Stratigraphy and Hydrothermal Alteration of Archean Volcanic Rocks at the Headway-Coulee Massive Sulfide Prospect, Northern Onaman Lake Area, Northwestern Ontario

A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Steven Arvid Osterberg in partial fulfillment of the requirements for the degree of Master of Science, October 1985. Plates 1-2 referenced in the thesis are also attached to this record.The Headway-Coulee massive sulfide prospect of northwestern Ontario is situated within the Superior Province of the Canadian Shield. Rocks at the prospect form part of the Archean Wabigoon greenstone belt and consist of an intensely hydrothermally altered succession of mafic and felsic volcanic and intrusive rocks. Subaqueously deposited pillowed and amygdaloidal to massive and autobrecciated mafic lava flows form a 1-2 km thick succession which is locally interlayered with, and overlies a thin sequence of felsic volcanic rocks. The felsic volcanic rocks are laterally limited (2 km) and are composed dominantly of bedded ash tuffs capped by massive to brecciated and flow-banded lavas. The tuffs are fine-grained, generally fragment-poor, and vary from laminated to thickly-bedded. An extensive polymictic diamictite deposit, which contains clasts of granite, mafic and felsic volcanic rocks, and iron formation, is interlayered with the felsic 1olcanic rocks and is believed to represent a debris flow deposit which had its source to the southwest of the study area. Based on their fine-grain size, limited lateral extent, and thin to thickly-bedded nature, the felsic tuffs are interpreted to be products of hydrovolcanic eruptions. Based on stratigraphic relationships the deposits are believed to have formed on the submerged flanks of two adjacent tuff cones. It is envisioned that the capping felsic lavas formed either under low water/magma ratio conditions as access of water to the erupting magma was restricted, and/or under high water/magma ratio conditions within a water flooded vent or on the submerged flanks of the cones. The majority of the volcanic rocks were intensely altered by hydrothermal solutions during the waning stages of felsic volcanism. Alteration in the rocks is relatively widespread and is subconcordant to stratigraphically conformable in distribution. The altered rocks have been subdivided into four distinct mineral zones. The zones, in order of formation and increasing alteration intensity, are: (1) least altered, (2) quartz-sericite, (3) iron chlorite, and (4) chloritoid. The progressive alteration of the rocks was studied by mass balance comparisons of the altered rocks and their less intensely altered, stratigraphic equivalents. These comparisons indicate that Al was generally immobile, and that volume losses during alteration range from 0 to approximately 50%; the largest volume losses occurred during alteration of the felsic ash tuffs. Major chemical trends involved in alteration of the rocks include large gains in K and loss of Na during sericitization, and generally addition of Fe, and loss of Ca and Na during formation of iron chlorite and subsequent development of the chloritoid alteration type. Based on the distribution of the alteration types as well as the alteration mineralogy and chemistry it is proposed that, by shallow circulation through porous volcanic rocks, an acidic, K-rich fluid evolved and caused widespread sericitization within the study area. Deeper circulation evolved an Fe-rich fluid which was discharged along synvolcanic faults from a pressurized reservoir at depth. The solution chemically reacted with the sericitized rocks to produce the iron chlorite assemblage, and the pre-metamorphic equivalent of the chloritoid assemblage. The chloritoid assemblage developed as pre-metamorphic, coexisting iron chlorite + hydrous Al--silicate became unstable and reacted to form chloritoid during regional greenschist facies metamorphism

Alkalic-Type Epithermal Gold Deposit Model: Chapter R of Mineral Deposit Models for Resource Assessment

This report summarizes the primary characteristics of alkalic-type epithermal gold (Au) deposits and provides an updated descriptive model. These deposits, primarily of Mesozoic to Neogene age, are among the largest epithermal gold deposits in the world. Considered a subset of low-sulfidation epithermal deposits, they are spatially and genetically linked to small stocks or clusters of intrusions containing high alkali-element contents. Deposits occur as disseminations, breccia-fillings, and veins and may be spatially and genetically related to skarns and low-grade porphyry copper (Cu) or molybdenum (Mo) systems. Gold commonly occurs as native gold, precious metal tellurides, and as sub-micron gold in arsenian pyrite. Quartz, carbonate, fluorite, adularia, and vanadian muscovite/roscoelite are the most common gangue minerals. Alkalic-type gold deposits form in a variety of geological settings including continent-arc collision zones and back-arc or post-subduction rifts that are invariably characterized by a transition from convergent to extensional or transpressive tectonics. The geochemical compositions of alkaline igneous rocks spatially linked with these deposits span the alkaline-subalkaline transition. Their alkali enrichment may be masked by potassic alteration, but the unaltered or least altered rocks (1) have chondrite normalized patterns that are commonly light rare earth element (LREE) enriched, (2) are heavy rare earth element (HREE) depleted, and (3) have high large ion lithophile contents and variable enrichment of high-field strength elements. Radiogenic isotopes suggest a mantle derivation for the alkalic magmas but allow crustal contamination. Oxygen and hydrogen isotope compositions show that the fluids responsible for deposit formation are dominantly magmatic, although meteoric or other external fluids (seawater, evolved groundwater) also contributed to the ore-forming fluids responsible for these deposits. Carbon and sulfur isotope compositions in vein-hosted carbonates and sulfide gangue minerals, respectively, coincide with magmatic values, although a sedimentary source of carbon and sulfur is evident in several deposits. Deep-seated structures are critical for the upwelling of hydrous alkalic magmas and for focusing magmatic-hydrothermal fluids to the site of precious metal deposition. The source of gold, silver (Ag), tellurium (Te), vanadium (V), and fluorine (F) was probably the alkalic igneous rocks themselves, and the coexistence of native gold, gold tellurides, and roscoelite in several deposits is primarily a function of similar physicochemical conditions during deposition (for example, overlapping pH and oxygen fugacity (fO2). Potential environmental impacts related to the mining and processing of alkalic-type epithermal gold deposits include acid mine drainage with high levels of metals, especially zinc (Zn), copper, lead (Pb), and arsenic. However, because alkalic-type gold deposits typically contain carbonates, which contribute calcium and magnesium ions that increase water hardness, aquatic life may be afforded some protection. Impacts vary widely as a function of host rocks, climate, topography, and mining methods. Geologic mapping to (1) highlight the distribution of potassic alteration; (2) define fault density and orientation of structures; (3) determine the distribution of alkaline rocks and hydrothermal breccias; and (4) identify uniquely colored gangue minerals, such as fluorite and roscoelite, will be critical to exploration and future discoveries. Geophysical techniques that identify potassium (K) anomalies (for example, radiometric and spectroscopic surveys), as well as magnetic, resistivity, aeromagnetic, and gravity surveys, may help locate zones of high-permeability that control advecting hydrothermal fluids. Geochemical surveys that include analyses for Au, Ag, barium, Te, K, F, V, Mo, and mercury, which are key elements in these deposits, should be undertaken along with the measurement of other pathfinder elements such as arsenic, bismuth, Cu, iron, nickel, Pb, antimony, selenium, and Zn

Stratigraphy and Sedimentology of the Cover Rocks of the Maqna Area, Saudi Arabia

The Maqna area, part of the Midyan Peninsula, is characterized by well exposed synrift sediments of Oligocene and Miocene age which can be grouped into four formations: the Sharik, Musayr, Nutaysh and Bad Formations. These mark steps in the geodynamic evolution of the Red Sea associated with sea-floor spreading. The early Sharik Formation consists of fan delta sediments. It covers much of the northern half of the area and deposition was associated with the first movements along the Arabian Wrench Fault which caused the down-faulting of the Midyan peninsula. The Musayr Formation is divided into Lower Gypsum and Upper Limestone members. The Musayr Gypsum is a coastal lagoonal evaporite sequence and has a restricted (L-shaped) distribution along northern and western side of Jabel Tayran. Five lithofacies assemblages are identified in the Limestone sequence. These are: (I) conglomeratic limestone; (2) laminated limestone; (3) oyster limestone; (4) sandstone; and (5) brecciated limestone. The Musayr Limestones are marine sediments (previously known as reefal limestones) deposited in environments ranging from near-shore to slope. Macrofossils present indicate Mediterranean affinities. Two corals, species of Acanthastrea cf. echinata and Lithophyllia michelotti, are assigned the Burdigalian (Lower Miocene). The Nutaysh Formation is interpreted as a turdidite sequence with proximal coarse grained conglomerate and sandstone sediments concentrated in the northern and western parts of the Maqna area, while towards the southeast, distal fine grained marly sediments are predominant. The capping sequence, the Bad Formation, is a shallow-water deep-basin evaporite. Deposition of the evaporite sequence was followed by the second movement of the Arabian Wrench Fault, post Miocene-Pliocene, which resulted in emergence of the area and local deposition of tufa. The Quaternary coastal limestones and coarse braid delta sediments, a continuation of inland clastic terraces, may reflect tectonic controls related to eustatic falls in sealevel. The Tertiary formations of the Maqna area contain similar cycles of diagenetic sequences which indicate that burial resulted in similar general diagenetic environments

Low-grade regional metamorphism of paleozoic rocks in the Midland valley of Scotland

Low-grade burial metamorphism in the Midland Valley of Scotland, has been investigated with reference to the Silurian sediments and to the Carboniferous volcanics. In the Silurian sediments, facies definitive phyllosilicates are absent. Thin-section examination indicates that cementation was early and despite strong deformation, the lack of cleavage is related to the isotropic dispersal of domains during burial. Scanning electron microscopy and X-ray diffraction define clay mineral assemblages which characterize the transformation of montmorillonite to illite during burial. Illite crystallinity, bo and conodont alteration, show values consistent with this transformation and are indicative of diagenetic/anchizone conditions. Metamorphism is related to Siluro-Devonian syn-sedimentary burial. Despite tentative links between the Midland Valley and the Southern Uplands during the Llandovery, the relative simplicity of the burial metamorphic sequence in the former region suggests that the Silurian trough became palaeo-geographically distinct. The Carboniferous volcanics have undergone burial metamorphism in the zeolite facies, which occurred once the bulk of the lavas had been extruded, and following burial beneath the Central and Ayrshire Basins. Alteration was dominated by hydrothermal processes and has resulted in the production of early greenstones, later burial metamorphic zones and palaeo-geothermal plumes. Seven zones have been defined upon the distribution of amygdale minerals. Thin-section examination however divides the zeolite facies in the Midland Valley into an upper analcime and a lower laumontite zone. Mineralogical assemblages are conducive with metamorphism at a) Pfluid = 2-4 kb at 200 °C and b) Pfluid = 2 kb at 350-420 °C, for the zeolite zones and the palaeo-geothermal plumes respectively. These values are compatible with burial depth estimates, with homogenization temperatures in fluid inclusions and with calcite-water fractionation temperatures. Water/rock ratios indicate that metamorphism was related to the flow of seawater and meteoric water through the volcanic sequences. Evidence for episodic boiling in fluid inclusions indicates fluid convection occurred, and was related to fracturing associated with a change from a lithostatic to a hydrostatic pressure regime. Seismic pumping was related to fracturing and to renewed magmatic activity in shallow chambers beneath the Midland Valley

Traitement passif du drainage minier neutre contaminé au nickel : cinétique et isothermes de sorption, essais en mode cuvée et essais en colonnes

Résumé Dans l’industrie minière, les réacteurs passifs à écoulement gravitaire sont considérés comme une technologie appropriée pour traiter les effluents contaminés. Des systèmes à court temps de résidence hydraulique (TRH), conçus pour l’enlèvement des métaux par sorption sur des matériaux organiques, pourraient fournir une solution économique pour traiter les drainages neutres contaminés (DNC) qui contiennent des concentrations de métaux et de sulfates typiquement plus faibles que les drainages miniers acides. Dans ces réacteurs, quelques heures de contact entre le DNC et le substrat pourraient suffire à atteindre le niveau de traitement souhaité. Les coûts de transport des matériaux vers les sites miniers éloignés peuvent être très importants, et c’est pourquoi il est intéressant d’étudier les capacités de sorption des matériaux qui sont disponibles localement ainsi que de comparer leurs performances dans des systèmes à écoulement continu. Dans ce contexte, les principaux objectifs de cette thèse sont de: 1) de comparer la capacité d’enlèvement du nickel de cinq matériaux organiques peu coûteux (tourbe, compost, algues brunes, sciures et cendres de bois) au cours d’expériences à court- (24 h) et à moyen-terme (56 jours), afin de sélectionner les meilleurs substrats potentiels pour des essais en colonnes; 2) de comparer la performance long terme (2.5-4 mois) de trois matériaux (compost, tourbe-calcite et cendres de bois) pour le traitement d’un DNC dans des colonnes à court TRH; et 3) d’identifier les propriétés des matériaux qui déterminent leurs performances en système à écoulement continu. Dans une première étape (article #1), les propriétés d’adsorption et de rétention du nickel des cinq matériaux ont été comparées lors d’expériences cinétiques et d’expériences d’équilibration à court-terme. Les essais d’adsorption et de désorption en mode cuvée ont été effectués dans du NaNO3 0.05M, à pH 7, pour simuler la force ionique et le pH d’un DNC. Les modèles cinétiques ont été comparés par régression non-linéaire. Les résultats d’adsorption, mieux représentés par le modèle d’Elovich, montraient que les vitesses étaient supérieures pour la tourbe (796 075 mg/g·min) et le compost (791 mg/g·min). Les résultats des expériences d’équilibration ont été ajustés aux isothermes de Langmuir et de Freundlich, et les plus grandes capacités d’adsorption ont été observées avec la tourbe (environ 22 mg/g) et le compost (environ 9 mg/g). Les expériences de désorption ont révélé que la tourbe et le compost ont libéré un pourcentage moindre du nickel adsorbé lorsqu’exposés à une solution dépourvue de nickel. Dans cette partie de l’étude, aucune des caractéristiques physicochimiques des matériaux (surface spécifique, point de charge nulle, capacité d’échange cationique, etc.) n’a pu être désignée, à elle seule, comme contrôlant la performance des matériaux en termes d’adsorption et de rétention du nickel. Néanmoins, le relargage de grandes concentrations de carbone organique dissout de certains substrats a été identifié comme une propriété indésirable. Dans une deuxième étape (article #2), l’effet du pH et de la présence d’ions compétiteurs ont été évalués en effectuant des expériences de sorption du nickel à court- et à moyen-terme dans un DNC synthétique. Ces expériences en mode cuvée ont indiqué que les matériaux ayant une capacité de sorption plus faible (algues, sciures de bois, cendres) retenaient 10-20% moins de nickel dans le DNC que dans le NaNO3, que l’augmentation du pH affectait favorablement la rétention du nickel. Lorsque le pH du DNC n’était pas ajusté, le compost, la tourbe et les cendres de bois retenaient plus de nickel que les autres matériaux. De plus, pour le compost et les cendres, les pH mesurés demeuraient neutres. En l’absence d’un substrat organique, une légère augmentation du pH du DNC synthétique (environ 1 unité de pH) entrainait l’enlèvement du nickel par une réaction de précipitation. Des cinq matériaux testés, les cendres de bois ont été les seules à augmenter le pH du DNC, et ainsi, ce matériau pourrait potentiellement retenir une quantité supplémentaire de nickel par des mécanismes de précipitation/coprécipitation. En se basant sur les résultats des expériences court-terme dans le NaNO3 et dans le DNC synthétique, deux tourbes additionnées de calcite (tourbe-HD et -LT), le compost et les cendres de bois ont été sélectionnés et comparés lors d’une expérience à moyen-terme en mode cuvée. Durant cette expérience, tous les matériaux ont bien performé, retirant plus de 97% du nickel provenant d’un DNC synthétique contenant 7.7 mg/L de nickel. Des extractions chimiques post-traitement ont révélé que le nickel était fixé de manière prédominante sur la fraction réductible (F3) des cendres et sur la fraction oxydable (F4) dans le compost et le mélange tourbe-calcite. Dans cette partie de l’étude, les propriétés alcalines et la capacité de sorption par unité de volume des matériaux ont été identifiées comme des paramètres importants pour leur performance dans des systèmes à écoulement continu. Dans une troisième étape (article #3), une expérience en colonne (4.8L) d’une durée de 2.5 à 4 mois a permis de comparer la performance de trois matériaux (compost, tourbe-calcite et cendres de bois) pour l’enlèvement du nickel. Durant cette expérience, les trois types de colonnes étaient alimentés par le bas à un TRH d’environ 16.5 h et elles ont toutes traitées plus de 400 L de DNC synthétique contenant 4.05 mg/L de nickel. Des conditions réductrices ont été observées dans les colonnes de tourbe-calcite et de compost, et des précipités noirs, probablement des sulfures de fer, ont été observés au sommet des colonnes de compost. Dans les sections riches en nickel à la base des trois différents types de colonnes, aucune évidence claire de précipitation n’a été observée. Ainsi, la sorption a été considérée comme le mécanisme principal d’enlèvement du nickel dans les sections du bas de toutes les colonnes. Basé sur les résultats de percée du nickel à mi-colonne (TRH ∼ 9 h), les cendres de bois ont été le matériau le plus efficace pour l’enlèvement du nickel. De plus, une procédure d’extraction séquentielle a indiqué que le nickel retiré était potentiellement moins mobile dans les résidus de cendres que dans les autres types de résidus. Le pH plus élevé des colonnes de cendres a probablement été la clef de leur meilleure performance. Cependant, une correction de pH serait requise dans les premiers stades d’un traitement à pleine échelle afin de maintenir le pH de l’effluent à l’intérieur des limites règlementaires permises (6-9.5). Lorsqu’extrapolés à pleine grandeur, les résultats obtenus à mi-colonne indiquent que le volume d’une cellule conçue pour le traitement annuel d’un effluent neutre contaminé (10 m3/h, 4.05 mg/L Ni) serait plus petit avec des cendres de bois (< 500 m3) qu’avec du compost (600 ± 140 m3) ou de la tourbe-calcite (720 ± 50 m3). ---------- Abstract In the mining industry, gravity feed passive reactors are considered an appropriate technology to treat mining effluents. Short hydraulic residence time (HRT) systems, designed for metal removal by sorption onto organic materials, may provide an economical solution to treat contaminated neutral drainage (CND), which typically possess lower metal and sulfate concentrations than acid mine drainage. In these reactors, contact times of a few hours between the CND and the substrate may suffice to achieve the desired remediation level. The financial cost of transporting materials to remote mining sites can be substantial and, thus, studying the sorption capacity of locally available materials and comparing their performance in fixed-bed systems is of great interest. In this context the principal objectives of the thesis are: 1) to compare the nickel removal capacity of five low-cost organic materials (peat, compost, brown algae, sawdust and wood ash) during short- (24 h) and medium-term (56 days) sorption experiments and to select the best potential substrates for fixed-bed column experiments; 2) to compare the long term (2.5-4 months) performance of three materials (compost, peat-calcite and wood ash) for the treatment of a CND in short-HRT columns; and 3) to identify the keys properties that determine the performance of materials in fixed-bed systems. In a first step (article #1), the nickel adsorption and retention properties of the five materials were compared during short-term kinetic and equilibration experiments. Batch adsorption and desorption experiments were conducted at pH 7 in 0.05M NaNO3, to simulate the ionic strength and pH of a CND. Non-linear regressions were used to compare kinetic models. Adsorption results, best represented by the Elovich model, indicated higher rates with peat (796 075 mg/g·min) and compost (791 mg/g·min). Results of equilibration adsorption experiments were fitted to Langmuir and Freundlich isotherms and the highest adsorption capacities were observed for peat (around 22 mg/g) and compost (around 9 mg/g). Desorption experiments revealed that peat and compost released a lower percentage of the adsorbed nickel upon exposure to Ni-free solutions. In this part of the study, none of the physicochemical characteristics tested (specific surface area, point of zero charge, cation exchange capacity, etc.) could be solely relied on to predict the nickel adsorption and retention performance of the materials. Nevertheless, the leaching of high dissolved organic carbon concentrations from some organic materials was highlighted as an undesirable property. In a second step (article #2), the effect of pH and of the presence of competing ions was evaluated by conducting short-term nickel sorption experiments in synthetic CND. Results of these batch experiments indicated that materials with lower sorption capacities (algae, sawdust, wood ash) retained 10-20% less nickel in CND than in NaNO3, and that increasing pH favorably affected nickel removal. When the pH of the synthetic CND was allowed to drift, compost, peat and wood ash removed the most nickel. Furthermore, the pH of compost and wood ash slurries remained within the circum-neutral range. In the absence of organic materials, a slight increase in the pH of the synthetic CND (about 1 pH unit) lead to nickel removal by precipitation of Ni-sequestering solids. Of the five materials tested, wood ash was the only one to naturally increase the pH of the CND, implying that this material could potentially sequester additional nickel though precipitation/co-precipitation mechanisms. Based on the results of short-term experiments in NaNO3 and in synthetic CND, two calcite-amended peats (HD- and LT-peat), compost and wood ash were selected and compared in a medium-term batch experiment. During this experiment, all materials performed equally well, sequestering over 97% of the nickel from a synthetic CND initially containing 7.7 mg/L of nickel. Chemical extractions revealed that nickel was retained predominantly on the reducible fraction (F3) of the wood ash residue and on the oxidizable fraction (F4) in the compost and peat-calcite residues. In this part of the study, the pH-increasing properties and the sorption capacity by unit of volume of the materials were identified as important parameters for their performance in fixed-bed systems. In a third step (article #3), a fixed-bed experiment (4.8L columns) that lasted 2.5 to 4 months compared the performance of three materials (compost, peat-calcite and wood ash) for the removal of nickel. During this experiment, the three types of columns had an upward flow and a HRT of about 16.5h, and they all treated over 400 L of a synthetic CND containing 4.05 mg/L of nickel. Reducing conditions were observed in compost and peat-calcite columns, and black precipitates, presumably iron sulfides, were observed in the top sections of compost columns. In the Ni-rich sections at the base of the different columns, no clear evidence of precipitation was observed. Hence, sorption was considered the main nickel removal mechanism in the bottom section of all columns. According to mid-column breakthrough results (HRT ∼ 9 h), wood ash was the most effective material for nickel removal. Furthermore, a sequential extraction procedure revealed that the sequestered nickel was potentially less mobile in the wood ash residue than in other organic materials. The higher pH of wood ash columns was probably key to their better performance. However, a pH correction would be required in the initial stages of field-scale treatment to maintain the effluent pH within the regulatory limits (6-9.5). Scaled to full size, mid-column results indicated that treatment cell sizes, designed for the one-year treatment of a contaminated neutral effluent (10 m3/h, 4.05 mg/L Ni), would be smaller with wood ash (< 500 m3) than with compost (600 ± 140 m3) and peat-calcite (720 ± 50 m3)