Abstract The Bathurst Mining Camp is made up of several different tectonic blocks and slivers—the Fournier, California Lake, Tetagouche, and Sheephouse Brook blocks and the blueschist and Bamford Brook slivers. These blocks and slivers are characterized by unique Arenig-Caradoc volcanic stratigraphies, indicating they represent widely separated, ensialic to ensimatic portions of the Tetagouche-Exploits back-arc basin. Their structural juxtaposition took place during the Ashgill-Ludlow closure of the Tetagouche-Exploits back-arc basin. The Tetagouche-Exploits back-arc basin formed in response to rifting of the northwest-facing Popelogan arc, although the extension-rifting history was diachronous and involved multiple stages. The rifting responsible for the California Lake block (ca. 472–468 Ma) took place before the rifting of the Tetagouche (ca. 467–465 Ma) and Sheephouse Brook blocks (ca. 466–464 Ma). These three blocks have ensialic to transitional crust and share a similar pre-Arenig basement consisting of Miramichi Group deep-water sandstones and shales. Oceanic to transitional back-arc crust is preserved in the Fournier block and the blueschist and Bamford Brook slivers. The various blocks and slivers were sequentially incorporated into the Brunswick subduction complex during closure of the back-arc basin. Massive sulfide deposits in the Brunswick mining camp mainly occur in the California Lake, Tetagouche, and Sheephouse Brook blocks. Radiometric age dating indicates that massive sulfide deposition took place during a protracted period of ca. 12 m.y., although occurring at different intervals in each block. High heat flow due to extension and/or rifting of the Popelogan arc combined with anoxic bottom conditions in the associated basins seem to be a prerequisite for formation of the large massive sulfide deposits. The oldest known massive sulfides are hosted by early Arenig (ca. 478 Ma) dacites of the Clearwater Stream Formation of the Sheephouse Brook Group, which may represent the earliest stages of extension of the Popelogan arc. The main massive sulfide bodies in the California Lake Group are represented by the middle to upper Arenig (ca. 472–470 Ma) Caribou-type deposits, whose formation coincides with the early stages of rifting of the California Lake block from the Popelogan arc. The large, massive sulfide deposits in the Tetagouche Group (referred to as the Brunswick-type deposits) are typically hosted by, or intimately associated with, the pyroclastic and tuffaceous sedimentary rocks that occur near or at the top of the Nepisiguit Falls Formation (ca. 469–468 Ma). The Brunswick-type deposits formed during extension rather than rifting of the Tetagouche block from the Popelogan arc, because mafic volcanism does not accompany felsic volcanism in the Nepisiguit Falls Formation. Rifting-related mafic volcanism becomes abundant in the overlying Flat Landing Brook Formation (ca. 467–465 Ma), the rhyolites of which host a few small massive sulfide deposits. Some contemporaneous massive sulfide mineralization occurs also in the coeval feldspar-porphyritic rhyolites of the Sheephouse Brook Group.

Abstract The chemical signatures of the sedimentary rocks of the Bathurst Mining Camp of northern New Brunswick define a regionally consistent stratigraphy with the chemical variations reflecting the changes in provenance over time. The Cambro-Ordovician Miramichi Group metasedimentary rocks indicate a derivation from a continental source (relatively low concentrations of Cr, Ni, and V, with high Zr and Y contents). In contrast, those of the Middle Ordovician California Lake, Tetagouche, and Fournier Groups are predominantly the erosional products of obducted ultramafic rocks (relatively depleted in Nb, Ti, Y, and Zr, and enriched in Cr and Ni). However, a transitional sequence of felsic (remnant arc-derived) rocks occurs in the earliest stages of the California Lake and Tetagouche Groups (i.e., Vallée Lourdes Member of the Nepisiguit Falls Formation) prior to the establishment of the mafic provenance that typifies the majority of sedimentary rocks in these groups. Subtle chemical variations have been identified throughout the Miramichi, California Lake, and Tetagouche Groups, such as the higher Mn content of the Chain of Rocks Formation compared to the Knights Brook Formation and the higher nickel content of the Little River Formation compared to the Nepisiguit Falls and Flat Landing Brook Formations. These chemical characteristics have locally enabled the resolution of stratigraphy within allochthonous thrust panels that are devoid of petrographically distinguishable sedimentary rocks, volcanic rocks, and/or fossil locations. The changing sediment provenance closely reflects the tectonic evolution of the region. Most of the Miramichi Group sedimentary rocks are derived from the generally granodioritic Avalonian basement. However, the uppermost part of the Miramichi Group (the Patrick Brook Formation) and the earliest parts of the California Lake and Tetagouche Groups (the Charlotte Brook and Vallée Lourdes Members, respectively) are juvenile products of the eroding remnant arc. In contrast, the great majority of the California Lake and Tetagouche Groups, as well as the coeval to slightly younger Fournier Group, contain clastic sedimentary rocks derived from an ophiolitic source, with the sedimentary rocks becoming progressively more mafic as the obducted sequence is unroofed. The development of indistinguishable clastic sedimentary stratigraphies within several groups that were deposited on potentially widely separated crustal blocks within the Tetagouche-Exploits back-arc basin dictates that the sedimentary rocks were not locally derived. As such, the sedimentary stratigraphy is able to complement the volcanic stratigraphies that are unique to each block in resolving the tectonic evolution of the region. For example, the possible remnant-arc volcanic rocks of the Clearwater Stream Formation are built on the arc-derived Patrick Brook Formation. This indicates that the history of arc development and rifting is diachronous from one block to another.