a subsequent generation of quartz veins host fluid inclusions with a distinctly saline brine, with compositions between 11.9 and 23.2 wt percent NaCl equiv (fluid 3), indistinguishable from fluid inclusion compositions recorded in sphalerite from the Century and Walford Creek Zn deposits in the Lawn Hill platform and the quartz-dolomite-chalcopyrite veins at Mount Isa. Some of these quartz veins formed at ca. 400°C, based on quartz-hematite geothermometry, but fluid inclusion homogenization temperatures between 86° and 260°C suggest that another set of quartz veins, also containing high-salinity fluid inclusions, is preserved in the basin but formed at lower temperatures. Irrespective of formation temperature or timing, it is noteworthy that quartz veins hosting high-salinity fluid inclusions have δ 18 O fluid and δ D fluid values that are indistinguishable from those recorded by (1) illite and chlorite in the diagenetic aquifers, (2) fluid inclusion water in sphalerite and synore quartz and illite in the Zn deposits in the Lawn Hill platform, and (3) various alteration minerals from the Mount Isa Cu deposit. Collectively, this suggests that the quartz veins represent fluids that migrated along faults from the diagenetic aquifers during late diagenesis to form the low-temperature Zn-Pb deposits between 1650 and 1575 Ma and later during the Isan orogeny to form the high-temperature Cu deposits. Metamorphic quartz-hematite ± feldspar ± chlorite veins exist in the basin and formed between 325° and 450°C during the Isan orogeny from a brine having salinities between 12.6 and 23.2 wt percent NaCl equiv (fluid 4). These veins have distinct δ 18 O fluid and δ D fluid values of 11.8 ± 2.0 and 30 ± 2 per mil, respectively, consistent with formation from fluids derived from graywackes and arkoses during greenschist facies metamorphism. The last recognized fluid identified in the basin (fluid 5) is only found in secondary fluid inclusions that form trails across earlier formed quartz veins. This fluid was trapped after the Isan orogeny, has a low salinity, between 0.0 and 8.1 wt percent NaCl equiv, records temperatures between 131° and 256°C, and is indistinguishable from postore fluids that have been reported in the Mount Isa Cu deposit and the Zn lodes in the Burketown mineral field.

The Sigma-Lamaque mine (>100 metric tons (t) of gold) is an example of an Archean greenstone belt gold deposit formed by processes related to multistage hydrothermal fluid circulation. The earliest recognized vein systems are steeply to moderately dipping fault-fill veins within shear zones and contemporaneous subhorizontal veins, which were overprinted by the late North Dipper vein system. The latter strikes east-west, dips moderately to the north, and exhibits complex internal geometry with features similar to fault-fill and extensional veins, and therefore is interpreted as extensional shear veins. This late vein system was considered one of the major sources of gold in the shallow underground and open-pit ore reserve estimations. These late North Dipper veins were studied in detail in the Sigma pit where they contain ore-grade gold and are hosted by the calc-alkaline tuffs of the Val d’Or Formation and in the North zone where they are barren and hosted by the tholeiitic volcanic rocks of the Jacola Formation. In the Sigma pit, these veins have apparent thicknesses of 0.8 to 3 m and very irregular contacts with the vein walls. They comprise irregular zones of milky quartz filling, disrupted blocks of layered quartz and tourmaline and slabs of foliated pyrite-rich wall rock. Layers with tourmaline and quartz crystals oriented perpendicular to the vein walls are observed close to the vein walls. The veins contain minor amounts of calcite, pyrite, rutile, and traces of chlorite, muscovite, pyrrhotite, chalcopyrite, galena, bismuth tellurides, and gold. Locally, the sulfide content can attain 10 modal percent of the vein mineralogy. In the veins, native gold (with 6 wt % Ag) occurs rarely associated with the main vein-filling minerals, commonly as inclusions in pyrite (main vein-filling stage), and most commonly filling fractures in pyrite, tourmaline, and quartz, where it is alloyed with 8 to 17 wt percent Ag and is associated with calcite and Bi tellurides (late auriferous stage). The proximal wall-rock alteration related to the auriferous North Dipper veins overprints the metamorphic assemblage and is characterized by abundant fine-grained plagioclase, calcite, quartz and minor chlorite, tourmaline, and pyrite in the tuffs and more abundant muscovite in the intrusive feldspar porphyry. In the wall rock, gold with 6 to 28 wt percent Ag is found locally filling fractures in pyrite, where it is associated with a late generation of calcite. The barren North Dipper vein also comprises mainly quartz and tourmaline but lacks calcite and gold, has a very low content of sulfides ( Aqueous-carbonic fluid inclusions with salinities less than 8 wt percent (NaCl equiv) and homogenization temperatures between 228° and 440°C, and carbonic fluid inclusions with less than 0.2 mol percent CH 4 coexisting in the same healed fractures, are common in the auriferous North Dipper veins but very rare in the barren vein where aqueous fluid inclusions have lower temperatures (dominantly 125°–225°C). Crush leaching and laser ablation time-of-flight inductively coupled mass spectrometry (LA-TOF-ICPMS) of fluids in the inclusions indicate elevated concentrations of Ni, Cu, Sb, Pb, and Ag in the fluids in the auriferous veins compared to the aqueous fluids in the barren veins. This suggests different sources for the metals in the fluids associated with the gold, possibly including both igneous and sedimentary rocks. Calculated oxygen isotope equilibration temperatures for quartz-tourmaline pairs from the auriferous main vein-filling stage are 323° to 370°C. This is within the range documented in fluid inclusions related to the late auriferous stage, indicating that the temperature of the auriferous hydrothermal fluids did not change appreciably during the evolution of the system. Calculated δ 18 O H 2 O values for the mineralizing fluids are 9.5 per mil, consistent with either low water/rock ratio systems associated with high-grade metamorphism or a magmatic origin for the fluids. Gold included in pyrite may have precipitated during the main vein-filling stage due to the decrease of H 2 Sconcentration in the hydrothermal fluid following the deposition of sulfides. However, gold in fractures in the main vein-filling minerals precipitated later, due probably to dilution of the auriferous aqueous-carbonic fluids by mixing with aqueous fluids. The absence of ore-grade gold in the barren North zone vein is probably due to the lack of circulation of auriferous aqueous-carbonic fluids in the North zone, located distal to the first-order Larder-Lake Cadillac fault, which may have served as the main regional conduit for the auriferous aqueous carbonic fluids.

Accumulation of carbonate mud is minor on the Northwest Shelf (Western Australia), a broad (< 200–300 km wide), distally steepened, tropical carbonate ramp. It is negligible along most of the inner ramp (0 to 50 m water depth) owing to siliciclastic (riverine) input. It is also negligible along the mid (from 50 to 120 m) ramp, and where the entire ramp narrows to < 100 km, owing to constant reworking by storm waves and ocean swell. In these areas, carbonate mud is derived mostly from mechanical degradation of skeletal fragments, but this does not include calcified remains of calcareous green algae (e.g., Halimeda) although these plants grow locally. Only along the outer (120 to 200 m water depth) ramp and slope is there any relatively abundant accumulation of carbonate mud. Here the sediment consists of modern pelagic (foraminifer, pteropod, and nannoplantkon) ooze and aragonitic needle-rich (< 2 μm) micrite, the latter having an age (based on AMS 14C) of ~ 19 ka. Distribution of aragonite micrite defines an extensive (5.0 × 104 km2), yet relatively narrow (< 40 km), tract running ~ 600 km along the platform margin. Crystal morphology, mineralogy, and isotope (C, O) composition identify the micrite to be a seawater precipitate, its production and seaward export having occurred during the Last Glacial Maximum, when lowered sea level transformed the otherwise broad platform into a narrow epicontinental shelf margin, now the modern distal slope. Today, this sediment body lies stranded in deep water, about 200–300 km seaward of the shallow inner ramp. The volume of micrite produced appears equal to the present-day production potential of the Great Bahama Bank. Rapid postglacial rise in sea level, and change in platform geometry, climate, and oceanography, were very influential factors, in addition to water depth and area of submergence, in the production and distribution of aragonite micrite along the Northwest Shelf. In general: (1) epicontinental carbonate platforms can lack substantial micrite accumulation when oceanic current and wave energies sweep unimpeded across a platform, and coastal clastics and absence of shoal barriers prevent development of protective lagoons and carbonate tidal flats; (2) not all highstand carbonate systems are associated with significant amounts of micrite in shallow water environments, nor do they necessarily export large volumes of micrite to the periplatform realm; and (3) some lowstand systems can produce and export volumes of carbonate mud that rival highstand systems.

Surficial carbonate sediments on the southern continental shelf of Australia are cool-water in aspect and composed of biogenic particles produced largely during the late Quaternary. Current understanding is that such sediments are calcite-dominated, as were their older Cenozoic counterparts. The Holocene fraction of these sediments in modern open-shelf, neritic environments between 30 and 350 meters water depth is, however, 50% to 80% aragonite. Scant evidence of significant former aragonite in many cool-water carbonate sedimentary rocks implies that most aragonite is lost before such sediments exit the marine diagenetic environment. Although marine dissolution must be taking place in such settings, the conundrum is exacerbated because seawater over the shelf in southern Australia is saturated with respect to aragonite. It is proposed that the aragonite, from skeletons of gastropods, infaunal bivalves, and certain bryozoans, is dissolved in the shallow subsurface, probably as the byproduct of bacterial degradation of sedimentary organic matter. As a consequence, the geological and paleontological record of many cool-water carbonates is strongly biased, and the inferred original calcitic composition of such sediments is the product of early diagenetic taphonomic loss, not selective biogenic productivity. The net result is not only dissolution of aragonite but also neomorphism of Mg-calcite to calcite with a marine geochemical signature. Synsedimentary aragonite loss, by removing CaCO3 that is usually available for calcite cementation during meteoric diagenesis, leads to retarded lithification of these cool-water carbonates until deeply buried. Such removal of a significant carbonate fraction during deposition likely contributes to the low rates of cool-water sediment accumulation.

The Pierina high-sulfidation epithermal Au–Ag deposit (9°26.5′S; 77°35′W) was emplaced in the Middle Miocene into a hypabyssal-to-extrusive “pumice-tuff” and an underlying, older, dacitic flow-dome complex, both of which are cut by hydrothermal breccias and small dacitic domes. Stage I advanced argillic alteration generated a core of vuggy silica, focused in the tuff, and surrounded successively by zones of quartz–alunite, dickite±kaolinite±pyrophyllite, and illite–montmorillonite±kaolinite. Laser-ablation ICP-MS analysis of the sulfide minerals of the succeeding, Stage II, Cu (–Pb, Bi, Sb, Zn, As)–barite mineralization, largely confined to the vuggy-silica zone, reveals that both Au and Ag were introduced at that time. This assemblage was almost entirely obliterated during Stage III, when oxidation by low-temperature meteoric waters generated botryoidal hematite–goethite assemblages, which are now the main precious-metal hosts. Stage IV barite–acanthite mineralization shows limited temporal overlap with Stage III, but dominantly overprints the hematite–goethite assemblage. The deposit incorporates alunite exhibiting a wide range of modes of occurrence, grain size, and morphology. Disseminated alunite dominates Stage I alteration, which replaced phenocrysts and fragments, and locally hosts corroded, ≤40 μm alumino-phosphate-sulfate (APS) inclusions. The alunite shows limited Na substitution [molar Na/(Na+K)=

The Early Devonian Lake George granodiorite stock, New Brunswick, Canada, is spatially and temporally associated with early W‐Mo‐Au and later Au‐Sbmineralization. The former mine was the largest antimony producer in North America until the mid-1990s. On the basis of fluid-inclusion analyses, multiple generations of fluids evidently interacted with the granodiorite, with the dominant fluids approximated by the system H2O‐NaCl‐CO2‐CH4. Additional components of the fluid, S‐Ca‐Fe‐K‐Mg‐ Mn, reflect fluid‐rock reaction and partial re-equilibration among the rock-forming minerals (i.e., plagioclase, orthoclase, biotite, and hornblende) in the granodiorite. The CO2-bearing inclusions (Type 1) have a relatively low salinity, ranging from 0 to 15 wt.% equiv. NaCl (ave. 4 wt.%), and most homogenize to the CO2 phase at temperatures of 200 to 470°C. Inclusions that homogenize to the aqueous phase do so over a narrower range of temperatures (250‐350°C). Fluid pressures were probably 740 to 2210 bars for Type-1 inclusions. Aqueous liquid + vapor (Type 2) and aqueous liquid + vapor + halite or sylvite (Type 3) inclusions are recorded as well. Type-2 inclusions show a broader range of temperatures of homogenization (mostly to the aqueous phase), from 150 to 580°C, with a salinity between 2 and 19 wt.% equiv. NaCl. The stable isotope compositions of the rock-forming minerals in the granodiorite exhibit a disequilibrium relationship, e.g., either � 18 OK-feldspar > � 18 Oquartz, � 18 Oplagioclase > � 18 Oquartz, or � 18 Oplagioclase > � 18 OK-feldspar. The whole-rock � 18 O values range from 9.4 to 10.7‰, consistent with derivation by

A group of dyke rocks from the Frederick E. Hyde Fjord area form the southern termination of a prominent dyke-swarm in Peary Land, northernmost Greenland. The melanocratic dykes are NS- to NW–SE-trending, vertically dipping, ≤10–12 m wide, and have narrow chilled margins. Whole-rock 40 Ar/ 39 Ar dating of three dyke rocks indicates emplacement at ca. 85 Ma, some 15 to 20 Ma older than previous K–Ar whole-rock dating indicated. Whole-rock 40 Ar/ 39 Ar dating of three Lower Paleozoic metasedimentary rocks collected hundreds of meters away from the dykes reflects partial resetting during dyke-rock emplacement and suggests that the area experienced a greater thermal disturbance than the outcrop distribution of the dyke rocks would suggest. The dyke rocks contain normally zoned, euhedral microphenocrysts of titaniferous ( ≤4 wt.% TiO2) clinopyroxene in a matrix of olivine (Fo 69–35), plagioclase (An69–35, ≤1.0 wt.% K2O), clinopyroxene and ilmenite; rare matrix biotite [Fe/(Fe + Mg) = 0.65] occurs, and intergranular granophyre is present in the most evolved dykes. Whole-rock geochemistry indicates a basaltic composition, with the least evolved rocks containing 5.7% MgO, 14% FeOT, 4% TiO2, 2.8% Na2O, and 0.9% K2O (by weight). In terms of major elements, the rocks correspond to sodic-type alkali basalts; the normative mineralogy indicates an affinity t o both olivine tholeiites and alkali basalts. Trace-element contents (45 ppm Ni, 45 ppm Co, 80 ppm Cr, 335 ppm V, on average) and mg numbers between 0.42 and 0.45 indicate that the rocks do not represent primitive magmas. Abundances of the rare-earth elements (REE = 170 to 200 ppm, LaN = 100) and strongly fractionated patterns (La N/LuN = 10) are consistent with the alkaline nature of the dyke rocks. The lack of negative Eu anomalies in chondrite-normalized REE profiles is consistent with the absence of plagioclase phenocrysts, suppressed by a high H 2O content of the magma. Normalized extended trace-element diagrams and 87 Sr/ 86 Sr versus 143 Nd/ 144 Nd isotopic plots indicate affinities with OIB. Although the 87 Sr/ 86 Sri values (0.70467 ± 10) do not indicate crustal contamination, 18 O values (+6.0 to +7.9‰) are above typical mantle values and suggest some crustal influence.

The 3-27 m-thick cap carbonate overlying "Marinoan" Ice Brook Formation glacigene sediments and Keele Formation carbonate and terrigenous clastic rocks consists of two distinctive stratigraphic units. A lower, splintery, buff-weathering, microcrystalline dolostone of extensive lateral uniformity comprises mm-laminated peloidal sediment with local, low-angle, hummocky-like cross-stratification, micro-ridges, and synsedimentary tepees, all elongated perpendicular to depositional strike. This dolostone is unconformably overlain by an upper limestone that exhibits pronounced facies variation from inboard peloidal lime grainstone and mudstone to shelf-edge cementstone to outboard lime wackestone and mudstone. Calcite cementstones range from isolated crystal fans in laminated limestone to huge, decimetre-scale crystal arrays, to hemispherical and elongate crystal stromatolites wholly composed of acicular crystals that form decametre-scale reeflike structures. Crystal stromatolites are precipitates and replaced microbiolites that constructed biostromes and bioherms, like those on many flat-topped, reef-rimmed platforms. The calcite crystals have all the physical and chemical attributes of neomorphosed aragonite. This aragonite extensively replaced sediment and microbiolite just below the sea floor and grew upward into the overlying water column. Such interpreted massive synsedimentary replacement is rare in geological history and attests to the highly saturated state of the immediate postglacial ocean. All sediment is interpreted to have been CaCO3 originally. Low and constant δ18O values reflect diagenetic modification of these carbonates, although chemical attributes, such as Sr and C isotopes in some lithologies, are near pristine. Lower dolostones, virtually identical to most other coeval Marinoan caps worldwide, were part of a global precipitation event of remarkable similarity. Upper limestones are a more local phenomenon, deposited during sea-level rise in an aragonitic sea returning to equilibrium after global glaciation. Low 87Sr/86Sr ratios and varying δ13C values with carbonate sedimentary facies indicate that both units must have formed relatively rapidly, prior to significant fluvioglacial runoff, or that the influence of this runoff on the chemistry of seawater along continental shelves was minimal. The cap carbonate is thus interpreted to have formed in two steps: (1) during initial marine ice melting accompanied by oceanic overturn and upwelling, preceding continental margin rebound, and (2) during initial stages of sea-level rise accompanying continental deglaciation. While confirming brief, but extensive, carbonate precipitation from an ocean highly perturbed by global glaciation, the rocks also suggest that this event did not permanently affect either late Neoproterozoic ocean chemistry or the contained marine biosphere.

The Oligo-Miocene Gambier Limestone is a poorly lithified, fine-grained, bryozoan-rich grainstone/wackestone and marl. Allochems in these rocks, which are typical of many modern and ancient cool-water carbonates, were originally calcite (LMC), Mg-calcite (IMC and HMC) and minor aragonite, but most are now neomorphosed to LMC. With the exception of calcretes, most limestones have < 5% cement, 13C and 18O values from 0 to +1.5o/oo, and preserved 87Sr/86Sr ratios that indicate that neomorphism occurred in seawater rather than meteoric or evolved pore waters. Marine diagenesis of the limestones was facilitated by their slow accumulation rates, which were ca. 15 mm/ky based on Sr-isotope stratigraphy, relatively fine grain size, and high porosities which locally reach 50%. The Sr and Mg contents of grainstones are significantly lower than in the original sediments, whereas a less porous marl has higher Sr and Mg contents. The grainstones have about 300 ppm Sr and 6000 ppm Mg, consistent with slow abiotic precipitation of calcite under near-equilibrium conditions with seawater, which is the thermodynamic drive for this diagenesis. The higher Sr and Mg content of the marl results from variable preservation of original allochems of biotic calcite. The results from this study and others on modern cool-water carbonates indicate that the extent of diagenesis varies with lithology, but much neomorphism occurred in seawater, with minimal effects from meteoric waters. As such, the chemical characteristics of seawater may be effectively preserved in some ancient cool-water carbonates.

Rossmanite is a new tourmaline species from near Rozna, western Moravia, Czech Republic. It forms pale pink columnar crystals about 25 mm long and 5 mm thick, elongated along c with striations parallel to c on the prism faces. It is brittle, H = 7, D meas = 3.00 g/cm 3 , D calc = 3.06 g/cm 3 . In plane-polarized light, it is colorless. Rossmanite is uniaxial negative, omega = 1.645(1), epsilon = 1.624(1), trigonal, space group R3m, in the hexagonal setting a = 15.770(2), c = 7.085(1) Aa, V = 1525.8(4) Aa 3 , Z = 3. The strongest six X-ray diffraction lines in the powder pattern are at d = 3.950 Aa with I = 100% for (hkl) = (220); 2.552 Aa, 93%, (051); 1.898 Aa, 72% (342); 4.181 Aa, 58%, (211); 2.924 Aa, 56%, (122); and 3.434 Aa, 53%, (012). Analysis by a combination of electron microprobe, SIMS, H-line extraction, and crystal-structure refinement gave SiO 2 38.10 wt%, Al 2 O 3 44.60, Na 2 O 1.43, Li 2 O = 1.13, B 2 O 3 = 10.88, H 2 O = 3.70, F = 0.20, O identical with F 0.08, sum = 99.96 wt%, Fe, Mg, Ca, Mn, Ti, F, K not detected. The formula unit (31 anions) is x ([] (sub 0.57) Na (sub 0.43) ) Y (Li (sub 0.71) Al (sub 2.17) ) Z Al 6 (Si (sub 5.92) O 18 ) (B (sub 2.92) O 9 ) (OH) (sub 3.83) F (sub 0.10) O (sub 0.07) , with the ideal end-member formula [](LiAl 2 )Al 6 (Si 6 O 18 ) (BO 3 ) (OH) 4 ; thus rossmanite can be derived from elbaite [Na(Al (sub 1.5) Li (sub 1.5) ) (Si 6 O 18 ) (BO 3 ) 3 (OH) 4 ] by the substitution x [] 2 + Y Al--> x Na 2 + Y Li, where [] = vacancy. The crystal structure of rossmanite was refined to an R index of 1.7% using 1094 observed (5sigma ) reflections collected with MoKalpha X-radiation from a single crystal. The structure refinement confirmed the low occupancy of the X site and the presence of Li at the Y site. There is considerable positional disorder at the O1 and O2 sites induced by the local variations in bond-valence distribution associated with []-Na disorder at X and Li-Al disorder at Y.

The Contact Lake lode gold deposit is situated in northern Saskatchewan within the Proterozoic La Ronge domain of the Trans-Hudson orogen ( degrees 1.9-1.7 Ga). The deposit is associated with a high-angle, reverse shear zone, which crosscuts the central granitic and granodioritic phases of the composite Little Deer Lake pluton. Four temporally distinct stages of veining within the shear zone have been identified on the basis of mineralogical, textural, and crosscutting relationships. The vein mineralogy, the size of the veins, and the extent of alteration distinguishes this deposit from other epigenetic gold deposits in the La Ronge domain. The four discernable vein types (two devoid of gold and two containing gold mineralization) permit the detailed study of fluids responsible for gold mineralization versus barren fluids, which is critical to gold exploration. Stage I veins are the earliest, consist of feldspar and quartz + or - biotite, are devoid of gold, and occur as pods and stringers 3 to 100 cm in width and several meters in length. Stage II quartz-biotite veins are 1 to 100 cm wide, are also devoid of gold, and have a narrow (

Syn- to postkinematic two-mica granite dikes, sills, and sheets intrude late Precambrian sillimanite and K-feldspar-sillimanite zone metasedimentary and metavolcanic rocks in the northern Monashee Mountains of British Columbia. U-Pb ages indicate that two periods of granite emplacement occurred ∼40 m.y. apart, at 100 Ma, concurrent with peak regional metamorphism, and at 63 Ma, which marked the beginning of a period of accelerated cooling in the area. Rare earth element contents, high initial 87 Sr/ 86 Sr ratios, inheritance of Precambrian zircons, and the restriction of most of the peraluminous granites to the highest-grade metamorphic zones are all compatible with derivation of the granitic magmas by partial melting of associated metasedimentary rocks. However, stable isotope studies of whole-rock samples and minerals indicate that the source of the peraluminous granitic magmas could not be simple whole-sale melting of spatially associated pelitic rocks, but likely was Precambrian lower continental crust that must have included metapelites. The disparate ages of the granites in conjunction with what is known about the tectonic evolution of the area indicate that the granites are tectonically displaced from their source areas. Isotopic equilibration temperatures of coexisting muscovite and biotite in the granites are near 400 °C and are lower than temperatures estimated for the same mineral pairs in the metapelitic rocks. This difference in equilibration temperatures is likely the result of differential rates of exchange related to cooling in the presence of fluids in the granites. Although the δD values of muscovites from both the granites and the metapelites indicate equilibration with fluids having a relatively restricted range of δD values near -50, the calculated δ 18 O values of fluids in equilibrium with the granites are ∼2 per mille lower than those in equilibrium with the associated metapelitic rocks. In contrast to the hydrogen isotope systematics in the muscovites, δD values of biotite in the granites and metapelites range from -173 to -91, implying that the biotites were affected by early Tertiary meteoric water when this area was at high latitudes and elevations, concurrent with an episode of tectonic denudation that occurred at ca. 45 Ma.

A three-component, diffusion-limited, open-system exchange model for pyroxene, olivine and fluid is presented that reproduces the range of oxygen isotope compositions of coexisting silicates from mantle-derived samples. Closed-system exchange cannot reproduce observed disequilibrium fractionations. Measured oxygen self-diffusion data were used to constrain fluid-silicate reaction rates. The magnitudes of fluid-mineral fractionations for typical mantle fluids are presented and show that equilibrated fluid will always be more 18O-rich than coexisting silicates. Three conditions are necessary to generate the disequilibrium pyroxene-olivine oxygen isotope fractionations observed in the mantle dataset. There must be at least an order of magnitude difference between the fluid-pyroxene and fluid-olivine reaction rates, fluid and solid phases must be out of equilibrium prior to reaction, and fluid must be moving several orders of magnitude faster than it is reacting with the silicates. Assuming initial isotopic equilibrium between pyroxene and olivine and reasonable porosities, the following constraints apply. If pyroxene is reacting faster than olivine, to be expected when pyroxene and olivine grain sizes are subequal, a fluid flow rate of at least 5 × 103 times the pyroxene/fluid reaction rate is needed to generate the most extreme negative pyroxene-olivine fractionations seen in natural samples. If olivine reacts faster, the case when its effective grain size is 0.2 cm/y at 1200°C and >3 cm/y at 1400°C are needed when pyroxene is the faster reactant. Flow rates >1 cm/y at 1200°C and >15 cm/y at 1400°C are necessary in the olivine dominated system. Regardless of which silicate reacts faster, large amounts of fluid are required, with fluid/rock ratios approaching unity, implying a fluid-focusing mechanism operating in the mantle source region of the xenoliths. Measurable, negative, disequilibrium pyroxene-olivine 18O fractionations are very short-lived at mantle conditions, surviving

Equilibrium oxygen isotopic fractionation factors between coexisting olivine and enstatite at mantle temperatures and pressures, 1000–1400°C and ≥ 13 kbar, were determined from a series of silicate-witherite oxygen isotope exchange experiments. Silicate-witherite fractionations ranged from − 2%0 at 1000°C to − 1%0 at 1400°C, and showed a systematic jump in magnitude at 1200°C of ~0.5%0 which remains to be explained. Enstatite-witherite fractionations varied nonlinearly with respect to inverse temperature squared. The high-temperature pyroxene-witherite data suggest enstatite undergoes a reversible structural change as it approaches an incongruent breakdown reaction to olivine, quartz, and sanbornite, which may account for the observed nonlinearity. A least-squares fit to the low-temperature equilibrium enstatite-olivine fractionation data forced through the origin has the functional form 1000 In αen-olT(K) = (1.41 ± 0.43) × 106/T2−(0.0 ± 0.24) for temperatures greater than 1000°C ( ± 2σ errors). At equilibrium under mantle conditions, the oxygen isotopic composition of enstatite is always heavier than, or equal to, that of coexisting olivine.

Clear-cutting of forests affects the nitrogen cycle and the nitrogen isotopic composition of bioavailable ammonium and nitrate in the soil. Here, we have used nitrogen isotopic variations of tree-rings in red oak (Quercus rubra) and white oak (Quercus alba) as indicators of changes in the nitrogen cycle on a local scale. The delta15N values of late-wood from trees at two remnant forest stands in Ontario, Canada, that underwent large-scale tree-clearing and permanent land-use change at different times were measured. Trees from the perimeter of each stand record a marked 1.5-2.5 per thousand increase in the delta15N values of their tree-rings relative to the values in trees from the center of the stand, with the shift synchronous with the tree-clearing and land-use change. This shift was most likely due to increased rates of nitrification and nitrate leaching in the soil as a result of tree-clearing combined with permanent changes in hydrology and probable fertilizer use accompanying the change in land-use. Nitrogen concentration in tree-rings was not affected bytree-clearing and the associated change in land-use. These results indicate that changes in nitrogen cycling in forest ecosystems, whether due to climate change, land-use change, or other environmental changes (increased O3, other atmospheric pollutants, insects, etc.), can be faithfully monitored with nitrogen isotopic compositions of tree-rings and that dendrogeochemical analysis can be incorporated into studies of the effects of long-term anthropogenic effects on forest ecosystems.

The Paleoproterozoic Animikie Basin in the Lake Superior region of North America is the benchmark for understanding one of the most significant changes in seawater chemistry in Earth history—the transition to a sulfidic ocean (ca. 1.84 Ga). This transition marks a dramatic increase in ocean sulfide produced by bacterial reduction of sulfate formed through the oxic chemical weathering of pyrite during the Great Oxidation Event. Such a change is thought to have caused the cessation of widespread iron formation deposition and marks the beginning of a long lull in the evolution of eukaryotes. The feasibility of using the Animikie Basin to understand this transition is re-evaluated by comparing new sulfur isotope data (δ 34 S pyrite ) from the Michigamme Formation in northern Michigan, United States, to published results from the correlative Rove Formation in Ontario, Canada. These data suggest that microbial sulfate reduction was restricted to organic-rich environments away from the influence of deltas, which delivered low-sulfate river water to the coast. Sulfur isotope data and the patchiness of sulfate reduction within the Animikie Basin suggest strong lateral and vertical gradients in seawater sulfate concentrations. When viewed in the context of the most recent tectonic and sedimentologic models, these observations are best interpreted as reflecting an evolving basin with restricted water circulation, not open circulation with the global ocean as previously postulated. Thus, the Animikie Basin does not contain an accurate record of open-ocean structure and composition during the onset of sulfidic conditions. What is clear is that marginal seas must be carefully evaluated before they are used to model the global ocean, especially given the rarity of preserved Precambrian deep-sea sediments.

Garnet peridotite xenoliths in the Quaternary Pali-Aike alkali olivine basalts of southernmost South America are samples of the deeper portion of continental lithosphere formed by accretion along the western margin of Gondwanaland during the Phanerozoic. Core compositions of minerals in garnet peridotites indicate temperatures of 970 to 1160°C between 1.9 and 2.4 GPa, constraining a geothermal gradient which suggests a lithospheric thickness of approximately 100 km below this region. Previously, this lithosphere may have been heated and thinned to 175°C, and thickening, by about 20 km, of the lithosphere is reflected in low-temperature ( 970°C) peridotites by textural evidence for the transformation of spinel to garnet. A recent heating event, which probably occurred in conjunction with modal metasomatism related to the genesis of the Pali-Aike alkali olivine basalts, has again thinned the lithosphere to 970°C) peridotites as chemical zonation of pyroxenes involving a rimward increase in Ca, and by kelyphitic rims around garnet. The majority of moderate- and high-temperature (>970°C) xenoliths are petrochemically similar to the asthenospheric source of mid-oceanic ridge basalts: fertile (>20% modal clinopyroxene and garnet), Fe-rich garnet lherzolite with major element composition similar to estimates of primitive mantle, but large-ion lithophile and light-rare-earth element depletion relative to heavy-rare-earth elements, and with Sr, Nd, Pb, Os, and O isotopic compositions similar to MORB. In contrast, infertile, Mg-rich spinel harzburgite is predominant among low-temperature (

δ 18 O values of coexisting garnet, clinopyroxene and phlogopite for twelve compositionally and texturally diverse Roberts Victor eclogite xenoliths range from +3.8 to +7.1, +4.0 to +7.4 and +5.9 to +7.4, respectively. Differences between theδ 18 O values of coexisting garnets and clinopyroxenes are normally zero; however, there is some variation in theδ 18 O values of different fractions of the same mineral in four samples which suggests the presence of isotopic zonation and inhomogeneity, possibly resulting from the introduction of a secondary fluid which metasomatized the eclogites and resulted in the formation of phlogopite, amphibole and celsian. Theδ 18 O value of the metasomatic fluid is generally buffered by the isotopic composition of the primary garnet and clinopyroxene, as indicated by a correlation between the isotopic composition of phlogopite and the primary pyroxene and garnet. The large range inδ 18 O values of the eclogites and the similarity in the isotopic composition of coexisting pyroxene and garnet support the interpretation that the Roberts Victor eclogites represent metamorphosed, altered basalts. The eclogites were subjected to infiltration metasomatism in the mantle prior to their incorporation in the kimberlite, and the source of this fluid was probably unrelated to the eclogite.

Kyser, O'Neil, and Carmichael (1981, 1982) measured theδ18O values of coexisting minerals from peridotite nodules in alkali basalts and kimberlites, interpreting the nodules as equilibrium assemblages. Using Ca-Mg-Fe element-partition geothermometric data, they proposed an empirical18O/16O geothermometer: T(°C)=1,151−173Δ−68Δ2, whereΔ is the per mil pyroxene-olivine fractionation. However, this geothermometer has an unusual “crossover” at 1,150 °C, and in contrast to what might be expected during closed-system equilibrium exchange, the most abundant mineral in the nodules (olivine) shows a much greater range inδ18O (+4.4 to +7.5) than the much less abundant pyroxene (all 50 pyroxene analyses from spinel peridotites lie within the interval +5.3 to +6.5). Onδ18O-olivinevs. δ18O-pyroxene diagrams, the mantle nodules exhibit data arrays that cut across theΔ18O=zero line. These arrays strongly resemble the non-equilibrium quartzfeldspar and feldspar-pyroxeneδ18O arrays that we now know are diagnostic of hydrothermally altered plutonic igneous rocks. Thus, we have re-interpreted the Kyser et al. data as non-equilibrium phenomena, casting doubt on their empirical geothermometer. The peridotite nodules appear to have been open systems that underwent metasomatic exchange with an external, oxygen-bearing fluid (CO2, magma, H2O, etc.); during this event, the relatively inert pyroxenes exchanged at a much slower rate than did the coexisting olivines and spinels, in agreement with available exchange-rate and diffusion measurements on these minerals. This accounts for the correlation betweenΔ18O pyroxene-olivine and the whole-rockδ18O of the peridotites, which is a major difficulty with the equilibrium interpretation.

Measurements have been made of the oxygen isotope and chemical composition of glass and phenocrysts in lavas and coexisting minerals in mantle nodules. Temperatures of formation of these assemblages have been estimated from various chemical thermometers and range from 855° to 1,300° C. The permil fractionations between coexisting orthopyroxene and clinopyroxene in the lavas and nodules are all near zero. The fractionations between pyroxene and olivine vary from +1.2 to −1.4 and are a smooth function of temperature over the entire range. This function is given by T(° C)=1151-173Δ (px-d)-68Δ2(px-d) and has an uncertainty of ±60° (2σ). At temperatures above 1,150° C, olivine in the nodules becomes more18O-rich than coexisting clinopyroxene, orthopyroxene, and plagioclase. In combination with the experimental work of Muehlenbachs and Kushiro (1974), the olivine-pyroxene fractionations indicate that olivine also becomes substantially more18O-rich than basaltic liquids above 1,200° C. Geothermometers based on the oxygen isotope equilibration of basaltic liquid with olivine, pyroxene, and plagioclase are presented.

Low bromine concentrations, radiometric ages, textural relations and large-scale dissolution and collapse features in Devonian potash deposits of the Elk Point Basin in southern Saskatchewan indicate that diagenetic processes and late influxes of water have variably recrystallized the salts. Lack of correlation between homogenization temperature (Th), δD or δ18O values of fluid inclusions in the salt with stratigraphic position further indicates that the sequence is not primary. The stable isotopic compositions of fluid inclusion waters, including those in chevron-texture halites, are not those expected for primary crystallization waters and, in conjunction with Th, indicate recrystallization occurred at temperatures of 35–70°C from water originating in formations above the Prairie Evaporite Formation. Using Th as an estimate of the depth of burial and stable isotopes as indicators of the source of fluids, three major recrystallization events related to the evolution of the Elk Point Basin can be recognized.

The Little Rocky Mountains, Montana, are a result of doming of Archean basement gneisses and Phanerozoic sedimentary rocks produced by the emplacement of a quartz monzonite to syenite intrusive complex of early Tertiary age. The intrusive rocks have whole-rock delta 18 O values near 8 per mil, variable initial epsilon Nd values from -11 to -19, and initial 87 Sr/ 86 Sr ratios from 0.7050 to 0.7061 all of which are compatible with derivation from lower crustal rocks having variable compositions. The Zortman and Landusky mining areas in the Little Rocky Mountains produce Au (and Ag) from fracture systems filled with clay minerals and low concentrations of Au-bearing pyrite within the intrusive rocks. K-Ar ages of illites associated with the Au mineralization are near 60 m.y. and are similar to K-Ar and fission-track ages of the intrusive rocks themselves. The delta D and delta 18 O values of these illites indicate that they, and the Au-bearing pyrite, formed at temperatures near 250 degrees C from meteoric fluids having delta 18 O values near 1 per mil and delta D values near -80 per mil. This Au event is characterized by illites having much higher initial 87 Sr/ 86 Sr ratios (as high as 0.7784) than the intrusive rocks which host the fracture system, suggesting that Sr, and by inference the Au, most likely was derived from Precambrian basement gneisses.After the gold was emplaced, later fluids released the gold by oxidizing the pyrite; they then formed kaolinite and hydrothermal fluorite and dolomite. The latter two are characterized by 87 Sr/ 86 Sr ratios near 0.708, similar to those of the intrusive rocks and Phanerozoic carbonates. Low-salinity fluid inclusions in fluorite homogenize at 100 degrees to 200 degrees C and have delta 18 O values near -10 per mil and delta D values near -110 per mil, consistent with those of Tertiary ground waters. The delta 34 S values of pyrite do not correlate with gold contents, and their wide variation from -11.4 to +6.3 per mil cannot be used to distinguish among igneous, sedimentary, and metamorphic sources.