The objective of this project was to develop a prototype of an automated positioning system for future APXS instruments. The current instruments on Mars rely solely upon the rover arm to place them against rocks or soils, making consecutive measurements with small offsets challenging and resource intensive to conduct. The prototype consists of an x-ray detector and an x-ray tube mounted to a computer controlled three-axis positioning system. Passive surface scans were completed over 55Fe and 244Cm sources to determine raster parameters and to characterize the detector field of view. Active XRF scans of a sample tray containing geological specimens, as well as heterogeneous natural rocks, were acquired to evaluate the system under a variety of field conditions. The results demonstrate that a microcontroller, similar to that used by the APXS for signal processing, is capable of automated scanning and rudimentary decision making based on short duration spectra. This involved using the elemental distribution within the scan field to automatically position the instrument to the region of greatest scientific interest in the xy plane, and adjusting the detector stand-off for optimal data acquisition. The achievable spatial resolution was sufficient to distinguish regions of distinct elemental composition as small as 5 mm, although smaller dimensions are possible. While several aspects of the system must be developed further in order to accommodate more complex sample geometries and enable more advanced decision making, the results clearly demonstrate the potential of such a system to significantly improve the scientific return of future instruments.