Cement in Cambrian Sandstone : Assessing the Potential for the Generation of Respirable Silica J. Brian Mahoney Kent M. Syverson Department of Geology University of Wisconsin-Eau Claire • Geologic Setting • Industrial Silica Sand • Community Concerns • Identifying Particulate Matter • Geologic Setting • Industrial Silica Sand • Community Concerns • Identifying Particulate Matter Mt. Simon Formation Eau Claire Eau Claire/Wonewoc Formation contact Tilden, WI Wonewoc/Lone Rock Formation contact Colfax, WI Jordan Formation Arcadia, WI A' A northwest Iowa southeastern west-central Minnesota Wisconsin Paleoseaward Oneota Dolomite RSL Paleolandward Jordan Ss FSL Jordan Ss St Lawrence Fm St Lawrence Fm FSL Mazom anie RSL RSL Wonewoc Ss Wonewoc Ss FSL FSL Wonewoc Ss Eau Claire Fm 100 ft 25 m Eau Claire Fm RSL Mt Simon Ss 25 miles RSL 0 40 km Fine- to coarse-grained, quartzose sandstone: nonmarine Fine- to coarse-grained, quartzose sandstone: nearshore marine Very fine grained, feldspathic sandstone, siltstone, shale: offshore siliciclas Carbonate: "offshore" subtidal and peritidal carbonate parasequence boundary or parallel to inferred parasequence boundaries unconformity correlative conformity • Geologic Setting • Industrial Silica Sand • Community Concerns • Identifying Particulate Matter Minnesota Grain Size Distribution Wisconsin Grain Size Distribution 50 50 s s e e v v e e i i S 40 s 40 n n o o ST. PETER d 30 ST. PETER d e e 30 n n i i JORDAN a JORDAN a t t e 20 e r 20 WONEWOC R WONEWOC % % MT. SIMON e e g g 10 10 a a r r e e v v A A 0 0 10-40 40-70 70-100 >1 00 10-40 40-70 70-100 >1 00 Sieve size Sieve size Upper Mississippi Valley is the source of the highly valued Northern White Frac Sand Quality The characteristics of a high quality frac sand include: • high-purity silica sand (>95% quartz) • easily disaggregated • grain size perfectly matched to job requirements • spherical shape that enables it to be carried in hydraulic fracturing fluid with minimal turbulence • durability to resist crushing forces of closing fractures • Geologic Setting • Industrial Silica Sand • Community Concerns • Identifying Particulate Matter Community concerns over frac sand mining: • Air quality: exposure to respirable silica • Water issues: quantity and quality • Transportation issues – increased truck/rail traffic • Aesthetic issues: alteration of landscape Preferred Sands, Bloomer, Wisconsin EPA estimates that 2.2M workers are exposed to respirable crystalline silica. 85% are in the construction industry. 15% are in general industry •Highway and bridge construction and repair •Building construction, demolition, and repair •Masonry work •Concrete finishing •Drywall finishing •Rock drilling •Mining •Sand and gravel screening •Rock crushing (for road base) •Abrasive blasting Silicosis is a known occupational health hazard First step to any Solution is determining the nature of the Problem Must determine: • composition of fugitive particulates • source of particulate matter . Interstitial cement? . Particle fracturing? • Size and composition of airborne particulates • Geologic Setting • Industrial Silica Sand • Community Concerns • Identifying Particulate Matter Four Cambrian-Ordovician sandstone units: Mt. Simon Formation Wonewoc Formation Jordan Formation St Peter Formation Different interstitial Cements: 1. Calcite 2. Authigenic Feldspar 3. Sericite 4. Hematite 5. Quartz Grain at sand/silt boundary, 62.5 microns (230 mesh) Sand grain, 210 microns = 0.21 mm (70 mesh). Smallest sand grain companies want to mine Respirable particle (silt fraction), 4 microns Thickness of average human hair = 100 microns Quartz grains (crystalline silica) Cement (i.e. “glue”) composition? If cement is crystalline silica, then this likely would be the major source of that material in airborne particulate matter. n=2 Polymict Quartz Detrital Feldspar + Clay + Authigenic Feldspar Quartz Mt Simon Formation, Eau Claire (F.O.V.=11 mm) Polymict Quartz Quartz Authigenic K-spar Detrital Microcline Mt Simon Formation, Eau Claire (F.O.V.=3 mm) n=17 n=17 Polymictic Quartz Quartz Wonewoc Formation, Colfax (F.O.V.=11 mm) Quartz Quartz Authigenic K-spar Fe2O3 rim Quartz Void space Wonewoc Formation, Colfax (F.O.V.=3 mm) Wonewoc Fm. Hematite filling pore space (F.O.V.= 1.9mm) Wonewoc Fm. Sericite filling pore space (F.O.V.= .64mm) Jordan Formation n=11 Quartz Jordan Formation, Arcadia (F.O.V.=11 mm) Quartz Void space Quartz Authigenic K-spar Quartz Jordan Formation, Arcadia (F.O.V.=3 mm) Jordan Fm. Fine grained, feldspathic arenite with calcite cement (F.O.V. = 1.9mm) Jordan Fm. Angular Calcite filling pore space (F.O.V.= .64mm) Jordan Fm. Authigenic K-spar overgrowth filling pore space (F.O.V.= .64mm) Carbonate cement Silica cement Carbonate cement Silica cementation in upper Jordan Formation, Arcadia, Wisconsin. Silica cement is rare, constituting <2% of strata in the region, and is constrained to the upper Jordan Formation. These zones cannot be disaggregated, and are treated as waste rock. Quartz Upper Jordan Formation, Monroe County (F.O.V.=11 mm) Quartz Quartz Quartz Overgrowth Quartz Upper Jordan Formation, Monroe County (F.O.V.=3 mm) NOT ECONOMIC, CANNOT BE DISAGGREGATED Quartz St Peter Sandstone, River Falls (F.O.V.=11 mm) Quartz Quartz Quartz Authigenic K-spar Void space St Peter Sandstone, River Falls (F.O.V.=3 mm) Sandstone Composition Sandstone units are dominated by: detrital quartz grains (60.5 to 74.5%) pore spaces (17.0 to 21.4%) minor constituents included K-spar, plagioclase, mica, and brachiopod fragments. Sandstone cements include (in decreasing order) Calcite Hematite Authigenic feldspar Sericite Silica . Diagenetic history The primary cements suggest a complex multi-phase diagenesis characterized by multiple precipitation and dissolution events. The order of events appears to be: 1) deposition 2) authigenic K-spar formation 3) pore space formation 4) hematite precipitation 5) calcite precipitation. The lack of authigenic quartz cement implies that the respirable particulate matter generated from the mining process should be low in crystalline silica EOG processing facility, Chippewa Falls, WI Ongoing Research • Increase sample density . Stratigraphically and regionally • Document fine-grained component . SEM/Geochemistry • Grain shape analysis . Quantify spalling Urgent need for detailed compositional analysis of captured airborne particulates to compare to airborne particulate size data OSHA proposed occupational daily limit Source: Air Control Techniques, P.C. Study of EOG plant/mines, Chippewa County, Fourth Quarter 2012 report, March 2013 .