The present study deals with three main mineralogical and geochemical problems related to the behaviour of two common clay minerals---illite and chlorite---in the Lower Paleozoic sedimentary sequences of high-grade diagenetic and very low grade metamorphic (VLGM) zones in the Quebec Appalachians, Gaspe Peninsula. / In high-grade diagenetic to VLGM zones, illite and chlorite coexist, but as they are notoriously fine-grained and intimately intergrown, tracing the chemical changes in chlorite with conventional (wet chemical method or electron microprobe) methods is a difficult task. A refined XRD method for the determination of the structural formula of chlorites was developed in this study. Application of this program to high-grade diagenetic to VLGM chlorite from the Gaspe Peninsula revealed that these chlorites are of "ripidolitic" to "pycnochloritic" composition and show a compositional homogenization in the anchizone, as compared to chlorite of the diagenetic zone. / With increasing metamorphic grade, chlorites become less siliceous, have decreasing octahedral-site vacancies, and approach the ideal trioctahedral chlorite composition. Although Fe-asymmetry increases, the [Fe (total)] decreases, which may reflect a preferential decrease in [Fe (total)] in the brucite-like sheet. / At high (>80%) illite levels in mixed-layer illite smectite, the gradual improvement of illite crystallinity (IC), coupled with advancing VLGM conditions, suggests some modification of the clay mineral structure, possibly involving loss of the still existing expandable layers. Failure to detect expandable components in anchimetamorphic illitic materials upon glycolation has led previous investigators to rule out the existence of expandable components beyond the high-grade diagenetic zone. X-ray diffraction (XRD) patterns and high-resolution transmission electron images of n-alkylammonium-cation-treated clay minerals showed the presence of expandable layers in high-grade diagenetic to VLGM phyllosilicates and document the impact of these expandable layers on IC measurements. / With advancing diagenetic to VLGM grade, the intermediate metastable phases of a rectorite-like R1-ordered layer structure, either with an intermediate or high-charge vermiculite interface, and an R3-ordered structure are found in the fine fraction. (Abstract shortened by UMI.)

The El Mochito mine, located in west-central Honduras, exploits a distal Zn-Pb-Ag skarn-hosted deposit. The bulk of economic mineralization, occurring either as steeply dipping pipes or flat-lying manto bodies, is hosted by Cretaceous Atima Formation limestone. Skarn mineralogy consists of early grossularitic garnet followed by andraditic garnet and hedenbergitic pyroxene, with pyroxene skarn the principal host to sphalerite mineralization. Ore minerals, which post-dated silicate precipitation, comprise sphalerite of variable Fe content, galena, magnetite, pyrrhotite, chalcopyrite, pyrite and trace amounts of arsenopyrite. The distribution of ore metals in the orebodies is zoned from Zn-Fe-rich cores to adjacent Pb- and Ag-rich zones reflecting the sequential saturation of sphalerite and galena in the fluid with decreasing temperature. / Skarn formation was accompanied by significant additions of Si, Fe, Mg, Al, and Mn and variable changes in Ca during early alteration. Apparent decreases in the concentrations of Ti and Zr suggest that the fluid:rock ratio was high. Variations in component activities of the hydrothermal fluid indicate that andraditic garnet skarn was stable at lower log(aCa2+/aH+ 2), log(aAl3+/aH+3), and log aSiO2aq , and higher log(aFe3+/aH+3) than its grossularitic garnet skarn precursor, whereas hedenbergitic pyroxene skarn was stable at lower log(aCa2+/aH+2) and log(aFe3+/aH+3) and higher log aSiO2aq than its andraditic skarn precursor. / delta34S values of sphalerite, galena and pyrrhotite cluster between -1 and +2‰, and their corresponding fluid delta 34 SH2S values ranged from -3.7 to +5.4‰, indicating that the sulphur was primarily igneous in origin, and lead isotope ratios of galena are similar to those of the Miocene-Pliocene Padre Miguel ignimbrite. Variation in the delta 34S values of sphalerite and the whole-rock Pb isotope ratios of the host limestone are interpreted to reflect decreasing alteration toward the southwest. / Microthermometric measurements for garnet-, pyroxene- and sphalerite-hosted fluid inclusions indicate that two end-member fluids, a saline formational brine and a Fe-rich orthomagmatic fluid, formed skarn and ore at the deposit. The first, hosted by grossularitic garnet and low-Fe sphalerite, is characterized by homogenization temperatures ranging from 260 to 390°C, and salinities from 7 to 45 wt.% NaCl equivalent. The second, hosted by pyroxene, andraditic garnet, and medium-Fe sphalerite, is characterized by a higher homogenization temperature (320 to 400°C), lower salinity (1 to 15 wt.% NaCl equivalent) and an elevated Fe concentration. (Abstract shortened by UMI.)

Field evidence suggests that the fate of sedimentary dissolved organic carbon (DOC) is linked to the diagenetic cycles of iron and manganese in marine sediments. Co-variations of their concentrations in sediment porewater, as well as the release of DOC upon the reductive dissolution of authigenic iron and manganese oxides lead us to believe that sorption (i.e., co-precipitation and/or adsorption) onto these oxides may play an important role on the diagenetic behavior of DOC. This DOC sink, if it exists, would considerably alter our views of the mechanisms that regulate DOC fluxes across the sediment-water interface as well as their quantification. Sorption onto authigenic metal oxides may also lead to a molecular and isotopic fractionation of DOC. / Oxic surface sediments recovered from the Amundsen Gulf, located south of Banks Island, Northwest Territories, Canada and the Saguenay Fjord, Quebec, Canada were extracted with two different mild reducing agents to determine the amount and composition (molecular and isotopic) of the DOC associated with the authigenic iron and manganese oxides. The reducing agents employed were: (i) 0.25 M hydroxylamine with 0.25 M HCl (HA, pH=1.7) and (ii) 1 N HCl (pH=0). Our results suggest that the sorbed DOC from the Saguenay Fjord sediment is both isotopically (delta13Corg) and molecularly fractionated with respect to the sedimentary particulate organic carbon (POC) pool whereas only molecular fractionation was evident in the Amundsen Gulf samples. The lack of isotopic fractionation in the latter sample set could be attributable to the inefficient extraction of iron oxides (50%) or simply isotopic uniformity, thereby limiting the isotopic fractionation. Molecular analyses by Fourier-Transform Infra-Red Spectroscopy (FTIR) indicate that the porewater and adsorbed DOC pools are most likely dominated by carbohydrates. Our results suggest that the adsorbed DOC pool may buffer the porewater DOC concentration and composition. Based on our preliminary results, we propose that authigenic and detrital iron and manganese oxides that accumulate in oxic sediments scavenge oxygen-rich organic acids diffusing upwards through the sediment column, thereby creating an "aging" reservoir in the oxic sediments. Slow diffusion across the sediment-water interface and desorption upon resuspension of these sediments in the overlying bottom waters may contribute to the "old" DOM pool found in benthic marine waters.

Gold solubility studies in hydrous subaluminous rhyolitic/granitic melts of three compositions (a subaluminous rhyolite (LCO), a subaluminous rhyolite with 1.2 wt.% fluorine (MRF), and a subaluminous rhyolite with ~0.35 wt.% chlorine (LCI)) were conducted in a piston cylinder apparatus at temperature and pressure ranges of 900--1250°C and 6--9 kbar (0.6--0.9 GPa). Starting rock powders were sealed in Au75Pd25 capsules (that acted as the source of Au) with 5--7 wt.% water. Oxygen fugacities were near 2 log units above the nickel-nickel-oxide (NNO) buffer. Gold contents in experimental glass products were analyzed by laser ablation - inductively coupled plasma - mass spectrometers (LA-ICP-MS). / Combining solubility data in "near" Cl saturated melts at an oxygen fugacity of 2 log units above the NNO buffer from this study and Au solubility data in H2O saturated with NaCl from Ballhaus et al. (1994), the fluid/melt partition coefficient for Au was calculated. A fluid/melt partition coefficient was calculated with Au solubility data that was extrapolated to 2 log units below the fayalite-magnetite-quartz (FMQ) buffer, using the relationship between log Au concentration and log fO2 from Borisov and Palme (1996). Sulfide/melt partition coefficients for Au were calculated by combining Au solubility data from this study with Au solubility data from Cygan and Candela (1995). (Abstract shortened by UMI.)

In order to model the transport and fate of aniline and chloroaniline in the subsurface, the geochemical reactions between these contaminants and important metals and minerals surfaces must be quantified. / The thermodynamic stabilities of the aqueous and surface aluminum-aniline and aluminum-2-chloroaniline complexes were investigated at 55$ sp circ$C and 80$ sp circ$C. Solubility and adsorption experiments place quantitative constraints on the thermodynamic properties of these complexes. No evidence was found for stable Al-aniline or Al-2-chloroaniline aqueous complexes. Conversely, the adsorption data provide unequivocal evidence for the presence of two distinct surface Al-aniline and A-chloroaniline complexes according to the following reactions: (1) $Aniline sp circ + { equiv}Al(OH) sp circ leftrightarrow { equiv}(AlOH(Aniline) sp circ$; (2) $Aniline sp circ + { equiv}Al(O) sp- leftrightarrow { equiv}AlO(Aniline) sp-$; (3) $Chloroaniline sp circ + { equiv}Al(OH) sp circ leftrightarrow { equiv}AlOH(Chloroaniline) sp circ$; (4) $Chloroaniline sp circ + { equiv}Al(OH sb2) sp+ leftrightarrow { equiv}AlOH sb2(Chloroaniline) sp+$. / A constant capacitance model is used to quantify the stability constants for reactions (1) - (4), and the results yield equilibrium constant values of 10$ sp{2.09}$, 10$ sp{2.67}$, 10$ sp{2.87}$ and 10$ sp{2.30}$ respectively. These results indicate that mineral surface complexation can significantly affect total aniline and chloroaniline budgets.

Fixed-slope P$ rm sb{s}$-$ mu sb{ rm H2O}$ diagrams have been generated for the pseudoternary systems $ rm SiO sb2$-$ rm Na sb2 ZrO sb3$-$ rm H sb2O$ and $ rm SiO sb2$-$ rm CaZrO sb3$-$ rm H sb2O$ as first approximations to P-T phase relations for the Na- and Ca-zirconosilicates, respectively. Two possible topologies were determined for each pseudoternary based on an interchange of stable and metastable invariant points. Although for the $ rm SiO sb2$-$ rm Na sb2 ZrO sb3$-$ rm H sb2O$ system the correct topology cannot yet be resolved, owing to a lack of constraints from experimental and field observations, chemographic analysis reveals that the critical observation would be either the coexistence or incompatibility of the divariant mineral assemblage: elpidite + parakeldyshite. / The observed replacement of armstrongite by gittinsite + quartz in the Strange Lake peralkaline complex, Canada, suggests that the preferred topology for the $ rm SiO sb2$-$ rm CaZrO sb3$-$ rm H sb2O$ system may be the one in which the calcium catapleiite-, quartz- and calciohilairite-absent invariant points are stable. / Synthesis experiments in the $ rm SiO sb2$-$ rm CaZrO sb3$-$ rm H sb2O$ system resulted in the formation of the compound $ rm{Ca sb2 ZrSi sb4 O sb{12}}$ as well as zircon, baddeleyite, xonotlite and wollastonite under various conditions, but synthesis of naturally-occurring Ca-zirconosilicates remained elusive.

Calcite overgrowths were precipitated from artificial seawater at 25$ sp circ$C on synthetic calcite seeds using a chemo-stat precipitation technique to investigate the influence of the $P sb{CO sb2}$ on magnesium incorporation. Powder X-ray diffraction (APXRD) analyses of the overgrowths indicate that the amount of MgCO$ sb3$ incorporated during precipitation is independent of the $P sb{CO sb2}$ over 4 orders of magnitude (10$ sp{-0.5}$ to 10$ sp{-4.6}$atm). The magnesium content of the overgrowths estimated from mass balance calculations of carbonate alkalinity of the reacting solutions ($ Delta$Ac) and flame spectrophotometric (AAS) analyses of the reacted solids yield similar results away from the extremes of $P sb{CO sb2}$ investigated in this study. These results contrast with those obtained from previous investigations and indicate that variations in the composition of magnesium calcite cements during the Phanerozoic cannot be explained solely on the basis of atmospheric $P sb{CO sb2}$ excursions. The concentration of sulfate and sodium in the overgrowths, however, appears to correlate with variations in $P sb{CO sb2}$. / In a separate set of experiments, using the same precipitation technique, the influence of a biogenic seed material on the composition and mineralogy of overgrowths was investigated. The mineralogy of these precipitates was characterized by APXRD and Guinier-Hagg film x-ray diffraction. Overgrowths of aragonite and a high Mg-calcite (16.7 mole % MgCO$ sb3$) were precipitated from artificial seawater on crushed interambulacral shells of the sea urchin Diadema at a $P sb{CO sb2}$ of 10$ sp{-2.5}$ atm over a range of saturation states ($ Omega sb{ rm calcite}$ = 6.0 to 11.6). When compared to results of the previous study, it was not possible to determine unequivocally if the difference in composition and mineralogy of the overgrowths resulted from the influence of either the structure of the seed material or residual skeletal matrix organic manner. / Transmission and scanning electron micrographs of solid overgrowths and substrates from the two series of experiments provide physical evidence of the existence and morphology of the precipitates.

Carbon, hydrogen and nitrogen contents of the Earth's mantle are poorly constrained. Mantle xenoliths brought to the surface by alkaline lavas at 6 volcanic centers along the northwestern margin of North America provide a way to estimate the contents of these volatiles in the upper mantle. Carbon (C), hydrogen (H$ sb2$) and nitrogen (N$ sb2$) are contained as several C-H-N phases in these xenoliths and lavas; light isotopic C-H-N, C in carbonates, C and N$ sb2$ in fluid inclusions, and dissolved C, H$ sb2$ and N$ sb2$ in anhydrous and hydrous minerals. The light isotopic C-H-N phase, which represents 30 to 95 % of the volatiles extracted from these xenoliths by combustion, contributes 10 to 250 ppm C and 10 to 100 ppm H$ sb2$, with $ delta sp{13}$C and $ delta$D values ranging from $-$31 to $-$23$ perthous$, and $-$150 to $-$100$ perthous$, respectively. This phase is composed of C-H-N hydrocarbon molecules, which are thought to occur along grain boundaries or fractures. Calcite contributes between 1 to 24 ppm C in the temperature range 600-800$ sp circ$C but reaches up to 240 ppm in host volcanic rocks. / Carbon of mantle origin is present as a supercritical CO$ sb2$-rich fluid contained in inclusions within the minerals of the xenoliths. Maximum pressures of entrapment are estimated from fluid densities in type I "primary" inclusions to range from 11 to 14 kb, in agreement with the spinel lherzolite stability field of these host xenoliths. / The hydrogen content extracted at temperatures $>$600$ sp circ$C from anhydrous spinel lherzolite and harzburgite xenoliths ranges from 3 to 15 ppm H$ sb2$, and from 10 to 25 ppm H$ sb2$ in anhydrous pyroxenites. The H$ sb2$ content extracted at temperatures $>$600$ sp circ$C from xenoliths containing hydrous minerals varies from 18 to 345 ppm H$ sb2$. Nitrogen reaches 8 ppm in the xenolith most enriched in fluid inclusions and 58 ppm in phlogopites from an amphibole clinopyroxenite. / Partial melting calculations indicate that the C, H$ sb2$ and N$ sb2$ contents of primary MORB magmas derived from a mantle source similar to the anhydrous spinel lherzolite of this study would contain 4-145 ppm C, 20-215 ppm H$ sb2$ and 0.2-7.0 ppm N$ sb2$. / The isotopic signature ranges of C, H$ sb2$ and N$ sb2$ in the upper mantle beneath the northwestern margin of North America are estimated to be; $-$10 to $-$4$ perthous$, $-$95 to $-$45$ perthous$, and $-$5 to +1.5$ perthous$ respectively, and to contain between 3 and 7 ppm C and 7 to 30 ppm H$ sb2$ with an average content of 4 ppm C and 8 ppm H$ sb2$. If these latter values are representative of the Earth's mantle as a whole, then the Earth is significantly more degassed than previously estimated. (Abstract shortened by UMI.)

The solubility of gold and copper chloride in liquid-undersaturated, HCl-bearing water vapour was investigated experimentally at elevated temperatures and pressures. Experimental results show that the solubility of gold and copper is significant, increasing at higher fHCl and fH2O for gold, and at higher fH2O for copper. These increases are attributed to the formation of hydrated gas species, with a metal:chlorine ratio of 1. Hydration numbers vary from 5 at 300°C to 3 at 360°C for gold, and from 7.6 at 280°C, to 6.0 at 300°C, and 6.1 at 320°C for copper; the results reflect the presence of trimer [Cu3Cl3•(H2O)n] or tetramer [Cu4Cl4•(H2O)n] species. Results indicate that solubility for both vapour species is retrograde, i.e., it decreases with increasing temperature, and formed via the reactions: Ausolid+m·HClgas+n·H2 Ogas=AuClm·H2 Ogasn+m 2·Hgas2 3CuClsolid+n·H2Ogas= Cu3Cl3·H2O gasn / Calculations based on the solubility data indicate an economic high-sulphidation Au deposit (e.g., Nansatsu, Japan; 36 tonnes) could form in ~30,000 years, whereas a porphyry copper deposit (e.g., 50 million tonnes at 0.5% Cu) could form in as little as ~20,500 years, assuming transport only in the vapour phase. / Precious- and base-metal-rich composite scales, containing up to 111 ppm Au and 628 ppm Ag, occur in surface pipes at the Momotombo geothermal field, Nicaragua. Polysulphide scale fragments, comprising chalcopyrite, sphalerite, galena, electrum and hessite grains in a matrix of amorphous silica, formed as a result of cooling and ligand loss induced by boiling, during fluid ascent in well MT-36. Secondary bornite, stromeyerite and chalcocite/digenite replaced chalcopyrite through the addition of Cu and Ag and an increase in fO2 . A drop in pH due to well closure resulted in replacement of primary and secondary sulphides by tetrahedrite. / Reaction-path modelling using the program CHILLER simulates deposition of minerals from the reconstructed deep geothermal fluid, at temperature intervals (depths) along excess enthalpy and isoenthalpic boiling paths. These simulations accurately reproduce the paragenetic sequence of base- and precious-metal mineralization in the scales. The modelling indicates excess enthalpy boiling results in metal precipitation at greater depths than would be expected for isoenthalpic boiling, and that at Momotombo this occurs through the destabilisation of bisulphide complexes in response to loss of CO2 and H2 S during phase separation.

High field strength elements (HFSE) are geologically and economically important. These elements were once thought to be immobile during metasomatic processes, however, a growing body of empirical evidence indicates that HFSE can be mobilized under certain conditions. Despite this evidence, little is known about the factors controlling solubility, transport and deposition of HFSE by aqueous fluids, apart from some theoretical estimates and rare experimental studies. Therefore, the study of natural systems (e.g., HFSE ore deposits) provides an excellent opportunity to evaluate HFSE mobility by aqueous fluids. Five localities where evidence of hydrothermal transport of HFSE has been previously documented were included in this study: Gallinas Mountains, New Mexico; South Platte, Colorado; Rock Canyon Creek, British Columbia; St. Lawrence, Newfoundland; and Strange Lake, Quebec/Labrador. Minerals and, in the case of South Platte, fluid inclusions from these localities were analyzed using petrography and laser ablation inductively-coupled plasma mass spectrometry (LA-ICPMS) to evaluate the source of the HFSE and the hydrothermal fluids responsible for HFSE transport, and factors controlling HFSE and gangue mineral (e.g., fluorite, quartz) precipitation. Analysis of some of the important gangue minerals, which are also the primary host of fluid inclusions in many of these deposits (e.g., fluorite), is difficult using 266 nm Nd:YAG-based LA-ICPMS. Furthermore, complex mineral intergrowths and the desire to quantify the chemical composition of unknown minerals required the development of analytical and data reduction protocols for LA-ICPMS. Methods for conducting traversed opening of fluid inclusions, removing the host mineral contribution to fluid inclusion signals by calculating count rate ratios, and quantifying the composition of minerals without using an internal standard are presented. In general, hydrothermal enrichment of HFSE in these deposits appears to have resulted from interaction of an HFSE- and F-bearing magmatic fluid with another, Ca-bearing fluid or with Ca-bearing wall rocks or preexisting minerals. In most cases, HFSE appear to be derived locally, within the associated igneous intrusion.