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 Petrogenetic analysis of arc-related Devonian magmatic rocks in relation to the formation of magmatic hydrothermal Cu±Mo±Au deposits in the New Brunswick segment of the Northern Appalachians(University of New Brunswick, 2024-10) Yousefi, Fazilat; Lentz, David R.; McFarlane, Christopher R. M.Devonian adakitic porphyritic intrusive rocks in New Brunswick (NB) are associated with porphyry Cu-Mo-Au mineralization and are similar to Cu-Mo-Au porphyries in Québec and Maine, implying a shared genesis. These granitoids are similar petrologically and feature oxidized I-type arc-like compositions with SiO2 ≥66.5 wt.% and Al2O3 >15.5 wt.%, among other distinctive geochemical characteristics. Trace element compositions characterize the link between adakite formation, slab failure, and porphyry Cu-Mo-Au system potential. These rocks are enriched in Cs, Rb, and Ba, but depleted in Nb, Ta, P, and Ti, reflecting subduction-related magmatism. The slab breakoff process involves the breaking of part of the subducted oceanic plate, leading to asthenosphere upwelling and selective partial melting of the slab, the suprasubduction zone lithospheric mantle, the upwelling mantle, and the basal continental crust; transpressional to transtensional tectonics can facilitate magma ascent and emplacement in the post-subduction setting. Zircon, because of its refractory nature and prevalence in igneous rocks, is useful for assessment of magmatic evolution, specifically its oxygen and U-Th-Pb isotopic compositions. This information can be used to predict magmatic fertility in terms of Cu ± Mo ± Au porphyry mineralization. LA-ICP-MS analyses of zircons from the adakitic intrusions investigated reveal diverse compositions, reflecting varied magmatic conditions. The Zr/Hf and Ce/Ce* values provide insights into porphyry fertility, aiding mineralization potential assessment. This study also employs petrography, µXRF-EDS mapping, and LA-ICP-MS to analyze titanite compositions in these oxidized I-type granitoids. Titanite is enriched in high field strength elements (Ta, Zr, Hf, Th, U), rare earth elements, and Sr and can serve as a petrogenetic and metallogenic indicator. Zr-in-titanite thermometry reveals varied crystallization temperatures (784° to 1098°C) among the intrusions investigated. Magnetite phenocrysts in these intrusions have euhedral to subhedral morphology and lack oscillatory zoning (according to SEM-BSE imaging). The diverse trace element compositions offer insight into the magmatic to magmatic-hydrothermal systems. EPMA analysis reveals variable concentrations of SiO2, Al2O3, MgO, Mn, Fe, Ti, Cr, and V in magnetite, with distinguishing features for various deposit systems. When comparing Ti+V with Al+Mn concentrations in magnetite crystals, all samples exhibit similar crystallization temperatures (>500ºC).Item Petrogenetic evaluation of the Cape Spencer gold deposit system, southern New Brunswick, Canada(University of New Brunswick, 2024-06) Cardenas Vera, Alan Fernando; Lentz, David R.The Cape Spencer gold deposit, southeast of Saint John, New Brunswick, presents features and characteristics of orogenic gold deposits with gold mineralization and associated alteration concentrated along strongly faulted and sheared contacts between the deformed lithologies in the Cape Spencer area. Although the fundamental controls of the late faults and thrust in the region are known, further constraints on the metals’ source, fluid channels, and timing of ore deposition were necessary to better understand the distribution of gold mineralization and the link with the development of the northern Appalachians and its related tectonic activity. U-Pb geochronology of monazite from leucocratic dykes that crosscut the various deformation fabrics associated with the gold mineralization provided an upper constraint age of 273.7 ± 1.3 Ma to ore deposition. Further study of these dykes indicated they were the result of partial melting of a crustal source with assimilation of Meguma metasedimentary rocks and/or Avalonian sedimentary rocks, based on their Nd-Hf isotopic signatures and whole-rock geochemistry composition. In situ 40Ar/39Ar and Rb-Sr geochronology was performed on illites linked to the alteration associated with the gold mineralization, and the geochronology results indicated different illite populations resulting from continuous recrystallization events occurring below the closure temperature for illite. Therefore, an age around ~300 Ma seems reasonable as a main illite crystallization event that further constrains the illitic alteration associated with the gold mineralization to ~ 300 – 318 Ma, when considering the age of the Lancaster Formation, the youngest unit affected by the hydrothermal fluid. Three generations of hydrothermal pyrite (Py1, Py2, and Py3) showing distinct textural, mineral paragenetic characteristics, and elemental compositions were identified in the ore bodies. In situ S and bulk pyrite Pb isotope analyses indicated the involvement of both Avalonian and Meguma intrusive and metasedimentary rocks as sources for the hydrothermal fluids and metals in the Cape Spencer gold deposit. The evolution of the ore-forming fluids is characterized by a decrease of δ34S values from the first pyrite generation (Py1) towards the last identified pyrite generation (Py3) that result from wall-rock sulphidation and phase separation as the main gold precipitation mechanisms.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