The Mariana intraoceanic volcanic arc system in the western Pacific Ocean hosts abundant ferromanganese (Fe-Mn) precipitates. A suite (n = 22) of Fe-Mn precipitates were collected from the southern portion of the arc and their mineralogies and chemical compositions were determined. These results were used to decipher their genetic assemblage, assess their potential as a source of trace metals, and place them into context with respect to Fe-Mn precipitates sampled at higher latitudes in the Mariana arc and from other locations, globally. Minerals identified include vernadite, birnessite, 10 angstrom manganate, manganite, hematite, goethite, maghemite, calcite, rhodochrosite, quartz, phillipsite, various feldspar, pyroxene, and clay minerals. Element discrimination diagrams indicate that the samples are predominantly of hydrothermal and hydrogenetic-hydrothermal (i.e., mixed) origin, with most reflecting some influence of both. Rare earth element and Y (REY) profiles are distinguished by negative Ce and Y anomalies and positive Eu anomalies. Together, the samples form a continuum from the hydrogenetic to hydrothermal endmembers. Samples with the largest hydrogenetic component are friable with branching oxide/oxyhydroxide growth structures, contain mostly vernadite, and have the greatest concentrations of most metals (including the REY elements). Hydrothermal input produces denser, cemented deposits that contain more 10 A and 7 A manganate minerals and lower minor-metal contents. Calculated growth rates range from 6 mm to >190 m Ma(-1). Average metal contents of Fe-Mn precipitates from the southern Mariana arc are low relative to hydrogenetic Fe-Mn crusts and hydrothermal Fe-Mn deposits from the northern Mariana arc and elsewhere, globally, and are therefore unlikely to be viable exploration targets.

ABSTRACT We report new isotopic data for H2 and CH4 gases and Sr for groundwater collected from Jurassic Kirkland Lake kimberlites in northern Ontario, Canada. Groundwaters interacting with kimberlites have elevated pH (up to 12.4), are reducing (Eh as low as the H2-H2O couple), are dominated by OH− alkalinity, and have non-radiogenic (mantle) 87Sr/86Sr values (∼0.706–0.707). Most significantly, the highest pH groundwaters have low Mg, high K/Mg, and are associated with abundant reduced gases (H2 ± CH4). Open system conditions favor higher dissolved inorganic carbon and CH4 production, whereas under closed system conditions low DIC, elevated OH− alkalinity, and H2 production are enhanced. Hydrogen gas is isotopically depleted (δ2HH2 = −771 to −801‰), which, combined with δ2HH2O, yields geothermometry temperatures of serpentinization of 5–25 °C. Deviation of H2-rich groundwaters (by up to 10‰) from the meteoric water line is consistent with Rayleigh fractionation during reduction of water to H2. Methane is characterized by δ13CCH4 = −35.8 to −68‰ and δ2HCH4 = −434‰. The origin of CH4 is inconclusive and there is evidence to support both biogenic and abiogenic origins. The modeled groundwater–kimberlite reactions and production of elevated concentrations of H2 gas suggest uses for diamond-production tailings, as a source of H2 for fuel cells and as a carbon sink.

There have been several advances in inductively coupled plasma-mass spectrometer (ICP-MS) analytical technologies in the last decade. Collision/reaction cell ICP-MS and triple quadrupole ICP-MS techniques can produce lower detection limits for select elements that experience interferences with a standard quadrupole (e.g. Se and As). Triple quadrupole ICP-MS, in particular, can eliminate virtually all polyatomic or isobaric interferences for highly accurate measurements of some element isotopes systematics that are of great interest in mineral exploration, namely Pb/Pb. Laser ablation ICP-MS has become more popular as an effective analytical tool to measure mineral grain trace elements, which could assist in vectoring to mineralization or exploration drill targets. The ablation of a spot on a Li-borate fused glass disk paired with XRF analysis has also gained popularity as an alternative to total whole rock characterization packages that employ several separate digestions and analytical methods. While there have been several advancements in ICP-MS technologies in exploration geochemistry, they have not been widely accepted or implemented. This slow adaptation could be due to the extended recession in the mining industry between 2012 and 2017. It is also possible that standard ICP-MS data (i.e. no collision/reaction cell) is still fit for purpose. This stands in stark contrast to implementation of ICP-MS in the previous decade (1997–2007), which was transformational for the industry. Consideration of all elements from large multi-element ICP-MS analytical suites for mineral exploration can be an extremely powerful tool in the exploration toolkit. The discovery of the White Gold District, Yukon, is a prime example of how the utilization of soil geochemical data, when plotted spatially, can vector to gold mineralization. The presence of Au + As + Sb soil anomalies were key to delineating mineralization, especially when accompanied by publicly available geological, geographical and geophysical data. Additionally, elements and element ratios not typically considered in Au exploration, including Ni and U, were utilized to determine the lithological and structural controls on mineralization. The availability of multi-element ICP-MS data was also useful in the discovery of the Cascadero Copper Taron Caesium deposit. Ore-grade Cs was discovered only because Cs was included in the multi-element ICP-MS exploration geochemistry suite. Before the availability of ICP-MS, it is unlikely that this deposit would have been discovered. Thematic collection: This article is part of the Exploration 17 collection available at: https://www.lyellcollection.org/cc/exploration-17

The Attawapiskat cluster of kimberlites in northern Ontario, Canada was chosen as a study site to evaluate geochemical anomalies in surface media associated with kimberlites. Kimberlites contain abundant ultramafic minerals and during weathering should impart electrochemically reducing conditions to surrounding surficial materials, both groundwater and sediments (Hamilton et al., 2004; Sader et al., 2007). The purpose of the study was to evaluate the processes of metal dispersion in wetlands overlying glacial and glaciomarine deposits, thereby assessing the validity of using geochemical techniques to discriminate kimberlites from other geophysical targets in similar terrain. Kimberlites in the Attawapiskat cluster are Jurassic in age (~170 Ma) and were emplaced through Ordovician and Silurian strata (Webb et al., 2004). They are overlain by glacial sediments which are capped by marine clays of the post-glacial Tyrrell Sea (~ 4000 – 12000 years BP). One to four meters of peat overlie kimberlites in this region (Fraser et al., 2005).

Lake Texoma is a large impoundment on the border of Texas and Oklahoma, formed from the confluence of two river systems with different salinities, the Red River (total dissolved salt, TDS, of 2700–11 900 mg/l, average of 4862 mg/l) and the Washita River (TDS of 420–915 mg/l, average of 701.4 mg/l). Systematic analyses for major and trace elements were conducted of water samples collected spatially and with depth in the lake in different seasons. Overall, Lake Texoma waters are characterized by Na-Ca-Cl-SO 4 -type waters with spatial distribution shifting from Na-Cl type to Ca-SO 4 type from the Red River arm to the main lake and to the Washita River arm. In addition, vertical and seasonal variations in major and trace elements concentrations indicate major elements in the lake are mainly controlled by different bedrock weathering from the two river systems. Trace elements that exhibit different distribution patterns to the major species are associated with variable sources such as river inflow, summer stratification effects, biological effects and anthropogenic activities. In Lake Texoma, differential inflow volumes and summer stratification are principal factors controlling the variation and geochemistry of lake waters and mixing dynamics. Supplementary material: Summary of major and trace element chemistry in the five zones of Lake Texoma for summer, fall and spring seasons (2003–2004) is available at http://www.geolsoc.org.uk/SUP18771

Shallow groundwaters were collected over and near buried kimberlites in the Attawapiskat River region of the James Bay Lowlands, Ontario, Canada in order to study the impact kimberlites have on CO2–CH4 systematics. Groundwaters collected from boreholes in kimberlites and limestone, and from groundwaters in overlying Tyrell Sea sediment (TSS) were analyzed for δ13CDIC, δ2HH2O, δ18OH2O, dissolved inorganic carbon (DIC), and metal concentrations. Methane gas samples from borehole and TSS groundwaters were analyzed for concentration, δ13CCH4, and δ2HCH4. The CH4 concentrations and Δ13CDIC–CH4 (isotope separation) values indicate biological carbonate reduction in TSS groundwaters overlying kimberlites. Whereas, Δ13CDIC–CH4 values from TSS groundwaters over limestone and from boreholes within limestone and kimberlite indicate the biological consumption of methane (oxidation). The δ2HH2O values from TSS over kimberlites are consistent with the variation in Δ13CDIC–CH4, as they are less negative compared to where they should fall on the local meteoric water line, suggesting that methanogens are using lighter δ2HH2O values to produce CH4. Biological DIC reduction requires H+ ions from H2O to form CH4. There is evidence in the water geochemistry to support the isotopic results, as the ratio of methane to calculated Fe3+ (as amorphous Fe hydroxide), SO42−, and O2(aq) is largest in the majority of TSS groundwaters over kimberlites (where Δ13CDIC–CH4 values indicate CH4 production). Low temperature serpentinization of olivine in kimberlite is not considered for CH4 production, as redox conditions in kimberlite groundwaters do not support abiogenic methane production. The findings here suggest that kimberlites are indirectly influencing the CO2–CH4 system by consuming oxidized ions in the overlying TSS, thereby creating a favorable environment for methane producing bacteria. In contrast, isotopes and geochemistry suggest methane oxidation in areas overlying limestone. The broader implication of this study is that variable lithology underlying sediment cover may impact biological methane production or consumption.

ABSTRACT Peat groundwater compositions at depths of 0.4 and 1.1 m below ground surface in the Attawapiskat region of the James Bay Lowlands are evaluated for diamond exploration applications. Samples were collected along transects that typically extended at least 200 m beyond the margins of Yankee, Zulu, and Golf kimberlites. Locations of upwelling groundwater usually occur at or near kimberlite margins based on hydrogeological measurements and variations in peat groundwater geochemical parameters (pH and EC are high, and the Eh is low relative to ombrotrophic peat groundwaters). Concentrations of the kimberlite pathfinder metals Ni, Cr, light rare earth elements (LREEs), Ba, Mg/Ca, and alkalis are commonly elevated at sample sites at or near kimberlite margins and where groundwaters are upwelling. The presence of elevated kimberlite pathfinders at these sites suggests that fractures along the boundaries between kimberlites and limestone formed during kimberlite emplacement provide dilation for upward movement of groundwater with elevated kimberlite pathfinder metals. Typically, Ni, Cr, LREE, and Ba behave similarly and thus high concentrations of these metals are found at similar locations along transects. On the other hand, locations of elevated alkalis and Mg/Ca vary. The spatial variations among pathfinder metals in peat groundwaters are possibly due to geochemical processes in the peat, such as metal binding to dissolved organic material, adsorption to insoluble organics or Fe-oxyhydroxides, and incorporation into secondary mineral precipitates, which can act to increase or decrease metal solubility. The findings of this study are readily applicable in diamond exploration in wetlands elsewhere.

The speciation and solubility of kimberlite pathfinder metals (Ni, Nd, Ba and K) in shallow peat groundwaters is investigated over the Yankee, Zulu and Golf kimberlites in the Attawapiskat region, James Bay Lowlands, Canada. The purpose of this study is to examine the relationship between dissolved organic matter (DOM) complexation with kimberlite pathfinder metals and determine the spatial distribution of those metals in shallow peat groundwaters along sampling transects over subcropping kimberlites. Nickel, Nd, Ba and K complexation with DOM and the adsorption of these metals onto ferrihydrite were calculated using Visual MINTEQ 3.0 and the NICA-Donnan database. Calculations predict almost 100% of soluble Nd, Ni and Ba form complexes with DOM at sampling sites with little to no contribution from upwelling groundwater (i.e., dissolved organic C (DOC) concentrations = 40-132 mg/L, pH = 3.9-5.5, and log ionic strength <=-3). In only the most ombrotrophic peat groundwater conditions does a majority fraction of K bind to DOM. By contrast, under conditions with large contributions from upwelling groundwaters (i.e., DOC concentrations <= 40 mg/L, pH = 5.5-6.5, and log ionic strength = -3 to -2), as little as 10% of Nd and Ni, and 0% K and Ba are predicted to complex with DOM. The modeling calculations suggest the dominant control on metal-DOM complexation, particularly with respect to Ni and Nd, is competitive effects for DOM binding sites due to elevated ionic strength where there is evidence of strong groundwater upwelling. Visual MINTEQ modeling of metal adsorption on ferrihydrite surfaces predicts that under strong upwelling conditions, Ni and Nd are scavenged from solution due to increased ferrihydrite precipitation and decreased fractions of metals complexed with DOM. Analytical geochemical data are consistent with model predictions of metal adsorption on ferrihydrite. Total dissolved Ni and Nd concentrations at sites of strong upwelling are up to five times lower than waters with little to no upwelling and log ferrihydrite saturation indices (logSl(ferr)) indicate precipitation (values up to 5) at sites of strong groundwater upwelling. Where the majority of Ni and Nd complex with DOM and ferrihydrite is highly under saturated (logSl(ferr) = -18 to -5), the concentrations of total Ni and Nd are elevated compared to other sites along sampling transects. Metal complexation with DOM effectively inhibits metal scavenging from solution via adsorption and/or from forming secondary mineral precipitates. Also, because alkaline earth metals do not compete strongly with Ni and Nd for adsorption sites on ferrihydrite surfaces, but do compete strongly for insoluble organic sites, Ni and Nd are more likely to adsorb onto ferrihydrite. (C) 2011 Elsevier Ltd. All rights reserved.

International Applied Geochemistry Symposium, 2009 1 Peat groundwater as a medium for surficial geochemical exploration Jamil A. Sader, Keiko Hattori, & Stewart M. Hamilton Unversity of Ottawa, Earth Sciences Department, Marion Hall, Room 121, Ottawa, Ontario, K1N 6N5, Canada (email: jamilsader@yahoo.com) Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario, P3E 6B5, Canada (e-mail: stew.hamilton@ontario.ca) ABSTRACT: Kimberlite-specific chemical responses are visible in shallow peat groundwater over Kimberlite-specific chemical responses are visible in shallow peat groundwater over kimberlites from the Attawapiskat region in the James Bay Lowlands, Canada. These chemical responses are visible due to the physical movement of deeper groundwater that has interacted with kimberlite and migrated through the Tyrell Sea sediment into shallow peat groundwater. The presence of elevated values of electrical conductivity, CaCO3 saturation index, Ca, and alkalinity indicate groundwater upwelling. Upwelling groundwaters that have high concentrations of Ni, Cr, Fe, Mg, and REEs are likely due to water-kimberlite rock interactions rather than interactions with limestone, or Tyrell Sea sediment. Some of these elements may behave more conservatively in peat groundwaters and are sometimes observed down the horizontal hydraulic gradient. This study has also determined that it is preferable to collect peat groundwater samples deeper into the saturated zone where waters are more reducing and are likely to have higher concentrations of elements. Increased depth into the saturated zone provides better groundwater geochemical resolution between locations of high element contents and lower contents along transects. More oxidized groundwaters near the surface tend produce oxyhydroxides that can adsorb to peat and lower element concentrations in peat groundwater.

Groundwaters from diamondiferous kimberlite pipes in the Kirkland Lake and Lake Timiskaming regions display unusual geochemical characteristics and signatures compared with groundwaters from the surrounding host rock. Reaction modelling was used to better constrain water/rock ratios, alteration mineralogy and groundwater geochemistry. A soil-zone Ca-HCO 3 − water from glacial till was reacted, using a reaction-modelling program, with three different suites of minerals: a kimberlite suite, a felsic intrusive suite and a mafic intrusive suite. Decreasing pH and alkalinity with increasing water/rock ratios in model reactions with the kimberlite suite suggest that sampled groundwaters are from both the hypabyssal facies (high pH and alkalinity; low water/rock ratios) and the diatreme facies (low pH and alkalinity; high water/rock ratios). Geochemical concentrations of sampled groundwaters from kimberlites were compared to modelled waters; results indicate that these waters are different from those flowing through local felsic or mafic intrusive rocks. The kimberlitic groundwaters, and modelled waters, contain low concentrations of Mg and Fe, high concentrations of K and Ca, have elevated pH (up to 12.45), and are defined as a Ca-OH − water for the A4 and B30 kimberlites. In contrast, the C14, Diamond Lake and 95-2 kimberlites contain groundwaters that have higher Mg and Fe, lower Ca and K concentrations, and relatively low pH (8.5–10). The reaction model suggests that different minerals precipitate where the water interacts with different kimberlite facies and/or where a different water/rock ratio exists. More hydroxide phases form where pH and hydroxide alkalinity are high. Where kimberlite waters interact with host-rock waters, minerals not likely to be found otherwise, such as magnesite, brucite and magnetite, may be detected along fractures, or near seeps or springs where groundwater comes to surface. Exploration for kimberlites can benefit from the use of groundwater. Groundwater interaction with kimberlitic rocks produces characteristic aqueous geochemical anomalies due to low-temperature serpentinization reactions. The identification of geochemical anomalies in the groundwaters down-flow of a kimberlite and the unusual mineral assemblages that may precipitate from these groundwaters may aid in the location of undiscovered kimberlites.