Correlating NORM with the mineralogical composition of shale at the microstructural and bulk scale

Radioactivity of Soil, Rock and Water in a Shale Gas Exploitation Area, SW China

“…At the same time, concerns regarding potential environmental pollution from hydraulic fracturing have also arisen [2,3], especially the potential contamination of shallow aquifers by hydraulic fracturing fluids and/or formation water from deep formations through induced and natural fractures [4], leaking from casings and cement or wastewater discharge [1,5]. Of the complex contaminants in hydraulic fracturing fluids and/or formation water, naturally occurring radioactive materials (NORM) are notable concerns [6][7][8]. For example, Warner et al [9] found that the radioactivity level of 226 Ra in stream sediments at the point of discharge at a waste treatment facility in central Pennsylvania was nearly 200 times greater than those of upstream and background sediments.…”

Potential Impacts of Shale Gas Development on Inorganic Groundwater Chemistry: Implications for Environmental Baseline Assessment in Shallow Aquifers

“…Shales are primarily composed of clay minerals (i.e., illite, mixed-layer illite/smectite, smectite, kaolinite, chlorite) and quartz and can contain significant proportions of other minerals such as feldspars (i.e., K-feldspars, plagioclase), micas (i.e., biotite, muscovite), and carbonate minerals (i.e., calcite, dolomite, siderite, ankerite). ,,,, Formed under reducing conditions, black shales contain abundant organic matter (>2% total organic carbon) and sulfide minerals, primarily pyrite. ,, Black shales are commonly enriched in trace elements that are primarily associated with sulfide minerals and to a lesser degree with organic matter and clay minerals. ,,, In particular, black shales are often enriched in trace metals and metalloids such as As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, U, V, and Zn ,,− and may contain significant contents of naturally occurring radioactive material (NORM). ,,, The high levels of radioactivity result from the natural abundance of U-238 and Th-232 and their decay products including isotopes of Ra, Po, Rn, and Pb in many organic-rich shale formations. , It is noteworthy that black shales can host sulfide ore deposits that usually contain very high contents of trace metals and metalloids. , As a result of water–rock interactions, elevated concentrations of trace metals/metalloids have been reported in shallow groundwater associated with organic-rich shale occurrences. ,− However, the concentrations of a number of trace metals/metalloids and NORMs were likely limited by sequestration in Fe–Mn oxyhydroxides and clay minerals in shallow oxidizing groundwater and by sulfide mineral and organic matter stability in reducing groundwater. , …”

“…Shales are primarily composed of clay minerals (i.e., illite, mixed-layer illite/smectite, smectite, kaolinite, chlorite) and quartz and can contain significant proportions of other minerals such as feldspars (i.e., K-feldspars, plagioclase), micas (i.e., biotite, muscovite), and carbonate minerals (i.e., calcite, dolomite, siderite, ankerite). 28,30,31,36,37 Formed under reducing conditions, black shales contain abundant organic matter (>2% total organic carbon) and sulfide minerals, primarily pyrite. 28,30,31 Black shales are commonly enriched in trace elements that are primarily associated with sulfide minerals and to a lesser degree with organic matter and clay minerals.…”

“…28,31,38,39 In particular, black shales are often enriched in trace metals and metalloids such as As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, U, V, and Zn 28,38,40−42 and may contain significant contents of naturally occurring radioactive material (NORM). 28,31,36,43 The high levels of radioactivity result from the natural abundance of U-238 and Th-232 and their decay products including isotopes of Ra, Po, Rn, and Pb in many organic-rich shale formations. 43,44 It is noteworthy that black shales can host sulfide ore deposits that usually contain very high contents of trace metals and metalloids.…”

“…106,116 These areas have been suggested to be at greater risk of contamination by upward fluid migration due to the occurrence of conductive pathways between deep formations and shallow aquifers, although the time scale for potential brine migration is poorly constrained 59,106 (Figure 1). A number of geochemical and isotopic tools have been applied to detect brine contribution to shallow groundwater in shale gas basins including concentrations and ratios of dissolved ions such as Cl, Br, Ba, Na, Li, Sr, and I, stable and radiogenic isotopes of dissolved elements (δ 11 B, δ 7 Li, 87 Sr/ 86 Sr, 228 Ra/ 226 Ra), and elemental and isotopic compositions of noble gases ( 3 He, 4 He, 20 Ne, 21 Ne, 22 Ne, 36 Ar, 38 Ar, 40 Ar). 21,59,115,117−121 Stable isotope ratios of water have been found to be less sensitive to small contributions of brines, in comparison with isotopes of dissolved constituents.…”