This U.S. Geological Survey (USGS) data release contains analytical data from a suite of rock and mineral samples collected from drill core within the Elk Creek alkaline complex, southeast Nebraska. This complex hosts the Elk Creek carbonatite, a multilithologic carbonatite enriched in niobium, rare earth elements (REEs), scandium, and titanium. Mineralized carbonatites are the world’s primary source of rare earth elements (REEs) and niobium, but only a few deposits are responsible for meeting the current demand of these critical elements such that there is increasing interest in other carbonatites that have the potential to help meet future demands. This study focuses on the Elk Creek carbonatite, the largest Nb resource in the United States and a REE exploration target. The Elk Creek carbonatite is comprised of three carbonatitic lithologies; apatite dolomite carbonatite, magnetite dolomite carbonatite, and barite dolomite carbonatite as well as multiple breccias. Samples were collected from drill core from mineral exploration holes drilled by the Molybdenum Corporation of America between 1973 and 1986. The drill cores are housed at the Nebraska Geological Survey storage facility near Lincoln, Nebraska. Geochemistry data include major and trace element analytical results for 105 samples including alkaline igneous rocks, carbonatites, and paleosol samples. Dolomite and apatite geochemical data were collected using electron microprobe and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses. A set of dolomite samples were analyzed for their carbon and oxygen isotopic compositions. Data are reported in comma-separated values (CSV) files. All column headings, abbreviations, and limits of the data values are explained in the Entity and Attribute Information section of these metadata.