Petrochemical discrimination of evolved granitic intrusions associated with Mount Pleasant deposits, New Brunswick, Canada

Abstract

The Mount Pleasant Sn-W-Mo-Bi-In base metal deposits that are spatially and temporarily related to multiple, Late Devonian granitic intrusions are located in southern New Brunswick, Canada. Regional rocks include a sequence of Ordovician-Silurian detrital rocks, with minor interbedded volcanic rocks, which were deformed in the Devonian Acadian orogeny. The Mount Pleasant subvolcanic-eruptive complex underlies part of a 17612 km caldera which constitutes a sequence of Upper Devonian volcanic and sedimentary rocks, intruded by subvolcanicplutonic rocks (e.g. the Mount Pleasant intrusions). Brittle deformation affected the rocks within parts of the caldera.At the Mount Pleasant, along the southwestern margin of this caldera, two mineralised zones, termed the Fire Tower Zone and the North Zone, occur within volcanic necks about 1 km apart. In both zones, multiple, successive Late Devonian granitic intrusions were emplaced into interbedded rhyolitic tuffs/sedimentary breccias overlain by rhyodacitic lavas. The volcanic necks are defined by magmatic-hydrothermal breccias. In the Fire Tower Zone, fine grained granite, granite porphyry and porphyritic granite were emplaced successively. The first is associated with porphyry type W-Mo-Bi-In mineralisation. Three successive generations of granitic intrusions (known as granites I, II and III) also occur in the North Zone. Here, similar but less expressive mineralisation occurs in granite I whereas the others are associated with several significant tin deposits.In both zones, the granitic rocks are pale, porphyritic, generally fine grained, biotitic, contain micrographic intergrowths of K-feldspar and quartz in K-feldspar phenocrysts, and are modally of alkaline-feldspar type. The granitic intrusions may be classified as crustal A-type, with intraplate, high heat production and peraluminous characteristics that are typical of a continental rift environment. Petrographic and geochemical evidence suggests that they formed under conditions of fluid saturation and undercooling. Incompatible and immobile trace element and elemental ratio data indicate that they are highly evolved tin bearing granites with a higher tin potential in the North Zone than in the Fire Tower Zone. There is no solid evidence for petrochemical equivalence between individual granites from these two zones.The endogranitic tin zone is an irregular, almost tabular, 400 m long body enclosed in granite II. The form and petrographic, mineralogical and chemical evidence as well as metal zoning show that the endogranitic tin zone is hosted in a distinct phase of granite, termed the endogranitic tin zone granite. Based on chemical data from thirty North Zone granite samples, but including only one sample from the endogranitic tin zone granite, incompatible (and immobile) trace element evidence indicates that granite III is more evolved and has a higher tin potential than granite II, and only suggests that the highest potential for tin may be found in a probable late differentiate of granite III, the endogranitic ti...

Mineralogical and geochemical characteristics of scheelite-bearing skarns, and genetic relations between skarn mineralization and petrogenesis of the associated granitoid pluton at Sargipali, Sundergarh District, Eastern India

“…5c, d, e and f). These discrimination plots not only suggest their tectonic setting, but also their protolith, melting, and crystallization histories (Christiansen and Keith, 1996;Inverno and Hutchison, 2006). This type of plot suggests continental collision or syncollisional granitoids (Pearce et al, 1984;Pearce, 1996), which is consistent with both geological and tectonic observations.…”

Re-Os geochronological constraints on the mineralizing events within the Mount Pleasant Caldera: implications for the timing of sub-volcanic magmatism

“…The precise age of the tin-zinc mineralization at Mount Pleasant, which is associated with Granite II and possibly with Granite III (Inverno and Hutchinson 2006), remains to be determined. A sample of Granite III was submitted to the Geological Survey of Canada's geochronology laboratory for dating; however, the sample did not yield any zircon.…”

“…Ruitenberg (1967), McCutcheon (1990), andMcCutcheon et al (1997) considered this pre-mineralization feldspar porphyry to be intrusive and contiguous with the southern pluton of the McDougall Brook microgranite (equivalent to the latite granophyre of Harris (1964)). On the other hand Sinclair et al (1988Sinclair et al ( , 2006 and Inverno and Hutchinson (2006) suggested that the feldspar porphyry is a massive lava flow based on its sub-horizontal contact with the Little Mount Pleasant tuff. Dagger (1972) described the presence of two types of mineralization at Mount Pleasant: tungsten-molybdenum concentrated in the Fire Tower Zone and tin-zinc concentrated in the North Zone.…”

Geochemical characteristics of biotite from felsic intrusive rocks around the Sisson Brook W–Mo–Cu deposit, west-central New Brunswick: An indicator of halogen and oxygen fugacity of magmatic systems

“…412 Ma, U-Pb zircon, McLeod et al, 2003) deposits, as they are genetically linked to magmatic hydrothermal fluids exsolved from felsic batholiths and plutons formed during the Acadian Orogeny. These granitoids are metaluminous to peraluminous and have transitional I-type to A-type granite signatures, which are enriched in incompatible elements and are generally evolved (> 65% SiO 2 , Kooiman et al, 1986;MacLellan and Taylor, 1989;Yang et al, 2002;Inverno and Hutchinson, 2006). Enrichment of these metallic elements may have resulted from a combination of crystal fractionation followed by aqueous phase saturation and separation, suggested by field and petrographic evidence including the presence of miarolitic cavities and myrmekite (Tucker et al, 1998;McLeod et al, 2003;Yang et al, 2008).…”