PBS-SEPM 2023 March Luncheon - Randy Blood

"The Occurrence of Critical Minerals in Fine-Grained Strata: Insights from the Upper Devonian of Western New York State." - D. Randy Blood, Scott D. McCallum, Ashley S.B. Douds, Wildlands Research, LLC
 
 
 
 
Abstract: 
Over the coming decades, global demand for critical minerals is projected to increase rapidly. Several organizations (the IEA and the USGS) have underscored the importance of defining the abundance and geographic distribution of these minerals, many of which are required materials for Li-ion battery development and may be found in black shale deposits. To-date, little attention has been given to understanding the geologic controls on the occurrence of these elements in black shale. Here we investigate depositional and diagenetic processes which may concentrate critical minerals into discrete beds, potentially providing more favorable economics for extraction.The Point Gratiot Bed, a prominent, laterally continuous black shale marking the Upper Devonian Mass Extinction occurs near the top of the Hanover Shale. An eastward thickening wedge of sediment, informally termed the Beaver Meadow Beds occurs between the Point Gratiot Bed, and the base of continuous black shale in the overlying Dunkirk Shale. The unit thickens eastward from about 15 cm at Dunkirk, NY to over 10 meters at Java Village, NY, roughly 75 km away. The section is dominated by grey shale with an eastward increase in the occurrence of abundant, thin, pyritic black shale beds. These beds merge westward via erosional overstep and/or non-deposition with the base of the continuous black shale of the Dunkirk. Thin black shale beds have sharp basal and upper contacts, with the upper contact often undulatory at outcrop scale, and bioturbated with planolites and chondrites-like burrows.We have identified two modes of deposition for thin black shale beds: 1) the lowermost beds are organic-rich hyperpycnites, likely the result of storms flushing lagoonal muds out to sea, and 2) beds associated with transgression which are often accompanied by a basal pyrite lag which may disappear upslope.We conducted elemental analysis using energy dispersive X-Ray Fluorescence across this interval at one-centimeter intervals from numerous exposures. Preliminary data shows enrichment of critical minerals, specifically Co, Cu, Ni, and to a lesser extent Zn, associated with pyrite. Moreover, we have identified four phases of pyrite occurrence in the unit: 1) Gray shale-hosted diagenetic pyrite forming in micro-anoxic environments within worm burrows and decaying organisms. Later, such material is often concentrated into erosional placer-like deposits of pyrite that form at the base of some thin black shale beds; 2) occurrence in some black shale beds of syngenetic framboidal pyrite; 3) later stage formation of larger framboidal and euhedral diagenetic pyrite hosted by black shale; and 4) diagenetic enrichment of pyrite in basal lags and underlying gray shale resulting from sulfide diffusing out of Fe-depleted black muds into underlying organic-lean, Fe-rich muds.We conclude that transitional deposits between black and gray shale may provide a source of critical minerals in fine-grained strata. Metals critical to the construction of lithium-ion batteries are closely associated with pyrite. While pyrite often occurs as microscopic grains within black shale, it often occurs as larger macroscopic nodules, concretions, and fossils within gray shale immediately subjacent to black shale.