Massive sulfide deposits of Zn-Pb-Cu-Ag type in the Bathurst Mining Camp, New Brunswick, are hosted within a Middle Ordovician bimodal volcanic and sedimentary sequence that has undergone complex polyphase deformation and associated regional metamorphism to the lower-to upper-greenschist grade. These factors are partly responsible for the present geometry and textural modification of these hydrothermal deposits, originally formed on the seafloor. Despite the importance of heterogeneous ductile deformation, some primary features are evident, in particular fine-grained colloform pyrite and base-and preciousmetal zonation within many of these deposits. The average Au content (bulk instrumental neutron-activation analyses; n = 215) of massive sulfides from 43 deposits in the Bathurst Mining Camp is 0.85 ppm, with values as high as 6.86 ppm. Positive correlations of Au content with Ag (r' = 0.53), As (r' = 0.57) and Sb = (r' = 0.65) suggest that Au is mainly associated with arsenian pyrite and a distal suite of elements (Au + Sb + As ± Ag). The submicroscopic Au contents of pyrite and arsenopyrite in eight deposits with elevated bulk Au contents were investigated using a Cameca IMS-4f secondary-ion mass spectrometer. Results suggest that arsenian pyrite is the most important host for Au in massive sulfides of the Bathurst Mining Camp, with an average Au content of 9.1 ppm, and values reaching 42.9 ppm. Arsenopyrite was found to contain much less Au, with an average of 2.7 ppm. Recrystallization of sulfides during greenschist-facies metamorphism has resulted in pyrite morphologies with variable Au contents. Invisible Au was in part released and adsorbed as submicroscopic inclusions on As-rich surfaces of pyrite and on arsenopyrite.
Mid‐Ocean Ridges host various types of hydrothermal systems including high‐T black‐smokers found in ultramafic rocks exhumed along slow spreading ridges. These systems are mostly described in two dimensions as their exposure on the present‐day seafloor lacks the vertical dimension. One way to understand these systems at depth is to study their fossilized equivalents preserved on‐land. Such observation can be done in the Platta nappe, Switzerland, where a Jurassic‐aged mineralized system is exposed in 3D. Serpentinites host a Cu‐Fe‐Ni‐Co‐Zn‐rich mineralization made of sulphides, magnetite and Fe‐Ca‐silicates either replacing serpentinites or within stockwork. Fe‐Ca‐silicates, abundant at the deepest levels, vanish in the mineralization close to the palaeo‐detachment. Fluids were channelized along mafic dykes and sills acting as preferential drains. Warm carbonation (~130°C) is the latest hydrothermal record. We propose that this system is an analog to the root zone of present‐day serpentinite‐hosted hydrothermal systems such as those found along the Mid‐Atlantic Ridge.
The Late Silurian Landry Brook and Dickie Brook plutons and Charlo plutonic suite underlie a combined area of approximately 80 km 2 in the northeastern part of the Ganderian Tobique-Chaleur tectonostratigraphic belt in northern New Brunswick. The Landry Brook pluton is divided into three units: gabbro to quartz diorite, quartz monzodiorite to monzogranite, and monzogranite. A sample from the quartz monzodiorite unit yielded a U-Pb (zircon) crystallization age of 419.63 ± 0.23 Ma. A granodioritic stock located near the Landry Brook pluton has yielded an age of 400.7 ± 0.4 Ma, indicating that it is a younger unrelated body, herein referred to as the Blue Mountain Granodiorite (new name). The Dickie Brook pluton also consists of three units: leucogabbro to quartz gabbro, diorite to quartz diorite and quartz monzodiorite to monzogranite. Two samples from the monzogranite unit yielded U-Pb (zircon) crystallization ages of 418 ± 1 Ma and 418.1 ± 1.3 Ma. The Charlo plutonic suite is a group of small plutons and dykes, located west of the Dickie Brook and Landry Brook plutons and consists mainly of diabase, quartz monzonite to monzogranite, rhyolite porphyry, and dacite porphyry. Chemical trends indicate that the quartz monzodiorite to monzogranite unit of the Landry Brook pluton, all of the units of the Dickie Brook pluton, and the quartz monzodiorite to monzogranite unit of the Charlo plutonic suite, as well as the volcanic host rocks of the Bryant Point and Benjamin formations, are co-magmatic. They formed following slab break-off and extension in the waning stages of the Salinic orogeny, which resulted from the collision of Ganderia and Laurentia. In contrast, the dacite porphyry of the Charlo plutonic suite may be cogenetic with the younger Blue Mountain Granodiorite and related to the collision of Avalonia with Laurentia. ABStRACt RÉSUMÉLes plutons des ruisseaux Landry et Dickie et le cortège plutonique de Charlo, du Silurien tardif, recouvrent une superficie totale d' environ 80 km 2 dans la partie nord-est du domaine tectonostratigraphique gandérien Tobique-Chaleur, dans le nord du Nouveau-Brunswick. Le pluton du ruisseau Landry se compose de trois unités : du gabbro à de la diorite quartzique, de la monzodiorite quartzique au monzogranite, et du monzogranite. Un échantillon de l'unité de monzodiorite quartzique a produit un âge de cristallisation de 419,63 ± 0,23 Ma par la méthode de datation U-Pb (sur zircon). Un bloc de granodiorite à proximité du pluton du ruisseau Landry a produit un âge de 400,7 ± 0,4 Ma, ce qui indiquerait qu'il s'agit d'un corps de formation plus récente et non relié, désigné ici comme la granodiorite de Blue Mountain (nouveau nom). Le pluton du ruisseau Dickie comprend lui aussi trois unités : du leucogabbro à du gabbro quartzique, de la diorite à de la diorite quartzique, et de la monzodiorite Fig. 9. Chemical affinity diagrams for samples from Blue Mountain Granodiorite, landry Brook and Dickie Brook plutons, and Charlo plutonic suite. (a) AFM diagram. (b) Molar Al 2 o 3 /(Cao+Na 2 o+K...
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