Browsing by Author "McFarlane, Christopher R.M."
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Item Petrogenesis, emplacement setting, and magmatic-hydrothermal mineralization of the peralkaline Flowers River Igneous Suite, Hopedale Block, Labrador(University of New Brunswick, 2020) Ducharme, Taylor A.; Van Rooyen, Deanne; McFarlane, Christopher R.M.The peralkaline Flowers River Igneous Suite intrudes the southernmost region of the Mesoproterozoic Nain Plutonic Suite composite batholith in north-central Labrador. The Flowers River complex comprises a voluminous series of peralkaline granite ring intrusions and their coeval volcanic assemblage, the latter of which has been identified as a target for rare metal exploration. Peralkaline igneous complexes throughout Labrador show a ubiquitous spatial association with earlier anorthosite-mangerite-charnockite-granite (AMCG)-affinity plutonism, suggesting the geodynamic conditions responsible for generating the latter may have systematically conditioned those sites to subsequently produce highly evolved, incompatible element-enriched magmas. Laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS) U-Pb zircon geochronology is used to define a high-resolution magmatic and hydrothermal timeline for the Flowers River complex and its host suites. The Flowers River Granite intruded the local Nain Plutonic Suite rocks after ca. 8 Myr of quiescence, though trace element compositions indicate these rocks share a common, incompatible element-enriched source. Protracted fractionation of the liquids derived from this source gave rise to two contrasting styles of magmatic-hydrothermal (Zr-Nb-Y-)REE mineralization, both hosted by the cogenetic volcanic rocks overlying the plutonic complex.Item Petrological and metallogenic studies of the Nashwaak granite and felsic dykes associated with the Sisson Book W-Mo-(Cu) deposit, west-central New Brunswick, Canada(University of New Brunswick, 2015) Zhang, Wei; Lentz, David; McFarlane, Christopher R.M.The Sisson Brook W-Mo-Cu deposit was formed by hydrothermal fluids likely related to the Nashwaak Granites and related felsic dykes. These granites consist of two pluton subfacies: muscovite-biotite granite (Group I) and biotite granite (Group II), and dykes with various textures (aplitic to pegmatoidal dykes, Group III; and a porphyry dyke, Group IV). This deposit formed at 376.45 ± 1.64 Ma to 378.54 ± 1.71 Ma (Re-Os molybdenite) that is older than the porphyry dyke (364.5 ± 1.3 Ma, earlier U-Pb zircon age), but younger than the volumetrically dominant medium- to coarse-grained biotite granitic dykes (405.6 ± 2.5 Ma, U-Pb zircon age), as well as the Nashwaak granitic plutons. The syn-hydrothermal dykes could be the other dykes with different textures in Group III, if they are not contemporary, or possibly related to a deeply buried large granitic pluton has not been intersected by drilling thus far. The Nashwaak Granite and related dykes are highly siliceous (SiO2 > 69 wt. %), peraluminous, calc-alkaline, and magnesian I-type granites. They formed in a volcanic arc type setting and are characterized by depletion of HFSE and enrichment of LILE. Oxygen isotope data (9.3 - 12.3 ‰), (87Sr/86Sr)i (0.702 - 0.710), and ɛNd(t) (-4.51 to -1.42) of the whole rock, and in situ δ18O analyses of magmatic zircons (4.9 - 9.9 ‰) and quartz show the granitic magmas are probably derived from bulk assimilation of Mesoproterozoic Gondwanan basement ± the overlying Gander Zone sedimentary prism, by mantle-derived melts. The magmas of the Nashwaak Granite and related dykes formed at temperatures below 800°C (TZr) with the aid of water-rich fluid infiltration. These magmas with a initial water content of 5-6 wt.% increased upwards until they intersect the watersaturated granite solidus at pressures lower than 2.5 to 3.0 kbar. Assimilation and fractional crystallization is the mechanism that controlled magma evolution. Trace element contents in quartz and biotite are not correlated with that of the whole rock, but the K/Rb of biotite decrease, and Al/Ti and Ge/Ti of quartz increase with differentiation of the magmas and show that the Group III is the most evolved. Oxygen fugacity of these magmas is close to the nickel-nickel oxide buffers, thus they are oxidized I-type magmas, and only the two-mica granite is reduced due to later, strongly supracrustal, contamination (ASI > 1.1, δ18OZr > 8‰). Halogen fugacity study shows that the Group I suite have higher F relative to Cl, with other groups having higher H2O and Cl activity than F, indicative of build-up of chlorine and water in the evolving magma. These high HCl/HF and H2O/HF ratios are suggested as tungsten mineralization vectors and only the dyke phases have similar HCl/HF ratios to that of granites typically associated with Sn-Wo-Bi deposits. Comparing the geochemical characteristics of all the Nashwaak Granites and associated dykes with the granites related to the W-Mo deposits, the biotite granitic dykes are the “best” candidates for the W-Mo deposit mineralization, since they are the most differentiated, oxidized, and relatively ‘wet’ type of magma (compared to magmas of porphyry Cu, < 4 H2O wt.%), and with a similar halogen fugacity. Further geochronology studies are needed in order to better identify the syn-mineralization intrusions.Item Recognizing and quantifying metamorphosed alteration zones through amphibolite facies metamorphic overprint at the Key Anacon Zn-Pb-Cu-Ag deposits, Bathurst Mining Camp, New Brunswick, Canada(Elsevier, June 2016) Zulu, Joseph D.S.; Lentz, David R.; Walker, James A.; McFarlane, Christopher R.M.The Key Anacon deposits, Bathurst Mining Camp, New Brunswick, are hosted in upper greenschist- to amphibolite-facies felsic volcanic rocks. The occurrence of cordierite-biotite and garnet-biotite-muscovite assemblages parallel to the regional tectonic fabric in the metamorphosed hydrothermal alteration zones point to a pre-metamorphic mineralization event that was synchronous with sub-aqueous volcanism. A combination of textural, mineralogical, lithogeochemical alteration indices and vectors, molar element ratios, and P-T diagrams have been used to recognize the effects of medium-grade metamorphism and establish the mass compositional changes associated with pre-metamorphic hydrothermal alteration. Modelling the altered felsic volcanic rocks in a K2O-Fe2O3-MgO-Al2O3-SiO2-H2O-TiO2 (KFMASHT) system and comparing the observed peak metamorphic assemblages with those produced in a petrogenetic grid allows us to interpret the style of pre-metamorphic hydrothermal alteration related to deposit formation. The compositional change in the stratigraphic footwall (structural hanging wall) is characterized by mass gains of 0.1 to 4.0 wt. % Fe2O3 (Total), 0.7 to 22.2 wt. % MgO, and 0.5 to 55.2 wt. % CaO, and mass losses of 25.1 to 56.7 wt. % SiO2, 0.2 to 2.0 wt. % Na2O, and 0.3 to 3.8 wt. % K2O. Variable gains and losses of Zn, Pb, and Cu are characteristic of the footwall alteration zones with Zn displaying gains proximal to the sulfide lens, and losses distal to the massive sulfide lens. The alteration indices (AI) values increase as the massive sulfide lens is approached from either the footwall or hanging wall, whereas the Ghandi index (GI) discriminates the intensely chlorite-altered rocks proximal to mineralization from the sericitic altered rock in more distal areas. Overall, there is an increase of the GI from the weakly to moderately altered zone (GI =1.3 to 6.0) to the more intensely altered zone (GI= 6.1 and 60). Although the Chlorite-Carbonate-Pyrite index (CCPI) is similar to the GI, it is preferable to adopt the more robust GI, because it is a ratio of the added chemical components (Fe2O3 (Total) +MgO) to those lost from the system (Na2O+K2O) during the most intense hydrothermal alteration. These physical and geochemical observations are consistent with early feldspar-destructive alteration followed by chloritization proximal to the sulfide lens and accompanied by sericitization alteration distal prior to sulfidation and oxidation during prograde metamorphismItem Volatile-element signatures of volcanogenic massive sulfide deposits in the Bathurst mining camp, New Brunswick, Canada(University of New Brunswick, 2017) Soltani Dehnavi, Azam; Lentz, David; McFarlane, Christopher R.M.Presented here is a comprehensive study of volatile-element signatures from massive sulfide deposits of the Bathurst Mining Camp (BMC), Canada. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) methods were developed and applied to measure As, Bi, Cd, Hg, In, Ga, Ge, Sb, Se, Sn, Te, and Tl in sulfides (pyrite, sphalerite, galena, chalcopyrite, pyrrhotite, arsenopyrite, and tetrahedrite/tennantite) and phyllosilicates (white mica, chlorite, and biotite). In addition, LA-ICP-MS analyses yielded concentrations of unpublished volatile elements in standards including Hg = 0.46 ppm and Te = 296 ppm in NIST610 (n = 245), Tl = 69 ppm in MASS-1 (n = 232), and Hg = 4.57 ppm and Te = 233 ppm in GSE-1G (n = 33). Pyrite from the BMC displays extensive textural arrays, which are categorized in two main types of pre-deformation and deformation textures. Texturally-distinct pyrite assists fabricating the evolutionary history of pyrite and consequently the massive sulfide deposits of the BMC. Most forms of pyrite from the BMC are arsenian, containing up to 7.3 wt. % As, as well as significant abundances of Tl, Sb, Sn, Bi, Ag, and Se. The examined sulfide minerals accommodate volatile elements to different extents. The integrated LA-ICP-MS data of all sulfides provide a means of differentiating the hydrothermal sulfide facies. Comparison the volatile-element budget of the examined minerals within host rocks demonstrates that white mica represents the most highly concentrated source of Tl, Sn, Hg, In, as well as Ba. On the other hand, sulfide minerals host the main concentration of Bi, As, Sb, Se, Cd, Pb, Ni, Cu, and Co. Chlorite, and to a lesser degree white mica, is distinctly enriched in Zn, relative to sulfide minerals (except sphalerite) of the host rocks. The abundances and compositional variation of sulfides, in particular, pyrite, chlorite, and white mica in the host rocks of the known VMS deposits investigated in the present study offer potential micro-chemical vectoring tools. The elevated concentration of volatile elements in sulfide minerals, in particular pyrite, and chlorite and white mica, occurred proximal to ore horizons as well as the subtle occurrence of volatile elements in white mica and pyrite distal to ore horizon present the potential footprint of buried sulfides.