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Quartz-hosted fluid inclusions associated with polymetallic mineralization (Fe-Co-Ni-Cu-As-Ag-Sb-Au-Pb) of the Nictaux Falls Dam, Lansdowne, and Cape St. Marys occurrences in the Meguma terrane, Nova Scotia, Canada.

This study is on quartz-hosted fluid inclusions (FI) from three metasedimentary rock-hosted polymetallic vein occurrences [Nictaux Falls (Co-Ni-As-Au-Bi), Lansdowne (Zn-As-Ag-Sb-Au-Pb), and Cape St. Marys (Co-Ni-Cu-Zn-Ag-Sb-Au-Pb-Bi)] in the southwestern Meguma terrane, Nova Scotia. Similarities in host rock-type, alteration, and metal association suggest a possible genetic link among these occurrences. This work aims to establish the P-T-X of fluids associated with all three sites to confirm their genesis.

Nictaux Falls FI are classified into three types: type-1 are liquid-rich, two-phase ([L.sub.H2O-NaCl]+[V.sub.H2O[+ or - ]CH4])> type-2 are liquid-rich, three-phase ([L.sub.H2O-CaCl2-NaCl]+[V.sub.H2O[+ or - ]CH4]+[S.sub.halite]), and type-3 are single-phase ([L.sub.H2O-CaCl2-NaCl]) inclusions. Textural observations indicate that types-1 and -2 inclusions are primary or pseudo-secondary in origin, while type-3 inclusions are secondary. Most inclusions (all types) did not freeze at/before -180[degrees]C, suggesting high divalent cation contents (likely C[a.sup.2+]). Final ice-melting temperatures ([]) were-47.1[degrees]C(n= 1),-49.8[degrees]C (n = 1) and -40.1 to-51.1[degrees]C(n = 3), for the three respective fluid types, suggesting minimum salinities of 43.2 wt% CaC[l.sub.2equiv]. Heating experiments yielded homogenization temperatures ([T.sub.h]; to liquid) of 127-213[degrees]C (n = 6) and 194-202[degrees]C (n = 3) for types-1 and -2 fluids. Calculated isochore data for type-1 inclusion assemblages combined with chlorite thermometry (~280[degrees]C) indicate a very low entrapment pressure (~110 bar).

Lansdowne FI are classified into four types: type-1 inclusions are single-phase ([L.sub.H2O.CaCl2-NaCl[+ or - ]CH4]) inclusions, type-2a are liquid-rich, two- or three-phase ([L.sub.H2O-NaCl]+[V.sub.CH4[+ or - ]CO2] or [L.sub.H2O.NaCl]+[L.sub.CO2]+[V.sub.CH4]). type-2b are two phase ([L.sub.H2O.NaCl]+[VCH4[+ or - ]CO2]) vapour-rich inclusions, and type-2c inclusions are one-phase ([V.sub.CH4[+ or - ]CO2[+ or - ]H2O]). Type-2 inclusions may occur in single assemblages. Crosscutting relationships show FI are primary or pseudosecondary in secondary quartz coeval with mineralization. Type-1 inclusions show [] between -44.0[degrees]C and -20.4[degrees]C (n = 26), suggesting salinities of 23.4-47.1 wt% CaC[l.sub.2equiv] Many type-1 inclusions did not freeze, suggesting high C[a.sup.2+]. Type-2a inclusions show [] between -8.3 and -3.9[degrees]C (n = 54), suggesting moderate to low-salinity (6 to 12 wt% NaC[l.sub.equiv]). Only C[H.sub.4-].poor, type-2a inclusions homogenized before decrepitation between 148-173[degrees]C (n = 7). Type-3 inclusions homogenized to vapour between -110 and -92[degrees]C (n = 10), indicating a very low entrapment pressure of ~ 150 bar.

The results of this study show that ore fluids at both Lansdowne and Nictaux Falls were variably Ca-rich and highly saline in a near-surface epigenetic environment. The co-entrapment of low salinity brines and C[H.sub.4] is unique to Lansdowne, where mingling between the two fluids is preserved in type-2 assemblages showing variable brine-hydrocarbon phase ratios. The characterization of Cape St. Marys samples is under way.

J. JACKMAN (1), N. WELT (1), E. ADLAKHA (1), J. HANLEY (1), M. KERR (1), N. KENNEDY (1), AND G. BALDWIN (2)

1. Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada <>;

2. Nova Scotia Department of Energy and Mines, Halifax, Nova Scotia B3J 2T9, Canada

(*) Honourable Mention: AGS Rupert MacNeill Award for best undergraduate student oral presentation
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Author:Jackman, J.; Welt, N.; Adlakha, E.; Hanley, J.; Kerr, M.; Kennedy, N.; Baldwin, G.
Publication:Atlantic Geology
Geographic Code:1CANA
Date:Jan 1, 2021
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