Journal Articles

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https://unbscholar.lib.unb.ca/handle/1882/12771

Articles. Typically the realization of research papers reporting original research findings published in a journal issue. (URI: http://purl.org/coar/resource_type/c_6501) Item types include:

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Browsing Journal Articles by Subject "Earth Sciences"

Now showing 1 - 3 of 3
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    Phyllosilicates geochemistry and distribution in the Altar porphyry Cu-(Au) deposit, Andes Cordillera of San Juan, Argentina:: Applications in exploration, geothermometry, and geometallurgy
    (Elsevier, August 2016) Maydagán, Laura; Franchini, Marta; Impiccini, Agnes; Lentz, David
    Biotite, chlorite, muscovite, illite, and kaolinite from the Altar porphyry Cu-(Au) deposit of the Andean Main Cordillera of San Juan Province (Argentina) were constrained using X-ray diffraction, electron microprobe, and infrared spectroscopy analyses to map compositional variations. Magmatic and hydrothermal biotites from the andesite-dacite mineralized porphyries have higher XMg, K, and F contents and lower Fe/(Fe+Mg) ratios compared to the magmatic biotites from the andesite-dacite barren porphyries of the district Hydrothermal biotites from deep levels with potassic alteration and high Cu grades have the highest XMg ratios and high F contents. The similarity of the log fH2O/fHF, log fHF/fHCl, and log fH2O/fHCl fugacity ratios of biotites from Altar mineralized porphyries and from the neighbouring Los Pelambres porphyry copper deposit suggests that these parameters may be a function of the magmatic source. Chlorite crystals associated with Cu mineralization (0.2 to 1.2 % Cu) show lower Fe and Mn and higher Mg contents than chlorite from shallow and distal zones. Potassic dioctahedral phyllosilicates are the most abundant phyllosilicates in the Altar deposit, occur in the phyllic and chloritic zones, and are superimposed on potassic alteration. In zones of high copper grades (> 0.8% Cu), potassic dioctahedral phyllosilicates have total Al (apfu) between 2.4 and 2.8 and intermediate compositions between muscovite, phengitic muscovite, and illite, whereas those with higher and lower Al contents come from zones with lower Cu grades. Temperatures obtained from XMg-Ti equilibria in biotite (691-800°C) and IVAl occupancy in chlorite (214-340C), agree with previous temperature estimates based on Ti in quartz and fluid inclusion microthermometry. Muscovite is stable at temperatures higher than ~300°C, whereas phengitic muscovite indicates temperatures between 280 and 400°C and higher K+/H+ conditions (less acidic enviroment) compared to muscovite. Illite represents a younger and cooler (220 to 310°C). Our study demonstrates that variations in phyllosilicate composition have the potential to be used as vectors in ore exploration and to differentiate between barren and fertile intrusions. A detailed analysis of type and proportion of phyllosilicates, as well as the presence of ore minerals in fine fractions, should be undertaken to optimize metal recoveries during the upcoming benefaction of these ores.
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    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 metamorphism
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    The Nucleus deposit: superposed Au-Ag-Bi-Cu mineralization systems at Freegold Mountain, Yukon, Canada with constraint from titanite U-Pb dating
    Betsi, Thierry Bineli; Lentz, David, R.; McFarlane, Chris
    In this paper we present titanite U-Pb (both single crystal CA ID-TIMS and in situ LA ICP-MS) data, coupled with ore and gangue mineralogy and geochemical (both lithogeochemistry and microanalysis) data from the Nucleus Au-Ag-Bi-Cu deposit, in the Yukon (Canada) portion of the Tintina Au province. Arsenic-bearing Au-Ag-Bi-Cu mineralization at Nucleus consists of two distinct styles of mineralization including: (i) reduced Au skarn and sulfide replacement; and (ii) a relatively shallow-emplaced (as supported by textures and temperature of formation), vein- controlled mineralization occurring mainly as veins and veinlets of various shapes (sheeted, single, stockworks, and crustiform), breccias, and disseminated. Whereas Au, Bi, and Cu mineralization from skarn is associated with hydrous retrograde alteration phases (actinolite, ferro-actinolite, hastingsite, cannilloite, and hornblende), numerous alteration types are associated with the vein-controlled style of mineralization and these include: potassic (biotitization), phyllic, argillic, propylitic, carbonate, and quartz (silicification) alterations. The mineralization-alteration processes took place over a wide temperature range that is bracketed between 340-568 °C, as indicated by chlorite and arsenopyrite geothermometers. The Au-rich Nucleus deposit is characterized by anomalously high content of As and Bi (as much as 1 %), and whereas Au moderately correlates with Bi (r = 0.40) in the skarn mineralization style (where native Au is spatially associated with native Bi and Bi-bearing sulfides), the two elements poorly correlate (r = 0.14) in the vein-controlled type, in which native Bi- and Bi-sulfide-bearing veins are locally observed. Sphalerite from the vein-controlled mineralized type is Fe-rich (9.92-10.54 mol % FeS), indicative of low sulfidation conditions, as well as high temperature, with the latter further supported by arsenopyrite geothermometry (up to 491 °C), low Ag content (3-7 wt %) in Au, and the high gold fineness (926-964). Whereas molybdenite Re-Os ages from quartz-molybdenite veins range from 75.8 to 76.2 ± 0.3 Ma, titanite from the skarn type mineralization recorded CA ID-TIMS and LA ICP-MS U-Pb ages of 182.6 ± 2.4 Ma and 191.0 ± 1.5 Ma, respectively, thus precluding any genetic link between the two spatially associated styles of mineralization from the Nucleus deposit area. The Au-Ag-Bi-Cu Nucleus deposit is therefore regarded as a superposed system in which two mineralization types, without any petrogenetic relationship, overlapped, possibly with remobilization of early formed mineralization.