The Brunswick #12 and #6 mines is located 30 km SSW of the city of Bathurst in northern New Brunswick. Heath Steele is a further 20 km south of Brunswick #12 and 51 km northwest of Newcastle. At least 35 deposits and over 100 Zn-Pb-Cu occurrences are known within the Bathurst Mining Camp.
The Brunswick #12 and #6 and the Heath Steele orebodies within the Bathurst Mining Camp are hosted by the Tetagouche Group, a Middle Ordovician sequence of metamorphosed bimodal felsic and basaltic volcanic rocks with intercalated sediments deposited in a marine back-arc continental rift. The Tetagouche Group was developed at the leading edge of Avalonia and forms part of the Miramichi massif, a tectonic terrane in the central mobile belt of the Canadian Appalachians. Three hydrothermal events spanning approximately 5 m.y. have been recognised, from oldest to youngest, the Caribou, Brunswick and Stratmat horizons. The Brunswick horizon was deposited at 469±2 Ma and hosts both the Brunswick #6 and #12 deposits.
Brunswick #12 & #6
The mineralised host rocks of the Bathurst district are underlain by a Cambro-Ordovician sequence of quartz-wacke and shaly phyllite, while the host unit comprises quartz-feldspar augen schist, quartz-eye schist, crystal tuff and sericite-chlorite schist. The immediate footwall rocks are chloritic phyllites with thin bands of chert and sulphides. The massive sulphide types comprise:
i). a massive pyrite zone containing minor amounts of sphalerite and galena, and variable chalcopyrite, magnetite and pyrrhotite;
ii). massive banded pyrite-sphalerite-galena with minor chalcopyrite and pyrrhotite; and
iii). massive pyrite with minor sphalerite, galena and chalcopyrite.
The sulphides are overlain by Algoma-type iron formation, which can be dominated by oxide, silicate or carbonate minerals. The geometry, grade and thickness of the Brunswick deposits have been heavily influenced by structure, with the ore being attenuated on the limbs of, and concentrated in the axial zone of, isoclinal F1 sheath folds where they are intersected by tight F2 folds. The ore and iron formation predates the oldest folding, although it is regarded that the attainment of ore grade and economic thickness is a result of the structural modification.
Reserves + production at Brunswick #12 and #6 amount to:
161 Mt @ 8.83% Zn, 3.55% Pb, 0.31%, Cu, 99 g/t Ag, plus 25 Mt @ 1.1% Cu.
Heath Steele, which is 65 km south west of Bathurst is the second largest Zn-Pb-Cu-Ag massive sulphide deposit in the Bathurst mining district. It occurs as a number of massive sulphide deposits of varying sizes within the Nepsiguit Falls Formation which forms the basal part of the Middle Ordovician Tetagouche Group. The host rocks are greenish-grey to dark-grey mudstones that are interbedded with fine- to medium-grained volcniclastic rocks which are generally chloritic and are interpretted to comprise a mixture of exhalative and epiclastic components. The Tetagouche Group was intruded by granite and gabbro masses at the onset of regional, low-grade greenschist metamorphism.
The 5 main deposits at Heath Steele, named A to E Zone inclusive, are hosted by crystal rich felsic volcaniclastic rocks and associated tuffaceous sediments of the Nepisiguit Falls Formation. The largest and the main deposit mined, the B Zone, comprises a drag folded slab of ore about 50 m thick, 1500 m along strike and 800 m down dip, and has three dominant ore types:
i). massive pyrite,
ii). banded pyrite-sphalerite-galena, comprising alternating layers of sphalerite and galena, and aggregates of chlorite, quartz and host rocks, interlayered with massive sulphides or disseminations of granoblastic pyrite, and
iii). pyrrhotite-chalcopyrite, copper-rich fragmental ore within breccia zones.
The bulk of the ores occur as stratabound accumulations of pyrite, galena, sphalerite, chalcopyrite accompanied by minor magnetite, arsenopyrite, tetrahedrite-tennantite, cosalite, boulangerite and complex Pb-Bi-Sb-Ag sulphosalts. Sphalerite is usually associated with pyrite and galena, but less frequently with chalcopyrite, pyrrhotite and tetrahedrite. Sphalerite grains contain inclusions of chalcopyrite, pyrite and stannite.
Cherty, chloritic and carbonate-rich phyllites occur in and near the sulphide deposits. The sulphides are associated with leucoxene-rich quartz-sericite schists which contain sulphides in layers or disseminations.
Overall the Cu, Co and As levels are higher and the Zn, Pb and Ag levels are lower than at Brunswick 12.
Discontinuous mining of the B Zone from 1957 to 1997 produced:
17.9 Mt @ @ 4.67% Zn, 1.73% Pb, 0.96%, Cu, 63 g/t Ag All 5 deposits together total around 25 Mt of ore and mineralisation.
(Source: Porter Geoconsultancy, http://www.portergeo.com.au/, 1999)