19 Field identification of on-land tailings deposits was based on their colour, vertical stratigraphy, and fine-grained texture. In Wine Harbour, contrasting depositional environments (i.e., terrestrial versus intertidal) have produced variably oxidized deposits, which exhibit distinct down-hole appearances. In drier environments, tailings typically display a vertical colour gradient ranging from rusty brown at the surface to dark grey at depth as conditions become anoxic (Fig. 4a). In waterlogged areas along the shoreline of Wine Harbour, the extent of oxidation displayed in tailings deposits is less variable. Here, tailings maintain a light- to dark-grey colour throughout as a result of reduced oxygen penetration at the surface (Fig. 4b).

20 Field observations and geochemical results (discussed below) confirmed previous assumptions that four main tailings deposits occupy the terrestrial and marine environments at Wine Harbour. Based on historical maps and ruins observed in the field, the distribution of these deposits is generally consistent with the locations of former mill structures (Fig. 3), and they are largely confined to the northeastern part of the district. Two deposits are located along the shoreline, directly down-gradient of the Plough Lead and Old Provincial mill sites. Northeast of these deposits, a third accumulation is located down-gradient of the Old Eureka mill, and a fourth is situated just east of this in a swampy area close to Barachois Cove.

21 Arsenic and Hg concentrations measured in subsamples from 10 on-land tailings sites at Wine Harbour (Table 1) are consistent with ranges reported for 14 other historical gold districts in Nova Scotia (Parsons et al. 2012). These tailings contain As concentrations ranging between 200 and 196 000 mg/kg (median 4880 mg/kg), and comparison with the Canadian environmental quality guideline for As in soils (12 mg/kg; Canadian Council of Ministers of the Environment (CCME 2001)) demonstrate that As burdens are exceedingly high. Mercury concentrations range from 4930 to 320 000 µg/kg (median 11 300 µg/kg), and 90% of these samples have concentrations in excess of the CCME Hg soil quality guideline (6600 µg/kg) (CCME 1999). Field observations, conventional XRD, and EPMA results confirm that the anomalous concentration of As (196 000 mg/kg) measured in sample T5B is caused by the abundance of arsenopyrite (Little 2006). Furthermore, the markedly high concentration of Hg (320 000 µg/kg) measured in T5B suggest that it may represent a sulphide-rich mill concentrate mixed with tailings. By comparison, concentration ranges for As and Hg measured in tailings and stream sediments from other gold districts in Nova Scotia are 10 mg/kg to 310 000 mg/kg (median 2550 mg/kg) and <5 µg/kg to 350 000 µg/kg (median 1640 µg/kg), respectively (Parsons et al. 2012).

22 Intertidal zone tailings (n = 4) sampled down-gradient of two near-shore mill sites contain concentrations of As and Hg that are considerably lower than tailings located above the high water line. Here, As ranges between 86 and 1550 mg/kg (median 348 mg/kg), and all sites have As concentrations in excess of the CCME 12 mg/kg soil quality guideline. In contrast, Hg ranges from 444 to 9510 µg/kg (median 922 µg/kg), and only one site has concentrations in excess of the 6600 µg/kg guideline. The comparatively low concentrations of As and Hg in the intertidal zone probably reflect mixing of the tailings with natural marine sediments, as well as settling of dense sulphide minerals (e.g., arsenopyrite) close to the original stamp mill sites.

23 The concentrations of As and Hg in the tailings and intertidal sediments at Wine Harbour are significantly higher than the naturally occurring levels of As and Hg in soils overlying mineralized bedrock within the Nova Scotia gold districts. Parsons and Little (2015) reported As and Hg concentrations in near surface (0–5 cm, <2 mm size fraction) soils collected from 85 sites at the Montague and Goldenville gold districts to be 2–273 mg/kg (median 23 mg/kg) and 39–490 µg/kg (median 137 µg/kg), respectively. The elevated As and Hg burdens documented in the tailings and intertidal zone samples at Wine Harbour suggest that they could present a risk to human and ecosystem health (CCME 1999, 2001).

24 The major mineralogy of 14 terrestrial tailings samples is consistent with studies conducted at other Nova Scotia gold districts, and dominant minerals reflect auriferous vein and host-rock compositions (Walker et al. 2009; Corriveau et al. 2011; DeSisto et al. 2011; Percival et al. 2014). Primary minerals identified through bulk XRD analyses include quartz, plagioclase feldspar, chlorite, muscovite, and graphite, with secondary Fe-oxide phases (goethite) probable in some samples. Moreover, qualitative energy-dispersive spectrometry (EDS) analyses using EPMA identified various accessory phases, including arsenopyrite, pyrite, pyrrhotite, ilmenite, zircon, and gold. EPMA photomicrographs and backscattered electron images in Little (2006) illustrate the contrast in mineralogical compositions between terrestrial tailings deposits and those in the intertidal marine environment. Most notably, Little (2006) observed an absence of sulphide grains at intertidal locations. This pattern implies that the tailings were heavily diluted upon entry into the harbour, and/or sulphide oxidation or settling is prevalent in shallow marine sediments. Elevated concentrations of sodium (Na, 1170–3280 mg/kg) and boron (B, 1–9 mg/kg) measured in the intertidal samples reflect compositional differences between near-shore and terrestrial samples (Harder 1970; Chester 2000).

25 Quantitative EPMA determined arsenopyrite to be the primary As-bearing phase present in Wine Harbour tailings. Under reduced conditions, the reactivity of sulphides such as arsenopyrite and pyrite is limited, which is illustrated by the absence of reaction rims observed in photomicrographs. In contrast, sulphides in well-drained terrestrial environments exhibited variable states of oxidation, producing secondary phases such as Fe-oxides and Ca-Fe arsenates near surface. The element map in Fig. 5a illustrates this by highlighting the distribution of As, Hg, iron (Fe) and sulphur (S) in an arsenopyrite grain in the Plough Lead mill concentrate sample. This sample was panned from within the foundation of the Plough Lead mill, and consists of a mixture of grey, Fe-rich spheres, visible gold, and Fe-stained, sand-size material. Here, the element map exhibits a distinct Fe-arsenate reaction rim formed at the edge of the grain as a result of sulphide oxidation. An area of elemental Hg was also identified in the same sample (Fig. 5b) and provides direct evidence of Hg loss during amalgamation.

26 Bulk chemical analyses of sediments captured in grab samples and gravity cores indicate that marine sediments in Wine Harbour were heavily influenced by the deposition of historical mine tailings. The ranges of As (4–568 mg/kg) and Hg (<5–7430 µg/kg) concentrations (Table 2) measured in Wine Harbour marine sediments are considerably larger than those reported in bottom sediments from 10 inlets and harbours along the Atlantic coastline of Nova Scotia (As 2–42 mg/kg, n = 157; Hg 10–390 µg/kg, n = 180; Loring et al. 1996). District-scale maps highlight three distinct areas of elevated As and Hg in marine sediments situated down-gradient of the Plough Lead and Old Provincial mill sites at the eastern end of the harbour, and to the west in a small inlet at the mouth of Cooper Brook (Figs. 6 a, b). These maps illustrate the average As and Hg concentrations in grab samples, and the top 15 cm of gravity cores. Reported concentrations in sediment cores are restricted to the top 15 cm on the basis of the ecological significance of these near-surface sediments, as the zone of active bioturbation in marine sediments extends to a mean global depth of 9.7 ± 4.5 cm (Boudreau 1998).

27 Dispersal patterns suggest that adjacent terrestrial tailings deposits are the main source of As and Hg to the marine sediments (Figs. 6 a, b). An exception to this includes the small inlet at the western end of the harbour, which also hosts a mussel aquaculture site. Early accounts by Malcolm (1929) indicate that in 1899, a cyanide plant was used to reprocess historical mine tailings on Cooper Brook, which drains directly into this inlet. However, this brook is not included on historical maps of the area (Faribault 1905), and no cyanide plant structural remains were identified in the field due to the dense cover of vegetation. Thus, definitive identification of the sources of As and Hg to the marine environment in this area will rely on future investigations. Overall, the footprint of elevated As and Hg concentrations in Wine Harbour is likely the combined product of the direct disposal of mine wastes into the harbour between 1862 and 1939, and the subsequent reworking of these contaminated sediments by marine processes.

28 Vertical sediment profiles for each of the gravity cores collected at Wine Harbour showed variations in As, Hg, and other elemental concentrations with depth. Paired with radionuclide tracer data (²¹⁰Pb, ¹³⁷Cs), chemical profiles for two of these cores (WH-04 and WH-23; Fig. 3) illustrate the chronology of metal contamination in Wine Harbour marine sediments (Fig. 7). Lead-210 and ¹³⁷Cs data for these two cores showed the least evidence of mixing near the sediment-water interface and should therefore provide the most robust geochronologies for the sediments in Wine Harbour. Overall, As and Hg profiles for all sediment cores show diminishing concentrations with increasing distance from historical mill sites. Metal(loid) concentrations measured in deep (>25 cm) bottom sediments located near the harbour’s entrance are relatively constant with depth and likely reflect background conditions that pre-date historical gold production. In core WH-02 (Fig. 3), the estimated ranges in naturally occurring As and Hg values are 4–6 mg/kg (median 5 mg/kg) and Hg 5–17 µg/kg (median 11 µg/kg), respectively. These background levels are below the Canadian Interim Marine Sediment Quality Guidelines for both As (7.24 mg/kg) and Hg (130 µg/kg) (CCME 2012). By comparison, As and Hg burdens in cores collected throughout most other areas of Wine Harbour remain above these background values down to a depth of at least 40 cm, with the highest As and Hg concentrations (up to 568 mg/kg and 6860 µg/kg, respectively) observed in sediments from cores WH-08 and WH-23.

29 Chronologically, the peaks in As and Hg concentrations in marine sediment cores correspond roughly with documented periods of mining and milling activity at Wine Harbour (Fig. 2). This pattern is especially evident in core WH-23 (Fig. 7a), where As, Au, and Hg profiles exhibit marked increases above background concentrations between a depth of 50 and 37 cm below the sediment-water interface, before decreasing to lower concentrations in shallower sediments. Lead-210 and ¹³⁷Cs data for this core indicate that the rapid increase in As, Au, and Hg concentrations at about 45 cm coincides with an increase in the amount of ore crushed in the late 1880s, and the subsequent drop in concentrations above 37 cm reflects the sudden halt in production in 1907 (Fig. 2). None of the cores collected during this study were of sufficient length to document the environmental impact of the earliest periods of gold production at Wine Harbour between 1862 and 1880. The down-core profiles of As, Au, and Hg also show that the concentrations of these elements remained elevated in the sediments long after mining activity had ceased in the Wine Harbour gold district, and that the near-surface baseline values of As, Au, and Hg are higher than pre-mining background concentrations.

30 Some cores collected from Wine Harbour also show pronounced peaks in As and Hg concentrations near the sediment-water interface (top 0–1 cm), followed by abrupt decreases in metal burdens directly below. For example, core WH-04 (Fig. 7b) was collected from the western end of the harbour (Fig. 3) and contains near-surface concentrations of 47 mg/kg As and 556 µg/kg Hg, as well as distinct peaks in the concentrations of other elements including cadmium, copper, gold, molybdenum, lead, silver, and sulphur (Little 2006). As discussed by Milligan and Law (2013), many contaminants in aquatic environments are associated with loosely packed aggregates of material called flocs, which consist of colloids, organic material, and small inorganic particles that accumulate at the sediment-water interface. This reactive material has a high specific surface area and is ideally suited to accumulate and transport contaminants in the marine environment. The presence of this floc layer is likely responsible for the spike in metalloid concentrations at the surface of core WH-04, and it may represent an important pathway for the uptake of contaminants by filter-feeding organisms (Koch et al. 2007; Whaley-Martin et al. 2012, 2013; Milligan and Law 2013).

31 The controls on flocculation include particle encounter rate, which depends nonlinearly on concentration, particle contact efficiency and stickiness, and particle break-up due to turbulence (Hill 1996; Milligan and Law 2005; Hill et al. 2013). Large particle concentrations and increases in particle “stickiness” associated with increased organic matter, in combination with low-to-moderate turbulent shear, will increase flocculation rates, which in turn increases the settling velocity and associated vertical flux of fine grained material to the seabed. Naturally occurring flocs have settling velocities on the order of 1 mm s^-1 (Hill et al. 2001; Fox et al. 2004; Curran et al. 2007) and can actively scavenge metals and organic contaminants and rapidly deposit them to the seabed (Milligan and Loring 1997). Downcore observations of the floc fraction in core WH-23 from 37 cm to 50 cm depth, in conjunction with grain size and trace element data, show increases in both the floc fraction and As and Hg concentrations at a time when grain size decreases (Fig. 8). The median diameter of the sediments (d50), calculated from the DIGS, dropped from approximately 16 μm in the upper 30 cm of the core to roughly 13 μm from 37 cm to 49 cm down-core. This increase in fine-grained sediment loading corresponds to the period of increased gold production between the late 1800s and 1907 (Fig. 2), when large volumes of tailings were deposited in Wine Harbour.

32 When interpreting the relative contributions of metal(loid)s from both natural and anthropogenic sources in marine sediments, it is important to consider the natural variability in sediment mineralogy and grain size distribution (Parsons and Cranston 2006). Normalization of metal concentrations against an element of geogenic origin can correct for such variations, and help to distinguish between natural and anthropogenic enrichments (Summers et al. 1996; Covelli and Fontolan 1997). In this study, we used lithium (Li) as a geochemical proxy for variations in sediment grain size, as it is a common component of clay minerals and micas in glaciomarine sediments, is not affected by post-depositional diagenetic remobilization, and is strongly correlated with changes in grain size in the marine sediments of eastern Canada (Loring 1991). Figure 9 shows the concentrations of As, Hg, nickel (Ni), and zinc (Zn) plotted against Li for all marine sediment subsamples (n = 210). The strong correlation between Li and Ni (r² = 0.92) and Li and Zn (r² = 0.83) demonstrates that changes in sediment grain size are the predominant control on the concentrations of these elements in Wine Harbour (cf. Loring 1991). In contrast, plots for As and Hg versus Li show no correlation between the two elements and Li. This lack of correlation confirms that As and Hg concentrations in the Wine Harbour sediments are largely controlled by an external source; in this case, the historical disposal and subsequent redistribution of gold mine tailings.

33 Figure 10 shows the concentrations of As and Hg in marine sediments collected from 14 coastal inlets along the southern and eastern shores of mainland Nova Scotia, including Wine Harbour and inlets near two neighbouring historical gold districts (Isaacs and Seal harbours; Fig. 1). The As concentrations in sediments near all three gold districts are much higher than levels reported for other coastal inlets in Nova Scotia, including industrialized embayments such as Lunenburg Harbour and the LaHave estuary (As data are not available for Halifax Harbour). The Hg burdens in sediments from Wine Harbour are particularly high, reflecting the continuous use of Hg amalgamation for the duration of gold production in this district. The comparatively lower Hg burdens in tailings-contaminated sediments from Seal Harbour reflect the extensive use of cyanidation during the last period of gold mining operations in the Lower Seal Harbour district in the late 1930s (Parsons et al. 2012). The high concentrations of Hg measured in Halifax Harbour sediments are representative of areas contaminated by domestic sewage and effluents from hospitals, dental offices, and industrial sources (Williams 2010).

34 Samples of stream water and mine drainage collected throughout the Wine Harbour gold district show relatively little contamination from historical gold mining operations under low-flow conditions. Table 3 shows selected water quality data from the five sampling sites labeled in Fig. 3. These results represent water compositions during a single sampling event on July 19, 2005, thus do not account for seasonal fluctuations inherent in some chemical parameters. Water pH remained relatively constant across sites, with a range of 5.4 to 5.8. The temperature of the three stream waters (W1, W3, W4) was warm (18–20 °C), whereas the mine drainage flowing from the collapsed adit beneath the Plough Lead mill (W2, W5) was distinctly cooler (6.9–8.6 °C) and had higher specific conductance.

35 All stream waters sampled in the Wine Harbour district exhibit relatively low concentrations of As and Hg. Dissolved concentrations (<0.45 µm) range from 1.0 to 17 µg/L and 4.4 to 7.5 ng/L for As and Hg, respectively. Total (unfiltered) concentrations measure between 1.5 and 23 µg/L for As, and 5.6 and 10 ng/L for Hg. Overall, most of the As and Hg in these freshwater streams is present in dissolved form, or as colloids <0.45 µm in diameter. As expected, the mine drainage originating beneath the Plough Lead Mill (W5) contains higher concentrations of dissolved (23 µg/L) and total As (140 µg/L), reflecting the abundance of arsenopyrite in the underground mine workings. Drainage from this portal also contains the highest total Hg concentration (25 ng/L) of all samples collected, which may be related to the extensive use of Hg in the Plough Lead Mill (Fig. 5b). As this mine drainage passes through the tailings at Site W2, the proportion of As and Hg in the dissolved phase increases and the total concentrations of each element decrease before entering Wine Harbour.

36 In general, dissolved As concentrations in Wine Harbour surface waters are considerably lower than those measured in streams and rivers impacted by mine tailings at 14 other historical gold districts in Nova Scotia. Parsons et al. (2012) reported a range of 0.2 to 6580 µg/L dissolved As (median 117 µg/L), with the highest concentrations associated with standing water on tailings surfaces and in streams running directly through tailings deposits. Background concentrations in mineralized, but unmined, catchments within these gold districts were generally <25 µg/L, which is consistent with the three stream water samples measured in this study. In contrast, dissolved Hg concentrations in surface waters from Wine Harbour are consistent with those measured in surface waters sampled in mined catchments at other historical gold districts (Parsons et al. 2012). Dissolved Hg in waters from the 14 other districts ranged from 1.2 to 61 ng/L. Even in close proximity to tailings deposits, dissolved Hg generally remained below 25 ng/L, suggesting that most Hg in the tailings is present in relatively insoluble forms (e.g., elemental mercury, amalgams, metacinnabar; Parsons et al. 2012).

37 In summary, the relatively low concentrations of As and Hg in stream waters and mine drainage suggest that these freshwater sources are not a major source of contamination to Wine Harbour under relatively low-flow conditions. Additional work would be required to assess the seasonal variations and effects of storms on As and Hg concentrations in the streams that drain into Wine Harbour. Concurrent sampling of marine water from 14 sites in Wine Harbour in July 2005 showed that the dissolved concentrations of As (0.75–1.4 µg/L) and Hg (0.17–4.1 ng/L) are also relatively low in the harbour water (P. Yeats, Fisheries and Oceans Canada, personal communication, 2006). These results are consistent with the work of Doe et al. (in press), who demonstrate that bioaccumulation of As and Hg by organisms living in direct contact with contaminated sediments is the primary risk to ecosystem and human health in the Wine Harbour gold district.