DEPOSITIONAL AND DIAGENETIC PROCESSES THAT CONCENTRATE CRITICAL MINERALS IN FINE-GRAINED STRATA: A CASE STUDY IN THE UPPER DEVONIAN HANOVER AND DUNKIRK SHALES OF WESTERN NEW YORK STATE

Over the coming decades, global demand for critical minerals is projected to increase rapidly. Several organizations including 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 interval between the Upper Kellwasser Bed of the Hanover Shale and the base of continuous black shale in the overlying Dunkirk Shale thickens eastward from roughly 15 cm at Dunkirk, NY to over 10 meters at Java Village, NY, a distance of roughly 75 km. The section is dominantly grey shale with increasing occurrence of siltstone to the east, interbedded with abundant thin, pyritic black shale beds which appear to merge westward via erosional overstep and/or facies changes with the base of the continuous black shale of the Dunkirk.

Of interest are thin black shales accompanied by 1) a basal erosional pyrite lag, 2) contain nodular pyrite, or 3) possess a sharp upper contact with overlying grey shale. Pyritic lags at the base of black shale beds result from subaqueous erosion of the seafloor by a pycnocline which leaves behind placer-like deposits of pyrite. Due to a process known as “burn-down” nodular pyrite and sharp upper contacts may result from the arrest of a downward diffusing oxidizing front which remobilizes elements normally deposited under anoxic conditions.

We conducted elemental analysis using energy dispersive X-Ray Fluorescence across this interval. Preliminary data shows enrichment of critical minerals in thin black shale beds, especially those with increased pyrite. For example, Co concentration is relatively constant in continuous black and grey shale at about 20 ppm, however the concentration doubles in beds which have undergone burn-down, and a seven-fold increase is observed in beds with erosional pyrite suggesting that depositional and diagenetic processes may increase critical mineral concentrations in fine-grained strata.