Abstract The Bathurst Mining Camp hosts 45 volcanic sediment-hosted massive sulfide deposits and 95 occurrences, including the supergiant Brunswick 12 deposit with a geologic resource of 230 million metric tons (Mt) grading 7.66 wt percent Zn, 3.01 wt percent Pb, 0.46 wt percent Cu, and 91 g/t Ag. Ten of these have been brought into production with a total production to 1999 of 128 Mt with an average grade of 2.87 wt percent Pb, 6.58 wt percent Zn, 0.93 wt percent Cu, and 82 g/t Ag; only the Brunswick 12 deposit remains in production. The Bathurst Mining Camp deposits belong to an ECONOMICally important subgroup of sea-floor hydrothermal deposits referred to as volcanic-sediment-hosted massive sulfide deposits. The Bathurst Mining Camp is interpreted to be a sediment-covered back-arc continental rift referred to as the Tetagouche-Exploits back-arc basin, which opened by rifting of Ganderian continental crust in the Early ordovician and closed by northwestward-directed subduction during the Late ordovician to Early Silurian.The Bathurst Mining Camp was intensely deformed and metamorphosed during multiple collisional events related to east-dipping subduction of the basin. Peak metamorphic conditions vary from 325° to 400°C and 6 to 7 kbars. The present distribution and shape of massive sulfide deposits and associated sulfide stringer zones are mainly controlled by D 1 and D 2 structures. The volcanic sedimentary sequence has been subdivided into the Tetagouche, California Lake, and Sheep- house Brook Groups. These groups reflect different parts of the back-arc basin that were tectonically juxtaposed in a west-dipping subduction-obduction complex. The bimodal volcanic pile in each of the groups evolved from felsic to mafic dominated through time due to crustal thinning during the rifting process. The ambient water column conditions within the Tetagouche basin alternated from stratified with anoxic bottom waters during the deposition of regionally extensive Arenigian black shale of the Knights Brook, Patrick Brook, Nepisiguit Falls, and Spruce Lake Formations, to well-oxygenated during the deposition of Llanvirian maroon shales and cherts of the Little River and Boucher Brook Formations, to anoxic during deposition of Caradocian black shales. Four hydrothermal events spanning 12 to 14 m.y. have been recognized, and from oldest to youngest these are the Chester (478 Ma), Caribou (472–470 Ma), Brunswick (469–468 Ma), and Stratmat (467–465 Ma) horizons. The Stratmat and Brunswick horizons both occur in the Tetagouche Group, whereas the Caribou and Chester horizons are hosted by the California Lake and Sheephouse Brook Groups, respectively. There are two major types of iron formation in the Bathurst Mining Camp. Type 1 is a carbonate-oxide-silicate iron formation that is spatially associated with most massive sulfide deposits of the Brunswick ore horizon and extends several kilometers from the sulfide deposit along mineralized horizons. Siderite, magnetite,Fe/Mn, Ba/A1, P/A1, Zn, Pb, Cu, Ag, As, Au, Bi, Cd, Co, Mo, Se, Sb, Sn, In, T1, and Eu/Eu* increase systematically with proximity to ore deposits and define vectors for mineral exploration. None of the other mineralized horizons in the Bathurst Mining Camp contain Algoma-type iron formations. Type 2 consists of widely distributed Llanvirian Fe-Mn oxides that are not spatially associated with massive sulfide deposits and formed during a period of oxygenated seawater conditions. Most deposits are zoned vertically and laterally from a high-temperature, vent-proximal, veined, and brecciated core to vent-distal hydrothermal sediments as follows: (1) vent complex (pyrrhotite + magnetite + pyrite + chalcopyrite + quartz ± sphalerite ± galena), (2) bedded ores (pyrite + sphalerite + galena ± chalcopyrite), and (3) bedded pyrite (pyrite ± sphalerite ± galena). This mineral zonation is accompanied by the following chemical changes: proximal (high Cu, Co, Bi, Cu/Cu + Pb + Zn); and distal (increased Zn, Pb, Ag, Au, Cd, Sn, In, As, Sb, Tl, and Hg; low Cu/Cu + Pb + Zn). The vent complex is commonly underlain by a highly deformed sulfide stringer zone that extends hundreds of meters beneath deposits and consists of veins and impregnations of sulfides, silicates, and carbonates that cut hydrothermally altered volcanic and sedimentary rocks. Hydrothermal alteration is widespread (1-5 km laterally and hundreds of meters vertically) and is zoned from the core to the margins of upflow zone as follows:Zone 1— quartz + Fe-rich chlorite + pyrrhotite + chalcopyrite (>300°C); zone 2— Fe-rich chlorite + sericite ± pyrite; zone 3—Fe-Mg chlorite + sericite + albite; and zone 4— albite + Mg-rich chlorite. Accompanying these mineralogical changes is a marked increase of Si, Fe, Mg, CO 2 , S, Zn, Pb, Cu, Cd, As, Sb, and Hg and a decrease of Na and Ca in zone 1; and an Mg and Na increase and a Ca decrease in the outer alteration zones. The massive sulfide deposits formed from low-salinity and high-temperature (>300°C) buoyant hydrothermal fluids, which explains the vent-proximal nature of most deposits. The reduced sulfur in Bathurst Mining Camp deposits originated mostly from an ambient-reduced water column. Variations among deposits of different age are controlled by the global secular δ 5 34 S curve for sedimentary sulfate and sulfide. The base metals were probably derived from both hydrothermal and magmatic fluids, whereas elements such as Sn, In, Au, As, and Sb probably originated from magmatic fluids. The Bathurst Mining Camp deposits share many of the attributes of SEDEX deposits, including large size, metal contents (Zn + Pb + Cu + Ag), hydrothermal architecture, anoxic sea-floor environment, and perhaps ambient seawater biogenic sulfur source. The large size of many Bathurst Mining Camp deposits, and volcanic sediment-hosted massive sulfide deposits in general, reflects a number of factors including: (1) hydrothermal architecture consisting of a hydrothermal reservoir capped by impervious fine-grained sediments, (2) the longevity of the hydrothermal system, (3) focused discharge from long-lived vent sites, (4) formation during a major hiatus in volcanism, (5) anoxic bottom waters that facilitated the total capture of metals in buoyant hydrothermal fluids, and (6) direct magmatic input of metals, particularly in the case of large deposits.

Description of Formations Browns Mountain Group The chloritized graywackes, slates, argillites, and hematite beds of this group occur on the southeast side of the Hollow Fault and were not examined closely during the present study. Williams (1914, p. 55) records the inarticulate brachiopod Obolus (Lingulobus) spissa from iron-ore beds and associated micaceous sandstones on the East Branch of Doctors Brook and north of the Little Hollow (which runs parallel to the Hollow three-quarters of a mile southeast of the West Branch of Doctors Brook). The same brachiopod occurs with the Arenig (Lower Ordovician) graptolite Didymograptus nitidus in the iron-ore beds of Belle Isle, Newfoundland (Williams, 1914, p. 55, footnote). The probability of an Ordovician age is strengthened by the fact that the Browns Mountain Group is intruded by monzonite stocks which do not intrude the Silurian, and further, because pebbles from these stocks occur in the Malignant Cove Formation; the Browns Mountain Group is therefore certainly pre-Silurian, and probably older than the Late Ordovician or lower Llandovery Bears Brook Volcanic Group. Browns Mountain conglomerates, with pebbles up to 1 cm, grits, and sandstones occur high on the east bank of Doctors Brook above stations L17 and L21 (Pls. 5A, 5B); and basic tuffs and serpentine are exposed in the Hollow Fault zone along the East Branch of Doctors Brook (stations U88 to U94, Pl. 5C). Other outcrops noted include grits on the West Branch of Doctors Brook 8,000 ft upstream from the junction of the East and West Branches, and epidotized basic rocks on the East . . .

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 In the Mackenzie Mountains, an arcuate foreland thrust-fold belt of Late Cretaceous–Paleocene age in the northern Canadian Cordillera, two discrete glacial–periglacial sequences of Cryogenian age (the Rapitan Group and the Stelfox Member of the Ice Brook Fm.) are separated by c. 1.0 km of non-glacial strata. The older Rapitan diamictite occurs in an amagmatic rift basin; the younger Stelfox diamictite occurs on a passive-margin continental slope. The Rapitan Group consists of three formations. The lower Mount Berg Fm. is a complex of diamictites and conglomerates of limited extent. The middle Sayunei Fm. is a thick sequence of maroon-coloured mudrocks hosting innumerable graded layers of silt- and fine-grained sandstone. It lacks wave- or traction current-generated bedforms, and is lightly sprinkled with granule aggregates (‘till pellets’) and lonestones of dolostone and rare extrabasinal granitoids. It is capped by a hematitic Fe-formation that was reworked into the disconformably overlying Shezal diamictite. The Shezal Fm. is a complex of olive-green coloured boulder diamictites with subordinate, dark-grey shales, siltstones and parallel-sided sandstones. Some of the boulders are faceted and striated, and include dolostone, quartzite, siltstone and gabbro in declining order of abundance. Diamictite terminates abruptly at the top of the Shezal Fm., which is sharply overlain by dark shales or by <52 m of fetid, dark-grey, 13 C-depleted limestone with graded bedding. The Stelfox Member is dominated by non-stratified, carbonate-clast diamictite with faceted and striated clasts, locally associated with subordinate, well-laminated shales containing till pellets and ice-rafted dropstones. It is thin or absent on the palaeocontinental shelf, but thickens seaward (southwestward) on the palaeocontinental slope. A thin clay drape separates it from a laterally continuous post-glacial ‘cap’ dolostone, which is a very pale coloured, micro- to macropeloidal dolostone with low-angle cross-laminae, giant wave ripples and local bioherms of corrugated stomatolites. In the NW, the dolostone is followed by reddish and greenish marls, followed by black shale of the Sheepbed Fm. In the SE, the dolostone is overlain by pink or grey limestones with well-developed sea-floor cements pseudomorphic after aragonite. In this area, the top of the dolostone is ferruginous and contains digitate rosettes of sea-floor barite cement, variably calcitized. The dolostone–limestone contact is perfectly conformable, and synclinal structures previously intepreted as karst features are tectonic in origin. The grand mean palaeomagnetic pole for the well-studied Franklin Large Igneous Province ( c. 718 Ma) of Arctic Laurentia, coeval with the basal Rapitan Group in the Mount Harper area, Yukon Territory, places the Mackenzie Mountains firmly in the tropics, at 18±3°N palaeolatitude, at the onset of the Rapitan glaciation. Carbon (δ 13 C), oxygen (δ 18 O) and strontium ( 87 Sr/ 86 Sr) isotopes have been measured in carbonates bracketing the Rapitan and Stelfox diamictites. Sulphur isotope data (δ 34 S) have been obtained from carbonate-associated sulphate and barite above the younger diamictite, and calcium isotope data (δ 44 Ca) from the younger carbonate itself. The results are broadly consistent with data from other areas. Iron isotope (δ 57 Fe) and cerium anomaly (Ce/Ce*) values increase systematically upwards through the Sayunei Fe-formation, supporting an interpretation that deposition occurred within a redox chemocline through which the basin floor descended as a consequence of isostatic loading by the advancing Shezal ice sheet. Supplementary material Data are available at http://www.geolsoc.org.uk/SUP18470 .

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 Elizabeth and Ely, which exploited Besshi-type massive sulfide deposits, are the two largest abandoned mines in the Vermont copper belt. The ore mineralogy of the deposits and their mine wastes are dominated by pyrrhotite with minor chalcopyrite and sphalerite. Gangue minerals include quartz, muscovite, biotite, amphibole, and minor carbonate. The watersheds of the Vermont copper belt away from the mines are characterized by neutral waters, with significant alkalinity and hardness due to the presence of carbonate rocks in the watersheds. The Elizabeth mine site discharges into the West Branch of the Ompompanoosuc River at three points, in order going downstream: the Air Vent, which drains the underground mine workings; Copperas Brook, which drains the area with most of the mine wastes; and Lord Brook, which drains an area impacted by drainage from two smaller mine workings. The Ely mine site is drained by Ely Brook, which empties into Schoolhouse Brook, which flows into the East Branch of the Ompompanoosuc River. Mine drainage from Elizabeth and Ely is characterized by low pH (1.9 to 6.9), high specific conductance (0.16 to 5.69 mS/cm), and elevated concentrations of Fe (0.286 to 1,000 mg/L), Ca (10.9 to 498 mg/L), Al (0.011 to 236 mg/L), Cu (6 to 200,000 μg/L), Zn (5 to 38,000 μg/L), Co (<0.2 to 7,200 μg/L), Cd (0.5 to 400 μg/L), and sulfate (92 to 4,900 mg/L). The chemistry of the drainage is linked to the physical and chemical character of the mine wastes, the stoichiometry of pyrrhotite weathering reactions, and the hydrologic and climatic settings of the sites, among other factors.

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.

Abstract The felsic volcanic rocks of the northern Bathurst Mining Camp occur in both the California Lake and Tetagouche Groups. The felsic volcanic rocks of these groups are in part coeval but differences in their chemistry, petrology, stratigraphic relationships, environments of deposition, and associated mafic volcanic rocks indicate that they formed in different regions of the Tetagouche-Exploits back-arc basin. They are both preserved within small fragments of attenuated continental arc crust that rifted away from the Popelogan arc during the Arenig. These crustal blocks became separated by oceanic basins underlain by transitional to oceanic lithosphere. By comparison with modern-day arc-back-arc systems it is apparent that these blocks underwent extension and subsequently rifting at different times. This indicates that the opening of the Tetagouche-Exploits back-arc basin was diachronous along the arc, such that at ca. 470 Ma the California Lake Group was within a rifting environment, while the Tetagouche Group was in the earlier extensional phase of arc break-up. The crustal blocks were later tectonically juxtaposed during the Late Ordovician to Late Silurian closure of the Tetagouche-Exploits basin.

Abstract The approximately coeval California Lake, Fournier, and Tetagouche Groups of the Bathurst Mining Camp formed separately and represent different tectonic settings within the Tetagouche-Exploits back-arc basin. They formed on small fragments of attenuated continental crust that rifted due to the northwestward migration of the Popelogan arc during the Arenig. These crustal fragments were subsequently tectonically juxtaposed by closure of the Tetagouche-Exploits basin in the Late Ordovician to Late Silurian.

Abstract A sulfurous spring emerges at an outcrop of Bowland Shale Formation on Crimpton Brook, Lancashire. The spring is marked by the precipitation of white and yellow jarosite. Comparable light sulfur isotope compositions suggest that the jarosite was derived from surface oxidation of pyritic shale. The shale contains anomalous concentrations of selenium and other trace elements, in common with other exposures of the Bowland Shale Formation in the north of England. The selenium is resident in the pyrite, and was released during oxidation and incorporated into the jarosite in Crimpton Brook. The small scale of the water flow at the site and the remote situation pose no environmental problem, but the data exemplify the potential danger of pyrite weathering into groundwater on a larger scale.