Five kimberlites have been discovered recently in Riley County, Kansas, within an area of six previously known kimberlites. Only one of the new kimberlites crops out; the others are covered by glacial and Recent colluvium.

The new kimberlites exhibit petrographic and magnetic similarities to the known kimberlites. Tuffaceous, crater-facies kimberlites (e.g., Fancy Creek, perhaps Baldwin Creek) are typically single phase, exhibit relatively low magnetic contrast (500–1,000 gammas), and tend to occur as topographic lows. Diatreme-facies kimberlites (e.g., Lonetree A, perhaps Lonetree B, perhaps Baldwin Creek) are brecciated and may be single or multiphase. They contain an abundance of crustal and mantle xenoliths, exhibit an intermediate magnetic contrast (2,000–3,000 gammas), and generally show slight positive relief beneath colluvial cover. Hypabyssal-facies kimberlites (e.g., Swede Creek) are single-phase, finer grained rocks containing smaller xenoliths and few kimberlite indicator minerals (e.g., pyrope garnet, Mg-ilmenite, chrome diopside); they generally exhibit slight to moderate positive relief, and are characterized by high magnetic contrast (3,500–6,000 gammas). Although the Baldwin Creek occurrence has not been confirmed by sampling, it is most likely of diatreme- or crater-facies, based on magnetic contrast comparisons.

Pervasive carbonatization and late-stage carbonate-magnetite alteration are characteristic of the diatreme- and hypabyssal-facies kimberlites. Fluid inclusion homogenization temperatures for late-stage carbonate veins yield relatively low temperatures (240–250°C).

Comparison of magnetic characteristics for most of the kimberlites in Riley County yields a correlation with kimberlite facies and may provide a technique for tentatively classifying other possible covered kimberlites.