GRAVITY AND MAGNETIC CONSTRAINTS ON THE ORIGIN OF ORE DEPOSITS WITHIN THE TRI-STATE MINING DISTRICT, MISSOURI, KANSAS AND OKLAHOMA

The Tri-State mining district of NE Oklahoma, SE Kansas and SW Missouri was one of the world class Mississippi Valley type lead-zinc mining districts. It is one of several such deposits found in the Ozarks region of the U.S. Even though the exact location of deposition of the strata-bound ore minerals are mainly related to carbonate lithologies including dolomitic breccias and bioherms, the fluids were brought into the mining district probably by tectonic activity within the Ouachita region of Arkansas by regional faults as there is a close association with major ore deposits and intersection of faults. To study the nature and extent of these structures plus the relationship between Precambrian basement topography and lithology to the known ore deposits, the existing gravity data which are relatively sparse especially in Missouri and Oklahoma were merged with 500 new data points. Aeromagnetic data were also obtained from the USGS. To remove the large amplitude regional north to south gravity and magnetic anomaly trend, residual gravity and magnetic maps were constructed using wavelength filtering. Both maps highlight an obvious NW-trending anomaly pattern which may be caused by variations in the Precambrian basement topography. In addition, the known mining fields (e.g., Picher, Joplin, Oronogo) are associated with either a gravity and/or magnetic anomaly. The type of anomaly varies by field but is either a gravity and magnetic maxima, or a magnetic maximum and gravity minimum. In addition, a horizontal magnetic gradient map was constructed which shows obvious NW and NE-trending anomalies especially in Oklahoma and Kansas. The Picher Field in Oklahoma occurs at one of these intersections. In order to aid in determining the source of the gravity and magnetic anomalies, three two-dimensional models were constructed across the Tri-State district. The number of constraints (e.g., Precambrian penetrating drill holes) is limited but the models suggest that the high-amplitude maxima are caused by a combination of basement topography and mafic material within the Precambrian. The known mining fields are found to be either at the intersection of NW- and NE-trending magnetic anomalies implying that these linear anomalies may be faults that carried the ore-fluids from the south and/or on the sides of mafic-rich Precambrian basement topographic highs.