Ore Geology Reviews 92 (2018) 318–347

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Ore Geology Reviews

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Microstructural characterization and in-situ sulfur isotopic analysis of silver- T bearing sphalerite from the Edmond hydrothermal ﬁeld, Central Indian Ridge ⁎ Zhongwei Wua,b,d, Xiaoming Suna,b,c, , Huifang Xud,1, Hiromi Konishid, Yan Wanga,e, Yang Lua,b, Kaijun Caoc, Chi Wanga, Haoyang Zhouc a School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China b Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China c School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China d NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA e South China Sea Branch, State Oceanic Administration, Guangzhou 510310, China

ARTICLE INFO ABSTRACT

Keywords: A close Zn-Ag association has been noted recently in several polymetallic sulfide ore deposits from the Indian Sphalerite Ocean. However, the role of nanotextural controls on “invisible” silver distribution within sphalerite (a sig- Silver nificant Ag-carrier) is still not well understood. In this study, typical Zn-sulfide samples from the Edmond vent Lattice defects field (Central Indian Ridge) can be roughly classified into three different groups based on their chemical com- Seafloor massive sulfide deposits positions and mineral textures. Among them, sulfosalt-bearing, Fe-poor zinc sulfides in sulfate-dominant outer Sulfur isotope chimney walls usually contain higher contents of Ag, Cu and Pb (up to wt% levels) than Fe-rich, massive to Edmond hydrothermal field disseminated sphalerite in Zn-(Fe)-rich chimney fragments coated by silicified crusts. Such sphalerite is represented by colloform/botryoidal aggregates of optically anisotropic ZnS with a strongly disordered structure or hexagonal habit, which are actually formed by coalescence and agglomeration of colloidal nanocrystalline particles. Using high-resolution transmission electron microscopy (HRTEM) and in-situ micro-XRD techniques, we have investigated the ultrastructure and crystal-chemistry of the {1 1 1} twin boundaries and wurtzite-type stacking faults that occur in Ag-rich, colloform or porous dendritic sphalerite. Submicroscopic electrum and Ag nanoparticles appear to nucleate on the micro-/nano-pore walls as cavity-fillings, or occur along grain boundaries between chalcopyrite-tennantite inclusions and the host sphalerite. Interestingly, the inhomogeneous distribution of precious metals and other chalcophile elements is generally concordant with the extent of recrystallization, intragranular porosity as well as various degrees of structural disordering/imperfectness (i.e., bulk defect density) in ZnS domains. Lattice defects and interfaces may play a limited role in promoting the simultaneous introduction of exotic impurities into colloform sphalerite during rapid growth. Even though certain morphological traits and aggregation state at the nanoscale seem to support a biogenic origin of these ZnS particles characterized by admixed polytypic intergrowth structures, the mineralogical and geochemical features of highly-defective sphalerite crystals, in addition to their microscale S-isotope signatures with relatively high δ34S values, exhibit signs of abiologically-mediated, rapid precipitation caused by extensive mixing and cooling at Edmond. The physicochemical conditions and seafloor disequilibrium processes indicated by ZnS formation mechanism might facilitate the incorporation and enrichment of Ag or other trace elements in hydrothermal sphalerite.

1. Introduction ancient/modern volcanogenic massive sulﬁde (VMS) deposits (Hannington and Scott, 1989; Cook et al., 2009; Ye et al., 2011; Sphalerite is one of the most common sulﬁde phases as well as an Lockington et al., 2014). Wurtzite, a high-temperature hexagonal important host mineral for a broad range of minor and trace elements in polymorph of sphalerite, is also the major ore mineral in a number of

⁎ Corresponding author at: School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China. E-mail addresses: [email protected] (X. Sun), [email protected] (H. Xu). 1 Co-corresponding author. https://doi.org/10.1016/j.oregeorev.2017.11.024 Received 21 December 2016; Received in revised form 21 November 2017; Accepted 27 November 2017 0169-1368/ © 2017 Elsevier B.V. All rights reserved. Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347 active and inactive chimneys. Over the past three decades, the potential certain trace elements and in-situ sulfur isotope signatures with TEM economic importance of precious-metal mineralization in zinc sulfide observations of microstructural features can provide us with abundant ores from submarine hydrothermal vent systems has aroused great at- useful information on the influence of deep-sea (extreme) environ- tention and interest. Zn-rich sulfide assemblages have been found to mental factors and mechanisms of the formation of polymetallic sulfide contain high concentrations of both Ag and Au, especially in many VMS deposits. deposits located at mid-ocean ridges (MORs) and back-arc spreading centers (Fouquet et al., 1993; Herzig et al., 1993; Herzig and 2. Geological setting Hannington, 1995; Moss and Scott, 2001). Typically, Ag-Au enrichment in seafloor hydrothermal precipitates is consistently related to a phase The Central Indian Ridge is classified as an intermediate-spreading of low-temperature (< 300 °C) venting, commonly within sulfide ridge, with a full opening rate of ∼47.5 mm/yr (DeMets et al., 1994), chimneys associated with Fe-poor sphalerite and late-stage Pb-Sb-As whose rift valley trends NNW and is 5–8 km wide (Briais, 1995). The sulfosalts (Hannington et al., 1986, 1991, 1995; Herzig et al., 1993). Edmond vent field (23°52.68′S, 69°35.80′E; at a depth range of Recently, the occurrence of “invisible” precious metals has been 3290–3320 m), approximately 160 km NNW away from the Kairei vent reported in a suite of sphalerite-bearing ores from the Edmond chimney field near the Rodriguez Triple Junction (RTJ), is located at the samples that contain up to 18.7 ppm Au and 1450 ppm Ag (Wu et al., northern end of CIR segment S3 on the eastern rift-valley wall about 2016). Similarly, a close Zn-Ag-(Au) association has also been noted in 6 km from the adjacent ridge axis (Fig. 1A). It is constructed on a small several sulfide deposits located along the Southwest Indian Ridge (Ye protrusion that extends south from the eastern rift-valley wall and et al., 2012; Nayak et al., 2014; Wang et al., 2014). These findings forms the northeast corner of a ∼60-m deep basin (Humphris and provide a unique opportunity to examine in greater detail some of the Fornari, 2001; Van Dover et al., 2001). geological factors controlling Au-Ag mineralization in the Indian Ocean The Edmond vent field (∼100 m long by 90 m wide) is dominated hydrothermal systems. However, the microstructural features of these by old, disaggregated sulfide structures, peripheral relict black-smoker zinc sulfides and their roles in facilitating silver or gold enrichment chimneys, and massive sulfide talus, indicating that hydrothermal ac- remain poorly understood. The physicochemical properties of ZnS tivity has been focused at this site over a long period of time (Humphris (especially at the nanoscale) are strongly affected by its formation and Fornari, 2001). Orange-brown, Fe-oxyhydroxide sediments covered processes, and thus may indicate its depositional mechanism and ore- by extensive microbial mats are common at this field, accumulating to forming environment (e.g., Šrot et al., 2003; Moreau et al., 2004; thicknesses of several cm within depressions and coating many of the Ciobanu et al., 2011; Xu et al., 2016). Hence, typomorphic character- sulfide structures and much of the talus. Hydrothermal venting (likely istics (such as textural and compositional fingerprints) of Ag-rich fault-controlled) exhibits a wide range of styles and chimney sphalerite samples may serve as important indicators of their crystal- morphologies. High-temperature venting is manifest as discrete clusters lization conditions. of large chimneys (up to 20 m in height and 2 m in diameter) with Furthermore, the relationship between impurity incorporation and vigorous black-smoker fluids emanating from multiple orifices and defects in crystal structure of sphalerite has not been well established “beehive” structures. Within and between these chimney clusters, yet. Although the solubility limits of trace elements in sphalerite are smaller (up to 5 m high), branched, candelabra-like structures with still not clearly known, previous LA-ICP-MS studies have suggested that orifice diameters of ∼2–20 cm ornament the seafloor and discharge the clustering of precious metals into nanoparticles is favored over their black-smoker fluids at slower flow rates (Van Dover et al., 2001). Like incorporation into the ZnS structure as solid solution (e.g., Cook et al., many other MOR vent fields, widespread diffuse flow and blocks of 2009). To some extent, the partitioning of Au and Ag into nanoparticles anhydrite suggest that sub-surface seawater entrainment and mixing (during sphalerite precipitation from hydrothermal fluids) may be af- processes occur over a broad area. It has also been inferred that sig- fected by non-equilibrium factors, especially the defect density and nificant albitization appears to occur below the Edmond field (Gallant chemical changes/compositional zoning of the host sphalerite. Like- and Von Damm, 2006). wise, extensive incorporation of arsenic and gold nanoparticles in pyrite The Edmond hydrothermal fluids are extremely hot, with a max- is commonly accompanied by formation of vacancies and defects imum temperature of 382 °C (Humphris and Fornari, 2001). All of the (Vikentyev, 2015). Thus, we propose that impurities and nanotextures fluids collected from various vent sites at Edmond (Table 1) are char- may have the same catalyzing effects stimulating the incorporation of acterized by low pH (∼3), high iron content (∼14 mmol/kg), and precious metals in the sphalerite structure. Similar mineralogical/ several mmol/kg of H2S(Gallant and Von Damm, 2006; Kumagai et al., crystallographic controls on trace-element uptake have also been re- 2008). Most notably, the Edmond end-member vent fluids have ported for auriferous sphalerite from some ancient and modern massive chlorinities about 70% greater than local ambient seawater due to sulfide deposits (Wohlgemuth-Ueberwasser et al., 2015; Maslennikov phase separation of seawater at supercritical conditions, making them et al., 2017). Until now, however, little convincing microanalytical by far some of the hottest brines yet observed venting from the Indian evidence has been presented for the precipitation-remobilization of Ocean hydrothermal systems (Van Dover et al., 2001), and thus re- “invisible” silver/gold enhanced by the effects of impurities, intrinsic sulting in unusually high concentrations of several dissolved transition defects or interface during ZnS crystal growth. metals. In this article, we present an integrated mineralogical and geochemical study on typical sphalerite samples from the Edmond hydro- 3. Materials and methods thermal system. This field was among the first two confirmed active vent sites discovered on the Central Indian Ridge (CIR) in the early 3.1. Sampling information 2000s, which represents a typical basaltic-hosted VMS deposit located on intermediate-spreading, sediment-starved oceanic ridges (Van Dover The Edmond hydrothermal precipitates were recovered from the et al., 2001). By using in-situ micro-XRD technique and HRTEM, careful surface of active mounds and relict sulfide deposits during the Chinese characterization of distinct textures and micro-environments in Ag-rich research cruises DY105-17A and DY115-19 (2005–2007) on board the zinc sulfides enable us to relate chemical measurements, phase identi- R/V Dayang Yihao. The locations of active vent sites, relict chimneys fication, and ultrastructural investigation specifically to the occurrences and three sampling stations are shown in a detailed bathymetric map of discrete Ag-Au nanoparticles. The aim of this work is to obtain fur- (Fig. 1B). Basic information about selected sampling sites and typical ther insight into the role of lattice defects in non-equilibrium impurity ore types is listed in Table 2. As described in a previously published incorporation, as well as the enrichment mechanism of precious metal article (Wu et al., 2011), hydrothermal precipitates collected by a TV- elements in hydrothermal sphalerite. Combining the abundance of guided grab sampler represent various types of hydrothermal products

319 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Fig. 1. (A) Regional bathymetric map of the Edmond hydrothermal field (23°52.68′S, 69°35.80′E; 3290–3320 m) located at the northern end of ridge segment S3 on the eastern rift-valley wall (after Van Dover et al., 2001). The inset shows the geographical location of our study area on the Central Indian Ridge (CIR) north of the Rodriguez Triple Junction (RTJ). (B) Detailed map (modified after Kumagai et al., 2008) showing the locations of active vent sites, relict (extinct) chimneys, and three sampling stations at or near the Edmond sulfide mounds.

from the Edmond vent field, including fragments of active “black software. XRD powder patterns of bulk ZnS samples were recorded by a smoker” chimneys, massive sulfide talus or oxidized debris from col- Rigaku D/MAX 2200 VPC X-ray diffractometer (Cu-Kα radiation) at lapsed extinct chimneys, as well as large blocks of anhydrite. Based on 40 kV and 30 mA, with 0.02° step size at a scan rate of 4°/min. the preliminary results of X-ray diffraction (XRD) and geochemical analyses, along with scanning electron microscopy (SEM) and optical 3.2.2. Scanning electron microscopy (SEM) microscopic observations, these representative samples can be gen- Zn-rich sulfide ores were mounted onto aluminum stubs with erally classified into four different ore types: silica-rich hydrothermal double-sided adhesive tapes. Direct observation of uncoated samples precipitates (i.e., silicified crusts), Zn-(Fe)-rich sulfide chimney debris, was performed at UW-Madison using a Hitachi S-3400 N variable sulfate-rich ores (i.e., anhydrite-dominant fragments of outer chimney pressure SEM equipped with Thermo Electron NORAN System SIX. The walls), and Fe-Cu-rich massive sulfide talus. The mineralogy and geo- VP-SEM was operated at 20 kV in low-vacuum mode. For higher spatial chemistry of such ore samples from the Edmond vent field has been resolution, a number of subsamples were further examined with a Zeiss studied in detail (Wu et al., 2016), thus providing a robust context for ΣIGMA field-emission SEM equipped with an X-MAX energy dispersive the TEM characterization. X-ray spectrometer (Oxford Instruments) at the School of Earth Science and Geological Engineering, Sun Yat-sen University (China). For EDS 3.2. Analytical techniques analysis, an accelerating voltage of 20 kV was used to obtain sufficient X-ray counts. The silicon drift detector is capable of high-resolution 3.2.1. X-ray diffraction (XRD) performance for the Au-Mα and Ag-Lα lines. To avoid oxidation during drying, Zn-rich chimney fragments were dried in a vacuum oven for 12 h at intermediate temperatures (∼60 °C). 3.2.3. Electron microprobe analysis (EPMA) In-situ, high-resolution XRD analyses of ZnS crystals were carried out Chemical composition analysis of Zn-sulfide minerals was per- using a Rigaku RAPID II X-ray diffraction system (Mo-Kα radiation) formed by JEOL JXA-8800R electron microprobe using wavelength combined with a microbeam collimator (0.03–0.1 mm in width) at the dispersive X-ray spectroscopy (WDS) at the Instrumental Analysis and Department of Geoscience, University of Wisconsin-Madison (USA). Research Center, Sun Yat-sen University. An accelerating voltage of − Individual grains of selected colloform sphalerite specimens were 20 kV and a beam current of 2 × 10 8 A were used for quantitative carefully polished to obtain flat cross-sections and then affixed onto the elemental determination in zinc sulfide specimens, with an electron end portions of small fiberglass rods attached to an aluminum sample beam diameter of 1 μm. Interference effects caused by peak overlaps holder. Micro-diffraction data were collected on a 2-D image-plate de- were minimized by manual correction. Peak counting times of 20 s were tector. The two-dimensional images were then integrated to produce chosen for most elements except Au, Co and Pb, for which extended conventional 2-theta versus intensity patterns using Rigaku’s 2DP counting times of 40 s were employed. EPMA detection limits for

320 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Table 1 Estimated end-member compositions of hydrothermal ﬂuids sampled from the Edmond vent ﬁeld.

Vent Site Name Marker 2 Marker 10 Marker 12 Marker A Nura Nura White Head Huge Monk Seawater

Depth (m) 3300 3303 3273 3281 3280 3290 3290 – Temperature 273 °C 293 °C 370 °C 382 °C –––2°C pH Value ≤3.02 ≤2.97 3.13 3.13 –––7.8 Cl (mmol/kg) 929 ± 3 926 ± 3 933 ± 3 927 ± 3 946 ± 6 973 ± 15 928 ± 15 542

H2S (mmol/kg) 1.00 ± 0.02 3.79 ± 0.08 4.66 ± 0.09 4.81 ± 0.10 3.98 ± 0.03 1.83 ± 0.04 1.15 ± 0.03 0

SO4 (mmol/kg) −6.72 ± 0.40 −0.385 ± 0.064 0.615 ± 0.012 0.415 ± 0.158 −0.30 ± 0.02 −8.30 ± 0.80 −2.19 ± 0.99 28.2

CH4 (mmol/kg) 0.415 ± 0.025 0.395 ± 0.024 0.381 ± 0.023 0.289 ± 0.017 0.314 ± 0.012 0.283 ± 0.020 0.233 ± 0.016 0.0003 Na (mmol/kg) 698 ± 14 718 ± 14 733 ± 14 721 ± 14 704 ± 14 713 ± 32 697 ± 32 465 Ca (mmol/kg) 58.1 ± 0.6 64.9 ± 0.6 64.1 ± 0.6 63.4 ± 0.6 58.5 ± 1.2 54.9 ± 2.3 55.3 ± 2.3 10.2 K (mmol/kg) 44.7 ± 0.4 45.4 ± 0.4 44.6 ± 0.4 44.2 ± 0.5 40.8 ± 1.2 41.5 ± 2.4 39.1 ± 2.3 10.1 Si (mmol/kg) 20.3 ± 0.2 19.0 ± 0.2 21.0 ± 0.2 20.8 ± 0.2 20.2 ± 0.6 19.6 ± 1.1 18.2 ± 1.1 0.116 Sr (μmol/kg) 165 ± 3 182 ± 4 183 ± 4 184 ± 4 181 ± 6 175 ± 11 177 ± 11 89.9 Fe (μmol/kg) 10500 ± 200 13100 ± 100 13600 ± 100 13900 ± 100 13900 ± 400 11500 ± 700 11800 ± 700 0.001 Mn (μmol/kg) 1450 ± 10 1430 ± 10 1410 ± 10 1430 ± 10 1360 ± 40 1420 ± 80 1360 ± 80 < 0.001 Cu (μmol/kg) 146 ± 7 403 ± 20 111 ± 6 161 ± 10 –––0.004 Zn (μmol/kg) 122 ± 6 149 ± 7 126 ± 6 134 ± 7 –––0.006

(“–”: Not analyzed) The original data cited above are given by Gallant and Von Damm (2006) & Kumagai et al. (2008). selected elements were approximately within the range of 3.2.5. Laser ablation multi-collector ICP-MS (LA-MC-ICP-MS) 100–300 ppm (see Table 3). The following reference materials were Due to the intimate intergrowth of ﬁne-grained sulﬁde aggregates, a used for EPMA measurement and calibration: using pure metals as clean separation of sphalerite and chalcopyrite/tennantite was almost standard materials for Au, Ag, Cd, Cu, Mn and Sn, respectively; syn- impossible to achieve by hand picking. In-situ measurements of S-iso- thetic sphalerite for Zn and S; marcasite for Fe; cobaltite tope ratios enable us to interpret various sulfur sources and precipita-

(Co0.6Ni0.2Fe0.22)1.02As0.95S1.03 for Co and Ni; galena for Pb; SbTe alloy tion mechanisms of ZnS formed at different mineralization stages. To for Sb; InAs compound for As and In. obtain a better understanding of detailed S reduction pathways and related conditions that cannot be resolved from bulk δ34S values, pre- cise and accurate S-isotope analysis at the micron scale was performed 3.2.4. Transmission electron microscopy (TEM) by LA-MC-ICP-MS technique using a New Wave Research (NWR) 193- Carbon-coated samples were carefully prepared by a Fischione nm ArF excimer laser ablation system coupled with a Neptune Plus Model 1010 ion mill with the argon-ion beam voltage ranging from 2.6 (Thermo Fisher Scientific, Bremen, Germany) multi-collector in- to 4.0 kV at a low angle of 10°. Ion-milled thin specimens were placed ductively coupled plasma mass spectrometer at the State Key on molybdenum grids. TEM and selected area electron diffraction Laboratory for Mineral Deposits Research, Nanjing University. Helium (SAED) measurements were carried out using a FEI Titan 80–200 gas was used to transport the ablated materials into the plasma. The spherical aberration-corrected STEM (equipped with a field-emission argon sample gas was mixed with the carrier gas in a cyclone coaxial gun, Cs corrector and Gatan Image Filtering system, operated at mixer before being transported into the ICP torch. The energy fluence of 200 kV) at the Materials Science Center, UW-Madison. HRTEM image the laser is about 3 J/cm2. For single spot analysis, the beam diameter is processing, including the fast Fourier transform (FFT), was completed 25 μm with a laser repletion rate of 8 Hz (see Zhu et al., 2017 for more using Gatan’s Digital Micrograph software (version 3.7). On the other details on experimental methods and instrumental operating para- hand, the morphologies and microstructures of ZnS particles were ob- meters). In this study, the international standard NBS-123 sphalerite served under a JEOL JEM-2010 transmission electron microscope was used as a certified reference material with a δ34S value of (equipped with an Oxford INCA EDS system) with an accelerated vol- +18.13‰ relative to the Vienna-Canyon Diablo Troilite (V-CDT) tage of 200 kV at the Instrumental Analysis and Research Center, Sun standard. For comparison, conventional analyses of bulk S-isotope Yat-sen University. Rinsed sub-samples (prepared by micro-drilling) compositions were performed on ten hand-picked mineral separates of were gently crushed into very fine powders using agate mortar and sphalerite, pyrite and chalcopyrite at the Beijing Research Institute of pestle. The specimens for HRTEM examination were directly prepared Uranium Geology for Nuclear Industry. by depositing an ultrasonically dispersed suspension of ZnS powder from an aqueous solution of alcohol on holey carbon-coated molybdenum grids.

Table 2 Basic information of selected sampling sites from the Edmond hydrothermal ﬁeld.

Station No. Location Depth (m) Types of Ore Samples Mineralogy*

17A-IR-TVG12 69°35.84′E 3293 Silica-rich hydrothermal precipitates Opl + Py + Sp + Gth + Brt 23°52.67′S Zn-(Fe)-rich sulﬁde chimney debris Sp + Py + Mrc + Gd + Gn + S 17A-IR-TVG13 69°35.80′E 3292 Sulfate-dominant fragments of outer chimney walls and anhydrite Anh + Brt + Sp + Py + Ccp + Cv + Tnt + Ttr + Prc + Ele 23°52.68′S blocks 19III-S18- 69°35.85′E 3277 Fe-Cu-rich massive sulﬁde samples and associated pyrite-bearing talus Py + Ccp + Mrc + Brt + Sp TVG9 23°52.64′S

(The above polymetallic sulﬁdes, water depth and longitude/latitude data are provided by China Ocean Sample Repository). * These minerals are roughly listed in descending order of their relative abundance (Wu et al., 2016). Abbreviations: Anh = anhydrite, Brt = barite, Ccp = chalcopyrite, Cv = cov- ellite, Ele = electrum, Gd = gordaite, Gn = galena, Gth = goethite, Mrc = marcasite, Opl = opal-A, Prc = pearceite, Py = pyrite, S = native sulfur, Sp = sphalerite, Tnt = tennantite, Ttr = tetrahedrite.

321 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347 0.014 0.003 0.673 0.014 0.172 0.009 2 apfu 2 apfu 2 apfu 1090 – – – ∼ 250 0.002 0.001 0.003 ∼ 210 ∼ 260 –– –– –– ∼ 210 0.003 0.004 ∼ 150 – – ∼ 190 ∼ Fig. 2. X-ray powder diﬀraction patterns of euhedral to subhedral sphalerite crystals from ed crusts (17A-IR-TVG12B)

fi the Edmond vent field. (A) Zn-Fe-rich sulfide chimney debris (No. 17A-IR-TVG12A); (B) Silica-rich, pyrite-bearing hydrothermal precipitates. 220 ––– 0.005 ∼

4. Results 200 0.001 ∼ 4.1. Morphology and geochemistry of diverse ZnS types de samples. ﬁ ﬁ

140 In typical chimney samples from the Edmond vent eld, the Zn- – ∼ bearing sulﬁde assemblage is dominated by sphalerite (Fig. 2). No. 17A- IR-TVG12 sample mainly consists of Fe-rich, massive sphalerite. Such

sphalerite (referred as SpI), which mostly exhibits dissolution textures 850 –––– 0.001 –––– 0.001 ∼ on mineral surfaces, occurs as coarse-grained, euhedral to subhedral crystals within Zn-(Fe)-rich layers of black smoker chimney (Fig. 3A). Many of these porous sphalerite grains are replaced by small irregular 310

∼ patches of pyrite or void-ﬁlling marcasite (Fig. 3B). Furthermore, SEM observations indicate complex combinations of colloform and dendritic textures becoming more massive along/near the edges of open vugs. 220

∼ Some SpI locally contains well-preserved primary dendritic or remnant colloform-banded textures (rather than exclusively massive or coarse- grained, idiomorphic) within the same sample, and appears to have erent ore types of the Edmond polymetallic sul 160 ﬀ 0.112 0.002 0.873 0.080 0.004 0.901 0.005 0.009 0.973 0.003 ∼ been partially recrystallized (Fig. 3C & D). To a lesser extent, subhedral

to anhedral sphalerite crystals (SpII) are found as isolated granules cemented by branched ﬁlament network or rod-shaped aggregates of 160 opal-A (Fig. 3E), coexisting with pyrite/marcasite disseminated – – – ∼ throughout the late-stage, amorphous silica matrix.

Coalesced globules of colloform sphalerite (SpIII) with at least two 130 ﬁ 34.55 0.04 25.30 1.82 66.21 < mdl 0.03 0.07 0.11 0.21 0.03 0.65 0.05 0.06 0.73 < mdl Coarse-grained, massive and euhedral33.49 or porous dendritic Fe-rich sphalerite in Zn-(Fe)-rich 0.01 chimney debris (17A-IR-TVG12A) 6.57 0.15 59.10 < mdl 0.01 0.01 0.03 0.05 0.01 0.30 < mdl 0.01 0.21 < mdl 99.93 0.128 34.19 0.03 9.46 0.87 64.95 0.09 0.04 0.06 0.09 0.17 0.03 0.89 0.02 0.08 0.39 < mdl Subhedral to anhedral crystals of relatively low-Fe sphalerite disseminated in pyrite-bearing silici 33.43 < mdl32.58 4.64 < mdl 0.24 0.92 60.90 < mdl 0.01 55.16 0.01 < mdl < mdl 0.01 < mdl 0.02 < mdl 0.05 < mdl < mdl < mdl 0.08 0.43 < mdl < mdl < mdl 0.02 < mdl 0.08 < mdl < mdl 99.83 0.078 33.14 0.01 0.60 2.58 66.49 0.99 0.03 0.14 0.06 0.04 0.03 1.43 0.02 0.06 1.04 < mdl Colloform globules or botryoidal32.57 aggregates of Fe-poor sphalerite in sulfate-dominated outer chimney < mdl walls (17A-IR-TVG13) 0.30 0.59 64.56 0.59 0.01 0.06 0.01 0.01 0.01 0.59 < mdl 0.01 0.36 < mdl 99.66 0.005 31.65 < mdl 0.17 0.04 61.98 0.04 < mdl < mdl < mdl < mdl < mdl 0.07 < mdl < mdl < mdl < mdl 32.17 < mdl 0.95 < mdl 37.61 < mdl < mdl < mdl < mdl < mdl < mdl 0.03 < mdl < mdl < mdl < mdl S∼ Se Fe Cu Zn Pb Mn As Sb Codistinct Ni growth Cd bands In can Sn be identi Aged Au particularly Total (wt%) Fe/Zn Ratio in anhydrite- dominant, exterior wall fragments of active chimneys (No. 17A-IR- TVG13). Most of the coarse spherulitic sphalerite fragments display outlines of idiomorphic fan-shaped or roughly rounded crystals that radiate outward from the central portion to the outer margin (Fig. 3F). Some botryoidal ZnS aggregates are observed to be overgrown by ” : below minimum detection limit). Analytical Institution: Electron Microprobe Laboratory, Sun Yat-sen University (China).

(N = 36) clusters of bladed barite grains, usually containing chalcopyrite inclu- (N = 33) (N = 44) I II III sions and/or a minor amount of sulfosalt minerals such as the ten- < mdl Maximum Average atoms per formula unit 1.007 Maximum Average atoms per formula unit 1.009 Minimum Sp Maximum Average atoms per formula unit 1.000 Minimum Minimum Sp Elements (wt%) Detection Limit (ppm) Sp “ ( Table 3 Average EPMA results of Ag-bearing sphalerite in di nantite-tetrahedrite series (Fig. 3G). Sphalerite framboids, which were

322 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Fig. 3. SEM photomicrographs of sphalerite aggregates with various morphologies observed in different ore types. (A) Coarse-grained, subhedral to euhedral sphalerite crystals within Zn- rich layers of sulfide chimneys; (B) Porous, massive sphalerite partially replaced by small irregular patches of pyrite or void-filling marcasite (Note the variation in grey shades indicating variable Fe contents); (C) Fine-grained, dendritic sphalerite overgrowing remnant colloform/spongy pyrite; (D) Relict primary colloform and porous textures locally preserved in massive sphalerite matrix, exhibiting signs of recrystallization; (E) The occurrence of anhedral to subhedral sphalerite grains cemented by branched filament network or rod-shaped aggregates of opal-A disseminated in silica-rich hydrothermal precipitates; (F) Large grains of colloform sphalerite with a roughly rounded shape in sulfate-rich ore samples; (G) Botryoidal/globular sphalerite aggregates containing chalcopyrite and Cu-As-Sb sulfosalt inclusions overgrown by radiating clusters of bladed barite; (H) Isolated framboidal aggregates of densely packed sphalerite microspheres deposited on the surface of euhedral anhydrite phenocrysts (Anh: anhydrite; Brt: barite; Ccp: chalcopyrite; Opl: opal-A; Py: pyrite; Sp: sphalerite; Tnt: tennantite; Ttr: tetrahedrite).

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Fig. 4. Scatter plots of major or minor element concentrations and related ratios for different types of sphalerite observed in the Edmond VMS deposit. (A) Fe versus Zn; (B) Fe versus Cu; (C) Zn/Fe versus Fe/Cd in sphalerite; (D) Total contents of Pb, Cd and Ag plotted against Zn/Fe ratios in massive to disseminated and colloform sphalerite. Note that the majority of sphalerite samples can be divided into two groups. deposited on the surface of euhedral anhydrite phenocrysts, have also limits of electron microprobe. Most dark-/reddish-brown, euhedral to been occasionally observed in individual sulfate-rich samples (Fig. 3H). subhedral grains contain relatively low but detectable levels of Cu, Cd, The EPMA data presented in Table 3 show a negative correlation Co, As and Sb, whereas some sphalerite dendrites with relict colloform between Zn and Fe in sphalerite (Fig. 4A), indicating substitution of Fe and porous textures carry even much higher amounts of Ag (up to for Zn. Hydrothermal sphalerite contains as much as ∼25 wt% Fe, and 0.73 wt%). By comparison, all yellowish-orange/light grey, colloform the Zn content decreases from 66.2 wt% to 37.6 wt%. In the Zn-Fe sphalerite (SpIII) in sulfate-dominated ore samples is uniformly Fe-poor diagram, sphalerite samples from the Edmond vent field are separated (varying from 0.17 to 0.60 wt% Fe), and exhibits only very limited into two distinct groups on the basis of variable Fe and Zn contents, variations with respect to Zn: S ratio. Over 30 spot analyses show that exhibiting two different trends of variation. The relatively low-iron this type of low-iron sphalerite is significantly enriched in Cu, Pb, Cd, sphalerite forms a steeper-slope correlation with a reduced range in Fe As (a few hundred to thousands of ppm) and Ag (with maximum con- (< 1 wt%) compared to the main data trend. Some anomalously ele- tents of 1.04 wt%). Such high Ag concentrations are consistent with our vated Cu concentrations (> 2 wt%) are most likely related to the so- unpublished data obtained by LA-ICP-MS (Fig. A1). called “chalcopyrite disease”, or submicroscopic Cu-As-Sb sulfosalt inclusions (Fig. 4B). 4.2. The occurrence and distribution of silver in sphalerite Based on the variability of minor constituents, these three morphological forms of sphalerite can simply be divided into two groups Besides the very high Ag contents in zinc sulfides, discrete silver- with distinct chemical compositions (Fig. 4C & D). In Zn-(Fe)-rich bearing phases were also commonly identified in those sulfate-domi- chimney debris coated by SiO2-rich crusts, massive to disseminated nant and Zn-(Fe)-rich ore fragments derived from the recent collapse of sphalerite (SpI &SpII) associated with pyrite or marcasite generally sulfide chimneys. Further studies using FESEM-EDS confirmed the contains high Fe concentrations ranging from about 1 to 10 wt%, while presence of abundant precious-metal minerals associated with the as- the abundances of Mn, In, Sn, Pb and Au are commonly below detection semblage of sphalerite + chalcopyrite + tennantite/tetrahedrite. The

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Fig. 5. SEM back-scattered electron (BSE) images of abundant Au-Ag minerals in sulfate-dominant and Zn-(Fe)-rich chimney fragments. (A) & (B) The presence of submicroscopic electrum particles along microcracks or cavity margins in porous sphalerite; (C) Pearceite appears as branch-like or elongated crystals enclosed in colloform sphalerite; (D) The occurrence of spindle-/irregular-shaped acanthite and argentotennantite inclusions as fine-grained patches within sphalerite-hosted tennantite; (E) The presence of submicroscopic acanthite as tiny inclusions or cavity-fillings in remnant colloform/dendritic, porous sphalerite; (F) Discrete native silver grains scattered around the rhythmically banded sphalerite relicts. EPMA spot analyses indicate that high Ag contents in some of the massive sphalerite samples were probably inherited from their colloform precursors (Acn: acanthite; Ag: native silver; Ag-Tnt: argentotennantite; Ccp: chalcopyrite; Ele: electrum; Prc: pearceite; Sp: sphalerite; Tnt: tennantite). geochemical affinity of Ag and Au for low-Fe, colloform sphalerite been found locally as tiny blebs or cavity-fillings in remnant colloform/ seems to be a general feature of primary precious-metal enrichment in dendritic, porous sphalerite (Fig. 5E). In some cases, isolated native Ag mid-ocean ridge VMS deposits. As shown in Fig. 5A & B, micron- to grains are scattered around the rhythmically banded/wavy-shaped submicron-sized electrum particles (with high Ag/Au ratios) are usually sphalerite relicts overgrown by (or partially recrystallized to) massive precipitated within microcracks or distributed along cavity margins in and euhedral SpI aggregates (Fig. 5F). porous sphalerite coexisting with Cu-Fe sulfides and sulfosalts. As de- In addition to spot analyses (N = 113), EPMA-WDS mapping was termined by EDS (Fig. A2), the normalized composition of these natural conducted on several grains to characterize the distribution patterns of

Au-Ag alloys expressed in mole fractions is Au0.31Ag0.69 – Au0.87Ag0.13 major and minor elements in sphalerite with various morphologies, (Wu et al., 2016). involving Fe, Cu, Zn, Pb, As, Sb, Cd and Ag. We have eliminated all the To a lesser extent, minor amounts of pearceite occur as branch-like Au maps representing spurious signals, because Au concentrations in or elongated crystals enclosed in Fe-poor, colloform SpIII globules (see sphalerite are mostly below the minimum detection limit of electron Fig. 5C). Moreover, ﬁne-grained patches of argentotennantite as well as microprobe (∼0.1 wt%). A representative set of WDS elemental maps spindle-/irregular-shaped acanthite inclusions are occasionally ob- shows apparent compositional zoning patterns in either fan-shaped/ served within sphalerite-hosted tennantite (Fig. 5D). In Zn-(Fe)-rich rounded globules or coarse-grained anhedral crystals, thus providing a chimney debris, a large amount of discrete acanthite particles have qualitative indicator of chemical variations in both colloform and

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Fig. 6. EPMA-WDS element maps of typical Ag-bearing sphalerite. (A) Fine-grained colloform sphalerite associated with tiny patches of tennantite rimming a core of chalcopyrite; (B) Roughly rounded sphalerite globules containing discrete micron-sized sulfosalt inclusions but without chalcopyrite. Note the relatively higher Ag, Cd and Cu levels near the inner parts (but often coupled with an increase of Pb intensity towards the outer margins) as revealed by colored scale bars shown in each image.

massive porous sphalerite samples (see Fig. 6 & Fig. A3). In many cases, (Fig. 6B). Anomalously high measured levels of As, Sb and Ag are a suite of complex Ag-rich sulfosalts (such as pearceite and argento- probably attributable to the presence of submicroscopic sulfosalt in- tennantite) are present as tiny patches surrounding the chalcopyrite clusions as described above. As revealed by colored scale bars shown in core (Fig. 6A), or as isolated inclusions hosted in the Fe-poor ZnS matrix each image, it should be noted that impurities of Ag, Cd, Fe and/or Cu

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Fig. 7. Colloform sphalerite globules within anhydrite-dominant chimney wall fragments in transmitted polarized light. (A) Optical photomicrograph in transmitted light (parallel nicols); (B) Optical micrograph obtained by polarized light microscopy (crossed nicols); (C) Numerous ZnS lamellae of variable length (from millimeter to micron scale) embedded within a layered matrix of sphalerite showing the characteristic acicular or radiating fibrous texture; (D) An ion-milled cross-section of anisotropic sphalerite revealing the morphology of microcrystalline aggregates. tend to be enriched near the central parts (but often coupled with an polarized transmitted light microscope (Fig. 7B). At higher magnifica- increase of Pb level towards the outer margins). tion, we have even observed numerous ZnS lamellae of variable length (from sub-mm- to μm-scale) embedded within a layered matrix of 4.3. In-situ micro-XRD characterization of colloform sphalerite sphalerite showing the characteristic acicular or radiating fibrous texture (Fig. 7C). In most cases, the ion-milled cross sections of anisotropic

In reflected light, doubly-polished thin sections of colloform spha- SpIII samples seem to reveal complex polycrystalline morphologies of lerite globules appear a homogeneous grey color and reveal no ob- colloidal sphalerite aggregates (Fig. 7D). servable effects induced by internal reflections. However, two sub- High-resolution X-ray diffraction (XRD) was carried out specifically generations of sphalerite with a well-defined band boundary can be to determine whether the ZnS forming colloform aggregates was the clearly recognized under plane-polarized light (as shown in Fig. 7A). more common cubic form “sphalerite” or its associated hexagonal

Both SpIII-a (occupying the inner parts of colloform sphalerite) and SpIII- polymorph “wurtzite”. As shown in Fig. 8, the micro-XRD patterns for b (constituting the micron-scale outer layer) display remarkable varia- all three SpIII samples (measured from core to rim across individual tions in color from light orange to pale yellow, but rarely exhibit a grains) match well to cubic sphalerite (3C-ZnS) phase, whereas most of multilayered structure of subtle growth-banding. The early-formed the interlayers or inner cores appeared to contain minor chalcopyrite subgeneration SpIII-a is slightly darker, and contains abundant chalco- and tennantite, as well as a small amount of wurtzite polymorph pyrite or tennantite inclusions which are totally lacking in the later (noting the appearance of two weak shoulder peaks that have similar subgeneration, relatively Pb-rich SpIII-b. positions in the standard spectrum of 6H-ZnS). By contrast, conven- It is well known that sphalerite is an isotropic mineral, which tional powder XRD analyses of two bulk samples (SpI &SpII) both crystallizes in the cubic system with space group Fm43 . Noteworthily, showed the well-deﬁned spectra of sphalerite ± pyrite with intense colloform sphalerite in outer chimney walls commonly exhibits distinct and sharp peaks (Fig. 2), but did not identify any wurtzite phase in Fe- optical anisotropy between crossed nicols, as revealed by cross- rich, euhedral-subhedral ZnS crystals.

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Fig. 8. (A)–(C) Representative SEM photomicrographs of colloform sphalerite in sulfate-rich ore samples. (D) In-situ XRD patterns from core to rim of these selected grains indicate that such optically anisotropic ZnS might crystallize in admixed polytypic intergrowth structures, perhaps with only a small amount of hexagonal wurtzite phases. Reference peaks are labeled with Miller indices corresponding to well-deﬁned crystal faces for cubic sphalerite.

It is worthy of note that X-ray diffraction peaks are significantly 4.4. Structural disorder in Ag-bearing ZnS crystals broadened when the crystal lattice becomes more imperfect, possibly due to the very small size of crystallites and extremely high density of Because of the high similarity between hexagonal and cubic ZnS dislocations or other lattice defects. Anomalous peak broadening ob- structures, we can neither unequivocally confirm/exclude the existence served in these XRD patterns may indicate a mixed-layer structure of of certain hexagonal ZnS polytype nor calculate the proportion of sphalerite and (extremely thin) wurtzite domains with highly dis- wurtzite phase according to the above XRD results alone. It is still ne- ordered stacking sequences. But in some cases, the stacking faults did cessary to combine the micro-XRD data with TEM examinations to in- not occur in sufficient abundance to produce visible diffraction effects vestigate the presence of lattice-scale defects and nanometer-sized in- on XRD spectra, thus causing very little change in the bulk stacking clusions in anisotropic ZnS. Here, we mainly focus on several specific sequence of the cubic close-packed (ccp) sphalerite structure. We rule regions containing high Ag concentrations. Abundant discrete grains of out the introduction of planar defects attributed to mechanical de- electrum and native silver occur predominantly as cavity-fillings formation, because the presence of structural disorder produced by (< 100 nm) trapped inside colloform sphalerite with high densities of crushing and grinding was almost negligible in preparation of ion- intragranular pores, microcracks and planar defects (Fig. 9A), or occupy milled/powder TEM samples. intermediate paragenetic positions between early-formed chalcopyrite and later tennantite (Fig. 9B & C). Some of the submicroscopic Ag

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Fig. 9. Low-magnification TEM bright field (BF) images of submicroscopic precious-metal minerals closely associated with sphalerite-chalcopyrite-tennantite assemblages. (A)–(D) Submicron- to nano-sized gold and silver particles are mostly present either as cavity- or fracture-fillings along grain boundaries between sphalerite and chalcopyrite/tennantite, or as tiny inclusions trapped inside fine-grained chalcopyrite and the host sphalerite. Note the relatively high density of planar defects distributed in porous ZnS domains adjacent to those electrum and/or native Ag inclusions (Ag: native silver; Ccp: chalcopyrite; Ele: electrum; Sp: sphalerite; Tnt: tennantite). particles are locally hosted in primary Cu-Fe sulfides adjacent to crystal rings (Fig. 11B). The d-spacing values and ring-pattern structure in- boundaries, preferentially localized next to stacking faults or twins dicate that ZnS aggregates consist of randomly oriented, finely crys- (Fig. 9D). talline sphalerite clusters with a primary size of ∼5–10 nm. Close in- Furthermore, TEM imaging of selected areas from the inner core and spection of randomly selected powder particles shows irregular interlayer of ion-milled samples shows the most common type of planar boundaries separating grains of different orientations. It is worth noting faults observed in the subgeneration SpIII-a crystals are twin boundaries that a majority of these ZnS nanocrystals contained structural defects, and stacking faults (Fig. 10A–E). As indicated by the SAED patterns such as simple twins and single or multiple stacking faults which mostly (Fig. 10B), numerous wurtzite-type stacking faults and multiple parallel extend along the {1 1 1} close-packed layers of ZnS structure twinning in strongly disordered sphalerite give rise to narrow streaks of (Fig. 11C–F). The presence of structural defects within the observed scattered X-ray intensity or elongated rel-rods (reciprocal-lattice rods) domains may play an important role in generating local lattice-fringe perpendicular to the stacking-fault plane. Likewise, within optically irregularities. Although most of these ZnS nanocrystals were identified anisotropic regions, strong streaking also indicates a high density of as sphalerite, the presence of wurtzite-2H was also confirmed based on stacking faults that extend along the {1 1 1} planes (Fig. 10E). In detail, the calculated interplanar spacing and angles using its corresponding the nanoscale textural complexity is further highlighted by sets of ir- FFT (Fig. 11G & H). regular [1 10] twins (Fig. 10F). By contrast, the dominant component of Fe-rich, massive and eu- On the other hand, a lot of 6H-ZnS nanolamellae with the super- hedral zinc sulfides is 3C sphalerite with the associated SAED patterns lattice structure have been commonly observed in anisotropic inter- suggestive of an almost perfectly ordered structure (Fig. 12A & B), layers coexisting with 3C-ZnS domains (Fig. 10G–J). Relevant crystal- featuring significantly less (lattice-scale) defects of which most abun- ∗ lographic relationships between the two polytypes are illustrated in the dant are twin boundaries and single stacking faults along (hkl) direc- HRTEM images (i.e., multiple domains of well-ordered lattice fringes tions (Fig. 12C). Indexing of the HRTEM image is illustrated by the with ∼9.3 Å), with orientations shown by indexed SAED patterns corresponding SAED (Fig. 12D), which does not reveal any pure wurt- (Fig. 10H). Relationships across the grain boundary can also be clearly zite (2H-ZnS) phase. However, similar to those colloform ZnS globules seen from the orientation of dominant lattice fringes. Transformation with twinned or disordered structures, an increase of (overall) defect ∗ into wurtzite-6H takes place by stacking/twinning along the (1 1 1) density has also been observed in relatively low-Fe, porous dendritic ∗ direction of initial sphalerite (3C polytype) which corresponds to the c sphalerite crystals (Fig. 12E & F). axis of wurtzite or other hexagonal ZnS polytypes. On the contrary, the outer rims of colloform sphalerite with low density of stacking faults 4.5. Sulfur isotope compositions of zinc sulfides and wurtzite domains display a relatively well-ordered or at least slightly disordered structure (Fig. 10K & L). Several tens of selected sphalerite grains from two sampling stations Crystal-structure information on polycrystalline ZnS colloidal par- (including a total of 32 spots) were analyzed by LA-MC-ICP-MS ticles was obtained by HRTEM study of spherulitic sphalerite samples (Table 4). Bulk sulfur isotope ratios were determined for a suite of (Fig. 11A). The corresponding SAED patterns display diffuse powder sulfide and sulfate species covering different ore types (Table 5). The

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Fig. 10. TEM images and corresponding SAED or FFT (inset) patterns of ion-milled sphalerite samples. (A) Strongly disordered ZnS domains adjacent to the inner core of colloform sphalerite containing chalcopyrite inclusions. (B) & (C) HRTEM photomicrographs and respective SAED patterns showing the structure of parallel {1 1 1} twin boundaries and stacking faults. (D)–(F) TEM images and corresponding SAED patterns of highly defective ZnS domains within the interlayer of colloform sphalerite containing acicular or ﬁbrous lamellae. (G)–(J) TEM images and corresponding SAED or FFT (inset) patterns of wurtzite-6H domains within the interlayer (optically anisotropic regions) of colloform sphalerite. Abundant planar defects observed in both polytypic structures probably represent a transitional stage of phase transformations in zinc sulﬁde crystals. (K) & (L) HRTEM image and SAED pattern of relatively well- ordered ZnS domains in the outer rim of (partially recrystallized) colloform sphalerite.

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two samples analyzed, implying a moderate admixture of magmatic S or show only minor effects of sulfide oxidation. However, it must be pointed out that spectral interferences of doubly-charged ions (68Zn2+ and 64Zn2+) currently cannot be removed completely during S isotopic analysis by MC-ICP-MS, because the mass resolution is not high enough to separate them from 34S+ and 32S+. Although the use of matrix-matched standards for calibration can provide a good alternative to resolve this problem, some of the Edmond sphalerite samples containing a significant amount of Fe were compo- sitionally different from the NBS-123 standard (2.41 wt% Fe) and did not minimize the matrix effects. Fortunately, a mixed solution of both 10-ppb Zn and S has been measured at Nanjing University using a Thermo Fisher Scientific Element XR high-resolution ICP-MS to evaluate the potential interferences of Zn2+ on 34S+ and 32S+. The in- tensities of Zn doubly-charged ions were found to be very intermittent (consistently less than 20 cps), which hence contribute only 0.39‰ bias; while the maximum range of S isotope variation in Fe-bearing sphalerite from both stations is up to about 3.6‰. It means that such a correlation trend in this study is robust, rather than caused by analytical artefacts.

5. Discussion

5.1. Textures and composition of sphalerite: Implication for Ag enrichment

The mineral associations and their paragenetic sequence are sum- marized in Fig. A4. Within the investigated samples, we have dis- tinguished several types of mineral textures and morphologies associated with initial crystallization or subsequent recrystallization, which are in accordance with at least three generations of sphalerite as previously identified (Wu et al., 2016). Zinc sulfides commonly form primary depositional structures that involve the aggregation of colloidal microcrystals, leading to the formation of immature “colloform” or “framboidal” textures. Barrie et al. (2009) suggested that the dominant factor was a high degree of supersaturation resulting in rapid nucleation/crystallization. Similarly, the porous dendritic sphalerite is formed by rapid cooling as vent fluids enter the chimney structure, but complex channelways through the ZnS matrix eventually impede the turbulent flow and cause more diffuse venting (Hannington et al., 1995). More compact but still porous textures might represent an intermediate stage of the modification of original sphalerite to fully massive aggregates, as porosity is reduced during replacement/recrystallization processes (Wohlgemuth-Ueberwasser et al., 2015). The continuous flow of fluids through the active mound during protracted, multistage hydrothermal events has led to progressive annealing, cementation and dissolution- reprecipitation of earlier chimney debris or sulfide talus, resulting in

subhedral to euhedral SpI crystals with well-defined, massive textures. Fig. 11. (A) & (B) High-magnification TEM image and corresponding SAED pattern of Overall, contents of minor/trace elements in three types of spha- defect-containing or defect-free ZnS polycrystalline nanoparticles obtained from powder samples (No. 17A-IR-TVG13) prepared by crushed spherulitic sphalerite grains on holey lerite typically range over several orders of magnitude. For example, carbon-coated molybdenum grids. (C)–(F) Detailed HRTEM images and respective FFT some ZnS samples are characterized by enrichment in Cu (varying from patterns showing lattice fringes in randomly oriented, finely crystalline sphalerite. Both hundreds of ppm to several wt%). To evaluate the relationships be- the identified twin boundary and single stacking faults (highlighted by yellow dash lines) tween Ag and other chalcophile elements, we have calculated correla- extend along the sphalerite {1 1 1} planes. The ZnS nanocrystal displayed in (G) & (H) has tion coefficients for EPMA spot analyses. It is evident that Ag have been identified as wurtzite-2H domain. strong correlations with both Cu and Cd, especially for most of the Fe-

poor SpIII globules (r > 0.8, N = 36), which are commonly associated 34 microscale S-isotope results showed a narrow range of δ S values with anhydrite or barite. Silver and lead concentrations in colloform varying from +6.66‰ to +10.23‰, with an average of +7.59‰ sphalerite matrix can even reach wt% levels and closely match our (Fig. 13). Notably, minor element variability in individual sphalerite unpublished LA-ICP-MS results, whereas later coarse-crystalline, sub- grains (e.g., zonation in Fe and Pb distribution) appears to be related to hedral to euhedral sphalerite become somewhat depleted in Ag and Pb 34 subtle changes in δ S (typical of hydrothermal sulfur in seaﬂoor VMS (Table A1), which are best explained by their slower growth rates at ores), with a heavier signature signiﬁcantly correlating with increasing higher temperature. Notably, minor sphalerite displaying both porous

Zn/Fe ratios or Pb concentrations towards the outer sections, either dendritic and colloform textures in Fe-rich massive SpI aggregates ﬁ across the Zn-(Fe)-rich layers coated by silici ed crusts or within sul- contains substantial amounts of Ag (comparable with SpIII) and mod- fate-rich exterior chimney walls (Fig. 14). In addition, anhydrite and erate Sb. Such remnant growth structures are likely resulted from fast barite clusters from some chimney fragments are characterized by quenching under high temperature-gradient conditions, which may be 34 unusually light sulfur, with δ S values of +15.5‰ and +16.1‰ in the particularly suitable for the deposition of silver and gold. Therefore,

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Fig. 12. Representative HRTEM images and corresponding SAED or FFT (inset) patterns of No. 17A-IR-TVG12 powder specimens. (A)–(D) Relatively ordered or slightly disordered ZnS particles with low density of lattice defects obtained from coarse-grained, massive sphalerite. Note a sparse distribution of twin boundaries and single stacking faults in the Fe-rich domains of euhedral to subhedral sphalerite crystals. (E) & (F) Relatively high defect density observed in low-Fe, porous dendritic sphalerite samples.

elevated Ag values in some of the SpI samples were probably inherited dendritic to massive texture. from their colloform/dendritic ZnS precursors (due to lack of an- The EPMA dataset demonstrates that (mean Ag concentrations) > nealing). Obviously, Ag and other trace elements might be expelled 1000 ppm levels within sphalerite make it a dominant carrier of silver from sphalerite during recrystallization from colloform or porous in the Edmond VMS deposit, when compared to other major sulﬁde

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Table 4 Microscale sulfur isotopic compositions of the Edmond zinc sulﬁdes analyzed by LA-MC-ICP-MS.

34 Spot No. Description of Sphalerite Occurrence and Textures δ SV-CDT (‰) Error (2σ) Fe/Zn Ratio

(N = 7) Zn-(Fe)-rich sulﬁde chimney debris (No. 17A-IR-TVG12A) 6.97 ± 0.18 (Average) 0.105

SpI-01 Fe-rich cores of euhedral granular sphalerite aggregates 6.66 0.16 0.172

SpI-02 High-iron zones of porous, massive sphalerite aggregates 6.88 0.21 0.104

SpI-03 Relatively low-iron margins of massive sphalerite crystals 6.96 0.18 0.123

SpI-04 High-iron zones of porous, massive sphalerite aggregates 6.89 0.18 0.101

SpI-05 Relatively low-iron margins of massive sphalerite crystals 7.09 0.21 0.087

SpI-06 Coarse-grained, subhedral sphalerite coexisting with pyrite 7.18 0.18 0.076

SpI-07 Coarse-grained, subhedral sphalerite coexisting with pyrite 7.16 0.15 0.076 (N = 5) Silica-rich hydrothermal precipitates (No. 17A-IR-TVG12B) 7.47 ± 0.20 (Average) 0.050

SpII-01 Subhedral sphalerite aggregates associated with pyrite 7.34 0.19 0.060

SpII-02 Subhedral sphalerite aggregates associated with pyrite 7.37 0.19 0.059

SpII-03 Subhedral sphalerite aggregates associated with pyrite 7.47 0.22 0.048

SpII-04 Fine-grained, anhedral sphalerite disseminated in silica matrix 7.62 0.20 0.042

SpII-05 Fine-grained, anhedral sphalerite disseminated in silica matrix 7.54 0.19 0.043 (N = 20) Sulfate-rich exterior chimney walls (No. 17A-IR-TVG13) 7.84 ± 0.20 (Average) 0.005

SpIII-01 Interlayer bands of Fe-poor, colloform sphalerite globules 7.46 0.16 0.005

SpIII-02 Interlayer bands of Fe-poor, colloform sphalerite globules 7.53 0.18 0.007

SpIII-03 Interlayers of sphalerite containing tennantite inclusions 7.22 0.13 0.005

SpIII-04 Rims of ﬁne-grained sphalerite overgrown by barite clusters 10.23 1.10 0.003

SpIII-05 Inner-core regions of tennantite-bearing sphalerite globules 7.56 0.18 0.005

SpIII-06 Botryoidal ZnS aggregates without chalcopyrite inclusions 7.46 0.12 0.003

SpIII-07 Interlayers of sphalerite containing Ag-sulfosalt inclusions 7.85 0.17 0.004

SpIII-08 Outer rims of chalcopyrite-bearing sphalerite globules 7.76 0.16 0.005

SpIII-09 Botryoidal ZnS aggregates without chalcopyrite inclusions 7.90 0.18 0.004

SpIII-10 Inner-core regions of tennantite-bearing sphalerite globules 7.50 0.11 0.004

SpIII-11 Interlayers of sphalerite containing Ag-sulfosalt inclusions 7.79 0.12 0.009

SpIII-12 Interlayers of colloform sphalerite without Cu-As sulfosalts 8.20 0.15 0.003

SpIII-13 Interlayers of sphalerite containing chalcopyrite inclusions 7.44 0.18 0.005

SpIII-14 Outer rims of tennantite-bearing, small sphalerite globules 8.17 0.16 0.005

SpIII-15 Outer rims of tennantite-bearing, small sphalerite globules 8.12 0.17 0.004

SpIII-16 Inner cores of sphalerite containing chalcopyrite inclusions 7.71 0.15 0.005

SpIII-17 Interlayer bands of Fe-poor, botryoidal sphalerite aggregates 7.70 0.14 0.005

SpIII-18 Inner cores of tennantite-bearing, coarse sphalerite globules 7.70 0.15 0.005

SpIII-19 Interlayers of sphalerite containing Ag-sulfosalt inclusions 7.86 0.18 0.005

SpIII-20 Interlayers of sphalerite containing chalcopyrite inclusions 7.54 0.17 0.004

Analytical Institution: State Key Laboratory for Mineral Deposits Research, Nanjing University (China). minerals with relatively low Ag contents (such as chalcopyrite and (such as galena or Pb-Ag sulfosalts) is not commonly detected under pyrite, see Tables A2 & A3). Although practice indicates that unusually field-emission SEM at magnifications of up to 5000×. In fact, most LA- high Ag and Pb concentrations are almost always attributed to sub- ICP-MS time-resolved spectra of massive to euhedral SpI show flat microscopic Ag- or Pb-mineral inclusions (e.g., Maslennikov et al., profiles for Ag and Pb, indicating homogeneity on the scale of the ab-

2009; Radosavljević et al., 2016), a discrete, visible Pb-bearing phase lation crater (∼50 μm); whereas in some colloform SpIII with

Table 5 Bulk S-isotope compositions of sulﬁde and sulfate minerals from the Edmond hydrothermal ﬁeld.

34 Station No. Sample Description Mineral δ SV-CDT (‰) Data Source

17A-IR-TVG12 Grey-black, Zn-(Fe)-rich chimney fragments coated by reddish-brown, partly siliciﬁed crusts and Sphalerite 5.5–5.9 This study associated sulﬁde-impregnated hydrothermal precipitates with nodular structures Pyrite + Marcasite 5.3–5.8 N=4 Sphalerite + Pyrite 5.7–6.5 (Wang et al., Pyrite + Sphalerite 7.0 2012) N=3 Sphalerite 6.14–6.38 (Zeng et al., Pyrite 5.22–6.57 2017) N=10

17A-IR-TVG13 Massive blocks of anhydrite-dominant ore samples with disseminated sulﬁdes and sulfate-rich Anhydrite + Barite 15.5–16.1 This study exterior wall fragments of columnar chimney structures with ﬂuid conduits coated by a thick Sphalerite + Chalcopyrite 7.9 N=3 layer of orange-brown ferric oxyhydroxides Pyrite 6.7–7.2 (Wang et al., 2012) N=3 Sphalerite 6.61–7.04 (Zeng et al., Chalcopyrite 7.54 2017) Pyrite 6.03–6.87 N=5

19III-S18-TVG9 Porous Fe-Cu-rich, pyrite-bearing massive sulﬁde talus with minor amounts of sphalerite and Pyrite + Marcasite 6.2–7.3 This study barite Chalcopyrite + Pyrite 7.4–7.8 N=5 Pyrite 7.25 (Zeng et al., Chalcopyrite 6.40 2017) N=2

Analytical Institution: Beijing Research Institute of Uranium Geology for Nuclear Industry (China).

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tetravalent cations would appear to enhance Ag incorporation (Belissont et al., 2014). The mechanism of As or Sb incorporation into sphalerite may involve vacancies accompanied by formation of defects, which is speciﬁed as follows: (As or Sb)3+ + nAg+ +(1− n)□ ↔ 2Zn2+, where n = 0 or 1. During ZnS crystal growth with increased amounts of Ag and Cu addition (via heterovalent substitution), the excess Ag ions may be preferentially located at interstitial sites in the lattice (Cu can provide charge balance), and thus could create a tensile strain or even structural distortion. Therefore, we believe these microanalytical data imply that “invisible” silver is most likely present as lattice-bound element and submicron- to nano-sized inclusions trapped within the sphalerite-chalcopyrite-tennantite assemblage (e.g., nucleated along interfaces near local defects, deposited on the pore walls, or adsorbed onto mineral surfaces). Moreover, the weak correlation between Pb and As (or Sb) can best be interpreted in terms of Pb-As-Sb sulfosalt nano-inclusions rather than any coupled substitution at the atomic level. Although minor amounts of Pb may be present in solid solution, as inferred from the

smooth profile for Pb in massive to euhedral SpI free of galena and sulfosalt inclusions (Fig. A1), the absence of correlation between Pb and Zn in the total dataset suggests that there is no direct evidence for 2+ 2+ Fig. 13. A histogram showing the sulfur isotopic composition of sphalerite with different isomorphous substitution of Zn by Pb in the crystal structure of modes of occurrence from the Edmond hydrothermal precipitates. Conventional bulk sphalerite and wurtzite. analytical data are also shown for comparison, including the δ34S values of hand-picked Silver concentrations vary in different ZnS types because the extent sulfide minerals measured in this study and given by Wang et al. (2012), Zeng et al. of element substitution and fractionation in sphalerite depends on (2017). crystallization temperature, pressure, pH values, metal source and the amount of sphalerite in these ore samples. The sensitivity of sphalerite significantly higher abundances of Ag, Cu, As and Sb, ragged/irregular composition to physicochemical variables of hydrothermal fluids in a profiles and high variability between individual ablation spots reflect large number of ore deposits are widely interpreted to reflect relative that these elements are clearly linked to the presence of tennantite- temperature and sulfur activities which may influence gold/silver tetrahedrite, argentotennantite or pearceite micro-inclusions. grades during the formation of polymetallic sulfide deposits (e.g., Cook Several authors have suggested that significant quantities of silver et al., 2009; Ye et al., 2011; Murakami and Ishihara, 2013; Frenzel can be incorporated in the sphalerite lattice (e.g., Taylor and Radtke, et al., 2016). Thus, the iron content of sphalerite (together with dif- 1969; Cook et al., 2009; Ye et al., 2011). The strong positive correla- ferent sulfide mineral equilibria) may be considered as useful petrologic tions between the contents of Ag and Cu (or Cd), as well as the oc- indicators of the sulfidation state or other conditions favorable for Au- currence of Ag in Cu-/Cd-rich domains (especially for colloform SpIII Ag mineralization in seafloor VMS deposits (Hannington and Scott, from the outer chimney walls) imply that Ag is possibly involved in a 1989). According to Scott and Barnes (1972), the observed Fe-content general coupled substitution mechanism proposed by Johan (1988).A decrease in sphalerite grains from the interior Zn-(Fe)-rich chimney negative correlation is also noted between (Zn + Fe + Cd) and portions to the exterior silicified crusts and sulfate-rich walls can be (Ag + Cu + As + Sb), probably reflecting a possible role for a limited attributed to decreasing temperature, increasing sulfur fugacity or both. degree of 2Zn2+ ↔ (Ag, Cu)+ + (As, Sb)3+ coupled substitution, to- Similarly, variations in Cd, Cu and Pb contents of colloform sphalerite gether with simple substitution of bivalent cations as Zn2+ ↔ (Fe, with sector zoning probably reflect fluctuating changes in fluid chem- Cd)2+. Hence, the presence of As3+,Sb3+ and other trivalent/ istry (e.g., trace-metal levels) and/or deposition temperature.

34 Fig. 14. Relatively heavier δ S values of sphalerite correlating with increasing Zn/Fe ratios (SpI &SpII) or Pb contents (SpIII) at each two sampling stations (A) No. 17A-IR-TVG12 and (B) No. 17A-IR-TVG13, respectively.

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Recently, Keith et al. (2014) found out that sphalerite from sedi- ordered and crystalline state, perhaps through the process of partial ment-starved MOR settings exhibits a positive correlation between the recrystallization. Fe/Zn ratios and fluid temperatures. Accordingly, we can estimate Interestingly, both sphalerite and minor wurtzite coexist in the same minimum temperatures of sphalerite precipitation in the Edmond field. grain, despite the fact that the inversion temperature (> 1000 °C) for This newly proposed thermometer is applicable for three types of impurity-free ZnS is far above the range of temperatures measured at sphalerite formed at different mineralization stages. After excluding this vent site. The formation of such distinct structures can be explained those samples affected by post-depositional metamorphic overprint, by different factors. Firstly, wurtzite is favored by rapid precipitation average ZnS formation temperatures of ∼326 °C (N = 44), ∼287 °C from highly oversaturated aqueous solutions characterized by a low (N = 33) and ∼231 °C (N = 36) were roughly calculated for dendritic fugacity of sulfur (Scott and Barnes, 1972). The growth rates tend to or massive to euhedral sphalerite within Zn-(Fe)-rich layers, subhedral have a positive correlation with the fraction of disordered crystals. In to anhedral sphalerite disseminated in silica-rich crusts and colloform many cases, extreme ZnS supersaturation may cause rapid metastable sphalerite from the outer chimney walls, respectively. These estimated precipitation of wurtzite rather than sphalerite, due to the relative temperatures are in a reasonable range and agree well with the mea- (kinetic) ease of wurtzite nucleation and growth (Haymon and Kastner, sured temperatures of hydrothermal fluid samples collected from four 1981; Kojima and Ohmoto, 1991; Nozaki et al., 2016). Moreover, high high-temperature vents at Edmond (Gallant and Von Damm, 2006), concentrations of impurities can possibly enhance the precipitation of which are also in agreement with the microthermometric results of fluid metastable wurtzite phase at low temperatures. Experimental studies inclusions hosted in coexisting barite (185–286 °C) obtained from the indicate that the incorporation of trace elements such as Fe, Cd, Mn and same vent site (Wang et al., 2017). Nevertheless, SpIII has Fe/Zn ratio Ga can significantly decrease the inversion temperature of wurtzite to too low for the high fluid temperatures (ranging from 273 to 382 °C) sphalerite (Ueno et al., 1996). Nonstoichiometry (sulfur/metal > 1 for detected near these vent sites. Since previous investigators have shown sphalerite) may allow the stable formation of wurtzite at lower sulfur that a thermal gradient of as much as 100 °C exists between the inner fugacity (Scott and Barnes, 1972). Besides depositional temperatures and outer walls of black smoker chimney (Herzig et al., 1993), we infer and the ratio of components in hydrothermal solutions, the particle size that the temperatures of Ag-bearing sphalerite formation within the of ZnS crystallites is also regarded as a significant factor affecting their exterior chimney environment may have been considerably less than growth and structural features. It is well established that dissolved those measured near the central conduit. Zn2+ initially forms fine colloids when ZnS nucleation occurs in hydrothermal plumes. These colloidal clusters of ZnS nanoparticles sub- 5.2. Mechanism of anisotropic sphalerite formation sequently aggregate to form coarser particulates (Luther et al., 1999; Hsu-Kim et al., 2008; Sands et al., 2012; Gartman et al., 2014). The Previous studies suggested that optical anisotropy arises in spha- phase stability of polycrystalline ZnS may depend not only on the lerite primarily due to either tiny oriented chalcopyrite intergrowths aqueous environment, but also on their size. Due to the low activation formed by replacement or the presence of small domains with hex- energy for phase transformation, smaller wurtzite nanoparticles tend to agonal symmetry (Fleet, 1977a; Seal et al., 1985; Kojima, 1992). In the be more thermodynamically stable than sphalerite under low-tem- former scenario, such pseudo-anisotropic zoning in the host sphalerite perature conditions (Zhang et al., 2003; Zhang and Banfield, 2004; was interpreted to be of secondary origin. Obviously, this is not the case Huang and Banfield, 2005). with the Edmond colloform SpIII deficient in “chalcopyrite disease”. Our Among several explanations, the most plausible cause for twinning findings have demonstrated that the occurrence of wurtzite interlayers and wurtzite-like stacked layers seems to be related to sulfur deficiency, within the sphalerite structure might result in anomalously anisotropic which can be the main reason for a (partial) cubic-hexagonal trans- ZnS. Generally, zinc sulfide minerals crystallize in cubic close-packed formation and local ccp-hcp stacking disorder in natural sphalerite (ccp) and hexagonal close-packed (hcp) forms, and their polytype crystals (Šrot et al., 2003; Bortnikov et al., 2007). Unsurprisingly, as mixtures. For 2H/6H-type wurtzite structure, the stacking sequence is determined by EPMA, atomic ratios of total metals (including Zn, Fe, expressed as ABABAB/ABCACBA… along the [0 0 0 1] direction (or z- Cd, etc.) to sulfur negatively correlate with varied S contents in collo- axis). In contrast, the sphalerite structure is cubic close-packed and may form SpIII from the outer margins to the porous inner parts (Fig. 15), be represented by the 3C stacking sequence ABCABCABC… along the indicative of metal-deficient SpIII-b formed under highly sulfidizing [1 1 1] direction (Fleet, 1977b). Wherever a stacking fault or twin conditions (relative to more or less sulfur-deficient SpIII-a). The very low boundary was introduced, the original cubic stacking order in the de- abundance of wurtzite in the inactive Zn-rich chimney debris or sulfide fect-free sphalerite (ccp) matrix was locally modified into the hexagonal talus may result from recrystallization or rapid breakdown of me- packing order (hcp) representing wurtzite-phase lamellae (Xu et al., tastable wurtzite by oxidation/dissolution on seafloor, probably re-

2016). placed by gordaite [Zn4Na(OH)6(SO4)Cl·6H2O] or other Zn-oxyhydr- As mentioned above, most colloform ZnS samples have a strongly oxides. Therefore, wurtzite content decreases over geologic time as the disordered sphalerite structure distorted by numerous, very thin hex- Edmond sphalerite develops towards a massive to idiomorphic texture, agonal lamellae, which can be treated as either twinned sphalerite or even though wurtzite-2H/6H domains can form under conditions of low the more randomly faulted structure similar to wurtzite polytype sulfur fugacity and temperature in colloform sphalerite.

(Pósfai et al., 1988). Since the formation of natural ZnS polytypes is In sum, the morphological and textural characteristics of SpIII in- most likely related to solid-phase transformation of the 2H structure dicate that the formation processes of these ZnS spherulites usually during cooling (Fleet, 1975), abundant planar defects observed in involve heterogeneous nucleation around chalcopyrite inclusions and polytypic admixture probably represent a structural state of phase overgrowths of relatively ordered SpIII-b on defective SpIII-a. During the transition in colloform sphalerite. Twinning is one of the main me- early stage of crystal growth, hydrothermal coarsening and agglom- chanisms for phase transformation between the 3C cubic and 2H hex- eration of colloidal ZnS particles might occur via Ostwald ripening or agonal ZnS polytypes (Fleet, 1977b, 1983; Akizuki, 1981, 1983). Si- crystallographically speciﬁc oriented attachment (Huang et al., milar irregular packing defects and twinning have also been described 2003a,b). The observed trend of increasing wurtzite versus sphalerite for Fe-rich hydrothermal ZnS from the eastern Manus back-arc basin ratio from the outer margin to the chalcopyrite-bearing core suggests (Bortnikov et al., 2007). Hence, the 6H-ZnS superlattice structure of that the rate of nucleation is also an important factor. Owing to the anisotropic SpIII-a is considered to arise from a wurtzite-sphalerite phase inﬁltration of cold seawater into the porous exterior chimney walls, transition which transforms the short-range order of microcrystalline rapid nucleation caused by quenching apparently results in the for- grains into a layer with long-range ordered structure, whereas the SpIII-b mation of wurtzite domains within colloform sphalerite matrix, might be transformed from a highly disordered structure to a more whereas slower nucleation in a warmer environment (e.g., the interior

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facilitate formation of Ag-Au nanoparticles due to the preservation of polytypic planar faults or long-range structural order. Similarly, some

authors have reported a preferential segregation of CuFeS2 particles to the {1 1 1} twin boundaries in natural Fe-rich sphalerite crystals, while the sulfur concentration drops significantly near twin boundaries accompanied by an increase in oxygen (Šrot et al., 2003). Moreover, structural distortion caused by extensive substitution of transition-metal cations in sphalerite may also be expected to promote incorporation of other chalcophile elements into solid solution. For example, substitutional Mn2+ ions are preferentially localized in a {1 1 1} layer (at Zn2+ site with its tetrahedrally coordinating sulfur ligands) subjected to an axial lattice distortion, which is attributed to the presence of neighboring extended planar defects (Nistor et al., 2010). Therefore, the presence of such extended lattice defects, confirmed by our HRTEM investigation, seems to be essential in enhancing the incorporation of impurities, possibly by lowering their binding energy at the surface of cubic ZnS nanocrystallites during colloidal growth at low temperatures. It is a well known experimental fact that Fig. 15. Atomic ratios of total metals (including Zn, Fe, Cu, Pb, Cd and Ag) to sulfur defects and interfaces (such as stacking faults, twinning or grain concentrations versus varied sulfur contents in colloform sphalerite crystals from the boundaries) can play an important role in controlling physicochemical inner parts (SpIII-a) to the outer margins (SpIII-b). properties of zinc sulfide minerals (e.g., Holt, 1962, 1964; Garrett et al., 1982), often through chemical interaction with dislocations. of chimneys) leads to the precipitation of Fe-rich massive sphalerite. In Rapid growth rate may cause the formation of intrinsic defects in an analogous study, Radosavljević et al. (2016) have observed that colloform or porous dendritic sphalerite. The presence of randomly colloform zoned areas occurring in central parts of Pb-Sb-bearing oriented ZnS nanoparticles and various degrees of the ordering-dis- sphalerite show a tendency towards hexagonal forms. This case also ordering in layer packing probably reflect changing physicochemical points to possible initial crystallization of wurtzite from gels, which parameters of the Edmond hydrothermal fluids. Owing to the stacking later recrystallized into sphalerite. irregularities in ZnS disordered structures, sphalerite and minor wurtzite are intergrown at the atomic level. From a macroscopic perspective,

the colloform or framboidal textures displayed by fibro-radial SpIII 5.3. The role of stacking faults and twin boundaries in sphalerite spherulites indicate rapid crystallization associated with an under- cooling event, as well as thermodynamic disequilibrium in deep-sea Sphalerite can incorporate a diverse suite of chemical elements into extreme environments. In contrast, later coarse-grained, partially re- its structure. Fe, Cd, Mn and Cu commonly substitute for Zn in spha- crystallized massive SpI aggregates, which appear to have formed at lerite, whereas In, Ga, Ge, Hg, As, Sb, Sn, Tl, Pb, Au and Ag occur more higher temperature with slower growth rates, rarely contain any planar sporadically (Cook et al., 2009; Pfaff et al., 2011; Ye et al., 2011). The defects or dislocations. incorporation of trace elements generally takes place via substitution Here, we propose a descriptive model with a set of schematic dia- for atomic positions in ZnS crystal lattices, which is likely to depend grams illustrating the relationship between seafloor hydrothermal upon the diffusion versus growth velocity ratio. Ordered substitution processes and growth mechanisms of colloform ZnS from macro- to leads to a superstructure, whereas random substitution will preserve nano-scale (see Fig. 16). After a phase of venting at temperatures up to the basic structure of the host sphalerite. It has been increasingly ac- 382 °C, saturation of the Edmond fluids likely resulted from the com- knowledged that incorporation or reconcentration of exotic elements is bined effects of cooling and mixing in the porous exterior walls. Sub- either accommodated by structural modifications (e.g., ZnS polytypes) sequent oxidation of H2S accompanied by efficient co-precipitation of or attributable to the effects of lattice defects (Ciobanu et al., 2011, sulfosalt-bearing SpIII and submicroscopic electrum particles might take 2013). Zinc sulfides of different ore deposits and even of different place between 270 °C and 230 °C. A high rate of crystallization is an sampling sites at the same hydrothermal field may differ in chemical important factor in precipitating colloform sphalerite, particularly from compositions, essentially due to distinctions related to impurities and vigorous “black smoker” fluids ascending quickly through a chimney structural defects in the crystal lattice (Bortnikov et al., 2007; Ciobanu conduit. Although cooling and pH increase upon mixing with ambient et al., 2011; Cook et al., 2015). However, this has not yet been proven seawater are the most likely depositional controls on primary enrich- unequivocally, or constrained relative to substitution via solid-solution. ment of precious metals, Ag is transported as chloride complexes over a It has been revealed that the clustering and stability of precious- much wider range of temperature, pH and oxidation state in contrast to metal nanoparticles is closely controlled by the composition and crystal Au (Seward, 1976; Gammons and Williams-Jones, 1995). Following the 0 − structure of host mineral phases (e.g., Palenik et al., 2004). As men- initial stages of mixing, the solubility of AuHS or AgCl2 rapidly de- tioned above, the WDS mapping results demonstrate elevated contents creases in hydrothermal solutions, considering the instability of their of Ag and other chalcophile elements (including Cd, Cu, and Fe) in aqueous complexes in response to the changing physicochemical strongly disordered areas with a higher density of packing defects and properties of ore-forming fluids (Pal’yanova, 2008). A higher propor- lamellar twin boundaries. On one hand, the hexagonal symmetry of tion of seawater infiltrating into the active chimney may lead to a nanoscale domains that impart the anisotropic character to SpIII is dramatic depletion of Ag contents, elevated pH values and oxygen fu- probably stabilized by its nonstoichiometry and exotic elements repla- gacity, as well as higher S-isotope compositions towards the Pb-rich cing Zn in the structure. Conversely, the majority of Ag-poor ZnS rims coexisting with barite. samples are represented by euhedral to subhedral SpI &SpII grains with Although the role of microstructural controls on Ag distribution in a nearly perfect cubic structure (merely distorted by minor amounts of sphalerite is not purposely highlighted, we should not rule out the twinning and packing defects). On the other hand, segregation of impossible impacts (i.e., assisting effects) of lattice defects. Structural purities to these defects at interfaces can further stabilize them and defects, intragrain fractures and permeable porosity generated in col- produce a large strengthening effect. Colloform SpIII cores enriched in loform/dendritic sphalerite may enhance fluid infiltration and create Ag have smaller capacity to accumulate exotic elements, and they may potential traps for Ag-Au nanoparticles, thus promote the enrichment or

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Fig. 16. Schematic diagrams illustrating a descriptive model for the complex relationships among seafloor hydrothermal processes, crystal growth mechanisms of colloform ZnS from macro- to nano-scale, as well as structural factors controlling the incorporation/distribution of precious metals and other trace elements. redistribution of precious metals. Indeed, we have observed increasing Edmond hydrothermal products (Peng et al., 2007, 2010), in order to defect density and overall microporosity in Ag-rich colloform/dendritic determine whether or not BSR took place in the formation of Ag- varieties compared to euhedral, coarse-crystalline sphalerite with neg- bearing zinc sulfides, it is necessary to investigate their δ34S signatures. ligible Ag concentrations. During hydrothermal reworking and post- Morphological or nanotextural evidence may also shed light on the depositional supergene processes involving oxidation, leaching or biogenesis of ZnS. It has been demonstrated that wurtzite is often coupled dissolution-reprecipitation replacement reactions (Putnis, present as a minor component of Zn-sulfide assemblages formed in 2002), early-formed “invisible” silver or gold in highly defective do- association with sulfate-reducing bacteria (Xu et al., 2016). Spherical mains can be remobilized through a variety of pathways, probably via aggregates of ZnS nanoparticles are commonly twinned on very fine structural weaknesses, defects/interfaces or along grain boundaries and scales and contain multiple stacking faults, which cause a structural microcracks/voids (where it may recrystallize as secondary high-purity, disorder resulting in layers of wurtzite intercalated between domains of coarse-grained precious metals). sphalerite (Moreau et al., 2004). Likewise, our TEM results also clearly reveal a number of microstructural features which might be identified 5.4. Sources of sulfur for abiogenic ZnS nanoparticles as potential biosignatures. To a certain extent, these recognizable characteristics seem to support a low-temperature, biogenic origin of

Sulfide sulfur in global MOR hydrothermal vents can be derived polycrystalline SpIII from the Edmond field. However, such sphalerite- from three main sources: (1) leaching from host rocks; (2) thermo- barite assemblages are considered to have been deposited under in- chemical reduction of seawater sulfate; and (3) leaching of sulfide mi- termediate-temperature conditions, as indicated by microthermometric nerals in sediments (Shanks, 2001; Seal, 2006). S-isotope compositions data (Halbach et al., 2002; Wang et al., 2017). Although microbial re- of hydrothermal precipitates reflect the combination of the processes of duction of seawater sulfate may occur at temperatures up to 110 °C in simple adiabatic mixing, thermochemical reduction, and/or dissolution hydrothermal sediments around hot vents (Jørgensen et al., 1992), ore- of biogenic sulfide minerals. However, it is difficult to distinguish be- forming temperatures inferred from fluid inclusion studies would be too tween thermochemical and bacterial sulfate reduction (BSR) in modern high for sulfate-reducing bacteria to survive. The absence of thick se- seafloor VMS deposits. S-isotope ratios of sulfide products can be used diments at Edmond also precludes a potential contribution of iso- as distinguishing criteria, and provide geochemical evidence for iden- topically light sulfur which is usually hypothesized to have biogenic tification of a bacterial versus a thermochemical origin (Machel et al., origins. Conversely, sulfide deposits at sediment-covered MORs may 1995). Furthermore, some authors (Labrenz et al., 2000; Kucha et al., carry negative δ34S signatures via introduction of sulfide from overlying 2010; Pfaff et al., 2011) have proposed various mechanisms for biolo- sediments (Ono et al., 2007). Hence, undetectably small contribution of gically mediated precipitation of colloform sphalerite by BSR in many BSR in colloform sphalerite may be characteristic to those VMS deposits of the world’s sulfide ore deposits. Biological processes can also effi- along the (sediment-free) Central Indian Ridge. ciently remove silver from hydrothermal solutions by bacterial sorp- S-isotope studies of basaltic-hosted massive sulfide deposits at se- tion, thus may contribute to Ag enrichment within some vent fields diment-starved mid-ocean ridges have shown a range of δ34S ratios (e.g., Zierenberg and Schiffman, 1990). There is no doubt that bacteria from +0.7‰ to +6.3‰ with a mean value of +3.2‰ (Herzig et al., may play an important role in deep-sea hydrothermal systems 1998b). Bulk sulfur isotopic compositions of the Edmond zinc sulfides (Jørgensen et al., 1992; Weber and Jørgensen, 2002), and thus can fall into the above-mentioned range, while the LA-MC-ICP-MS results influence the sulfur isotopic systematics in polymetallic sulfides tend to be slightly heavier (see the δ34S histogram) compared to the (Seewald et al., 1994; Herzig et al., 1998a). Since abundant occurrences conventional analyses. Since pyrite should have higher δ34S values than of microbial mats and biomineralization have been documented in the coexisting sphalerite under equilibrium conditions (Ohmoto, 1972), the

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δ34S data of bulk samples suggest strong isotopic disequilibrium be- Edmond. These ZnS samples can be subdivided into three groups based tween pyrite and sphalerite. But measured isotopic fractionation be- on variable Fe contents with respect to their morphological character- tween them is negligibly small, particularly in sulfate-rich chimney istics: Fe-rich, massive to euhedral sphalerite with relict dendritic or walls. This implies that fractionation did not occur because these mi- porous textures (SpI:Feaverage = 6.57 wt%, N = 44); relatively low-Fe, nerals were deposited episodically at lower temperatures (< 350 °C). anhedral disseminated sphalerite (SpII:Feaverage = 4.64 wt%, N = 33); Although dissolution and replacement of pre-existing anhydrite may be and Fe-poor, colloform sphalerite (SpIII:Feaverage = 0.30 wt%, N = 36). common in some black smoker chimneys, heavy sulfur in sphalerite- Almost all Ag-Au mineralization in the Edmond hydrothermal system is barite assemblages is likely to have been predominantly derived from restricted to sphalerite-barite assemblages precipitated at less than admixed seawater. In general, sulfur isotopic data lying between two 270 °C under relatively high-sulfidation conditions. extreme values (MORB: δ34S ≈ ±0‰; seawater: δ34S ≈ +21‰) can The degree of recrystallization is reflected by the distribution of be explained by non-equilibrium mixing between sulfur of basaltic silver, the bulk density of lattice defects as well as intragranular por- origin and sulfur from reduced seawater (Sakai et al., 1984). Based on a osity. Fe-rich massive SpI (except their dendritic or colloform pre- two-component mixing model, we simply estimate the proportional cursors) within the Zn-Fe-rich chimney debris becomes more euhedral contributions of seawater-derived and igneous sulfur to the Edmond and coarse-crystalline upon subsequent recrystallization, along with a hydrothermal precipitates. The mean δ34S value of +6.97‰ for the decrease in Ag content, mineral porosity and defect density; whereas main-stage massive SpI indicates a seawater vs. basalt S ratio of about Fe-poor SpIII samples in the outer chimney walls occur primarily as 32: 68 on average. By contrast, heavier S isotopes in colloform SpIII colloform or botryoidal aggregates with a strongly disordered structure (δ34S up to +10.23‰) exhibit a larger contribution of sulfur derived and are characterized by an abundance of tennantite, pearceite and from reduced seawater sulfate (ranged from approximately 34% to other Ag-bearing sulfosalts, with the highest Ag concentrations mea- 48%), as indicated by sulfate-sulfide mineral pairs. sured in Cu-rich cores. This type of sphalerite exhibits distinct optical We also note that the δ34S values, Zn/Fe ratios and Ag-Pb contents anisotropy, which might result from the presence of small domains of of the Edmond sphalerite samples generally show a slight but sig- hexagonal symmetry created by numerous {1 1 1} stacking faults and nificant increase progressively from high-temperature to relatively low- twinning in the 3C sphalerite. On the contrary, most of the Ag-poor, temperature mineralization stage. Due to mixing and cooling, Fe-poor, euhedral sphalerite crystals tend to have a relatively well-ordered cubic colloform sphalerite primarily formed at the early stage under condi- structure distorted only by sparsely distributed twin boundaries. tions favoring the incorporation of Ag into the ZnS crystal structure, Such a unique microstructure appears to result from abundant whereas the replacement of Zn by Fe gets gradually weakened with the planar defects causing an extremely high degree of stacking disorder decrease of fluid temperature. As Fe-rich, massive sphalerite in black that formed contemporaneously with the precipitation of Ag-rich SpIII, smoker chimneys formed at the main episode of hydrothermal activity, reflecting the dynamic changes of physicochemical conditions of ore- Fe has strong capacity of isomorphous substitution for Zn at > 350 °C. forming fluids in a disequilibrium system. A significant decrease of However, other researchers have noted a lack of correlation between S temperature and sulfur fugacity is a principal mechanism triggering isotopes and minor/trace element concentrations related to zoning precipitation of submicroscopic precious metals. Rapid growth rate patterns (Belissont et al., 2014). It seems to imply that certain factors (due to mixing and cooling rather than biologically mediated processes (i.e., crystallographic controls, fluid evolution at the crystal interface) involving BSR, as supported by in-situ sulfur isotopic evidence) may triggering cation enrichment and compositional zoning during spha- cause the formation of intrinsic defects or interfaces in colloform lerite precipitation might not affect the sulfur isotopic system, but ra- sphalerite, thus possibly promote the incorporation of monovalent Ag ther as a signature of the processes occurring in ore-forming fluids and Cu (via coupled substitutions with trivalent or tetravalent cations) before ZnS deposition (e.g., sulfur sources or reduction mechanisms). during ZnS crystallization. Actually, considering the Edmond hydrothermal solutions with S concentrations close to that of ambient seawater, whereas the Fe, Cu, Pb and Ag contents are seven orders of magnitude higher in end-member Acknowledgements fluids (Table 1), it is not surprising that even subtle variations in high- resolution S isotopic records may reflect the changing compositions and This research project was jointly funded by National Natural Science physicochemical conditions of mixed fluids, which can be easily af- Foundation of China (Grant Nos. 41273054, 41503036 & 41702066), fected by the overprinting of variable proportions of seawater. the doctoral program of Higher Education Research Fund In summary, the δ34S values of the Edmond massive sulfides are (20120171130005), Guangdong Province Universities and Colleges relatively high in contrast to previously published data reported from Pearl River Scholar Funded Scheme (2011), the Fundamental Research the fast-spreading East Pacific Rise at 11° N and 13° N where the highest Funds for Central Universities (No. 12lgjc05) and the China Ocean δ34S values for the ZnS phases are between +2.5‰ and +4.2‰ (Bluth Mineral Resources Research and Development Association (DYXM-115- and Ohmoto, 1988). The Edmond vent field is located at an inter- 02-1-11). We thank the crews and scientists of the DY105-17A and mediate- to slow-spreading center in the Central Indian Ocean, which DY115-19 cruises on board the R/V Dayang Yihao, as well as the includes a greater component of shallow seawater entrainment, per- Autonomous Benthic Explorer (ABE) group, who contributed to suc- vasive low-temperature diffuse flows, sub-seafloor extensive hydro- cessful sample collections from the Edmond vent field, CIR during thermal circulation and basalt alteration, compared to fast-spreading 2005–2007. Xu and Konishi acknowledge financial support from NASA centers (Humphris and Fornari, 2001; Van Dover et al., 2001; Cao et al., Astrobiology Institute (N07-5489). The authors are also grateful to the 2016). Obviously, these processes are more conducive to thermo- Major Research Instrumentation (MRI) program of NSF for funding the chemical reduction of seawater sulfate, which imparts higher δ34S va- aberration-corrected HRTEM at the University of Wisconsin-Madison. lues to the resulting sulfides. Such unique geological features are EPMA-EDS measurements were performed by Dr. Wenxia Zhao at the somewhat similar to the gold-rich TAG hydrothermal system on the Instrumental Analysis and Research Center, Sun Yat-sen University. We slow-spreading Mid-Atlantic Ridge (Herzig et al., 1998b). are also grateful to Dr. Fangfu Zhang and Dr. Zhizhang Shen from UW- Madison for their assistance with in-situ micro-XRD and SEM analyses. 6. Conclusions Finally, we thank Editor-in-Chief Prof. Franco Pirajno, Associate Editor Cristiana Ciobanu, and five anonymous reviewers for their thoughtful Sphalerite is regarded as one of the main Ag-carriers, and usually and thorough reviews/suggestions, which greatly assisted with im- encountered as a host mineral for native gold/electrum particles at provement of this manuscript.

338 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Appendix

Fig. A1. (A)–(D) Representative LA-ICP-MS time-resolved spectra for different types of zinc sulfides at Edmond. Note the relatively high counts of Cu, Pb, Cd, Ag and Au in dendritic SpI or colloform SpIII compared to Fe-rich, massive SpI. (C) Also note smooth profiles for As, Sb, Cd, Pb and Ag, despite the common presence of submicron- to nano-sized electrum particles or Ag-bearing sulfosalt inclusions (D) in these sphalerite grains.

339 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Fig. A2. (A)–(D) Representative EDS spectra of submicroscopic electrum inclusions within Ag-bearing colloform sphalerite.

340 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Fig. A3. EPMA-WDS element maps of typical Ag-bearing massive and colloform sphalerite samples (SpI & SpIII). (A) Large fan-shaped crystals of chalcopyrite-bearing sphalerite; (B) Coarse-grained, irregular-shaped sphalerite containing both chalcopyrite and a suite of complex Cu-Ag-As-Sb sulfosalts; (C) Fe-rich, subhedral to anhedral granules of porous sphalerite.

341 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Fig. A4. Modal mineralogy and paragenetic sequence of the Edmond polymetallic sulfide samples (modified after Wu et al., 2016). Major mineral associations and paragenesis are related to ore-forming temperature, oxygen and/or sulfur fugacity, as well as the degrees of mixing between hydrothermal vent fluids and cold ambient seawater.

Table A1 EPMA data (wt%) of sphalerite in diﬀerent types of the Edmond hydrothermal precipitates.

Sample No. S Se Fe Cu Zn Pb Mn As Sb Co Ni Cd In Sn Au Ag Total

IR-12A Sp-01 33.70 < mdl 9.60 0.15 55.89 < mdl < mdl < mdl < mdl < mdl 0.01 0.39 < mdl < mdl < mdl < mdl 99.73 IR-12A Sp-02 34.36 0.02 17.36 0.48 46.61 < mdl < mdl 0.02 < mdl < mdl < mdl 0.62 < mdl < mdl < mdl < mdl 99.46 IR-12A Sp-03 34.35 < mdl 25.30 1.59 37.62 < mdl < mdl < mdl < mdl < mdl < mdl 0.46 < mdl < mdl < mdl < mdl 99.31 IR-12A Sp-04 34.54 < mdl 21.40 0.61 43.80 < mdl < mdl < mdl < mdl < mdl < mdl 0.51 < mdl < mdl < mdl < mdl 100.85 IR-12A Sp-05 33.99 0.02 8.97 < mdl 56.26 < mdl < mdl 0.04 < mdl 0.17 < mdl 0.49 < mdl < mdl < mdl 0.12 100.05 IR-12A Sp-06 33.66 < mdl 6.39 < mdl 59.79 < mdl 0.02 < mdl < mdl 0.13 < mdl 0.27 < mdl < mdl < mdl 0.18 100.44 IR-12A Sp-07 34.23 < mdl 25.15 1.82 37.61 < mdl < mdl < mdl < mdl < mdl 0.03 0.40 < mdl < mdl < mdl < mdl 99.24 IR-12A Sp-08 34.55 < mdl 16.58 0.36 47.94 < mdl < mdl 0.04 < mdl < mdl < mdl 0.56 < mdl < mdl < mdl < mdl 100.02 IR-12A Sp-09 34.03 < mdl 11.32 0.19 53.66 < mdl < mdl < mdl < mdl < mdl < mdl 0.65 < mdl < mdl < mdl < mdl 99.85 IR-12A Sp-10 33.64 < mdl 4.93 0.06 60.48 < mdl 0.03 < mdl < mdl 0.07 0.01 0.33 < mdl < mdl < mdl 0.46 100.01 IR-12A Sp-11 33.07 < mdl 5.45 0.01 59.96 < mdl < mdl < mdl 0.01 0.12 < mdl 0.40 < mdl 0.01 < mdl 0.51 99.52 IR-12A Sp-12 33.26 < mdl 3.89 < mdl 62.75 < mdl < mdl < mdl < mdl 0.06 < mdl 0.26 < mdl 0.06 < mdl 0.30 100.57 IR-12A Sp-13 33.08 < mdl 1.07 0.04 65.27 < mdl < mdl < mdl 0.10 < mdl < mdl 0.13 < mdl < mdl < mdl < mdl 99.69 IR-12A Sp-14 32.89 < mdl 2.49 0.08 65.63 < mdl < mdl 0.07 0.05 < mdl 0.01 0.09 < mdl < mdl < mdl < mdl 101.32 IR-12A Sp-15 33.06 0.01 1.23 0.04 65.14 < mdl < mdl < mdl 0.11 < mdl < mdl 0.12 < mdl < mdl < mdl < mdl 99.71 IR-12A Sp-16 33.43 0.01 4.47 0.04 61.41 < mdl 0.01 < mdl 0.07 0.09 0.02 0.34 < mdl < mdl < mdl 0.66 100.54 IR-12A Sp-17 33.59 < mdl 5.17 0.03 60.61 < mdl 0.02 < mdl < mdl 0.12 < mdl 0.30 < mdl < mdl < mdl 0.42 100.26 IR-12A Sp-18 32.60 0.02 4.63 0.11 62.05 < mdl < mdl < mdl < mdl < mdl < mdl 0.11 < mdl < mdl < mdl < mdl 99.52 IR-12A Sp-19 33.77 < mdl 10.06 0.16 55.06 < mdl < mdl < mdl < mdl < mdl 0.02 0.60 < mdl < mdl < mdl < mdl 99.67 IR-12A Sp-20 33.60 0.02 5.16 0.15 60.92 < mdl < mdl < mdl < mdl < mdl < mdl 0.10 < mdl < mdl < mdl < mdl 99.95 IR-12A Sp-21 33.19 < mdl 4.67 0.01 61.13 < mdl 0.01 < mdl < mdl 0.10 < mdl 0.30 < mdl 0.02 < mdl 0.37 99.79 IR-12A Sp-22 33.58 < mdl 5.26 < mdl 60.40 < mdl 0.02 0.06 < mdl 0.10 0.02 0.24 < mdl 0.06 < mdl 0.36 100.11 IR-12A Sp-23 33.75 0.03 3.52 0.11 62.31 < mdl < mdl 0.04 0.08 < mdl < mdl 0.17 < mdl < mdl < mdl 0.03 100.03 IR-12A Sp-24 32.87 < mdl 0.95 0.06 66.21 < mdl < mdl < mdl 0.09 < mdl < mdl 0.11 < mdl < mdl < mdl < mdl 100.27 IR-12A Sp-25 32.98 < mdl 4.57 0.03 60.92 < mdl < mdl 0.03 0.03 0.07 < mdl 0.33 < mdl < mdl < mdl 0.49 99.43 IR-12A Sp-26 33.36 < mdl 1.12 < mdl 64.92 < mdl 0.01 < mdl < mdl 0.05 < mdl 0.03 < mdl < mdl < mdl < mdl 99.49 IR-12A Sp-27 33.38 < mdl 3.14 0.02 61.77 < mdl < mdl < mdl 0.08 0.05 < mdl 0.29 < mdl 0.02 < mdl 0.68 99.43 IR-12A Sp-28 33.05 < mdl 3.98 < mdl 60.55 < mdl 0.02 < mdl 0.11 0.08 0.01 0.42 < mdl < mdl < mdl 0.73 98.95 IR-12A Sp-29 33.20 < mdl 1.74 0.08 64.21 < mdl < mdl < mdl 0.07 0.02 0.01 0.16 < mdl 0.02 < mdl 0.46 99.96 IR-12A Sp-30 32.89 < mdl 1.23 < mdl 64.75 < mdl 0.01 < mdl 0.03 0.02 0.01 0.09 < mdl < mdl < mdl 0.38 99.40 IR-12A Sp-31 33.21 < mdl 3.18 0.05 63.23 < mdl < mdl 0.04 0.09 0.05 < mdl 0.23 < mdl 0.04 < mdl 0.50 100.62 IR-12A Sp-32 33.32 < mdl 4.62 0.02 60.75 < mdl 0.01 < mdl 0.06 0.10 < mdl 0.41 < mdl < mdl < mdl 0.59 99.86 IR-12A Sp-33 34.25 < mdl 9.65 < mdl 55.60 < mdl < mdl < mdl < mdl 0.21 < mdl 0.54 < mdl < mdl < mdl < mdl 100.25 IR-12A Sp-34 32.86 < mdl 2.70 0.05 65.17 < mdl < mdl 0.01 0.02 < mdl 0.01 0.04 < mdl < mdl < mdl < mdl 100.86 IR-12A Sp-35 33.32 < mdl 2.28 < mdl 63.56 < mdl < mdl < mdl < mdl < mdl 0.01 0.09 0.05 < mdl < mdl < mdl 99.30 IR-12A Sp-36 33.23 0.04 1.56 0.01 64.91 < mdl < mdl 0.01 0.07 < mdl < mdl 0.11 < mdl < mdl < mdl < mdl 99.93 IR-12A Sp-37 33.79 < mdl 4.25 0.01 61.58 < mdl 0.02 < mdl < mdl 0.06 0.01 0.30 < mdl < mdl < mdl 0.42 100.43 IR-12A Sp-38 33.68 0.04 2.85 0.02 63.58 < mdl < mdl 0.01 0.05 < mdl 0.02 0.08 < mdl < mdl < mdl < mdl 100.34 IR-12A Sp-39 32.89 < mdl 7.93 0.09 57.00 < mdl 0.01 < mdl 0.04 0.12 < mdl 0.59 < mdl 0.05 < mdl 0.44 99.14 IR-12A Sp-40 32.17 < mdl 2.44 0.04 63.20 < mdl < mdl < mdl 0.03 0.04 < mdl 0.27 < mdl < mdl < mdl 0.53 98.70 IR-12A Sp-41 33.67 0.01 9.41 0.05 56.13 < mdl 0.01 < mdl < mdl 0.19 0.01 0.55 < mdl 0.03 < mdl 0.11 100.17 IR-12A Sp-42 34.03 < mdl 7.17 0.04 59.13 < mdl < mdl < mdl < mdl 0.13 < mdl 0.37 < mdl < mdl < mdl < mdl 100.88 IR-12A Sp-43 33.50 0.02 3.41 0.02 62.96 < mdl < mdl < mdl < mdl < mdl < mdl 0.10 < mdl < mdl < mdl < mdl 100.02 IR-12A Sp-44 33.81 < mdl 6.95 0.02 57.90 < mdl 0.02 0.02 0.08 0.14 0.02 0.45 < mdl 0.04 < mdl 0.44 99.88 IR-12B Sp-01 32.93 < mdl 8.03 0.18 56.47 < mdl 0.01 0.02 < mdl 0.17 0.01 0.59 < mdl < mdl < mdl 0.06 98.47 (continued on next page)

342 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Table A1 (continued)

Sample No. S Se Fe Cu Zn Pb Mn As Sb Co Ni Cd In Sn Au Ag Total

IR-12B Sp-02 32.74 < mdl 5.29 0.10 60.13 < mdl 0.03 < mdl < mdl 0.09 < mdl 0.36 < mdl < mdl < mdl 0.18 98.92 IR-12B Sp-03 33.25 < mdl 4.86 0.20 59.88 < mdl 0.01 0.02 < mdl 0.11 < mdl 0.69 < mdl 0.06 < mdl 0.17 99.25 IR-12B Sp-04 33.39 < mdl 4.77 0.21 61.30 < mdl < mdl < mdl 0.04 0.14 0.03 0.43 < mdl < mdl < mdl < mdl 100.30 IR-12B Sp-05 33.11 < mdl 6.09 0.87 57.85 < mdl 0.02 < mdl 0.05 0.14 < mdl 0.89 < mdl 0.02 < mdl < mdl 99.04 IR-12B Sp-06 33.40 < mdl 4.20 0.40 60.50 < mdl < mdl 0.01 < mdl 0.11 0.01 0.57 < mdl < mdl < mdl 0.22 99.41 IR-12B Sp-07 33.25 < mdl 6.34 0.82 57.29 < mdl 0.01 0.04 0.09 0.13 < mdl 0.72 < mdl 0.07 < mdl < mdl 98.75 IR-12B Sp-08 32.96 0.03 5.19 0.76 59.13 < mdl < mdl < mdl 0.05 0.10 < mdl 0.72 < mdl 0.08 < mdl 0.10 99.11 IR-12B Sp-09 32.73 < mdl 2.55 < mdl 64.03 < mdl < mdl < mdl 0.01 0.03 < mdl 0.12 < mdl 0.06 < mdl 0.10 99.64 IR-12B Sp-10 33.03 < mdl 6.97 0.11 58.86 < mdl < mdl < mdl 0.02 0.15 < mdl 0.19 0.01 < mdl < mdl < mdl 99.34 IR-12B Sp-11 32.99 < mdl 5.28 0.02 60.55 < mdl < mdl < mdl < mdl 0.12 < mdl 0.21 0.01 < mdl < mdl < mdl 99.18 IR-12B Sp-12 33.38 0.02 2.72 < mdl 63.79 < mdl < mdl < mdl < mdl 0.08 < mdl 0.08 0.02 < mdl < mdl < mdl 100.09 IR-12B Sp-13 33.19 0.02 1.99 0.02 64.02 < mdl 0.01 < mdl < mdl 0.06 < mdl 0.22 < mdl 0.03 < mdl 0.10 99.66 IR-12B Sp-14 32.89 0.01 2.66 0.52 62.11 < mdl < mdl < mdl 0.07 0.05 0.01 0.54 < mdl 0.04 < mdl 0.39 99.27 IR-12B Sp-15 33.17 < mdl 5.26 0.38 60.24 < mdl 0.01 < mdl < mdl 0.11 < mdl 0.17 < mdl < mdl < mdl 0.01 99.33 IR-12B Sp-16 34.04 0.02 9.46 0.11 55.16 < mdl 0.02 < mdl 0.05 < mdl < mdl 0.63 < mdl < mdl < mdl < mdl 99.50 IR-12B Sp-17 33.79 0.02 4.68 0.19 61.63 < mdl 0.04 < mdl 0.04 < mdl < mdl 0.61 < mdl 0.07 < mdl < mdl 101.06 IR-12B Sp-18 33.97 < mdl 5.18 0.44 59.82 < mdl < mdl 0.03 0.08 < mdl < mdl 0.87 < mdl 0.01 < mdl 0.30 100.69 IR-12B Sp-19 34.07 0.01 7.16 0.14 58.28 < mdl < mdl < mdl < mdl < mdl < mdl 0.38 < mdl 0.03 < mdl 0.12 100.18 IR-12B Sp-20 33.80 < mdl 6.01 0.10 59.57 < mdl 0.01 < mdl < mdl < mdl < mdl 0.58 < mdl 0.03 < mdl 0.22 100.31 IR-12B Sp-21 33.58 < mdl 6.09 0.29 58.55 < mdl 0.01 < mdl < mdl < mdl < mdl 0.64 < mdl 0.04 < mdl 0.02 99.20 IR-12B Sp-22 34.19 < mdl 4.65 0.40 60.93 < mdl < mdl 0.01 0.07 < mdl 0.01 0.81 < mdl < mdl < mdl < mdl 101.06 IR-12B Sp-23 34.08 0.01 3.02 0.06 63.39 < mdl 0.01 0.02 < mdl < mdl 0.01 0.25 < mdl 0.02 < mdl 0.04 100.91 IR-12B Sp-24 33.92 < mdl 3.68 0.03 62.85 < mdl 0.02 < mdl < mdl < mdl < mdl 0.32 < mdl 0.02 < mdl < mdl 100.84 IR-12B Sp-25 33.88 < mdl 3.71 0.05 62.33 < mdl 0.01 0.02 0.08 < mdl 0.01 0.30 < mdl < mdl < mdl 0.17 100.55 IR-12B Sp-26 33.85 < mdl 2.74 0.05 63.52 < mdl 0.01 < mdl < mdl < mdl < mdl 0.16 < mdl < mdl < mdl 0.22 100.55 IR-12B Sp-27 33.66 < mdl 2.68 0.10 63.33 < mdl < mdl 0.05 < mdl < mdl < mdl 0.29 < mdl < mdl < mdl 0.19 100.30 IR-12B Sp-28 33.45 < mdl 2.56 < mdl 63.77 < mdl < mdl < mdl < mdl < mdl < mdl 0.10 < mdl < mdl < mdl 0.06 99.93 IR-12B Sp-29 33.07 < mdl 2.92 < mdl 64.42 < mdl < mdl < mdl 0.05 0.04 < mdl 0.14 < mdl < mdl < mdl 0.03 100.66 IR-12B Sp-30 34.09 < mdl 6.43 0.10 59.02 < mdl < mdl 0.03 0.08 0.05 < mdl 0.67 < mdl 0.02 < mdl < mdl 100.47 IR-12B Sp-31 32.58 < mdl 1.31 0.85 64.03 0.09 < mdl < mdl < mdl < mdl < mdl 0.42 < mdl < mdl < mdl < mdl 99.28 IR-12B Sp-32 33.45 < mdl 0.92 0.52 64.95 0.08 < mdl 0.06 < mdl < mdl < mdl 0.24 < mdl < mdl < mdl < mdl 100.22 IR-12B Sp-33 33.27 < mdl 7.59 < mdl 57.87 < mdl < mdl 0.03 < mdl 0.01 < mdl 0.18 < mdl 0.02 < mdl 0.07 99.03 IR-13 Sp-01 32.43 < mdl 0.25 0.46 64.02 0.53 < mdl 0.02 0.03 0.01 0.02 0.67 < mdl 0.04 < mdl 0.67 99.16 IR-13 Sp-02 32.34 < mdl 0.21 0.42 64.35 0.74 < mdl 0.10 < mdl < mdl < mdl 0.57 < mdl 0.02 < mdl 0.31 99.05 IR-13 Sp-03 32.42 < mdl 0.20 0.36 64.07 0.92 0.01 0.08 0.02 < mdl < mdl 0.55 < mdl 0.01 < mdl 0.44 99.06 IR-13 Sp-04 31.94 < mdl 0.25 0.61 64.01 0.55 0.02 0.03 < mdl 0.01 0.02 0.73 < mdl < mdl < mdl 0.60 98.77 IR-13 Sp-05 32.81 < mdl 0.30 0.27 65.44 0.46 < mdl 0.02 < mdl 0.02 0.01 0.46 < mdl < mdl < mdl 0.29 100.07 IR-13 Sp-06 32.41 < mdl 0.22 0.24 64.12 0.99 < mdl 0.10 0.01 0.01 < mdl 0.56 < mdl 0.02 < mdl 0.13 98.81 IR-13 Sp-07 33.14 < mdl 0.23 0.30 64.80 0.90 0.03 0.14 < mdl < mdl 0.03 0.52 < mdl < mdl < mdl 0.11 100.19 IR-13 Sp-08 32.81 < mdl 0.29 0.23 65.39 0.55 < mdl 0.04 < mdl < mdl < mdl 0.18 < mdl < mdl < mdl 0.03 99.52 IR-13 Sp-09 32.98 < mdl 0.18 0.04 65.14 0.71 < mdl 0.08 0.03 < mdl 0.02 0.25 0.02 0.04 < mdl < mdl 99.48 IR-13 Sp-10 32.49 < mdl 0.33 1.14 63.84 0.33 < mdl 0.07 < mdl 0.02 0.02 1.14 < mdl < mdl < mdl 0.96 100.35 IR-13 Sp-11 32.74 < mdl 0.20 0.22 64.51 0.83 0.01 0.01 < mdl 0.01 0.01 0.49 < mdl < mdl < mdl 0.33 99.36 IR-13 Sp-12 33.05 < mdl 0.28 1.38 62.89 0.49 < mdl 0.01 0.02 < mdl 0.01 1.13 < mdl 0.04 < mdl 0.94 100.22 IR-13 Sp-13 31.65 < mdl 0.30 1.98 62.25 0.63 < mdl 0.04 0.01 < mdl 0.02 1.43 < mdl < mdl < mdl 1.00 99.31 IR-13 Sp-14 33.01 < mdl 0.31 0.14 65.34 0.42 0.01 < mdl < mdl < mdl < mdl 0.31 < mdl 0.06 < mdl 0.22 99.82 IR-13 Sp-15 32.26 0.01 0.55 2.58 61.98 0.80 < mdl < mdl < mdl < mdl < mdl 1.37 < mdl 0.04 < mdl 0.78 100.36 IR-13 Sp-16 31.98 < mdl 0.34 2.14 62.66 0.80 < mdl 0.02 < mdl 0.01 < mdl 1.30 < mdl < mdl < mdl 0.81 100.06 IR-13 Sp-17 32.79 < mdl 0.33 0.10 66.48 0.29 < mdl 0.04 < mdl 0.02 0.01 0.24 < mdl 0.03 < mdl < mdl 100.33 IR-13 Sp-18 32.95 < mdl 0.32 0.13 65.47 0.40 < mdl 0.07 < mdl 0.01 0.01 0.38 < mdl 0.01 < mdl < mdl 99.75 IR-13 Sp-19 32.75 < mdl 0.33 0.13 64.95 0.39 0.01 0.07 < mdl < mdl < mdl 0.34 < mdl 0.02 < mdl 0.12 99.10 IR-13 Sp-20 32.33 < mdl 0.17 0.06 65.32 0.50 < mdl 0.07 0.02 < mdl 0.01 0.20 0.01 0.01 < mdl < mdl 98.70 IR-13 Sp-21 32.69 < mdl 0.34 1.62 63.37 0.60 < mdl 0.01 < mdl < mdl < mdl 0.94 < mdl 0.01 < mdl 0.90 100.48 IR-13 Sp-22 31.96 < mdl 0.19 0.08 64.60 0.89 < mdl 0.14 < mdl < mdl < mdl 0.26 < mdl 0.01 < mdl < mdl 98.12 IR-13 Sp-23 32.45 < mdl 0.24 0.42 63.78 0.85 < mdl 0.09 0.06 0.02 0.01 0.74 < mdl < mdl < mdl 0.30 98.95 IR-13 Sp-24 32.16 < mdl 0.24 0.44 65.09 0.76 0.02 0.12 < mdl < mdl < mdl 0.65 < mdl < mdl < mdl 0.57 100.04 IR-13 Sp-25 32.97 < mdl 0.41 0.26 65.59 0.57 < mdl 0.05 < mdl < mdl < mdl 0.40 < mdl < mdl < mdl < mdl 100.26 IR-13 Sp-26 32.88 < mdl 0.36 0.11 66.49 0.04 0.01 0.01 < mdl < mdl 0.01 0.19 < mdl < mdl < mdl 0.01 100.11 IR-13 Sp-27 31.91 < mdl 0.24 0.61 63.91 0.84 < mdl 0.13 < mdl < mdl 0.01 0.51 < mdl < mdl < mdl 0.52 98.66 IR-13 Sp-28 32.17 < mdl 0.32 2.06 62.63 0.74 < mdl 0.08 0.01 < mdl < mdl 1.30 < mdl 0.04 < mdl 0.95 100.31 IR-13 Sp-29 32.75 < mdl 0.35 0.39 65.28 0.53 0.02 0.04 0.01 < mdl < mdl 0.39 0.01 0.01 < mdl 0.24 100.01 IR-13 Sp-30 32.71 < mdl 0.23 0.04 65.79 0.63 < mdl 0.09 < mdl < mdl < mdl 0.25 < mdl 0.04 < mdl < mdl 99.78 IR-13 Sp-31 32.71 < mdl 0.60 1.20 63.67 0.28 < mdl 0.05 < mdl 0.04 < mdl 1.16 < mdl < mdl < mdl 1.04 100.74 IR-13 Sp-32 33.11 < mdl 0.30 0.62 65.05 0.48 0.03 0.11 < mdl < mdl 0.01 0.53 < mdl < mdl < mdl 0.42 100.66 IR-13 Sp-33 33.14 < mdl 0.31 0.09 65.58 0.65 < mdl 0.05 < mdl < mdl < mdl 0.14 < mdl < mdl < mdl < mdl 99.95 IR-13 Sp-34 32.03 < mdl 0.32 0.23 64.79 0.48 0.02 0.05 0.01 < mdl < mdl 0.60 < mdl < mdl < mdl 0.39 98.92 IR-13 Sp-35 32.50 < mdl 0.48 0.11 66.38 0.23 0.03 0.02 0.02 0.01 < mdl 0.30 < mdl 0.05 < mdl < mdl 100.12 IR-13 Sp-36 32.96 < mdl 0.32 0.16 65.10 0.58 < mdl 0.03 0.01 0.03 0.01 0.07 < mdl 0.04 < mdl < mdl 99.31 Avg. (N = 113) 33.18 < mdl 4.01 0.32 61.36 0.19 0.01 0.02 0.02 0.04 0.01 0.43 < mdl 0.01 < mdl 0.22 99.82

(“ < mdl”: below minimum detection limit). Analytical Institution: Electron Microprobe Laboratory, SYSU.

343 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Table A2 EPMA data (wt%) of chalcopyrite in diﬀerent types of the Edmond hydrothermal precipitates.

Sample No. S Se Fe Cu Zn Pb Mn As Sb Co Ni Cd In Sn Au Ag Total

IR-12 Ccp-01 35.35 < mdl 31.88 30.64 0.59 < mdl < mdl < mdl 0.03 0.08 < mdl 0.04 < mdl < mdl 0.04 0.01 98.67 IR-12 Ccp-02 34.50 < mdl 33.06 29.63 1.12 < mdl < mdl < mdl < mdl 0.07 0.02 0.01 < mdl < mdl < mdl 0.06 98.46 IR-12 Ccp-03 35.30 < mdl 31.95 32.04 0.49 < mdl < mdl < mdl 0.03 0.06 < mdl < mdl < mdl < mdl < mdl 0.04 99.90 IR-12 Ccp-04 35.92 < mdl 31.18 32.19 0.33 < mdl < mdl < mdl < mdl 0.02 < mdl < mdl < mdl 0.03 < mdl 0.05 99.72 IR-12 Ccp-05 35.10 < mdl 33.60 29.96 0.64 < mdl < mdl < mdl < mdl 0.03 < mdl < mdl < mdl < mdl 0.16 0.14 99.62 IR-12 Ccp-06 36.47 < mdl 30.78 31.87 0.15 < mdl < mdl < mdl < mdl 0.08 < mdl < mdl < mdl < mdl 0.03 0.03 99.42 IR-12 Ccp-07 35.99 < mdl 31.27 30.86 0.46 < mdl < mdl 0.03 < mdl 0.06 < mdl < mdl < mdl < mdl < mdl < mdl 98.66 IR-13 Ccp-01 35.51 0.04 27.97 34.10 0.44 < mdl < mdl 0.13 0.19 0.78 < mdl 0.01 0.12 0.02 < mdl 0.07 99.37 IR-13 Ccp-02 35.30 < mdl 29.40 33.82 1.42 < mdl 0.02 0.02 < mdl 0.76 < mdl < mdl 0.10 < mdl < mdl 0.02 100.85 IR-13 Ccp-03 36.43 0.01 29.74 33.33 0.91 < mdl < mdl 0.05 0.05 0.09 < mdl 0.01 0.01 < mdl 0.02 0.08 100.71 IR-13 Ccp-04 35.86 < mdl 29.18 33.12 1.04 0.05 < mdl < mdl 0.05 0.05 < mdl < mdl 0.01 < mdl 0.02 0.09 99.45 IR-13 Ccp-05 35.87 < mdl 28.39 33.96 0.39 < mdl < mdl < mdl < mdl 0.74 < mdl < mdl < mdl < mdl < mdl 0.01 99.36 IR-13 Ccp-06 34.27 < mdl 30.06 34.02 0.39 < mdl < mdl 0.04 < mdl 0.73 < mdl 0.01 < mdl < mdl < mdl 0.06 99.59 IR-13 Ccp-07 35.42 < mdl 29.32 32.66 1.04 0.04 < mdl 0.02 0.08 0.05 < mdl < mdl 0.06 < mdl < mdl 0.04 98.72 IR-13 Ccp-08 36.79 0.01 28.79 32.37 1.45 0.29 < mdl 0.03 < mdl 0.06 < mdl < mdl < mdl < mdl < mdl 0.16 99.93 IR-13 Ccp-09 35.08 0.01 30.21 33.95 0.77 < mdl 0.01 < mdl < mdl 0.77 < mdl 0.01 < mdl < mdl < mdl < mdl 100.79 IR-13 Ccp-10 35.83 0.04 29.39 33.11 0.89 < mdl < mdl < mdl 0.01 0.03 < mdl < mdl 0.06 < mdl < mdl 0.04 99.38 IR-13 Ccp-11 35.88 < mdl 29.85 32.97 1.18 < mdl < mdl < mdl < mdl 0.07 < mdl < mdl < mdl < mdl < mdl 0.05 100.01 IR-13 Ccp-12 35.27 < mdl 30.57 33.45 0.05 0.07 < mdl < mdl < mdl 0.05 < mdl < mdl < mdl < mdl < mdl < mdl 99.46 IR-13 Ccp-13 35.88 < mdl 29.07 32.60 1.30 0.11 < mdl 0.06 < mdl 0.06 < mdl 0.02 0.14 < mdl < mdl 0.05 99.29 S18-9 Ccp-01 34.85 < mdl 29.96 32.85 < mdl < mdl 0.03 < mdl < mdl 0.75 < mdl < mdl 0.01 < mdl < mdl < mdl 98.44 S18-9 Ccp-02 35.43 < mdl 30.41 32.77 < mdl < mdl < mdl 0.07 < mdl 0.69 0.01 0.01 < mdl < mdl 0.08 < mdl 99.46 S18-9 Ccp-03 35.82 0.03 31.23 32.28 0.04 0.11 < mdl 0.01 < mdl 0.09 < mdl 0.03 0.01 < mdl 0.03 0.03 99.70 S18-9 Ccp-04 34.89 0.01 31.41 33.80 0.05 0.01 < mdl 0.02 0.05 0.06 < mdl < mdl < mdl < mdl 0.05 0.03 100.38 S18-9 Ccp-05 34.74 < mdl 30.21 32.91 < mdl < mdl < mdl < mdl < mdl 0.75 < mdl 0.03 < mdl < mdl 0.07 0.02 98.72 S18-9 Ccp-06 35.33 0.08 31.15 33.35 0.04 < mdl < mdl < mdl < mdl 0.09 < mdl 0.01 < mdl < mdl < mdl < mdl 100.04 S18-9 Ccp-07 35.32 < mdl 30.34 32.79 < mdl < mdl < mdl < mdl < mdl 0.75 < mdl < mdl < mdl 0.01 < mdl < mdl 99.20 S18-9 Ccp-08 35.48 < mdl 30.07 32.93 < mdl < mdl < mdl < mdl < mdl 0.73 < mdl < mdl < mdl < mdl < mdl 0.02 99.23 S18-9 Ccp-09 35.16 0.01 31.23 33.77 < mdl 0.02 < mdl < mdl 0.05 0.08 < mdl < mdl < mdl < mdl < mdl 0.02 100.33 S18-9 Ccp-10 34.80 0.04 32.91 31.00 0.14 0.05 < mdl < mdl 0.04 0.09 < mdl 0.01 < mdl 0.04 < mdl 0.06 99.16 S18-9 Ccp-11 34.98 < mdl 30.23 32.89 < mdl < mdl < mdl < mdl < mdl 0.76 < mdl 0.05 0.02 < mdl < mdl < mdl 98.92 S18-9 Ccp-12 35.02 < mdl 30.47 33.16 < mdl < mdl < mdl 0.07 < mdl 0.78 < mdl < mdl 0.03 0.02 0.04 < mdl 99.58 S18-9 Ccp-13 34.98 0.03 30.54 33.05 < mdl < mdl < mdl 0.04 < mdl 0.76 0.01 0.02 < mdl < mdl 0.08 < mdl 99.50 S18-9 Ccp-14 35.45 0.04 31.04 33.94 0.03 < mdl < mdl < mdl < mdl 0.05 < mdl < mdl < mdl < mdl < mdl 0.03 100.58 S18-9 Ccp-15 36.00 0.03 31.73 32.12 0.02 0.01 < mdl 0.02 < mdl 0.07 < mdl < mdl < mdl < mdl < mdl 0.01 100.01 Avg. (N = 35) 35.44 0.01 30.53 32.69 0.44 0.02 0.01 0.02 0.02 0.32 < mdl 0.01 0.02 < mdl 0.02 0.03 99.56

(“ < mdl”: below minimum detection limit). Analytical Institution: Electron Microprobe Laboratory, SYSU.

Table A3 EPMA data (wt%) of pyrite in diﬀerent types of the Edmond hydrothermal precipitates.

Sample No. S Se Fe Cu Zn Pb Mn As Sb Co Ni Cd In Sn Au Ag Total

IR-12 Py-01 53.40 < mdl 43.22 0.08 3.67 < mdl < mdl 0.03 < mdl < mdl 0.01 0.04 0.02 < mdl < mdl < mdl 100.46 IR-12 Py-02 51.74 0.04 44.02 0.29 2.47 < mdl < mdl 0.02 < mdl < mdl < mdl 0.02 < mdl < mdl 0.15 0.22 98.97 IR-12 Py-03 51.21 < mdl 41.00 0.10 6.35 < mdl < mdl < mdl < mdl < mdl 0.02 0.01 < mdl < mdl < mdl 0.03 98.72 IR-12 Py-04 53.62 0.02 45.15 0.04 1.59 < mdl < mdl < mdl < mdl < mdl 0.01 0.03 0.01 < mdl < mdl 0.03 100.49 IR-12 Py-05 51.70 0.01 40.77 0.19 7.93 < mdl < mdl < mdl < mdl < mdl < mdl < mdl < mdl < mdl 0.27 0.06 100.93 IR-12 Py-06 53.01 0.01 42.88 0.78 1.91 < mdl < mdl < mdl < mdl < mdl < mdl < mdl < mdl < mdl < mdl 0.89 99.48 IR-12 Py-07 53.56 0.02 45.10 0.03 0.05 < mdl < mdl 0.18 < mdl 1.10 < mdl 0.03 < mdl < mdl < mdl < mdl 100.06 IR-12 Py-08 53.64 < mdl 45.29 0.03 < mdl < mdl < mdl < mdl < mdl 1.12 < mdl < mdl < mdl < mdl < mdl < mdl 100.07 IR-12 Py-09 53.04 < mdl 45.21 0.05 0.47 < mdl < mdl 0.06 < mdl 1.12 0.01 0.03 < mdl 0.03 < mdl < mdl 100.01 IR-12 Py-10 53.36 < mdl 44.74 0.12 0.02 < mdl < mdl < mdl < mdl 1.59 < mdl < mdl 0.03 0.01 < mdl 0.01 99.88 IR-12 Py-11 53.24 < mdl 44.30 0.05 < mdl < mdl < mdl 0.24 < mdl 1.81 < mdl < mdl < mdl < mdl < mdl < mdl 99.65 IR-12 Py-12 53.72 < mdl 44.78 0.05 < mdl < mdl 0.01 0.11 < mdl 1.42 0.01 < mdl < mdl < mdl < mdl < mdl 100.10 IR-12 Py-13 53.40 < mdl 44.41 0.03 0.03 < mdl < mdl 0.30 < mdl 1.32 < mdl < mdl < mdl < mdl < mdl < mdl 99.48 IR-12 Py-14 53.32 < mdl 45.11 0.04 0.04 < mdl 0.01 0.01 < mdl 1.13 0.01 0.01 < mdl 0.01 < mdl < mdl 99.67 IR-12 Py-15 52.49 0.02 44.52 < mdl 0.03 < mdl < mdl < mdl < mdl 1.05 < mdl 0.02 < mdl < mdl < mdl 0.01 98.15 IR-12 Py-16 53.77 0.01 44.67 0.02 0.09 < mdl < mdl < mdl < mdl 1.07 < mdl 0.03 < mdl < mdl < mdl < mdl 99.65 IR-13 Py-01 51.31 < mdl 46.66 0.17 0.02 0.01 < mdl 0.01 0.01 0.17 < mdl < mdl 0.02 < mdl 0.09 0.03 98.50 IR-13 Py-02 55.60 < mdl 44.97 < mdl 0.02 0.01 < mdl < mdl 0.04 0.10 < mdl 0.01 < mdl < mdl 0.06 < mdl 100.81 IR-13 Py-03 54.66 < mdl 45.90 0.02 0.02 0.14 < mdl 0.01 < mdl 0.13 < mdl 0.05 < mdl < mdl 0.07 < mdl 101.00 IR-13 Py-04 54.78 < mdl 45.23 0.07 0.05 0.01 < mdl 0.01 < mdl 0.07 < mdl < mdl < mdl < mdl < mdl < mdl 100.22 IR-13 Py-05 54.72 < mdl 46.25 0.27 0.05 < mdl < mdl < mdl < mdl 0.08 < mdl 0.04 0.04 < mdl < mdl < mdl 101.45 IR-13 Py-06 54.68 0.02 45.74 0.02 0.02 0.01 < mdl < mdl 0.02 0.10 < mdl 0.01 < mdl < mdl < mdl < mdl 100.62 IR-13 Py-07 54.40 < mdl 43.98 0.02 < mdl 0.06 < mdl < mdl < mdl 2.26 < mdl < mdl 0.01 < mdl 0.01 < mdl 100.73 IR-13 Py-08 57.51 < mdl 42.68 0.02 0.07 0.06 < mdl 0.02 0.01 0.10 < mdl < mdl < mdl < mdl < mdl 0.02 100.50 IR-13 Py-09 54.98 < mdl 44.56 0.02 < mdl < mdl < mdl 0.01 < mdl 0.09 < mdl < mdl < mdl < mdl < mdl < mdl 99.65 S18-9 Py-01 53.02 0.09 44.39 0.09 < mdl < mdl < mdl 0.06 < mdl 1.12 0.02 0.02 < mdl < mdl < mdl < mdl 98.82 S18-9 Py-02 53.51 < mdl 44.77 0.05 0.01 < mdl < mdl 0.01 < mdl 1.08 < mdl < mdl 0.02 0.04 < mdl 0.03 99.52 S18-9 Py-03 53.77 0.04 45.18 0.02 0.04 < mdl < mdl 0.04 < mdl 1.11 < mdl 0.02 < mdl 0.02 0.10 < mdl 100.32 S18-9 Py-04 53.33 < mdl 44.63 0.34 < mdl < mdl < mdl 0.01 < mdl 0.45 < mdl < mdl < mdl < mdl < mdl 0.01 98.78 (continued on next page)

344 Z. Wu et al. Ore Geology Reviews 92 (2018) 318–347

Table A3 (continued)

Sample No. S Se Fe Cu Zn Pb Mn As Sb Co Ni Cd In Sn Au Ag Total

S18-9 Py-05 53.59 0.01 44.49 0.23 0.03 0.04 < mdl 0.05 0.02 0.69 < mdl < mdl < mdl < mdl < mdl 0.02 99.17 S18-9 Py-06 53.28 < mdl 44.56 0.07 0.01 < mdl < mdl 0.02 < mdl 1.19 0.01 0.04 < mdl < mdl < mdl < mdl 99.18 S18-9 Py-07 54.00 < mdl 45.24 0.03 0.03 < mdl < mdl 0.03 < mdl 1.14 < mdl < mdl < mdl < mdl 0.11 0.01 100.58 S18-9 Py-08 53.71 < mdl 45.26 0.28 0.01 < mdl < mdl 0.02 < mdl 1.26 < mdl 0.05 < mdl < mdl < mdl < mdl 100.60 S18-9 Py-09 53.34 < mdl 44.99 0.15 < mdl 0.01 < mdl < mdl < mdl 0.40 0.01 < mdl < mdl < mdl 0.05 0.04 98.98 S18-9 Py-10 53.23 < mdl 44.38 0.31 0.02 0.07 < mdl < mdl < mdl 0.62 < mdl 0.05 0.01 < mdl < mdl < mdl 98.69 S18-9 Py-11 53.83 < mdl 44.65 0.15 0.03 < mdl < mdl < mdl < mdl 1.07 0.01 < mdl 0.04 0.05 < mdl 0.02 99.84 S18-9 Py-12 53.45 < mdl 44.88 0.10 0.06 < mdl < mdl 0.01 < mdl 1.09 < mdl < mdl < mdl < mdl < mdl < mdl 99.60 S18-9 Py-13 55.36 0.01 45.84 0.14 < mdl < mdl < mdl < mdl < mdl 0.15 < mdl < mdl 0.05 < mdl < mdl 0.05 101.59 S18-9 Py-14 53.93 < mdl 43.93 0.10 0.01 < mdl < mdl 0.08 < mdl 2.05 < mdl < mdl < mdl < mdl 0.01 < mdl 100.11 S18-9 Py-15 55.35 < mdl 45.63 0.25 < mdl < mdl < mdl 0.11 0.01 0.28 < mdl < mdl < mdl < mdl 0.10 < mdl 101.73 S18-9 Py-16 53.79 0.02 45.24 0.31 0.02 0.02 < mdl 0.22 < mdl 0.88 0.01 < mdl 0.02 < mdl 0.08 < mdl 100.61 S18-9 Py-17 54.18 < mdl 46.05 0.11 < mdl 0.04 < mdl 0.06 < mdl 0.20 0.02 < mdl < mdl < mdl < mdl < mdl 100.67 S18-9 Py-18 52.79 < mdl 43.98 0.35 0.06 < mdl < mdl 0.01 0.01 0.68 < mdl 0.02 < mdl < mdl 0.16 0.02 98.08 S18-9 Py-19 53.12 0.01 43.83 0.37 < mdl < mdl < mdl < mdl < mdl 1.15 0.02 0.01 < mdl < mdl < mdl < mdl 98.51 S18-9 Py-20 53.17 < mdl 45.28 0.09 0.07 < mdl < mdl < mdl 0.01 0.43 < mdl 0.01 < mdl < mdl < mdl 0.01 99.06 S18-9 Py-21 53.77 0.02 45.40 0.16 0.01 0.08 < mdl 0.03 0.02 0.37 < mdl < mdl < mdl < mdl < mdl 0.01 99.88 S18-9 Py-22 53.59 0.05 45.02 0.05 0.03 < mdl < mdl 0.03 < mdl 1.43 < mdl < mdl < mdl < mdl < mdl 0.04 100.24 S18-9 Py-23 52.92 0.04 44.86 0.45 0.02 < mdl 0.01 < mdl < mdl 1.34 < mdl 0.02 < mdl 0.01 0.10 < mdl 99.76 S18-9 Py-24 53.15 < mdl 45.62 0.14 0.02 0.01 < mdl < mdl < mdl 0.24 < mdl < mdl 0.07 < mdl 0.08 < mdl 99.33 S18-9 Py-25 52.92 < mdl 45.18 0.18 0.02 0.08 < mdl < mdl < mdl 0.19 < mdl < mdl < mdl < mdl < mdl 0.03 98.61 S18-9 Py-26 52.88 < mdl 45.41 0.22 0.02 < mdl < mdl < mdl < mdl 0.23 0.01 0.04 0.01 < mdl 0.15 < mdl 98.97 S18-9 Py-27 53.61 0.03 44.95 0.24 < mdl 0.10 < mdl < mdl 0.01 0.35 < mdl 0.01 < mdl < mdl < mdl < mdl 99.29 S18-9 Py-28 52.22 < mdl 47.87 0.11 0.04 0.02 < mdl 0.03 0.02 0.15 < mdl < mdl < mdl 0.01 < mdl 0.01 100.47 Avg. (N = 53) 53.58 0.01 44.77 0.14 0.48 0.01 < mdl 0.03 < mdl 0.70 < mdl 0.01 0.01 < mdl 0.03 0.03 99.82

(“ < mdl”: below minimum detection limit). Analytical Institution: Electron Microprobe Laboratory, SYSU. Note that some spot analyses with anomalously high measured levels of Au and Ag up to thousands of ppm are probably attributable to the presence of submicroscopic native gold, electrum and/or other Ag-mineral inclusions hosted within pyrite/marcasite matrix (considering secondary excitation eﬀects of surrounding Au-Ag particles).

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