Browsing by Author "Lentz, David R."
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Item Examination of mesothermal to epithermal orogenic- to intrusion-related Sb-bearing gold systems in a southern New Brunswick segment of the Northern Appalachians(University of New Brunswick, 2022-04) Heidarian, Hassan; Lentz, David R.Several Sb-Au mineralization styles are diversely scattered within the boundary of Gondwana and Laurasia in southern New Brunswick. Some research has been completed regarding the timing and genesis of the structurally-controlled, mesothermal to epithermal orogenic and intrusion-related Sb-Au mineralization types in the regionally correlative Annidale (New River and Annidale belts) and Clarence Stream areas (St. Croix and Mascarene belts). LA-ICP-MS U-Pb and 40Ar-39Ar geochronology of hydrothermal rutile and white mica in the Annidale area suggested that orogenic gold type mineralization is related to Ordovician Penobscot orogeny. However, several further orogenies overprinted some mineralization in the area. The apatite and titanite U-Pb and white mica 40Ar39Ar data confirmed the Early Devonian age for intrusion-related gold type in the Clarence Stream area. Zircon U-Pb data on several mafic to felsic intrusive rocks showed the age range of Silurian to Late Devonian; however, the relation of the Early Devonian intrusions (Magaguadavic and Lower Tower Hill granites) to the gold mineralization has been reaffirmed. The sulphur isotope data suggests a mantlederived source for sulphide phases. The lead isotope results show highly radiogenic Pb, which might be due to the addition of Pb during or after ore formation, that overprinted the initial Pb isotopic system. As no later major magmatic activities occurred, Ordovician orogenic gold was preserved in the Annidale area. It is probable that similar orogenic gold mineralization was formed at the same time in the southwestern part of the New River Belt (Clarence Stream area). A combination of several factors, including preexisting orogenic gold deposits, advanced hydrothermal activities related to the emplacement of multi-phase intrusions during Devonian, and the presence of local brittle-ductile shear zones, were crucial, explaining the greater concentration of gold in intrusion-related deposits in the Clarence Stream area than the orogenic gold deposits in the Annidale area.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 metamorphism