Abstract T he M ining and mineral processing industry is important to the Canadian economy and in 2001 contributed $35.1 billion, or 3.7 percent, to the Gross Domestic Product and employed approximately 376,000 Canadians (Minerals and Metals Sector, Natural Resources Canada). However, over the past decade, Canada’s base metal reserves have declined by more than 25 percent, and significant new discoveries will be required if Canada’s role as a major base metal producer is to be maintained into the twenty-first century. The Bathurst Mining Camp is one of Canada’s most important base metal mining districts, accounting in 2001 for 30 percent of Canada’s production of Zn, 53 percent of Pb, and 17 percent of Ag. In 1999, the Bathurst Mining Camp accounted for 32 percent of the Zn, 80 percent of the Pb, and 25 percent of the Ag reserves (Minerals and Metals Sector, Natural Resources Canada). The value of production from the Bathurst Mining Camp in 2001 exceeded $500 million and accounted for 70 percent of total mineral production in New Brunswick. Approximately 2,000 people are directly employed by the mining industry in the Bathurst Mining Camp. Without the discovery of new ore reserves, however, production will decline and will cease within about 10 yr at current production rates, and with it the principal source of economic activity in northeastern New Brunswick will also disappear. To address the major decline of mineral resources in Canada’s economically important mining districts, EXTECH (Exploration and Technology) projects were established by the Geological Survey of Canada.

Abstract The Bathurst Mining Camp has a long history of discovery and mineral development with the first volcanogenic massive sulfides (VMS) being discovered and drilled at Orvan Brook in 1938. However, the camp did not gain national and international prominence until the discovery of the Brunswick Mining and Smelting 6 deposit was announced in 1953. After that, the Bathurst Mining Camp saw a number of important VMS “firsts” in North America; namely, the first deposits to be described in terms of a syngenetic sea-floor model, the first discovery by airborne electromagnetic surveying, the first discovery by stream-silt geochemistry, the first routine application of gravity surveys to screen ground electromagnetic anomalies, the first (in Canada) heap- and vat-leach operations to recover gold from gossans, and the first major mining camp to be described in terms of ensialic, back-arc–basin-depositional and subduction-related accretionay models. To date, a total of 141 massive sulfide occurrences, including 45 deposits, have been discovered in the Bathurst Mining Camp, a subcircular area approximately 60 km in diameter. About half of the discoveries were made in the 1950s and resulted from the use of geophysics, although geochemistry and prospecting were responsible for many. Later discoveries in the camp can be attributed to improved technology and a better understanding of the stratigraphy and structure. Production to the end of 1998 was over 130 million metric tons (Mt) from 12 deposits. The total massive sulfide resources, including production, from the known deposits in the Bathurst Mining Camp are estimated to be over 500 Mt. The geologic picture of the Bathurst Mining Camp has evolved dramatically since the first massive sulfide discovery. During the early 1950s, the epigenetic period, the geology of the camp was virtually unknown but by the end of the decade five informal units were recognized in the Ordovician Tetagouche Group. The sulfide deposits were considered to be replacement bodies genetically related to Devonian granites. By the 1960s, the syngenetic period, the picture was much the same although the Tetagouche Group was being interpreted in terms of geosynclinal theory and the sulfides were considered to be a facies of iron-formation. By the 1970s, the Kuroko period, plate tectonic theory had been applied to the Bathurst Mining Camp and it was being interpreted as an ensialic arc-related to easterly subduction. The stratigraphic framework of the Tetagouche Group, though informal, and significance of the polydeformational structures were more fully appreciated, and the sulfide deposits were considered to be genetically linked to convective circulation of seawater in proximity to calc-alkaline rhyolite domes. During the 1980s, the VMS period, the geologic picture of the Bathurst Mining Camp started to change because of new mapping and lithogeochemical studies. The Tetagouche Group was interpreted to have formed in an ensialic back-arc rift, with much of its structural complexity related to its amalgamation in an accretionary wedge above a westerly dipping subduction zone. The sulfides were considered to be exhalative, deposited in mounds or brine pools, and to have formed from convective circulation of seawater around subvolcanic intrusions. The deposits were divided into two groups with proximal and distal types in each. In the 1990s, the EXTECH period, the Tetagouche Group was redefined and formally subdivided, largely based on lithogeochemistry and geochronology. Many rocks previously included in this group were reassigned to new groups including the California Lake, Fournier, Miramichi, and Sheephouse Brook Groups. The new data and interpretations resulting from the EXTECH project are described in the papers that follow in this volume.

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 A new geologic map of the Bathurst Mining Camp was produced by integrating outcrop data with a large rock geochemical database, geochronology, and high resolution, multiparameter airborne geophysical data. These datasets were manipulated with geographic information systems (GIS) that enabled compiled point data, such as a whole-rock geochemical analyses and field observations for individual outcrops, to be spatially linked with the various geophysical images. The resulting new map outlines the regional distribution of six different complexly deformed, crustal blocks and slivers, each comprising a unique volcanic stratigraphy and associated massive sulfide deposits. The blocks and slivers, which represent widely separated crustal fragments that formed in the Early to Middle ordovician Tetagouche-Exploits back-arc basin, have been amalgamated into a tectonic collage of thrust nappes during their incorporation into the Brunswick subduction complex. The individual lithostratigraphic units of the blocks, comprising five groups of rocks, have been assembled together in the Bathurst Supergroup.

Abstract Massive sulfide deposits of the Bathurst Mining Camp experienced the following M 1 metamorphic conditions in the Ashgillian to Llandoverian ages (442–430 Ma): Caribou = 350°C, 5.5 kbars; Brunswick 12 = 360°C, 5.8 kbars; Heath Steele and Stratmat = 365°C, 5.5 kbars; and Brunswick 6 = 400°C, 5.8 kbars. Some deposits underwent a Late Silurian or Early Devonian M 2 metamorphism at pressures of ˜3 to 4 kbars and temperatures locally reaching 350° to 400°C. Silicate assemblages within, and in the host rocks of, the deposits exhibit metamorphic conditions identical to those of the sulfide assemblages of the deposits, showing that the deposits were emplaced prior to peak M 1 conditions, compatible with a syngenetic origin. Sphalerite barometry provided accurate, consistent pressure estimates when applied to appropriate assemblages (sphalerite-pyrite- hexagonal pyrrhotite). Arsenopyrite and chlorite-phengite thermometry gave useful temperature estimates. The latter assemblage was calibrated by least squares fitting of 51 pairs of analyses of coexisting chlorite and white mica to a formula deduced from thermodynamic reasoning giving where T e is the temperature of equilibration, and where is the mol fraction of j in the k site. x cl , x am , and x da are the proportions of clinochlore, amesite, and daphnite in chlorite analyses reduced to these three end members plus aluminum-free chlorite. Standard deviation between temperatures estimated from chlorite-phengite thermometry and those estimated by other means is 35°C. The narrow range of P-T observed in the Bathurst camp (350°-400°C, 5.5–5.8 kbars) supports structural observations that some of the nappes containing the California Lake and Tetagouche Groups were assembled and internally deformed prior to the recorded M 1 metamorphism. Abstract Massive sulfide deposits of the Bathurst Mining Camp experienced the following M 1 metamorphic conditions in the Ashgillian to Llandoverian ages (442–430 Ma): Caribou = 350°C, 5.5 kbars; Brunswick 12 = 360°C, 5.8 kbars; Heath Steele and Stratmat = 365°C, 5.5 kbars; and Brunswick 6 = 400°C, 5.8 kbars. Some deposits underwent a Late Silurian or Early Devonian M 2 metamorphism at pressures of ˜3 to 4 kbars and temperatures locally reaching 350° to 400°C. Silicate assemblages within, and in the host rocks of, the deposits exhibit metamorphic conditions identical to those of the sulfide assemblages of the deposits, showing that the deposits were emplaced prior to peak M 1 conditions, compatible with a syngenetic origin. Sphalerite barometry provided accurate, consistent pressure estimates when applied to appropriate assemblages (sphalerite-pyrite- hexagonal pyrrhotite). Arsenopyrite and chlorite-phengite thermometry gave useful temperature estimates. The latter assemblage was calibrated by least squares fitting of 51 pairs of analyses of coexisting chlorite and white mica to a formula deduced from thermodynamic reasoning giving where T e is the temperature of equilibration, and where is the mol fraction of j in the k site. x cl , x am , and x da are the proportions of clinochlore, amesite, and daphnite in chlorite analyses reduced to these three end members plus aluminum-free chlorite. Standard deviation between temperatures estimated from chlorite-phengite thermometry and those estimated by other means is 35°C. The narrow range of P-T observed in the Bathurst camp (350°-400°C, 5.5–5.8 kbars) supports structural observations that some of the nappes containing the California Lake and Tetagouche Groups were assembled and internally deformed prior to the recorded M 1 metamorphism. Abstract Massive sulfide deposits of the Bathurst Mining Camp experienced the following M 1 metamorphic conditions in the Ashgillian to Llandoverian ages (442–430 Ma): Caribou = 350°C, 5.5 kbars; Brunswick 12 = 360°C, 5.8 kbars; Heath Steele and Stratmat = 365°C, 5.5 kbars; and Brunswick 6 = 400°C, 5.8 kbars. Some deposits underwent a Late Silurian or Early Devonian M 2 metamorphism at pressures of ˜3 to 4 kbars and temperatures locally reaching 350° to 400°C. Silicate assemblages within, and in the host rocks of, the deposits exhibit metamorphic conditions identical to those of the sulfide assemblages of the deposits, showing that the deposits were emplaced prior to peak M 1 conditions, compatible with a syngenetic origin. Sphalerite barometry provided accurate, consistent pressure estimates when applied to appropriate assemblages (sphalerite-pyrite- hexagonal pyrrhotite). Arsenopyrite and chlorite-phengite thermometry gave useful temperature estimates. The latter assemblage was calibrated by least squares fitting of 51 pairs of analyses of coexisting chlorite and white mica to a formula deduced from thermodynamic reasoning giving where T e is the temperature of equilibration, and where is the mol fraction of j in the k site. x cl , x am , and x da are the proportions of clinochlore, amesite, and daphnite in chlorite analyses reduced to these three end members plus aluminum-free chlorite. Standard deviation between temperatures estimated from chlorite-phengite thermometry and those estimated by other means is 35°C. The narrow range of P-T observed in the Bathurst camp (350°-400°C, 5.5–5.8 kbars) supports structural observations that some of the nappes containing the California Lake and Tetagouche Groups were assembled and internally deformed prior to the recorded M 1 metamorphism.

Abstract The present study was undertaken to document the lithogeochemistry of the principal volcanic units hosting the Early Ordovician Bald Mountain Cu-Zn-Au-Ag massive sulfide deposit in northern Maine as well as that of volcanic units from the surrounding region. Results document several distinct petrochemical associations that reflect variations in the tectono-magmatic evolution of an intraoceanic arc to continental arc–back-arc complex along the convergent Ordovician margin of Gondwana. Footwall and immediate hanging-wall rocks at Bald Mountain are composed of tholeiitic basalt-andesite massive to pillowed lava flows and hyaloclastite breccias, and felsic aphyric, pumice- and crystal-rich ignimbrites. Mafic rocks are characterized by low incompatible element contents, flat to slightly light rare earth element-depleted patterns, and prominent negative anomalies for Nb, Ta, Zr, Hf, and Ti on chondrite-normalized trace element plots. The felsic ignimbrites are tholeiitic dacite-rhyodacite having trace element characteristic similar to that of the associated mafic rocks. The footwall and immediate hanging-wall rocks define a bimodal tholeiitic, mafic-dominated intraoceanic arc volcanic suite similar in composition to recent volcanic rocks from the Kermadec arc in the southwest Pacific. In contrast to the lower, mafic-dominated section, the upper hanging-wall section at Bald Mountain is composed of dominantly felsic volcaniclastic rocks and associated sediments with only minor andesite flows and/or sills. The volcanic rocks are transitional to calc-alkaline with the felsic rocks showing high Th (˜3–18 ppm) and light REE (La ˜11–68 ppm) contents, and negative Nb, Ta, P, and Ti anomalies. Their geochemistry and isotopic signatures indicate significant involvement of an enriched continental crust component in their source region. The upper hanging-wall rocks are similar in composition to calc-alkaline suites from mature arc and continental margin arc–back-arc settings like the Taupo Volcanic Zone of New Zealand. Volcanic rocks from the surrounding Munsungun-Pennington Mountain and Weeksboro-Lunksoos Lake anticlinoria in northern Maine include basalts having arc, continental back-arc, and within-plate non-arc (no negative Nb-Ta anomalies) petrotectonic affinities. Associated felsic volcanic rocks have enriched calc-alkaline compositions with continental crustal geochemical and isotopic signatures. The various volcanic units partially overlap in composition with some volcanic rocks from the hanging-wall portion of the Bald Mountain sequence. Volcanic rocks hosting the Mount Chase Zn-Pb-Cu-Ag-Au massive sulfide deposit in the Weeksboro- Lunksoos Lake anticlinorium, southeast of Bald Mountain, are coeval with upper hanging-wall units at Bald Mountain and have continental back-arc basin compositional affinities. The Bald Mountain sequence is interpreted to reflect the progression from an oceanic to transitional continental crustal setting as part of the evolving Popelogan Arc–Tetagouche-Exploits back-arc basin system. The setting may have been analogous to that observed along the present Kermadec-Havre Trough-Taupo Volcanic Zone arc and back-arc system in the southwest Pacific. The Bald Mountain deposit most likely formed in a submarine oceanic arc volcano caldera located proximal to, but offshore from, the continental back-arc basin in which the Mount Chase deposit developed.

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.

Abstract The Bathurst Mining Camp, which hosts over 45 massive sulfide deposits, formed in a back-arc rift that developed on a passive margin sequence of turbiditic and hemipelagic sediments overlying Ganderian continental crust. The provenance of these clastic sediments changed from Avalonian basement during the prerift passive margin stage and the early stages of back-arc rifting (Arenig) to obducted ultramafic rocks during later sedimentation (upper Llanvirn). The water column conditions alternated from stratified with anoxic bottom waters during the deposition of regionally extensive Tremadoc and Arenig black shale of the Knights Brook, Patrick Brook, Nepisiguit Falls, and Spruce Lake Formations, to well-oxygenated during the deposition of Llanvirn maroon shales and cherts, and anoxic during deposition of the Caradoc black shales. Evidence for anoxic conditions include the absence of bioturbation, the high S/C ratios and low Mn contents of black shales, the lack of seawater oxidation associated with most sea-floor sulfide deposits, and the highly positive δ 34 S values for sedimentary pyrite that are consistent with closed system, Raleigh fractionation of sulfur isotopes in a restricted basin. Although the metal/reduced sulfur ratio of the hydrothermal fluids cannot be precisely constrained, highly positive δ 34 S values for massive sulfides, and the similarity of these values to coeval pyrite in host sediments, indicate that reduced sulfur in the ambient water column played a major role in the precipitation of sulfides. In addition, a water column with reduced and stagnant bottom waters enhanced the efficiency of sulfide precipitation near hydrothermal vents. Unlike modern black smokers, where over 95 percent of the metals is lost to the oxygenated water column, metals carried in buoyant hydrothermal plumes in an anoxic water column would precipitate as sulfides and settle to the sea floor to form sedimentary sulfide deposits. Massive sulfides are rare in the Llanvirn due to the change to oxidizing sea-floor conditions. As a result, maroon shale and chert containing hydrothermal Fe-Mn oxides occur over large areas of the Bathurst Mining Camp, similar to modern Fe-Mn oxyhydroxides along oceanic rifts. Mass-balance calculations show that the flux of hydrothermal Zn is comparable to that which generated the Bathurst massive sulfide deposits, although in the oxygenated ocean most of the metals were dispersed over a wide area. The redox conditions in the Bathurst back-arc rift have therefore exerted a fundamental control on the formation and preservation of massive sulfide deposits. The role of a reduced water column in forming and preserving massive sulfide deposits may also explain why volcanogenic massive sulfide (VMS) deposits cluster at particular times in the Earth’s history when the oceans were stratified. Although most Bathurst sulfide deposits are associated with felsic volcanic rocks, the occurrence of metalliferous oxidized sediments in younger mafic volcanic sequences suggests that this association may be controlled as much by the ambient sea-floor environment as by the supply of metals from hydrothermal sources.