A broad beam proton-induced X-ray emission system was used to successfully supplement the original PIXE emulation of the MSL Curiosity rover alpha particle X-ray spectrometer. Analysis of single mineral samples in this work confirms that PIXE is able to deduce correct concentrations for homogenous, powdered geological reference materials. Three additional sample subsets were analyzed. R-values, defined as the ratio of GUPIX concentration to reference concentration, were deduced and are explained. The range of detectable elements was extended through the implementation and calibration of a second detector, the silicon lithium detector. Lastly, in collaboration with NASA Goddard Space Flight Centre, 19 samples were analyzed in attempt to improve understanding of differences in sulfur concentrations measured by the APXS and SAM suite of instruments on the MSL Curiosity rover. A simple mathematical model was developed to predict a general trend of which R-values may be higher or lower than others.