Papers by Anthony Williams-jones
Geochimica et Cosmochimica Acta, 2016
The Mid-Proterozoic peralkaline Strange Lake pluton (Québec-Labrador, Canada) exhibits extreme en... more The Mid-Proterozoic peralkaline Strange Lake pluton (Québec-Labrador, Canada) exhibits extreme enrichment in high field strength elements (HFSE), including the rare earth elements (REE), particularly in pegmatites. On the basis of a study of melt inclusions, we proposed recently that fluoride-silicate melt immiscibility played an important and perhaps dominant role in concentrating the REE within the pluton. Here we present further evidence for silicate-fluoride immiscibility at Strange Lake from a sample of the hypersolvus granite, which contains an inclusion composed largely of REE and HFSE minerals. The inclusion (~5 cm in diameter) comprises a narrow rim containing chevkinite-(Ce) and zircon in a fluorite matrix, a core of fluorbritholite-(Ce) and bastnäsite-(Ce) and a transition zone between the rim and the core consisting of a fine-grained intergrowth of bastnäsite-(Ce), gagarinite-(Y) and fluorite. We propose that the inclusion formed as a result of silicate-fluoride immiscibility, which occurred early in the emplacement history of the Strange Lake pluton, and that it represents the fluoride melt. After separation of the two melts, the boundary between them acted as a locus of crystallisation, where crystals formed repeatedly due to heterogeneous (surface catalysed) nucleation. Zircon crystallised shortly after melt phase separation, and was
Chemical Geology, Dec 1, 2016
Strange Lake is a mid-Proterozoic peralkaline granite pluton (Québec-Labrador, Canada) that under... more Strange Lake is a mid-Proterozoic peralkaline granite pluton (Québec-Labrador, Canada) that underwent extreme enrichment in high field strength elements (HFSE), including the rare earth elements (REE). The HFSE mineralisation is confined to highly altered pegmatites and the most altered parts of the granites, implying a genetic association between hydrothermal fluids and HFSE enrichment. This study uses analyses of fluid inclusions to investigate the hydrothermal evolution of the Strange Lake pluton and the role of hydrothermal processes in concentrating the HFSE to potentially exploitable levels. Five groups of inclusions were distinguished. From earliest to latest, these groups are: primary aqueous inclusions (~25 wt.% NaCl eq.) associated with melt inclusions (Group 1); primary *Revised manuscript with no changes marked Click here to view linked References
Chemical Geology, Feb 1, 2019
Large peralkaline complexes are 'factories' that have produced a variety of 'exotic' minerals inc... more Large peralkaline complexes are 'factories' that have produced a variety of 'exotic' minerals including high field strength element minerals. In most cases, these minerals are secondary and crystallise in a hydrothermal paragenesis that is extremely difficult to decipher due to the complexity of the textural relationships. The Strange Lake pluton is one of these complexes, and contains 37 exotic minerals, most of which are secondary. Adding to the difficulty in establishing a comprehensive paragenesis for these minerals and an alteration/precipitation path for the pluton is the fact that there were several stages of crystallisation of the same exotic and common secondary minerals, e.g., bastnäsite, fluocerite, gadolinite, aegirine, fluorite, and zircon. In this paper, we present a model, which describes a detailed path for the alteration and precipitation of minerals in the closed hydrothermal system of a peralkaline granitic pegmatite, based on direct measurements of the evolving composition of the aqueous fluid that exsolved from the late-stage magma crystallising rare-metal pegmatites in the Strange Lake pluton. The driving force for this evolution was cooling-induced oxidation that ultimately transformed the CH4-H2 gas in this fluid to CO2. This lead to a large drop in the pH, which was a major control on the composition of the fluid and the crystallisation of secondary minerals. Although large numbers of minerals formed and were replaced during the different stages of fluid evolution, the changing chemistry of the fluid was largely a response to the alteration of four minerals, namely arfvedsonite, elpidite, narsarsukite and fluorite. The earliest stage of alteration, which took place at ~360 o C, was marked by the replacement of arfvedsonite by aegirine. This alteration decreased salinity and released K, Li, and Rb to the fluid, causing Kmetasomatism. At ~ 300 o C, CH4 and higher hydrocarbons reacted to produce CO2. This caused a massive drop in pH from a value > 10 to a value of ~ 3 and intense alteration, which included the dissolution of fluorite, the breakdown of elpidite to zircon and quartz and the replacement of
Chemical Geology, Apr 1, 2018
Granites and pegmatites in the Strange Lake pluton experienced extreme enrichment in high field s... more Granites and pegmatites in the Strange Lake pluton experienced extreme enrichment in high field strength elements (HFSE), including the rare earth elements (REE). Much of this enrichment took place in the most altered rocks, and is expressed as secondary minerals, showing that hydrothermal fluids played an important role in HFSE concentration. Vasyukova et al. (2016) reconstructed a P-T-X path for the evolution of these fluids and provided evidence that hydrothermal activity was initiated by exsolution of fluid during crystallisation of border zone pegmatites (at ~450-500 o C and 1.1 kbar). This early fluid comprised a high salinity (25 wt.% NaCl) aqueous phase and a CH 4 +H 2 gas. During cooling, the gas was gradually oxidised, first to higher hydrocarbons (e.g., C 2 H 6 , C 3 H 8), and then to CO 2 , and the salinity decreased to 4 wt.% (~250-300 o C), before increasing to 19 wt.%, due to fluid-rock interaction (~150 o C). Here we present crush-leach fluid inclusion data on the concentrations of the REE and major ligands at different stages of the evolution of the fluid. The chondrite-normalised REE profile of the fluid evolved from light REE (La-Nd)-enriched at high temperature (~400 o C, Stages 1-2a) to middle REE (Sm-Er)-enriched at 360 to 250 o C (Stages 2b-3) and strongly heavy REE (Tm-Lu)-enriched at low temperature (150 o C, Stage 5). These changes in the REE distribution were accompanied by changes in the concentrations of major ligands, i.e., Clwas the dominant ligand in Stages 1, 2, 4 and 5, whereas HCO 3 was dominant in Stage 3. The fluorine content decreased from 0.6 wt.% in Stage 2a to 0.1-0.4 wt.% in Stages 2b and 3 and to 0.05 wt.% in Stages 4-5. Alteration of arfvedsonite to aegirine and/or hematite contributed strongly to the mobilisation of the REE. This alteration released middle REE (MREE) and heavy REE (HREE), which either partitioned into the fluid or precipitated directly as bastnäsite-(Ce), ferri-allanite-(Ce) or *Manuscript Click here to download Manuscript: CrushLeach_text.docx Click here to view linked References
Economic geology and the bulletin of the Society of Economic Geologists, Jun 1, 2018
Scandium is currently in high demand because of a number of technological advances in the aerospa... more Scandium is currently in high demand because of a number of technological advances in the aerospace and automotive sectors of the global economy. In this paper, we review the properties of scandium, the geology of the major economic and potentially economic scandium deposits and the processes that may concentrate scandium to exploitable levels. We also show that, although scandium is classified as a rare earth element (REE), it behaves very differently from the rest of its family. The reason for this is that it has an ionic radius very similar to that of iron and magnesium and consequently concentrates easily in major ferromagnesian rock-forming minerals, notably clinopyroxene. Unlike the other REE, it is therefore a compatible element. In many scandium deposits, clinopyroxene is the main ore mineral, although in some deposits, scandium is hosted by minerals that also concentrate the other REE. As is the case for these other REE, the main source of scandium is the mantle and the conveyors of scandium are alkaline igneous rocks (and carbonatites) including Alaskan-type ultramafic rocks. The main magmatic processes involved in scandium concentration are partial melting and fractional crystallization. We model the fractional crystallization of clinopyroxene to predict the scandium content of Alaskan-type ultramafic rocks, and use this information in conjunction with a simple model of fluid-assisted partial melting to explain the genesis of scandium-rich pegmatites. In addition to magmatic processes, aqueous fluids may play an important or even essential role in scandium ore formation. The lack of reliable high temperature thermodynamic data for the aqueous scandium species precludes modeling their transport in hydrothermal fluids. However, the availability of ambient temperature data allowed us to model scandium concentration by rainwater in laterite developed above an Alaskan-type ultramafic complex. This review is no more than an introduction to the economic geology of scandium and the processes that appear to be responsible for the genesis of scandium ores, but one, which we hope will provide a guide to future in-depth studies of scandium deposits and strategies for their successful exploration and exploitation.
Economic geology and the bulletin of the Society of Economic Geologists, May 23, 2016
Extreme enrichment and post-magmatic hydrothermal mobilization of the rare earth 22 elements (REE... more Extreme enrichment and post-magmatic hydrothermal mobilization of the rare earth 22 elements (REE), Zr and Nb have been reported for a number of anorogenic peralkaline 23 intrusions, including the world-class REE-Zr-Nb deposit at Strange Lake, Quebec, Canada. Establishing lithogeochemical vectors for these types of deposits is a challenging 25 task because the effects of hydrothermal processes on element distribution are poorly 26 known and the relationships of alteration types to mineralization stages have not been 27 well documented. Here, we present results of a detailed mineralogical and geochemical 28 investigation involving a dataset of over 500 mineral and bulk rock analyses of a NE-SW 29 section through the potential ore zone at Strange Lake. Based on these data, we develop a 30 model that explains the role of hydrothermal processes in concentrating metals in 31 peralkaline granitic systems, and identify lithogeochemical vectors for their exploration. 32 The B Zone, located along the northwestern margin of the Strange Lake pluton, 33 contains a lens-shaped pegmatite-rich domain comprising sub-horizontal sheets of 34 pegmatites hosted by granites with a total indicated resource of 278 Mt grading 0.93 35 wt.% total rare earth oxides (TREO), of which 39 % are heavy (H)REE. Within this 36 resource, there is an enriched zone containing 20 Mt of ore grading 1.44 wt.% TREO, of 37 which 50 % are HREE. The pegmatites are characterized by a core enriched in quartz, 38 fluorite and light (L)REE fluorocarbonates, and a granitic border enriched in 39 zirconosilicates and granitic minerals. The pegmatite sheets and surrounding granites 40 evolved in three essential stages: I) a magmatic stage, II) a near neutral hydrothermal 41 stage involving their interaction with NaCl-bearing orthomagmatic fluids, and III) an 42 acidic hydrothermal stage (comprising high (IIIa) and low (IIIb) temperature substages) 43 that resulted from their interaction with pegmatite-sourced HCl-HF-bearing fluids. Stage 44 IIIa led to pseudomorphic mineral replacement reactions (e.g., Na-Ca exchange during 45 replacement of zirconosilicates) and formation of an aegirinization/hematization halo 46 around the pegmatites. In contrast, Stage IIIb, which was responsible for the 47 hydrothermal mobilization of Zr and REE, is manifested by fluorite and quartz veins, 48 zircon spherules, gadolinite-group minerals, gittinsite and ferriallanite-(Ce) and a 49 pervasive replacement of the granite by these minerals. The distribution of REE, Zr, Nb 50 and Ti was controlled by the competition between hydrothermal fluids and the stability of 51
Aspects of the geochemistry of zinc: a journey to sphalerite
Our journey to sphalerite begins with a review of the occurrence and behavior of Zn in a wide spe... more Our journey to sphalerite begins with a review of the occurrence and behavior of Zn in a wide spectrum of natural fluids. Measured Zn concentrations in crustal fluids vary over at least six orders of magnitude, from around 0.01 to 20,000 ppm (2 wt %). Whist water-rock interaction and boiling influence Zn concentration, the origin of the fluids and in particular their temperature, pH and ligand concentrations are major factors in their capacity to transport Zn. However, in contrast to previous reviews, our compilation shows no significant overall correlation between Zn and Cl concentrations. Fluid chemistry (mainly mCl-, mΣS, pH and fO2) and temperature, and the resultant speciation determine the solubility of Zn and control precipitation of sphalerite. Bisulphide complexes only dominate under relatively high ΣS, low Cl-, and high pH, and are favoured by low temperatures, in most natural systems though chloride complexes dominate. The limited oxidation state of Zn leads to a narrow r...
Source of fluids forming distal Zn-Pb-Ag skarns: Evidence from laser ablation–inductively coupled plasma–mass spectrometry analysis of fluid inclusions from El Mochito, Honduras
Geology, 2008
Economic Geology, 1989
The Madeleine copper deposit comprises steeply plunging stockwork orebodies in cordieritcbiotite ... more The Madeleine copper deposit comprises steeply plunging stockwork orebodies in cordieritcbiotite hornfels adjacent to a Devonian granitic pluton. Mineralization in each orebody is zoned outward from bornite-chalcopyrite in the core through chalcopyrite to chalcopyritepyrrhotite and is associated with local biotite, calc-silicate, and chlorite-muscovite alteration. Sulfide deformation textures suggest that mineralization was pre-to synmetamorphic. The •34S values of chalcopyrite range from -26.7 to +32.5 per mil. Higher •34S values correlate with calc-silicate beds or with calc-silicate alteration. Shales corresponding to the cordieritcbiotite hornfels have •34S values ranging from +7.1 to -19.1 per mil and limestones •34S > 14 per mil. It is proposed that cupriferous fluids, partly emanating from a granite, dissolved sulfur from the overlying sediments and rose through bedding plane-controlled permeability to deposit the ores at higher structural but similar stratigraphic levels.
Economic Geology, 1998
The Zn-Pb-Ba-Cu-Ag-F deposits hosted by Lower Windsor Group (early Carboniferous) carbonates in N... more The Zn-Pb-Ba-Cu-Ag-F deposits hosted by Lower Windsor Group (early Carboniferous) carbonates in Nova Scotia are located along the southern margin of the Maritimes basin. Various geochemical studies indicate that the deposits were formed by fluids expelled from the basin, but it remains unclear whether the ore-forming fluids for different deposits were derived from a common source region in the central part of the basin, as proposed previously, or from separate source regions. It is also unknown how the ore fluids were conveyed from the source regions to the sites of mineralization and whether or not the mineralizing systems of different deposits were hydrologically related. This paper addresses these problems through a compilation of regional fluid composition and temperature data and thermal comparisons between the oreforming fluids and their host rocks. The compositions and temperatures of the fluids were evaluated from fluid inclusion data, whereas host-rock temperatures were estimated from vitrinite reflectance measurements. The ore-forming fluids are characterized by: (1) variable, but generally high salinities (mainly between 15 and 30 wt % NaG1 equiv), (2) variable, but generally detectable amounts of bivalent cations (mainly Ca'2+), (3) significant concentrations of hydrocarbon species, and (4) high temperatures (mainly between 150 ø and 250øC). NaC1/(NaC1 + CaC12) wt ratios in fluid inclusions show a broad district-scale variation: mainly <0.6 for the Jubilee deposit and several showings on Cape Breton Island, and mainly >0.4 for the Gays River and Walton deposits in mainland Nova Scotia. CH4/higher hydrocarbons ratios of the gas components are greater for the Gays River deposit (3.8-9.7) than the Jubilee deposit (0.7-1.3). Fluid inclusion homogenization temperatures do not show a negative correlation with the distance between the deposits and the central part of the Maritimes basin, as might be expected if the fluids for different deposits were derived from the same source region. The background temperatures prior to mineralization were estimated from mean vitrinite reflectance (Ro) in host rocks which were relatively far from the deposit, and were probably least affected by the mineralizing events, and from homogenization temperatures of fluid inclusions in preore minerals. These temperatures are in the range of 70 ø to 155øC, which are significantly lower than those of the ore-forming fluids. The palcogeothermal gradients estimated from the background temperatures and burial depths are ca. 65øC/km. Vitrinite reflectance values in host rocks adjacent to the deposits indicate that these rocks were heated by the mineralizing fluids to variable degrees, but thermal equilibrium between the fluids and rocks was not attained in most eases. This thermal relationship suggests focused and short-lived, rather than pervasive and long-lived, fluid flow. The regional variation of fluid composition and thermal patterns supports a model in which the ore-forming fluids of individual deposits were derived from separate sources; fluid flow was focused along confined conduits and individual mineralizing systems were unconnected hydrologically. Under palcogeothermal gradients of ca. 65øC/kin, fluids with temperatures of ca. 250øC could have been generated in sub-basins proximal to the deposits. Sudden release of overpressured fluids from the basal part of the proximal sub-basins, characterized by high flow rate and short duration, is proposed as the mechanism of ore-forming fluid flow.
The Association of Tourmaline With Cassiterite Ores: Implications for the Genesis of the World's Richest Tin Lode
AGUSM, May 1, 2004
An experimental investigation of the solubility and speciation of scandium in fluoride-bearing aqueous liquids at temperatures up to 250 °C
Geochimica et Cosmochimica Acta, 2022
Silver isotope fractionation in ore-forming hydrothermal systems
Geochimica et Cosmochimica Acta, 2022
Goldschmidt Abstracts, 2020
Goldschmidt Abstracts, 2020
Goldschmidt Abstracts, 2020
Arabian Journal of Geosciences, 2018
Igneous rocks of Nusab El Balgum are formed as an elongated complex mass covering an area of abou... more Igneous rocks of Nusab El Balgum are formed as an elongated complex mass covering an area of about 4 km × 12.5 km (50 km 2), in the NNE-SSW direction of the Tarfawi-Qena-South Sinai trend, which is a branch of the Trans-African shear zone at the intersection with the Kalabsha fault, which is a branch from Guinean-Nubian lineaments. The continuous reactivation of these two major weakness zones from the late Triassic to recent times has created many generations of the magma batches. The exposed granitic rocks of these batches at Nusab El Balgum were represented by the fresh peralkaline granite (youngest) and hydrothermally altered granites (oldest). The fresh peralkaline granite takes the form of a small stock composed essentially of perthites, quartz, sodic pyroxenes, amphiboles (secondary), and rare albite according to the proportion of presence, respectively. The accessory minerals are zircon, bastnaesite-(Ce), columbite-(Fe), magnetite, barite, and sphalerite. The geochemical study indicated that this granite is peralkaline, ferroan, A-type (specifically belongs to the A1-subgroup), anorogeny, emplaced in a within-plate, and crystallized at relatively shallow depth from the alkali basaltic magma similar to the OIBs. Furthermore, it is enriched in the HFSE (e.g., Th, U, Nb, REE, and Zr). The hydrothermally altered granites are formed as an incomplete ring shape and a small stock. They were formed during the late Cretaceous age and were altered due to the hydrothermal solutions from the continuous reactivation affected weakness zones and the new magmatic batches. The hydrothermally altered granites are extremely rich in HFSE found in the accessory minerals such as zircon (different in shape, size, and contains inclusions of bastnaesite and columbite), columbite-(Fe&Mn), rare gittinsite, pyrochlore minerals (ceriopyrochlore and plumbopyrochlore) carlosbarbosaite, changbaiite, bastnaesite-(Ce), monazite-(Ce), stetindite, cerianite-(Ce), thorite, and uranothorite. These rocks were subjected to many highly superimposed hydrothermal alteration types, including propylitic, sericitic, potassic, silicification, argillic, and Fe-Mn oxy-hydroxides. The hydrothermal solutions with low temperatures and containing F 1− and CO 3 2− , PO 4 3− and H 2 O caused redistribution; transportation and redeposition of the HFSE in these rocks, in addition to the clay minerals and Kmetasomatism, were formed. The relations between the silicification index (SI = SiO 2 /(SiO 2 + Al 2 O 3) and Zr, Nb, Th, U, LREE, and HREE are positive but they become negative with the K-metasomatism.
An experimental investigation of the solubility and speciation of uranium in hydrothermal ore fluids
Experimental data on the solubility and speciation of uranium in hydrothermal solution is require... more Experimental data on the solubility and speciation of uranium in hydrothermal solution is required to improve genetic models for the formation of ore deposits, yet very few data of this type have been published. Of particular interest is the oxidation state of the uranium in solution, as conventional wisdom suggests that U is dissolved in the oxidized U(VI) state and precipitated as reduced U(IV) minerals, yet recent experiments have shown ppm-level solubility for U(IV). This study investigated the mobility of reduced U(IV) and oxidized U(VI) in acidic (pH = 2), fluoride- bearing and alkaline (pH = 10), chloride-bearing solutions at 100-200°C and 1 to 15.8 bars (0.1-1.58 MPa). Preliminary data for the mobility of U(IV) in pH 2 fluids with 0.01 m F- show concentrations of 1.76 to 3.92 ppm U at 200°C, indicating that, contrary to common belief, the reduced U(IV) can be transported in solution. We have also conducted experiments on U(VI) solubility in pH 2 fluoride-bearing, and pH 10 chloride-bearing solutions. Uranium concentrations in the F- -bearing experiments ranged from 624 to 1570 ppm (avg. 825 ppm, n = 6) at 100°C, 670 to 1560 ppm (avg. 931 ppm, n = 4) at 150°C, and 3180 to 7550 ppm (avg. 5240, n = 9) at 200°C. In comparison, U concentrations in the Cl- -bearing runs range from 86.1 to 357 ppm (avg. 185 ppm, n = 15) at 200°C. Clearly, oxidized U(VI) is very readily mobilized in hydrothermal fluids. However, the measured concentrations of U(VI) are independent of those of F- or Cl-, suggesting the formation of U oxide or hydroxide species rather than U chlorides or fluorides. These experimental data will be verified and supplemented in future experiments, which will be used to derive the stoichiometry and thermodynamic constants for the dominant uranium species in hydrothermal solutions. The data from this study will then be integrated into a comprehensive genetic model for uranium ore-forming systems.
Chemical Geology, 2018
Co-magmatic rare-element (Be, Li, Nb, Ta) granitic pegmatites associated with the Lacorne monzogr... more Co-magmatic rare-element (Be, Li, Nb, Ta) granitic pegmatites associated with the Lacorne monzogranite pluton of the Preissac-Lacorne batholith (Québec) range from a least evolved beryl-type in the pluton through a transitional beryl + spodumene-type to a most evolved spodumene-type in mafic country rocks. They possess internal lithologic fabrics and primary fluid inclusions that provide evidence for saturation of the magma with aqueous fluids immediately after the formation of aplite in the beryl pegmatite, and pene-contemporaneously with formation of the beryl + spodumene and spodumene pegmatites. The early fluids are represented by aqueous liquid-vapor (Type 1a) and aqueous liquid-vapor-solid (Type 2) inclusions in beryl from beryl and beryl + spodumene pegmatites and are estimated to have been trapped between 500 and 550 C and at 3.5 Kb. On the basis of microthermometric measurements, analyses of the compositions of the precipitates from decrepitated inclusions and the nature of the solids (trapped), these fluids are interpreted to have been NaCl-dominated (≤ 16 wt.% NaCl eq.) and to have contained appreciable Fe and dissolved CO2. In spodumene pegmatite, the equivalent fluid, which was trapped at 450 to 500 C, contained significant Mn, Li and Cs in place of Fe, consistent with corresponding trends in the chemical evolution of the host rock. Volatile-rich, mainly secondary, aqueous fluid inclusions (Type 1b) trapped in beryl are interpreted to reflect temporary sharp drops in pressure later in the crystallization history of the beryl-bearing pegmatites due to local fluid overpressures that led to brecciation and consequent pressure release. These inclusions have high salinity, are CaCl2-rich and are considered to represent magmatic hydrothermal fluids that acquired their calcium as a result of their interaction
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Papers by Anthony Williams-jones