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The oxidation of pyrite is often one of the main drivers affecting groundwater quality during managed aquifer recharge in deep aquifers. Data and techniques that allow detailed identification and quantification of pyrite oxidation are therefore crucial for assessing and predicting the adverse water quality changes that may be associated with this process. In this study, we explore the benefits of combining stable sulphur isotope analysis with reactive transport modelling to improve the identification and characterisation of pyrite oxidation during an aquifer storage and recovery experiment in a chemically and physically heterogeneous aquifer. We characterise the stable sulphur isotope signal (δ34S) in both the ambient groundwater and the injectant as well as its spatial distribution within the sedimentary sulphur species. The identified stable sulphur isotope signal for pyrite was found to vary between −32 and +34‰, while the signal of the injectant ranged between +9.06 and +14.45‰ during the injection phase of the experiment. Both isotope and hydrochemical data together suggest a substantial contribution of pyrite oxidation to the observed, temporally variable δ34S signals. The variability of the δ34S signal in pyrite and the injectant were both found to complicate the analysis of the stable isotope data. However, the incorporation of the data into a numerical modelling approach allowed to successfully employ the δ34S signatures as a valuable additional constraint for identifying and quantifying the contribution of pyrite oxidation to the redox transformations that occur in response to the injection of oxygenated water.

Optimizing uncertainty reduction in evaluations of geological CO2 storage site scenarios requires a robust database that allows an accurate reconstruction of the targeted storage rock/fluid volume, especially with respect to spatial heterogeneity. Previous numerical simulations of the Rock Springs Uplift site (southwest Wyoming, USA) relied on a generalized regional database to populate a homogenous rock/fluid volume based on average reservoir properties. The results from this approach yielded general insights into injection/storage characteristics but lacked specificity, resulting in performance assessments plagued by substantial uncertainty. To move from idealistic, highly generalized assessments to realistic, low-risk assessments of the Rock Springs Uplift, it was necessary to acquire high-resolution data specific to the storage site of interest (carbonate and sandstone reservoirs, and confining layers in an 8 km × 8 km area). The foundation of the new database is a 4,000-meter-deep stratigraphic test well, an 8 km × 8 km 3-D seismic survey, 290 meters of high-quality core, a specialized log suite, fluid samples, and a diverse set of analytical laboratory measurements. These data made it possible to correlate seismic attributes with observations from log suites, a VSP survey, core, fluid samples, and laboratory analyses, including continuous permeability scans. From seismic data, 3-D spatial distribution volumes of reservoir and confining layer properties were constructed that represent geological heterogeneity at the targeted CO2 storage site. Consequently, the latest numerical simulations and performance assessments are characterized by substantially lower geological uncertainties. The new CO2 plume migration simulations for a set of defined CO2 injection rates and volumes occupy larger rock/fluid volumes and display pronounced marginal irregularities when compared to early simulations derived from homogenous reservoir parameter volumes. The spatial distributions of the injected CO2 plumes in previous simulations are conical with few marginal irregularities, whereas in the new simulations, the CO2 plumes occupy a larger up-dip volume and display pronounced marginal irregularities. These irregularities denote zones of higher porosity and permeability, such as collapsed breccias associated with karst zones and/or dolomitized grainstone zones in the Madison Limestone. Using the new numerical simulations which include heterogeneous rock/fluid parameter distributions, it is apparent that in all injection/storage scenarios of > 1 Mt/year CO2, substantial displaced fluid production/treatment is essential to manage pressure and maintain the integrity of confining layers. The total dissolved solids concentrations of the formation fluids retrieved from the Madison Limestone range from 80,000 to 90,000 ppm, and will necessitate customized water treatment strategies and facilities at the surface. The new data and upgraded evaluations demonstrate that the Rock Springs Uplift in southwestern Wyoming remains an outstanding large-scale geological CO2 storage site, and provides a realistic basis for designing commercial CO2 injection/storage operations on the Uplift. The 2010 U.S. Environmental Protection Agency Greenhouse Gas Reporting Program reports that in the Greater Green River Basin of southwest Wyoming, the CO2 emissions from stationary sources (sources that emit more than 25,000 tons of CO2 per year) total 29+ million tons annually, or approximately 50 percent of Wyoming's annual CO2 emissions. These CO2 sources include coal-fired power plants, gas and trona processing plants, pipeline compression stations, chemical production facilities, and gas-field complexes, among others. The Rock Springs Uplift in the center of the Greater Green River Basin is ideally located to serve as a large-scale commercial geological CO2 storage facility for half of all of Wyoming's industrial CO2 emissions. The new numerical simulations suggest that the Madison Limestone has the ability to permanently store the annual CO2 emissions from stationary sources in the Greater Green River Basin for 130 years (i.e., a total of 3.8 billion tons). The overlying Paleozoic Weber Sandstone on the Rock Springs Uplift has additional commercial-scale CO2 storage capacity. The Rock Springs Uplift has the attributes to serve as a regional CO2 storage site, and importantly, this site could be used as a storage/surge tank to supply CO2 to EOR projects throughout Wyoming.

We describe preliminary application of the CO2-PENS performance and risk analysis tool to a planned geologic CO2 sequestration demonstration project in the Rock Springs Uplift (RSU), located in south western Wyoming. We use data from the RSU to populate CO2-PENS, an evolving system-level modeling tool developed at Los Alamos National Laboratory. This tool has been designed to generate performance and risk assessment calculations for the geologic sequestration of carbon dioxide. Our approach follows Systems Analysis logic and includes estimates of uncertainty in model parameters and Monte-Carlo simulations that lead to probabilistic results. Probabilistic results provide decision makers with a range in the likelihood of different outcomes. Herein we present results from a newly implemented approach in CO2-PENS that captures site-specific spatially coherent details such as topography on the reservoir/cap-rock interface, changes in saturation and pressure during injection, and dip on overlying aquifers that may be impacted by leakage upward through wellbores and faults. We present simulations of CO2 injection under different uncertainty distributions for hypothetical leaking wells and faults. Although results are preliminary and to be used only for demonstration of the approach, future results of the risk analysis will form the basis for a discussion on methods to reduce uncertainty in the risk calculations. Additionally, we present ideas on using the model to help locate monitoring equipment to detect potential leaks. By maintaining site-specific details in the CO2-PENS analysis we provide a tool that allows more logical presentations to stakeholders in the region.

The Xinjie layered intrusion is one of a number of major ultramafic-mafic bodies hosting Fe-Ti-V deposits and Cu-Ni-PGE sulfide deposits in the Pan-Xi (Panzhihua-Xichang) area of the Sichuan Province, SW China. The Xinjie ultramafic-mafic layered intrusion, genetically related to the Permian plume-related Emeishan flood basalts, consists of three lithological cycles, each representing a sequence from ultramafic to mafic-felsic composition. The basal part of the intrusion is composed of three lithological units, namely, the Marginal Unit (MU), Peridotite Unit (PeU) and Pyroxenite Unit (PyU). In the present study, three major PGE-mineralised Cu-Ni sulfide layers were discovered within the Marginal and Pyroxenite Units. The major base-metal sulfides (BMS) comprise chalcopyrite, pyrrhotite, and pentlandite. Detailed microscopic and microprobe analyses revealed the presence of the sperrylite and Pd-Pt-Bi-Te minerals (merenskyite, moncheite, and michenerite). These PGMs are commonly associated with the BMS, or magnetite coexisting with BMS in the PGE-enriched layers. The 1:1 substitution between Pt and Pd, as well as between Te and Bi, confirms the complete solid-solution series between moncheite and merenskyite. The textural association of the PGMs with BMS and Fe-Ti oxides (magnetite) suggests that the PGMs may have crystallised slightly later than the hosting magnetite and BMS. The formation of magnetite may have played an important role in producing the sulfur-saturated melt and the PGEs thus concentrated in the sulfide liquid during the crystallisation history. It is therefore suggested that the Cu-Ni-PGE-bearing layers in the basal part of the Xinjie intrusion were generated by magma evolution processes.

The Lengshuiqing Cu–Ni sulfide deposit of the Yanbian area in Sichuan Province, SW China, is hosted by relatively small mafic–ultramafic bodies that intruded Mesoproterozoic metavolcanic rocks and schists. The mafic–ultramafic complex is mainly composed of the olivine-hornblende pyroxenite and hornblende gabbro units. 40 Ar/ 39 Ar age, elemental and Sr–Nd–Pb isotopic results of the complex are reported in this paper. 40 Ar/ 39 Ar dating of hornblende yielded an age of 821 ± 1 Ma for the mafic–ultramafic complex. This age is similar to the SHRIMP U–Pb zircon age of 825 ± 12 Ma for the adjacent Gaojiacun mafic–ultramafic complex. This suggests that the Lengshuiqing mafic–ultramafic complex originated from Neoproterozoic mafic magma. The olivine-hornblende pyroxenite unit is characterized by high MgO contents (24.25–28.08%), Mg # values (74.5–78.0) and compatible elements (Cr = 1179–2336 ppm, Ni = 732–1303 ppm), low ΣREE (19.5–44.6 ppm) and other incompatible element contents. The hornblende gabbro unit has MgO = 7.32–12.51%, Mg # = 55.0–69.3, Cr = 37.7–1131 ppm, Ni = 50.0–243 ppm and ΣREE = 37.2–75.4 ppm. Most of the rocks are moderately enriched in LREE ((La/Yb) N = 2.28–7.67), and significantly depleted in Nb–Ta ((Nb/La) PM = 0.17–0.47; (Ta/La) PM = 0.19–0.58), with slightly moderately positive Eu anomalies ( δ Eu = 0.95–1.65). The trace element feature of the ore-bearing samples is similar to that of the rocks in the complex. The variations in major and trace elements can be well explained by magma crystal fractionation. Isotopically, the rocks in Lengshuiqing mafic–ultramafic complex are characterized by low 87 Sr/ 86 Sr(i) (0.7039–0.7044), positive ɛ Nd (i) (+2.2 − +4.3) and low radiogenic Pb values ( 206 Pb/ 204 Pb(i) = 17.382–17.913, 207 Pb/ 204 Pb(i) = 15.518–15.578, 208 Pb/ 204 Pb(i) = 37.227–38.019). The ores also have positive ɛ Nd (i) (+2.4 − +5.4), and low radiogenic Pb values ( 206 Pb/ 204 Pb(i) = 17.256–17.733, 207 Pb/ 204 Pb(i) = 15.484–15.555, 208 Pb/ 204 Pb(i) = 36.924–37.665). All the samples exhibit positive ɛ Nd (i) values, suggesting that their parental magmas were derived from a long-term depleted asthenospheric mantle. The relatively large variations in 87 Sr/ 86 Sr(i) of the ores (0.7012–0.7046) could be ascribed to the interaction between magma and country rocks. A good positive correlation between Nb/La and Nb/Th reveals that crustal assimilation was involved in their genesis. This contamination resulted in the observed depletion of Nb and Ta in rocks and ores. The crustal contamination and fractional crystallization, similar to the process of magmatic assimilation and fractional crystallization (AFC), are thus critical for the formation of the Lengshuiqing Cu–Ni ore deposit. The Neoproterozoic Lengshuiqing Cu–Ni sulfide-bearing mafic–ultramafic intrusions formed in an intraplate continental rift, which was most likely related to a mantle plume underneath the supercontinent Rodinia.

The Gaojiacun mafic-ultramafic intrusive complex in the Yanbian area, Sichuan Province, is a stratiform intrusive body that has undergone intensive magmatic differentiation. This intrusive body involves two magmatic accumulating cycles. Systematic U-Pb dating of single zircon grains and40Ar/39Ar dating of hornblende were conducted, and the results showed that the age of hornblende gabbro, which was formed at the main phase of intrusion of the Gaojiacun intrusive complex, is 840–5 Ma, casting doubt on the concept of “Yanbian Ophiolite”. It is believed that the formation of the Gaojiacun intrusive complex seems to be related to a super-mantle plume underneath the super-continent Rodinia. The above research results are helpful for us to get a better understanding of the characteristics of Neoproterozoic tectonic evolution of the Yanbian area in Sichuan Province.